The increased production of biogas through the anaerobic digestion (AD) process has raised several concerns regarding the management of liquid digestate, which can present some environmental risks if not properly handled. Among the different techniques to treat AD digestate, microalgae and cyanobacteria cultivation has emerged as a sustainable approach to valorizing di-gestate while producing valuable biomass for production of biofuels and high value bioproducts. However, the intrinsic parameters of the liquid digestate can strongly limit the microalgae or cya-nobacteria growth as well as limit the uptake of residual nutrients. In this study, the detoxification potential of activated carbon (AC) was evaluated on agro-industrial liquid digestate prior to Spir-ulina platensis cultivation. Different doses of AC, ranging from 5 to 100 g/L, were tested during ad-sorption experiments in order to determine the adsorption capacity as well as the removal efficiency of several compounds. Experimental results showed the high reactivity of AC, especially towards phosphate (PO4-P), total phenol (TP) and chemical oxygen demand (COD). At a dosage of 50 g/L, the AC pretreatment successfully achieved 54.7%, 84.7% and 50.0% COD, TP and PO4-P removal, corresponding to adsorption capacity of 94.7 mgDCO/g, 17.9 mgTP/g and 8.7 mgPO4-P/g, respectively. Even if the AC pretreatment did not show significant effects on Spirulina platensis growth during toxicity assays, the AC adsorption step strongly participated in the digestate detoxification by removing hardly biodegradable molecules such as phenolic compounds.
Biodegradable plastics, if they are not properly managed at their end-of-life, can have the same hazardous environmental consequences as conventional plastics. This study investigates the treatment of the main biodegradable plastics under mesophilic and thermophilic anaerobic digestion using biochemical methane potential test and the microorganisms involved in the process using amplicon sequencing of the 16 S rRNA. Here we showed that, only PHB and TPS undergone important and rapid biodegradation under mesophilic condition (38 °C). By contrast, PCL and PLA exhibited very low biodegradation rate as 500 days were required to reach the ultimate methane yield. Little or no degradation occurred for PBAT and PBS at 38 °C. Under thermophilic conditions (58 °C), TPS, PHB, and PLA reached high levels of biodegradation in a relatively short period (< 100 d). While PBS, PBAT, and PCL could not be converted into methane at 58 °C. PHB degraders (Enterobacter and Cupriavidus) and lactate-utilizing bacteria (Moorella and Tepidimicrobium) appeared to play an important role in the PHB and PLA degradation, respectively. This work not only provides crucial data on the anaerobic digestion of the main biodegradable plastics but also enriches the understanding of the microorganisms involved in this process, which are of great importance for future development of the treatment of biodegradable plastics in anaerobic digestion systems.
The influence of the inoculum-substrate ratio (ISR) on the mesophilic and thermophilic biochemical methane potential test of two biodegradable plastics was evaluated. Poly(lactic acid) (PLA) and polyhydroxybutyrate (PHB) were selected for this study, the first for being recalcitrant to mesophilic anaerobic digestion (AD) and the second, by contrast, for being readily biodegradable. Several ISRs, calculated on the basis of volatile solids (VS), were tested: 1, 2, 2.85, 4, and 10 g(VS of inoculum).g(VS of substrate)⁻¹. A high ISR was associated with an enhanced methane production rate (i.e., biodegradation kinetics). However, the ultimate methane production did not change, except when inhibition was observed. Indeed, applying the lowest ISR to readily biodegradable plastics such as PHB resulted in inhibition of methane production. Based on these experiments, in order to have reproducible degradation kinetics and optimal methane production, an ISR between 2.85 and 4 is recommended for biodegradable plastics. The active microbial communities were analyzed, and the active bacteria differed depending on the plastic digested (PLA versus PHB) and the temperature of the process (mesophilic versus thermophilic). Previously identified PHB degraders (Ilyobacter delafieldii and Enterobacter) were detected in PHB-fed reactors. Thermogutta and Tepidanaerobacter were detected during the thermophilic AD of PLA, and they are probably involved in PLA hydrolysis and lactate conversion, respectively.
