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© 2019 The Royal Society of Chemistry. A hybrid process combining a single compartment aerobic membrane bioreactor (MBR) and a membrane microalgal reactor (MMR) was evaluated for nutrient removal and microalgal biomass production. When operated without biomass extraction, the microalgal biomass in the MMR reached 920 mg L-1 on day 18 and then collapsed, rendering nutrient removal ineffective. Stable operation of the MMR was achieved by regular biomass extraction (i.e. 1/30 of the microalgal biomass in the reactor daily). The biomass production at steady state was approximately 26 g m-3 d-1. The NO3- and PO43- uptake values by microalgae were 4.0 ± 1.1 and 1.5 ± 0.9 g m-3 d-1, respectively. A facile flocculation and separation technique capable of recovering 98% microalgal biomass was demonstrated. Although the hybrid process can significantly enhance nutrient removal and biomass production, further research is needed to intensify the microalgal growth rate. At the current microalgal growth rate, a large MMR volume (37 times that of the MBR) is necessary for synchronous operation.

Laccase enzyme from white-rot fungi is a potential biocatalyst for the oxidation of emerging contaminants (ECs), such as pesticides, pharmaceuticals and steroid hormones. This study aims to develop a three-step platform to treat ECs: (i) enzyme production, (ii) enzyme concentration and (iii) enzyme application. In the first step, solid culture and liquid culture were compared. The solid culture produced significantly more laccase than the liquid culture (447 vs. 74 &micro, M/min after eight days), demonstrating that white rot fungi thrived on a solid medium. In the second step, the enzyme was concentrated 6.6 times using an ultrafiltration (UF) process, resulting in laccase activity of 2980 &micro, M/min. No enzymatic loss due to filtration and membrane adsorption was observed, suggesting the feasibility of the UF membrane for enzyme concentration. In the third step, concentrated crude enzyme was applied in an enzymatic membrane reactor (EMR) to remove a diverse set of ECs (31 compounds in six groups). The EMR effectively removed of steroid hormones, phytoestrogen, ultraviolet (UV) filters and industrial chemical (above 90%). However, it had low removal of pesticides and pharmaceuticals.

Global water quantity and quality are anticipated to decrease in the coming decades, as a result of both increasing global populations and the effects of climate change. Reusing and recycling water is a key part of reducing the pressure on our existing water supplies and the aquatic environment. However, the occurrence of nonsteroidal anti-inflammatory drugs (NSAIDs) in secondary, and in some tertiary, treated effluents- and sewage-impacted water bodies is one of the major obstacles for the implementation of water reuse. For several decades, NSAIDs have been extensively used for therapeutic purposes in both humans and domestic livestock. The negative effects of NSAIDs on aquatic biota are just beginning to be realized. Currently, intensive treatments are required to remove effectively NSAIDs from recycled treated effluent in order to minimize or eliminate risks to human health and aquatic environment. In this chapter, we focus the discussion on contemporary methods for NSAID removal including biological, physical, chemical, and combined process that may provide a more effective and efficient alternative.

The management of brine produced by the reverse osmosis process is challenging due to its high salt and organic content. Limitations in brine disposal options sometimes necessitate the use of zero liquid discharge (ZLD) approach. ZLD systems may include a membrane process – which is used to recover water and to further concentrate brine – followed by thermal treatment. In such systems, a high-water recovery rate is difficult to achieve due to the early onset of membrane scaling and fouling. Brine pre-treatment is therefore necessary to protect the membrane and facilitate ZLD. Literature shows that the most common brine pre-treatment process, chemical precipitation, is generally costly because of high chemical consumption and hazardous sludge production. Moreover, its performance may be hindered by the temporal fluctuations in brine chemistry and the occurrence of residual antiscalants in the brine. A critical evaluation of alternative pre-treatment options was performed. It was found that electrocoagulation and nanofiltration processes have promising performance in terms of hardness and organic removals. Meanwhile, coagulation and adsorption processes show potential for organic removal. Further studies should be performed on process optimization and cost analysis to determine the feasibility of applying these technologies in ZLD systems.

