Yu Liu

• PhD
• Professor (Full) at Nanyang Technological University

According to Food and Agricultural Organization (FAO), one third of food produced globally for human consumption is lost along the food supply chain. In many countries food waste are currently landfilled or incinerated together with other combustible municipal wastes for possible recovery of energy. However, these two approaches are facing more and...

Although the activated sludge process, one of the most remarkable engineering inventions in the 20 th century, has made significant contribution to wastewater reclamation in the past 100 years, its high energy consumption is posing a serious impact and challenge on the current wastewater industry worldwide and is also inevitably linked to the issue...

Food waste (FW) management is a global conundrum because of the rapid population growth and growing economic activity. Currently, incineration and landfill are still the main means for FW management, while their environmental sustainability and economic viability have been in question. Recently, the biological processes including anaerobic digestio...

The principle of the conventional activated sludge (CAS) for municipal wastewater treatment is primarily based on biological oxidation by which organic matters are converted to biomass and carbon dioxide. After more than 100 years’ successful application, the CAS process is receiving increasing critiques on its high energy consumption and excessive...

As light intensity plays a pivotal role in the microalgal-bacterial granular sludge (MBGS) process, understanding its impact on system performance and energy dynamics is essential. This study investigated the effects of varying light intensities (20, 100, 200, and 300 μ mol/m²/s) on the performance of MBGS in urban wastewater treatment, with a part...

The boosting development of AI is contributing to rapid exponential surge of computing power demand, which results in the concerns on the increased energy consumption and carbon emission. To highlight the environmental impact of AI, a quantified analysis on the carbon emission associated with AI systems was conducted in this study, with the hope of...

The microalgal-bacterial granular sludge (MBGS) process, enhanced with sodium bicarbonate (NaHCO3), offers a sustainable alternative for wastewater treatment aiming for carbon neutrality. This study demonstrates that NaHCO3, which can be derived from the flue gases and alkaline textile wastewater, significantly enhances pollutant removal and biomas...

Interactions between algae and bacteria are pivotal in transforming complex organics for microalgal-bacterial granular sludge process, but the intrinsic removal mechanisms have not been well understood. Here, we investigate the mechanisms by which complex organics are removed from municipal wastewater. Complex organics can be disposed during day-ni...

So far, little has been known about how the combined collection systems of sewage and rainfall runoff (CCSs) affect emerging contaminants in river water. To fill up the knowledge gap, this study was conducted to investigate the spatial distributions of three natural estrogens (NEs, i.e., estrone (E1), 17β-estradiol (E2) and estriol (E3)) and their...

There have been many analytical methods for natural estrogens in commercial dairy milk samples, but in most of which, only four major estrogens (estrone (E1), 17β-estradiol (E2), estriol (E3), and 17α-estradiol (αE2)) were included. This work developed an effective GC–MS analytical method for simultaneous analysis of twelve natural estrogens in com...

The mainstream deammonification of municipal wastewater has been recognized as one of the greatest challenges in wastewater engineering. The conventional activated sludge process has disadvantages of high energy input and sludge production. To tackle this situation, an innovative A-B process, where an anaerobic biofilm reactor (AnBR) was functioned...

This work reported the development, performance and microbial community of microalgal-bacterial biofilms cultivated in a continuous-flow photoreactor for municipal wastewater treatment under various conditions. Results showed that microalgal-bacterial biofilms were successfully developed at a HRT of 9 h without external aeration, with a biofilm con...

The rapidly evolving global climate change has an unprecedented impact sustainable water supply, but also challenges and water shortage global food security. In such a dynamic situation, this study explored direct recovery of ammonium from the effluent of a pilot-scale anaerobic membrane bioreactor (AnMBR) treating actual municipal wastewater via b...

As an emerging green wastewater treatment technology, the microalgal-bacterial granular sludge (MBGS) process has attracted increasing interest under the current situation of global climate change. However, little information is available for its performance in treating municipal wastewater under outdoor conditions. Thus, this study evaluated the b...

