Activated Sludge Bioreactor Research Articles

Bacterial Community Dynamics and Taxa-Time Relationships within Two Activated Sludge Bioreactors

BackgroundBiological activated sludge process must be functionally stable to continuously remove contaminants while relying upon the activity of complex microbial communities. However the dynamics of these communities are as yet poorly understood. A macroecology metric used to quantify community dynamic is the taxa-time relationship (TTR). Although the TTR of animal and plant species has been well documented, knowledge is still lacking in regard to TTR of microbial communities in activated sludge bioreactors.Aims1) To characterize the temporal dynamics of bacterial taxa in activated sludge from two bioreactors of different scale and investigate factors affecting such dynamics; 2) to evaluate the TTRs of activated sludge microbial communities in two bioreactors of different scale.MethodsTemporal variation of bacterial taxa in activated sludge collected from a full- and lab-scale activated sludge bioreactor was monitored over a one-year period using pyrosequencing of 16S rRNA genes. TTR was employed to quantify the bacterial taxa shifts based on the power law equation S = cTw.ResultsThe power law exponent w for the full-scale bioreactor was 0.43 (R2 = 0.970), which is lower than that of the lab-scale bioreactor (w = 0.55, R2 = 0.971). The exponents for the dominant phyla were generally higher than that of the rare phyla. Canonical correspondence analysis (CCA) result showed that the bacterial community variance was significantly associated with water temperature, influent (biochemical oxygen demand) BOD, bioreactor scale and dissolved oxygen (DO). Variance partitioning analyses suggested that wastewater characteristics had the greatest contribution to the bacterial community variance, explaining 20.3% of the variance of bacterial communities independently, followed by operational parameters (19.9%) and bioreactor scale (3.6%).ConclusionsResults of this study suggest bacterial community dynamics were likely driven partly by wastewater and operational parameters and provide evidence that the TTR may be a fundamental ecological pattern in macro- and microbial systems.

Microbial biogeography across a full-scale wastewater treatment plant transect: evidence for immigration between coupled processes

Wastewater treatment plants use a variety of bioreactor types and configurations to remove organic matter and nutrients. Little is known regarding the effects of different configurations and within-plant immigration on microbial community dynamics. Previously, we found that the structure of ammonia-oxidizing bacterial (AOB) communities in a full-scale dispersed growth activated sludge bioreactor correlated strongly with levels of NO2 (-) entering the reactor from an upstream trickling filter. Here, to further examine this puzzling association, we profile within-plant microbial biogeography (spatial variation) and test the hypothesis that substantial microbial immigration occurs along a transect (raw influent, trickling filter biofilm, trickling filter effluent, and activated sludge) at the same full-scale wastewater treatment plant. AOB amoA gene abundance increased >30-fold between influent and trickling filter effluent concomitant with NO2 (-) production, indicating unexpected growth and activity of AOB within the trickling filter. Nitrosomonas europaea was the dominant AOB phylotype in trickling filter biofilm and effluent, while a distinct "Nitrosomonas-like" lineage dominated in activated sludge. Prior time series indicated that this "Nitrosomonas-like" lineage was dominant when NO2 (-) levels in the trickling filter effluent (i.e., activated sludge influent) were low, while N. europaea became dominant in the activated sludge when NO2 (-) levels were high. This is consistent with the hypothesis that NO2 (-) production may cooccur with biofilm sloughing, releasing N. europaea from the trickling filter into the activated sludge bioreactor. Phylogenetic microarray (PhyloChip) analyses revealed significant spatial variation in taxonomic diversity, including a large excess of methanogens in the trickling filter relative to activated sludge and attenuation of Enterobacteriaceae across the transect, and demonstrated transport of a highly diverse microbial community via the trickling filter effluent to the activated sludge bioreactor. Our results provide compelling evidence that substantial immigration between coupled process units occurs and may exert significant influence over microbial community dynamics within staged bioreactors.

