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Nutrient-energy-water recovery from synthetic sidestream centrate using a microbial electrolysis cell - forward osmosis hybrid system
Abstract and Figures
Recovery of nutrients, water, and energy from high-strength sidestream centrate offers benefits such as reusable resource, minimized discharge and cost-savings in mainstream treatment. Herein, a microbial electrolysis cell - forward osmosis (MEC-FO) hybrid system has been investigated for integrated nutrient-energy-water (NEW) recovery with emphasis on quantified mass balance and energy evaluation. In a closed-loop mode, the hybrid system achieved recovery of 54.2 ± 1.9% of water (70.4 ± 2.4 mL), 99.7 ± 13.0% of net ammonium nitrogen (8.99 ± 0.75 mmol, with extended N2 stripping), and 79.5 ± 0.5% of phosphorus (as struvite, 0.16 ± 0.01 mmol). Ammonium loss primarily from reverse solute flux was fully compensated by the reclaimed ammonium under 6-h extended N2 stripping to achieve self-sustained FO process. The generated hydrogen gas could potentially cover up to 28.7 ± 1.5% of total energy input, rendering a specific energy consumption rate of 1.73 ± 0.08 kWh m−3 treated centrate, 0.57 ± 0.04 kWh kg−1 COD, 1.10 ± 0.05 kWh kg−1 removed NH4+-N, 1.17 ± 0.06 kWh kg−1 recovered NH4+-N, or 5.75 ± 0.54 kWh kg−1 struvite. Recycling of excess Mg2+ reduced its dosage to 0.08 kg Mg2+/kg struvite. These results have demonstrated the successful synergy between MEC and FO to achieve multi-resource recovery, and encouraged further investigation to address the challenges such as enhanced hydrogen production, reducing nutrient loss, and optimizing MEC-FO coordination towards an energy-efficient NEW recovery process.
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April 2017
... After the treatment with BESs and stripping or TMCS, a significant portion of ammonium still remains in the anode effluent, i.e., the ammonium recovery is still limited. Therefore a new approach involving the integration of forward osmosis (FO) has been proposed to concentrate the TAN of the anode effluent and hence allowing for additional nitrogen recovery to further enhance the recovery efficiency (Qin et al., 2016;Qin & He, 2014;Zou et al., 2017). In forward osmosis coupled with a BES, a high-solute-concentration solution is used to draw water off the anode effluent, which subsequently returns to the anode for additional nitrogen removal. ...
... Thus different BES approaches can be combined to concomitantly remove the nutrients. For example, a BES can be coupled with an FO system not only to improve nitrogen recovery through concentrating ammonium in anode effluent but also to enable efficient phosphorus recovery through more struvite precipitation in the concentrated anolyte (Zou et al., 2017). In their study, Zou et al. (2017) used a two-chamber MFC/MEC consisting of a carbon brush-based bioanode, a CEM, and a Pt/C-coated carbon cloth cathode to treat digestion centrate. ...
... For example, a BES can be coupled with an FO system not only to improve nitrogen recovery through concentrating ammonium in anode effluent but also to enable efficient phosphorus recovery through more struvite precipitation in the concentrated anolyte (Zou et al., 2017). In their study, Zou et al. (2017) used a two-chamber MFC/MEC consisting of a carbon brush-based bioanode, a CEM, and a Pt/C-coated carbon cloth cathode to treat digestion centrate. The anode effluent of the reactor was fed to an FO unit that could remove 54.2 AE 1.9% of the anode effluent water before the concentrated anode effluent was fed back to the anode chamber. ...
Biofertilizers are the substances containing variety of microbes having the capacity to enhance plant nutrient uptake by colonizing the rhizosphere and make the nutrients easily accessible to plant root hairs. Biofertilizers are well known for their cost effectiveness, environment-friendly nature, and composition. These are effective alternatives to the hazardous synthetic fertilizers. This chapter covers various types of microbial biofertilizers pronouncing symbiotic and free-living nitrogen-fixers, phosphorus-solubilizer and mobilizers, their formulations, applications of few commercially available biofertilizers toward sustainable agriculture, and recent approaches to develop next-generation biofertilizers.
... After the treatment with BESs and stripping or TMCS, a significant portion of ammonium still remains in the anode effluent, i.e., the ammonium recovery is still limited. Therefore a new approach involving the integration of forward osmosis (FO) has been proposed to concentrate the TAN of the anode effluent and hence allowing for additional nitrogen recovery to further enhance the recovery efficiency (Qin et al., 2016;Qin & He, 2014;Zou et al., 2017). In forward osmosis coupled with a BES, a high-solute-concentration solution is used to draw water off the anode effluent, which subsequently returns to the anode for additional nitrogen removal. ...
... Thus different BES approaches can be combined to concomitantly remove the nutrients. For example, a BES can be coupled with an FO system not only to improve nitrogen recovery through concentrating ammonium in anode effluent but also to enable efficient phosphorus recovery through more struvite precipitation in the concentrated anolyte (Zou et al., 2017). In their study, Zou et al. (2017) used a two-chamber MFC/MEC consisting of a carbon brush-based bioanode, a CEM, and a Pt/C-coated carbon cloth cathode to treat digestion centrate. ...
... For example, a BES can be coupled with an FO system not only to improve nitrogen recovery through concentrating ammonium in anode effluent but also to enable efficient phosphorus recovery through more struvite precipitation in the concentrated anolyte (Zou et al., 2017). In their study, Zou et al. (2017) used a two-chamber MFC/MEC consisting of a carbon brush-based bioanode, a CEM, and a Pt/C-coated carbon cloth cathode to treat digestion centrate. The anode effluent of the reactor was fed to an FO unit that could remove 54.2 AE 1.9% of the anode effluent water before the concentrated anode effluent was fed back to the anode chamber. ...
Purple nonsulfur bacteria (PNSB), a diverse group of photosynthetic microorganisms, inhabit in a wide variety of aquatic habitats where sunlight penetrates. These microorganisms show pigmentation ranging from deep red to brown and propagate under anoxic conditions. Depending on the presence of nutrients, oxygen concentration, and light intensity, they can shift their modes of metabolism between photoautotrophy, photoheterotrophy, and chemoheterotrophy. Most promisingly, many of the PNSB are known to thrive in the presence of various toxicants such as heavy metals and thus play an important role in the remediation of contaminated sites. PNSB are one of the most potential candidates for the production of biohydrogen, taking us a step further towards the era of “green technology.” They also serve as a potential source of single-cell proteins, enzymes, biofertilizers, carotenoids, plant growth-producing hormones, and several precursor molecules. This chapter discusses the versatile and important role of PNSB in biotechnology.
... However, only around 50% of phosphorus can be recovered from influent wastewater because of the efficiency losses at EBPR and inefficient struvite crystallization under an imbalanced N/P ratio, leaving abundant amounts of unrecovered nitrogen in the centrate. Recycling the nutrient-rich centrate back to the aerobic biological treatment process leads to significant increase of nutrient loading rate and additional energy demand (Zou et al., 2017). Thus, development of an integrated process is required for sustainable nitrogen and phosphorous recovery from wastewater. ...
... Simultaneous nutrient, energy, and water recovery was achieved in a novel MEC-FO system. The hybrid system recovered B54% of water, B99% of net ammonium nitrogen (by extended N 2 stripping), and B80% of phosphorous from digestion centrate (Zou et al., 2017). Struvite is crystallized on cathode surfaces; hence cathode configuration plays a significant role in the efficient struvite precipitation in BES. ...
Nutrient removal and recovery have gained much attention to achieve pollution control and sustainable resource management. Bioelectrochemical systems (BESs) have been extensively explored for the recovery of energy, metals, and intermediate chemicals, and lately, research has focused on the recovery of valuable nutrients. It can avoid the complex and energy-intensive nutrient removal process in downstream wastewater treatment facilities. Nitrogen removal and/or recovery in BES can be achieved via nitrification and cathodic denitrification, anaerobic ammonium oxidation process, and ammonia transport across the membrane. Simultaneous nitrogen and phosphorous recovery can occur via struvite precipitation, electromigration and concentration, and algal uptake. This chapter summarizes the basic principles of nutrient removal and recovery from various waste streams in BES, the influential factors, and the key issues to be addressed in further research. Future development and industrialization of the BES can establish a nexus between nutrient, energy, and water recovery.
... 0.7-2.0 kWh/kg COD) (Pant et al., 2011;Zou et al., 2017). For example, at lab-scale, using MECs for treating real municipal wastewater with a soluble COD concentration of 160 mg/L, the NER was found to be 2.14 kWh/kg COD removed at an energy input of 2.0 kWh/kg COD removed, suggesting a net potential energy output of 0.14 kWh/kg COD (Cusick et al., 2010). ...
The activated sludge process is regarded by many as a remarkable engineering development of the 20th Century which has made a great contribution to wastewater treatment. But after more than 100 years of successful application, the conventional activated sludge (CAS) process has recently been receiving an increasing number of critiques due to the high energy consumption and excessive sludge generation associated with it. Increasing efforts have been devoted to energy recovery in the form of biogas produced from waste sludge through anaerobic digestion (AD). However, the recoverable electrical energy generated from the AD of waste sludge can only offset about 50–60% of the total input energy of wastewater treatment plants (WWTPs) with CAS as the core process, while energy efficiency could be increased further to about 75% with upgraded AD equipped with pre-treatment of thickening sludge and a combined heat and power (CHP) process (Cao, 2011). Moreover, process upgrading and retrofitting are urgently needed in more and more WWTPs around the world to meet the tightened effluent discharge standards applied in recent years which inevitably lead to a rising trend of in-plant energy consumption. For example, it has been reported that the effluent discharge standards in China have been gradually migrated to quasi Class IV for surface water bodies with very low discharge limits. Consequently, it appears almost impossible or highly challenging to realize energy self-sufficient municipal wastewater treatment through further process optimization if the CAS process continues to serve as the core biological unit.
Facing such challenging situations, instead of continuing with the current practice it is necessary to explore novel process configurations and emerging technologies. The solutions moving forward should rely on ways to enhance energy recovery from biosolids and wastewater, while minimizing energy consumption. This chapter thus presents and elucidates a roadmap of emerging technologies with potentials for energy recovery and for energy saving together with possible resource recovery, as a way to move towards the ultimate goal of energy self-sufficient municipal wastewater treatment.
... (i) Microbial electrolysis cells Nutrient-energy-water recovery from wastewater has been demonstrated with the combination of FO with microbial electrolysis cells (MEC) Qin and He, 2014) as illustrated in Fig. 8. Zou et al. (Zou et al., 2017) produce hydrogen gas from synthetic wastewater digestate with MEC by applying an electrical current between an anode chamber and cathode chamber (Fig. 8). The anode chamber contains digestate and exoelectrogens, which are electrochemically active microorganisms degrading COD. ...
