Performance of a MBR pilot plant treating high strength wastewater subject to salinity increase: analysis of biomass activity and fouling behaviour

Acute impact of salinity and C/N ratio on the formation and properties of soluble microbial products from activated sludge

The present study investigated the shock of NaCl and C/N ratio on properties of soluble microbial products (SMPs), focusing on their sized fractions. The results indicated that the NaCl stress increased the content of biopolymers, humic substances, building blocks, and LMW substances in SMPs, while the addition of 40 g NaCl L^-1 significantly changed their relative abundance in SMPs. The acute impact of both N-rich and N-deficient conditions accelerated the secretion of SMPs, but the characteristics of LMW substances differed. Meanwhile, the bio-utilization of SMPs has been enhanced with the increase of NaCl dosage but decreased with the increase of the C/N ratio. The mass balance of sized fractions in SMPs + EPS could be set up when NaCl dosage <10 g/L and C/N ratio >5, which indicates the hydrolysis of sized fractions in EPS mainly compensated for their increase/reduction in SMPs. Besides, the results of the toxic assessment indicated that the oxidative damage caused by the NaCl shock was an important factor affecting the property of SMPs, and the abnormal expression of DNA transcription cannot be neglected for bacteria metabolisms with the change of C/N ratio.

Performance enhancement, membrane fouling mitigation and eco-friendly strategy by electric field coupled membrane bioreactor for treating mariculture wastewater

An eco-friendly strategy for mariculture wastewater treatment using an electric field attached membrane bioreactor (E-MBR) was evaluated and compared with a conventional membrane bioreactor (C-MBR). The removal efficiencies of total nitrogen (TN) and chemical oxygen demand (COD) increased significantly and the membrane fouling rate reduced by 44.8% in the E-MBR. The underlying mechanisms included the enriched nitrifiers and denitrifiers, the enhanced salinity-resistance, the increased activities and upregulated genes of key enzymes involved in nitrification and denitrification for improving the performance of mariculture wastewater treatment, and the enriched extracellular polymeric substance (EPS)-degrading genera, the downregulated EPS biosynthesis genes, the repressed biofilm-forming bacteria, the enhanced zeta potential absolute value and the generated H₂O₂ for membrane fouling mitigation by electrical stimulation. Compared with the C-MBR, the energy consumption, carbon emissions, and nitrogen footprint were reduced. These findings provide novel insights into mariculture wastewater treatment using an applied electric field.

Treatment of fracturing wastewater by anaerobic granular sludge: The short-term effect of salinity and its mechanism

The effects of salinity shock on the anaerobic treatment of fracturing wastewater regarding chemical oxygen demand (COD) removal performance, sludge characteristics and microbial community were investigated. Results showed COD removal efficiency decreased from 76.0% to 69.1%, 65.6%, 33.7% and 21.9% with the increase of salinity from 2.5 g/L to 10, 15, 25 and 45 g/L, respectively. The cumulative biogas production decreased by 13.8%-81.1% when salinity increased to 15-85 g/L. The increase of salinity led to the decline in particle size of granular sludge, and the activity of granular sludge, including SMA, coenzyme F₄₂₀ and dehydrogenase, was inhibited significantly. Flow cytometry indicated the percentage of damaged cells in granular sludge gradually increased with the increase of salinity. Sequence analysis illustrated that microbial community structure in anaerobic digestion reactor was influenced by the salinity, high salinity reduced the diversity of archaea and decreased the abundance of methanogens, especially Methanosaeta.

The Influence of Different Operation Conditions on the Treatment of Mariculture Wastewater by the Combined System of Anoxic Filter and Membrane Bioreactor

The mariculture wastewater treatment performance for the combined system of anoxic filter and membrane bioreactor (AF-MBR) was investigated under different hydraulic retention times (HRTs), influent alkalinity, and influent ammonia nitrogen load. The results showed that the removal efficiencies of TOC and total nitrogen were slightly better at the HRT of 8 h than at other HRTs, and the phosphate removal efficiency decreased with the increase of HRT. With the increase of influent alkalinity, the removal of TOC and phosphate did not change significantly. With the increase of influent alkalinity from 300 mg/L to 500 mg/L, the total nitrogen removal efficiency of AF-MBR was improved, but the change of the removal efficiency was not obvious when the alkalinity increased from 500 mg/L to 600 mg/L. When the influent concentration of ammonia nitrogen varied from 20 mg/L to 50 mg/L, the removal efficiencies of TOC, phosphate, and total nitrogen by AF-MBR were stable. An interesting finding was that in all the different operation conditions examined, the treatment efficiency of AF-MBR was always better than that of the control MBR. The concentrations of NO₃⁻-N in AF-MBR were relatively low, whereas NO₃⁻-N accumulated in the control MBR. The reason was that the microorganisms attached to the carrier and remained fixed in the aerobic and anoxic spaces, so that there was a gradual enrichment of bacteria characterized by slow growth in a high-salt environment. In addition, the microorganisms could gather and grow on the carrier forming a biofilm with higher activity, a richer and more stable population, and enhanced ability to resist a load impact.

