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Water shortage, public health and environmental protection are key motives to treat wastewater. The widespread adoption of wastewater as a resource depends upon development of an energy-efficient technology. Anaerobic membrane bioreactor (AnMBR) technology has gained increasing popularity due to their ability to offset the disadvantages of conventional treatment technologies. However there are several hurdles, yet to climb over, for wider spread and scale-up of the technology. This paper reviews fundamental aspects of anaerobic digestion of wastewater, and identifies the challenges and opportunities to the further development of AnMBRs. Membrane fouling and its implications are discussed, and strategies to control membrane fouling are proposed. Novel AnMBR configurations are discussed as an integrated approach to overcome technology limitations. Energy demand and recovery in AnMBRs is analyzed. Finally key issues that require urgent attention to facilitate global penetration of AnMBR technology are highlighted., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Conventional aerobic treatment of high-strength wastewater is not economical due to excessively high energy requirement for compressed air supply. The use of passive aeration avoids the use of compressed air and enables energy efficient oxygen supply directly from the air. This study evaluates a passively aerated simultaneous nitrification and denitrification performing biofilm to treat concentrated wastewater. The biofilm reactor was operated > 5-months under alternating anaerobic/aerobic conditions. For 4-times concentrated wastewater, > 80% COD (2307 mg L -1  h -1 ) and > 60% N (60 mg L -1  h -1 ) was removed at a hydraulic retention time (HRT) of 7 h. A double application in the same reactor enabled > 95% COD and 85% N-removal, at an overall HRT of 14 h which is substantially shorter than what traditional activated sludge-based systems would require for the treatment of such concentrated feeds. Microbial community analysis showed Candidatus competibacter (27%) and nitrifying bacteria (Nitrosomonas, and Nitrospira) as key microbes involved in COD and N-removal, respectively., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Treatment of coking wastewater is a great challenge due to their instinct characteristics of high concentration, complex composition and biological toxicity. In this work, a novel integrated system comprising three-dimensional electrochemical reactors (3DERs) and three-dimensional biofilm electrode reactors (3DBERs) in series is developed for coking wastewater treatment. Results indicate that 79.63% of COD as well as 76.30% of total nitrogen could be removed at the low energy consumption of 15.6 kWh/m 3 . 3DERs mainly contribute to COD and nitrogen removal through electrochemical oxidation/reduction, while 3DBERs are responsible for nitrification process by enriched functional microbes. After treating by the integrated system, only long-chain alkanes are left in the wastewater and the toxicity of effluent is significantly reduced. This integrated 3DERs-3DBERs system exhibits capability of simultaneously eliminating carbonaceous and nitrogenous contaminants in coking wastewater, and greatly saves the energy with synergy of electricity and biofilm., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

In this work, modified plastic carriers; polypropylene (PP), low-density polyethylene- polypropylene (LDPE-PP), and polyurethane foam-polypropylene (PUF-PP) were developed and used in moving bed bioreactor (MBBR) for the wastewater treatment containing naphthalene. To optimized the process parameters using response surface methodology (RSM), two numerical variables; pH (5.0-9.0) and hydraulic retention time (HRT) (1.0-5.0 day) along with the type of carriers (PP, LDPE-PP, and PUF-PP) were selected as a categorical factor. At 7.0 pH and 5 days HRT, maximum removal efficiencies were observed to be 72.4, 84.4, and 90.2% for MBBR packed with PP, LDPE-PP, and PUF-PP carriers, respectively. Gas chromatography-mass spectrometry (GC-MS) analysis reveals catechol and 2-naphthol were observed as intermediate metabolites for naphthalene degradation. Modified Stover-Kincannon model was applied for biodegradation kinetic and constants were observed as U max : 0.476, 0.666, and 0.769 g/L.day and K B : 0.565, 0.755, and 0.874 g/L.day for PP, LDPE-PP, PUF-PP, respectively., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

An efficient way to solve the environmental pollution deriving from hydrolyzed polyacrylamide (HPAM)-containing drilling wastewater is urgent. This work adopted a novel method coupling Fenton oxidation with sequencing batch reactor (SBR) to treat gas-field drilling wastewater successively. This Fenton-SBR process reduced COD, HPAM, NH 4 + -N and total phosphorus (TP) concentrations of drilling wastewater by 98.35%, 87.58%, 94.50% and 93.52%, respectively. While simulated HPAM wastewater with similar HPAM concentration to Fenton-oxidized drilling wastewater was treated only by biological process, and the COD and HPAM removal efficiencies reached 78.26% and 62.95%. The result indicates that the biodegradability of the drilling wastewater was enhanced after Fenton oxidation. Moreover, the analysis on microbial community structure indicates the dominant bacteria in treated drilling wastewater were different from that in treated simulated-wastewater. It can be considered the Fenton-SBR process possesses potential to be applied to treating the drilling wastewater., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The application of aerobic granular sludge (AGS) is a promising biological method for wastewater treatment. In the present study, the AGS method was used for the treatment of petroleum wastewater. The granulation process and organic/nitrogen compound removal efficiencies were determined and correlated with the microbiological communities. Granulation of the aerobic sludge occurred after 35 days of operation. The compacted granules had a diameter of 0.46-0.9 mm. Extracellular polymeric substances (EPS) contents increased as granulation progressed and reached 128 mg/g·VSS. The granulated sludge efficiently reduced COD by 95% and petroleum compound contents by 90%. NH 4 + -N and TN removal were inefficient due to the inhibition of nitrobacteria and denitrificans, but were significantly improved by the addition of glucose. The microorganisms in the granules capable of degrading petroleum chemicals consisted of the genera Propioniciclava, Micropruina, Alphaproteobacteria, Flavobacterium, and Sulfuritalea., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A membrane electro-bioreactor (MEBR) embracing biological treatment, electrokinetic phenomena and membrane filtration was established by applying intermittent direct current (DC) to MBR. MEBR exhibited significant improvement of treatment performance and reduction of membrane fouling. COD and total phenols removal efficiencies increased to 83.53% and 93.28% at an exposure mode of 24'-OFF/6'-ON, compared to 71.24% and 82.43% in MBR. Trans-membrane pressure increment rate declined dramatically in MEBR, which was mainly attributed to the increase of sludge floc size and decrease of zeta potential, soluble microbial products and specific resistance to filtration, resulted from electrokinetic effects such as electrocoagulation, electrophoresis, electroosmosis and electromigration of ions. It was notable that DC exposure exerted distinct evolution on microbial community, with the improvement of microbial community richness and diversity. The relative abundances of functional genera were promoted noticeably in MEBR. An interactive relevance existed among microbial community structure, mixed liquor properties and operational parameters., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

