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Addition of conductive materials (CMs) has been reported to facilitate direct interspecies electron transfer (DIET) and improved anaerobic digestion (AD) performance. This review summarises the benefits and outlines remaining research challenges of the addition of CMs with a focus on the downstream processing of AD. CM addition may alter biogas quality, digestate dewaterability, biosolids volume, and centrate quality. Better biogas quality has been observed due to the adsorption of H 2 S to metallic CMs. The addition of CMs results in an increase in solid content of the digestate and thus an additional requirement for sludge dewatering and handling and the final biosolids volume for disposal. This review highlights the need for more research at pilot scale to validate the benefits of CM addition and to evaluate CM selection, doses, material costs, and the impact on downstream processes. The lack of research on the impact of CMs on the downstream process of AD is highlighted., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Recent developed sequencing techniques have resulted in a new and unprecedented way to study biological wastewater treatment, in which most organisms are uncultivable. This review provides (i) an insight on state-of-the-art sequencing techniques and their limitations; (ii) a critical assessment of the microbial community in biological reactor and biofouling layer in a membrane bioreactor (MBR). The data from high-throughput sequencing has been used to infer microbial growth conditions and metabolisms of microorganisms present in MBRs at the time of sampling. These data shed new insight to two fundamental questions about a microbial community in the MBR process namely the microbial composition (who are they?) and the functions of each specific microbial assemblage (what are their function?). The results to date also highlight the complexity of the microbial community growing on MBRs. Environmental conditions are dynamic and diverse, and can influence the diversity and structural dynamics of any given microbial community for wastewater treatment. The benefits of understanding the structure of microbial communities on three major aspects of the MBR process (i.e. nutrient removal, biofouling control, and micropollutant removal) were symmetrically delineated. This review also indicates that the deployment of microbial community analysis for a practical engineering context, in terms of process design and system optimization, can be further realized., (Copyright © 2019 Elsevier B.V. All rights reserved.)

This study demonstrates continuous enantiomeric inversion and further biotransformation of chiral profens including ibuprofen, naproxen and ketoprofen by an enzymatic membrane bioreactor (EMBR) dosed with laccase. The EMBR showed non-enantioselective transformations, with high and consistent transformation of both (R)- and (S)-ibuprofen (93 ± 6%, n = 10), but lower removals of both enantiomers of naproxen (46 ± 16%, n = 10) and ketoprofen (48 ± 17%, n = 10). Enantiomeric analysis revealed a bidirectional but uneven inversion of the profens, for example 14% inversion of (R)- to (S)- compared to 4% from (S)- to (R)-naproxen. With redox-mediator addition, the enzymatic chiral inversion of both (R)- and (S)-profens remained unchanged, although the overall conversion became enantioselective; except for (S)-naproxen, the addition of redox mediator promoted the degradation of (R)-profens only.

