Full-scale Membrane Bioreactor Research Articles

Mechanisms of pathogenic virus removal in a full-scale membrane bioreactor.

Four pathogenic virus removal mechanisms were investigated in a full-scale membrane bioreactor (MBR; nominal pore size 0.04 μm): (i) attachment of virus to mixed liquor solids; (ii) virus retention by a just backwashed membrane; (iii) virus retention by the membrane cake layer; and (iv) inactivation. We quantified adenovirus, norovirus genogroup II (GII), and F+ coliphage in the influent wastewater, the solid and liquid fractions of the mixed liquor, return flow, and permeate using quantitative PCR (adenovirus and norovirus GII) and infectivity assays (F+ coliphage). Permeate samples were collected 4-5 days, 1 day, 3 h, and immediately after chlorine enhanced backwashes. The MBR achieved high log removals for adenovirus (3.9 to 5.5), norovirus GII (4.6 to 5.7), and F+ coliphage (5.4 to 7.1). The greatest contribution to total removal was provided by the backwashed membrane, followed by inactivation, the cake layer, and attachment to solids. Increases in turbidity and particle counts after backwashes indicated potential breakthrough of particles, but virus removal following backwashes was still high. This study demonstrates the ability of the MBR process to provide over 4 logs of removal for adenovirus and norovirus GII, even after a partial loss of the cake layer, and provides evidence for assigning virus disinfection credit to similar MBRs used to reclaim wastewater for reuse.

Risk assessment of Giardia from a full scale MBR sewage treatment plant caused by membrane integrity failure

Membrane bioreactors (MBR) are highly efficient at intercepting particles and microbes and have become an important technology for wastewater reclamation. However, many pathogens can accumulate in activated sludge due to the long residence time usually adopted in MBR, and thus may pose health risks when membrane integrity problems occur. This study presents data from a survey on the occurrence of water-borne Giardia pathogens in reclaimed water from a full-scale wastewater treatment plant with MBR experiencing membrane integrity failure, and assessed the associated risk for green space irrigation. Due to membrane integrity failure, the MBR effluent turbidity varied between 0.23 and 1.90NTU over a period of eight months. Though this turbidity level still met reclaimed water quality standards (≤5NTU), Giardia were detected at concentrations of 0.3 to 95 cysts/10L, with a close correlation between effluent turbidity and Giardia concentration. All β-giardin gene sequences of Giardia in the WWTP influents were genotyped as Assemblages A and B, both of which are known to infect humans. An exponential dose–response model was applied to assess the risk of infection by Giardia. The risk in the MBR effluent with chlorination was 9.83×10−3, higher than the acceptable annual risk of 1.0×10−4. This study suggested that membrane integrity is very important for keeping a low pathogen level, and multiple barriers are needed to ensure the biological safety of MBR effluent.

Bacteriophage removal in a full-scale membrane bioreactor (MBR) – Implications for wastewater reuse

The aim of this study was to assess the potential removal efficacy of viruses in a full-scale membrane bioreactor (MBR) wastewater reuse system, using a range of indigenous and ‘spiked’ bacteriophages (phages) of known size and morphology. Samples were taken each week for three months from nine locations at each treatment stage of the water recycling plant (WRP) and tested for a range of microbiological parameters (n = 135). Mean levels of faecal coliforms were reduced to 0.3 CFU/100 ml in the MBR product and were undetected in samples taken after the chlorination stage. A relatively large reduction (5.3 log) in somatic coliphages was also observed following MBR treatment. However, F-specific and human-specific (GB124) phages were less abundant at all stages, and demonstrated log reductions post-MBR of 3.5 and 3.8, respectively. In ‘spiking’ experiments, suspended ‘spiked’ phages (MS2 and B-14) displayed post-MBR log reductions of 2.25 and 2.30, respectively. The removal of these suspended phages, which are smaller than the membrane pore size (0.04 μm), also highlights the possible role of the membrane biofilm as an effective additional barrier to virus transmission. The findings from this study of a full-scale MBR system demonstrate that the enumeration of several phage groups may offer a practical and conservative way of assessing the ability of MBR to remove enteric viruses of human health significance. They also suggest that phage removal in MBR systems may be highly variable and may be closely related on the one hand to both the size and morphology of the viruses and, on the other, to whether or not they are attached to solids.