In this study, a novel upflow microaerobic sludge reactor (UMSR) was constructed to conduct anaerobic digestion of municipal wastewater with low carbon and nitrogen ratio (C/N). Oxygen in the UMSR was supplied by falling water and external recirculation. Excellent nitrogen removal performance was obtained in the UMSR for treating wastewater with low C/N ratio at a temperature of 25 °C and a hydraulic retention time of 24 h. Ammonium and total nitrogen removal efficiencies averaged 92.35% and 90.41%, respectively, and sludge granulation occurred during acclimation. The inferred metabolism of nitrogen removal and ecological positions of functional microbe were integrated into a granule model by scanning electron microscopy. Additionally, the analysis of microbial community indicated that aerobic nitrifying bacteria and heterotrophic bacteria survived on the surface of sludge floc and granules while the anaerobic autotrophic, heterotrophic denitrifying, and anaerobic ammonia oxidation bacteria were present in the inner layer., (Copyright © 2018. Published by Elsevier Ltd.)

A novel pilot gravity-driven anoxic/oxic fed-batch membrane bioreactor (AFMBR) was developed to treat real domestic wastewater. In this process, the anoxic and oxic stages created favorable conditions for stable and continuous nitritation-denitritation/denitrification-nitrification links without adding external carbon source. Excellent removals of organic carbon/nitrogen (NH 4 + -N: 71-97%, COD: 78-96%, UV 254 : 70-95%, TN: 20-60%) and spontaneous permeability recovery were achieved simultaneously. It was assessed at micro levels by characterizing sludge particle morphologies, microbiota functional evolutions, fouling layer properties and energy consumptions. It was demonstrated that the aerobic granular sludge (AGS) was cultivated successfully. Notable differences of microbial diversity were observed in different regions of AFMBR. The SEM and AFM spectra suggested the loose cake layers can shed automatically due to low pressure and continue flushing. The energy consumption in AFMBR was around 0.042 kWh/m 3 , far lower than that of conventional MBR. Overall, the AFMBR has a potential on improvement of domestic wastewater treatment., (Copyright © 2018. Published by Elsevier Ltd.)

Autotrophic denitrification has attracted increasing attention for wastewater with insufficient organic carbon sources. Nevertheless, in situ identification of autotrophic denitrifying communities in reactors remains challenging. Here, a process combining micro-electrolysis and autotrophic denitrification with high nitrate removal efficiency was presented. Two batch reactors were fed organic-free nitrate influent, with H 13 CO 3 - and H 12 CO 3 - as inorganic carbon sources. DNA-based stable-isotope probing (DNA-SIP) was used to obtain molecular evidence for autotrophic denitrifying communities. The results showed that the nirS gene was strongly labeled by H 13 CO 3 - , demonstrating that the inorganic carbon source was assimilated by autotrophic denitrifiers. High-throughput sequencing and clone library analysis identified Thiobacillus-like bacteria as the most dominant autotrophic denitrifiers. However, 88% of nirS genes cloned from the 13 C-labeled "heavy" DNA fraction showed low similarity with all culturable denitrifiers. These findings provided functional and taxonomical identification of autotrophic denitrifying communities, facilitating application of autotrophic denitrification process for wastewater treatment., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The modification of the physical properties of aerobic granular sludge treating fish-canning wastewater is discussed in this paper. The structure and composition of the Extracellular Polymeric Substances (EPSs) were analyzed at different salinity levels and related to granules stability. Results outlined that the total EPSs content increased with salinity, despite the EPSs increment was not proportional to the salt concentration. Moreover, the EPSs structure was significantly modified by salinity, leading to a gradual increase of the not-bound EPSs fraction, which was close to the 50% of the total EPSs content at 75gNaClL -1 . The increasing salt concentration modified also the EPSs composition, causing the gradual reduction of protein content resulting in a decrease of granule hydrophobicity. The results pointed out that the granules stability significantly reduced above 50gNaClL -1 , suggesting the existence of a salinity threshold above which granules stability is compromised., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