Laccase was immobilized on granular activated carbon (GAC) and the resulting GAC-bound laccase was used to degrade four micropollutants in a packed-bed column. Compared to the free enzyme, the immobilized laccase showed high residual activities over a broad range of pH and temperature. The GAC-bound laccase efficiently removed four micropollutants, namely, sulfamethoxazole, carbamazepine, diclofenac and bisphenol A, commonly detected in raw wastewater and wastewater-impacted water sources. Mass balance analysis showed that these micropollutants were enzymatically degraded following adsorption onto GAC. Higher degradation efficiency of micropollutants by the immobilized compared to free laccase was possibly due to better electron transfer between laccase and substrate molecules once they have adsorbed onto the GAC surface. Results here highlight the complementary effects of adsorption and enzymatic degradation on micropollutant removal by GAC-bound laccase. Indeed laccase-immobilized GAC outperformed regular GAC during continuous operation of packed-bed columns over two months (a throughput of 12,000 bed volumes)., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Redox-mediators such as syringaldehyde (SA) can improve laccase-catalyzed degradation of trace organic contaminants (TrOCs) but may increase effluent toxicity. The degradation performance of 14 phenolic and 17 non-phenolic TrOCs by a continuous flow enzymatic membrane reactor (EMR) at different TrOC and SA loadings was assessed. A specific emphasis was placed on the investigation of the toxicity of the enzyme (laccase), SA, TrOCs and the treated effluent. Batch tests demonstrated significant individual and interactive toxicity of the laccase and SA preparations. Reduced removal of resistant TrOCs by the EMR was observed for dosages over 50μg/L. SA addition at a concentration of 10μM significantly improved TrOC removal, but no removal improvement was observed at the elevated SA concentrations of 50 and 100μM. The treated effluent showed significant toxicity at SA concentrations beyond 10μM, providing further evidence that higher dosage of SA must be avoided., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The removal of four recalcitrant trace organic contaminants (TrOCs), namely carbamazepine, diclofenac, sulfamethoxazole and atrazine by laccase in an enzymatic membrane reactor (EMR) was studied. Laccases are not effective for degrading non-phenolic compounds; nevertheless, 22-55% removal of these four TrOCs was achieved by the laccase EMR. Addition of the redox-mediator syringaldehyde (SA) to the EMR resulted in a notable dose-dependent improvement (15-45%) of TrOC removal affected by inherent TrOC properties and loading rates. However, SA addition resulted in a concomitant increase in the toxicity of the treated effluent. A further 14-25% improvement in aqueous phase removal of the TrOCs was consistently observed following a one-off dosing of 3g/L granular activated carbon (GAC). Mass balance analysis reveals that this improvement was not due solely to adsorption but also enhanced biodegradation. GAC addition also reduced membrane fouling and the SA-induced toxicity of the effluent., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The degradation of 30 trace organic contaminants (TrOC) by a white-rot fungus-augmented membrane bioreactor (MBR) was investigated. The results show that white-rot fungal enzyme (laccase), coupled with a redox mediator (1-hydroxy benzotriazole, HBT), could degrade TrOC that are resistant to bacterial degradation (e.g. diclofenac, triclosan, naproxen and atrazine) but achieved low removal of compounds (e.g. ibuprofen, gemfibrozil and amitriptyline) that are well removed by conventional activated sludge treatment. Overall, the fungus-augmented MBR showed better TrOC removal compared to a system containing conventional activated sludge. The major role of biodegradation in removal by the MBR was noted. Continuous mediator dosing to MBR may potentially enhance its performance, although not as effectively as for mediator-enhanced batch laccase systems. A ToxScreen3 assay revealed no significant increase in the toxicity of the effluent during MBR treatment of the synthetic wastewater comprising TrOC, confirming that no toxic by-products were produced., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

This study investigated the removal of trace organic contaminants by a combined membrane bioreactor - granular activated carbon (MBR-GAC) system over a period of 196 days. Of the 22 compounds investigated here, all six hydrophilic compounds with electron-withdrawing functional groups (i.e., metronidazole, carbamazepine, ketoprofen, naproxen, fenoprop and diclofenac) exhibited very low removal efficiency by MBR-only treatment. GAC post-treatment initially complemented MBR treatment very well; however, a compound-specific gradual deterioration of the removal of the above-mentioned problematic compounds was noted. While a 20% breakthrough of all four negatively charged compounds namely ketoprofen, naproxen, fenoprop and diclofenac occurred within 1000-3000 bed volumes (BV), the same level of breakthrough of the two neutral compounds metronidazole and carbamazepine did not occur until 11,000 BV. Single-solute isotherm parameters did not demonstrate any discernible correlation individually with any of the parameters that may govern adsorption onto GAC, such as log D, number of hydrogen-bond donor/acceptor groups, dipole moment or aromaticity ratio of the compounds. The isotherm data, however, could differentiate the breakthrough behaviour between negatively charged and neutral trace organic contaminants., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The removal efficiency of 22 selected trace organic contaminants by sequential application of granular activated carbon (GAC) and simultaneous application of powdered activated carbon (PAC) with membrane bioreactor (MBR) was compared in this study. Both sequential application of GAC following MBR treatment (MBR-GAC) and simultaneous application of PAC within MBR (PAC-MBR) achieved improved removal (over 95%) of seven hydrophilic and biologically persistent compounds, which were less efficiently removed by MBR-only treatment (negligible to 70%). However, gradual breakthrough of these compounds occurred over an extended operation period. Charged compounds, particularly, fenoprop and diclofenac, demonstrated the fastest breakthrough (complete and 50-70%, in MBR-GAC and PAC-MBR, respectively). Based on a simple comparison from the long-term performance stability and activated carbon usage points of view, PAC-MBR appears to be a better option than MBR-GAC treatment., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The removal of trace organics by a membrane bioreactor-granular activated carbon (MBR-GAC) integrated system were investigated. The results confirmed that MBR treatment can be effective for the removal of hydrophobic (log D>3.2) and readily biodegradable trace organics. The data also highlighted the limitation of MBR in removing hydrophilic and persistent compounds (e.g. carbamazepine, diclofenac, and fenoprop) and that GAC could complement MBR very well as a post-treatment process. The MBR-GAC system showed high removal of all selected trace organics including those that are hydrophilic and persistent to biological degradation at up to 406 bed volumes (BV). However, over an extended period, breakthrough of diclofenac was observed after 7320 BV. This suggests that strict monitoring should be applied over the lifetime of the GAC column to detect the breakthrough of hydrophilic and persistent compounds which have low removal by MBR treatment., (Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.)