Socioeconomic development and new technological advancements have greatly increased the demand for metals, minerals and nutrients. Thus, substantial interest in developing technologies to recover these commodities from seawater, various brines and wastewater streams (industrial and domestic) has emerged. Less explored and innovative membrane processes including membrane crystallization (MCr), forward osmosis (FO) and membrane capacitive deionization (MCDI) are gaining interest in this regard. The current study provides a critical review of the current trends in applying MCr, FO and MCDI for recovery of metals, minerals and nutrients from various streams. The processes are compared in terms of types of fouling, energy consumption, overall composition of suitable feed solutions, feasible concentration ranges and potential to recover the targeted metal from a multi-component solution. The ultimate objective is to establish future research directions for further improvement of each process and to identify which of the processes is more suitable under a given scenario.
... On the cathode surface, crystal blooms accumulated in patches, which might be due to hydrogen bubble formation at the corresponding locations (Fig. 6a). Although there are different types of struvite (irregular, cubic, and rod-like irregular crystals), the crystal growth exhibited the typical acicular prismatic morphology of struvite (Fig. 6b) [28][29][30]. As expected, EDS analysis of the crystals on the cathode surface also confirmed that the composition of the accumulated crystals was that of pure struvite, with the EDS spectra showing the presence of Mg, P, and O (Fig. 6c) [9]. ...
In this research, a novel Microbial reverse-electrodialysis electrolysis struvite-precipitation cell (MRESC) was developed for energy recovery through struvite (MgNH4PO4·6H2O) crystallization and hydrogen production concurrently in a single process without any electrical-grid energy consumption. This hybrid system can effectively transfer the salinity gradient energy to electrical energy as a driving force to produce hydrogen gas coupled with struvite recovery and organic wastewater degradation. A MRESC containing 10 pairs of RED cells, supplied solutions typical of high concentration (600 mM NaCl) and low concentration (12 mM NaCl) at 1.0 mL/min, was operated in the fed-batch mode. The rates of hydrogen production and struvite crystallization were determined to be 0.71 m³-H2/m³-Van/d and 7.62 g/m²/h, respectively. The gas produced was > 92% H2. The Coulombic efficiency was close to or above 100% with a COD removal of 84 ± 6%, and an overall energy efficiency of 28%. The morphology and structure of the main component of accumulated crystal at the cathode were verified by a scanning electron microscope with energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction. These results showed that the MRESC system could be used as an effective bioelectrochemical method for energy recovery in the form of pure hydrogen gas and struvite simultaneously.
... In MECs, the anode oxidizes organic matter to electrons and transfers electrons to the cathode, where they reduce the protons (H + ) to H 2 (Bond et al., 2002;Lu et al., 2012;Park et al., 2019). At the anode, almost all kinds of organic matters, such as volatile fatty acids (VFAs), carbohydrates and alcohols, can be used directly by exoelectrogens for electrohydrogenesis (Cheng and Logan, 2007;Lu et al., 2012;Zou et al., 2017). At the cathode, H 2 production consumes H + constantly and further increases the pH (Coma et al., 2013;Luo et al., 2014;Blázquez et al., 2016). ...
Anaerobic digestion (AD) of organics is a challenging task under high-strength sulfate (SO42-) conditions. The generation of toxic sulfides by SO42--reducing bacteria (SRB) causes low methane (CH4) production. This study investigated the feasibility of alleviating sulfide inhibition and enhancing CH4 production by using an anaerobic reactor with built-in microbial electrolysis cell (MEC), namely ME-AD reactor. Compared to AD reactor, unionized H2S in the ME-AD reactor was sufficiently converted into ionized HS- due to the weak alkaline condition created via cathodic H2 production, which relieved the toxicity of unionized H2S to methanogenesis. Correspondingly, the CH4 production in the ME-AD system was 1.56 times higher than that in the AD reactor with alkaline-pH control and 3.03 times higher than that in the AD reactors (no external voltage and no electrodes) without alkaline-pH control. MEC increased the amount of substrates available for CH4-producing bacteria (MPB) to generate more CH4. Microbial community analysis indicated that hydrogentrophic MPB (e.g. Methanosphaera) and acetotrophic MPB (e.g. Methanosaeta) participated in the two major pathways of CH4 formation were successfully enriched in the cathode biofilm and suspended sludge of the ME-AD system. Economic revenue from increased CH4 production totally covered the cost of input electricity. Integration of MEC with AD could be an attractive technology to alleviate sulfide inhibition and enhance CH4 production from AD of organics under SO42--rich condition.
... In light of the advances in the last few decades, the research goal has now shifted toward implementing low-cost materials (electrodes and CEM) and improving configurations (stack MFCs) to make the technology commercially viable on a large scale along with resource recovery to reduce the expenditure incurred per unit of power generation. Valuable recovery of products such as hydrogen, methane, ammonia, phosphorus, and water has been made through MFCs, MECs, and MDCs, either individually or assisted with conventional treatment technologies such as forward osmosis (Zou et al. 2017) and the Fenton process (Mahmoud et al. 2016). Nowadays, the application of BESs is being extended to develop biosensors (Nakanishi et al. 2019) and sustain robotic activity (Ieropoulos et al. 2007;Zhang 2019). ...
The review discusses the transformation of waste to energy (WTE) through bioelectrochemical systems (BESs) treating organic waste, which makes up 47% of the total municipal solid waste generated. Emphasis is given to the intermediate step—use of a leach bed reactor—to successfully convert WTE by explaining the constructional elements and factors affecting the hydrolysis of organic waste. As hydrolysis is a rate-limiting step of anaerobic digestion (AD), operating parameters controlling solubilization of the readily degradable compounds are essential to obtain a volatile fatty acid and nutrient-rich leachate. The leachate treatment in BESs such as a microbial fuel cell, a microbial electrolysis cell, and a microbial desalination cell, along with factors that will affect the performance of these systems, is reviewed. Further, it describes the mechanisms involved to remove organics and nutrients, as well as the advantages, disadvantages, and challenges of individual systems. Finally, this review will aid future efforts to recover the energy present in organic waste with the help of BESs and to develop integrated solid waste management systems.
... Many researchers have proposed integration of these different systems into a single term called "microbial electrochemical cells" and abbreviated them as an MXC, where the "X" stands for the application of interest [8][9][10]. MXCs have also been implemented for the applications of nutrient recovery [11,12] and production of chemicals, such as hydrogen peroxide [13,14] from waste and wastewater. Due to the extensive studies since the early 2000's, several studies have been implemented for scaling up the energygenerating MXCs [15][16][17][18]. ...
The environmental monitoring of recalcitrant contaminants, such as aromatic compounds in water samples, became globally essential as they pose significant threats to the ecosystem and public health. More importantly, commonly-used lab-based analytical techniques, such as mass-spectrometry- and chromatography-based methods, are laborious, expensive, and time-consuming, which may not be suitable for continuous and field monitoring of these recalcitrant contaminants. As an alternative, microbial electrochemical cell-based (MXC) biosensors demonstrated tremendous potentials for the rapid detection and monitoring of various recalcitrant contaminants by overcoming the challenges of the aforementioned analytical methods. In general, MXC biosensors can perform a low-cost, simple, and on-site quantification of target analytes. Despite their advantages, studies have reported several challenges and drawbacks, such as selecting optimal MXC type and sensing element (anode vs. cathode), procedures to enhance sensitivity and selectivity, and field applicability, which may limit their applications to recalcitrant contaminants. Up to date, no review articles have been published to focus on MXC biosensors for the environmental monitoring of recalcitrant contaminants. Therefore, this review paper provides a comprehensive evaluation of recent advances in optimizing MXC biosensors in terms of configurations, sizes, electrochemical operating modes, sensing biofilms, and other operating parameters to aid the MXC biosensor's applications to recalcitrant contaminants. It also further highlights the current and future opportunities to incorporate 3D printing and machine learning to develop advanced MXC biosensors. Ultimately, this report summarizes prospects and proposed a roadmap for developing MXC biosensors for recalcitrant contaminants, emphasizing aromatic compounds and their derivatives.
... Microbial electrochemical technologies (METs) are unique platforms that combine microbial metabolism with electrochemistry for various value-added applications (Sravan et al., 2021). Over the last 2 decades, many different applications of METs have been demonstrated: 1) bioenergy generation, such as bio-electricity in microbial fuel cells (MFCs) (Munoz-Cupa et al., 2020;Sravan et al., 2021), bio-hydrogen in microbial electrolysis cells (MECs) (Hua et al., 2019;Rousseau et al., 2020), and bio-methane in MEC assisted anaerobic digesters (Zakaria and Dhar, 2019;Huang et al., 2020); 2) synthesis of platform chemicals, such as hydrogen peroxide (Chung et al., 2020b;Zhao et al., 2021); 3) nutrient recovery (Zou et al., 2017;Barua et al., 2019); 4) water desalination (Al-Mamun et al., 2018;Jafary et al., 2020); 5) biosensors (Do et al., 2020;Chung et al., 2020a); and many more. Despite such tremendous potential, studies emphasized the challenges in system design and fabrication, which must be addressed to improve their performance and robustness, especially for scaling-up and commercialization (Dhar et al., 2016b;Sim et al., 2018;Zakaria and Dhar, 2019). ...
For the past two decades, many successful applications of microbial electrochemical technologies (METs), such as bioenergy generation, environmental monitoring, resource recovery, and platform chemicals production, have been demonstrated. Despite these tremendous potentials, the scaling-up and commercialization of METs are still quite challenging. Depending on target applications, common challenges may include expensive and tedious fabrication processes, prolonged start-up times, complex design requirements and their scalability for large-scale systems. Incorporating the three-dimensional printing (3DP) technologies have recently emerged as an effective and highly promising method for fabricating METs to demonstrate power generation and biosensing at the bench scale. Notably, low-cost and rapid fabrication of complex and miniaturized designs of METs was achieved, which is not feasible using the traditional methods. Utilizing 3DP showed tremendous potentials to aid the optimization of functional large-scale METs, which are essential for scaling-up purposes. Moreover, 3D-printed bioanode could provide rapid start-up in the current generation from METs without any time lags. Despite numerous review articles published on different scientific and applied aspects of METs, as per the authors’ knowledge, no published review articles explicitly highlighted the applicability and potential of 3DP for developing METs. Hence, this review targets to provide a current overview and status of 3DP applications for advancing METs and their future outlook.
... Forward osmosis (FO) has been explored for several novel applications including sludge dewatering [14][15][16], resource recovery from wastewater [17][18][19][20][21][22][23], food processing [24,25] and produced water treatment for the oil and gas industry [26,27]. Of a particular note, Feron et al., [28] have recently proposed to replace the trim cooler by FO in post combustion CO 2 capture. ...
This study evaluates the feasibility of forward osmosis (FO) for simultaneous post-combustion CO 2 capture and make-up water provision using seawater and treated effluent as the feed. Three amine-based CO 2 adsorbents (glycine, sodium glycinate, and monoethanolamine (MEA)) were used as draw solutes. A non-linear relationship between concentration of these adsorbents and conductivity (thus osmotic pressure) was observed. Glycine showed higher water flux and lower reverse salt flux and specific reverse salt flux than sodium glycinate and MEA in both membrane orientations, thus was selected for further investigations. A higher water flux but with the considerable flux decline were observed when active layer faced draw solution. In addition, temperature increase in draw solution could alter thermodynamic properties of glycine, resulting in an increase of reverse salt flux. Water flux increase was also observed due to diminishing concentrative internal concentration polarisation. Changes in water flux were insignificant when active layer faced feed solution even as temperature increased. Temperature increase was likely to aggravate the severity of dilutive internal concentration polarisation and offset the growth of osmotic pressure. Seawater could also be a potential source for simultaneous cooling and providing the make-up water, although the water flux was lower compared to treated effluent.