A continuous fixed-bed study was carried out utilising a breakthrough biosorbent, specifically multi-metal binding biosorbent (MMBB) for removing cadmium, copper, lead and zinc. The effect of operating conditions, i.e. influent flow rate, metal concentration and bed depth was investigated at pH 5.5±0.1 for a synthetic wastewater sample. Results confirmed that the total amount of metal adsorption declined with increasing influent flow rate and also rose when each metal concentration also increased. The maximum biosorption capacities of 38.25, 63.37, 108.12 and 35.23mg/g for Cd, Cu, Pb and Zn, respectively, were achieved at 31cm bed height, 10mL/min flow rate and 20mg/L initial concentration. The Thomas model better described the whole dynamic behaviour of the column rather than the Dose Response and Yoon-Nelson models. Finally, desorption studies indicated that metal-loaded biosorbent could be used after three consecutive sorption, desorption and regeneration cycles by applying a semi-simulated real wastewater., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Single-chamber microbial fuel cells (S-MFCs) with bio-anodes and activated carbon (AC) air-cathodes showed high nitrobenzene (NB) tolerance and NB removal with concomitant electricity production. The maximum power over 25Wm -3 could be obtained when S-MFCs were operated in the NB loading range of 1.2-6.2molm -3 d -1 , and stable electricity production over 13.7Wm -3 could be produced in a NB loading range of 1.2-14.7molm -3 d -1 . The present S-MFCs exhibited high NB removal performance with NB removal efficiency over 97% even when the NB loading rate was increased to 17.2molm -3 d -1 . The potential NB reduced product (i.e. aniline) could also be effectively removed from influents. The findings in this study means that single-chamber MFCs assembled with pre-enriched bio-anodes and AC air-cathodes could be developed as effective bio-electrochemical systems to remove NB from wastewaters and to harvest energy instead of consuming energy., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Anaerobic treatment of wastewater and waste organic solvents originating from the pharmaceutical and chemical industries was tested in a pilot anaerobic membrane bioreactor, which was operated for 580days under different operational conditions. The goal was to test the long-term treatment efficiency and identify inhibitory factors. The highest COD removal of up to 97% was observed when the influent concentration was increased by the addition of methanol (up to 25gL -1 as COD). Varying and generally lower COD removal efficiency (around 78%) was observed when the anaerobic membrane bioreactor was operated with incoming pharmaceutical wastewater as sole carbon source. The addition of waste organic solvents (>2.5gL -1 as COD) to the influent led to low COD removal efficiency or even to the breakdown of anaerobic digestion. Changes in the anaerobic population (e.g., proliferation of the genus Methanosarcina) resulting from the composition of influent were observed., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

A simultaneous nitrification, denitrification and organic matter removal (SNDOR) process in sequencing batch biofilm reactor (SBBR) was established to treat saline mustard tuber wastewater (MTWW) in this study. An average COD removal efficiency of 86.48% and total nitrogen removal efficiency of 86.48% were achieved at 30gNaClL -1 during 100days' operation. The underlying mechanisms were investigated by PacBio SMRT DNA sequencing (V1-V9) to analyze the microbial community structures and its variation from low salinity at 10gNaClL -1 to high salinity at 30gNaClL -1 . Results showed elevated salinity did not affect biological performance but reduced microbial diversity in SBBR, and halophilic bacteria gradually predominated by succession. Despite of high C/N, autotrophic ammonia-oxidizing bacteria (AOB) Nitrosomonas and ammonia-oxidizing archaea (AOA) Candidatus Nitrososphaera both contributed to ammonium oxidation. As salinity increasing, nitrite-oxidizing bacteria (NOB) were significantly inhibited, partial nitrification and denitrification (PND) process gradually contributed to nitrogen removal., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Glycogen accumulating organisms (GAO) are known to allow anaerobic uptake of biological oxygen demand (BOD) in activated sludge wastewater treatment systems. In this study, we report a rapid transition of suspended activated sludge biomass to a GAO dominated biofilm by selective enrichment using sequences of anaerobic loading followed by aerobic exposure of the biofilm to air. The study showed that within eight weeks, a fully operational, GAO dominated biofilm had developed, enabling complete anaerobic BOD uptake at a rate of 256mg/L/h. The oxygen uptake by the biofilm directly from the atmosphere had been calculated to provide significant energy savings. This study suggests that wastewater treatment plant operators can convert activated sludge systems readily into a "passive aeration" biofilm that avoids costly oxygen transfer to bulk wastewater solution. The described energy efficient BOD removal system provides an opportunity to be coupled with novel nitrogen removal processes such as anammox., (Copyright © 2016. Published by Elsevier Ltd.)

Toilet-paper cellulose with rich but refractory carbon sources, are the main insoluble COD fractions in sewage. An anaerobic membrane bioreactor (AnMBR) was configured for sewage treatment at room temperature and its performance on methanogenic degradation of toilet paper was highlighted. The results showed, high organic removal (95%), high methane conversion (90%) and low sludge yield (0.08gVSS/gCOD) were achieved in the AnMBR. Toilet-paper cellulose was fully biodegraded without accumulation in the mixed liquor and membrane cake layer. Bioconversion efficiency of toilet paper approached 100% under a high organic loading rate (OLR) of 2.02gCOD/L/d and it could provide around 26% of total methane generation at most of OLRs. Long sludge retention time and co-digestion of insoluble/soluble COD fractions achieving mutualism of functional microorganisms, contributed to biodegradation of toilet-paper cellulose. Therefore the AnMBR successfully implemented simultaneously methanogenic bioconversion of toilet-paper cellulose and soluble COD in sewage at room temperature., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

A bioelectrochemically-assisted constructed wetland (BECW) system was used to treat nitrate-contaminated wastewater without organic carbon source. The denitrification performance and microbial community composition of a BECW in closed-circuit mode (BECW-C) was compared to a BECW in open-circuit mode (BECW-O). The highest denitrification efficiency (78.92±3.12%) was obtained in the BECW-C with an applied current of 15mA. No nitrite accumulation was observed during the autotrophic denitrification process in the BECW-C. The significantly higher denitrification efficiency of the BECW-C compared to the BECW-O suggested enhanced denitrification due to in situ generation of hydrogen. The bacterial communities in the anode, cathode and rhizosphere regions collected from the BECW-C (with 10 or 15mA) and the BECW-O were characterized using 16S rRNA pyrosequencing technology, which revealed different microbial community structures among the treatments. The results also indicated that Thiohalophilus and Clostridium sensu stricto might be responsible for autotrophic denitrification in the BECW-C., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