Dynamic characteristics of microbial community and soluble microbial products in partial nitrification biofilm system developed from marine sediments treating high salinity wastewater

High salinity wastewater generally resulted in microorganism death and low treatment efficiency of nutrient in conventional activity sludge system. Marine sediments, containing a huge amount of natural salt-tolerant microorganisms, provide a feasible option for the rapid construction of halophilic biological treatment system. However, the dynamic of native microorganisms and the fate of soluble microbial products (SMP) in halophilic biofilm system developed from marine sediments needs to be further studied. In this study, a partial nitrification system was successfully established by inoculation of marine sediments in sequential batch biofilm reactor. Satisfactory chemical oxygen demand (COD) and NH₄⁺-N removal efficiency (95% and 99%) and nitrite accumulation rate (NAR) (>90%) was achieved for treatment of synthetic seawater blackwater. High cell surface hydrophobicity (CSH) and proteins to polysaccharide ratio of extracellular polymeric substance (EPS) were beneficial to the initial biofilm formation. High-throughput sequencing results revealed Nitrosomonas halophila was the sole ammonia oxidizing bacteria (AOB). Thauera and Paracoccus were the main denitrifying bacteria in three biofilm samples. Excitation emission matrix (EEM) spectroscopy coupled with parallel factor analysis (PARAFAC) clarified that proteins were significantly degraded than the other two components (humic-like and fulvic acid-like substance). This study will provide a feasible approach for developing halophilic biological treatment system and present an in-depth insight of the dynamic characteristics of SMP in partial nitrification biofilm system.

In-situ membrane fouling control by electrooxidation and microbial community in membrane electro-bioreactor treating aquaculture seawater

Ammonia and nitrite in aquaculture recirculating seawater need to be strictly controlled to avoid deleterious effects on aquatic organisms. However, traditional biological approach can hardly meet the standard due to the short hydraulic retention time (HRT) and nitrite accumulation. A Membrane Electro-Bioreactor (MEBR) was developed for ammonia removal enhancement and in-situ electrochemical membrane fouling mitigation. The fouling mechanism was first found to proceed via the standard filtration model. The flux decrease was mainly caused by an internal pore clogging phenomenon. Membrane fouling resistance was enhanced by increasing anode potential from 0 to 1.4 V vs. SCE (Saturated Calomel Electrode). The ammonia removal rate in the MEBR was above 95% (HRT: 2 h, after day-13) and membrane fouling was mitigated that operation duration was extended by 71.4%. Higher total proportion of Proteobacteria, Bacteroidetes, Planctomycetes and Actinobacteria was obtained in the MEBR, suggesting higher nitrification and nitrogen removal potentials.

Impacts of bio-carriers on the characteristics of soluble microbial products in a hybrid membrane bioreactor for treating mariculture wastewater