Modification of PES membrane with Ag–SiO2: Reduction of biofouling and improvement of filtration performance

Fouling is a critical problem in membrane filtration processes. Creating advanced membrane materials with antifouling properties is one of the practical strategies to reduce biofouling. To improve the antifouling performance and enhance the dispersion of silver in the membrane, the silver nanoparticle was deposited on the silica sphere surface to form Ag–SiO2. Ag–SiO2 nanocomposite polyethersulfone (PES) membranes were fabricated by phase inversion method. The effect of Ag–SiO2 content on the membrane performance was investigated. Surface and cross-section morphologies, hydrophilicity and permeability of the membranes were characterized by Scanning Electron Microscopy (SEM), contact angle measurement and filtration test, respectively. The results demonstrated that the prepared membranes showed a typical asymmetric structure and the contact angle of the membrane decreased from 67.7° to 52.6° with the increase of the Ag–SiO2 loading. The stability of the silver in the nanocomposite membranes was evaluated during the membrane fabrication and filtration. The anti-bacterial and anti-formation properties of the membranes were systematically studied with pure cultures of both Escherichia coli and Pseudomonas sp. and also with a mixed bacteria culture in an activated sludge bioreactor. The results showed that the prepared Ag–SiO2/PES membrane exhibited improved filtration performance and excellent anti-bacterial and anti-biofouling properties.

English

The treatment performance of two parallel continuous single stage activated sludge bioreactor: an aerobic bioreactor (ABR) operated at dissolved oxygen (DO) levels of 3-4 mg/L, and an innovative micro-aerobic bioreactor (MABR) operated at DO levels of 0.4-0.8 mg/L and the microbial diversity of MABR was investigated and compared. Under the similar conditions, at a hydraulic time (HRT) of 25 h, an organic loading rate (OLR) of 3.4±0.1 kg COD /m3·d, the influent total phosphate (TP) was 44±2 mg/L. The COD removal efficiencies of the MABR and the ABR were 93±3 and 90±3%, respectively, and no significant difference in performance was noted between the two systems (P=0.087>0.05). It was, however, noted that TP removal efficiency of the MABR (62±4%) was significantly higher than that of ABR (43±2%) (P=0.00). Phylogenetic analysis indicated that bacteria in the MABR was highly diverse. It is likely that facultative anaerobes, microaerophile and aerobes were able to coexist in the MABR. These findings might be helpful in developing an economic treatment system, which can be a better alternative for treatment of many pollutants requiring aerobic/anaerobic sequential treatment.   Key words: Biodiversity, micro-aerobic bioreactor, phosphorous removal, phylogenetic analysis.

Genome sequences of rare, uncultured bacteria obtained by differential coverage binning of multiple metagenomes

Reference genomes are required to understand the diverse roles of microorganisms in ecology, evolution, human and animal health, but most species remain uncultured. Here we present a sequence composition-independent approach to recover high-quality microbial genomes from deeply sequenced metagenomes. Multiple metagenomes of the same community, which differ in relative population abundances, were used to assemble 31 bacterial genomes, including rare (<1% relative abundance) species, from an activated sludge bioreactor. Twelve genomes were assembled into complete or near-complete chromosomes. Four belong to the candidate bacterial phylum TM7 and represent the most complete genomes for this phylum to date (relative abundances, 0.06-1.58%). Reanalysis of published metagenomes reveals that differential coverage binning facilitates recovery of more complete and higher fidelity genome bins than other currently used methods, which are primarily based on sequence composition. This approach will be an important addition to the standard metagenome toolbox and greatly improve access to genomes of uncultured microorganisms.

Application of Universal Stress Proteins in Probing the Dynamics of Potent Degraders in Complex Terephthalate Metagenome

The culture-independent strategies to study microbial diversity and function have led to a revolution in environmental genomics, enabling fundamental questions about the distribution of microbes and their influence on bioremediation to be addressed. In this research we used the expression of universal stress proteins as a probe to determine the changes in degrading microbial population from a highly toxic terephthalate wastewater to a less toxic activated sludge bioreactor. The impact of relative toxicities was significantly elaborated at the levels of genus and species. The results indicated that 23 similar prokaryotic phyla were represented in both metagenomes irrespective of their relative abundance. Furthermore, the following bacteria taxa Micromonosporaceae, Streptomyces, Cyanothece sp. PCC 7822, Alicyclobacillus acidocaldarius, Bacillus halodurans, Leuconostoc mesenteroides, Lactococcus garvieae, Brucellaceae, Ralstonia solanacearum, Verminephrobacter eiseniae, Azoarcus, Acidithiobacillus ferrooxidans, Francisella tularensis, Methanothermus fervidus, and Methanocorpusculum labreanum were represented only in the activated sludge bioreactor. These highly dynamic microbes could serve as taxonomic biomarkers for toxic thresholds related to terephthalate and its derivatives. This paper, highlights the application of universal stress proteins in metagenomics analysis. Dynamics of microbial consortium of this nature can have future in biotechnological applications in bioremediation of toxic chemicals and radionuclides.

