Membrane Bioreactor Configuration Research Articles

Microbial Selection for the Densification of Activated Sludge Treating Variable and High-Strength Industrial Wastewater

This study investigates the densification/granulation of activated sludge with poor settleability, treating real industrial wastewater from a tank truck cleaning company. The wastewater is low in nutrients, acidic in nature, and high and variable in chemical oxygen demand (COD, ranging from 2770 mg·L−1 to 14,050 mg·L−1). A microbial selection strategy was applied to promote slow-growing glycogen-accumulating microorganisms (GAO) by the implementation of an anaerobic feast/aerobic famine strategy in a sequencing batch reactor (SBR). After 60 to 70 days, the uptake of carbon during the anaerobic phase exceeded 80%, the sludge morphology improved, and the sludge volume index (SVI) dropped below 50 mL·g−1. 16S rRNA gene sequencing showed the enrichment of the GAOs Defluviicoccus and Candidatus Competibacter. Stable sludge densification was maintained when using a constant organic loading rate (OLR) of 0.85 ± 0.05 gCOD·(L·d)−1, but the sludge quality deteriorated when switching to a variable OLR. In view of the integration of densified/granular sludge in a membrane bioreactor configuration, the filtration properties of the densified SBR sludge were compared to the seed sludge from the full-scale plant. The densified sludge showed a significantly lower resistance due to pore blockage and a significantly higher sustainable flux (45 vs. 15 L·(m2·h)−1).

Anoxic Treatment of Agricultural Drainage Water in a Venturi-Integrated Membrane Bioreactor.

Due to low sludge production and being a clean source without residuals, hydrogen-based autotrophic denitrification appears to be a promising choice for nitrate removal from agricultural drainage waters or water/wastewater with a similar composition. Although the incorporation of hydrogen-based autotrophic denitrification with membrane bioreactors (MBRs) enabled almost 100% utilization of hydrogen, the technology still needs to be improved to better utilize its advantages. This study investigated the anoxic treatment of both synthetic and real drainage waters using hydrogen gas in a recently developed membrane bioreactor configuration, a venturi-integrated submerged membrane bioreactor, for the first time. The study examined the effects of the inflow nitrate concentration, and the use of a venturi device on the removal efficiency, as well as the effects of the presence of headspace gas circulation and circulation rate on membrane fouling. The study found that using the headspace gas circulation through a venturi device did not significantly affect the treatment efficiency, and in both cases, a removal efficiency of over 90% was achieved. When the inlet NO3--N concentration was increased from 50 mg/L to 100 mg/L, the maximum removal efficiency decreased from 98% to 92%. It was observed that the most significant effect of the headspace gas circulation was on the membrane fouling. When the headspace gas was not circulated, the average membrane chemical washing period was 5 days. However, with headspace gas circulation, the membrane washing period increased to an average of 12 days. The study found that the headspace gas circulation method significantly affected membrane fouling. When the upper phase was circulated with a peristaltic pump instead of a venturi device, the membrane washing period decreased to one day. The study calculated the maximum hydrogen utilization efficiency to be approximately 96%.

Membrane Bioreactors: A Promising Approach to Enhanced Enzymatic Hydrolysis of Cellulose

The depletion of fossil fuel resources and the negative impact of their use on the climate have resulted in the need for alternative sources of clean, sustainable energy. One available alternative, bioethanol, is a potential substitute for, or additive to, petroleum-derived gasoline. In the lignocellulose-to-bioethanol process, the cellulose hydrolysis step represents a major hurdle that hinders commercialization. To achieve economical production of bioethanol from lignocellulosic materials, the rate and yield of the enzymatic hydrolysis of cellulose, which is preferred over other chemically catalyzed processes, must be enhanced. To achieve this, product inhibition and enzyme loss, which are two major challenges, must be overcome. The implementation of membranes, which can permeate molecules selectively based on their size, offers a solution to this problem. Membrane bioreactors (MBRs) can enhance enzymatic hydrolysis yields and lower costs by retaining enzymes for repeated usage while permeating the products. This paper presents a critical discussion of the use of MBRs as a promising approach to the enhanced enzymatic hydrolysis of cellulosic materials. Various MBR configurations and factors that affect their performance are presented.

