Chromium(VI) reduction in a membrane bioreactor with immobilized Pseudomonas cells

Chromate reduction was studied in a membrane bioreactor under action of Pseudomonas bacteria immobilized in agar–agar films on the surface of synthetic membrane. Immobilized cells are protected from the excessive toxic action at high chromate concentration that improves cell activity compared with free cells. Almost complete chromate reduction was observed at stepwise introducing of chromate in feed solution allowing maintenance of optimal chromate concentration. Reduction is suppressed by high metabolite concentrations, which reached on the sixth step of chromate adding in studied system. Cell ability to reduce chromate is restored after changing of feed and receiving solutions allowing remediation of Cr(VI)-contaminated water in semi-batch operation of membrane bioreactor.     

Anaerobic co-reduction of chromate and nitrate by bacterial cultures of Staphylococcus epidermidis L-02

Industrial wastewater is often polluted by Cr(VI) compounds, presenting a serious environmental problem. This study addresses the removal of toxic, mutagenic Cr(VI) by means of microbial reduction to Cr(III), which can then be precipitated as oxides or hydroxides and extracted from the aquatic system. A strain of Staphylococcus epidermidis L-02 was isolated from a bacterial consortium used for the remediation of a chromate-contaminated constructed wetland system. This strain reduced Cr(VI) by using pyruvate as an electron donor under anaerobic conditions. The aims of the present study were to investigate the specific rate of Cr(VI) reduction by the strain L-02, the effects of chromate and nitrate (available as electron acceptors) on the strain, and the interference of chromate and nitrate reduction processes. The presence of Cr(VI) decreased the growth rate of the bacterium. Chromate and nitrate reduction did not occur under sterile conditions but was observed during tests with the strain L-02. The presence of nitrate increased both the specific Cr(VI) reduction rate and the cell number. Under denitrifying conditions, Cr(VI) reduction was not inhibited by nitrite, which was produced during nitrate reduction. The average specific rate of chromate reduction reached 4.4 μmol Cr 10¹⁰ cells⁻¹ h⁻¹, but was only 2.0 μmol Cr 10¹⁰ cells⁻¹ h⁻¹ at 20 °C. The maximum specific rate was as high as 8.8–9.8 μmol Cr 10¹⁰ cells⁻¹ h⁻¹. The role of nitrate in chromate reduction is discussed.     

Effects of short solids retention time on microbial community in a membrane bioreactor

Effects of operating lab-scale nitrifying membrane bioreactors (MBR) at short solids retention times (SRT = 3, 5 and 10d) were presented with focus on reactor performance and microbial community composition. The process was capable of achieving over 87% removal of ammonia and 95% removal of chemical oxygen demand (COD), almost regardless of SRT. The denaturing gradient gel electrophoresis (DGGE) analysis shown that bacterial communities evolved in time in a similar way at different SRT. The results of clone library analysis indicated that Betaproteobacteria was the dominant bacterial group in all the reactors but there were significant difference of species for different SRT with higher species diversity at longer SRT. Ammonia and COD removal efficiencies were not correlated with the number of bacterial species or their diversity.     

Effect of membrane bioreactor configurations on sludge structure and microbial activity

The aim of this paper was to determine the effect of two different membrane bioreactor (MBR) configurations (external/immersed) on sludge structure and microbial activity. Sludge structure was deduced from rheological measurements. The high shear stress induced by the recirculation pump in the external MBR was shown to result in decreasing viscosity due to activated sludge (AS) deflocculation. Besides, soluble microbial products (SMP) release was higher in the external MBR (5 mg_COD g_MLVSS⁻¹) than in the immersed configuration (2 mg_COD g_MLVSS⁻¹). Microbial activity was followed from respirometry tests by focusing on the distinction between heterotrophs and autotrophs. An easier autotrophic microbe development was then observed in the immersed MBR compared to the external one. However, the external MBR was shown to allow better heterotrophic microbe development.     