The development of selective biowaste collection in most European countries provides new opportunities for the anaerobic digestion sector. In parallel, extensive development of biodegradable plastics like polylactic-acid (PLA) and polyhydroxybutyrate (PHB), which facilitates the replacement of conventional plastics, has taken place in the past decade. This study investigated anaerobic co-digestion in semi-continuous reactors of biowastes (75% VS) and biodegradable plastics (25% Volatil Solids, PLA and PHB). PHB was estimated to be fully biodegraded in the reactors. By contrast, PLA accumulated in the reactor, and an average biodegradation of 47.6 ± 17.9% was estimated during the third hydraulic retention time. Pretreatment of PLA, by thermo-alkaline hydrolysis at 70 °C, with 2.5 w/v of Ca(OH)2 for 48 h, improved the biodegradation yield of PLA to 77.5 ± 9.3%. Finally, it was highlighted that PLA or PHB addition to the feed did not further affect the agronomic properties of the digestate.
This paper aims to investigate the effect of extrusion at high solid loading on corn stover (CS) properties and its enzymatic hydrolysis. This biomass was extruded under different screw speeds and different solid loadings and the impact of these parameters on physicochemical properties was evaluated. It was found that lignocellulosic components were not significantly affected by the pretreatment, while surface area increased with solid loading and rotation speed. Different enzyme cocktails were used for the enzymatic hydrolysis of extruded and untreated CS. Overall, mild twin‐extrusion enhanced the enzymatic hydrolysis of corn stover through an increase in glucose and xylose yields by 134‐212% and 214‐294% respectively when using T. longibrachiatum cellulase. The highest sugar content was obtained from CS extruded under 400 g total solids (TS) per liter and 200 rpm. The energy efficiency of the pretreatment was also assessed and was found to be maximal at 400 gTS/L and 200 rpm. This article is protected by copyright. All rights reserved.
Urban wastewater and industrial effluents are treated by conventional technologies according to their biological or physicochemical properties. Yet new approaches to waste treatment are needed due to the problems associated with micropollutants (phenolic compounds, organochlorines and organofluorines, antibiotics, etc.) present in surface water. Some of these contaminants are refractory to commonly used wastewater treatments, and could have long-term impacts on the environment and on human health. Efficient waste treatments are needed to tackle this issue without adversely affecting the cost-effective environmental balance. This study aimed to define a strategy to choose the best waste treatment process based on the nature of the wastewater and the treatment objectives. A customizable methodology was devised to analyze and compare three different technologies (ozonation, membrane filtration, and activated carbon adsorption) to choose the best treatment strategy based on environmental, technical, and economic criteria. These various criteria were compiled by weighting and rating them to generate a scoring table of the overall performance of the technologies in question. A conceptual study was then performed to test the methodology designed for the treatment of an industrial effluent. The results show that activated carbon adsorption yielded the best results when the spent carbon was reactivated. Membrane filtration resulted in a good water quality that, when reused, improved its score. Based on these results, a decision tree was devised to determine the best strategy for the treatment of organic pollutants in order to reach reuse or discharge objectives. Highlights Advance treatments are efficient at treating recalcitrant organics. A multicriteria approach was devised. Optimization of these treatments is needed to limit environmental issues. GAC with reactivation of the carbon resulted in the best process performance. Internal water reuse increases the overall performance of a process.
Anaerobic digestion (AD) of sewage sludge is an already well-developed technology to convert waste to bioenergy and digestate. Despite its deployment, AD process still raises environmental, technical and economic issues and many researches have been done to improve the process yield, reduce environmental burdens from digestate application and allow a better distribution of energy. The integration of thermal processes with anaerobic digestion is explored to overcome some of the anaerobic digestion limitations. In this study, a cradle-to-grave life cycle assessment (LCA) is performed to compare a system integrating anaerobic digestion and pyrolysis (PY) with single anaerobic digestion, for the co-digestion of sewage sludge and quinoa residue. The results suggest that the environmental impacts of the two pathways are quite similar except for three impact categories: single anaerobic digestion is the best scenario in terms of global warming potential (−769 vs. -604 kg CO2 eq./t substrate), ozone depletion (−33.7 vs −2.11 mg CFC-11 eq./t substrate) and fossil resources use (−9900 vs −6900 MJ/t substrate). The multifunctional process could be a viable competitor to single anaerobic digestion by improving pyrolysis products upgrading. The application of liquid digestate to crop field revealed to have significant burdens to particulate matter, acidification and terrestrial eutrophication impact categories and must be carefully monitored in both pathways.