Treatment of mature landfill leachate in tropical climate using membrane bioreactors with different configurations

This study describes the collection of landfill leachate from seven sites in different climatic zones of Sri Lanka and characterizes the landfills through the analyses of leachate quality. Membrane bioreactors (MBRs) with different configurations were employed to treat some of those leachates. An aerobic MBR (AMBR) system was operated in three Phases. In the first Phase, an AMBR alone, in the second Phase an anaerobic reactor followed by an anoxic reactor and an AMBR and in the third Phase an anoxic reactor followed by an AMBR were operated. In Phases I and II, the sludge retention time (SRT) and the hydraulic retention time (HRT) were kept at infinite (as no intentional wasting of sludge was made) and 96 h; in Phase III, the SRT was varied from 60, 30, 20 to 10 days and under each SRT, the HRT was varied from 96, 48, 24 and 12 h. The optimum operating conditions for the configuration used in Phase III was established through extensive experiments which had a SRT. The three MBR configurations removed more than 93%, 64.8% and 59% of BOD5, COD and total nitrogen respectively. They also removed large amounts of slowly biodegradable substances and nitrogenous compounds other than NH4+, NO3− and NO2−. Relationships between SRT and MLSS as well as SRT and fouling rate of membrane have been found. The study illustrates the capabilities of MBR in treating landfill leachate.

A Review on Opportunities and Limitations of Membrane Bioreactor Configuration in Biofuel Production.

Biofuels are a clean and renewable source of energy that has gained more attention in recent years; however, high energy input and processing cost during the production and recovery process restricted its progress. Membrane technology offers a range of energy-saving separation for product recovery and purification in biorefining along with biofuel production processes. Membrane separation techniques in combination with different biological processes increase cell concentration in the bioreactor, reduce product inhibition, decrease chemical consumption, reduce energy requirements, and further increase product concentration and productivity. Certain membrane bioreactors have evolved with the ability to deal with different biological production and separation processes to make them cost-effective, but there are certain limitations. The present review describes the advantages and limitations of membrane bioreactors to produce different biofuels with the ability to simplify upstream and downstream processes in terms of sustainability and economics.

Effects of novel anaerobic baffled biofilm membrane bioreactor configurations on membrane fouling mitigation and microbial community in treating liquor condensate

A novel anaerobic baffled biofilm-membrane bioreactor (AnBB-MBR) was developed to treat industrial liquor condensate. In order to minimize membrane fouling, three different reactor configurations of R1:No media (anaerobic baffled MBR), R2:FF (Fixed Film AnBB-MBR) and R3:FF + MVB (Fixed Film and Moving Bed AnBB-MBR) were evaluated at the same operating hydraulic retention time of 3 days. The specific fouling rates of the ceramic membranes were 0.98, 0.84 and 0.5 kPa/L/m2 for R1:No media, R2:FF and R3:FF + MVB, respectively. The R2:FF and R3:FF + MVB reactors could mitigate the membrane fouling rates by 14.1% and 48.9%, compared to R1:No media due to biomass retention in the fixed film and mechanical scouring of the MVB. From the microbial community analysis, higher relative abundances of Methanosaeta were found in the biofilm whereas more Methanobacterium was found in the suspended sludge. Moreover, higher accumulations of humic and fulvic substances in the system could inhibit the methanogenic activity.

Biological cyanide removal from industrial wastewater by applying membrane bioreactors

AbstractBACKGROUNDThis work investigates whether the membrane bioreactor (MBR) process can effectively treat industrial wastewater containing high cyanide concentrations; cyanide may inhibit the biological processes, rendering such processes inadequate. In this work, the changes in process performance and microbial activity under gradually increased free cyanide (CN−) concentrations (1,3 and 10 mgCN−L−1) were investigated in two pilot‐scale MBR configurations. The MBR systems consisted of two parallel operating lines: a single aerobic (MBR1) and an aerobic/anoxic (MBR2).RESULTSCyanide removal was not adversely affected by the increase in cyanide concentration since removals up to 90% were obtained. Despite the inhibition that occurred, ammonia and organic carbon removal efficiency did not decrease, even at the highest cyanide concentration of 10 mgCN−L−1, and it remained high (>95%) in both systems. Nitrification (sAUR) was inhibited by 35%, 54%, and 64% in MBR1 and by 16%, 25%, and 36% in MBR2, with the addition of 1, 3, and 10 mgCN−L−1, respectively. The aerobic respiration (sOUR) was inhibited considerably less with an inhibition of 19%, 37%, and 45% in MBR1 and 9%, 16%, and 21% in MBR2. The biomass maintained under both aerobic and anoxic conditions (MBR2) was more tolerant to cyanide compared to the biomass that was acclimated under only aerobic conditions (MBR1).CONCLUSIONAt high cyanide load conditions, the MBR systems showed satisfactory removal of both cyanide and conventional pollutants despite the inhibition observed, indicating that MBR systems can successfully respond to the treatment of industrial wastewater that is heavily contaminated with cyanide. © 2020 Society of Chemical Industry