硝酸盐还原促进毒害性有机污染物降解的研究进展

大量具有高毒性、持久性和生物蓄积性的有机污染物被排放到环境中,对生态环境和人类健康造成了严重威胁。近年来,利用硝酸盐作电子受体在厌氧条件下降解毒害性有机污染物,已取得一定的进展。本文综述了硝酸盐还原体系中几种典型毒害性有机污染物(多环芳烃、单环或杂环芳烃类有机物及卤代有机物)的厌氧降解研究进展。在此基础上,提出了硝酸盐还原促进毒害性有机污染物降解研究中存在的主要问题及其在加速污染环境净化方面的应用前景。     

Removal of microbial indicators from municipal wastewater by a membrane bioreactor (MBR)

The impact of removable and irremovable fouling on the retention of viral and bacterial indicators by the submerged microfiltration membrane in an MBR pilot plant was evaluated. Escherichia coli, sulphite-reducing Clostridium spores, somatic coliphages and F-specific RNA bacteriophages were used as indicators. The membrane demonstrated almost complete removal of E. coli and sulphite-reducing Clostridium spores. However, there was no correlation with membrane fouling. The phage removal varied in accordance with the irremovable fouling, rising from 2.6 to 5.6 log₁₀ units as the irremovable fouling increased (measured by the change in the transmembrane pressure). In contrast, removable fouling did not have any effect on the retention of viruses by the membrane. These results indicate that irremovable membrane fouling may affect the removal efficiency of MBRs and, therefore, their capacity to ensure the required microbiological standards for the permeate achieved.     

Contribution of microfiltration on phosphorus removal in the sequencing anoxic/anaerobic membrane bioreactor

This study investigated the contribution of microfiltration to phosphorus removal in the sequencing anoxic/anaerobic membrane bioreactor. The phosphorus content in activated sludge was fractionated by the Schmidt–Thannhauser–Schneider method. The size distribution of phosphorus in the influent was analyzed to estimate the portion of particulate phosphorus rejected physically by the 0.2 μm microfiltration. The result was that along with the high removal of phosphorus (83%) the phosphorus content of activated sludge was measured as 58.66 mgP/gVSS corresponding to 5.87% on dry weight basis. About 9% of total phosphorus was chemically precipitated phosphates while 56% was stored inside the microbial cell by activity of PAOs, and 35% was the sum of minor intracellular compositions and the particulate residuals, which could be rejected completely by the microfiltration. The biological activity is the dominant way of phosphorus removal in the process. However, the microfiltration also contributed significantly to phosphorus removal by retaining the particulate phosphorus inside the system.     

Performance of a submerged membrane bioreactor for the aerobic treatment of abattoir wastewater

The performance of a submerged membrane bioreactor (SMBR) has been investigated for abattoir wastewater (AW) treatment. The chemical oxygen demand (COD) of permeate has not exceeded 25 mg L⁻¹ providing an average COD removal of 98%. Microbiological analysis showed that the SMBR has allowed a complete removal of fecal coliforms, Listeria and Salmonella. A significant reduction in the excess biomass production was also observed. In fact, the yield of biomass production (Yobs) ranged between 0 and 0.106 g suspended solids/g COD removed.The study of the dynamic of bacterial communities using the single strand conformation polymorphism (SSCP) method showed a significant change in the population structure and revealed a correlation between the sludge production yield and the bacterial communities.     

Aerobic chromate reduction by chromium-resistant bacteria isolated from serpentine soil

A group of 34 chromium-resistant bacteria were isolated from naturally occurring chromium percolated serpentine soil of Andaman (India). These isolates displayed different degrees of chromate reduction under aerobic conditions. One of the 34 isolates identified as Bacillus sphaericus was tolerant to 800 mg l⁻¹ Cr(VI) and reduced >80% Cr(VI) during growth. In Vogel Bonner broth, B. sphaericus cells (10¹⁰ cells ml⁻¹) reduced 62% of 20 mg l⁻¹ of Cr(VI) in 48 h with concomitant discoloring of yellow medium to white one. Reduction of chromate was pronounced by the addition of glucose and yeast extract as electron donors. In the presence of 4.0 g l⁻¹ of glucose, 20 mg l⁻¹ of Cr(VI) was reduced to 2.45 mg l⁻¹ after 96 h of incubation. Optimum pH and temperature for reduction were 6.0 and 25 °C, respectively. Increase in cell density and initial Cr(VI) concentration increased chromate reduction but was inhibited by metal ions like, Ni²⁺, Co²⁺, Cd²⁺ and Pb²⁺. Experiments with cell-free extracts indicated that the soluble fraction of the cell was responsible for aerobic reduction of Cr(VI) by this organism.     