A ratio control strategy was implemented in a continuous moving bed biofilm reactor (MBBR) to investigate the response to different temperatures. The control strategy was designed to maintain a constant ratio between dissolved oxygen (DO) and total ammonia nitrogen (TAN) concentrations. The results revealed that a stable nitritation in a biofilm reactor could be achieved via ratio control, which compensated the negative influence of low temperatures by stronger oxygen-limiting conditions. Even with a temperature as low as 6°C, stable nitritation could be achieved when the controlling ratio did not exceed 0.17. Oxygen-limiting conditions in the biofilm reactor were determined by the DO/TAN concentrations ratio, instead of the mere DO concentration. This ratio control strategy allowed the achievement of stable nitritation without complete wash-out of NOB from the reactor. Through the ratio control strategy full nitritation of sidestream wastewater was allowed; however, for mainstream wastewater, only partial nitritation was recommended., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Nitrogen and organic carbon are major pollutants in wastewater causing environmental problems. Alcaligenes faecalis strain NR, isolated from activated sludge, exhibited the ability to remove ammonium and organic carbon from wastewater simultaneously under sole aerobic conditions in batch culture. Changes in carbon type, C/N ratio, oxygen concentration and inorganic ions significantly affected the treatment efficiency. Furthermore, a continuous bioreactor, solely inoculated with A. faecalis strain NR, was conducted to assess its feasibility for simultaneous nitrogen and organic matter removal in a single aerated reactor. Approximately 66.7-78.3% of NH 4 + -N and 85.8-92.2% of TOC were removed by using synthetic wastewater with 150-200mg/L of NH 4 + -N and 1350-2000mg/L of TOC. This research would be valuable to develop an innovative treatment method for ammonium-rich wastewater under aerobic conditions., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Enhanced aerobic/anoxic Downflow Hanging Sponge (DHS) bioreactors were assessed for carbon (C) and total nitrogen (TN) removal for decentralised domestic wastewater treatment applications. The initial design included upper aerobic and lower anoxic sponge layers, and effluent recirculation, and achieved >80% COD s and >90% NH 4 -N removal. However, effluent TN was higher. It was concluded the anoxic layer was C-limited for denitrification, therefore an influent bypass was added to the anoxic layer to provide supplemental C. Differed bypass ratios were compared, including 0%, 10%, 20% and 30% (% of total influent), and effluent TN declined with increasing bypass; i.e., 50.1±23.3mg-N/L, 49.9±27.8mg-N/L, 31.9±18.4mg-N/L and 10.7±5.8mg-N/L, respectively, and all reactors removed >80% COD s . This design has potential because it uses limited energy, tolerates variable flows, and simultaneously removes C and TN; all key for effective decentralised treatment applications., (Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The performance and microbial community of activated sludge from a sequencing batch reactor (SBR) were investigated under long-term exposure of magnetic Fe 3 O 4 nanoparticles (Fe 3 O 4 NPs). The COD removal showed a slight decrease at 5-60mg/L Fe 3 O 4 NPs compared to 0mg/L Fe 3 O 4 NPs, whereas the NH 4 + -N removal had no obvious variation at 0-60mg/L Fe 3 O 4 NPs. It was found that 10-60mg/L Fe 3 O 4 NPs improved the denitrification process and phosphorus removal of activated sludge. The microbial enzymatic activities of activated sludge could be affected by Fe 3 O 4 NPs, which had similar variation trends to the nitrogen and phosphorus removal rates of activated sludge. The reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) release demonstrated that Fe 3 O 4 NPs led to the toxicity to activated sludge and destroyed the integrity of microbial cytomembrane. High throughput sequencing indicated that Fe 3 O 4 NPs could obviously affect the microbial richness and diversity of activated sludge., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Results obtained from three aerobic granular sludge reactors treating brewery wastewater are presented. Reactors were operated for 60d days in each of the two periods under different cycle duration: (Period I) short 6h cycle, and (Period II) long 12h cycle. Organic loading rates (OLR) varying from 0.7kgCODm -3 d -1 to 4.1kgCODm -3 d -1 were tested. During Period I, granules successfully developed in all reactors, however, results revealed that the feast and famine periods were not balanced and the granular structure deteriorated and became irregular. During Period II at decreased 12h cycle time, granules were observed to develop again with superior structural stability compared to the short 6h cycle time, suggesting that a longer starvation phase enhanced production of proteinaceous EPS. Overall, the extended famine conditions encouraged granule stability, likely because long starvation period favours bacteria capable of storage of energy compounds., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Five reactors were operated with low upflow superficial air velocities (0.41cmmin -1 ) in order to observe granulation on synthetic wastewaters with different characteristics: 1) 340mg-CODL -1 ; 2) 630mg-CODL -1 ; and 3) 1300mg-CODL -1 . Stable granulation was only observed under low hydrodynamic shear for low-strength wastewater. 55-70% of soluble chemical oxygen demand (COD) was utilized before aeration and 91% COD, 62% total nitrogen (TN), and 96% total phosphorus (TP) were removed from the low-strength wastewater. Although medium-strength wastewater did generate granules they rapidly acquired a filamentous surface layer that resulted in decreased performance and loss of nitrification. 94% COD, 30% TN, and 85% TP were removed from the medium-strength wastewater. The high-strength wastewater did not develop granules and 85% COD was removed. Results demonstrated that high shear force was not required for granulation. Rather, granulation depended on multiple parameters to out-select rapidly growing aerobic microorganisms., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The aim of this study was to evaluate the influence of hydraulic retention time (HRT) on linear alkylbenzene sulfonate (LAS) removal in fluidized bed reactors (FBRs). FBR1 (HRT of 8h) and FBR2 (HRT of 12h) were fed laundry wastewater with 18.6±4.1 to 27.1±5.6mg/L of LAS in the following conditions: ethanol and nitrate addition (Phases I, II and III), nitrate (Phase IV), ethanol (Phase V) and laundry wastewater (Phase VI). LAS removal was 93±12% (FBR1) and 99±2% (FBR2). In FBR1, nitrate influenced significantly on LAS removal (99±3% - Phase IV) compared to the phase without nitrate (90±15% - Phase V). In FBR1 the absence of ethanol was more favourable for LAS removal (99±3% - Phase IV) compared to ethanol addition (87±16% - Phase II). In FBR2, 99±2% LAS removal was found up to 436days. By microbial characterization were identified bacteria as Acinetobacter, Dechloromonas, Pseudomonas and Zoogloea., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In this work, a plug flow reactor was developed for continuous dry digestion processes and its efficiency was investigated using untreated manure bedded with straw at 22% total solids content. This newly developed reactor worked successfully for 230days at increasing organic loading rates of 2.8, 4.2 and 6gVS/L/d and retention times of 60, 40 and 28days, respectively. Organic loading rates up to 4.2gVS/L/d gave a better process stability, with methane yields up to 0.163LCH 4 /gVS added /d which is 56% of the theoretical yield. Further increase of organic loading rate to 6gVS/L/d caused process instability with lower volatile solid removal efficiency and cellulose degradation., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