Nutrient removal performance and microbiome of an energy-efficient reciprocation MLE-MBR operated under hypoxic conditions

A critical challenge in the application of membrane bioreactors (MBR) for domestic wastewater treatment is its high energy consumption caused by continuous aeration for biofouling control. To reduce energy consumption and mitigate fouling in membranes, alternative configurations using dynamic shear-enhanced filtration by membrane reciprocation, rotation, and vibration to mechanically impose shear on membrane surfaces have been recently introduced. However, although these methods are effective at lowering energy usage, the nutrient removal efficiencies and microbial community compositions of these systems have not been well studied. In this study, a lab-scale no-aeration reciprocation membrane bioreactor was used to characterize the microbial composition, functional profile and nutrient removal of the reciprocation MBR system operated under hypoxic conditions. Microbial community analysis showed Proteobacteria (35%) and Saccharibacteria (27%) to be the most abundant phyla in the sludge and the biofilm samples, respectively. Nitrogen and phosphorus removal efficiencies were observed at 70% and 50% while the chemical oxygen demand concentration had about a 99% decrease in the effluent. Quantitative PCR of nutrient-removing genes revealed the presence of complete ammonia-oxidizing organisms (comammox) with a mean abundance of 1.88 × 104 gene copies/g sludge, which explains the high ammonia removal despite a low abundance of canonical ammonia-oxidizing bacteria (AOB). Fluorescence in-situ hybridization showed a prevalence of nitrite-oxidizing bacteria (NOB) with clusters that are distant from other nutrient-removing communities, suggesting that their metabolism is not dependent on ammonia oxidizers. The reciprocation MBR configuration may be a suitable, more energy-efficient alternative to conventional air-scouring systems because of its biofouling mitigation and promising nutrient removal performed by the diverse microbial communities in its system.

Human Adenovirus 40 Removal in Sidestream Membrane Bioreactor

AbstractThis preliminary study investigates how the removal of human adenovirus in a membrane bioreactor (MBR) depends on the MBR configuration. Results from a sidestream MBR (ssMBR) are compared w...

Current Status and Future Prospects of Membrane Bioreactors (MBRs) and Fouling Phenomena: A Systematic Review

AbstractMembrane bioreactors (MBRs) have been widely used for municipal and industrial wastewater treatment around the world due to their advantages, which include higher efficiency, smaller footprint, and lower sludge production over other conventional activated sludge (CAS) processes. However, membrane fouling that results from physicochemical interactions between the membrane and the components of the mixed liquor still remains the most challenging matter preventing the broad application of MBR technology. Recently, a considerable number of experimental and modelling investigations have been conducted concerning MBRs and membrane fouling. Despite the development of low‐fouling membrane systems, more research and engineering activities with a focus on surface modification, wastewater specifications, pre‐treatment and treatment conditions, and efficient fouling control and remedy strategies are still needed to minimize the probability of the occurrence of fouling. It is vital to investigate important aspects of the characterization and mechanisms of the fouling phenomenon to find reliable and long‐term solutions. This review provides a detailed survey of the main aspects of the MBR processes, configurations, advantages and disadvantages, fouling phenomenon, and fouling control strategies in MBRs. Past research and engineering activities in this area are critically reviewed such that pros and cons of recent developments in fouling inhibition and mitigation approaches are also discussed. The main practical and theoretical challenges for the effective utilization of MBRs in various municipal and industrial sectors are then addressed. At the end, we offer useful practical guidelines and recommendations for the better design and operation of MBRs in industrial and public communities.

Greenhouse gas emissions from membrane bioreactors: analysis of a two-year survey on different MBR configurations.

This study aimed at evaluating the nitrous oxide (N2O) emissions from membrane bioreactors (MBRs) for wastewater treatment. The study investigated the N2O emissions considering multiple influential factors over a two-year period: (i) different MBR based process configurations; (ii) wastewater composition (municipal or industrial); (iii) operational conditions (i.e. sludge retention time, carbon-to-nitrogen ratio, C/N, hydraulic retention time); (iv) membrane modules. Among the overall analysed configurations, the highest N2O emission occurred from the aerated reactors. The treatment of industrial wastewater, contaminated with salt and hydrocarbons, provided the highest N2O emission factor (EF): 16% of the influent nitrogen for the denitrification/nitrification-MBR plant. The lowest N2O emission (EF = 0.5% of the influent nitrogen) was obtained in the biological phosphorus removal-moving bed-MBR plant likely due to an improvement in biological performances exerted by the co-presence of both suspended and attached biomass. The influent C/N ratio has been identified as a key factor affecting the N2O production. Indeed, a decrease of the C/N ratio (from 10 to 2) promoted the increase of N2O emissions in both gaseous and dissolved phases, mainly related to a decreased efficiency of the denitrification processes.

