Microbial community analysis of an aerobic nitrifying-denitrifying MBR treating ABS resin wastewater

A two-stage aerobic membrane bioreactor (MBR) system for treating acrylonitrile butadiene styrene (ABS) resin wastewater was carried out in this study to evaluate the system performance on nitrification. The results showed that nitrification of the aerobic MBR system was significant and the highest TKN removal of approximately 90% was obtained at hydraulic retention time (HRT) 18 h. In addition, the result of nitrogen mass balance revealed that the percentage of TN removal due to denitrification was in the range of 8.7-19.8%. Microbial community analysis based on 16s rDNA molecular approach indicated that the dominant ammonia oxidizing bacteria (AOB) group in the system was a β-class ammonia oxidizer which was identified as uncultured sludge bacterium (AF234732). A heterotrophic aerobic denitrifier identified as Thauera mechernichensis was found in the system. The results indicated that a sole aerobic MBR system for simultaneous removals of carbon and nitrogen can be designed and operated for neglect with an anaerobic unit.     

Removal of carbamazepine and sulfamethoxazole by MBR under anoxic and aerobic conditions

This study reveals for the first time that near-anoxic conditions (dissolved oxygen, DO=0.5 mg/L) can be a favorable operating regime for the removal of the persistent micropollutant carbamazepine by MBR treatment. The removal efficiencies of carbamazepine and sulfamethoxazole by an MBR were systematically examined and compared under near-anoxic (DO=0.5 mg/L) and aerobic (DO>2 mg/L) conditions. Preliminary batch tests confirmed that sulfamethoxazole is amenable to both aerobic and anoxic biotransformation. However, carbamazepine-a known persistent compound-showed degradation only under an anoxic environment. In good agreement with the batch tests, during near-anoxic operation, under a high loading of 750 μg/Ld, an exceptionally high removal (68±10%) of carbamazepine was achieved. In contrast, low removal efficiency (12±11%) of carbamazepine was observed during operation under aerobic conditions. On the other hand, an average removal efficiency of 65% of sulfamethoxazole was achieved irrespective of the DO concentrations.     

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.     

Effect of anoxic/aerobic phase fraction on N2O emission in a sequencing batch reactor under low temperature

Laboratory scale anoxic/aerobic sequencing batch reactor (A/O SBR) was operated around 15 °C to evaluate the effect of anoxic/aerobic phase fraction (PF) on N₂O emission. The ammonia removal exhibited a decrease trend with the increase of PF, while the highest total nitrogen removal was achieved at PF = 0.5. Almost all the N₂O was emitted during the aerobic phase, despite of the PF value. However, the net emission of N₂O was affected by PF. Under the premise of completely aerobic nitrification, the lowest N₂O emission was achieved at PF = 0.5, with a N₂O-N conversion rate of 9.8%. At lower PF (PF = 0.2), N₂O emission was stimulated by residual nitrite caused by uncompleted denitrification during the anoxic phase. On the other hand, the exhaustion of the easily degradable carbon was the major cause for the high N₂O emission at higher PF (PF = 0.5). The N₂O emission increased with the decreasing temperature. The time-weighted N₂O emission quantity at 15 °C was 2.9 times higher than that at 25 °C.     

Factors affecting the performance of membrane bioreactor for piggery wastewater treatment

This study was conducted to identify the factors affecting the performance of membrane bioreactor (MBR) for piggery wastewater treatment. The change of organic and nitrogen concentrations in piggery wastewater was studied to investigate the treatment efficiency. The increase of COD, BOD and NH₃–N from 1150 to 2050 mg/L, 683 to 1198 mg/L and 154 to 248 mg/L has led to the decrease of treatment efficiency. Removal efficiencies of COD, BOD and NH₃–N have decreased from 96.0% to 92.0%, 97.0% to 92.7% and 93.2% to 69.5%, respectively. The effects of biomass characteristics on membrane fouling were determined based on Pearson’s correlation coefficient (r_p). It was found that MLSS had a negative correlation with permeate flux (r_p = −0.745, at significant level of 0.05) while sludge floc size a positive correlation (r_p = 0.731, at significant level of 0.05). MLSS and sludge floc size were found to be the dominant factors that controlled the membrane filterability while sludge viscosity, EPS, SMP and SV₃₀ have taken as the sub-factors affecting membrane fouling.     