Optimization of full-scale membrane bioreactors for wastewater treatment through a model-based approach

Despite the high number of advantages of membrane bioreactors (MBR), operational costs still remain as one of the main obstacles of this technology. In that sense, a full-scale MBR was studied in order to explore and identify viable optimization strategies for improving effluent quality and reducing operational costs through a model-based approach. Opportunities for optimization strategies, identified through the initial experimental phase, were focused on improving the nitrogen removal efficiencies and reducing the aeration energy costs through the aerobic DO set point and recirculation modifications. A mechanistic model was developed to reproduce the operation of the full-scale MBR and predict the effects of the optimization actions. Moreover, a qualitative risk model was also applied to ensure that the DO set point reduction did not negatively affect the microbiology of the activated sludge. The best viable control scenario was identified and then tested in the full-scale MBR. The results achieved maximum improvements on the nitrogen removal efficiencies of 27% and reduction on the aeration energy (7%) without affecting the sludge properties or the filtration performance. The model approached proved in this study and the optimization strategies identified can be generalized for municipal MBRs.

Membrane bioreactor wastewater treatment plants reveal diverse yeast and protist communities of potential significance in biofouling

The yeast community was studied in a municipal full-scale membrane bioreactor wastewater treatment plant (MBR-WWTP). The unexpectedly high diversity of yeasts indicated that the activated sludge formed a suitable environment for them to proliferate, with cellular concentrations of 2.2 ± 0.8 × 103 CFU ml−1. Sixteen species of seven genera were present in the biological reactor, with Ascomycetes being the most prevalent group (93%). Most isolates were able to grow in a synthetic wastewater medium, adhere to polyethylene surfaces, and develop biofilms of variable complexity. The relationship between yeast populations and the protists in the MBR-WWTP was also studied, revealing that some protist species preyed on and ingested yeasts. These results suggest that yeast populations may play a role in the food web of a WWTP and, to some extent, contribute to membrane biofouling in MBR systems.

REUSE OF TREATED MUNICIPAL WASTEWATER FOR IRRIGATION IN APULIA REGION: THE "IN.TE.R.R.A." PROJECT

The use of non-conventional water resources including treated municipal wastewater has been increasing in the Mediterranean regions over the last decades to cope with water shortages and uneven rainfalls due to climate change. The aim of this paper is to present the first results from two years of experimental field activities carried out in two different demo-places in Southern Italy: the municipal wastewater treatment plants of Noci and Castellana Grotte (Apulia region). In these sites different vegetable crops (cucumber, lettuce, melon, endive in Noci and fennel, lettuce, fennel in Castellana Grotte) were grown in succession and irrigated in parallel with treated wastewater and conventional water pumped from wells, for comparing the effects of the different water sources on soil and vegetables. Reclaimed water quality was monitored for chemical and microbial parameters and compared with conventional water. At harvesting time, microbial indicators were measured on edible part of crops and in soil. Results show that the effluents produced by a full scale membrane bioreactor (MBR) treatment plant (Noci) comply with the stringent Italian standards for reuse in agriculture, and its microbiological quality is higher than the conventional well water. In Castellana Grotte the effluent quality of the two pilot plants was different according to the adopted technologies (MBR and tertiary cloth filtration), and sometimes depended on the quality of incoming wastewater. As for the agronomic results, in both sites crop yields were higher in the plots irrigated with treated wastewater, and the microbial indicators Escherichia coli and Salmonella were never found, at harvesting time, on edible parts of crops and in the soil.

Investigating the effect of sparger configuration on the hydrodynamics of a full-scale membrane bioreactor using computational fluid dynamics

A three-phase computational fluid dynamics (CFD) simulation was carried out in a full-scale membrane bioreactor to investigate the effect of sparger configuration on various hydrodynamic parameters.

