Upflow Anaerobic Sludge Blanket Effluent Research Articles

Calcium Alginate Core–Shell Liquid Beads Encapsulated with Microalgae for Wastewater Treatment

Liquid beads are core–shell particles with a liquid core and a solid shell. Calcium alginate liquid beads have been emerging as a promising platform for cell encapsulation. These beads have demonstrated their capability of encapsulating and culturing a wide range of human cells for tissue engineering. However, a significant research gap remains in the application of alginate liquid beads for encapsulating photosynthetic microorganisms. Herein, fast‐growing microalgae strain Chlorella vulgaris is encapsulated into calcium alginate liquid beads to facilitate the removal of nutrients from wastewater, minimizing the risk of eutrophication. Liquid bead‐microalgae systems are prepared, using different calcium ion concentrations as crosslinking ions. It has been thoroughly characterized for their morphologies, cell growth patterns, nutrient removal capabilities, and overall stability throughout the wastewater treatment process, with upflow anaerobic sludge blanket effluent as the wastewater model. The results indicate that the liquid bead‐microalgae system with the highest calcium ion concentration (5%) performs more efficiently, exhibiting a well‐formed crosslinking structure, leading to rapid cell growth with the highest cell density and the most effective removal of nutrients. The findings from this study provide valuable insights for future optimization and upscaling efforts in wastewater treatment systems based on calcium alginate liquid beads.

Sustainable treatment of municipal secondary effluent from UASB systems by solar photo-Fenton: CECs removal and toxicity control

Upflow Anaerobic Sludge Blanket (UASB) systems are vastly implemented for municipal wastewater treatment in developing tropical countries. Despite that, efforts related to the removal of contaminants of emerging concern (CECs) from municipal secondary effluents (MSE) via post-treatment by solar photo-Fenton are mainly conducted with MSE from Conventional Activated Sludge (CAS). Hence, it is critical to investigate the efficiency of solar photo-Fenton to treat MSE from UASB systems. This is the first study to evaluate the performance of solar photo-Fenton and dark Fenton conducted with intermittent additions of Fe2+ and at circumneutral pH for the removal of CEC from UASB followed by Trickling Filter (UASB+TF) and UASB effluent. Acute and chronic ecotoxicity to Aliivibrio fischeri and Raphidocelis subcapitata, respectively, and phytotoxicity to Lactuca sativa were also evaluated for both matrixes. Solar photo-Fenton removed 83% of ΣCECs from UASB+TF effluent and resulted in non-toxic samples. Solar photo-Fenton performed in MSE from UASB system alone showed 65% ΣCECs removal and reduced chronic effect to R. subcapitata (growth inhibition) from 11% to 26%. In addition, no acute toxicity was verified for A. fischeri nor L. sativa. This work shows the feasibility of applying solar photo-Fenton at circumneutral pH to improve the quality of MSE resulting from UASB systems prior to wastewater discharge or reuse in agriculture.

Study on the Treatment of Refined Sugar Wastewater by Electrodialysis Coupled with Upflow Anaerobic Sludge Blanket and Membrane Bioreactor.

In this paper, refined sugar wastewater (RSW) is treated by electrodialysis (ED) coupled with an upflow anaerobic sludge blanket (UASB) and membrane bioreactor (MBR). The salt in RSW was first removed by ED, and then the remaining organic components in RSW were degraded by a combined UASB and MBR system. In the batch operation of ED, the RSW was desalinated to a certain level (conductivity < 6 mS·cm-1) at different dilute to concentrated stream volume ratios (VD/VC). At the volume ratio of 5:1, the salt migration rate JR and COD migration rate JCOD were 283.9 g·h-1·m-2 and 13.84 g·h-1·m-2, respectively, and the separation factor α (defined as JCOD/JR) reached a minimum value of 0.0487. The ion exchange capacity (IEC) of ion exchange membranes (IEMs) after 5 months of usage showed a slight change from 2.3 mmol·g-1 to 1.8 mmol·g-1. After the ED treatment, the effluent from the tank of the dilute stream was introduced into the combined UASB-MBR system. In the stabilization stage, the average COD of UASB effluent was 2048 mg·L-1, and the effluent COD of MBR was maintained below 44-69 mg·L-1, which met the discharge standard of water contaminants for the sugar industry. The coupled method reported here provides a viable idea and an effective reference for treating RSW and other similar industrial wastewaters with high salinity and organic contents.