Bacterial Community Dynamics in Full-Scale Activated Sludge Bioreactors: Operational and Ecological Factors Driving Community Assembly and Performance

The assembling of bacterial communities in conventional activated sludge (CAS) bioreactors was thought, until recently, to be chaotic and mostly unpredictable. Studies done over the last decade have shown that specific, and often, predictable random and non-random factors could be responsible for that process. These studies have also motivated a “structure–function” paradigm that is yet to be resolved. Thus, elucidating the factors that affect community assembly in the bioreactors is necessary for predicting fluctuations in community structure and function. For this study activated sludge samples were collected during a one-year period from two geographically distant CAS bioreactors of different size. Combining community fingerprinting analysis and operational parameters data with a robust statistical analysis, we aimed to identify relevant links between system performance and bacterial community diversity and dynamics. In addition to revealing a significant β-diversity between the bioreactors’ communities, results showed that the largest bioreactor had a less dynamic but more efficient and diverse bacterial community throughout the study. The statistical analysis also suggests that deterministic factors, as opposed to stochastic factors, may have a bigger impact on the community structure in the largest bioreactor. Furthermore, the community seems to rely mainly on mechanisms of resistance and functional redundancy to maintain functional stability. We suggest that the ecological theories behind the Island Biogeography model and the species-area relationship were appropriate to predict the assembly of bacterial communities in these CAS bioreactors. These results are of great importance for engineers and ecologists as they reveal critical aspects of CAS systems that could be applied towards improving bioreactor design and operation.

Denitrification of nitrate-contaminated groundwater using a simple immobilized activated sludge bioreactor

A simple anaerobic-activated sludge system, in which microorganisms are immobilized by a novel functional carrier, was used for removing nitrate in groundwater. The operating conditions, including hydraulic retention time (HRT), C/N ratio, temperature and NO(3)(-)-N loading concentration were investigated. The NO(3)(-)-N concentration, residual chemical oxygen demand (COD) and nitrite accumulation were used as indicators to assess the water quality of the effluent. The anaerobic biomass loading capacity in the carrier was 12.8 g/L and the denitrifying Pseudomonas sp. and Rhodocyclaceae bacterium were dominant among the immobilized microorganisms in the anaerobic-activated sludge. Under operating conditions of HRT= 1.5 h, C/N= 2-3 and T= 16.8-20 °C, the removal efficiency of NO(3)(-)-N exceeded 93%, corresponding to a relatively high denitrification rate of 0.73 kg NO(3)(-)-N m(-3) d(-1), when the NO(3)(-)-N loading concentration was 50 mg/L. The NO(3)(-)-N concentration of the effluent always met regulatory criteria for drinking water (<10 mg/L) in the main developed and developing countries. The effluent COD was also below 10 mg/L. Although some nitrite accumulated (0-1.77 mg/L) during the operating period, it can be decreased through adjusting the operating pH and HRT. The immobilized activated sludge system may be useful for the removal of nitrate from groundwater.

General and rare bacterial taxa demonstrating different temporal dynamic patterns in an activated sludge bioreactor

Temporal variation of general and rare bacterial taxa was investigated using pyrosequencing of 16S rRNA gene from activated sludge samples collected bimonthly for a two-year period. Most of operational taxonomic units (OTUs) were allocated to rare taxa (89.6%), but the rare taxa comprised a small portion of the community in terms of abundance of sequences analyzed (28.6%). Temporal variations in OTUs richness significantly differed between the two taxa groups in which the rare taxa showed a higher diversity and a more fluctuating pattern than the general taxa. Furthermore, the two taxa groups were constrained by different explanatory variables: influent BOD, effluent BOD, and DO were the significant (P < 0.05) parameters affecting the pattern of the general taxa, while temperature was the factor for the rare taxa. Over the test period, the general taxa persisted for a longer time (i.e., lower turnover rate) in the bioreactor than the rare taxa. In conclusion, this study demonstrated clear differences in temporal dynamic patterns for the general and rare bacterial taxa in an activated sludge bioreactor, which would be a foundation for better understanding the bacterial ecology of activated sludge.