... 54 Externally added Mg 2+ ions were an option using NH 4 + -based DS, in which reversed-fluxed ammonium combined with phosphate in the feed solution to produce struvite. 55 This still presents opportunities for improvement since salinity buildup is not directly targeted and precipitation would only occur with supplemented resources that may not be available in the feed. ...
Forward osmosis (FO) has shown advancement towards recovery of useful water from various waste streams. A major issue that arises is the accumulation of salts due to reverse solute flux (RSF) from a draw solution into a feed solution that can result in several negative effects such as decreased water flux and inhibiting biological activities. This paper aims to provide a concise discussion and analysis of methods that can help to alleviate the effects of solute build up. New parameters, solute removal/recovery rate (SRR) and removal/recovery ratio (ReR), are proposed to help better define the performance of reducing solute buildup and employed in case studies to evaluate the selected reduction methods. Solute removal can be accomplished by physical separation, chemical precipitation, and biological removal. Recovery of solutes, one step beyond removal, is discussed and demonstrated by using bioelectrochemical systems and electrodialysis as examples. This work has highlighted the concerns associated with solute buildup and encouraged further exploration of effective tools to mitigate solute buildup for improved performance of FO-based water/wastewater systems.
... More recently, MXCs were engineered to produce various biogas, such as bio-hydrogen in microbial electrolysis cell (MEC) Wagner et al., 2009) and bio-methane in microbial electrolysis cell assisted anaerobic digester (MEC-AD) (Huang et al., 2020;Zakaria and Dhar, 2019). Nonetheless, the MXCs were also implemented for many other applications, such as water desalination in microbial desalination cell (MDC) (Al-Mamun et al., 2018;Jafary et al., 2020), nutrient recovery (Barua et al., 2019;Qin et al., 2016;Zou et al., 2017), CO 2 -reduction-to-value-added-products in microbial electrosynthesis (MES) (Lovley and Nevin, 2013;Rabaey and Rozendal, 2010;Zhang and Angelidaki, 2014) and production of chemicals, such as hydrogen peroxide in microbial peroxide producing cells (MPPCs) (Chung et al., 2020b;Rozendal et al., 2009). Due to the extensive studies since the early 2000s, several studies have been dedicated to scaling-up the MXCs (Dhar et al., 2016;Heidrich et al., 2014;Hiegemann et al., 2016;Liang et al., 2018;Sim et al., 2018). ...
Many countries have set up policies to decrease fossil fuel dependency and petro‐based synthesis of commodity chemicals. Fermentative biofuels and bioresource recovery processes are expected to assist considerably in this context of sustainable transition to a bio‐based economy. The utilization of renewable resources such as waste biomass is often considered an attractive feature of fermentative bioprocesses. However, limitations regarding the robustness of process and selectivity of target products are often considered bottlenecks to their sustainable commercialization. Particularly, in conventional fermentation processes, microorganisms produce undesired by‐products to attain intracellular redox balance, which leads to a low yield of target products. Recently, electro‐fermentation has emerged as an innovative approach for changing metabolic pathways of fermentative microorganisms towards target products with higher yields and productivities by changing intracellular redox potential. Lab‐scale EF studies have successfully demonstrated superior performance over conventional fermentation to produce a wide variety of biofuels and commodity chemicals. This book chapter provides an overview of fundamental and applied aspects of various value‐added products synthesis with the EF process and identifies research gaps for future development.
... d) The potential of the MECs is also been evaluated for their role in the production of organic chemicals using the mechanism of microbial electrosynthesis. This can also be an alternate source for chemical generation [39]. Apart from the above-mentioned advantages, other advantages include reducing the use of fossil fuels which ultimately reduces greenhouse emissions, promotes the use of renewable substrates for energy generation, reducing the burden on the environment by processing organic wastes and upholding ecological recycling, etc [40]. ...
Wastewater is one of the most common by-products of almost every industrial process. Treatment of wastewater alone, before disposal, necessitates an excess of energy. Environmental concerns over the use of fossil fuels as a source of energy have prompted a surge in demand for alternative energy sources and the development of sophisticated procedures to extract energy from unconventional sources. Treatment of municipal and industrial wastewater alone accounts for about 3% of global electricity use while the amount of energy embedded in the waste is at least 2–4 times greater than the energy required to treat the same effluent. The microbial electrolysis cell (MEC) is one of the most efficient technologies for waste-to-product conversion that uses electrochemically active bacteria to convert organic matter into hydrogen or a variety of by-products without polluting the environment. This paper highlights existing obstacles and future potential in the integration of Microbial Electrolysis Cell with other processes like anaerobic digestion coupled system, anaerobic membrane bioreactor and thermoelectric micro converter
... Although it is possible to operate BES in a membrane-less configuration (i.e. no ion exchange membrane is interposed between the anode and the cathode), the use of membrane is vital for instance to obtain high-purity hydrogen in microbial electrolysis cells (MEC) [12], to recover nutrients (nitrogen, phosphorus, potassium, etc) [13] from nutrient-rich substrates or to avoid any interference between the anodic and cathodic process (e.g. to prevent oxygen from reaching the anode in microbial fuel cells, MFC). The few studies that have tackled the effect of using real substrates on membrane performance and durability [14,15] have shown that membrane fouling by microorganisms, extracellular polymers and inorganic salts are the most important factors behind the observed degradation in the BES performance due to the physical blockage of cation transfer that may cause a decay in the current. ...
First large-scale experiences of bioelectrochemical systems (BES) are underway. However, there is still little knowledge on how the different elements that integrate a BES behave in near real-life conditions. This paper aims at assessing the impact of long-term operation on the cation exchange membrane and on the anodic biofilm of two 16 L Microbial Electrolysis Cells (MEC) designed for hydrogen production and ammonia recovery from pig slurry. Membrane deterioration was examined by physical, chemical and microscopy techniques at different locations, revealing a strong attachment of microorganisms and a significant decay in membrane properties such as ion exchange capacity and thermal stability. Anode microbial communities did not show a dramatic shift in the eubacteria composition at different sampling areas, although the relative abundance of some bacterial groups showed a clear vertical stratification. After 100 days of continuous operation, MEC performance did not declined significantly maintaining ammonium transport rates and H 2 production rates of 15.3 gN d ⁻¹ m ⁻² and 0.2 LH 2 ·L ⁻¹reactor ·d ⁻¹ respectively.
... A 99.5% removal rate of lead(II) in 48 h was observed [196]. An MEC coupled with FO achieved water recovery of 54.2%, net ammonium nitrogen of 99.7% and phosphorus of 79.5% [197]. The integration of MFC with MEC also promoted the process of ANAMMOX (anaerobic ammonium oxidation) without the requirement of an external carbon source [198]. ...
The microbial fuel cell (MFC) technology relies on electroactive bacteria to degrade organic molecules for bioelectricity production. MFC is a potentially useful approach for wastewater treatment with concomitant energy production. The main advantages of MFC for treating wastewater include energy saving, sludge volume reduction and bioenergy generation. In the past two decades, tremendous advances have been made in improving MFC performances. However, MFCs still face significant hurdles for practical deployments due to their low power densities and high costs. Further improvements are becoming harder to achieve for standalone MFC devices. In recent years, MFCs have been integrated with physical, chemical and biological processes for wastewater treatment, bioelectricity production, chemical production and desalination. The hybrid systems are more promising compared with standalone MFCs. This comprehensive and state-of-the-art review discusses different systems coupled with MFCs using different working principles, reactor designs, operating parameters and their effects on system performances. These systems include bioelectro-Fenton-MFC, microbial desalination cell, MFC-electrosorption cell, microbial solar cell, microbial reverse-electrodialysis cell, plant-MFC and constructed wetland-MFC. Synergistic effects and mechanisms of process coupling as well as the challenges for practical applications of each hybrid system are assessed. Although MFC-hybrid systems are more promising than standalone MFCs, much more research is needed to overcome significant hurdles for practical deployment.
... Finally, for MEC performances, H 2 production rates have increased from 0.1 to 50 m 3 /m 3 ·d, mainly through multiple optimizations of reactor configuration, electrode materials, catalyst materials, and experimental parameters [32] . In addition, some researches have been reported from other different perspectives, such as biocathode [33] , recovery of nutrient [34] , energy production [35,36] , extracellular electron transfer [37] . However, many previous studies just focused on simple substrates such as defined compounds (sodium acetate, glucose, etc.) at the lab scale. ...
... Although BES were proved as promising for ammonium nitrogen recovery from high ammonium concentration streams (Wu & Modin 2013;Gildemyn et al. 2015;Zhang & Angelidaki 2015;Zou et al. 2017), studies about nitrogen recovery from agro-industrial wastes are still limited (Cerrillo et al. 2016(Cerrillo et al. , 2018. ...
Growing food and biomass production at the global scale has determined a corresponding increase in the demand for and use of nutrients. In this study, the possibility of recovering nitrogen from agro-industrial digestate using bioelectrochemical systems was investigated: two microbial electrolysis cells (MECs) were fed with synthetic and real digestate (2.5 gNH4+-N L−1). Carbon felt and granular graphite were used as anodes in MEC-1 and MEC-2, respectively. As to synthetic wastewater, the optimal nitrogen load (NL) for MEC-1 and -2 was 1.25 and 0.75 gNH4+-N d−1, respectively. MEC-1 showed better performance in terms of NH4+-N removal efficiency (39 ± 2.5%) and recovery rate (up to 70 gNH4+-N m−2d−1), compared to MEC-2 (33 ± 4.7% and up to 30 gN m−2d−1, respectively). At the optimal hydraulic retention time, lower NH4+-N removal efficiencies and recovery rates were observed when real digestate was fed to MEC-1 (29 ± 6.6% and 60 ± 13 gNH4+-N m−2d−1, respectively) and MEC-2 (21 ± 7.9% and 10 ± 3.6 gNH4+-N m−2d−1, respectively), likely due to the higher complexity of the influent. The average energy requirements were 3.6–3.7 kWh kgNremoved−1, comparable with values previously reported in the literature and lower than conventional ammonia recovery processes. Results are promising and may reduce the need for costly and polluting processes for nitrogen synthesis. HIGHLIGHTS
Bio-electrochemical nitrogen recovery from agro-industrial digestate was achieved.;
Carbon felt anode allowed higher nitrogen recovery than granular graphite.;
Reducing the HRT had an opposite effect on nitrogen removal, depending on the anode material.;
Nitrogen removal rates were negatively affected by real digestate complexity.;
Specific energy consumption was competitive with conventional technologies for nitrogen recovery.;
... Besides, the production of ammonium through BMISs must be more economical than the conventional ammonia synthesis process, so the energy consumption per unit of nitrogen recovery was the most crucial factor. Although some studies have conducted such analyses (Mohammadi et al., 2021;Qin et al., 2017;Ward et al., 2018;Zou et al., 2017), most of these values used for the current calculation are achieved in lab-scale reactors for short-term experiments. Hence, the commercial application of BMISs is still questionable, including lack of solid outcomes in pilot-scale operations of BMISs, uncertain durability, and costly component materials (e.g., membrane and electrode). ...