This study investigates the role of plant (Elodea nuttallii) and effect of supplementary aeration on wastewater treatment and bioelectricity generation in an up-flow constructed wetland-microbial fuel cell (UFCW-MFC). Aeration rates were varied from 1900 to 0mL/min and a control reactor was operated without supplementary aeration. 600mL/min was the optimum aeration flow rate to achieve highest energy recovery as the oxygen was sufficient to use as terminal electron acceptor for electrical current generation. The maximum voltage output, power density, normalized energy recovery and Coulombic efficiency were 545.77±25mV, 184.75±7.50mW/m 3 , 204.49W/kg COD, 1.29W/m 3 and 10.28%, respectively. The variation of aeration flow rates influenced the NO 3 - and NH 4 + removal differently as nitrification and denitrification involved conflicting requirement. In terms of wastewater treatment performance, at 60mL/min aeration rate, UFCW-MFC achieved 50 and 81% of NO 3 - and NH 4 + removal, respectively. E. nuttallii enhanced nitrification by 17% and significantly contributed to bioelectricity generation., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The performance and microbial community of a sequencing batch biofilm reactor (SBBR) treating synthetic mariculture wastewater were evaluated under long-term exposure to norfloxacin (NFX) due to the overuse of antibiotics during the mariculture. The COD and NH 4 + -N removals had no distinct change at 0-6mgL -1 NFX and were inhibited at 6-35mgL -1 NFX. The specific oxygen uptake rate (SOUR), specific ammonium oxidation rate (SAOR), specific nitrite oxidation rate (SNOR) and specific nitrate reduction rate (SNRR) of the biofilm kept a decreasing tendency with the increase of NFX concentration from 0 to 35mgL -1 . The presence of NFX promoted the microorganisms to secrete more extracellular polymeric substances (EPS) and affected the chemical compositions of EPS. The microbial richness and diversity showed some obvious variations at different NFX concentrations. The present results demonstrated that NFX inhibited the SBBR performance and should decrease the NFX dosage in the mariculture., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Membrane fouling (especially biofouling) as a critical issue during membrane reactor (MBR) operation has attracted much attention in recent years. Although previous review papers have presented different aspects of MBR's fouling when treating various wastewaters, the information related to biofouling in MBRs has only simply or partially reviewed. This work attempts to give a more comprehensive and elaborate explanation of biofilm formation, biofouling factors and control approaches by addressing current achievements. This also suggests to a better way in controlling biofouling by developing new integrated MBR systems, novel flocculants and biomass carriers., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Interspecies electron transfer (IET) between microbial populations with different functions is critical to stable anaerobic digestion. This study, in an attempt to facilitate IET, investigated the effect of magnetite supplementation on the biomethanation of dairy effluent in continuous mode. The magnetite-added reactor (RM) was significantly more resistant and resilient to process imbalance than the reactor run without magnetite addition (RC). RC showed unstable performance with repeated process upsets, but its performance improved to be comparable to that of RM after applying magnetite supplementation. Magnetite was particularly effective in stabilizing a build-up of propionic acid and therefore improving the process robustness and reliability. The enhanced biomethanation in terms of productivity and stability was attributed to the facilitated direct IET (DIET) between exoelectrogens and methanogens via magnetite particles. Methanosaeta was the predominant methanogen group in the experimental reactors and likely played a key role in both DIET-mediated carbon dioxide-reducing and aceticlastic methanogenesis., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

A laboratory scale nutrient removal activated sludge system coupled with an anaerobic side-stream reactor was operated for 300 days treating real urban wastewater. A significant decrease in sludge production was obtained increasing the anaerobic solid retention time (SRT ASSR ) and decreasing the sludge interchange ratio (IR). In this study, the microbial community structure was analyzed and compared with the sludge reduction performance. Quantitative polymerase chain reaction analyses encoding 16 ribosomal RNA and functional genes revealed a wide diversity of phylogenetic groups in each experimental period, resulting from long solids retention time and recirculation of sludge under aerobic, anoxic and anaerobic conditions. However, decreasing SRT ASSR from 10 to 2.5d and increasing IR from 27 to 100%, an increasing selection of both fermenting bacteria able to release extracellular polymeric substances and hydrolyze organic matter and slow growing bacteria involved in nutrient removal were detected and linked to the sludge reduction mechanisms., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