Since the end of the 20th century, the engineering field, like many other sectors, has been faced with society's new preoccupations. Eco-design strives to reduce the harmful effect of industrial production and mass consumption on the environment. It makes use of tools and methods which, besides being built on technical and scientific foundations, borrow a vocabulary from economics and management science (“cost-benefits”, “needs”, “stakeholders”, etc.) and puts a fundamental category -“value”-, back on the agenda. This research endeavors to show how these foundational concepts “contaminate” the tools colonized by an economical imaginary. Researchers' and scientists' attempts to modify or overturn the existing order come up against a blind spot: the definition of value in the engineering field and, more specifically in sustainable development, finds its theoretical origins in the political economics of the 18th century, more precisely in the neo-classical economy of the 19th century. Through a narrative review methodology, we first argue that eco-design have not broken away from the ideology of orthodox economics, where riches are reduced to a simple monetary expression, and the social and environmental consequences are evaluated in terms of cost/benefits in the light of a rational instrumentality. Then, to illustrate these propositions, we base our arguments on the analysis of three tools used to develop ideas of sustainable development/innovation: Life Cycle Assessment; the Value Mapping tool, and the Triple Layered Business Model Canvas.
Growing concern regarding non-biodegradable plastics and the impact of these materials on the environment has promoted interest in biodegradable plastics. The intensification of separate biowastes collection in most European countries has also contributed to the development of biodegradable plastics, and the subject of their end-of-life is becoming a key issue. To date, there has been relatively little research to evaluate the biodegradability of biodegradable plastics by anaerobic digestion (AD) compared to industrial and home composting. However, anaerobic digestion is a particularly promising strategy for treating biodegradable organic wastes in the context of circular waste management. This critical review aims to provide an in-depth update of anaerobic digestion of biodegradable plastics by providing a summary of the literature regarding process performances, parameters affecting biodegradability, the microorganisms involved, and some of the strategies (e.g., pretreatment, additives, and inoculum acclimation) used to enhance the degradation rate of biodegradable plastics. In addition, a critical section is dedicated to suggestions and recommendations for the development of biodegradable plastics sector and their treatment in anaerobic digestion.
To date, the introduction of biodegradable plastics such as PLA in anaerobic digestion systems has been limited by a very low rate of biodegradation. To overcome these limitations, pretreatment technologies can be applied. In this study, the impact of pretreatments (mechanical, thermal, thermo-acid, and thermo-alkaline) was investigated. Mechanical pretreatment of PLA improved its biodegradation rate but did not affect the ultimate methane potential (430–461 NL CH4 kg⁻¹ VS). In parallel, thermal and thermo-acid pretreatments exhibited a similar trend for PLA solubilization. Both of these pretreatments only achieved substantial solubilization (>60%) at higher temperatures (120 and 150 °C). At lower temperatures (70 and 90 °C), negligible solubilization (between 1 and 6%) occurred after 48 h. By contrast, coupling of thermal and alkaline pretreatment significantly increased solubilization at the lower temperatures (70 and 90 °C). In terms of biodegradation, thermo-alkaline pretreatment (with 5% w/v Ca(OH)2) of PLA resulted in a similar methane potential (from 325 to 390 NL CH4 kg⁻¹ VS) for 1 h at 150 °C, 6 h at 120 °C, 24 h at 90 °C, and 48 h at 70 °C. Reduction of the Ca(OH)2 concentration (from 5% to 0.5% w/v) highlighted that a concentration of 2.5% w/v was sufficient to achieve a substantial level of biodegradation. Pretreatment at 70 and 90 °C using 2.5% w/v Ca(OH)2 for 48 h resulted in biodegradation yields of 73% and 68%, respectively. Finally, a good correlation (R² = 0.90) was found between the PLA solubilization and its biodegradation.