The conventional activated sludge (CAS) process as one of the greatest engineering marvels has made irreplaceable contributions towards the human development in the past one hundred years. However, the underlying principle of CAS which is primarily based on biological oxidation has been challenged by accelerating global climate change. In such a si...

Anaerobic digestion (AD) has been widely employed for converting various biowastes into renewable energy. However, AD of gentamicin mycelial residues (GMRs, a byproduct of gentamicin production) is limited by ammonia inhibition and antimicrobial resistance risk. Compared to mesophilic AD (MMAD) of GMRs, this study looked into three semicontinuous A...

This work was the first to report twelve natural estrogens (NEs) in the urines of six threatened or endangered mammalians in a Zoo Park of Guangzhou (i.e., panda, gorilla, elephant, African lion, jaguar, and leopard). Ten out of twelve NEs were detected at least in one urine sample of the six mammalians studied, including the four major NEs (i.e.,...

One-stage anammox-based autotrophic nitrogen removal technology has attracted increasing interest to sustainable biological nitrogen removal for future wastewater treatment. However, its application in mainstream municipal wastewater treatment is still challenging due to low nitrogen and high organics of raw wastewater. Herein, a novel Simultaneous...

It is important to keep natural estrogen conjugates (C-NEs) intact in aqueous environmental sample before sample preparation; otherwise, this may influence the accurate determination of NEs. Therefore, this work thoroughly investigated the stability of C-NEs in three different aqueous environmental samples under four different storage conditions, r...

Various anaerobic processes have been explored for the energy-efficient treatment of municipal wastewater. However, dissolved methane in anaerobic effluent appears to be a barrier towards the energy and carbon neutrality of wastewater treatment. Although several dissolved methane recovery methods have been developed, their engineering feasibility a...

Recently, increasing interest has been placed in microalgal-bacterial granular sludge (MBGS) in the journey towards the energy and carbon neutrality of municipal wastewater treatment. Different from aerobic granular sludge, the performance of MBGS is mainly determined by the mutualism and symbiosis between coexisting microalgae and bacteria. It app...

Novel sandwich-structured carriers were developed for fast immobilizing anammox sludge, with which a fixed-film membrane bioreactor was further established for treating municipal wastewater. Results showed that fast start-up of the fixed-film reactor with anammox bacteria could be achieved without lag phase, indicated by the respective nitrogen rem...

With the speedy evolution of global climate change and water shortage, there is a growing need for the energy and carbon neutral wastewater reclamation technology. To tackle this challenge, an innovative anaerobic membrane bioreactor (AnMBR)-biochar adsorption-RO process was developed for reclaiming municipal wastewater to high-grade product water...

Steroid arylsulfatase is an important enzyme in human, which plays an important role in dynamic equilibrium of natural estrogens. On the other hand, sulfite can be endogenously produced as a consequence of human body’s metabolism of sulfur-containing amino acids, while its main sources to human are mainly derived from food as it is a widely used ad...

In this study, ferric-loaded magnetic burley tobacco stem biochar (MBTS) was synthesized via pyrolysis to improve the removal of Cr (VI). The results showed that MBTS had an adsorption capacity of 54.92 mg Cr (VI)/g, which was about 14 times higher than raw burley tobacco stem biochar (i.e., 3.84 mg/g). According to the findings obtained, a three-s...

This study developed a continuous-flow non-aerated microalgal-bacterial granular tubular reactor for aquaculture wastewater treatment under natural day-night conditions. Results showed that daytime was favorable for ammonia removal while nighttime for nitrate removal. Over 99% of nitrite-N could be removed over the day-night cycles at a hydraulic r...

In this study, four groups of microalgal-bacterial granules with averaged diameters of about 356, 760, 951 and 1,444 µm were used to investigate their characteristics and performance in treating wastewater. A strong correlation between extracellular polymeric substances of microalgal-bacterial granules and the granule size was observed. Moreover, g...

Microfiltration and ultrafiltration for water/wastewater treatment have gained global attention due to their high separation efficiency, while membrane fouling still remains one of their bottlenecks. In such a situation, many researchers attempt to obtain a deep understanding of fouling mechanisms and to develop effective fouling controls. Therefor...