To gain greater insights into impacts of bio-carriers on the fate and characteristics of soluble microbial products (SMPs) for mariculture wastewater treatment, the hybrid membrane bioreactor (HMBR) and conventional membrane bioreactor (CMBR) were investigated. Both protein and polysaccharide exhibited lower level in HMBR (8.95 ± 0.28 mg/L and 20.49 ± 1.3 mg/L for anoxic stage, 5.16 ± 0.22 mg/L and 17.85 ± 0.92 mg/L for aerobic stage) than CMBR (14.6 ± 0.68 mg/L and 28.3 ± 2.99 mg/L for anoxic stage, 10.53 ± 0.68 and 26.04 ± 3.15 mg/L for aerobic stage). Three-dimensional fluorescence excitation emission matrix (EEM) revealed bio-carriers reduced the production of aromatic protein-like components in anoxic and aerobic supernatant and caused a blue-shift of soluble microbial product in aerobic stage. Molecular weight (Mw) distribution indicated that bio-carriers ameliorated the excretion of biopolymer (Mw > 500 kDa) in anoxic supernatant and intermediate Mw fractions (20-500 kDa) in aerobic supernatant. Moreover, little changes were observed in SMPs with Mw < 3 kDa down the whole treatment process of both systems. Gas chromatography-mass spectrometry (GC-MS) demonstrated that the major SMPs were long-chain alkanes and aromatics in all units of both systems and fewer aromatics were detected in HMBR. For anoxic stage, more peaks were identified in the HMBR (138) than CMBR (115), while for aerobic stage, more compounds were observed in the CMBR (94) than HMBR (70). Over 50% of the compounds in the anoxic supernatant for the HMBR were the same as in the CMBR. And 27 compounds were the same in aerobic supernatant for the HMBR and CMBR. Fewer compounds in the HMBR effluent (52) was observed, compared to CMBR effluent (80). Approximately 25.7% of compounds in the aerobic stage of the HMBR were rejected by membrane, while this value decreased to 14.9% in the CMBR.

Performance and microbial communities of different biofilm membrane bioreactors with pre-anoxic tanks treating mariculture wastewater

The performance of pollutant removals, activated sludge characteristics, and microbial communities of two biofilm membrane bioreactors coupled with pre-anoxic tanks (BF-AO-MBRs) (one using fiber bundle bio-carriers (FB-MBR) and the other using suspended bio-carriers (MB-MBR)) were compared at the salinity between zero and 60 g/L. At all salinities, three bioreactors showed good COD average removal efficiencies (>94.1%), and FB-MBR showed the best TN removal efficiency (90.4% at 30 g/L salinity). Moreover, FB-MBR had the faster process start-up time and better salt shock resistance. At high salinities (30-60 g/L), more extracellular polymeric substances were produced by the BF-AO-MBRs to avoid the penetration of salt and protect the bacterial community. Because of the different attachment patterns of biofilms, the microbial community structure in the FB-MBR exposed to 30 g/L salinity had higher nitrite-oxidizing/ammonia-oxidizing bacteria ratio (6.44) with more abundance of denitrifiers, which contribute to higher TN removal efficiency and lower nitrite accumulation.

Effects of salinity on the biological performance of anaerobic membrane bioreactor

The performance of anaerobic membrane bioreactor (AnMBR) was evaluated treating synthetic wastewater with various concentrations of NaCl (0-40 g/L), as well as the recovery phase. The effluent COD removal efficiency decreased from 96.4% to 95.0%, 91.4%, 86.7% and 77.7% with stepwise increasing of salt concentration from 0 to 5, 10, 20 and 40 g NaCl/L, respectively, then gradually increased to 94.1% during the recovery phase. Additionally, the significant changes in the content and composition of soluble microbial products (SMP) and extracellular polymer substance (EPS) were obtained under higher salt stress. GC-MS analyses were carried out for the effluent, and some new types of compounds, such as Dodecane, Undecane, and Ethyl Acetate, were found during salt exposure phases. The characterization of the microbial community was also investigated based on the analysis of genomic 16S rDNA, revealing the increasing salinity (5-40 g NaCl/L) could reduce the diversity of sludge microbial community in AnMBR. Meanwhile, the significant effects on the composition of dominate phyla (Proteobacteria, Bacteroidetes, Firmicutes and Chloroflexi) were found during the salt exposure phase.

A Brief Review on the Resistance-in-Series Model in Membrane Bioreactors (MBRs)

The cake layer deposited on the membrane modules of membrane bioreactors (MBRs), especially under a submerged configuration, represents a relevant and fundamental mechanism deeply influencing the development of membrane fouling. It negatively affects the total resistance to filtration, while exerting a positive effect as a "pre-filter" promoting the "dynamic membrane" that protects the physical membrane from internal fouling. These two opposite phenomena should be properly managed, where the submerged membranes are usually subjected to a periodical cake layer removal through ordinary (permeate backwashing and air scouring) and/or irregular cleaning actions (manual physical cleaning). In this context, the physical removal of the cake layer is needed to maintain the design filtration characteristics. Nevertheless, the proper evaluation of the effect of physical cleaning operations is still contradictory and under discussion, referring in particular to the correct evaluation of fouling mechanisms. The aim of the present work was to summarize the different aspects that influence the fouling investigations, based on simple models for the evaluation of the resistance to filtration due to the cake layer, through physical cleaning operations.