© 2017 Elsevier B.V. The oxic-settling-anoxic (OSA) process, which involves an aerobic tank attached to oxygen- and substrate-deficient external anoxic reactors, minimizes sludge production in biological wastewater treatment. In this study, the microbial community structure of OSA was determined. Principal coordinate analysis showed that among the three operational factors, i.e., (i) redox condition, (ii) external reactor sludge retention time (SRText), and (iii) sludge interchange between aerobic and anoxic reactors, redox condition had the greatest impact on microbial diversity. Generally, reactors with lower oxidation-reduction potential had higher microbial diversity. The main aerobic sequencing batch reactor of OSA (SBROSA) that interchanged sludge with an external anoxic reactor had greater microbial diversity than SBRcontrol which did not have sludge interchange. SBROSA sustained high abundance of the slow-growing nitrifying bacteria (e.g., Nitrospirales and Nitrosomondales) and consequently exhibited reduced sludge yield. Specific groups of bacteria facilitated sludge autolysis in the external reactors. Hydrolyzing (e.g., Bacteroidetes and Chloroflexi) and fermentative (e.g., Firmicutes) bacteria, which can break down cellular matter, proliferated in both the external aerobic/anoxic and anoxic reactors. Sludge autolysis in the anoxic reactor was enhanced with the increase of predatory bacteria (e.g., order Myxobacteriales and genus Bdellovibrio) that can contribute to biomass decay. Furthermore, β- and γ-Proteobacteria were identified as the bacterial phyla that primarily underwent decay in the external reactors.

© 2017 Elsevier Ltd This study investigated the fate of trace organic contaminants (TrOCs) in an oxic-settling-anoxic (OSA) process consisting of a sequencing batch reactor (SBR) with external aerobic/anoxic and anoxic reactors. OSA did not negatively affect TrOC removal of the SBR. Generally, low TrOC removal was observed under anoxic and low substrate conditions, implicating the role of co-metabolism in TrOC biodegradation. Several TrOCs that were recalcitrant in the SBR (e.g., benzotriazole) were biodegraded in the external aerobic/anoxic reactor. Some hydrophobic TrOCs (e.g., triclosan) were desorbed in the anoxic reactor possibly due to loss of sorption sites through volatile solids destruction. In OSA, the sludge was discharged from the aerobic/anoxic reactor which contained lower concentration of TrOCs (e.g., triclosan and triclocarban) than that of the control aerobic digester, suggesting that OSA can also help to reduce TrOC concentration in residual biosolids.

© 2019 Elsevier B.V. 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.

In the concept of a circular economy, wastewater is no longer waste but a resource for water, energy and nutrients. In this study, a hybrid system containing an anaerobic membrane bioreactor (AnMBR) and a microalgal membrane reactor (MMR) was developed to harvest energy, nutrients, and microalgal biomass from food and agribusiness industrial wastewater. The AnMBR removed over 97% of chemical oxygen demand (COD) and generated 4.7 ± 0.15 L (n=80) of biogas equivalent to 2.4 kWh kg−1 COD (feed) d−1. Through anaerobic metabolism, the microorganism in AnMBR generated NH 4 + and PO 4 3 − -rich effluent. Their effluent concentrations were 1.9 and 1.4 times of that in the influent, respectively. NH 4 + and PO 4 3 − -rich effluent was directly used (i.e. without filtration or sterilization) to culture microalgae Chlorella vulgaris in the MMR. . Microalgal biomass production reached up to 700 mg/L after 6 days of operation and nutrient removal rates of above 75% were achieved. However, biomass production and nutrient removal declined towards the end of experiment. The generated biomass was completely harvested using cationic polyacrylamide at the dose of 36 mg g−1 dry weight. Overall, the AnMBR has great potential to produce energy. Future research is needed to intensify the microalgal growth (e.g. genetic modification of strains, addition of plant hormones) in the MMR for continuous operation of the hybrid system.