Comparison between a moving bed membrane bioreactor and a conventional membrane bioreactor on membrane fouling

A membrane bioreactor filled with carriers instead of activated sludge named a moving bed membrane bioreactor (MBMBR) was investigated to minimize the effect of suspended solids on membrane fouling. The MBMBR and a conventional membrane bioreactor (CMBR) were operated in parallel for about two months. Unexpectedly, the rate of membrane fouling in MBMBR was about three times of that in CMBR. MBMBR showed a higher cake layer resistance than CMBR due to plenty of filamentous bacteria inhabited in suspended solids in MBMBR. Protein and polysaccharide contents of soluble EPS in MBMBR were obviously larger than those in CMBR. It could be speculated that the overgrowth of filamentous bacteria in MBMBR resulted in severe cake layer and induced a large quantity of EPS, which deteriorated the membrane fouling.     

Cytotoxicity micropollutant removal in a crossflow membrane bioreactor

The application of membrane bioreactor (MBR) technology was investigated with the aim of evaluating its potential for cytostatic drug and cytotoxicity bioremoval. The toxicity removal was assessed from biomarker test. CP removal of up to 80% was achieved under the operating conditions studied (HRT of 48 h and a SRT of 50 days). The increase of TMP was associated with an increase of supernatant toxicity as if fouling led to retention of the toxicity. Peaks of supernatant cytotoxicity were correlated with peaks in supernatant humic acid contents. It may suggest that molecules with a toxic effect may be adsorbed or entrapped in humic acids substances. Our study then points out that advances in wastewater treatment using an MBR can provide a suitable process for lowering CP concentrations before discharge into the aqueous environment. However, a tertiary treatment is necessary if complete elimination of toxicity is targeted.     

Dissimilatory nitrate and dimethylsulphoxide reduction in Rhodopseudomonas capsulata

Abstract The electron flow to the dissimilatory nitrate reductase (NRII), and dimethylsulphoxide (DMSO) oxidoreductase in Rhodopseudomonas capsulata strains was studied. Our results support the view that DMSO reduction, like dissimilatory nitrate reduction was linked to the electron transfer chain and probably coupled to energy conservation.     

Hexavalent chromate reduction by immobilized Streptomyces griseus

Hexavalent chromium, which is a mutagen and carcinogen, was efficiently reduced by Streptomyces griseus. This activity was associated with the cell. Cr⁶⁺ reduction by free as well as immobilized cells was studied: cells in PVA-alginate had the highest (100%) Cr⁶⁺ removal efficiency in 24 h with reduction rates similar to free cells. Immobilized cells completely reduced 25 mg Cr⁶⁺ l⁻¹ in 24 h. PVA-alginate immobilized cells could be reused four times to completely reduce 25 mg Cr⁶⁺ l⁻¹ in 24 h each time. Chromate in a simulated effluent containing Cu²⁺, Mg²⁺, Mn²⁺ and Zn²⁺ was completely reduced by PVA-alginate immobilized cells within 9 h.     

Cheese whey treatment performance of an aerobic jet loop membrane bioreactor

The raw chess whey (CW) treatment capacity of a jet loop membrane bioreactor (JLMBR) was evaluated. Raw CW was first characterized for carbonaceous, nitrogenous and phosphorus compounds. The total COD range of the raw CW was between 73 and 86 kg m⁻³ and 82% of the total COD was found to be soluble. The JLMBR system, of 32 l capacity was operated continuously for 3 months with a sludge age of 1.1–2.8 days and COD loads of 3.5–33.5 kg-COD m⁻³ per day. A treatment efficiency of 97% was obtained for 1.6 days of sludge age and COD loads of 22.2 kg-COD m⁻³ per day. The sludge flocks observed in the system were highly motile, dispersed and had poor settling properties. The membrane filtration characteristics of this sludge were investigated and increasing MLSS concentration decreased membrane flux values.     