Impact of salinity on the population dynamics of microorganisms in a membrane bioreactor treating produced water

Biomass characteristics may change subject to a salinity increase when treating high strength wastewater. In this study, the impact of salinity in a membrane bioreactor (MBR) was investigated for the treatment of produced water (PW). MBR was operated as a pre-treatment prior to nanofiltration (NF) and reverse osmosis (RO). Mixed PW, that was originated from different oil, gas, and oil-gas wells, were subjected to pre-treatment for 146 days including three different operational phases: Low-salinity (~10 mS/cm), gradual increased salinity (10-40 mS/cm) and high salinity (~40 mS/cm). The results of this study showed that microorganisms could adapt using real wastewater and treat PW up to a certain level of the salinity. At high salinity levels of PW, the floc structure started to be disrupted and membrane fouling was accelerated. PCR-DGGE analysis confirmed the changes in microbial communities' composition in relation with high salinity. The results of the final treatment experiments presented that NF and RO treatment produced high-quality effluents that could be suitable for reuse.

The characteristic evolution of soluble microbial product and its effects on membrane fouling during the development of sponge membrane bioreactor coupled with fiber bundle anoxic bio-filter for treating saline wastewater

Membrane fouling mitigation was observed during the development of novel sponge membrane bioreactor coupled with fiber bundle anoxic bio-filter (AF-MBMBR). Soluble microbial product (SMP) was found to be positively correlated with membrane fouling. To further clarify the mechanism of fouling mitigation, the effects of bio-carriers (sponge and fiber bundles) on characteristics and fouling potential of SMP were investigated. Characterization of SMP implied that as a consequence of employing bio-carriers, tyrosine and tryptophan in SMP significantly decreased, instead relative proportions of humic and fulvic acids increased. Meanwhile, batch filtration tests demonstrated that fouling potential of SMP was significantly alleviated, flux decline caused by filtrating SMP decreased from 84.5% to 60.1%. Further analysis on foulants and filtrate revealed that proteins performed high adhesion propensity on membrane while humic and fulvic acids mainly can pass through the membrane; this finding could well explain the mitigation of SMP fouling potential induced by bio-carriers.

Evaluating the effect of different draw solutes in a baffled osmotic membrane bioreactor-microfiltration using optical coherence tomography with real wastewater

This study investigated the performance of an integrated osmotic and microfiltration membrane bioreactor for real sewage employing baffles in the reactor. To study the biofouling development on forward osmosis membranes optical coherence tomography (OCT) technique was employed. On-line monitoring of biofilm growth on a flat sheet cellulose triacetate forward osmosis (CTA-FO) membrane was conducted for 21 days. Further, the process performance was evaluated in terms of water flux, organic and nutrient removal, microbial activity in terms of soluble microbial products (SMP) and extracellular polymeric substance (EPS), and floc size. The measured biofouling layer thickness was in the order sodium chloride (NaCl) > ammonium sulfate (SOA) > potassium dihydrogen phosphate (KH₂PO₄). Very high organic removal (96.9 ± 0.8%) and reasonably good nutrient removal efficiency (85.2 ± 1.6% TN) was achieved. The sludge characteristics and biofouling layer thickness suggest that less EPS and higher floc size were the governing factors for less fouling.

Enhancement of Organic Matter Removal in an Integrated Biofilm-Membrane Bioreactor Treating High-Salinity Wastewater

High salinity can strongly inhibit microbial activity and decrease the sedimentation ability of activated sludge. The combination of biofilm and membrane bioreactor is a practical approach towards effective removal of pollutants and low fouling rate. An integrated biofilm-membrane bioreactor (BMBR) treating mustard tuber wastewater was investigated. An average COD removal efficiency of 94.81% and ammonium removal efficiency of 96.84% were achieved at an organic load of 0.5 kg COD/(m³·d). However, the reactor showed a relatively low efficiency in total nitrogen and soluble phosphorus removal due to the lack of anaerobic environment. The increase of influent organic load resulted in a performance degradation because a balance between the degradation ability and pollution has been reached. Images of scanning electron microscopy revealed that halophilic bacteria were the dominant microbe in the system that leads to a loose sludge structure and declined settling properties. It was found that membrane fouling was the consequence of the interaction of microbial activities and NaCl crystallization.