Granular activated carbon stimulated microbial extracellular secretions in anaerobic digesters: An egalitarian act and beyond

Granular activated carbon (GAC) has been widely studied for its roles in improving anaerobic digestion (AD) through its conductive properties in stimulating direct interspecies electron transfer or its surface functional groups in altering redox conditions in AD. In the present study, the impacts of GAC on the biosynthesis of extracellular microbial secretions (e.g., amino acids and vitamins), and the roles of these secretions in AD were investigated. Four continuous laboratory reactors were operated under ambient temperature (20 ± 0.5 °C) conditions, including two up-flow anaerobic sludge blanket (UASB) bioreactors with GAC addition to one of the UASBs; and two anaerobic sequencing batch reactors (ASBRs) each fed with the centrifuged supernatants (to remove suspended biomass and GAC debris) of UASB effluents supplemented with additional carbon source (glucose). Our finding shows that GAC addition stimulated extracellular microbial secretions in UASB, and these secretions, which can work as essential nutrients, enhanced COD removal (from 48 ± 3 % to 60 ± 1 %) and methane production (31 ± 3 % to 47 ± 5 %) in its downstream ASBR. Interestingly, microbial kinetics test showed that extracellular microbial secretions from the GAC-amended UASB improved methane production rate from 72.5 ± 1.5 to 105.6 ± 1.2 mg CH4-COD/g VSS/d without dramatic microbial community shift. We conclude that the impact of GAC on AD does not only rely on the direct contact of microorganisms and GAC materials, and the GAC-stimulated microbial extracellular secretions represent an important mechanism in conductive material amended AD.

Effect of organic loading rate and effluent recirculation on biogas production of desulfated skim latex serum using up-flow anaerobic sludge blanket reactor

High sulfate contents in skim latex serum (SLS) can be reduced by rubber wood ash (RWA). Subsequently, the desulfated skim latex serum (DSLS) can be further anaerobically treated more effectively with the accompanying generated biomethane. In this study, DSLS was treated using an up-flow anaerobic sludge blanket (UASB) reactor operated at 10-day HRT and under mesophilic (37 °C) conditions. The effect of organic loading rates (OLR) at 0.89, 1.79 and 3.57 g-COD/L-reactor∙d on DSLS biodegradability was investigated in Phase I-IV using NaHCO3 as an external buffering agent. Maximum methane production yield of 226.35 mL-CH4/g-CODadded corresponding to 403.25 mL-CH4/L reactor·d was achieved at the suitable OLR of 1.79 g-COD/L-reactor∙d. UASB effluent recirculation which was then applied to replace the NaHCO3. It was found that with 53% effluent recirculation similar to an OLR of 2.01 g-COD/L-reactor∙d, an average of 185.70 mL-CH4/g-CODadded corresponding to 371.40 mL/L reactor·d of methane production was reached. The dominant bacteria in UASB reactor were members of Proteobacteria, Bacteroidota, Firmicutes, and Desulfobacterota phyla. Meanwhile, the archaeal community was majorly dominated by the genera Methanosaeta sp. and Methanomethylovorans sp. The study clearly indicates the capabilities of UASB reactor with effluent recirculation to treat DSLS anaerobically.