The oxic-settling anoxic (OSA) process interchanges activated sludge between alternating redox conditions (e.g., aerobic and anoxic) to reduce biosolids production. Iron salts addition to wastewater is performed to remove phosphorous, but this study demonstrated that it may impair OSA performance. Batch test results showed that the addition of iron salt (as Fe 2+ ) decreased the volatile solids reduction of an intermittently aerated batch reactor ( i.e. , aerobic/anoxic), probably because iron reduced the destruction of extracellular polymeric substances (EPS) that serve as the structural framework of sludge flocs. The effect of different FeCl 2 dosages (0, 15, and 30 mg l −1 ) on the sludge yield and EPS profile of an OSA system consisting of a sequencing batch reactor (SBR) attached to external aerobic/anoxic and anoxic reactors was compared to those of a control system consisting of an SBR attached to a single-pass aerobic digester. The two SBRs were fed with real wastewater and operated continuously in parallel for 230 d. Without FeCl 2 addition, the sludge yield (g MLVSS g −1 COD) of the SBR in the OSA system was 24.8% less than that of the control SBR. Moreover, the waste sludge of the OSA system had lower volatile solids content than that of the control system. When 15 or 30 mg l −1 FeCl 2 was added to the influent, OSA was unable to decrease the sludge yield of the SBR and the volatile solids content of the waste sludge. FeCl 2 dosing increased the EPS concentration of sludge in the external aerobic/anoxic reactor, confirming that floc destruction in that reactor was reduced by the presence of iron.

The nitrogen content of waste water generated by the thin film transistor-liquid crystal display (TFT-LCD) industry is not satisfactorily removed through the conventional aerobic-activated sludge process. In this study, the performance of three reactors – suspended type TiO2 membrane photoreactor (MPR), anoxic/oxic membrane bioreactor (AOMBR), and their combination (MPR-AOMBR) – was evaluated using feedwater containing TFT-LCD discharge. The parameters that maximized monoethanolamine (MEA) removal in the MPR were continuous ultraviolet (UV) irradiation and pH 11. Among the tested loadings, 0.1 g/l of TiO2 promoted MEA removal but degradation rate may further increase with photocatalyst concentration. The nitrified sludge recycle ratio R of the AOMBR was adjusted to 1.5 to minimize the amount of nitrate in the effluent. The AOMBR greatly decreased chemical oxygen demand and MEA, but removed only 32.7% of tetramethyl ammonium hydroxide (TMAH). The MPR was configured as the pre-treatment unit for AOMBR, and the combined MPR-AOMBR has improved TMAH removal by 80.1%. The MPR bolstered performance by decomposing slowly biodegradable compounds, and had no negative effects on denitrification and carbon removal.

Poly(vinylidene fluoride) (PVDF) membrane is easily fouled due to its hydrophobic nature. This study attempted to reduce fouling by combining PVDF with hydrophilic poly(methyl vinyl ether-alt-maleic anhydride) (PVMVE-alt-MA) and TiO2 nanoparticles by phase inversion method. Results showed that the average pore size of the blended membranes increased when the amount of PVME-alt-MA that was added to the casted dope was increased from 0% to 3%, but beyond 3% there was no change in pore size. The membrane made from 6% PVME-alt-MA displayed minimal macrovoid formation, and sustained the highest flux in both pure water crossflow filtration and 1% bovine serum albumin (BSA) laboratory-scale filtration. It also exhibited the highest flux recovery after water rinsing and UV treatment. Flux and transmembrane pressure (TMP) trends indicate that membrane morphology (pore size and sub-layer pore arrangement) have greater impact on preventing cake layer formation than hydrophilicity. Water rinsing caused the membranes to recover 50–95% of their initial flux, whereas UV treatment had minimal effect. The membranes exhibited Reactive Black 5 (RB5) dye removal by photocatalysis.