Cost aspects of membrane bioreactors for wastewater treatment

There is a tendency of more and more intensive annual growth of popularity of membrane process reactor technology. Membrane bioreactors (MBRs) have become serious competitors to other methods on the part of the quality of water cleaning. This is the new and perspective technology; however it is still rather expensive, although not so complicated to operate it. The choice of such a technology demands taking into account all its advantages and disadvantages. Nowadays customers are able to choose between different varieties of configurations of MBRs, smart choice of which may provide economic efficiency.

Discriminating activated sludge flocs from biofilm microbial communities in a novel pilot-scale reciprocation MBR using high-throughput 16S rRNA gene sequencing

Membrane bioreactors (MBRs) are a well-established filtration technology that has become a popular solution for treating wastewater. One of the drawbacks of MBRs, however, is the formation of biofilm on the surface of membrane modules. The occurrence of biofilms leads to biofouling, which eventually compromises water quality and damages the membranes. To prevent this, it is vital to understand the mechanism of biofilm formation on membrane surfaces. In this pilot-scale study, a novel reciprocation membrane bioreactor was operated for a period of 8 months and fed with domestic wastewater from an aerobic tank of a local WWTP. Water quality parameters were monitored and the microbial composition of the attached biofilm and suspended aggregates was evaluated in this reciprocating MBR configuration. The abundance of nitrifiers and composition of microbial communities from biofilm and suspended solids samples were investigated using qPCR and high throughput 16S amplicon sequencing. Removal efficiencies of 29%, 16%, and 15% of chemical oxygen demand, total phosphorus and total nitrogen from the influent were observed after the MBR process with average effluent concentrations of 16 mg/L, 4.6 mg/L, and 5.8 mg/L respectively. This suggests that the energy-efficient MBR, apart from reducing the total energy consumption, was able to maintain effluent concentrations that are within regulatory standards for discharge. Molecular analysis showed the presence of amoA Bacteria and 16S Nitrospira genes with the occurrence of nitrification. Candidatus Accumulibacter, a genus with organisms that can accumulate phosphorus, was found to be present in both groups which explains why phosphorus removal was observed in the system. High-throughput 16S rRNA amplicon sequencing revealed the genus Saprospira to be the most abundant species from the total OTUs of both the membrane tank and biofilm samples.

An innovative bioreactor set-up that reduces membrane fouling by adjusting the filamentous bacterial population

Membrane bioreactors (MBR) constitute an advanced wastewater treatment technology over conventional activated sludge processes, however, membrane fouling remains the basic obstacle preventing their universal application. Extended research has been carried out on this issue but an optimal solution has not yet been found. This research proposes an innovative solution to mitigate membrane fouling by manipulating the filamentous bacterial population in activated sludge. The filamentous bacterial population was adjusted by modifying the MBR set-up, where the aerated bioreactor was divided into two in-series chambers. When a food to microorganisms (F/M) ratio of between 0.4 and 0.5g COD/g MLSS*d and a dissolved oxygen concentration of 0.5 ± 0.3mg/L was applied in the first chamber, the filamentous index (FI) ranged between 2 and 3 and the activated sludge presented high porosity, thus resulting in low trans-membrane pressure (TMP) and reversible membrane fouling. In the second chamber, the dissolved oxygen concentration was adjusted to 2.5 ± 0.5mg/L and the F/M ratio ranged between 0.01 and 0.02g COD/g MLSS*d, resulting in an overall F/M ratio within the typical range of 0.08–0.10g COD/g MLSS*d. Thus, further filamentous bacteria growth was inhibited and soluble microbial products (SMP) concentration was minimized. Finally, TMP was controlled within the range of 2–2.5kPa for over three months, in contrast to the corresponding TMP of the conventional membrane bioreactor that gradually increased from 2.5 to 5kPa in the first 25 days and reached 12kPa after 43 days working time. Therefore, reversible and irreversible membrane fouling was controlled successfully through the proposed innovative filamentous MBR configuration.