Preliminary Study of Up-Flow Anaerobic Sludge Blanket (UASB) Technology for Energy Recovery from Domestic Wastewater

New efforts are increasingly oriented towards the search for sustainable Waste Water Treatment Plant (WWTP) designs. The use of anaerobic digestion processes allows energy production during the treatment of wastewater. However, this technology has been poorly implemented for domestic wastewater due its low organic matter content. In this work, the generation of biogas from municipal wastewater has been studied through anaerobic digestion treatment. UASB effluent has been fed to a membrane photobioreactor (MPBR) where developed indigenous microalgae-bacteria consortia contributes to organic matter and nutrients recovery from digested wastewater and membrane allows continuous regenerated wastewater production as permeate stream. The study was performed at pilot scale making use of an Y configuration UASB, operated under psychrophilic conditions. In addition, the energy production potential of different valorisable substrates, which are residual streams from different treatment processes, was studied at lab scale: concentrate from direct ultrafiltration (DUF) membrane and sludge from conventional membrane bioreactors (MBR), in order to define the potentiality of technological trains with UASB reactors. Anaerobic digestion yields interesting results that should be considered, such as the fact that energy recovery in MBR is lower than that achieved in DUF, where a higher concentration of organic matter is obtained, and therefore, a greater energy obtainment is achieved.

Performance evaluation of a full-scale upflow anaerobic sludge blanket reactor coupled with trickling filters for municipal wastewater treatment in a developing country

Poor wastewater management remains a critical health and environmental challenge in most developing countries in Sub-Saharan Africa due to the lack of adequate infrastructure for collection and treatment. This study evaluated the performance and methane production of a full-scale upflow anaerobic sludge blanket (UASB) reactor of capacity 18000 m3/d, with post-treatment unit: trickling filters followed by final settling tanks for municipal wastewater treatment in Ghana. Data was collected on operational conditions and physicochemical parameters of wastewater (influent and effluent) over a period of 35 weeks in 2021 (from January to August). The influent biochemical oxygen demand to chemical oxygen demand (BOD:COD) ratio was 0.58 ± 0.16, indicating the presence of highly biodegradable compounds in the sewage. Operational conditions for the UASB reactors were observed to be within the optimal range for anaerobic systems, with an applied organic loading rate of 1.30 ± 0.79 kgCOD/m3/d. Generally, Plant performance was satisfactory with carbon removal at 93% for COD and 98% for BOD. Biogas yield was 0.2 m3/kgCOD removed, culminating in an average biogas production rate of 831.6 ± 292.7 m3/d. Average methane composition was 64.7 ± 11.9% of the biogas output, whilst an estimated 35% of the methane generated remained dissolved in the UASB effluent. The UASB reactor presents an efficient technology that can be implemented in developing countries for effective and sustainable wastewater management.

Removal of micropollutants by UASB reactor and post-treatment by Fenton and photo-Fenton: Matrix effect and toxicity responses

Literature is scarce on the performance of Fenton-based processes as post-treatment of municipal wastewater treated by upflow anaerobic sludge blanket (UASB) reactor. This study aims to perform Fenton and photo-Fenton from UASB influent and effluent matrices to remove micropollutants (MPs) models: atrazine (ATZ), rifampicin (RIF), and 17α-ethynylestradiol (EE2). A UASB reactor at bench-scale (14 L) was operated with these MPs, and the AOPs experiments at bench-scale were performed on a conventional photochemical reactor (1 L). A high-pressure vapor mercury lamp was used for photo-Fenton process (UVA-Vis) as a radiation source. Microcrustacean Daphnia magna (acute toxicity) and seeds of Lactuca sativa (phytotoxicity) were indicator organisms for toxicity monitoring. The UASB reactor showed stability removing 90% of the mean chemical oxygen demand, and removal efficiencies for ATZ, RIF, and EE2 were 16.5%, 45.9%, and 15.7%, respectively. A matrix effect was noted regarding the application of both Fenton and photo-Fenton in UASB influent and effluent to remove MPs and toxicity responses. The pesticide ATZ was the most recalcitrant compound, yet the processes carried out from UASB effluent achieved removal >99.99%. The post-treatment of the UASB reactor by photo-Fenton removed acute toxicity in D. magna for all treatment times. However, only the photo-Fenton conducted for 90 min did not result in a phytotoxic effect in L. sativa.