This study investigated the pyrolysis of microalgal-bacterial granular sludge for producing bio-oil and biochar. Results showed that the bio-oil productivity of pyrolyzed MBGS reached 39.5 to 45.4 wt%, while 23.8-41.2% for the nitrogen-containing bio-oil at the temperature of 673 - 1073 K. Meanwhile the biochar with a nitrogen content of 3.7 - 7.0...

Wastewater usually contains various species of heavy metals, thus understanding of competitive adsorption kinetics of metallic ions in a multi-component system is necessary for developing an innovative adsorption process for wastewater decontamination. In this study, a novel adsorbent, namely nanostructured layered sodium vanadosilicate, was synthe...

A novel coronavirus (SARS-CoV-2) causing corona virus disease 2019 (COVID-19) has attracted global attention due to its highly infectious and pathogenic properties. Most of current studies focus on aerosols released from infected individuals, but the presence of SARS-CoV-2 in wastewater also should be examined. In this review, we used bibliometrics...

With gradual transformation of global linear economy to circular economy, the present municipal wastewater treatment processes designed with the philosophy of take-make-dispose are facing incredible economic and environmental pressures due to high energy consumption, emission of greenhouse gases, waste generation etc. In such a situation, “we canno...

Although four major natural estrogens (i.e., estrone (E1), 17β-estradiol (E2), estriol (E3) and 17α-estradiol (αE2)) have been commonly found in livestock urine, this study reports the occurrence of eight other less-studied natural estrogens in urine of swine and cattle, i.e. 2-hydroxyestone (2OHE1), 4-hydroxyestrone (4OHE1), 2-hydroxyestradiol (2O...

Transparent exopolymer particles (TEPs) are a class of transparent gel-like polysaccharides, which have been widely detected in almost every kind of feed water to membrane systems, including freshwater, seawater and wastewater. Although TEP have been thought to be related to the membrane fouling, little information is currently available for their...

In current biological nitrogen removal (BNR) processes, most of ammonium in municipal wastewater is biologically transformed to nitrogen gas, making ammonium recovery impossible. Thus, this article aims to provide a holistic review with in-depth discussion on (i) current BNR processes for municipal wastewater treatment, (ii) environmental and econo...

17α-ethynylestradiol (EE2) is a synthetic estrogen with very strong estrogenic potency. Due to its wide usage in human and livestock as well as its high recalcitration to biodegradation, it was ubiquitous in different environment. This review summarized EE2 concentration levels in surface waters among 32 countries across seven continents. EE2 conce...

In this study, waste cooking oil (WCO) co-fermentation with food waste by variable pH strategy was developed for microbial lipid production. Results showed that when WCO substitution rate within the range of 1.56–4.68% (corresponding to the WCO content in food waste), lipid production from Rhodosporidium toruloides 2.1389 could be increased by 7.2...

Freshwater resilience is facing to an increasing challenge, while carbon neutral wastewater reclamation has been put onto agenda in more and more countries. The activated sludge-microfiltration (MF)-reverse osmosis (RO) process has been currently adopted for reclamation of municipal wastewater to high-grade product water (e.g. NEWater). However, th...

Municipal wastewater is a very unique pool full of energy and useful substances. Though the innovative integrated anaerobic membrane bioreactor and reverse osmosis-ion exchange (AnMBR-RO-IE) process can produce high-grade reclaimed water with high energy efficiency, phosphorus resources recovery in the WWTPs has been rarely reported thus far. This...

In this study, a eukaryotic microalgae dominated microalgal-bacterial granular sludge process was explored for municipal wastewater treatment under simulated natural diel cycles. Different from previous studies with constant illumination, the excellent performances were obtained in terms of organics, ammonia-N and phosphate-P removal under simulate...

Tetracycline has been frequently detected in municipal wastewater due to its extended use for various purposes. This study investigated the influence of tetracycline on non-aerated microalgal-bacterial granular sludge cultivated for municipal wastewater treatment. It was found that ammonia-N removal rate decreased at the tetracycline concentrations...