In this study, maghemite (γ-Fe 2 O 3 ) with mesoporous sized powder (∼500 nm), BET surface area 38.79 m 2 /g, pore volume 0.14 cm 3 /g and pore size 25.02 nm was prepared by simple hydrothermal method in order to reduce protein-induced fouling. Maghemite attained maximum adsorption of 30.01 mg/g for bovine serum albumin (BSA). The small surface area of maghemite and electrostatic repulsion between maghemite and BSA molecules probably limited the adsorption capacity. It was found that the application of maghemite to a laboratory-scale reactor mitigated the fouling of commercial poly(vinylidene fluoride) PVDF membrane by protein. The efficiency of the maghemite particles was reliant on liquid shear intensity from mechanical mixing: at low stirring rates maghemite increased membrane output and permeability, contrary to the results of higher stirring rates. The optimum mitigation effect was found at stirring rate 50 rpm. In favorable condition, maghemite improved the performance of the membrane filtering proving its effectiveness as foulant reducer.

The modified polyvinylidene fluoride (PVDF) membranes were fabricated by grafting acrylic acid on the membrane and coating it with titanium dioxide sol. TiO2 sols were prepared using varying precursor volume and solution pH. The TiO2 coated membranes were tested for its photocatalytic property using Reactive Black 5 (RB5) dye and antifouling and self-cleaning properties using 1%BSA solution. FT-IR spectroscopy and contact angles confirmed the presence of polyacrylic acid (PAA) and TiO2 on the membrane surface. The performance of the membranes, evaluated via crossflow filtration experiment, significantly improved as evident in the increase in flux and permeability of modified membranes. The rate of RB5 dye color removal due to immobilized TiO2 follows a pseudo-first-order kinetics. PVDF/PAA/TiO2/pH1.25 exhibited superior photocatalytic property, removing 98.77% of the color in a span of 5 h. The resistance study showed that modified membranes have lower total filtration resistance (RT) with PVDF/PAA/TiO2/PH1.25 having the lowest. The performance of fouled membranes flux and transmembrane pressure (TMP) was recovered through UV irradiation, and the highest recovery was demonstrated by PVDF/PAA/TiO2/pH1.25.

Soluble microbial products (SMP) that persist in the effluent of membrane bioreactors (MBRs) impact not only discharge quality, but also the performance of advanced filtration processes. This study investigated the effect of SMP on the characteristics and fouling potential of a laboratory-scale MBR effluent. First, the domestic wastewater influent, mixed liquor supernatant, and effluent were assessed. Variations in specific ultraviolet adsorption (SUVA) and molecular weight distribution (MWD) confirmed the degradation of pollutants, generation of SMP, and permeation of SMP through the membrane. The effluent contained more carbohydrates than proteins, but the two species combined had minority contribution to the total organic load. Instead, humic acids were the most abundant as confirmed by excitation–emission matrix (EEM) fluorescence spectroscopy analysis. Second, the MBR effluent was subjected to crossflow ultrafiltration (UF). The UF membrane quickly lost 60% of its initial flux, and dramatic transformations in surface morphology and roughness occurred. It also had poor SMP removal efficiency, as most of the carbohydrates and humic acids were not rejected. More proteins were identified on the fouled membrane surface, suggesting that they have a significant role in UF membrane fouling formation.

Magnetic particles were explored as means to prevent membrane fouling. Porous micro-sized magnetite (Fe 3 O 4 ) powder was prepared via the simple co-precipitation method. It did not demonstrate significant adsorption of alginate at ambient temperature and pH, but was able to achieve a maximum adsorption of 5.18 mg/g for bovine serum albumin (BSA) as per the Langmuir adsorption model. The electrostatic repulsion between magnetite and BSA molecules and the small pore size of the particles probably restricted adsorption capacity. Despite this, the addition of magnetite to a laboratory-scale reactor successfully inhibited the protein-induced fouling of commercial poly(vinylidene fluoride) PVDF membrane. Its effectiveness was dependent on liquid shear intensity from mechanical mixing: at low stirring rates magnetite increased membrane output and permeability, whereas at higher rates it was counterproductive. Stirring at 60 rpm yielded the greatest fouling mitigation effect. Furthermore, magnetite improved the performance of the membrane during batch filtration of aerobic sludge, validating its potential as foulant reducer.