On-site domestic wastewater treatment system using shredded waste plastic bottles as biofilter media: Pilot-scale study on effluent standards in Bhutan

In this study, a 1000 L/d capacity one-off on-site wastewater treatment system was operated for over a year as a pilot alternative to the conventional on-site treatment as currently used in urban Bhutan. An up-flow anaerobic sludge blanket (UASB) was used for blackwater treatment (to replace “septic tank followed by an anaerobic biofilter (ABF) (to replace soak pits) for the treatment of a mixture of greywater and UASB effluent. Shredded waste plastic bottles were used as the novel biofilter media in the ABF. During a yearlong operation, the pilot system produced a final treated effluent from ABF with average BOD5 28 mg/L, COD 38 mg/L, TSS 85 mg/L and 5 log units of Escherichia coli. These effluents met three out of four of the national effluent discharge limits of Bhutan, but unsuccessful to meet the Escherichia coli standard over a yearlong operation. Further, process optimisation may enable more significant Escherichia coli removal. An economic analysis indicates that the total unit cost (capital and operating expenditures) of this alternative wastewater treatment system for more than 50 users range between USD 0.27–0.37/person/month comparable to USD 0.29–0.42/person/month for the current predominant on-site system, i.e., “septic tanks”. This pilot study, therefore, indicates that this wastewater treatment system using shredded waste plastic biofilter media has high potential to replace the current conventional treatment, i.e., “septic tanks”, which are often overloaded with greywater and discharging effluents which does not meet the national standards.

Reduction and partitioning of viral and bacterial indicators in a UASB reactor followed by high rate algal ponds treating domestic sewage

Human enteric pathogens are a major global concern, as they are responsible for thousands of preventable deaths every year. New pathogens in wastewater are constantly emerging. For example, SARS-CoV-2 has been recently detected in domestic sewage and primary sludge. Knowledge about the reduction of viruses in wastewater treatment and their partitioning between the treated liquid effluent versus the sludge or biosolids is still very scarce, especially in countries with emerging economies and tropical climates. Upflow anaerobic sludge blanket (UASB) reactors are among the top three most commonly used technologies for the treatment of sewage in Latin America and the Caribbean, and their use has become increasingly common in many other low- and middle-income countries. High-rate algal ponds (HRAP) are regarded as a sustainable technology for the post-treatment of UASB effluent. This study evaluated the overall reduction and the liquid-solid partitioning of somatic coliphages, F-specific coliphages, and E. coli in a pilot-scale system comprised of a UASB reactor followed by HRAPs treating real wastewater. Average log removal for somatic and F-specific coliphages were 0.40 and 0.56 for the UASB reactor, and 1.15 and 1.70 for HRAPs, respectively. The overall removal of both phages in the system was 2.06-log. Removal of E. coli was consistently higher. The number of viruses leaving the system in the UASB solids and algal biomass was less than 10% of the number leaving in the clarified liquid effluent. The number of E. coli leaving the system in solids residuals was estimated to be approximately one order of magnitude higher than the number of E. coli leaving in the liquid effluent. Results from this study demonstrate the suitability of UASB-HRAP systems to reduce viral and bacterial indicators from domestic sewage and the importance of adequately treating sludge for pathogen reduction before they are used as biosolids.

Exploring shredded waste PET bottles as a biofilter media for improved on-site sanitation

This study explores an improved alternative on-site treatment for unsewered urban Bhutan. The system combines up-flow anaerobic sludge blanket for blackwater treatment and anaerobic biofilter for a mixture of up-flow anaerobic sludge blanket effluent and greywater. Shredded waste plastic bottles are used as novel biofilter media that provides a large surface area for attached growth while addressing waste plastic problems. A bench-scale up-flow anaerobic sludge blanket (operated at hydraulic retention time or HRT of 1–10 days) and anaerobic biofilter (HRT of 0.25–3 days) study were conducted for 188 days. At 2-d HRT, up-flow anaerobic sludge blanket removed 70–80 % of chemical oxygen demand (COD) while anaerobic biofilter achieved 90–98 % COD removal at eight-hour HRT. Combined up-flow anaerobic sludge blanket and anaerobic biofilter achieved final effluent with COD less than 50 mg/L and turbidity of less than 3 NTU that meets the discharge standard of Bhutan. The study shows that shredded waste plastic bottles can be an effective biofilter support medium for low-cost on-site treatment while helping address waste plastic problems.