The amount of sewage sludge generated has been continuously increasing with the expansion of global population and economic activity, which has posed a serious environmental challenge. Thermal‐chemical processes have been considered as an emerging technology for sewage sludge management with the aims for concurrent volume reduction, pathogen destru...

Water shortage is currently regarded as a pressing issue in urban sustainability around the world. Reclamation of municipal wastewater offers an emerging avenue for future urban water supply. In the past few decades, membrane technologies have evolved considerably, playing an increasingly important role in municipal wastewater reclamation, due to t...

This paper investigated the performance of non-aerated microalgal-bacterial granular sludge (MBGS) process in municipal wastewater treatment at different temperatures. Results showed that the 70.5%, 81.9% and 86.1% of chemical oxygen demand (COD) could be removed at 15, 22 and 30 °C, respectively, indicating that a high temperature favored removal...

Since the last several decades, there has been a growing concern on the presence of endocrine-disrupting compounds (EDCs) in potable water due to their negative impacts on public health of mankind. As such, more and more EDCs have been regulated in many national drinking water quality standards. Given this situation, this work attempted to delibera...

The volume reduction and subsequent solidification of soluble radionuclides have been known as the major challenges in global radioactive water management, with the urgent needs for new technology development. Thus, a novel forward osmosis (FO)-adsorption process was developed for decontamination of strontium-containing radioactive water. The FO fi...

This article is in the hope to open a fundamental discussion on what should future municipal wastewater treatment process be. A paradigm shift of treatment technology from present single functionality of removing to multiple-functionality of synergetic water-resource-energy recovery and carbon neutral for maximizing both environmental and economic...

This work for the first time showed that sulfated BPA could be directly analyzed as BPA with GC-MS after the derivatization with N,O-bis-(trimethylsilyl) trifluoroacetamide (BSTFA)+1% trimethylchlorosilane (TMCS), i.e. the deconjugation step was not necessary. This was because sulfated BPA indeed could be simultaneously deconjugated and derivatized...

As a synthetic estrogen, 17α-ethynylestradiol (EE2) has been known to show the strong estrogenic potency. This work critically reviewed the occurrence and removal of EE2 in municipal wastewater treatment plants (WWTPs). Based on the on-site investigations from 282 municipal WWTPs across 29 countries, the concentrations of EE2 in influent and efflue...

Endocrine disrupting compounds (EDCs) are well known emerging contaminants, which have the capacity to elicit negative effects on endocrine systems of both humans and wildlife. As the conventional wastewater treatment plants cannot stably remove these EDCs, post-treatment with advanced chemical oxidation methods such as ozonation are proven effecti...

So far, the microalgal-bacterial granular sludge process has attracted growing interest as an emerging wastewater treatment technology. Cadmium ion (Cd²⁺) commonly found in wastewater is toxic to microorganisms, thus its effect on microalgal-bacterial granules was investigated in this study. Results showed that Cd²⁺ at the concentration above 1 mg/...

With rapid global urbanization and increasing population, the water shortage is becoming a pressing issue for urban sustainability due to limited availability of natural water resource and increasing demand on fresh water. In such a situation, reclaimed municipal wastewater has been actively considered as a supplementary water source for sustaining...

In this study, a single-stage ceramic membrane moving bed biofilm reactor (CMMBBR) was developed for simultaneous COD and nitrogen removal, while its effluent was further reclaimed to ultra-clean water by a coupled reverse osmosis (RO) unit. Results showed that approximately 97% of COD and 93% of total nitrogen (TN) removal were obtained in CMMBBR,...

Developing efficient photocatalysts has been proved of great importance for many emerging applications, including removal of recalcitrant organic pollutants in wastewaters and transforming solar energy into important chemical feedstocks. One of major challenges for high performance photocatalysts is that most semiconductor-mediated photocatalysts s...