Evaluation of biomarkers in Mytilus galloprovincialis as an integrated measure of biofilm-membrane bioreactor (BF-MBR) system efficiency in mitigating the impact of oily wastewater discharge to marine environment: a microcosm approach

The large volumes of oily wastewater discharged to marine environment cause heavy impacts on the coastal marine ecosystem. The selection of an appropriate technology to reduce these impacts should be based on the respect of the discharge limits and on the effective assessment and monitoring of its effects on biological organism preservation. To this aim, we set up a controlled microcosm-scale system to compare the effects of a treated and untreated oily wastewater discharge in which the restore process is performed through a Membrane Bio-Reactor. The system is completed by other three microcosms to control and isolate any possible concurrent effect on the Mytilus galloprovincialis, used as sentinel organism. Mytilus galloprovincialis have been kept in all these microcosms, and then mRNA expression and morphology were evaluated on gills and digestive gland. The genes considered in this work are Heat Shock Protein 70 and Metallothionein 10, involved in response to physicochemical sublethal stressors, Superoxide dismutase 1, Catalase, and Cytochrome P450 involved in oxidative stress response. Our results evidenced a significant overexpression, both in gills and digestive gland, of HSP70 in samples maintained in the microcosm receiving the untreated effluent, and of MT10 in those animals kept in microcosm where the effluent was treated. Even though the mRNA modifications are considered "primary" and transient responses which do not always correspond to protein content, the study of these modifications can help to gain insights into the mechanisms of action of xenobiotic exposure. Morphological analysis suggested that, although different, depending on the microcosm, the most serious damages were found in the gill epithelium accompanied with severe haemocyte infiltration, whilst in digestive gland the tissue architecture alterations and the haemocyte infiltration were less pronounced. These observations suggest that the immune system was activated as a general response to stressful stimuli such as the presence of toxic compounds. Moreover, the results indicate that the treatment process is useful. In fact, samples derived from the microcosm receiving the treated effluent, even though presenting some signs of stress, seemed to partially recover the normal structure, although their mRNA expression indicated some cellular suffering.

Effect of salinity variation on the autotrophic kinetics of the start-up of a membrane bioreactor and hybrid moving bed biofilm reactor-membrane bioreactor at low hydraulic retention time

A membrane bioreactor (MBR) and a hybrid moving bed biofilm reactor-membrane bioreactor (hybrid MBBR-MBR) for municipal wastewater treatment were studied to determine the effect of salinity on nitrogen removal and autotrophic kinetics. The biological systems were analyzed during the start-up phase with a hydraulic retention time (HRT) of 6 h, total biomass concentration of 2,500 mg L^-1 in the steady state, and electric conductivities of 1.05 mS cm^-1 for MBR and hybrid MBBR-MBR working under regular salinity and conductivity variations of 1.2-6.5 mS cm^-1 for MBR and hybrid MBBR-MBR operating at variable salinity. The variable salinity affected the autotrophic biomass, which caused a reduction of the nitrogen degradation rate, an increase of time to remove ammonium from municipal wastewater and longer duration of the start-up phase for the MBR and hybrid MBBR-MBR.

Feasibility of treating emulsified oily and salty wastewaters through coagulation and bio-regenerated GAC filtration

In the present study, chemical oxygen demand (COD) removal by coagulation and packed-columns of both fresh and bioregenerated granular activated carbon (GAC) is reported as a feasible treatment for saline and oily wastewaters (slops) generated from marine oil tankers cleaning. The use of Ferric chloride (FeCl₃), Aluminium sulphate (Al₂(SO₄)₃) and Polyaluminum chloride (Al₂(OH₃)Cl₃) was evaluated in the pre-treatment by coagulation of a real slop, after a de-oiling phase in a tank skimmer Comparison of coagulation process indicated that Polyaluminum chloride and Aluminium sulphate operate equally well (20-30% of COD removal) when applied at their optimal dose (40 and 90 mg/l respectively) but the latter should be preferred in order to significantly control the sludge production. The results from the column filtration tests indicated the feasibility of using the selected GAC (Filtrasorb 400 -Calgon Carbon Corporation) to achieve the respect of the discharge limits in the slops treatment with a carbon usage rate in the range 0.1-0.3 kg/m³ of treated effluent. Moreover, biological regeneration through Alcalinovorax borkumensis SK2 was proved to be a cost-effective procedure since the reuse of spent GAC through such regeneration process for further treatment could still achieve approximately 90% of the initial sorption capacity, reducing then costs for the use of new sorbents and also the need for waste disposal.