Comparison of soluble microbial product (SMP) production in full-scale anaerobic/aerobic industrial wastewater treatment and a laboratory based synthetic feed anaerobic membrane system

This study focused on the characterisation of soluble microbial products (SMPs) produced from a full-scale multi-stage (anaerobic/aerobic) industrial wastewater treatment plant, and contrasted them to the SMPs detected in the effluent of a lab-scale AnMBR treating synthetic wastewater to determine if there were any common solutes detected irrespective of the feed organics. Recently developed analytical methods using gas chromatography coupled mass spectrometry (GC–MS) and liquid chromatography coupled quadrupole-time-of-flight (LC-Q-ToF) for SMP characterisation in a wide molecular weight (MW) range of 30–2000 Da (Da) were applied. Samples collected from the Industrial Wastewater plant were the upflow anaerobic sludge blanket (UASB) influent and effluent, and aerobic membrane bioreactor (MBR) effluent before discharge. The GC–MS detected a spike in cyclooctasulphur in the UASB effluent, an indicator of shock-loading, which disappeared after the MBR process. Alkanes, acids and nitrogenous compounds were found to be the end-products from the GC–MS results, while LC-Q-ToF analysis revealed that eicosanoids, a group of cell-signalling molecules, were produced in the aerobic MBR, and made up 71% of its effluent. A comparison of the submerged anaerobic membrane bioreactor (SAMBR) and aerobic MBR effluents using GC–MS showed that there was only a small degree of similarity between the SMPs, comprising mainly long chain alkanes and phthalate. On the other hand, LC-Q-ToF showed a large contrast in compound composition, mostly having cell-signalling functions, which deepened our understanding of the different metabolic processes occurring in aerobic and anaerobic systems. These data could be useful for future work in various areas such as controlling quorum-sensing and biofilm formation, process optimisation and control, and microbial ecology.

Wetting- and fouling-resistant hollow fiber membranes for dissolved methane recovery from anaerobic wastewater treatment effluents

Anaerobic wastewater treatment processes are becoming increasingly widespread due to their advantages in sludge management and net energy consumption. One major reason behind the energy benefit of the mainstream anaerobic processes is methane (CH4) production. Nevertheless, over one-third of the produced CH4 typically remains in effluent streams in dissolved form. To recover the dissolved CH4 (dCH4) from anaerobic effluents, the membrane contactor (MC) process enabled by porous membranes offers a promising way. However, membrane wetting and fouling issues hinder the practical implementation of the concept. Here we report a wetting- and fouling-resistant hollow fiber membrane that can operate with realistic anaerobic effluents. Coating of a highly porous (~85%) hollow fiber support with a conformal layer of polydimethylsiloxane (PDMS) provides resistance to wetting, but fouling persists. To tackle the fouling issue, we post-treated the uncured PDMS-coatings with PDMS-based amphiphilic copolymers with short (147 Da) or long (~1570 Da) side chains. Both types of post-treated membranes exhibited an improved performance when tested against effluent samples taken not only from an anaerobic membrane bioreactor but also from an upflow anaerobic sludge blanket (UASB) reactor. The membrane treated with the short-side-chain copolymer could sustain 7 days of continuous operation with UASB effluent with a performance loss of only ~10%. We observed that the fouling layers were much richer in proteins rather than subtances similar to humic and fulvic acids and microbial byproducts. Besides, we calculated that our wetting/fouling-resistant membranes provide a net energy benefit for the MC process (when the recovered CH4 is retrofitted to the process as fuel). Thus, our results suggest that the MC-based dCH4 recovery process is a viable alternative for industrial practices in case the demonstrated custom-designed membranes are employed.