焦化废水O/H/O生物处理工艺二级好氧生物反应器的微生物结构和功能

【背景】焦化废水O/H/O生物处理工艺的二级好氧生物反应器O₂具有剩余污染物矿化和完全硝化功能,对废水的达标排放有重要作用。【目的】阐明O₂生物反应器的微生物结构和功能。【方法】利用16S rRNA基因测序,研究O₂生物反应器的微生物多样性和组成并进行功能预测,揭示其共现性特征和环境影响因子。【结果】O₂的优势菌门以变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)、绿菌门(Chlorobi)为主。主要菌属中红游动菌属(Rhodoplanes)、溶杆菌属(Lysobacter)、硫杆菌属(Thiobacillus)等参与化学需氧量(chemical oxygen demand,COD)、酚类(phenols)和硫氰酸盐(thiocyanate,SCN^-)等剩余污染物的去除,亚硝化弧菌属(Nitrosovibrio)和硝化螺菌属(Nitrospira)分别作为氨氧化细菌(ammonia-oxidizing bacteria,AOB)和主要的亚硝酸盐氧化细菌(nitrite-oxidizing bacteria,NOB)。功能预测结果显示苯甲酸酯降解、氨基苯甲酸酯降解、氯烷烃和氯烯烃的降解、氟代苯甲酸酯降解和硝基甲苯降解是外源物质生物降解和代谢的前五大通路,广泛分布在主要菌属中,验证了微生物降解剩余污染物的作用。基因pmoA/B/C-amoA/B/C、hao和nxrA/B编码相关的酶,组成了完整的硝化途径。共现网络结果揭示溶杆菌属、Candidatus Solibacter和红游动菌属在O₂生态中的重要地位。通过冗余分析(redundancy analysis,RDA)表明COD和NH₃是影响O₂微生物群落的主要因素。【结论】红游动菌属和溶杆菌属是O₂中最核心的功能菌属,在污染物矿化和维持群落生态稳定上有重要作用。亚硝化弧菌属和硝化螺菌属是硝化作用的核心菌属。O₂中的代谢通路以剩余污染物矿化和完全硝化为主,微生物群落主要受COD和NH₃的影响。本研究阐明了O₂的微生物结构与功能,为焦化废水O/H/O生物处理工艺的改进提供了微生物学上的依据。     

Reduction in excess sludge production in a dairy wastewater treatment plant via nozzle-cavitation treatment: Case study of an on-farm wastewater treatment plant

Nozzle-cavitation treatment was used to reduce excess sludge production in a dairy wastewater treatment plant. During the 450-d pilot-scale membrane bioreactor (MBR) operation, when 300 l of the sludge mixed liquor (1/10 of the MBR volume) was disintegrated per day by the nozzle-cavitation treatment with the addition of sodium hydrate (final concentration: 0.01% W/W) and returned to the MBR, the amount of excess sludge produced was reduced by 80% compared with that when sludge was not disintegrated.     

Enhanced COD and nitrogen removals for the treatment of swine wastewater by combining submerged membrane bioreactor (MBR) and anaerobic upflow bed filter (AUBF) reactor

In order to enhance performances of organics removal and nitrification for the treatment of swine wastewater containing high concentration of organic solids and nitrogen than conventional biological nitrogen removal process, a submerged membrane bioreactor (MBR) was followed by an anaerobic upflow bed filter (AUBF) reactor in this research (AUBF–MBR process). The AUBF reactor is a hybrid reactor, which is the combination of an anoxic filter for denitrification and upflow anaerobic sludge blanket (UASB) for acid fermentation. In the AUBF–MBR process, it showed a considerable enhancement of the effluent quality in terms of COD removal and nitrification. The submerged MBR could maintain more than 14,000 mg VSS/L of the biomass concentration. Total nitrogen (T-N) removal efficiency represented 60% when internal recycle ratio was three times of flow-rate (Q), although the nitrification occurred completely. Although the volatile fatty acids produced in AUBF reactor can enhance denitrification rate, but the AUBF–MBR process showed reduction of overall removal efficiency of the nitrogen due to the reduction of carbon source by methane production in the AUBF reactor compared to that of theoretical nitrogen removal efficiency.