Catalytic pyrolysis of rain tree biomass (RTB), a typical horticultural waste, was investigated with nano-NiO as catalyst produced from hazardous nickel plating slag (NPS). It appeared from the analyses by FTIR, TGA, XRD, BET, and FESEM/EDX that nano-NiO produced had a SBET and mean particle size of 53.4 m²/g and 112.3 nm. The catalytic pyrolysis k...

To overcome the limitations of existing hydrophobic membranes for membrane distillation (MD) to treat industrial wastewater with complex contaminants, a composite membrane was developed in this study via incorporating graphene oxide (GO) on commercial polytetrafluoroethylene (PTFE) membrane. The dual-layer GO/PTFE membrane demonstrated asymmetric w...

The reclamation of municipal wastewater to obtain high-grade product water is a growing need due to the pressing global water shortage. However, the existing municipal wastewater treatment plants (WWTPs) with the conventional activated sludge process as a core is not a sustainable engineering solution towards future water sustainability. To tackle...

Straw as an agricultural byproduct has been recognized as a potential resource. However, open-field straw burning is still the main mean in many regions of the world, which causes the wasting of resource and air pollution. Recently, many technologies have been developed for energy and resource recovery from straw, of which the biological approach h...

Microparticle sorbents (MPSs) containing nano-Fe3O4 core, nano-layered double hydroxides shell modified with different transitional elements (TE-MPSs) are effective for capturing phosphate from wastewater. In present article, different TE-MPSs loaded with Ce, La, Zr and Hf were synthesized and the phosphorous removal performances were compared. The...

In this study, waste fallen leaves of Magnolia denudate (MDL), Magnolia grandiflora (MGL) and Michelia figo (MFL) were used as adsorbent for removing soluble methylene blue (MB) from aqueous solution. Results showed that the maximum adsorption capacity of MDL, MGL, and MFL were determined to be 185.19 mg/g, 149.25 mg/g, and 238.10 mg/g, which was h...

Layered sodium vanadosilicates was synthesized for removing soluble strontium ion (Sr²⁺) from simulated radioactive wastewater. SEM, EDS and TEM images indicated that layered sodium vanadosilicates had a nanostructure with flake-like shape providing an extremely large surface area. XRD, FTIR and XPS analyses further revealed a framework structure o...

Microalgal-bacterial granular sludge processes are attracting increasing research interest in fields of biological municipal wastewater treatment. However, these processes currently suffer from inefficient phosphorus removal and long hydraulic reaction time. As such, a self-sustaining synergetic microalgal-bacterial granular sludge process was expl...

Transparent exopolymer particles (TEP) as gel-like particulate acidic polysaccharide have been commonly found in marine, surface water and wastewater. Currently, increasing interest has been devoted to TEP-associated membrane fouling in different membrane systems for water and wastewater treatment, thus this review attempts to provide a holistic vi...

As endocrine disruptors, natural estrogens including estrone (E1), 17β-estradiol (E2), and estriol (E3) in wastewaters of municipal wastewater treatment plant (WWTP) as well as other environmental matrix have been widely studied. However, the far-less studied natural estrogens such as 2-hydroxyestrone (2OHE1), 16α-hydroxyestrone (16α-OHE1), 4-hydro...

Globally increasing concerns have been raised on the high energy consumption and greenhouse gas emissions in conventional municipal wastewater treatment processes over the past decades. In this study, a self-sustaining synergetic microalgal-bacterial granular sludge process was thus developed to address these challenges. The results showed that the...

This study reported a novel pretreatment approach with combination of alkaline protease (AP) and pH 10 for enhancing short-chain fatty acids (SCFAs) production from waste activated sludge (WAS). Through the AP-based pretreatment, WAS flocs were disintegrated with cell lysis, leading to release of biodegradable organic matters. At the external AP do...

Online chemical cleaning of membrane bioreactor (MBR) has been widely applied as a promising alternative to alleviate membrane fouling, while sustaining the permeability of MBR. However, the conventional chlorine-based chemical cleaning of MBR has been receiving increasing concerns on product water quality, environmental sustainability and human he...