Anaerobic digestion (AD) is considered an important brick of the circular economy allowing to treat and stabilize organic residues, produce renewable energy and promote the return to soil of organic matter and mineral nutrients. Digestate has been historically seen as a biogas by-product with a fertilizing value while representing a significant cost sector to AD plant operators. A paradigm shift is now necessary as other renewable energy sources with lowering production costs tend to disrupt an AD economic model greatly relying on subsidized biogas valorisation either via electricity or purification to biomethane. This chapter is focused on digestate post-treatments allowing to generate value-added products while closing and enhancing the loop between major agricultural inputs and outputs, the latter being indirectly present in digestates. Several options exist to generate mineral fertilizers, soil amendments, organo-mineral fertilizers, biostimulants, biocontrol products, energy and beyond from digestate. Consumer behaviour and regulatory framework evolution are necessary for increasing the demand and enabling a more sustainable agriculture based on biosourced upcycled materials. A major global milestone has been recently achieved as the EU has introduced a new fertilizer regulation (CE 2019/1009) that will tend to boost the commercialisation of digestate-based products within the world’s largest common market.
Anaerobic digestion for the valorization of organic wastes into biogas is gaining worldwide interest. Nonetheless, the sizing of the biogas plant units require knowledge of the quantity of feedstock, and their associated methane potentials, estimated widely by Biochemical Methane Potential (BMP) tests. Discrepancies exist among laboratories due to variability of protocols adopted and operational factors used. The aim of this study is to verify the influence of some operational factors (e.g., analysis frequency, trace elements and vitamins solution addition and flushing gas), feedstock conservation and the source of inoculum on BMP. Among the operational parameters tested on cellulose degradation, only the type of gas used for flushing headspace of BMP assays had shown a significant influence on methane yields from cellulose. Methane yields of 344 ± 6 NL CH4 kg−1 VS and 321 ± 10 NL CH4 kg−1 VS obtained from assays flushed with pure N2 and N2/CO2 (60/40 v/v). The origin of inoculum (fed in co-digestion) only significantly affected the methane yields for straw, 253 ± 3 and 333 ± 3 NL CH4 kg−1 VS. Finally, freezing/thawing cycle effect depended of the substrate (tested on biowaste, manure, straw and WWTP sludge) with a possible effect of water content substrate.
Bio-refining of algal biomass is currently considered as a key strategy to cut down the cost and improve the overall feasibility of algal-derived biodiesel. With that aim, in this study it was implemented a three-stage biorefinery process for the recovery of five differentiated bio-products from heterotrophically Chlorella protothecoides biomass. In the first stage, which was conducted at pilot scale from 14 kg of wet biomass, direct saponification converted 40% of dry algal biomass into free fatty acids. The obtained fatty acids were successfully turned into high quality biodiesel, whereas the analysis of unsaponifiables revealed the presence of interesting high-value biomolecules such as sterols (62%), squalene and carotenoids (1.7% each). The de-oiled biomass underwent an enzymatic hydrolysis process. This second process led to the valorization of 9% (0.09 kg/kg) of the remaining algal components which were recovered in a liquid hydrolysate mainly composed of soluble amino acids (15 g/L) and sugars (27.9 g/L). In the last biorefinery stage, the leftover solid fraction after enzymatic hydrolysis (0.36 kg/kg) was used as substrate in an anaerobic digestion process which yielded biogas at 196 ± 4 NL CH4/kg VS. The digestate co-produced in this stage was chemically characterized and assessed as fertilizer (at a dose of 170kg N/ha) for wheat and tomato plant growth, with comparable effect to that of industrial fertilizers. This use allowed a closed-loop system through the recycling of nutrients for primary production. The exposed cascade-processing, which was demonstrated technically feasible, could potentially improve the value of algal biomass through the production of multiple products.