Occurrence and fate of potential pathogenic bacteria as revealed by pyrosequencing in a full-scale membrane bioreactor treating restaurant wastewater

Efficient diagnosis based on pyrosequencing can address the highly likely pathogenic bacteria in wastewater.

Energy and chemical efficient nitrogen removal at a full-scale MBR water reuse facility

With stringent wastewater discharge limits on nitrogen and phosphorus, membrane bioreactor (MBR) technology is gaining popularity for advanced wastewater treatment due to higher effluent quality and smaller footprint. However, higher energy intensity required for MBR plants and increased operational costs for nutrient removal limit wide application of the MBR technology. Conventional nitrogen removal requires intensive energy inputs and chemical addition. There are drivers to search for new technology and process control strategies to treat wastewater with lower energy and chemical demand while still producing high quality effluent. The NPXpress is a patented technology developed by American Water engineers. This technology is an ultra-low dissolved oxygen (DO) operation for wastewater treatment and is able to remove nitrogen with less oxygen requirements and reduced supplemental carbon addition in MBR plants. Jefferson Peaks Water Reuse Facility in New Jersey employs MBR technology to treat municipal wastewater and was selected for the implementation of the NPXpress technology. The technology has been proved to consistently produce a high quality reuse effluent while reducing energy consumption and supplemental carbon addition by 59% and 100%, respectively. Lab-scale kinetic studies suggested that NPXpress promoted microorganisms with higher oxygen affinity. Process modelling was used to simulate treatment performance under NPXpress conditions and develop ammonia-based aeration control strategy. The application of the ammonia-based aeration control at the plant further reduced energy consumption by additional 9% and improved treatment performance with 35% reduction in effluent total nitrogen. The overall energy savings for Jefferson Peaks was $210,000 in four years since the implementation of NPXpress. This study provided an insight in design and operation of MBR plants with NPXpress technology and ultra-low DO operations.

Linking operation parameters and environmental variables to population dynamics of Mycolata in a membrane bioreactor

The community structure and population dynamics of Mycolata were monitored in a full-scale membrane bioreactor during four experimental phases under changing operating and environmental conditions, by means of temperature-gradient gel electrophoresis of partial 16S-rRNA genes amplified from community DNA and RNA templates (total and active populations). Non-metric multidimensional scaling and BIO-ENV analyses demonstrated that population dynamics were mostly explained (30–32%) by changes in the input of nutrients in the influent water and the accumulation of biomass in the bioreactors, while the influence of hydraulic and solid retention times, temperature and F/M ratio was minor. Significant correlations were observed between particular Mycolata phylotypes and one or more variables, contributing information for the prediction of their abundance and activity under changing conditions. Fingerprinting and multivariate analyses demonstrated that two foaming episodes, recorded at temperatures <20°C, were connected to the increase of the relative abundance of Mycolata unrelated to Gordonia amarae.