Radioactive waste is a byproduct of nuclear power generation and applications of various radioactive materials in many fields. This waste has been strictly regulated as a highly hazardous material to all forms of life and the environment. The technologies currently adopted for managing radioactive waste are mainly based on segregation and storage....

Recently, the production of short-chain fatty acids (SCFAs) from waste activated sludge (WAS) has received increasing attention. Although several pretreatment methods had been investigated, sludge hydrolysis through depletion of multivalent cations has rarely been reported. In this work, cation exchange resin (CER) was used for enhancing WAS hydrol...

Polycarbonate (PC) and polyethylene terephthalate (PET) as the package materials have been widely used for Chinese bottled water, from which estrogenic bisphenol analogues might migrate into bottled water. Therefore, there is a strong need to investigate the occurrence and potential risk of such estrogenic bisphenol analogues in Chinese bottled wat...

Due to the lack of natural water resources and the rapid growth of population and economy, China is currently facing the pressing challenge of water shortage. Current evidence suggests that the traditional water resources including surface water and groundwater could not be enough to sustain increasing water demand which has been projected to hit 8...

This study compared the performance of an anaerobic fluidized bed membrane bioreactor (AFMBR)-zeolite adsorption-reverse osmosis (RO) system and an anoxic-aerobic MBR-RO system for municipal wastewater reclamation. Both MBR-RO systems were operated in parallel with the same operating conditions. The results showed that the MBR systems achieved exce...

The conventional biological nitrogen removal process is receiving increasing pressure partially due to its energy-negative operation. To address this challenge, various mainstream deammonification processes have been explored for energy-neutral municipal wastewater treatment, whereas these processes appear challenging to be sustainably and stably a...

On-line chemical cleaning with sodium hypochlorite (NaOCl) is widely employed for sustaining MBR permeability, during which the inevitable contact between activated sludge and NaOCl had been shown to trigger substantial release of dissolved organic matter (DOM). Therefore, this work further explored the formation mechanisms of such DOM by looking i...

Today, a paradigm shift of biological processes is necessary to move towards energy self-sufficient municipal wastewater treatment. The A-B process configurations presented in Chapter 3 provide a feasible engineering solution, in which the A-stage is primarily designed for COD capture for energy recovery instead of biological oxidation, while the B...

Ferrous salts have been widely used to enhance phosphorus removal in full-scale wastewater treatment plants, with an average dosage of 0.24-0.35 mM. However, such high dosage inevitably caused serious concerns on operation, potential biological toxicity and excessive sludge production. Thus, this study investigated the effect of micro-dosing of fer...

This work investigated the presence of seven major phthalates in nine different kinds of edible oils (i.e. olive, rapeseed, peanut, sesame, tea seed, corn, soybean, sunflower, and blended oil) and their potential impacts on human. The respective total average phthalates concentrations in the oils studied were found to be 6.01, 2.79, 2.63, 2.03, 1.7...

In this work, to probe the crucial role of photo nanosensitizer clusterization played in determining the performance of the photoelectrocatalytic process, an illustrative nano-regional heterostructure was constructed via novel in-situ loading ultra-small cobalt oxide nanodots (<3 nm) onto the surface of titanium dioxide nanorod array grown on FTO s...

Online chemical cleaning of membrane bioreactor (MBR) with sodium hypochlorite (NaClO) has been extensively applied for membrane fouling mitigation. However, it was recently revealed that residual NaClO from the online cleaning of MBR caused serious microbial lysis with the subsequent formation of dissolved organic matter (DOM), in which a substant...

To relieve the increasing pressure on water scarcity, reclamation and reuse of municipal wastewater represent a global trend. However, the current process for high-grade reclaimed water production faces increasing pressure because of the intensive energy consumption, excessive sludge generation, highly complicated process configuration and large fo...

This study was aimed at the exploration of high-efficiency and low-cost technique for glucoamylase (GA) production from food waste; moreover, the produced GA could be directly used in the hydrolysis of food waste. A mixture of food waste, rice waste and cake waste as a sole feedstock was investigated for the production of GA via solid-state ferment...