As part of the circular economy, grassroots initiatives from the social and solidarity economy (SSE) that promote reuse, reemployment and repair could be seen as ‘local sustainable initiatives’ and as citizen-based contributions to sustainability transitions that require favorable conditions to emerge. Despite a diversity of existing solutions, repair and reuse activities remain limited due to social, institutional and technical lock-ins. This study relies on two French case studies and mobilizes a theoretical framework that combines pragmatic sociology and science technology studies. The study illustrates that there are different modes of commitment to repair and that repair initiatives appeal primarily to people of the militant mode of commitment. Even though a rather broad range of citizens is somehow committed to the practice of repairing, repair initiatives generally fail to attract this broad range of citizens because the type of citizen commitment that they assume occurs only at marginal levels.
The worldwide growing population, challenged by an ever-increasing global demand for food production, is also concomitant with increased waste production, particularly organic waste. During the last decades, several waste processing technologies have been developed such as anaerobic digestion and pyrolysis. Recently, there has been an increased interest in creating industrial synergies by combining technologies in order to increase the efficacy of the process and improve waste management in the circular economy. In this review, we report on the importance of coupling anaerobic digestion and pyrolysis while providing evidence on the synergistic effects that may occur within such a combined waste bi-functional process. Specific attention has been paid to multiple symbiosis features that exist when coupling both processes, mainly 1) maximizing energy recovery through pyrolysis of solid digestate or feeding of the aqueous bio-oil phase in anaerobic digestion, 2) biogas purification by biochar or activated biochar, and 3) improving anaerobic digestion process stability by biochar addition to the system. In addition, the effects of coupling anaerobic digestate with biochar on soil biochemical properties and crop production were also presented. Improving the dual symbiosis of coupling anaerobic digestion and pyrolysis is likely to be a sustainable based approach that holds promise for wiser and more eco-efficient processing of organic wastes for versatile applications.
Targeting sustainability in our industrial society requires integrating specific criteria in the design process of products and processes. A paradigm shift is necessary in the economical, social and political systems to ensure the natural ecosystems preservation on the planet while fulfilling society needs. Various research methods have therefore emerged to change the way products and services are designed, developed, used and discarded considering territorial contexts. Design for Sustainability, Design for Sustainable Transition, Socially Responsible Design, post-growth design, etc. provide several methods integrating the sustainable principles in the design process. However those approaches remain mainly experimental and are limited to the industrial context. In parallel to those approaches a wide variety of grassroots initiatives have emerged in territories. They propose alternative ways to design systems and they integrate new constraints in a practical manner. This research therefore aims to confront the diversity of Design to Environment (DtE) approaches with ‘grassroots’ initiatives in order to understand the possible evolution of the integration of sustainability into the design process of products and services used in industry. This paper presents the first literature review results of a started project in 2020. An original research protocol is proposed in this paper, based on specific focus groups with grassroots initiatives practitioners and eco-design experts from research and industry. The presentation of four DtE frameworks are analysed in this paper. This research finally discusses the opportunity of integrating the grassroots enriched DtE frameworks by non-official-designers in life cycle engineering. This bottom-up process may drive an expression of sustainability in industry aligned with some emerging local socio-technical systems.
The sustainability of the anaerobic digestion industry is closely related to proper digestate disposal. In this study, an innovative cascading biorefinery concept coupling anaerobic digestion and subsequent pyrolysis of the digestate was investigated with the aim of enhancing the energy recovery and improving the fertilizers from organic wastes. Continuous anaerobic co-digestion of quinoa residues with wastewater sludge (45/55% VS) exhibited good stability and a methane production of 219 NL CH4/kg VS. Subsequent pyrolysis of the solid digestate was carried out (at 500 °C, 1 h, and 10 °C/min), resulting in a products distribution of 40 wt% biochar, 36 wt% bio-oil, and 24 wt% syngas. The organic phase (OP) of bio-oil and syngas exhibited higher and lower heating values of 34 MJ/kg and 11.8 MJ/Nm³, respectively. The potential synergy of coupling biochar with liquid digestate (LD) for agronomic purposes was investigated. Interestingly, coupling LD (at 170 kg N/ha) with biochar (at 25 tons/ha) improved the growth of tomato plants up to 25% compared to LD application alone. In parallel, co-application of biochar with LD significantly increased the ammonia volatilization (by 64%) compared to LD application alone, although their simultaneous use did not impact the C and N mineralization rates.