This study investigated aeration rate (0, 0.2, 0.4 and 1.0L/min) effects on algal-bacterial symbiosis (ABS) and conventional activated sludge (CAS) systems while treating domestic wastewater in sequencing batch reactors. Experiment results showed that ABS system performed better on NH 4 + -N, total nitrogen and total phosphorus removal than CAS system, especially under lower aeration rate condition (0.2Lair/min), with removal efficiencies improvements of 18.90%, 12.45% and 46.66%, respectively. The mechanism study demonstrated that a favorable aeration rate reduction (half of traditional value in CAS system) could enhance algae growth but weaken hydraulic shear force, which contributed to the interactions between algae and sludge flocs and further stability of ABS system. In addition, algae growth protected both ammonia and nitrite oxidizing bacteria from optical damage. It is expected that the present study would provide some new insights into ABS system and be helpful for development of low-energy demand wastewater treatment process., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

While the adsorptive fouling in membrane bioreactors (MBRs) is highly dependent of the surface morphology, little progress has been made on modeling biocake layer surface morphology. In this study, a novel method, which combined static light scattering method for fractal dimension (D f ) measurement with fractal method represented by the modified two-variable Weierstrass-Mandelbrot function, was proposed to model biocake layer surface in a MBR. Characterization by atomic force microscopy showed that the biocake surface was stochastic, disorder, self-similarity, and with non-integer dimension, illustrating obvious fractal features. Fractal dimension (D f ) of sludge suspension experienced a significant change with operation of the MBR. The constructed biocake layer surface by the proposed method was quite close to the real surface, showing the feasibility of the proposed method. It was found that D f was the critical factor affecting surface morphology, while other factors exerted moderate or minor effects on the roughness of biocake layer., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Although microalgae can serve as an appropriate alternative feedstock for biofuel production, the high microalgal cultivation cost has been a major obstacle for commercializing such attempts. One of the feasible solution for cost reduction is to couple microalgal biofuel production system with wastewater treatment, as microalgae are known to effectively eliminate a variety of nutrients/pollutants in wastewater, such as nitrogen/phosphate, organic carbons, VFAs, pharmaceutical compounds, textile dye compounds, and heavy metals. This review aims to critically discuss the feasibility of microalgae-based wastewater treatment, including the strategies for strain selection, the effect of wastewater types, photobioreactor design, economic feasibility assessment, and other key issues that influence the treatment performance. The potential of microalgae-bacteria consortium for treatment of industrial wastewaters is also discussed. This review provides useful information for developing an integrated wastewater treatment with microalgal biomass and biofuel production facilities and establishing efficient co-cultivation for microalgae and bacteria in such systems., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In this study, different inoculation strategies for continuously operated microbial anodes are analyzed and compared. After 20daysof operation with municipal wastewater anodes pre-incubated with a biofilm of the exoelectrogenic species Geobacter and Shewanella showed current densities of (65±8) μA/cm 2 . This is comparable to the current densities of non-inoculated anodes and anodes inoculated with sewage sludge. Analysis of the barcoded pre-grown multispecies biofilms reveal that 99% of the original biofilm was detached after 20daysof operation with municipal wastewater. This is in contrast to previous experiments where a pre-grown biofilm of exoelectrogens was operated in batch mode. To implement pre-grown biofilms in continuous systems it will thus be necessary to reveal a window of process parameters in which typical exoelectrogenic microorganisms including model organisms can be kept and/or enriched on anodes., (Copyright © 2016. Published by Elsevier Ltd.)

A novel configured fluidized bed reactor (FBR) with granular rubber as the fluidized media was operated without internal recirculation to achieve denitrification. This FBR could operate under a low hydraulic retention time (HRT) of 50min due to the low rubber media density and absence of recirculation. Synthetic nitrate-rich wastewater with a fixed nitrate (NO 3 - -N) concentration and varying COD concentrations was fed into the FBR. The nitrate removal profile showed a rapid nitrate reduction at the bottom of the reactor with a high performance under the low HRT. Different microbial communities were identified using Illumina Miseq sequencing. The dominant microorganisms belonged to the Beta- and Gamma-proteobacteria classes and played important roles in nitrate reduction. Acidovorax was abundant at low COD: NO 3 - -N ratios, while Rhizobium and Zoogloea were dominant at high COD: NO 3 - -N ratios. The COD: NO 3 - -N ratio strongly influenced the composition of the microbial community including the dominant species., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

This study focused on a physical separator in the form of a screen to out-select nitrite oxidizing bacteria (NOB) for mainstream sewage treatment. This separation relied on the principle that the NOB prefer to grow in flocs, while anammox bacteria (AnAOB) reside in granules. Two types of screens (vacuum and vibrating) were tested for separating these fractions. The vibrating screen was preferred due to more moderate normal forces and additional tangential forces, better balancing retention efficiency of AnAOB granules (41% of the AnAOB activity) and washout of NOB (92% activity washout). This operation resulted in increased NOB out-selection (AerAOB/NOB ratio of 2.3) and a total nitrogen removal efficiency of 70% at influent COD/N ratio of 1.4. An effluent total nitrogen concentration <10mgN/L was achieved using this novel approach combining biological selection with physical separation, opening up the path towards energy positive sewage treatment., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Chloramphenicol (CAP) is a frequently detected environmental pollutant. In this study, an electroactive biofilm for CAP reduction was established by initially in the anode and then inverting to the cathode. The established biocathode could enhance the reduction of CAP to the nitro-group reduced CAP (AMCl2) and further dechlorinated form (AMCl), both had lost the antibacterial activity. The phylogenetic diversity of the acclimated biofilm was decreased after the polar inversion. Proportions of functional bacterial genera, including Geobacter, Desulfovibrio and Pseudomonas responsible for the bidirectional electron transfer and nitroaromatics reduction, had increased 28%, 104% and 43% in the cathode. The relatively high abundances (over 50%) of Geobacter in anode and cathode were rarely detected for the nitroaromatics reduction. This study provides new insights into the electroactive biofilm structure improvement by the polarity inversion strategy for refractory antibiotics degradation., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Discharge of wastewater with high nitrogen and phosphorus content is a major cause of eutrophication. In this study, a microfiltration-based membrane photobioreactor (MPBR) and forward osmosis-based osmotic membrane photobioreactor (OMPBR) have been operated with Chlorella vulgaris for continuous tertiary wastewater treatment. Both the bioreactors exhibited good biomass accumulation (over 2g/L), although the OMPBR achieved better nutrients removal due to high rejection properties of the membranes. At 2days HRT, the OMPBR achieved nitrogen and phosphorus removal efficiencies of 86-99% and 100%, respectively, whereas the corresponding values in the MPBR were 48-97% and 46%, respectively. Based on the energy input, the total operating costs for OMPBR were 32-45% higher than that of the MPBR, and filtration cost for OMPBR was 3.5-4.5 folds higher than that of the MPBR. These results indicate that the integration of membrane filtration with photobioreactors is promising in microalgae-based tertiary wastewater treatment., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