Wastewater contains a significant amount of recoverable nitrogen. Hence, the recovery of nitrogen from wastewater can provide an option for generating some revenue by applying the captured nitrogen to producing bio-products, in order to minimize dangerous or environmental pollution consequences. The circular bio-economy can achieve greater environmental and economic sustainability through game-changing technological developments that will improve municipal wastewater management, where simultaneous nitrogen and energy recovery are required. Over the last decade, substantial efforts were undertaken concerning the recovery of nitrogen from wastewater. For example, bio-membrane integrated system (BMIS) which integrates biological process and membrane technology, has attracted considerable attention for recovering nitrogen from wastewater. In this review, current research on nitrogen recovery using the BMIS are compiled whilst the technologies are compared regarding their energy requirement, efficiencies, advantages and disadvantages. Moreover, the bio-products achieved in the nitrogen recovery system processes are summarized in this paper, and the directions for future research are suggested. Future research should consider the quality of recovered nitrogenous products, long-term performance of BMIS and economic feasibility of large-scale reactors. Nitrogen recovery should be addressed under the framework of a circular bio-economy.
Biomimetic membranes have high water permeability with high selectivity. Recent developments will increase their applications and variety in membrane technologies. This chapter focuses on the type and characteristics of water channels that can be used in these membranes. Also, strategies that can be used for fabrication of biomimetic membranes; lipid/polymer types and concentration that can be used in these membranes; and substrate types that are appropriate to use are summarized in details. The chapter is continued with applications of biomimetic membranes for the treatment of water and wastewater.
Nitrate occurrence in groundwater is a worldwide issue, due to the high exploitation of the resource for water supply, and the worldwide diffusion of the contamination. The consumption of nitrate-contaminated drinking water may lead to severe health issues. Several technologies have been applied; in the last 15 years, bioelectrochemical systems (BES) have emerged as an alternative to conventional technologies for water and wastewater treatment. BESs can be defined as electrochemical systems in which microorganisms act as catalysts in the anode and/or cathode reactions. In the thesis, the design, and application of BESs for groundwater denitrification was described, analyzed, and discussed. Firstly, the development of a denitrifying biocathode was described and analyzed: the biocathode was obtained by the reversal of the anode of a Microbial Fuel Cell (MFC), following a procedure described in literature on smaller scale reactors. Then, the obtained CBD (Controlled Biocathodic Denitrification system) was operated under different operational conditions (i.e. hydraulic retention times, nitrate loading rate, nitrate concentration in the influent). The performances of the CBD in terms of denitrification and energy consumption were analyzed and discussed, and the limitations of the systems were identified. To overcome the emerged limitations, a sequential system composed by 2 CBDs connected in series was developed, and operated at decreasing hydraulic retention times. The combined system showed to obtain high nitrate and total nitrogen removal rates, and to decrease its specific energy consumption (in terms of mass of nitrate removed, and volume treated) at the decrease of the hydraulic retention times. Then, the operation of a buried biocathode for in situ groundwater denitrification was described and analyzed. The biocathode was immersed in sand or gravel, to simulate its displacement in a saturated aquifer. The lack or recirculation in the reactor due to the presence of the sand/gravel led to a substantial decrease in the total nitrogen removal rate, with consequent accumulation of intermediate N-forms, and to an increase in the specific energy consumption. The operation of the buried biocathode suggested the necessity of the development of specially-designed BES for in situ applications. The
analysis of the energy consumption of CBD and MFC for groundwater denitrification in ex situ, and in situ configurations was calculated using data from literature and assumptions, and highlighted the fact that, even though the operation of the CBD was more energy expensive compared to the MFC due to the necessary use of a power supply or a potentiostat, the CBD was the only option to achieve satisfactory performance in terms of nitrate and total nitrogen removal rates. In the last chapter of the thesis, the application of BES for the removal of other contaminants (arsenic, cadmium, chromium, perchlorate, and vanadium) from groundwater is reviewed.
Study of forward osmosis (FO) has been increasing steadily over recent years with applications mainly focusing on desalination and wastewater treatment processes. The working mechanism of FO lies in the natural movement of water between two streams with different osmotic pressure, which makes it useful in concentrating or diluting solutions. FO has rarely been operated as a stand-alone process. Instead, FO processes often appear in a hybrid or integrated form where FO is combined with other treatment technologies to achieve better overall process performance and cost savings. This article aims to provide a comprehensive review on the need for hybridization/integration for FO membrane processes, with emphasis given to process enhancement, draw solution regeneration, and pretreatment for FO fouling mitigation. In general, integrated/hybrid FO processes can reduce the membrane fouling propensity; prepare the solution suitable for subsequent value-added uses and production of renewable energy; lower the costs associated with energy consumption; enhance the quality of treated water; and enable the continuous operation of FO through the regeneration of draw solution. The future potential of FO lies in the success of how it can be hybridized or integrated with other technologies to minimize its own shortcomings, while enhancing the overall performance.
A comparison of different techniques for nitrogen recovery from wastewater to draw conclusions on economic and energetic benefits
The recovery of fertilizer-used nutrients from wastewater is a sustainable approach for wastewater management and helping social sustainability. This is especially the case given the strict discharge requirements and shortages existing in nutrients supply. Recognizing that wastewater is a very useful resource and the value of recycled nutrients has made researchers consider the recovery of nutrients from wastewater. This review described the current technologies used to recover nutrients in wastewater treatment and their mechanisms, including chemical methods, biological technologies, membrane systems and advanced membrane systems. Also, an economic analysis of these nutrient recovery systems was discussed and compared them in terms of positive and negative aspects. The economic feasibility of recovered nutrients was investigated. Finally, future perspectives expects some possible research directions regarding recovery system which can be more economically accessible for wastewater treatment, in which the osmotic membrane bioreactors (OMBR) and bioelectrochemical systems (BES)-based hybrid systems are highly recommended.
To advance nutrient recovery from waste streams by electrodialysis (ED), a decoupled ED system with separated anode/cathode units was developed in this study. The use of an additional cation exchange membrane in the anode unit was designed to prevent chloride oxidation and collect phosphate at a higher concentration. The results show that the decoupled ED removed 92 ± 2% of ammonia and 81 ± 3% of phosphate from a synthetic solution, or 75 ± 4% (ammonia) and 62 ± 2% (phosphate) from a real centrate. Both current generation and nutrient removal could be improved with increasing the applied voltage from 3 to 5 V, and a higher voltage of 6 V did not pose positive effects on removal efficiency but resulted in higher energy consumption. A shorter electrodes distance benefited the decoupled ED operation with a lower internal resistance. The solar energy was successfully applied to power the decoupled ED that exhibited comparable performance (removing 74 ± 4% of ammonia and 60 ± 2% of phosphate) to that by a power supply, although the use of solar energy would depend on the illumination condition. The quality of the recovered struvite was enhanced by either a pre-treatment step to precipitate calcium ions or using a small quantity of the catholyte for struvite formation. These results have demonstrated a promising approach to recover nutrients from sidestream centrate as struvite and ammonium sulfate, encouraging further exploration of ED application towards enhancing flexibility and utilizing clean energy.
Fertilizer drawn forward osmosis (FDFO) was proposed to extract fresh water from flowback and produced water (FPW) from shale gas extraction for irrigation, with fertilizer types and membrane orientations assessed. Draw solution (DS) with NH4H2PO4 displayed the best performance, while DS with (NH4)2HPO4 resulted in the most severe membrane fouling. DS with KCl and KNO3 led to substantial reverse solute fluxes. FDFO operation where the active layer of the membrane was facing the feed solution outperformed that when the active layer was facing the DS. Diluted DS and diluted FPW samples were used for irrigation of Cherry radish and Chinese cabbage. Compared to deionized water, irrigation with diluted DS (total dissolved solid (TDS) = 350 mg·L-1) promoted plant growth. In contrast, inhibited plant growth was observed when FPW with high salinity (TDS = 5000 mg·L-1) and low salinity (TDS = 1000 mg·L-1) was used for irrigation of long-term (8-week) plant cultures. Finally, upregulated genes were identified to illustrate the difference in plant growing. The results of this study provide a guide for efficient and safe use of FPW after FDFO treatment for agricultural application.
Salinity accumulation in osmotic membrane bioreactors (OMBRs) is one of the key challenges, which can be mitigated in situ by reverse-fluxed solute transport through integration of bioelectrochemical systems (BES). The effects of several key operating parameters on salinity accumulation were investigated. Salinity accumulation depended on balance between reversal solute flux (RSF) and reverse-fluxed ammonium (RFA) transport, which was driven by electrical migration and concentration diffusion. DS concentration was the primary factor influencing RSF, and the lowest DS concentration exhibited the minimum solute leakage. Aeration played a vital role in RFA transport, and a higher aeration helped to enhance RFA transport. Increased current generation (i.e., influent flow rate of 0.5 mL min-1 and external resistance of 5.0 Ω) contributed to RFA migration. The lack of electrolyte addition in catholyte contributed to RFA diffusion. These optimal parameters encourage the further development of an effective strategy for salinity mitigation in BES-based OMBR technology.
In recent years, the concept of nutrient removal/recovery has been applied as a sustainable solution to develop and design various modern wastewater treatment technologies for recovering nutrients from waste streams and is one of the high-priority research areas. Forward osmosis (FO) technology has received increasing interests as a potential low-fouling membrane process and a new approach to remove/recover nutrients from wastewater and sludge. The main objective of this review is to summarize the state of FO technology for nutrient removal/recovery from wastewater and sludge in order to identify areas of future improvements. In this study, nutrient removal processes, FO membrane technology, main factors affecting the FO process performance, the source water for nutrient recovery, the previous studies on the FO membrane process for nutrient removal/recovery from wastewater and sludge, membrane fouling, and recent advances in FO membranes for nutrient removal/recovery were briefly and critically reviewed. Then, the proposed possible designs to apply FO process in conventional wastewater treatment plants (WWTPs) were theoretically presented. Finally, based on the gaps identified in the area, challenges ahead, future perspectives, and conclusions were discussed. Further investigations on the properties of FO associated with real wastewater, wastewater pre-treatment, the long-term low fouling operation, membrane cleaning strategies, water flux and the economic feasibility of the FO process are still desirable to apply FO technology for nutrient removal/recovery at full-scale (decentralized or centralized) in the future.
Wastewater is widely recognized as a sink of active nitrogen and phosphorus, and the recovery of both nutrients as fertilizers is widely studied in recent years. Electroactive bacteria increasingly attract attentions in this area because they are able to produce an electric field in microbial electrochemical systems to concentrate ammonium and phosphate for recovery. Importantly, these unique bacteria are able to convert nitrate and nitrite directly to ammonium, maximizing the active nitrogen species capable of recovery. Ferric ions produced by electroactive bacteria can be precipitated with phosphate to recover as vivianite in neutral wastewaters. All these processes employed electroactive bacteria as both nitrate and iron reducer and bioelectric field generator. The mechanism as well as technologies are summarized, and the challenges to further improve their performance are discussed.