Membrane Bioreactors for Pharmaceutical Applications: Optically Pure Enantiomers Production

In biological systems, recognition at molecular level is governed by chiral interactions. Therefore, optical isomers have very different effect in natural systems. For example, one can have beneficial effect while the other can be very harmful. For these reasons, chiral drugs nowadays are mainly admitted in the optically pure form. Given these requirements, it is clear why demand for chiral drugs has grown dramatically and the singleenantiomer drug segment has become an important part of the overall pharmaceutical market. As a consequence, the development of new chiral separation techniques is a very hot topic in both academic research and industrial innovation. Membrane bioreactors have proven their feasibility in the production of optically pure enantiomers by combining enantiospecific biochemical reactions with mass transport through membranes. The principles and the applications of enantioselective membrane bioreactors in kinetic resolution for pharmaceutical applications will be discussed. Various membrane bioreactors configurations and operation mode will be illustrated. The type of enzymes utilized to produce chiral drugs or their intermediates will be also reported. Multistep syntheses, conducted in sequential reactions catalysed by spatially aligned biocatalysts, as promising technology for the synthesis of fine chemicals will be highlighted.

Preparation of conductive microfiltration membrane and its performance in a coupled configuration of membrane bioreactor with microbial fuel cell

A conductive flat microfiltration membrane with graphene (G-FM) was prepared with polyvinylidene fluoride (PVDF) and reduced graphene oxide (RGO) on stainless steel mesh base by the method of immersion-precipitation phase transformation.

Impact of anaerobic dynamic membrane bioreactor configuration on treatment and filterability performance

Submerged and external anaerobic dynamic membrane bioreactors (AnDMBRs) have been compared in terms of removal efficiency, filtration characteristics and microbial community structure. High COD removal efficiencies were obtained with both submerged and external AnDMBRs. To obtain an effective dynamic membrane (DM) layer enabling high quality permeate, longer time was required in the external AnDMBR configuration compared to the submerged one. A difference in microbial community structure was identified using pyrosequencing analyses between the submerged and external AnDMBRs. The number of archaeal types decreased in the bulk sludge of the external AnDMBR. External sludge recirculation might have had a negative effect on the archaeal community in the bulk sludge of the external AnDMBR. However, the sludge recirculation in the external AnDMBR configuration led to a filtration at lower total filtration resistance and TMP in comparison to the submerged one at the same gas sparging rate. Results showed that the submerged AnDMBR system can provide a shorter start-up period, slightly better permeate quality in terms of COD concentration, and higher biogas production in comparison to the external one in gas-lift mode.

Performance of semi-continuous membrane bioreactor in biogas production from toxic feedstock containing d-Limonene

A novel membrane bioreactor configuration containing both free and encased cells in a single reactor was proposed in this work. The reactor consisted of 120g/L of free cells and 120g/L of encased cells in a polyvinylidene fluoride membrane. Microcrystalline cellulose (Avicel) and d-Limonene were used as the models of substrate and inhibitor for biogas production, respectively. Different concentrations of d-Limonene i.e., 1, 5, and 10g/L were tested, and an experiment without the addition of d-Limonene was prepared as control. The digestion was performed in a semi-continuous thermophilic reactor for 75days. The result showed that daily methane production in the reactor with the addition of 1g/L d-Limonene was similar to that of control. A lag phase was observed in the presence of 5g/L d-Limonene; however, after 10days, the methane production increased and reached a similar production to that of the control after 15days.

Deposit membrane fouling: influence of specific cake layer resistance and tangential shear stresses.

Cake fouling is the leading cause of membrane permeability decrease when filtering mixed liquor suspension containing high suspended solid concentrations. A simple model is proposed to simulate the cake resistance evolution with time by considering a macro-scale fouling linked only to the accumulation of particles on the membrane surface. This accumulation appears as the difference between the flux of deposited particles due to the filtration and the flux of particles detached from the membrane surface due to the tangential shear stresses caused by recirculation flow in the sidestream membrane bioreactor (MBR) or gas sparging close to the membrane surface for submerged MBR configuration. Two determining parameters were then highlighted: the specific cake resistance and the 'shear parameter'. Based on these parameters it is possible to predict model outputs as cake resistance and permeate flux evolution for short-time filtration periods.

Comparison of four types of membrane bioreactor systems in terms of shear stress over the membrane surface using computational fluid dynamics

Membrane bioreactors (MBRs) have been used successfully in biological wastewater treatment to solve the perennial problem of effective solids-liquid separation. A common problem with MBR systems is clogging of the modules and fouling of the membrane, resulting in frequent cleaning and replacement, which makes the system less appealing for full-scale applications. It has been widely demonstrated that the filtration performances in MBRs can be greatly improved with a two-phase flow (sludge-air) or higher liquid cross-flow velocities. However, the optimization process of these systems is complex and requires knowledge of the membrane fouling, hydrodynamics and biokinetics. Modern tools such as computational fluid dynamics (CFD) can be used to diagnose and understand the two-phase flow in an MBR. Four cases of different MBR configurations are presented in this work, using CFD as a tool to develop and optimize these systems.