Biodegradable plastics market is increasing these last decades, including for coffee capsules. Anaerobic digestion, as a potential end-of-life scenario for plastic waste, has to be investigated. For this purpose, mesophilic (38 °C) and thermophilic (58 °C) anaerobic digestion tests on three coffee capsules made up with biodegradable plastic (Beanarella®, Launay® or Tintoretto®) and spent coffee (control) were compared by their methane production and the microbial communities active during the process. Mesophilic biodegradation of the capsules was slow and did not reach completion after 100 days, methane production ranged between 67 and 127 NL (CH4) kg⁻¹ (VS). Thermophilic anaerobic digestion resulted in a better biodegradation and reached completion around 100 days, methane productions were between 257 and 294 NL (CH4) kg⁻¹ (VS). The microbial populations from the reactors fed with plastics versus spent coffee grounds were significantly different, under both the mesophilic and the thermophilic conditions. However, the different biodegradable plastics only had a small impact on the main microbial community composition at a similar operational temperature and sampling time. Interestingly, the genus Tepidimicrobium was identified as a potential key microorganisms involved in the thermophilic conversion of biodegradable plastic in methane.
In this study, the effect of thermo‐alkaline pretreatment and recycling of the liquid fraction (black liquor) for successive pretreatment steps on chemical composition and methane yields from horse manure was investigated. At first, horse manure was subjected to alkaline pretreatment at 70 °C for 1 h (8.6 g NaOH/100 g total solids). Pretreated biomass was then separated into solid and liquid fractions (black liquor). In the subsequent stages, black liquor was mixed with 20% (v/v) of fresh NaOH and was reused to pretreat subsequent batches of horse manure (cycles 1–4). Chemical analyses showed that thermo‐alkaline pretreatment was effective in the delignification and solubilization of organic matter and thereby increased the holocellulose (cellulose and hemicelluloses) content in the solid fraction of horse manure. On comparison with untreated horse manure methane yields (225 ± 1 L CH4 kg−1 VSadded), thermo‐alkaline pretreatment improved the methane yields of horse manure by 39% (313 ± 16 L CH4 kg−1 VSadded). However, the effectiveness of black liquor recycling on methane production decreased (from 39 to 12%) with an increase in the number of recycling steps (from 1 to 4). Nevertheless, recycling of black liquor reduced the consumption of NaOH (40%) and water use (60%). Thus, thermo‐alkaline pretreatment with liquor recycling was found to be an effective pretreatment with an economic gain of 2.4 to 10.4 compared to pretreatment without recycling. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd
This study aimed to produce activated biochars (BC) from Moroccan algae residue (AG) and olive pomace (OP) using mechanochemical activation with NaOH and ball milling (BM) for treating artificial textile wastewater containing methylene blue (MeB). The produced OP activated-BC by BM showed the highest absolute value of zeta potential (-59.7 mV) then high removal efficiency of MeB compared to other activated-BC. Non-linear pseudo-first order kinetic model was the most suitable model to describe the kinetic of adsorption of MeB into all biochar produced from AG and the NaOH activated BC from OP, whereas non-linear pseudo-second order kinetic model suits the OP raw biochar and BM activated BC. Non-linear Langmuir isotherm were the most suitable models for describing MeB adsorption onto BC compared to non-linear Freundlich isotherm model. The maximum adsorption capacities for AG activated-BC with NaOH and BM were 13.1 mg/g and 9.1 mg/g, respectively, while the maximum adsorption of OP activated-BC were 2.6 mg/g and 31.8 mg/g, respectively. The thermodynamic study indicates the spontaneous and endothermic nature of the adsorption process of most activated-BC. In addition, ΔS0 suggested the increase of randomness at the interface of solid-liquid during MeB sorption onto BC.
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