Carbon nanotube/titanium(IV) oxide composites (CNT/TiO 2 ) were prepared by hydrothermal method using commercial and self-prepared CNT (synthesized via chemical vapor deposition technique). Self-made CNT possessed significantly higher surface area (255.4 m 2 /g) than its commercial counterpart (77.5 m 2 /g), but Raman spectroscopy revealed that it led to composites containing greater proportion of amorphous carbon. Hence, high purity commercial CNT was selected as the base material. Increasing the amount of TiOSO 4 precursor enhanced TiO 2 growth but decreased the composite's surface area and porosity. This is because of uneven TiO 2 formation, aggregation, and pore-plugging. It was found that CNT to TiOSO 4 ratio of 1:1.710 (w/w) maximized the photocatalytic degradation of model pollutant 2-chlorophenol. Furthermore, degradation efficiency increased with CNT/TiO 2 loading until it reached 0.1 g/l, after which it declined due to photo-shielding effect. Solution pH 11 promoted degradation in spite of photocatalyst–substrate electrostatic repulsions because of robust free radical formation.

© 2016 Elsevier Ltd This paper critically reviews the multidimensional benefits of ozonation in wastewater treatment plants. These benefits include sludge reduction, removal of emerging trace organic contaminants (TrOC) from wastewater and sludge, and resource recovery from sludge. Literature shows that ozonation leads to sludge solubilisation, reducing overall biomass yield. Sludge solubilisation is primarily influenced by ozone dosage, which, in turn, depends on the fraction of ozonated sludge, ozone concentration, and sludge concentration. Additionally, sludge ozonation facilitates the removal of TrOCs from wastewater. On the other hand, by inducing cell lysis, ozonation increases the chemical oxygen demand (COD) and nutrient concentration of the sludge supernatant, which deteriorates effluent quality. This issue can be resolved by implementing resource recovery. Thus far, successful retrieval of phosphorous from ozonated sludge supernatant has been performed. The recovery of phosphorous and other resources from sludge could help offset the operation cost of ozonation, and give greater incentive for wastewater treatment plants to adapt this approach.

In this study, the effect of sludge retention time (SRT) on oxic-settling-anoxic (OSA) process was determined using a sequencing batch reactor (SBR) attached to external aerobic/anoxic reactors. The SRT of the external reactors was varied from 10 to 40 d. Increasing SRT from 10 to 20 d enhanced volatile solids destruction in the external anoxic reactor as evidenced by the release of nutrients, however, increasing the SRT to 40 d did not enhance volatile solids destruction further. Relatively short SRT (10–20 d) favoured the conversion of destroyed solids into inert products. The application of an intermediate SRT (20 d) of the external reactor showed the highest sludge reduction performance (>35%). Moreover, at the optimum SRT, OSA improved sludge dewaterability as demonstrated by lower capillary suction time and higher dewatered cake solids content.

Immobilization of TiO(2) is a promising approach that produces antifouling and photocatalytic membranes that could help advance wastewater treatment and re-use processes. In this study, poly(acrylic acid) (PAA) was plasma-grafted on commercial poly(vinylidene fluoride) (PVDF) to introduce functional groups on the membrane surface that can support the nanoparticles. It was found that plasma treatment at 100 W for 120 s followed by liquid grafting with 70% aqueous AA at 60°C for 2h maximized the number of TiO(2) binding sites. Membrane hydrophilicity was tremendously enhanced by the self-assembly of TiO(2), following a direct proportionality to TiO(2) loading. The membrane with 0.5% TiO(2) loading maintained the highest pure water flux and the best protein antifouling property. UV irradiation triggered the photodegradation of strongly bound foulants, but at least 1.5% TiO(2) and 30 min cumulative irradiation were necessary to completely recover the membrane's original performance. The TiO(2)-modified membranes removed 30-42% of 50mg/l aqueous Reactive Black 5 (RB5) dye. The fabricated membranes demonstrate huge potential for use in membrane reactors with high hydrophilicity, fouling mitigation, and photocatalytic capability.