Nutrient recovery from wastewater is important to the circular economy and requires technological advancements. Herein, a novel electrochemical membrane system (EMS) was developed to recover both phosphorus and nitrogen from real digester centrate. The EMS synergistically coupled electrodialysis with membrane contactor to facilitate the selective recovery of individual nutrient. Under a constant current of 10 mA cm⁻², the EMS recovered more than 95% of PO4³⁻-P and 80% of NH4⁺-N, at energy consumption of 670 ± 48 kWh kg⁻¹ P and 52 ± 2 kWh kg⁻¹ N. It should be noted that the same energy was used to recover two nutrients. When the acid produced from the anodic reaction was directly reused for N absorption, the final concentrations of PO4³⁻-P and NH4⁺-N reached 144 ± 3 and 1232 ± 130 mg L⁻¹, respectively. Adding extra acid did not affect phosphorus recovery but significantly enhance nitrogen recovery to 1797 ± 83 mg L⁻¹. The results of this study have demonstrated the feasibility of the proposed EMS and encouraged further investigation to reduce its energy consumption and improve nutrient recovery.
Microbial desalination cells (MDCs) have been experimentally proven as a versatile bioelectrochemical system (BES). They have the potential to alleviate environmental pollution, reduce water scarcity and save energy and operational costs. However, MDCs alone are inadequate to realise a complete wastewater and desalination treatment at a high-efficiency performance. The assembly of identical MDC units that hydraulically and electrically connected can improve the performance better than standalone MDCs. In the same manner, the coupling of MDCs with other BES or conventional water reclamation technology has also exhibits a promising performance. However, the scaling-up effort has been slowly progressing, leading to a lack of knowledge for guiding MDC technology into practicality. Many challenges remain unsolved and should be mitigated before MDCs can be fully implemented in real applications. Here, we aim to provide a comprehensive chronological-based review that covers technological limitations and mitigation strategies, which have been developed for standalone MDCs. We extend our discussion on how assembled, coupled and scaled-up MDCs have improved in comparison with standalone and lab-scale MDC systems. This review also outlines the prevailing challenges and potential mitigation strategies for scaling-up based on large-scale specifications and evaluates the prospects of selected MDC systems to be integrated with conventional anaerobic digestion (AD) and reverse osmosis (RO). This review offers several recommendations to promote up-scaling studies guided by the pilot scale BES and existing water reclamation technologies.
Hybrid osmotic membrane bioreactor (OMBR) takes advantage of the cooperation of varying biological or desalination processes and can achieve NEWS (nutrient-energy-water-solute) recovery from wastewater. However, a lack of universal parameters hinders our understanding. Herein, system configurations and new parameters are systematically investigated to help better evaluate recovery performance. High-quality water can be produced in reverse osmosis/membrane distillation-based OMBRs, but high operation cost limits their application. Although bioelectrochemical system (BES)/electrodialysis-based OMBRs can effectively achieve solute recovery, operation parameters should be optimized. Nutrients can be recovered from various wastewater by porous membrane-based OMBRs, but additional processes increase operation cost. Electricity recovery can be achieved in BES-based OMBRs, but energy balances are negative. Although anaerobic OMBRs are energy-efficient, salinity accumulation limits methane productions. Additional efforts must be made to alleviate membrane fouling, control salinity accumulation, optimize recovery efficiency, and reduce operation cost. This review will accelerate hybrid OMBR development for real-world applications.
Electrochemical processes are considered promising technologies for ammonia recovery from wastewater. In electrochemical processes, cation exchange membrane (CEM), which is applied to separate compartments, plays a crucial role in the separation of ammonium nitrogen from wastewater. Here we provide a comprehensive review on the application of CEM in electrochemical systems for ammonia recovery from wastewater. Four kinds of electrochemical systems, including bioelectrochemical systems, electrochemical stripping, membrane electrosorption, and electrodialysis, are introduced. Then we discuss the role CEM plays in these processes for ammonia recovery from wastewater. In addition, we highlight the key performance metrics related to ammonia recovery and properties of CEM membrane. The limitations and key challenges of using CEM for ammonia recovery are also identified and discussed.
In recent years, due to rapid globalization and urbanization, the demand for fuels, energy, water and nutrients has been continuously increasing. To meet the future need of the society, wastewater is a prominent and emerging source for resource recovery. It provides an opportunity to recover valuable resources in the form of energy, fertilizers, electricity, nutrients and other products. The aim of this review is to elaborate the scientific literature on the valorization of wastewater using wide range of treatment technologies and reduce the existing knowledge gap in the field of resource recovery and water reuse. Several versatile, resilient environmental techniques/technologies such as ion exchange, bioelectrochemical, adsorption, electrodialysis, solvent extraction, etc. are employed for the extraction of value-added products from waste matrices. Since the last two decades, valuable resources such as polyhydroxyalkanoate (PHA), matrix or polymers, cellulosic fibers, syngas, biodiesel, electricity, nitrogen, phosphorus, sulfur, enzymes and a wide range of platform chemicals have been recovered from wastewater. In this review, the aspects related to the persisting global water issues, the technologies used for the recovery of different products and/or by-products, economic sustainability of the technologies and the challenges encountered during the valorization of wastewater are discussed comprehensively.
Forward osmosis (FO) is an emerging permeation-driven membrane technology that manifests advantages of low energy consumption, low operating pressure, and uncomplicated engineering compared to conventional membrane processes. The key issues that need to be addressed in FO are membrane fouling, concentration polarization (CP) and reverse solute diffusion (RSD). They can lead to problems about loss of draw solutes and reduced membrane lifetime, which not only affect the water treatment effectiveness of FO membranes, but also increase the economic cost. Current research has focused on FO membrane preparation and modification strategies, as well as on the selection of draw solutions. Unfortunately, these intrinsic solutions had limited success in unraveling these phenomena. In this paper, we provide a brief review of the current state of research on existing external field-assisted FO systems (including electric-, pressure-, magnetic-, ultrasonic-, light- and flow-assisted FO system), analyze their mitigation mechanisms for the above key problems, and explore potential research directions to aid in the further development of FO systems. This review aims to reveal the feasibility of the development of external field-assisted FO technology to achieve a more economical and efficient FO treatment process.
In this study, a promising strategy is reported to synthesize a high water-permeable polyamide (PA) rejection layer using ZIF-67 nanoparticle as a sacrificial templating material. ZIF-67 nanoparticle was incorporated into the PA rejection layer using two different strategies (i) conventional blending interfacial polymerization (IP) and (ii) newly introduced in-situ growth methods. The primary aim was to study the effects of various incorporation strategies on template removal efficiency. In the conventional blending IP method, the pre-synthesized ZIF-67 nanoparticle was dispersed in the amine monomer solution and incorporated into the PA layer of thin-film composite membranes (TFN-ZIF-PS, modified with pre-synthesized ZIF-67). But in the in-situ method, ZIF-67 was synthesized and incorporated simultaneously with the formation of the PA layer via interfacial reaction of aqueous amine/Co⁺² and organic acid chloride/Hmim solutions (TFN-ZIF-IS, modified with in-situ synthesized ZIF-67). After IP reaction, ZIF-67 nanoparticles were removed by water dissolution, which created nanovoids within the PA layer. Systematic membrane characterization confirmed that the incorporation method significantly affects template removal efficiency, where the TFN-ZIF-IS membrane shows a quite different morphology after ZIF-67 removal (membrane with nanovoids (NV), TFC-NV-IS). The effective incorporation and removal of ZIF-67 nanoparticles increased the water permeability of TFC-NV-IS to 5.6 LMH/bar, which is about 5-fold compared with the control TFC membrane. Additionally, TFC-NV-IS exhibited forward osmosis water flux that was raised about 2-fold compared with the control TFC one with a negligible decrease in selectivity. These considerably enhanced separation performances can be attributed to the improved water transport through the as-formed nanovoids. Thus, our strategies (incorporation and template removal) in this study provide a new avenue to synthesize advanced TFC-FO membranes with exceptional performance.
The chapter highlights the role and importance of electroactive biofilm (EAB) formation in microbial electrochemical system (MES). The strategies for the development of such biofilm and factors affecting its formation on MES electrodes are discussed. A brief idea about microbes involved in electron transfer (ET) and electron transfer mechanism of EAB is given. This chapter also includes an explanation of methods for direct or indirect study of EAB that will help the future researchers. The shift in the dynamic role of EAB in MES during the journey of technology from lab to field is an important part of this chapter. Further, a brief discussion is included on application of electroactive biofilms (EAB) and its future perspective.
Anaerobic digestion (AD) serves as a potential bioconversion process to treat various organic wastes/wastewaters, including sewage sludge, and generate renewable green energy. Despite its efficiency, AD has several limitations that need to be overcome to achieve maximum energy recovery from organic materials while regulating inhibitory substances. Hence, bioelectrochemical systems (BESs) have been widely investigated to treat inhibitory compounds including ammonia in AD processes and improve the AD operational efficiency, stability, and economic viability with various integrations. The BES operations as a pretreatment process, inside AD or after the AD process aids in the upgradation of biogas (CO2 to methane) and residual volatile fatty acids (VFAs) to valuable chemicals and fuels (alcohols) and even directly to electricity generation. This review presents a comprehensive summary of BES technologies and operations for overcoming the limitations of AD in lab-scale applications and suggests upscaling and future opportunities for BES-AD systems.
Bioelectrochemical technologies taking advantage of electrochemical activities of microorganisms have recently gained special attention. Electroactive microorganisms can either transfer electrons to or receive electrons from an electrode. Such unique properties can be exploited to create either a microbial fuel cell, a microbial electrolysis system, or a microbial electrosynthesis system, and thus can offer a variety of possible technologies for various applications. In this chapter, we provide an overview of plausible applications of bioelectrochemical technologies, particularly in agriculture resource recovery, as this is an increasing demand from the massive human population on the earth. Those applications may include, but are not limited to, recovering energy from agriculture wastes as electricity and fuel chemicals, upgrading agriculture wastes to valuable products or biomass, recovering nutrients from agriculture wastes, etc. Furthermore, novel bioelectrochemical processes and the potentials of applying BES technologies to achieve a future circular agriculture economy will also be discussed.
Microbial electrolysis cell (MEC) is a promising and relatively newer bioelectrochemical process for sustainable H2, value-added compounds production, and simultaneous wastewater treatment. As compared to other alternative technologies, the MEC has shown numerous strengths: primarily, the MECs pledge the feasibility to generate H2 at proportionately less energy consumption than the usual energy demand for water electrolysis. In addition, MECs are not restricted by dark fermentation (DF) barriers; H2 could be completely extracted from the spent medium in MECs, achieving remarkable H2 recovery than all kinds of processes. What is more, significantly pure H2 is generated in the MECs cathodes. Besides, MECs incorporate both treatment of waste and bioenergy generation, thereby the MEC possesses the benefits of being environmentally friendly, efficient, and waste disposal. Also, MEC has the ability to produce a wide variety of value-added products, such as methane, hydrogen peroxide, ethanol, and so on, and all these attracted enormous attention in both academia and industry. The MEC must be robust enough to be used in the field for bioremediation or energy production.