454高通量焦磷酸测序法鉴定膜生物反应器膜污染优势菌种

【目的】对诱发膜-生物反应器(Membrane bioreactors,MBR)膜污染的优势菌种进行研究。【方法】利用454高通量焦磷酸测序法对MBR污泥混合液样品与膜污染物样品中微生物信息进行统计,并对两组样品的Chao丰度指数与Shannon生物多样性指数计算,对测序结果进行系统发育学分析。【结果】从污泥混合液样品与膜污染物样品中获得9 353与7 504条优化序列,发现膜污染物中微生物丰度与多样性均高于污泥混合样品。借助基因频谱对OTU分布特点进行统计,表明源于污泥混合液中的微生物在膜表面定殖生长过程中发生了种群变化,在膜面污染物样品中,β-变形菌纲丰度显著降低,α-变形菌纲、γ-变形菌纲与Phycisphaerae在微生物种群结构中比重增加。【结论】454焦磷酸测序分析表明,黄色单胞菌(Xanthomonadaceae),嗜热厌氧杆菌(Thermoanaerobacter),Phycisphaera以及2株尚未培养出的细菌(Candidate_division_TM7及Candidate_division_OD1)是诱发MBR膜污染的优势菌种(微生物丰度1%)。诱发膜污染的细菌既包括了黏性高、表面疏水的种类(如γ-变形菌),从而引发细菌在膜表面的定殖,也包括了代谢能力强的物种(如Candidate_division_OD1)可以确保种间递氢顺畅。     

Effects of temperature and temperature shock on the performance and microbial community structure of a submerged anaerobic membrane bioreactor

Effects of temperature and temperature shock on the performance and microbial community structure of a submerged anaerobic membrane bioreactor (SAnMBR) treating thermomechanical pulping pressate were studied for 416 days. The results showed that the SAnMBR system were highly resilient to temperature variations in terms of chemical oxygen demand (COD) removal. The residual COD in treated effluent was slightly higher at 55 °C than that at 37 and 45 °C. There were no significant changes in biogas production rate and biogas composition. However, temperature shocks resulted in an increase in biogas production temporarily. The SAnMBR could tolerate the 5 and 10 °C temperature shocks at 37 °C and the temperature variations from 37 to 45 °C. The temperature shock of 5 and 10 °C at 45 °C led to slight and significant disturbance of the performance, respectively. Temperature affected the richness and diversity of microbial populations.     

Fractionation of proteins and carbohydrates of extracellular polymeric substances in a membrane bioreactor system

The major operational problem associated with membrane bioreactors (MBR) is membrane fouling, for which extracellular polymeric substances (EPS) are primarily responsible. In this work both the soluble and bound EPS (i.e. SMP and EPS) produced in an MBR system operating under sludge retention times (SRT) of 10, 15, 20 and 33 days were fractionized by means of membranes having variable molecular weight cutoffs (300 kDa, 100 kDa, 10 kDa & 1 kDa). The results show that increasing the SRT leads to a reduction of SMP and EPS and that these reductions are more pronounced for the SRTs in the range 10–20 days. This reduction is more significant for carbohydrates than for proteins. The decrease of SMP and EPS with increasing SRT from 10 to 20 days led to a significant decrease of the level of fouling. The further increase of SRT to 33 days did not significantly impact on the level of fouling as the SMP and EPS concentrations did not change much.     

Microbes involved in dissimilatory nitrate reduction in the human large intestine

Nitrate-limited batch cultures, incorporating 20 different fermentation substrates and inoculated with human faeces, mainly selected for the growth of enterobacteria. The microbial diversity involved was determined by a combination of phenotypic and genotypic procedures. Continuous culture with lactate as the sole electron donor selected for similar micro-organisms, but when antibiotics were incorporated to inhibit Escherichia coli and lactate was replaced with choline, there was a wider microbial diversity recovered. Clostridium ramosum and Bacteroides vulgatus were then isolated as well as enterobacteriaceae.     

Assessments of critical flux in a pilot-scale membrane bioreactor

In this study, the influence of various parameters such as determination methods and step height and length of incremental flux on critical flux values were investigated. Experiments were carried out on a pilot-scale membrane bioreactor (MBR) treated municipal wastewater. Three of the five critical flux determination methods, such as flux linearity, 90% permeability and flux cycling conducted in this study, indicated a decline in critical flux values as the step height of incremental flux increased. However, the hysteresis method and the two-third (2/3) flux limitation method showed an increase and independence of critical flux to the step height of incremental flux, respectively. On the other hand, the step length of incremental flux had no obvious effect on critical flux values evaluated by all critical flux determination methods. Like critical flux, sustainable flux has negative relationship with the increase of step height but no influence of step length was found in this study.