Long-term operation of the submerged MBR showed that the throughputs of the submerged MBR were respectively 74, 63, and 31 days at 10, 15, and 30 L/m² h (LMH) of permeate flux. Resistance to filtration by rejected solid is the primary cause of fouling, however the priority of cake resistance (R_c) and fouling resistance (R_f) with respect to filtration phenomenon was different according to the amount of permeate flux. The submerged MBR, here, achieved a steady-state flux of 15 LMH at 0.4 atm. of trans-membrane pressure (TMP) but the flux can be enhanced in the future because shear force by tangential flow will be greater when multi-layer sheets of membrane were used.     

Enhanced denitrifying phosphorous removal in a novel anaerobic/aerobic/anoxic (AOA) process with the diversion of internal carbon source

A novel anaerobic/aerobic/anoxic (AOA) process is proposed to realize denitrifying phosphorous removal in this study, and the characteristic of the AOA process is transferring part of the anaerobic mixed liquor to the post-anoxic zone for providing the carbon source needed for denitrification. The AOA process was operated for 3 months, and the average removal efficiencies of NH4+-N, TN and PO4(3-)-P were 93.0±3.1%, 70.3±2.9% and 87.3±11.8%, respectively. A mass balance analysis indicated that 0.49±0.02 g VSS(-1) d(-1) of PO4(3-)-P and 0.23±0.04 g VSS(-1) d(-1) of NO3--N were simultaneously removed in the anoxic zone, and it is speculated that denitrifying phosphorous removal occurred in the AOA process. Furthermore, 0.24±0.06 g VSS(-1) d(-1) of TN was removed in the aerobic zone via simultaneous nitrification and denitrification (SND). The results demonstrate that the multi-zone structure of the AOA process favors the enhancement of denitrifying phosphorous removal and SND for municipal wastewater treatment.     

Effect of ferrous sulphate on nitrification during simultaneous phosphorus removal from domestic wastewater using a laboratory scale anoxic/oxic reactor

In the present study a laboratory scale anoxic/oxic reactor was used to remove the important eutrophication nutrients such as phosphorus and nitrogen from synthetic domestic wastewater. Phosphorus was removed through simultaneous precipitation and was carried out using the coagulant ferrous sulphate FeSO₄ · 7H₂O. Total phosphorus in the effluent was controlled to below 1 mg/l using a ferrous to phosphorus molar ratio of 2.1. pH after the addition of coagulant plays a major role in determining the molar ratio of the precipitant. Nitrogen was removed biologically in the anoxic/oxic system and the effect of simultaneous precipitation on nitrification and denitrification was investigated. The nitrification rate of the system remained unaffected during simultaneous precipitation and varied from 0.046 to 0.059 g N–NH₄ ⁺/g VSS/day. Denitrification was complete and was not affected by the coagulation process. The nitrogen removal efficiency varied from 78% to 85%. COD removal efficiency was not affected during simultaneous precipitation and was varied from 94% to 98%. The highly efficient nitrogen removal in the presence of simultaneous precipitant ferrous sulphate makes the process an ideal option for nutrient removal.     

Experimental study of the anaerobic urban wastewater treatment in a submerged hollow-fibre membrane bioreactor at pilot scale

The aim of this study was to assess the effect of several operational variables on both biological and separation process performance in a submerged anaerobic membrane bioreactor pilot plant that treats urban wastewater. The pilot plant is equipped with two industrial hollow-fibre ultrafiltration membrane modules (PURON? Koch Membrane Systems, 30 m2 of filtration surface each). It was operated under mesophilic conditions (at 33 °C), 70 days of SRT, and variable HRT ranging from 20 to 6h. The effects of the influent COD/SO?-S ratio (ranging from 2 to 12) and the MLTS concentration (ranging from 6 to 22 g L?1) were also analysed. The main performance results were about 87% of COD removal, effluent VFA below 20 mg L?1 and biogas methane concentrations over 55% v/v. Methane yield was strongly affected by the influent COD/SO?-S ratio. No irreversible fouling problems were detected, even for MLTS concentrations above 22 g L?1.     