This study revealed that the gross indicators commonly adopted for monitoring the performance of aerobic granular sludge processes are not capable of probing the microstructural deterioration of granule interior upon organic loading swaps. These granules subjected to loading swaps retained their global characteristics: appearances, sizes and settling velocities, chemical oxygen demand (COD) and ammonia-nitrogen removal capacities. However, the granule interior strength, as determined by ultrasound method, was largely weakened upon COD switch-off and was not recovered in the subsequent COD re-supply stage. In response to COD switch-off, the 5.6kDa polysaccharides component of granule extracellular polymeric substances (EPS) was diminished. Correspondingly, two bacterial species, Thauera and Sphingomonas sp., were faded away together with the significant decline in contents of intracellular cyclic dimeric GMP (c-di-GMP). The microstructural integrity of granules was seriously deteriorated upon COD switch-off, which was not detectable by the commonly adopted gross indicators., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Performance of internal circulation anaerobic reactor (IC) treating wastewater at high organic loading rate (OLR) and role of external hydraulic circulation were evaluated. When the OLR was increased from 2.50 to 18.94kgCOD/m 3 /d, COD removal decreased to 85% slightly and methane production increased to 4.49L/L/d with the upflow velocity of 1.0m/h resulted from the additional hydraulic circulation. Withdrawal of external hydraulic circulation led to decrease of COD removal to lower than 60% drastically and methane production by 81%. Accumulation of volatile fatty acids caused decline of pH to below 6.0 and the shift of substrate metabolic pathway to the hybrid fermentation. In addition, both maximum methane production rate and maximum substrate degradation rate obtained from mathematical models decreased significantly. Hydrogenotrophic methanogens including Methanobacterium and Methanocorpusculum predominated in the anaerobic sludge and the shift of microbial community was also observed., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The aim of this study was to assess the effect of increasing feedstock treatment rate on the performance of full-scale anaerobic digestion using laboratory-scale reactors with digestate and feedstock from full-scale digesters. The studied nitrogen-containing feedstocks were i) a mixture of industrial by-products and pig slurry, and ii) municipal sewage sludge, which digestion was studied at 41 and 52°C, respectively. This study showed the successful reduction of hydraulic retention times from 25 and 20days to around 15days, which increased organic loading rates from 2 to 3.5kg volatile solids (VS)/m(3)d and 4 to 6kgVS/m(3)d. As a result, the optimum retention time in terms of methane production and VS removal was 10-15% lower than the initial in the full-scale digesters. Accumulation of acids during start-up of the co-digestion reactor was suggested to be connected to the high ammonium nitrogen concentration and intermediate temperature of 41°C., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

High Rate Algae Ponds (HRAP) are the simplest way to grow microalgae biomass and an interesting alternative for wastewater treatment. In this work the performance of these systems was evaluated using anaerobically digested wastewater as culture medium. Two variables were studied in long-term mode: the carbon dioxide supply and the modification of the dilution rates. The results showed that CO2 supply increases the productivity but less than expected considering the potential biomass generation calculated based on the ratios of carbon to nitrogen of microalgae and wastewater. The assimilation into biomass only accounted for 57% of the inlet nitrogen under the best conditions because nitrification and volatilization reduced the availability of this element. The operation under short hydraulic retention times presented a more interesting performance with higher biomass productivities. The biomass produced was efficiently harvested with in a Dissolved Air Flotation (DAF) unit., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

High rate algal pond (HRAP) was combined with constructed wetland (CW) to intensify nitrogen removal through optimizing nitrification and denitrification. Nitrification and denitrification process mainly depends on the oxygen content and carbon source level in CWs. Algal biomass was enriched in HRAP, and dissolved oxygen (DO) concentration was increased via photosynthesis. Algal debris increased COD as degradable bioresource. The results showed that HRAP-CW hybrid systems effectively promoted the nitrogen removal performance due to rich DO and COD. The extension of hydraulic retention time in HRAP significantly improved NH4-N and TN removals by 10.9% and 11.1% in hybrid systems, respectively. The highest NH4-N and TN removals in hybrid systems respectively reached 67.2% and 63.5%, which were significantly higher than those in single CW. The study suggested that the hybrid system had the application potentials in nitrogen removal from wastewater., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