Advanced Technologies for Produced-Water Treatment and Reuse

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 17394, ’Advanced Technologies for Produced-Water Treatment and Reuse,’ by A. Hussain, J. Minier-Matar, A. Janson, S. Gharfeh, and S. Adham, ConocoPhillips, prepared for the 2014 International Petroleum Technology Conference, Doha, Qatar, 20-22 January. The paper has not been peer reviewed. Historically, the treatment of produced water (PW) has been limited to free-oil and suspended-solids removal, using physical separation technologies and injection in disposal wells. However, because of new regulations, combined with geological restrictions and local water scarcity, the drive to have a greater fraction of the PW treated more extensively and ultimately to be reused is increasing. This paper presents the results of a laboratory investigation in which treatment processes were evaluated as treatment methods for PW from different oil and gas fields. Introduction A combination of factors is putting great pressure on operators to find new ways of treating and managing PW that promote water conservation and sustainability. However, treating PW to produce a good-quality effluent is a challenging task. PW characteristics can vary considerably. In order to treat PW to a water-quality standard that enables it to be reused, advanced water-treatment technologies (AWTTs) have to be applied, alone or in combination. To investigate the suitability of several AWTTs to treat and reuse PW from Qatari gas fields, the authors, in conjunction with an operator’s research center, carried out a laboratory investigation in which various treatment processes were evaluated. Four treatment methods were selected to target main contaminants identified in PW from a Qatari gas field: Membrane processes were used to target field chemicals, membrane-distillation (MD) methods were used to target salinity, membrane-bioreactors (MBRs) were used to target organics, and ozonation was used to target field chemicals. Overview of AWTTs Membrane Processes. The potential for membrane processes to treat PW has been demonstrated successfully in various field studies; moreover, a number of upstream petroleum full-scale facilities have already installed membrane processes to treat and reuse PW. The treatment trains either are a combination of different membrane processes or involve other conventional water-treatment technologies such as media filtration or clarification. For two case studies involving the use of membrane processes, please see the complete paper. Thermal Evaporators. These entered the PW-treatment market by finding niche opportunities. Moreover, because almost all waste streams are recycled back to the evaporator, the volumes of fresh water required for makeup are dramatically reduced. With the proliferation of shale-gas wells in the past decade in the US, the demand for treating flowback water with total-dissolved-solids (TDS) concentrations greater than 100 000 mg/L has expanded the opportunities for thermal systems. Another niche market in which the application of evaporators has been very successful is the steam-assisted- gravity-drainage enhanced-recovery process. MBRs. MBRs are now considered by the downstream petroleum industry as an excellent solution to treat various wastewater streams. Although MBRs have not yet been applied to treat PW at upstream oil and gas facilities, a number of bench-scale and pilot studies report that PW is biodegradable, achieving chemical-oxygen-demand (COD) and oil-and-grease (O&amp;G) removals greater than 95%. Moreover, full-scale MBRs are also operating successfully in other industries, treating highly contaminated organic streams (COD greater than 15 000 mg/L) and achieving COD removals greater than 95%.

Impact of suspended solids concentration on sludge filterability in full-scale membrane bioreactors

The relation between activated sludge filterability and mixed liquor suspended solids (MLSS) concentration in membrane bioreactors (MBRs) is framed in a single hypothesis, explaining results seemingly contradictory. A total of 44 activated sludge samples were collected and analyzed on a variety of parameters, i.e. filterability, MLSS concentration, soluble microbial products (SMP) concentrations and particle size distribution in the range of 2–100μm and of 0.4–5.0μm. The sludge filterability was assessed by using the Delft Filtration Characterization method (DFCm). In order to investigate the impact of MLSS concentration, identical samples were diluted with permeate. Results showed that dilution of the samples led to an increased activated sludge filterability, but only when the starting MLSS concentration was below the apparent critical value of 10.5g/L. As opposed, the filterability of sludge with MLSS concentrations above 10.5g/L, and which was characterized by a moderate to good filtration quality, i.e. ΔR20<1 [×1012m−1], worsened when diluted. The specific resistance times the particle concentration of a cake layer obtained when filtrating sludge of moderate to good filterability and MLSS concentration above the apparent critical value was 5.5 times smaller compared to the cake layer of sludge with MLSS concentration below the critical value. Results from SMP assessment and particle counting in the range 2–100µm showed that reduction in sludge mass and de-flocculation occurred, upon dilution of all samples. However, when diluting sludge samples with MLSS concentrations exceeding 10.5g/L and which were characterized by a moderate to good filtration characteristics, there was also release of particles below 0.4µm, opposite to dilutions of samples with MLSS concentrations below 10.5g/L. We postulate that sludge, which is characterized by a moderate to good filterability, having an MLSS concentration above the apparent critical value of 10.5g/L, is likely to retain particles smaller than 0.4μm in its mass, as opposed to sludge with MLSS concentration below the apparent critical value. Our work indicates that there are optimal MLSS concentration ranges in MBR technology, to promote good filterable sludge quality in order to avoid fouling.