Modeling and experimental study on the anaerobic/aerobic/anoxic process for simultaneous nitrogen and phosphorus removal: The effect of acetate addition

A mathematical model based on the simulation software AQUASIM was developed to validate an anaerobic/aerobic/anoxic (AOA) process that enables simultaneous nitrogen and phosphorus removal in a single reactor by adding external organic carbon to preclude excess aerobic phosphate uptake by polyphosphate-accumulating organisms (PAOs) and provide phosphate for denitrifying PAOs (DNPAOs). Aerobic batch tests after anaerobic phosphate release with different chemical oxygen demand (COD) concentrations indicated that the effect of COD concentration on the phosphate uptake preclusion could be expressed by a simple formula. The reduction factor reflecting the formula, which retards the aerobic phosphate uptake in the presence of COD, was added to the process rates of aerobic polyphosphate storage and PAOs growth in the model. The improved model, which included the reduction factor, reasonably matched the experimental result regarding aerobic phosphate uptake behavior whereas the model without it did not; thus, the former precisely predicts the AOA process behavior.     

Effects of the internal recycling rate on biological nutrient removal and microbial community structure in a sequential anoxic/anaerobic membrane bioreactor

This study investigated the effects of the internal recycling rate on nutrients removal in a sequential anoxic/anaerobic membrane bioreactor (SAM). Microbial community structure in sludge from the SAM was studied using quinone profile method. Above 98% COD, 68% nitrogen, and 55% phosphorus removal efficiencies were achieved when the internal recycling rate was 2.5 times influent flow. At that rate, the optimum specific nitrate loading rate and COD/NO(3)-N ratio were found to be 2.24 mgNO(3)-N g(-1) MLSS h(-1) and 9.13, respectively. Batch tests demonstrated that anoxic condition suppressed phosphorus release, and that denitrification was also influenced by initial substrate concentration. Denitrification appeared to have some priority over phosphorus release for substrate uptake. Microbial community analysis revealed a predominance of the subclass beta-Proteobacteria. Furthermore, it was found that Rhodocyclus-related bacteria were efficient at phosphorus removal than Actinobacteria.     

Effect of the concentration of suspended solids on the enzymatic activities and biodiversity of a submerged membrane bioreactor for aerobic treatment of domestic wastewater

A pilot-scale submerged membrane bioreactor was used for the treatment of domestic wastewater in order to study the influence of the variations in the concentration of volatile suspended solids (VSS) on the enzymatic activities (acid and alkaline phosphatases, glucosidase, protease, esterase, and dehydrogenase) and biodiversity of the bacterial community in the sludge. The influence of VSS concentration was evaluated in two separated experiments, which were carried out in two different seasons of the year (experiment 1 through spring–summer and experiment 2 through autumn–winter). Cluster analysis of the temperature gradient gel electrophoresis (TGGE) profiles demonstrated that the community composition was significantly different in both experiments. Within the same experiment, the bacterial community experienced sequential shifts as the biomass accumulated, as shown by the evolution of the population profiles through time as VSS concentration increased. All enzymatic activities studied were significantly lower during experiment 2, except for glucosidase. Concentrations of VSS over 8 g/l induced a strong descent of all enzymatic activities, which overlapped with a significant modification of the community composition. Sequences of the major TGGE bands were identified as representatives of the Alpha-proteobacteria, filamentous bacteria (Thiotrix), and nitrite oxidizers (Nitrospira). Some sequences which were poorly related to any validated bacterial taxon were obtained.     

Assessment of olive-mill wastewater as a growth medium for lipase production by Candida cylindracea in bench-top reactor

Olive-mill wastewater (OMW) was investigated for its suitability to serve as a medium for lipase production by Candida cylindracea NRRL Y-17506. The OMW that best supported enzyme production was characterized by low COD and low total sugars content. In shake flask batch cultures, OMW supplementation with 2.4 g l⁻¹ NH₄Cl and 3 g l⁻¹ olive oil led to an enzyme activity of about 10 U ml⁻¹. The addition of glucose or malt extract and supplements containing organic N (e.g., peptone, yeast extract) either depressed or did not affect the enzyme production. Further experiments were then performed in a 3-l stirred tank reactor to assess the impact of medium pH and stirring speed on the yeast enzyme activity. The lipase activity was low (1.8 U ml⁻¹) when the pH was held constant at 6.5, significantly increased (18.7 U ml⁻¹) with uncontrolled pH and was maximum (20.4 U ml⁻¹) when the pH was let free to vary below 6.5. A stirring regime, that varied depending on the dissolved oxygen concentration in the medium, both prevented the occurrence of anoxic conditions during the exponential growth phase and enabled good lipase production (i.e., 21.6 U ml⁻¹) and mean volumetric productivity (i.e., 123.5 U l⁻¹ h⁻¹).