Production of bioenergy with concomitant value-added products recovery is considered as one of the promising ways of sustainable wastewater treatment owing to the upfront energy crisis and limited resource availability. The bio-electrochemical system (BES) is one of the potential techniques that possess the capability of bioenergy production and resource recovery while simultaneously treating the wastewater. The overview on the recovery of nutrients, heavy metals, industrial chemicals, and bioenergy recovery from the wastewater using BES has been elaborated in this article. Additionally, a brief future scope to overcome current bottlenecks and potential upcoming research areas of BES have been described.
Nitrous oxide (N 2 O) has been studied intensively in 6 wastewater treatment as a detrimental greenhouse gas. However, 7 increasingly more studies have adopted a contrasting objective, 8 recovering N 2 O from wastewater as an energy resource. This article 9 critically reviewed and analyzed the current status of N 2 O recovery 10 research in wastewater treatment, to identify knowledge gaps and 11 guide future research. Overall, N 2 O recovery is a promising 12 research direction while still in active development. At present, 13 unstable nitritation, the low energy potential, and potential 14 environmental risks of N 2 O harvesting render the recovery of 15 N 2 O from mainstream wastewater technically and economically challenging. High-strength wastewater treatment is more favorable 16 for N 2 O recovery due to the high energy potential, established nitritation approaches, and significant carbon/aeration savings. The 17 coupled aerobic−anoxic nitrous decomposition operation (CANDO) process is currently the most investigated and promising N 2 O 18 recovery process. Nevertheless, more research is needed for its implementation on a large scale. Research opportunities for the 19 CANDO process have been identified in this paper. Meanwhile, N 2 O recovery via autotrophic denitritation is a more recent concept, 20 with limited studies hitherto. More experiments are needed to investigate its technological feasibility. Furthermore, other novel N 2 O 21 recovery processes, e.g., truncated denitrification and chemical oxidation, should also be explored to facilitate the recovery of N 2 O 22 from wastewater.
Forward osmosis (FO), considered as a promising separation process for nutrient enrichment in wastewater, is attracting increasing interest in integration with chemical precipitation and other technologies for recovering nutrients in wastewater treatment. In this chapter, the processes of nutrients recovery via FO‐based systems are introduced in terms of mechanisms and influencing factors. Additionally, the key challenges related to the recovery systems are discussed and some approaches are proposed to resolve these challenges. Roadmaps for future research and development on the nutrients recovery using FO‐based systems are identified. Compared to aerobic FO‐based systems, anaerobic FO‐based processes need more investigations into their integration's efficiency in the context of nutrient recovery from wastewater. Emphasis is given to carry out more economic assessment and pilot‐ and plant‐scale evolutions of the recovery systems, which makes the nutrients recovery via FO‐based technologies more sustainable in wastewater treatment.
Microbial fuel cell (MFC) technology is a promising solution for both organic and inorganic effluent treatment, as it is capable of handling a variety of complex contaminants with simultaneous energy and resource recovery. Unlike conventional treatment technologies, MFCs can achieve removal of organic matter, persistent organic compounds, heavy metals and nutrients from categorically different waste effluents, while recovering energy and valuable substances. This makes the technology economically attractive, and viable for a wide range of industries for their waste treatment applications. However, in order to implement this technology as an on-site treatment unit, limitations pertaining to costs, scale-up and performance have to be addressed, with due emphasis on developing strategies that can be easily applied in industrial settings. This review summarizes the recent progress in the field of waste treatment and environmental remediation using MFCs, and examines these operational challenges. Cost-effective materials that have been implemented on the field and at large scales have also been highlighted. In addition, the review highlights the fact that there is a need to optimize the technology depending on energy or resource recovery. The MFC-based technology utilizes the synergy of bioremediation and bioelectricity production from wastes, offering a sustainable approach to industrial waste management.
Bioelectrochemistry and, more specifically, microbial electrochemistry are research fields that establish their fundaments on the molecular and electrochemical link between microbes (also known as exoelectrogens or, focusing only on bacteria, electrochemically active bacteria) and electrodes. Bioelectrochemistry can be used as a strategy in bioremediation when traditional bioremediation is not an option due to the lack of suitable electron acceptors, and in which bioelectrochemical systems (BESs) are used for the removal of pollutants from the environment. For example, in subsurface hydrocarbon-polluted water, the absence of final electron acceptors may limit the biodegradation rate. Therefore, bioelectrochemical systems can be used as a sustainable remediation technology. Moreover, microbial metabolism can be stimulated in a BES when overpotential is applied, increasing the rate of pollutant degradation. BES has been studied for the remediation at laboratory and pilot scale of water, soil, and sediments affected by organic pollutants, such as hydrocarbons (aliphatic, aromatic) and chlorinated compounds. In addition, BES can be exploited as biosensors to detect organic pollutants in environmental matrices and remote sites. One of the main challenges in this field is to scale up the technology towards the commercial BES remediation applications.
Bioelectrochemical systems (BESs) with the coexistence of denitrifiers and electricigens were generally observed for simultaneous nitrogen removal and electricity production. As the increasing of nitrate, the percentage of denitrifiers increased and the percentage of electricigens relatively decreased until it lost its dominant position. In denitrifying BES, anodic heterotrophic denitrification could improve organics removal and energy recovery efficiency during the treatment of nitrate-containing wastewater. In this chapter, the developments of denitrifying BES as well as the evolution of the microbial community were comprehensively introduced. Furthermore, a special type of bacteria, denitrifying electricigens, was also introduced and utilized in BES for the treatment of nitrate-contaminated waters.
As the rapid increase of the worldwide population, recovering valuable resources from wastewater have attracted more and more attention by governments and academia. Electrochemical technologies have been extensively investigated over the past three decades to purify wastewater. However, the application of these technologies for resource recovery from wastewater has just attracted limited attention. In this review, the recent (2010−2020) electrochemical technologies for resource recovery from wastewater are summarized and discussed for the first time. Fundamentals of typical electrochemical technologies are firstly summarized and analyzed, followed by the specific examples of electrochemical resource recovery technologies for different purposes. Based on the fundamentals of electrochemical reactions and without the addition of chemical agents, metallic ions, nutrients, sulfur, hydrogen and chemical compounds can be effectively recovered by means of electrochemical reduction, electrochemical induced precipitation, electrochemical stripping, electrochemical oxidation and membrane-based electrochemical processes, etc. Pros and cons of each electrochemical technology in practical applications are discussed and analyzed. Single-step electrochemical process seems ineffectively to recover valuable resources from the wastewater with complicated constituents. Multiple-step processes or integrated with biological and membrane-based technologies are essential to improve the performance and purity of products. Consequently, this review attempts to offer in-depth insights into the developments of next-generation of electrochemical technologies to minimize energy consumption, boost recovery efficiency and realize the commercial application.
The excess availability of wastewater and reduction in the energy resources has initiated a new thought process of ‘waste to energy’. The green technology like solar and wind system utilises natural unending resources for production of valuable energy. To utilise waste as a source of energy we require process that a convert the chemical energy trapped in waste to green energy. The conventional technologies like anaerobic digestor produce methane, but the purity of product and time duration taken for the production makes the system unsustainable. The new bio-electrochemical system has been rectified as a potential process that can utilise waste, produce valuable products and is being optimised towards sustainability. This chapter presents a comparative review with respect to this new technology and its ability for resource recovery.
Forward osmosis can be used to treat wastewater using seawater as the draw solution. This has been done for both water purification and nutrient concentration. However, the loss of ammoniacal nitrogen to the draw solution may be a key issue, reducing nutrient recovery and preventing the discharge of untreated seawater draw solution – a cost-saving strategy for the industrialisation of forward osmosis for wastewater treatment. In this study, forward ammoniacal nitrogen flux was studied using digester centrate from a wastewater treatment plant as the feed solution. The draw solution contained various NaCl concentrations in order to determine the effect of reverse sodium flux on forward ammoniacal nitrogen flux. The forward ammoniacal nitrogen flux was measured to be 1.5 × 10 –6 –8.0 × 10 –5 mol m ⁻² s ⁻¹ , and increased with pH and sodium concentration in the draw solution. The forward ammonium flux increased with draw solution reverse salt flux below pH = 9, whereas it was unaffected by this flux above pH = 9. Therefore, the reverse flux of sodium ions facilitates the forward transport of ammonium ions at low pH. The transport of the positively charged ammonium was lower than that of the neutral ammonia due to its higher hydrodynamic radius.
Zero liquid discharge (ZLD) — a wastewater management strategy that eliminates liquid waste and maximizes water usage efficiency — has attracted renewed interest worldwide in recent years. Although implementation of ZLD reduces water pollution and augments water supply, the technology is constrained by high cost and intensive energy consumption. In this critical review, we discuss the drivers, incentives, technologies, and environmental impacts of ZLD. Within this framework, the global applications of ZLD in the United States and emerging economies such as China and India are examined. We highlight the evolution of ZLD from thermal- to membrane-based processes, and analyze the advantages and limitations of existing and emerging ZLD technologies. The potential environmental impacts of ZLD, notably greenhouse gas emission and generation of solid waste, are discussed and the prospects of ZLD technologies and research needs are highlighted.
Ammonia and sulfate, which are prevalent pollutants in agricultural and industrial wastewaters, can cause serious inhibition in several biological treatment processes, such as anaerobic digestion. In this study, a novel bioelectrochemical approach termed bipolar bioelectrodialysis was developed to recover ammonia and sulfate from waste streams and thereby counteracting their toxicity during anaerobic digestion. Furthermore, hydrogen production and wastewater treatment were also accomplished. At an applied voltage of 1.2 V, nitrogen and sulfate fluxes of 5.1 g NH4(+)-N/m(2)/d and 18.9 g SO4(2-)/m(2)/d were obtained, resulting in a Coulombic and current efficiencies of 23.6% and 77.4%, respectively. Meanwhile, H2 production of 0.29 L/L/d was achieved. Gas recirculation at the cathode increased the nitrogen and sulfate fluxes by 2.3 times. The applied voltage, initial (NH4)2SO4 concentrations and coexistence of other ions were affecting the system performance. The energy balance revealed that net energy (≥16.8 kWh/kg-N recovered or ≥4.8 kWh/kg-H2SO4 recovered) was produced at all the applied voltages (0.8-1.4 V). Furthermore, the applicability of bipolar bioelectrodialysis was successfully demonstrated with cattle manure. The results provide new possibilities for development of cost-effective technologies, capable of waste resources recovery and renewable energy production.
Copyright © 2015 Elsevier Ltd. All rights reserved.