Pre-coagulation assisted ultrafiltration membrane process for anaerobic effluent

Abstract Membranes can be used as alternative for post-treatment of upflow anaerobic sludge blanket (UASB) reactors. However, mainly for anaerobic effluent, fouling is still a challenge and major drawback can be minimized by coagulant addition before membrane filtration. In this work, three concentrations of aluminum sulfate (20, 150, and 950 mg L−1) were applied in UASB effluent to evaluate pollutant removal and fouling mitigation potential in two steps: coagulation/flocculation and crossflow filtration with ultrafiltration membrane. All coagulant dosages removed foulants (e.g. carbohydrates and proteins) before filtration and supernatants showed lower flux decrease in relation to UASB effluent, with an enhancement in reversible fouling fraction in comparison with total fouling resistance. Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy (SEM-EDX) analyses showed efficient coagulation and precipitation resulting in less residual aluminum in membrane surface for 950 mg L−1 coagulant dosage. All coagulants concentrations altered the cake layer, assisting crossflow filtration. Coagulation of UASB effluent before membrane filtration indicate an interesting alternative for post-treatment of anaerobic effluent.

Impact of microaeration bioreactor on dissolved sulfide and methane removal from real UASB effluent for sewage treatment.

Two bioreactors were investigated as an alternative for the post-treatment of effluent from an upflow anaerobic sludge blanket (UASB) reactor treating domestic sewage, aiming at dissolved sulfide and methane removal. The bioreactors (R-control and R-air) were operated at different hydraulic retention times (HRT; 6 and 3 h) with or without aeration. Large sulfide and methane removal efficiencies were achieved by the microaerated reactor at HRT of 6 h. At this HRT, sulfide removal efficiencies were equal to 61% and 79%, and methane removal efficiencies were 31% and 55% for R-control and R-air, respectively. At an HRT of 3 h, sulfide removal efficiencies were 22% (R-control) and 33% (R-air) and methane removal did not occur. The complete oxidation of sulfide, with sulfate formation, prevailed in both phases and bioreactors. However, elemental sulfur formation was more predominant at an HRT of 6 h than at an HRT of 3 h. Taken together, the results show that post-treatment improved the anaerobic effluent quality in terms of chemical oxygen demand and solids removal. However, ammoniacal nitrogen was not removed due to either the low concentration of air provided or the absence of microorganisms involved in the nitrogen cycle.

Treatment of UASB-treated recycled paper wastewater using SBR and SBBR: A comparison

Anaerobic-oxic (AO) systems have been extensively adopted for the biological treatment of wastewater from recycled paper mills, which is characterized by high chemical oxygen demand (COD) concentrations and contains hundreds of organic compounds. In this study, an up-flow anaerobic sludge blanket (UASB) served as the anaerobic treatment of recycled paper mill wastewater. Then, either a sequential batch reactor (SBR) or a sequential batch biofilm reactor (SBBR) were adopted as aerobic treatment to treat the UASB effluent respectively. Parameters such as COD, BOD5, and TSS were measured to compare the treatment performance of SBR and the SBBR. After 80 days’ operation, COD removal efficiency of SBR and SBBR were 21.79 ± 3.4% and 38.38 ± 2.69% respectively; TSS removal efficiencies were 20.84 ± 5.15% and 47.02 ± 5.84% respectively. The results indicated that SBR was effective for removing residual organic matter in UASB effluent. However, SBBR showed significant advantages for the removal of COD and total suspended solids (TSS), which are ascribed to the effective biomass retention and biofiltration of SBBR.

A simple anaerobic and filtration combined system for domestic wastewater treatment

Anaerobic treatment of domestic wastewater can only partially treat the effluent and still contains concentration of organic matter, suspended solids, nutrients and pathogens beyond the recommended safe limit. This study aims to observe the effect of sand filter as a low cost post treatment solution. A 250 L pilot scale upflow anaerobic sludge blanket (UASB) reactor was fed septic tank effluent and operated at an average ambient temperature of 19 °C. The reactor was fed intermittently at 6 h hydraulic retention time and the performance was monitored. The UASB effluent was filtered in a 1 m3 sand filter unit. The removal efficiencies of Total Suspended Solid, Chemical Oxygen Demand and Faecal Coliform for combined system were 93%, 87% and 93%, respectively. However, the top layer of the sand in the filter needs to be replaced in every two to three months to maintain acceptable filtration capacity performance. The tested combined anaerobic and filtration system was sufficient to treat effluents from a typical Nepalese family and the result could be useful to design and develop a suitable compact, low cost onsite sanitation system in developing countries like Nepal. The result should encourage investigating on the establishment of a safe route of sand replacement and handling as well as alternative low cost filtration media in order to avoid frequent replacement of the sand.