Biogenic silver nanoparticles (bio-Ag0) decrease biofouling of bio-Ag0/PES nanocomposite membranes

Biofouling is a major problem for the application of membrane technology in water and wastewater treatment. One of the practical strategies to decrease biofouling is the use of advanced anti-biofouling membrane material. In this study, different amounts of biogenic silver nanoparticles (bio-Ag0) were embedded in polyethersulfone (PES) membranes, using the phase-inversion method. The effects of the bio-Ag0 content on the structure of the membrane and its filtration performance were systematically investigated. The results demonstrated that silver-containing nanostructures were uniformly distributed on membrane surface. Bio-Ag0 incorporation slightly increased the hydrophilicity of the PES membrane and increased the permeate flux. The anti-bacterial and anti-biofouling properties of the bio-Ag0/PES nanocomposites membrane were tested with pure cultures (Escherichia coli and Pseudomonas aeruginosa) and a mixed culture (an activated sludge bioreactor), respectively. The bio-Ag0/PES composite membranes, even with the lowest content of biogenic silver (140mgbio-Ag0m−2), not only exhibited excellent anti-bacterial activity, but also prevented bacterial attachment to the membrane surface and decreased the biofilm formation during a 9 weeks test.

Characteristics and fate of organic nitrogen in municipal biological nutrient removal wastewater treatment plants

The aim of this study was to investigate the occurrence and fate of colloidal and dissolved organic nitrogen (CON and DON) across biological nutrient removal (BNR) activated sludge bioreactors. Primary and secondary effluent total nitrogen (TN) measurements and component fractionation, CON and DON concentration profiles across BNR bioreactors, and laboratory batch experiments with the process mixed liquor were carried out at several full-scale BNR plants in northern Poland. The organic nitrogen (ON) components were divided into high CON, low CON, and DON based on sequential filtration through 1.2, 0.45 and 0.1 μm pore-size filters. The average influent DON0.1μm (<0.1 μm) concentrations ranged from 1.1 g N/m3 to 3.9 g N/m3 and accounted for only 4–13% of total organic nitrogen. In the effluents, however, this contribution increased to 12–45% (the DON0.1μm concentrations varied in a narrow range of 0.5–1.3 g N/m3). Conversions of ON inside the bioreactors were investigated in more detail in two largest plants, i.e. Gdansk (565,000 PE) and Gdynia (516,000 PE). Inside the two studied bioreactors, the largest reductions of the colloidal fraction were found to occur in the anaerobic and anoxic compartments, whereas an increase of DON0.1μm concentrations was observed under aerobic conditions in the last compartment. Batch experiments with the process mixed liquor confirmed that DON0.1μm was explicitly produced in the aerobic phase and significant amounts of ON were converted in the anoxic phase of the experiments.

Fine-scale bacterial community dynamics and the taxa–time relationship within a full-scale activated sludge bioreactor

In activated sludge bioreactors, aerobic heterotrophic communities efficiently remove organics, nutrients, toxic substances, and pathogens from wastewater, but the dynamics of these communities are as yet poorly understood. A macroecology metric used to quantify community shifts is the taxa–time relationship, a temporal analog of the species–area curve. To determine whether this metric can be applied to full-scale bioreactors, activated sludge samples were collected weekly over a one-year period at a local municipal wastewater treatment plant. Bacterial community dynamics were evaluated by monitoring 16S rRNA genes using Terminal Restriction Fragment Length Polymorphism (T-RFLP), corroborated by clone libraries. Observed taxa richness increased with time according to a power law model, as predicted by macroecological theory, with a power law exponent of w = 0.209. The results reveal strong long-term temporal dynamics during a period of stable performance (BOD removal and nitrification). Community dynamics followed a gradual succession away from initial conditions rather than periodicity around a mean “equilibrium”, with greater within-month then among-month community similarities. Changes in community structure were significantly associated via multivariate statistical analyses with dissolved oxygen, temperature, influent silver, biomass (MLSS), flow rate, and influent nitrite, cadmium and chromium concentrations. Overall, our results suggest patterns of bacterial community dynamics likely regulated in part by operational parameters and provide evidence that the taxa–time relationship may be a fundamental ecological pattern in macro- and microbial systems.