A combined process between micro-electrolysis and biological denitrification (MEBD) using iron scraps and an activated carbon-based micro-electrolysis carrier was developed for nitrogen removal under a microaerobic condition. The process provided NH4(+)-N and total nitrogen (TN) removal efficiencies of 92.6% and 95.3%, respectively, and TN removal rate of 0.373±0.11kgN/(m(3)d) at corresponding DO of 1.0±0.1mg/L and HRT of 3h, and the optimal pH of 7.6-8.4. High-throughput sequencing analysis verified that dominant classes belonged to β-, α-, and γ-Proteobacteria, and Nitrospira. The dominant genera Hydrogenophaga and Sphaerotilus significantly increased during the operation, covering 13.2% and 6.1% in biofilms attached to the carrier in the middle of the reactor, respectively. Autotrophic denitrification contributed to >80% of the TN removal. The developed MEBD achieved efficient simultaneous nitrification and autotrophic denitrification, presenting significant potential for application in practical low organic carbon water treatment., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In this study, a two-year experiment was carried out to investigate variation of carbon dioxide (CO2) flux from free water surface constructed wetlands (FWS CW) systems treating sewage treatment plant effluent, and treatment performance was also evaluated. The better 74.6-76.6% COD, 92.7-94.4% NH4(+)-N, 60.1-84.7% TN and 49.3-70.7% TP removal efficiencies were achieved in planted CW systems compared with unplanted systems. The planted CW was a net CO2 sink, while the unplanted CW was a net CO2 source in the entire study period. An obvious annual and seasonal variability of CO2 fluxes from different wetland systems was also presented with the average CO2 flux ranging from -592.83mgm(-2)h(-1) to 553.91mgm(-2)h(-1) during 2012-2013. In addition, the net exchange of CO2 between CW systems and the atmosphere was significantly affected by air temperature, and the presence of plants also had the significant effect on total CO2 emissions., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The performance, microbial enzymatic activity and microbial community of a sequencing batch reactor (SBR) were investigated under long-term exposure to cerium dioxide nanoparticles (CeO2 NPs). The COD removal kept a stable value at 0-5mg/L CeO2 NPs and then decreased at 10-60mg/L CeO2 NPs. The NH4(+)-N removal had no obvious changes at 0-30mg/L CeO2 NPs, and a minor decrease appeared at 60mg/L CeO2 NPs. Compared to 0mg/L CeO2 NPs, the phosphorus removal showed a decrease at 2mg/L CeO2 NPs and slightly increased at 5-60mg/L CeO2 NPs. The nitrogen and phosphorus removal rates had similar variation trends to the microbial enzymatic activities. The variations of reactive oxygen species (ROS) and lactate dehydrogenase (LDH) indicated that high CeO2 NPs concentration could result in the biotoxicity to activated sludge. The presence of CeO2 NPs had obvious effect on the microbial richness and diversity of activated sludge., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Due to the limited nutrient removal from low carbon/nitrogen (⩽4) wastewater, a process combined simultaneous nitrification-endogenous denitrification and phosphorus removal (SNDPR) with post-denitrification (PD) in a SBR was proposed for deep-level nutrient removal without external carbon addition. SNDPR driven by PAOs and GAOs reduced PO4(3-)-P (98.3%) and partial TN (59.0%) at low DO conditions (0.5±0.1mg/L), and post-dentrification achieved further NOX(-) (produced by SNDPR) removal (24.0%) anoxically by utilizing the residual intracellular polymers in GAOs. Combined control of anaerobic/aerobic/anoxic durations and low DO inhibition to aerobic GAOs and NOB conducted partial nitrification-endogenous denitrification (PNED) (66%), which saved 44.3% intracellular polymers to further reduce 64% TN in effluent. After 115-day operation, the average effluent PO4(3-)-P and TN concentrations were 0.4 and 3.9mg/L, respectively, with 92.1% of TN removal. Highly enriched PAOs (36%±2%), GAOs (22%±2%) and AOB (15%±3%) over NOB (3%±1%) facilitated P uptake, PNED and post-denitrification in the SNDPR-PD system., (Copyright © 2016. Published by Elsevier Ltd.)

High levels of organics negatively affect Anammox for treating landfill leachate. To enhance the ability of Anammox to survive against adverse environments, a lab-scale two-stage Anammox system using a Sequencing Biofilm Batch Reactor was applied to treat mature landfill leachate under 35°C. Over 107days, with influent total nitrogen (TN) and chemical oxygen demand (COD) concentrations of 3000±100 and 3000±100mg/L, effluent TN was below 20mg/L. For extracellular polymeric substance (EPS) of Anammox, slime-EPS and loosely-bound-EPS of floccules were both higher than biofilm, while tight-bound-EPS of biofilm was significantly higher, contributing to biofilm formation. Quantitative microbial analysis showed that as influent COD increased, Anammox gene ratios of biofilm increased from 1.34% to 13.28%; the gene ratios of floccule first increased, then decreased to 3.88%. This indicated that Anammox and heterotrophic bacteria could coexist because of the biofilm, leading to stable nitrogen removal performance, even when organics were present., (Copyright © 2016. Published by Elsevier Ltd.)

In this study, two anaerobic membrane bioreactors (AnMBRs) were operated for 150days to treat bamboo industry wastewater (BIWW), and one of them was enhanced with bamboo charcoal (B-AnMBR). During the steady period, average chemical oxygen demand (COD) removal efficiencies of 94.5±2.9% and 89.1±3.1% were achieved in B-AnMBR and AnMBR, respectively. The addition of bamboo charcoal (BC) increased the amount of biomass and improved the performance of the systems. A higher biogas production and methane yield were also observed in B-AnMBR. Regarding the issue of membrane fouling, BC lowered the soluble microbial product (SMP) content by approximately 62.73mg/L and decreased the membrane resistance, thereby mitigating membrane fouling. Analysis of the microbial communities demonstrated that BC increased the microbial diversity and promoted the activity of Methanosaeta, Methanospirillum, and Methanobacterium, which are dominant in methane production., (Copyright © 2016 Elsevier Ltd. All rights reserved.)