Membrane fouling mitigation in a moving bed membrane bioreactor combined with anoxic biofilter for treatment of saline wastewater from mariculture

Membrane fouling mitigation in a novel AF-MBMBR system (moving bed membrane bioreactor (10L) coupled with anoxic biofilter (4L)) under high salinity condition (35‰) was systematically investigated. Pre-positioned AF served as a pretreatment induced significant decrease of suspended biomass by 85% and dissolved organic matters by 51.7% in subsequent MBR, which resulted in a reduction of cake layer formation. Based on this, sponge bio-carriers in MBMBR further alleviated the fouling propensity by modifying extracellular polymeric substances (EPS) properties. The protein component in EPS decreased from 181.4 to 116.5mg/g MLSS, with a decline of protein/carbohydrate ratio from 4.6 to 3.4. In particular, elimination of hydrophobic groups like aromatic protein-like substance in EPS was detected. These caused the less biomass deposition on membrane surface, thereby alleviating membrane fouling. In summary, mitigation of membrane fouling in AF-MBMBR should be attributed to contributions from both pre-positioned AF and sponge bio-carriers.

Effects of salinity on simultaneous reduction of perchlorate and nitrate in a methane-based membrane biofilm reactor

This study builds upon prior work showing that methane (CH₄) could be utilized as the sole electron donor and carbon source in a membrane biofilm reactor (MBfR) for complete perchlorate (ClO₄^-) and nitrate (NO₃^-) removal. Here, we further investigated the effects of salinity on the simultaneous removal of the two contaminants in the reactor. By testing ClO₄^- and NO₃^- at different salinities, we found that the reactor performance was very sensitive to salinity. While 0.2 % salinity did not significantly affect the hydrogen-based MBfR for ClO₄^- and NO₃^- removals, 1 % salinity completely inhibited ClO₄^- reduction and significantly lowered NO₃^- reduction in the CH₄-based MBfR. In salinity-free conditions, NO₃^- and ClO₄^- removal fluxes were 0.171 g N/m²-day and 0.091 g/m²-day, respectively, but NO₃^- removal fluxes dropped to 0.0085 g N/m²-day and ClO₄^- reduction was completely inhibited when the medium changed to 1 % salinity. Scanning electron microscopy (SEM) showed that the salinity dramatically changed the microbial morphology, which led to the development of wire-like cell structures. Quantitative real-time PCR (qPCR) indicated that the total number of microorganisms and abundances of functional genes significantly declined in the presence of NaCl. The relative abundances of Methylomonas (methanogens) decreased from 31.3 to 5.9 % and Denitratisoma (denitrifiers) decreased from 10.6 to 4.4 % when 1 % salinity was introduced.

Demonstration of a full-scale plant using an UASB followed by a ceramic MBR for the reclamation of industrial wastewater

This study comprehensively evaluated the performance of a full-scale plant (4550m(3)d(-1)) using a UASB reactor followed by a ceramic MBR for the reclamation and reuse of mixed industrial wastewater containing many inorganics, chemical, oil and greases. This plant was demonstrated as the first full-scale system to reclaim the mixed industrial wastewater in the world. During 395days of operation, influent chemical oxygen demand (COD) fluctuated widely, but this system achieved COD removal rate of 91% and the ceramic MBR have operated flux of 21-25LMH stably. This means that this system adsorbed the feed water fluctuation and properly treated the water. Energy consumption of this plant was achieved 0.76kWhmm(-3) and this value is same range of domestic sewage MBR system. The combination of an UASB reactor and ceramic MBR is the most economical and feasible solution for water reclamation of mixed industrial wastewater.

Membrane Bioreactor (MBR) Technology for Wastewater Treatment and Reclamation: Membrane Fouling

The membrane bioreactor (MBR) has emerged as an efficient compact technology for municipal and industrial wastewater treatment. The major drawback impeding wider application of MBRs is membrane fouling, which significantly reduces membrane performance and lifespan, resulting in a significant increase in maintenance and operating costs. Finding sustainable membrane fouling mitigation strategies in MBRs has been one of the main concerns over the last two decades. This paper provides an overview of membrane fouling and studies conducted to identify mitigating strategies for fouling in MBRs. Classes of foulants, including biofoulants, organic foulants and inorganic foulants, as well as factors influencing membrane fouling are outlined. Recent research attempts on fouling control, including addition of coagulants and adsorbents, combination of aerobic granulation with MBRs, introduction of granular materials with air scouring in the MBR tank, and quorum quenching are presented. The addition of coagulants and adsorbents shows a significant membrane fouling reduction, but further research is needed to establish optimum dosages of the various coagulants/adsorbents. Similarly, the integration of aerobic granulation with MBRs, which targets biofoulants and organic foulants, shows outstanding filtration performance and a significant reduction in fouling rate, as well as excellent nutrients removal. However, further research is needed on the enhancement of long-term granule integrity. Quorum quenching also offers a strong potential for fouling control, but pilot-scale testing is required to explore the feasibility of full-scale application.