Anaerobic/aerobic integration via UASB/enhanced aeration for greywater treatment and unrestricted reuse

Abstract The aim of the present study is to achieve an efficient treatment of greywater for reuse in food crops' irrigation. For this purpose, anaerobic followed by enhanced aerobic treatment system was examined via both bench scale and pilot plant. The greywater was separated and collected from the source. The examined systems consisted of Up flow Anaerobic Sludge Blanket (UASB) followed by anaerobic aeration enhanced by Effective Microorganism (EM). The characteristics of the raw greywater were within a high strength level due to the presence of detergents, phosphates, oil and grease. The BOD5/COD was 0.75, showing that biological treatment to this greywater could be achieved. Treatment with UASB showed high elimination of oil &amp; grease, BOD5, COD, total phosphates, and TKN in the range of 60 to 84%. However, TSS and ammonia were poorly removed. UASB effluent was further aerobically treated in a continuous aerated system where the predetermined optimum EM dose was added. Both aeration time and EM dose were previously examined to reach the optimum. Anaerobic/aerobic pilot plant in the continuing treatment was evaluated, where the final treated effluent successfully reached the permissible limits for unrestricted reuse according to the international regulation, namely FAO, WHO, US EPA and Egypt.

Fouling formation in membrane contactors for methane recovery from anaerobic effluents

Fouling in membrane contactors for recovery of dissolved methane (CH4) was investigated in this work. Two types of effluents from anaerobic membrane bioreactor (AnMBR) and upflow anaerobic sludge blanket (UASB) were tested under a continuous operational mode. Due to the higher fouling propensity of the UASB effluent, membrane fouling was more drastic, leading to a greater decline in the CH4 desorption flux with respect to the operational time. Also, the flux was observed to be influenced by the gas-liquid contact time and declined more severely with increasing liquid velocity. Membrane characterization revealed cake layer formation as the source of membrane fouling while foulants characterization indicated that the majority of the foulants were protein-like-substances with fluorescence spectra showing signals close to that of extracellular polymeric substances. On this basis, a mass transfer analysis was performed to understand the fouling resistance exerted by the cake layer and identify a parameter which best described the fouling mechanism. It was found that cake thickness can be used to express the change in fouling resistance in the case of the AnMBR effluent, while cake porosity was a better parameter in the case of the UASB effluent.

Methanotrophic community composition based on pmoA genes in dissolved methane recovery and biological oxidation closed downflow hanging sponge reactors

Dissolved methane in the effluent of anaerobic wastewater treatment processes is unrecovered and released into the atmosphere as methane, a greenhouse gas. To prevent methane emissions from effluent, a post-treatment system consisting of two closed downflow hanging sponge (DHS) reactors for the recovery and biological oxidation of dissolved methane was developed. More than 99% of the dissolved methane was completely eliminated using this system under ambient temperatures for 1year. In this study, the methanotrophic community composition of the two closed DHS reactors was investigated. The performance of the closed DHS reactor was evaluated at different heights of the reactor in summer and winter. The clone libraries and T-RFLP analyses based on the pmoA gene revealed that type I and type II methanotrophs were present in the closed DHS reactors. Furthermore, type I methanotrophs showed wide diversity and contained uncultured phylogenetic clusters of methanotrophs (FWs and LWs), while type II methanotrophs were dominated by Methylocystis- and Methylosarcina-related clusters. The relative abundance of type II methanotrophs increased during winter. The type I methanotroph population dynamically changed with height of the reactor. These results demonstrate the important role of methanotrophs in removal of dissolved methane from upflow anaerobic sludge blanket effluent treating sewage.