Isolation of estrogen-degrading bacteria from an activated sludge bioreactor treating swine waste, including a strain that converts estrone to β-estradiol

An estrogen-degrading bacterial consortium from a swine wastewater biotreatment was enriched in the presence of low concentrations (1mg/L) of estrone (E1), 17β-estradiol (βE2), and equol (EQO) as sole carbon sources. The consortium removed 99%± 1% of these three estrogens in 48h. Estrogen removal occurred even in the presence of an ammonia monooxygenase inhibitor, suggesting that nitrifiers are not involved. Five strains showing estrogen-metabolizing activity were isolated from the consortium on mineral agar medium with estrogens as sole carbon source. They are related to four genera ( Methylobacterium (strain MI6.1R), Ochrobactrum (strains MI6.1B and MI9.3), Pseudomonas (strain MI14.1), and Mycobacterium (strain MI21.2)) distributed among three classes (Alphaproteobacteria, Gammaproteobacteria, and Actinobacteria). Depending on the culture medium, strains MI6.1B, MI9.3, MI14.1, and MI21.2 partially transform βE2 into E1, whereas Methylobacterium sp. strain MI6.1R reduces E1 into βE2 under aerobic conditions, in contrast with the usually observed conversion of βE2 into E1. Since βE2 is a more potent endocrine disruptor than E1, it means that the presence of Methylobacterium sp. strain MI6.1R (or other bacteria with the same E1-reducing activity) in a treatment could transiently increase the estrogenicity of the effluent. MI6.1R can also reduce the ketone group of 16-ketoestradiol, a hydroxylated analog of E1. All βE2 and E1 transformation activities were constitutive, and many of them are favoured in a rich medium than a medium containing no other carbon source. None of the isolated strains could degrade EQO.

Enhanced lipid and biodiesel production from glucose‐fed activated sludge: Kinetics and microbial community analysis

AbstractAn innovative approach to increase biofuel feedstock lipid yields from municipal sewage sludge via manipulation of carbon‐to‐nitrogen (C:N) ratio and glucose loading in activated sludge bioreactors was investigated. Sludge lipid and fatty acid methyl ester (biodiesel) yields (% cell dry weight, CDW) were enhanced via cultivation in activated sludge bioreactors operated at high initial C:N ratio (≥40:1) and glucose loading (≥40 g L−1). Under C:N 70, 60 g L−1 glucose loading, a maximum of 17.5 ± 3.9 and 10.2 ± 2.0% CDW lipid and biodiesel yields, respectively, were achieved after 7 d of cultivation. The cultured sludge lipids contained mostly C16C18 fatty acids, with oleic acid consistently accounting for 40–50% of the total fatty acids. Microbial composition in activated sludge exposed to C:N 70 shifted toward specific gammaproteobacteria, suggesting their relevance in lipid production in wastewater microbiota and potential value in biofuel synthesis applications. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Analysis of the time dependency of ammonia-oxidizing bacterial community dynamics in an activated sludge bioreactor

An autoregressive error term model was applied to examine the dynamic oscillation of ammonia-oxidizing bacterial (AOB) lineages found in an activated sludge bioreactor. The current abundance of AOB lineages was affected by the past abundance of AOB lineages and past environmental and operational factors as well as current influencing factors.

Construction of a whole-cell catalyst displaying a fungal lipase for effective treatment of oily wastewaters

Abstract To combine the advantage of the oleaginous yeast Yarrowia lipolytica with the high activity of some fungal lipases for oily wastewater treatment, an effective lipase-displaying arming yeast was constructed using the flocculation functional domain of Saccharomyces cerevisiae as the protein anchor. To estimate the effect of the whole-cell oily wastewater treatment, the lipase-displaying arming yeast was added into an open activated sludge bioreactor. Within 72 h of whole-cell treatment, 96.9% of oil and 97.6% of chemical oxygen demand (COD) were removed, while only 87.1% of oil and 91.8% of COD were removed in control A ( Y. lipolytica Polg was added), 45.1% of oil and 67.5% of COD were removed in control B (no cell was added) in 72 h. The lipase-displaying arming yeast exhibited remarkable oil removal and COD degradation effect compared with the control samples, exemplifying its application potential.

Modeling organic nitrogen conversions in activated sludge bioreactors

For biological nutrient removal (BNR) systems designed to maximize nitrogen removal, the effluent total nitrogen (TN) concentration may range from 2.0 to 4.0 g N/m(3) with about 25-50% in the form of organic nitrogen (ON). In this study, current approaches to modeling organic N conversions (separate processes vs. constant contents of organic fractions) were compared. A new conceptual model of ON conversions was developed and combined with Activated Sludge Model No. 2d (ASM2d). The model addresses a new insight into the processes of ammonification, biomass decay and hydrolysis of particulate and colloidal ON (PON and CON, respectively). Three major ON fractions incorporated are defined as dissolved (DON) (<0.1 µm), CON (0.1-1.2 µm) and PON (41.2 µm). Each major fraction was further divided into two sub-fractions - biodegradable and non-biodegradable. Experimental data were collected during field measurements and lab experiments conducted at the ''Wschod'' WWTP (570,000 PE) in Gdansk (Poland). The accurate steady-state predictions of DON and CON profiles were possible by varying ammonification and hydrolysis rates under different electron acceptor conditions. With the same model parameter set, the behaviors of both inorganic N forms (NH4-N, NOX-N) and ON forms (DON, CON) in the batch experiments were predicted. The challenges to accurately simulate and predict effluent ON levels from BNR systems are due to analytical methods of direct ON measurement (replacing TKN) and lack of large enough database (in-process measurements, dynamic variations of the ON concentrations) which can be used to determine parameter value ranges.