Start-up of two moving bed membrane bioreactors treating saline wastewater contaminated by hydrocarbons

This work aims to assess the acclimation of microorganisms to a gradual increase of salinity and hydrocarbons, during the start-up of two moving bed membrane bioreactors (MB-MBRs) fed with saline oily wastewater. In both systems an ultrafiltration membrane was used and two types of carriers were employed: polyurethane sponge cubes (MB-MBRI) and polyethylene cylindrical carriers (MB-MBRII). A decreasing dilution factor of slops has been adopted in order to allow biomass acclimation. The simultaneous effect of salinity and hydrocarbons played an inhibitory role in biomass growth and this resulted in a decrease of the biological removal efficiencies. A reduction of bound extracellular polymeric substances and a simultaneous release of soluble microbial products (SMPs) were observed, particularly in the MB-MBRII system, probably due to the occurrence of a greater suspended biomass stress as response to the recalcitrance of substrate. On the one hand, a clear attachment of biomass occurred only in MB-MBRI and this affected the fouling deposition on the membrane surface. The processes of detachment and entrapment of biomass, from and into the carriers, significantly influenced the superficial cake deposition and its reversibility. On the other hand, in MB-MBRII, the higher production of SMPs implied a predominance of the pore blocking.

Calcium ion on membrane fouling reduction and bioflocculation promotion in membrane bioreactor at high salt shock

Fouling propensity of activated sludge in membrane bioreactor (MBR) is closely related to the disturbance of a salt shock. In this work, the characteristics of membrane fouling and bioflocculation were compared in two laboratory-scale MBRs (one with calcium addition, MBR-Ca, the other without, MBR-C) with a transient salt shock. Particle size distributions, zeta potential, relative hydrophobicity, modified fouling index, the content of polysaccharides, proteins and calcium ions in different layers of sludge were monitored prior to, during and after the salt shock. Comparison with MBR-C showed that the recovery time and fouling rate of MBR-Ca were reduced by 50% and 34%, respectively. Remarkable variations of sludge properties in terms of bioflocculation, such as larger particle sizes, higher relative hydrophobicity and zeta potential, lower polysaccharides in supernatant, higher proteins/polysaccharides ratio in slime and loose bound extracellular polymeric substances, were observed in MBR-Ca after the salt shock.

Performance of membrane bioreactor (MBR) systems for the treatment of shipboard slops: Assessment of hydrocarbon biodegradation and biomass activity under salinity variation

In order to prevent hydrocarbon discharge at sea from ships, the International Maritime Organization (IMO) enacted the MARPOL 73/78 convention in which any oil and oil residue discharged in wastewater streams must contain less than 5 ppm hydrocarbons. Effective treatment of this petroleum-contaminated water is essential prior to its release into the environment, in order to prevent pollution problem for marine ecosystems as well as for human health. Therefore, two bench scale membrane bioreactors (MBRs) were investigated for hydrocarbon biodegradation. The two plants were initially fed with synthetic wastewater characterised by an increasing salinity, in order to enhance biomass acclimation to salinity. Subsequently, they were fed with a mixture of synthetic wastewater and real shipboard slops (with an increasing slops percentage up to 50% by volume). The results indicated a satisfactory biomass acclimation level in both plants with regards to salinity, providing significant removal efficiencies. The real slops exerted an inhibitory effect on the biomass, partially due to hydrocarbons as well as to other concomitant influences from other compounds contained in the real slops difficult to evaluate a priori. Nevertheless, a slight adaptation of the biomass to the new conditions was observed, with increasing removal efficiencies, despite the significant slops percentage.