Bioelectrochemical systems (BES) and forward osmosis (FO) are two emerging technologies with great potential for energy-efficient water/wastewater treatment. BES takes advantage of microbial interaction with a solid electron acceptor/donor to accomplish bioenergy recovery from organic compounds, and FO can extract high-quality water driven by an osmotic pressure. The strong synergy between those two technologies may complement each other and collaboratively address water-energy nexus. FO can assist BES with achieving water recovery (for future reuse), enhancing electricity generation, and supplying energy for accomplishing the cathode reactions; while BES may help FO with degrading organic contaminants, providing sustainable draw solute, and stabilizing water flux. This work has reviewed the recent development that focuses on the synergy between BES and FO, analyzed the advantages of each combination, and provided perspectives for future research. The findings encourage further investigation and development for efficient coordination between BES and FO towards an integrated system for wastewater treatment and reuse.
A 100-L microbial electrolysis cell (MEC) was operated for a 12-month period fed on raw domestic wastewater at temperatures ranging from 1°C to 22°C, producing an average of 0.6L/day of hydrogen. Gas production was continuous though decreased with time. An average 48.7% of the electrical energy input was recovered, with a Coulombic efficiency of 41.2%. COD removal was inconsistent and below the standards required. Limitations to the cell design, in particular the poor pumping system and large overpotential account for many of the problems. However these are surmountable hurdles that can be addressed in future cycles of pilot scale research. This research has established that the biological process of an MEC will to work at low temperatures with real wastewater for prolonged periods. Testing and demonstrating the robustness and durability of bioelectrochemical systems far beyond that in any previous study, the prospects for developing MEC at full scale are enhanced.
The objective of this research was to investigate the sensitivity of electrodialysis performance to variations in voltage application and membranes when treating brackish water reverse osmosis concentrate waste. Synthetic BWRO concentrates from Arizona and Texas of 7890-14,800 mg/L total dissolved solids were prepared with poly-phosphonate antiscalants. Experimentation was performed using a laboratory-scale electrodialyzer with two sets of membranes (AMV-CMV and PCSA-PCSK) with a nominal transfer area of 64 cm(2) per membrane. Flow, pressure, conductivity, temperature, and pH were measured continuously, and periodic samples were analyzed for specific anion and cation concentrations. The BWRO concentrates were successfully treated with stack voltage applications of 0.5-1.5 V/cell-pair for salinity removal ratios up to 99% with current density less than 500 A/m(2). This paper highlights that (1) the specific energy consumption was proportional to the applied voltage and equivalent concentration separated (i.e., approximately 0.03 kW h/m(3) per Volt/cell-pair applied per meq/L separated); (2) lower voltage applications decreased the relative separation rate of sulfate compared to chloride; and (3) water transport by electro-osmosis was independent of voltage application or resulting current densities, while it is affected by the ion exchange membranes.
Air Gap Membrane Distillation (AGMD) has been implemented to treat produced water. The permeate fluxes, rejection factor and energy consumption for three different membranes, TF200, TF450 and TF1000, with pore sizes of 0.2, 0.45 and 1 μm, respectively, are measured at different operating parameters. The influence of membrane pore size is investigated for the produced water. Also, the effect of feed flow rate, coolant temperature and feed temperature on permeate flux is studied. The flux increases as the feed temperature and flow rate increase, and declines as the coolant temperatures increase. Moreover, the energy consumption was measured at different pore size and was found to be independent of membrane pore size.
A pilot-scale (1,000 L) continuous flow microbial electrolysis cell was constructed and tested for current generation and COD removal with winery wastewater. The reactor contained 144 electrode pairs in 24 modules. Enrichment of an exoelectrogenic biofilm required ~60 days, which is longer than typically needed for laboratory reactors. Current generation was enhanced by ensuring adequate organic volatile fatty acid content (VFA/SCOD ≥ 0.5) and by raising the wastewater temperature (31 ± 1°C). Once enriched, SCOD removal (62 ± 20%) was consistent at a hydraulic retention time of 1 day (applied voltage of 0.9 V). Current generation reached a maximum of 7.4 A/m(3) by the planned end of the test (after 100 days). Gas production reached a maximum of 0.19 ± 0.04 L/L/day, although most of the product gas was converted to methane (86 ± 6%). In order to increase hydrogen recovery in future tests, better methods will be needed to isolate hydrogen gas produced at the cathode. These results show that inoculation and enrichment procedures are critical to the initial success of larger-scale systems. Acetate amendments, warmer temperatures, and pH control during startup were found to be critical for proper enrichment of exoelectrogenic biofilms and improved reactor performance.
Enhanced biological phosphorus removal wastewater treatment plants that use anaerobic digesters for sludge treatment, have high phosphorus concentrations in the sidestreams from their sludge dewatering equipment. To remove phosphorus from such sidestreams controlled struvite crystallisation can be used. Struvite (or MAP) is a naturally occurring crystal of magnesium, ammonium and phosphate. We present operational results obtained with a continuously operated pilot-scale MAP reactor. The pilot-scale reactor (143 l) was an air agitated column reactor with a reaction and a settling zone, based on the Phosnix process of Unitika Ltd., Japan. The influent to the MAP reactor was centrate from the centrifuge that dewaters anaerobically digested sludge at the Oxley Creek wastewater treatment plant in Brisbane. We used a 60% magnesium hydroxide slurry to add the required magnesium to the process and to obtain the alkaline pH value required. The pilot-scale MAP process achieved an ortho-P removal ratio of 94% from an average influent ortho-P concentration of 61 mg/l. The reactor was operated at a pH of around 8.5. Insufficient dosing of magnesium reduced the P removal performance. There was no influence of the hydraulic residence time on the process in the range of 1-8 h. The dry MAP product had cadmium, lead and mercury concentrations well below the legal limits for fertilisers in Queensland, Australia and can be reused as a valuable slow-release fertiliser.
Microbial fuel cell (MFC) research is a rapidly evolving field that lacks established terminology and methods for the analysis of system performance. This makes it difficult for researchers to compare devices on an equivalent basis. The construction and analysis of MFCs requires knowledge of different scientific and engineering fields, ranging from microbiology and electrochemistry to materials and environmental engineering. Describing MFC systems therefore involves an understanding of these different scientific and engineering principles. In this paper, we provide a review of the different materials and methods used to construct MFCs, techniques used to analyze system performance, and recommendations on what information to include in MFC studies and the most useful ways to present results.
Forward osmosis (FO) has been widely studied for desalination or water recovery from wastewater, and one of its key challenges for practical applications is reverse solute flux (RSF). RSF can cause loss of draw solutes, salinity build-up and undesired contamination at the feed side. In this study, in-situ electrolysis was employed to mitigate RSF in a three-chamber FO system (“e-FO”) with Na2SO4 as a draw solute and deionized (DI) water as a feed. Operation parameters including applied voltage, membrane orientation and initial draw concentrations were systematically investigated to optimize the e-FO performance and reduce RSF. Applying a voltage of 1.5 V achieved a RSF of 6.78 ± 0.55 mmol m−2 h−1 and a specific RSF of 0.138 ± 0.011 g L−1 in the FO mode and with 1 M Na2SO4 as the draw, rendering ∼57% reduction of solute leakage compared to the control without the applied voltage. The reduced RSF should be attributed to constrained ion migration induced by the coactions of electric dragging force (≥1.5 V) and high solute rejection of the FO membrane. Reducing the intensity of the solution recirculation from 60 to 10 mL min−1 significantly reduced specific energy consumption of the e-FO system from 0.693 ± 0.127 to 0.022 ± 0.004 kWh m−3 extracted water or from 1.103 ± 0.059 to 0.044 ± 0.002 kWh kg−1 reduced reversed solute. These results have demonstrated that the electrolysis-assisted RSF mitigation could be an energy-efficient method for controlling RSF towards sustainable FO applications.
Using liquid fertilizer as a draw solute in forward osmosis (FO) to extract high-quality water from wastewater is of strong interest because it eliminates the need for regenerating draw solute, thereby requiring less energy input to system operation. However, energy consumption of such an approach has not been evaluated before. Herein, a submerged FO system with all-purpose liquid fertilizer as a draw solute was studied for energy consumption of water recovery from either deionized (DI) water or domestic wastewater. The results showed that a higher draw concentration led to higher water flux and lower energy consumption, for example 0.25 ± 0.08 kWh m⁻³ with 100% draw concentration, but reverse salt flux (RSF) was also more serious. Decreasing the recirculation flow rate from 100 to 25 mL min⁻¹ had a minor effect on water flux, but significantly reduced energy consumption from 1.30 ± 0.28 to 0.09 ± 0.02 kWh m⁻³. When extracting water from the secondary effluent, the FO system exhibited comparable performance of water flux and energy consumption to that of the DI water. However, the primary effluent resulted in obvious fouling of the FO membrane and higher energy consumption than that of the secondary effluent/DI water. This study has provided important implications to proper evaluation of energy consumption by the FO system using liquid fertilizer or other non-regenerating draw solutes.
Using fertilizers as draw solutes in forward osmosis (FO) can accomplish wastewater reuse with elimination of recycling draw solute. In this study, three commercial fast-release all-purpose solid fertilizers (F1, F2 and F3) were examined as draw solutes in a submerged FO system for water extraction from either deionized (DI) water or the treated wastewater. Systematic optimizations were conducted to enhance water extraction performance, including operation modes, initial draw concentrations and in-situ chemical fouling control. In the mode of the active layer facing the feed (AL-F or FO), a maximum of 324 mL water was harvested using 1-M F1, which provided 41% of the water need for fertilizer dilution for irrigation. Among the three fertilizers, F1 containing a lower urea content was the most favored because of a higher water extraction and a lower reverse solute flux (RSF) of major nutrients. Using the treated wastewater as a feed solution resulted in a comparable water extraction performance (317 mL) to that of DI water in 72 h and a maximum water flux of 4.2 LMH. Phosphorus accumulation on the feed side was mainly due to the FO membrane solute rejection while total nitrogen and potassium accumulation was mainly due to RSF from the draw solute. Reducing recirculation intensity from 100 to 10 mL min−1 did not obviously decrease water flux but significantly reduced the energy consumption from 1.86 to 0.02 kWh m−3. These results have demonstrated the feasibility of using commercial solid fertilizers as draw solutes for extracting reusable water from wastewater, and challenges such as reverse solute flux will need to be further addressed.
This study demonstrates that microbial fuel cells (MFCs) and osmotic membrane bioreactors (OMBRs) can be mutually beneficial when integrated together for wastewater treatment. When connecting MFCs with OMBRs, the solute buildup increased conductivity and buffer capacity, which greatly increased MFC power density from 3 W/m(3) up to 11.5 W/m(3). In turn, the MFCs conditioned and reduced sludge production and therefore reduced forward osmosis (FO) membrane fouling. The MFC-OMBR equipped with new thin-film composite (TFC) membrane showed excellent organic (>95%) and phosphorus removal (>99%) and therefore maintained effluent sCOD below 20 mg/L. However, the nitrogen removal was limited due to the negative surface charge of the thin-film composite membrane and solution chemistry, which led to higher flux of ammonium toward the OMBR draw solution. Further studies are needed to improve nitrogen removal, reduce fouling, and optimize system integration.