Cleaning strategies for iron-fouled membranes from submerged membrane bioreactor treatment of wastewaters

Cleaning strategies for iron-fouled membranes from submerged membrane bioreactors (MBRs) dosed with iron salts are investigated here. Severe membrane fouling resulting from iron dosing was observed with amorphous ferric oxyhydroxide particles and gelatinous assemblages containing Fe(III) bound to polysaccharide materials responsible particularly for irreversible membrane fouling. Sodium hypochlorite (NaOCl) and citric acid, the most commonly used chemical cleaning agents, were not particularly effective in removing iron species from the membrane surface while the Fe(III) reducing agents ascorbic acid and sodium dithionite were very effective in removing iron-containing deposits under the conditions used in this study. In the presence of oxygen, the Fe(III)-catalysed oxidation of ascorbic acid and direct oxygen-mediated oxidation of dithionite control the dissolution rate constant. Use of NaOCl followed by ascorbic acid at concentrations of 10–20mM is recommended as a reasonable balance between cleaning effectiveness and cost though further investigation of cleaning of fouled membranes from full scale MBRs is required.

Closing the water cycle for industrial laundries: An operational performance and techno-economic evaluation of a full-scale membrane bioreactor system

To reduce the consumption of freshwater in the laundry industry, a new trend of closing the water cycle has resulted in the reuse/recycling of water. In this study, the performance of a full-scale submerged aerobic membrane bioreactor (9m3) used to treat/reuse industrial laundry wastewater was examined over a period of 288 days. The turbidity and total solids (TS) were reduced by 99%, and the chemical oxygen demand (COD) effluent removal efficiencies were between 70% and 99%. The levels of COD removed by the membrane were significantly greater than the levels of biodegraded COD. This enabled the bioreactor to sustain COD levels that were below 100mg/L, even during periods of low wastewater biodegradation due to bioreactor sludge. An economic evaluation of the membrane bioreactor (MBR) system showed a savings of 1.13€ per 1m3 of water. The payback period for this system is approximately 6 years. The energy and maintenance costs represent only 5% of the total cost of the MBR system.

Analysis of a transmembrane pressure (TMP) jump prediction model for preventing TMP jumps

In water treatment process such as membrane bioreactors (MBRs), transmembrane pressure (TMP) must be monitored for process control when the process is operated under a condition of constant-rate filtration. One of the reasons making it difficult to monitor, predict, and control TMP is TMP jumps, which means that TMP rise-up rapidly even under the critical flux. We previously constructed a statistical model that predicts the time of a TMP jump by inputting elapsed time, flux, TMP, and other MBR parameters such as operating conditions and water quality. This model is called a TMP jump prediction model. The predictive ability of the TMP jump prediction model was demonstrated through many data sets obtained from real MBRs. In this study, we analyzed the TMP jump prediction model to search optimal operating conditions that can prevent TMP jumps. By changing the values of operating conditions and predicting the time of TMP jumps for each candidate of operating conditions, we could control the time of a TMP jump in a full-scale MBR.

Impact of inflow conditions on activated sludge filterability and membrane bioreactor (MBR) operational performance

Operation and performance of membrane bioreactors (MBRs) for wastewater treatment is influenced by changes in activated sludge properties. Therefore, understanding of the factors influencing sludge filterability is of major importance for efficient operation of MBR installations. This paper assesses the impact of the influent characteristics on activated sludge filterability and treatment performance of full-scale MBRs. The full-scale MBRs were closely monitored both in summer and winter. The measurement campaign, consisting of activated sludge filterability tests and physicochemical analyses, is supplemented with operational performance data evaluation of the various full-scale plants. Based on these data, it is shown that an undesired and refractory composition of incoming wastewater, hydraulic and/or organic load shocks, as well as abrupt temperature changes of the influent, lead to operational problems and affect sludge filterability.

Quantitative response of nitrifying and denitrifying communities to environmental variables in a full-scale membrane bioreactor

The abundance and transcription levels of specific gene markers of total bacteria, ammonia-oxidizing Betaproteobacteria, nitrite-oxidizing bacteria (Nitrospira-like) and denitrifiers (N2O-reducers) were analyzed using quantitative PCR (qPCR) and reverse-transcription qPCR during 9months in a full-scale membrane bioreactor treating urban wastewater. A stable community of N-removal key players was developed; however, the abundance of active populations experienced sharper shifts, demonstrating their fast adaptation to changing conditions. Despite constituting a small percentage of the total bacterial community, the larger abundances of active populations of nitrifiers explained the high N-removal accomplished by the MBR. Multivariate analyses revealed that temperature, accumulation of volatile suspended solids in the sludge, BOD5, NH4+ concentration and C/N ratio of the wastewater contributed significantly (23–38%) to explain changes in the abundance of nitrifiers and denitrifiers. However, each targeted group showed different responses to shifts in these parameters, evidencing the complexity of the balance among them for successful biological N-removal.