Correlation between microbial community structure and biofouling as determined by analysis of microbial community dynamics

Three lab-scale membrane bioreactors (MBRs) were continuously operated to treat saline wastewater under 0%, 0.75% and 1.5% NaCl stress. 0.75% and 1.5% NaCl reduced the COD and NH4(+)-N removal at the beginning, while the removal efficiencies could be recovered along with the operation of MBRs. Also, the polysaccharide in extracellular polymeric substances (EPS) and soluble microbial products (SMP) played an important role in the membrane fouling. Illumina sequencing of 16S rRNA gene showed that the increasing level of salinity reduced the diversity of the microbial community, and a higher salinity stimulated the growth of Bacteroidetes. At genus level, Flavobacterium, Aequorivita, Gelidibacter, Microbacterium, and Algoriphagus increased with the increase of salinity, which are shown to be highly salt tolerant. The strength of salinity or the duration of salinity could stimulate the microorganisms with similar functions, and the changes of polysaccharide in EPS and SMP were closely related to the membrane fouling rate as well as correlated with some saline-resistance genera.

Effect of chemical and biological surfactants on activated sludge of MBR system: microscopic analysis and foam test

A bench-scale MBR unit was operated, under stressing condition, with the aim of stimulating the onset of foaming in the activated sludge. Possible synergies between synthetic surfactants in the wastewater and biological surfactants (Extra-Cellular Polymeric Substances, EPSs) were investigated by changing C/N ratio. The growth of filamentous bacteria was also discussed. The MBR unit provided satisfactory overall carbon removal overall efficiencies: in particular, synthetic surfactants were removed with efficiency higher than 90% and 95% for non-ionic and ionic surfactants, respectively. Lab investigation suggested also the importance to reduce synthetic surfactants presence entering into mixed liquor: otherwise, their presence can significantly worsen the natural foaming caused by biological surfactants (EPSs) produced by bacteria. Finally, a new analytic method based on "ink test" has been proposed as a useful tool to achieve a valuation of EPSs bound fraction.

Treatment of hypersaline produced water employing a moderately halophilic bacterial consortium in a membrane bioreactor: effect of salt concentration on organic removal performance, mixed liquor characteristics and membrane fouling

In this study the organic pollutant removal performance and the mixed liquor characteristics of a membrane bioreactor (MBR), employing a moderately halophilic bacterial consortium, for the treatment of hypersaline synthetic produced water containing 100-250 g L(-1) NaCl were considered. The COD and oil and grease (O&G) removal efficiencies in the range 81.6-94.6% and 84.8-94.0% respectively and MBR effluent turbidity lower than 2NTU were achieved. There was no pronounced membrane fouling at any salt concentration. O&G accumulation (less than 11% of the influent O&G) occurred in the mixed liquor at all salt concentrations, but biodegradation was identified as the major organic removal mechanism. With increasing salt concentration, initially increase in SVI and later formation of oil/biomass bodies took place but due to the presence of the membrane biomass washout did not occur. The mixed liquor was pseudoplastic and the apparent viscosity and flow behavior index generally increased with salt concentration.

Comparison between moving bed-membrane bioreactor (MB-MBR) and membrane bioreactor (MBR) systems: influence of wastewater salinity variation

Two pilot plant systems were investigated for the treatment of wastewater subject to a gradual increase of salinity. In particular, a membrane bioreactor (MBR) and a moving bed biofilm membrane bioreactor (MB-MBR) were analyzed. Carbon and ammonium removal, kinetic constants and membranes fouling rates have been assessed. Both plants showed very high efficiency in terms of carbon and ammonium removal and the gradual salinity increase led to a good acclimation of the biomass, as confirmed by the respirometric tests. Significant biofilm detachments from carriers were experienced, which contributed to increase the irreversible superficial cake deposition. However, this aspect prevented the pore fouling tendency in the membrane module of MB-MBR system. On the contrary, the MBR pilot, even showing a lower irreversible cake deposition, was characterized by a higher pore fouling tendency.

The Effect of Salinity on Membrane Fouling Characteristics in an Intermittently Aerated Membrane Bioreactor

The effect of salinity on the membrane fouling characteristics was investigated in the intermittently aerated membrane bioreactor (IAMBR). Five different salinity loadings were set from 0 to 35 g·L−1(referring to NaCl), respectively. The removal of total organic carbon (TOC) and ammonia-nitrogen (NH4+-N) was gradually decreased with increasing salinity. The variation of membrane filtration resistance, particle size distribution (PSD), extracellular polymeric substances (EPS), soluble microbial products (SMP), and relative hydrophobicity (RH) analysis revealed that salinity has a significant effect on sludge characteristics in IAMBR. The results also indicated that the membrane fouling is often caused by the integration of sludge characteristics in saline wastewater.