In this study, a membrane distillation process was applied to treat the digestate produced from the anaerobic digestion of livestock wastewater with a high concentration of suspended solids, chemical oxygen demand (COD), total nitrogen (TN), and phosphorus (TP). Laboratory scale direct contact membrane distillation was performed to observe the variation of flux and rejection rate of each component according to the transmembrane temperature, cross flow velocity, and pH of the feed solution. In 90-min distillation, almost no fouling occurred and the permeate flux increased from 4.2 to 38.8 LMH by increasing the transmembrane temperature from 20 to 60 °C and cross flow velocity from 0.09 to 0.27 m/s. In long term distillation, a constant flux of 17.5 LMH was maintained for the initial 24 h but then decreased gradually to reach 5 LMH in 72 h. The flux decline occurred more rapidly as the pH of feed solution increased from 7 to 8.5. More than 99% rejection of COD and TP were achieved regardless of the distillation condition and processing time. The rejection rate of TN was affected dominantly by the extent of cake layer formed on the membrane surface rather than the pH and temperature of the feed solution.
The effect of the inoculation of a microalgae-bacteria system on the removal of nutrients and organic matter using municipal, piggery and digestate wastewaters was evaluated. Three conditions for each substrate were evaluated: (1) inoculation with activated sludge and illumination, (2) inoculation with activated sludge without illumination, and (3) inoculation with activated sludge plus a native microalgae consortium under illumination. The illuminated reactors that were inoculated only with activated sludge developed microalgae after 12 operation days. In these reactors, the formation of flocs was observed affecting the sedimentation of the biomass positively. The removal of chemical oxygen demand, ammonium and phosphorous reached 84%, 65% and 77%, respectively.
Microbial fuel cells (MFCs) have been intensively studied at a bench scale and further development of this technology requires system scaling up and understanding of their performance under a non-laboratory condition. In this study, a 200-L modularized MFC system consisting of 96 MFC modules was developed and operated in a local wastewater treatment plant for treating primary effluent. During more than 300 days’ operation, the MFC system removed more than 75% of total chemical oxygen demand and 90% of suspended solids, despite significant fluctuation in treatment performance affected by wastewater quality and operational factors. It achieved 68% removal of ammonia nitrogen, but phosphorous and accumulated nitrate due to nitrification needs further disposal. The frequency of the catholyte recirculation exerted a strong effect on energy consumption by the MFC system. Through both parallel and serial electric connections, the MFC system generated power of ~ 200 mW that was extracted by a power management system to drive a 60-W DC pump for catholyte recirculation. Over 60% of the material cost of the MFCs was due to cation exchange membrane, and the capital cost of the MFC system could be comparable to that of small wastewater treatment facilities. The results of this study encourage further development of MFC technology with reduced cost and improved performance towards sustainable wastewater treatment.
Wastewater nutrient recovery holds promise for more sustainable water and agricultural industries. We critically review three emerging membrane processes - forward osmosis (FO), membrane distillation (MD) and electrodialysis (ED) - that can advance wastewater nutrient recovery. Challenges associated with wastewater nutrient recovery were identified. The advantages and challenges of applying FO, MD, and ED technologies to wastewater nutrient recovery are discussed, and directions for future research and development are identified. Emphasis is given to exploration of the unique mass transfer properties of these membrane processes in the context of wastewater nutrient recovery. We highlight that hybridising these membrane processes with existing nutrient precipitation process will lead to better management of and more diverse pathways for near complete nutrient recovery in wastewater treatment facilities.
Forward osmosis (FO) has the potential to improve the energy efficiency of membrane-based water treatment by leveraging waste heat from steam electric power generation as the primary driving force for separation. In this study, we develop a comprehensive FO process model, consisting of membrane separation, heat recovery, and draw solute regeneration (DSR) models. We quantitatively characterize three alternative processes for DSR: distillation, steam stripping, and air stripping. We then construct a mathematical model of the distillation process for DSR that incorporates hydrodynamics, mass and heat transport resistance, and reaction kinetics, and we integrate this into a model for the full FO process. Finally, we utilize this FO process model to derive a first-order approximation of the water production capacity given the rejected heat quantity and quality available at US electric power facilities. We find that the upper bound of FO water treatment capacity using low-grade heat sources at electric power facilities exceeds process water treatment demand for boiler water make-up and flue gas desulfurization wastewater systems.
We report a hybrid microfiltration-forward osmosis membrane bioreactor (MF-FOMBR) for direct phosphorus recovery from municipal wastewater in the course of its treatment. In the process, a forward osmosis (FO) membrane and a microfiltration (MF) membrane are operated in parallel in a bioreactor. FO membrane rejects the nutrients (e.g. PO43-, Ca2+, Mg2+, etc.) and results in their enrichment in the bioreactor. The nutrients are subsequently extracted via the MF membrane. Phosphorus is then recovered from the nutrients enriched MF permeate via precipitation without the addition of an external source of calcium or magnesium. The use of seawater brine as a draw solution (DS) is another novel aspect of the system. The process achieved 90% removal of total organic carbon and 99% removal of NH4+-N. 97.9% of phosphate phosphorus (PO43--P) was rejected by the FO membrane and enriched within the bioreactor. >90% phosphorus recovery was achieved at pH 9.0. The precipitates were predominantly amorphous calcium phosphate with a phosphorus content of 11.1-13.3 %. In principal, this process can recover almost all the phosphorus, apart from that assimilated by bacteria for growth. Global evaluation showed an overall phosphorus recovery of 71.7% over 98 days.
Desalination of brackish water can provide freshwater for potable use or non potable applications such as agricultural irrigation. Brackish water desalination is especially attractive to microbial desalination cells (MDCs) because of its low salinity, but this has not been well studied before. Herein, three brackish waters prepared according to the compositions of actual brackish water in three locations in Israel were examined with domestic wastewater as an electron source in a bench-scale MDC. All three brackish waters could be effectively desalinated with simultaneous wastewater treatment. The MDC achieved the highest salt removal rate of 1.2 g L(-1) d(-1) with an initial salinity of 5.9 g L(-1) and a hydraulic retention time (HRT) of 0.8 d. The desalinated brackish water could meet the irrigation standard of both salinity (450 mg L(-1) TDS) and the concentrations of major ionic species, given a sufficient HRT. The MDC also accomplished nearly 70% removal of organic compounds in wastewater with Coulombic efficiency varied between 5 and 10%. A previously developed MDC model was improved for brackish water desalination, and could well predict salinity variation and the concentrations of individual ions. The model also simulated a staged operation mode with improved desalination performance. This integrated experiment and mathematical modeling approach provides an effective method to understand the key factors in brackish water desalination by MDCs towards further system development.
Copyright © 2015 Elsevier Ltd. All rights reserved.
Ammonia inhibition is one of the most frequent and serious problems in biogas plants. In this study, a novel hybrid system consisting of a submersible microbial desalination cell (SMDC) and a continuous stirred tank reactor (CSTR) was developed for counteracting ammonia inhibition during anaerobic digestion with simultaneous in-situ ammonia recovery and electricity production. The SMDC was powered by acetate in a buffer solution, while synthetic ammonia-rich wastewater was used as the feeding of the CSTR. Under continuous operation, ammonia recovery rate of 86 g-N/m2/d and current density of 4.33 A/m2 were achieved at steady-state condition. As a result, 112% extra biogas was produced due to ammonia recovery by the SMDC. High-throughput sequencing showed that ammonia recovery had an impact on the microbial community structures in the SMDC and CSTR. Considering the additional economic benefits of biogas enhancement and possible wastewater treatment, the SMDC may represent a cost-effective and environmentally friendly method for waste resources recovery and biomethanation of ammonia-rich residues. This article is protected by copyright. All rights reserved
This study has presented a proof-of-concept system for the self-sustained supply of ammonium-based draw solute for wastewater treatment through coupling a microbial electrolysis cell (MEC) and forward osmosis (FO). The MEC produced an ammonium bicarbonate draw solute via recovering ammonia from a synthetic organic solution, which was then applied in the FO for extracting water from the MEC anode effluent. The recovered ammonium could reach a concentration of 0.86 mol L–1, and with this draw solution, the FO extracted 50.1 ± 1.7% of the MEC anode effluent. The lost ammonium during heat regeneration could be supplemented with additional recovered ammonium in the MEC. The MEC achieved continuing treatment of both organic and ammonium in the returned feed solution mixed with fresh anolyte, although at lower efficiency compared to that with completely fresh anolyte. These results encourage further investigation to optimize the coordination between MEC and FO with improved performance.
Research in the field of Forward Osmosis (FO) membrane technology has grown significantly over the last 10 years, but its application in the scope of wastewater treatment has been slower. Drinking water is becoming an increasingly marginal resource. Substituting drinking water for alternate water sources, specifically for use in industrial processes, may alleviate the global water stress. FO has the potential to sustainably treat wastewater sources and produce high quality water. FO relies on the osmotic pressure difference across the membrane to extract clean water from the feed, however the FO step is still mostly perceived as a "pre-treatment" process. To prompt FO-wastewater feasibility, the focus lies with new membrane developments, draw solutions to enhance wastewater treatment and energy recovery, and operating conditions. Optimisation of these parameters are essential to mitigate fouling, decrease concentration polarisation and increase FO performance; issues all closely related to one another. This review attempts to define the steps still required for FO to reach full-scale potential in wastewater treatment and water reclamation by discussing current novelties, bottlenecks and future perspectives of FO technology in the wastewater sector.
We demonstrate the simultaneous extraction of phosphorus and clean water from digested sludge centrate using a forward osmosis (FO)–membrane distillation (MD) hybrid process. In this FO–MD hybrid process, FO concentrates orthophosphate and ammonium for subsequent phosphorus recovery in the form of struvite (MgNH4PO4·6H2O), while MD is used to recover the draw solution and extract clean water from the digested sludge centrate. A decline in water flux was observed during the FO process, but fouling was largely reversible after a brief, simple membrane flushing using deionized water. The FO process also provides an effective pretreatment capacity to the subsequent MD process, which exhibited stable water flux. The use of MgCl2 as the draw solute for the FO process is another novel aspect of the system. The reverse salt flux of magnesium to the concentrated digested sludge across the FO membrane and the diffusion of protons away from the digested sludge create favorable conditions for the formation of struvite crystals. The precipitates obtained in the hybrid process were verified to be struvite crystals by examining the crystal morphology, element composition, and crystal structure. Results reported here highlight the potential and robustness of the FO–MD hybrid process for extracting phosphorus from wastewater.
Nutrient removal and recovery has received less attention during the development of bioelectrochemical systems (BES) for energy efficient wastewater treatment, but it is a critical issue for sustainable wastewater treatment. Both nitrogen and phosphorus can be removed and/or recovered in a BES through involving biological processes such as nitrification and bioelectrochemical denitrification, the NH4(+)/NH3 couple affected by the electrolyte pH, or precipitating phosphorus compounds in the high-pH zone adjacent a cathode electrode. This paper has reviewed the nutrients removal and recovery in various BES including microbial fuel cells and microbial electrolysis cells, discussed the influence factors and potential problems, and identified the key challenges for nitrogen and phosphorus removal/recovery in a BES. It expects to give an informative overview of the current development, and to encourage more thinking and investigation towards further development of efficient processes for nutrient removal and recovery in a BES.