Treatment of cosmetic wastewater by a full-scale membrane bioreactor (MBR).

This work evaluates the treatment of wastewater from a personal care products factory by a full-scale side-stream membrane bioreactor (MBR) intermittently fed. The wastewater contained particulate and soluble chemical oxygen demand (COD) which is partially removed by physicochemical pretreatment. Steady removal efficiencies above 98 % were achieved for BOD5, COD and suspended solids. Fats, oils and grease present in the raw wastewater were also successfully removed. The MBR was operated at an average permeate flux of 12 L/m2 · h (LMH) working at a transmembrane pressure of 272 ± 97 mbar. The soluble microbial products concentration remained fairly stable at 175 ± 25 and 85 ± 15 mg/L for proteins and carbohydrates, respectively. This maintained the filtration characteristics of the mixed liquor unaltered over a long-term basis, which was evidenced by a constant permeability of 43 ± 19 LMH/bar. Most of the trace organics detected in the wastewater were completely removed and only some fragrances were detected in the permeate at trace concentrations.

Characterization of metoprolol biodegradation and its transformation products generated in activated sludge batch experiments and in full scale WWTPs

Metoprolol (MTP) is a compound of concern, considered as an emerging contaminant due to its high consumption, pseudopersistence and potential ecotoxicity. Activated sludge batch experiments were performed to evaluate the biological transformation of MTP and the formation of transformation products under different treatment conditions. Total MTP removal was obtained in aerobic conditions, and the formation of MTP known metabolites (metoprolol acid (MTPA), α-hydroxymetoprolol (α-HMTP) and O-desmethylmetoprolol (O-DMTP)) and unknown transformation products (TPs) was investigated. The three known metabolites and two new TPs generated along the experiments were identified by liquid chromatography coupled to high resolution mass spectrometry. For the two new TPs plausible structures were proposed based on the tentative identification. MTPA had the major ratio formation for the TPs identified along the experiments (up to 40% of initial MTP concentration after 96 h treatment) and its persistence through biological treatment was proven. Ecotoxicity studies using Vibrio fischeri bioluminescent bacteria in an acute toxicity test showed that MTP and its known TPs are not toxic with the exception of o-DMTP. Finally, MTP and its TPs were monitored in a full scale membrane bioreactor and in a full scale conventional urban wastewater treatment plant (WWTP) and the results were compared with those obtained in batch experiments. α-HMTP was detected for the first time in a WWTP influent whereas MTPA was detected in influent and effluent WWTP samples at much higher levels (up to 100 folds higher) than MTP itself remarking its high persistence.

Effect of simultaneous nitrification and denitrification on nitrogen removal performance and filamentous microorganism diversity of a full-scale MBR plant

The nutrient removal performance of a membrane bioreactor (MBR) plant treating the wastewater of 10,000 PE was investigated with dynamic simulations. The average process performance with respect to chemical oxygen demand and total nitrogen were reported to be 97 and 81%, respectively. The modeling study showed that low dissolved oxygen (DO) levels (0.2-0.3 mgO2/L) due to limited aeration capacity within aeration tank that provided additional total nitrogen removal of 15-20 mgN/L. Simultaneous nitrification and denitrification process was found to be the reason of performance increase. However, low DO levels <0.3 mgO2/L in the aeration tank triggered the proliferation of filamentous microorganisms within one month as a side effect. In this respect, the morphotypes of Type 0092 and Nocardia (Gordonia) amarae were found to be excessively abundant in the MBR system. Overflow of foam layer covering the tanks was frequently reported during bulking period. A hypochloride dosing of 4.5 gCL/kgMLSS/day was applied to get over filamentous bulking problem as a short term action.