The impact of sludge interchange rate (SIR) on sludge reduction by oxic-settling-anoxic (OSA) process was investigated. The sludge yield of an OSA system (a sequencing batch reactor, SBR, integrated with external anoxic reactors) was compared to that of a control (an SBR attached to a single-pass aerobic digester). SIR (%) is the percentage by volume of sludge returned from the external reactor into the main bioreactor of the OSA, and was varied from 0% to 22%. OSA achieved greater sludge reduction when fed with unsettled sewage (sCOD = 113 mg/L) rather than settled sewage (sCOD = 60 mg/L). The SIR of 11% resulted in the highest OSA performance. At the optimum SIR, higher volatile solids destruction and nitrification/denitrification ( i.e. , conversion of destroyed volatile solids into inert forms) were observed in the external anoxic and intermittently aerated ( i.e. , aerobic/anoxic) reactors, respectively. Denitrification in the aerobic/anoxic reactor was inefficient without SIR. Effluent quality and sludge settleability of the main SBR were unaffected by SIR.

This paper critically reviews the fate of trace organic contaminants (TrOCs) in biosolids, with emphasis on identifying operation conditions that impact the accumulation of TrOCs in sludge during conventional wastewater and sludge treatment and assessing the technologies available for TrOC removal from biosolids. The fate of TrOCs during sludge thickening, stabilisation (e.g. aerobic digestion, anaerobic digestion, alkaline stabilisation, and composting), conditioning, and dewatering is elucidated. Operation pH, sludge retention time (SRT), and temperature have significant impact on the sorption and biodegradation of TrOCs in activated sludge that ends up in the sludge treatment line. Anaerobic digestion may exacerbate the estrogenicity of sludge due to bioconversion to more potent metabolites. Application of advanced oxidation or thermal pre-treatment may minimise TrOCs in biosolids by increasing the bioavailability of TrOCs, converting TrOCs into more biodegradable products, or inducing complete mineralisation of TrOCs. Treatment of sludge by bioaugmentation using various bacteria, yeast, or fungus has the potential to reduce TrOC levels in biosolids.

Alternate cycling of sludge in aerobic, anoxic, and anaerobic regimes is a promising strategy that can reduce the sludge yield of conventional activated sludge (CAS) by up to 50% with potentially lower capital and operating cost than physical- and/or chemical-based sludge minimisation techniques. The mechanisms responsible for reducing sludge yield include alterations to cellular metabolism and feeding behaviour (metabolic uncoupling, feasting/fasting, and endogenous decay), biological floc destruction, and predation on bacteria by higher organisms. Though discrepancies across various studies are recognisable, it is apparent that sludge retention time, oxygen-reduction potential of the anaerobic tank, temperature, sludge return ratio and loading mode are relevant to sludge minimisation by sludge cycling approaches. The impact of sludge minimisation on CAS operation (e.g., organics and nutrient removal efficiency and sludge settleability) is highlighted, and key areas requiring further research are also identified. © 2014 Elsevier Ltd.

Polyhydroxyalkanoate (PHA) is a class of biodegradable plastics that have great potential applications in the near future. In this study, the micro-biodiversity and productivity of PHA-accumulating bacteria in activated sludge from a domestic wastewater treatment plant were investigated. A previously reported primer set and a selfdesigned primer set (phaCF1BO/phaCR2BO) were both used to amplify the PHA synthase (phaC) gene of isolated colonies. The new primers demonstrated higher sensitivity for phaC, and combining the PCR results of the two primer sets was able to widen the range of detected genera and raise the sensitivity to nearly 90%. Results showed that 85.3% of the identified bacteria were Gram-negative, with Ralstonia as the dominant genus, and 14.7% were Gram-positive. In addition, Zoogloea and Rhizobium contained the highest amounts of intracellular PHA. It is apparent that glucose was a better carbon source than pentone or tryptone for promoting PHA production in Micrococcus. Two different classes, class I and class II, of phaC were detected from alphaproteobacteria, betaproteobacteria, and gammaproteobacteria, indicating the wide diversity of PHA-accumulating bacteria in this particular sampling site. Simultaneous wastewater treatment and PHA production is promising by adopting the high PHAaccumulating bacteria isolated from activated sludge.