Evaluation of extracellular biopolymer and its impact on bioflocculation in activated sludge bioreactors

The influence and dynamics of bacterial extracellular polysaccharide (EPS) polymer production and its impact on bioflocculation in activated sludge (AS) bench-scale reactors were investigated. The impact of food to microorganism ratio (F/M), reactor configuration and easily biodegradable carbohydrates in influent streams on biological processes that support or weaken good floc formation and the link with EPS quantity was studied. Bioreactors were run as either sequencing batch or continuous systems using wastewater media with glucose or acetate as C source in different F/M ratios. EPS levels were quantified using mid-infrared spectroscopy which provided a rapid technique for monitoring biological processes within AS WWTP. The analysis revealed an interdependent link between EPS production, sludge settling characteristics and mode of reactor operation. An inverse relationship between F/M ratios and EPS quantities was seen but a positive link between EPS levels and aggregation indices, a measure of the efficiency of inter cell attachment and which indicates good settling properties, was also seen. This indicates that during high F/M conditions in lab-scale AS reactors, low levels of EPS may be produced which could have a negative impact on settling of the biomass. Floc architecture was examined under the microscope. Transient growth of filamentous bacteria was seen in the reactors.

Influence of physicochemical and operational parameters on Nitrobacter and Nitrospira communities in an aerobic activated sludge bioreactor

To understand how to optimize performance of a partially nitrifying plant, the dynamics of Nitrospira and Nitrobacter abundance were studied over a 1 year period using quantitative polymerase chain reaction (qPCR) and their relative contributions to nitrite oxidation assessed including the affects of temperature and dissolved oxygen (DO). Correlation coefficients linking shifts in the community composition of nitrite-oxidizing bacteria (NOB) to operational or environmental variables indicated Nitrospira was significantly and negatively correlated to nitrite concentrations ( r = −0.45, P < 0.01) and DO ( r = −0.46, P < 0.01), while temperature showed a strong positive correlation ( r = 0.59, P < 0.0001). However, the Nitrobacter portion of the total NOB populations showed a positive correlations with DO ( r = 0.38, P < 0.01) and hydraulic retention time (HRT) ( r = 0.33, P < 0.05), as well as being negatively correlated with temperature ( r = −0.49, P < 0.001) suggesting specific niche adaptations within the NOB community. Nitrospira was dominant being better adapted to the low DO and shorter sludge retention times (SRT) of this plant, while Nitrobacter increased in abundance during the winter months, when temperatures were lower and DO concentrations higher. Principal component analysis (PCA) results supported these findings by the close proximity of Nitrospira and temperature biplots of PC1 and PC2 as well as grouping Nitrobacter, NO 2 −-N, HRT, and DO in the loadings together. The clustering of samples from specific dates also exhibited a strong seasonality.

A real trial of an innovative membrane bioreactor for saline sewage treatment

We have recently developed non-woven membrane modules to be immersed in activated sludge bioreactor for treating saline sewage. To evaluate the feasibility and energy consumption of this technology, a pilot trial of up to 7 m3/day was conducted over 270 days at the Hong Kong University of Science and Technology (HKUST). This paper reports part of the data obtained from this pilot trial. The pilot plant produced steady and good quality effl uent. The average effluent total nitrogen (TN) was 7.7 mg N/L, total chemical oxygen demand (TCOD) 27 mg/L and total suspended solids (TSS) 15 mg/L, respectively. The maximum effective permeate flux was found to be up to 6 m/d, while the air-to-water volumetric ratio could be as low as 15. The transmembrane pressure (TMP) was maintained at 0.1 bars after each backwash with around 1% of the effluent. The backwash was conducted once in 48 hrs. The membrane modules worked well without clogging for 270 days until an accidental failure of power source, which lasted for 30 hr...