A novel membrane distillation – enzymatic membrane bioreactor (MD-EMBR) system was developed for efficient degradation of trace organic contaminants (TrOCs). Degradation of five TrOCs, namely carbamazepine, oxybenzone, diclofenac, atrazine and sulfamethoxazole was examined using two commercially available laccases (from Trametes versicolor and Aspergillus oryzae ). The MD system ensured complete retention (>99%) of both enzyme and TrOCs. Of particular interest was that the complete retention of the TrOCs resulted in high TrOC degradation by both laccases. Oxybenzone and diclofenac degradation in the MD-EMBR ranged between 80 and 99%. Compared to previously developed EMBRs, as much as 40% improvement in the removal of resistant non-phenolic TrOCs ( e.g., carbamazepine) was observed. Laccase from A. oryzae demonstrated better TrOC degradation and enzymatic stability. With the addition of redox mediators, namely 1-hydroxybenzotriazole (HBT) or violuric acid (VA), TrOC degradation was improved by 10–20%. This is the first demonstration of a laccase-based high retention membrane bioreactor for enhanced biodegradation of TrOCs. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to demonstrate the complementarity of combining membrane bioreactor (MBR) treatment with UV oxidation or high pressure membrane filtration processes such as nanofiltration (NF) or reverse osmosis (RO) for the removal of trace organic contaminants (TrOC). The results suggest that the removal mechanisms of TrOC by either UV oxidation or NF/RO membrane filtration differ significantly from those of an MBR system. Thus, they can complement MBR treatment very well to significantly improve the removal of TrOC. MBR treatment can effectively remove hydrophobic and readily biodegradable hydrophilic TrOC. The remaining hydrophilic and biologically persistent TrOC were shown to be effectively removed by either UV oxidation or NF/RO membrane filtration. The combination of MBR with UV oxidation or NF/RO membrane filtration resulted in a removal ranging from 85% to complete removal (or removal to below the analytical detection limit) of all 22 TrOC selected in this study. In particular, it is noteworthy that although MBR treatment and direct UV oxidation separately achieved low removal of carbamazepine (a widely reported problematic compound), the combination of these two processes resulted in more than 96% removal. [Copyright &y& Elsevier]

Abstract: The effects of controlled temperature variation in the range of 10–45°C were assessed in a lab-scale MBR that treated synthetic municipal wastewater spiked with selected micropollutants. The effects were evaluated with respect to total organic carbon (TOC) and total nitrogen (TN) removal, micropollutant removal, sludge growth, level of soluble microbial products (SMPs) in the mixed liquor and membrane fouling. Overall, the temperature shifts caused high variation in the TOC and TN levels in the reactor supernatant, however that in membrane-permeate was relatively more stable, substantiating the robustness of the MBR process. Results regarding the removal of micropollutants at ambient temperature (20°C) demonstrate an apparent correlation between hydrophobicity, chemical structures and the removal of micropollutants. Temperature variation below and above 20°C, especially the operation under 45°C appeared to significantly influence the removal of certain less hydrophobic (log D <3.2) micropollutants possessing strong electron withdrawing functional groups. The removal of most hydrophobic compounds (log D >3.2) was stable under the temperature range of 10–35°C, however, deteriorated at 45°C. The temperature shifts were also associated with higher levels of SMP in the mixed liquor which appeared to trigger membrane fouling as evidenced by a rapid increase in transmembrane pressure. [Copyright &y& Elsevier]

Abstract: Previous studies have confirmed significant removal of various trace organic contaminants (TrOCs) by white-rot fungal cultures under sterile batch test conditions. However, little is known about TrOC removal in continuous flow fungal reactors in a non-sterile environment. This study reports the removal of two TrOCs, namely, bisphenol A and diclofenac, by a fungal membrane bioreactor (MBR). Sterile batch tests with “active” (biosorption and biodegradation) and “chemically inactivated” (biosorption only) Trametes versicolor (ATCC 7731) confirmed biodegradation as the main mechanism for the removal of both compounds. An MBR inoculated with T. versicolor was operated in non-sterile conditions for a period of three months during which diclofenac and bisphenol A were continuously added to the synthetic wastewater. Relatively stable removal of bisphenol A (80–90%) and diclofenac (∼55%) was achieved by applying a hydraulic retention time of two days, at the bisphenol A and diclofenac loadings of 475 ± 25 and 345 ± 112 μg/L.d, respectively. [Copyright &y& Elsevier]