Continuous biological ferrous iron oxidation in a submerged membrane bioreactor.

Microbial oxidation of ferrous iron may be available alternative method of producing ferric iron, which is a reagent used for removal of H2S from biogas. In this study, a submerged membrane bioreactor (MBR) system was employed to oxidize ferrous iron to ferric iron. In the submerged MBR system, we could keep high concentration of iron-oxidizing bacteria and high oxidation rate of ferrous iron. There was membrane fouling caused by chemical precipitates such as K-jarosite and ferric phosphate. However, a strong acidity (pH 1.75) of solution and low ferrous iron concentration (below 3000 mg/I) significantly reduced the fouling of membrane module during the bioreactor operation. A fouled membrane module could be easily regenerated with a 1 M of sulfuric acid solution. In conclusion, the submerged MBR could be used for high-density culture of iron-oxidizing bacteria and for continuous ferrous iron oxidation. As far as our knowledge concerns, this is the first study on the application of a submerged MBR to high acidic conditions (below pH 2).     

BICT biological process for nitrogen and phosphorus removal.

An updated biological nitrogen and phosphorus removal process--BICT (Bi-Cyclic Two-Phase) biological process--is proposed and investigated. It is aimed to provide a process configuration and operation mode that has facility and good potential for optimizing operation conditions, especially for enhancing the stability and reliability of the biological nutrient removal process. The proposed system consists of an attached-growth reactor for growing autotrophic nitrifying bacteria, a set of suspended-growth sequencing batch reactors for growing heterotrophic organisms, an anaerobic biological selector and a clarifier. In this paper, the fundamental concept and operation principles of BICT process are described, and the overall performances, major operation parameters and the factors influencing COD, nitrogen and phosphorus removal in the process are also discussed based on the results of extensive laboratory experiments. According to the experimental results with municipal sewage and synthetic wastewater, the process has strong and stable capability for COD removal. Under well controlled conditions, the removal rate of TN can reach over 80% and TP over 90% respectively, and the effluent concentrations of TN and TP can be controlled below 15 mg/L and 1.0 mg/L respectively for municipal wastewater. The improved phosphorus removal has been reached at short SRT, and the recycling flow rate of supernatant between the main reactors and attached-growth reactor is one of the key factors controlling the effect of nitrogen removal.     

Quantitative analysis of biological effect on membrane fouling in submerged membrane bioreactor.

The objective of this study is to investigate solids concentration and extracellular polymeric substance (EPS) effects on the membrane fouling in the submerged membrane bioreactor. The relationship between the solids retention time (SRT) and the amount of EPS is observed in three lab-scale MBRs. Additionally, the EPS effect on membrane fouling is quantified by calculating the specific cake resistance (alpha) using an unstirred batch cell test. By observing the sludge over a long period under various SRT scenarios, a wide range of EPS and membrane fouling data is obtained. These observations provide sufficient evidence of the functional relationship between SRT, EPS and alpha. As SRT decreases, the amount of EPS bound in sludge floc becomes higher in the high MLSS condition (> 5,000 mg/L). The amount of EPS in the sludge floc has positive influence on alpha. A sigmoid trend between EPS and alpha is observed and the functional relationship obtained by dimensional analysis is consistent with the experimental results.     

In-situ characterization of microbial community in an A/O submerged membrane bioreactor with nitrogen removal.

The bacterial community involved in removing nitrogen from sewage and their preferred DO environment within an anoxic/oxic membrane bioreactor (A/O MBR) was investigated. A continuously operated laboratory-scale A/O MBR was maintained for 360 d. At a sludge age of 150 d and a C/N ratio of 3.5, the system was capable of removing 88% of the influent nitrogen from raw wastewater through typical nitrogen removal transformations (i.e. aerobic ammonia oxidation and anoxic nitrate reduction). Characterization of the A/O MBR bacterial community was carried out using fluorescence in situ hybridization (FISH) techniques. FISH results further showed that Nitrosospira spp. and Nitrospira spp. were the predominant groups of ammonia and nitrite oxidizing group, respectively. They constituted up to 11% and 6% of eubacteria at DO below 0.05 mg/l (low DO), respectively, and about 14% and 9% of eubacteria at DO between 2-5 mg/l (sufficient DO), respectively, indicating preference of nitrifiers for a higher DO environment. Generally low counts of the genus Paracoccus were detected while negative results were observed for Paracoccus denitrificans, Alcaligenes spp, and Pseudomonas stutzeri under the low and sufficient DO environments. The overall results indicate that Nitrosospira spp., Nitrospira spp. and members of Paracoccus spp. can be metabolically functional in nitrogen removal in the laboratory-scale A/O MBR system.     

Characterization of fouled membranes from a membrane enhanced biological phosphorus removal system.

Characterization of fouled membranes is the first step towards a good understanding of membrane fouling nature and thus formulating effective engineering measures for fouling prevention and control. In this study, fouled membrane fibres collected from a pilot scale membrane enhanced biological phosphorus removal (MEBPR) process were systematically examined. Several analytical tools, including scanning electron microscopy (SEM), conventional optical microscopy (COM), energy dispersive X-ray (EDX) microanalysis, matrix assisted laser desorption/ionization--mass spectrometry (MALDI-MS) analysis, and conventional chemical analysis techniques were used. The results indicated that membrane fouling in the MEBPR process was mainly of an organic nature, and most extractable foulants were carbohydrates and humic or humic-like substances. Unlike in other wastewater treatment membrane bioreactors, microbial growth on fouled membranes was not substantial, probably due to the vigorous aeration applied and the strong hydrodynamic conditions within the membrane pore structure. After a period of sludge filtration, membrane surfaces became more hydrophobic and the resultant hydrophobic interactions between the fouled membranes and mixed liquor constituents might have accelerated the fouling process.     

Two-stage thermophilic-mesophilic anaerobic digestion of waste activated sludge from a biological nutrient removal plant.

A two-stage thermophilic-mesophilic anaerobic digestion pilot-plant was operated solely on waste activated sludge (WAS) from a biological nutrient removal (BNR) plant. The first-stage thermophilic reactor (HRT 2 days) was operated at 47, 54 and 60 degrees C. The second-stage mesophilic digester (HRT 15 days) was held at a constant temperature of 36-37 degrees C. For comparison with a single-stage mesophilic process, the mesophilic digester was also operated separately with an HRT of 17 days and temperature of 36-37 degrees C. The results showed a truly thermophilic stage (60 degrees C) was essential to achieve good WAS degradation. The lower thermophilic temperatures examined did not offer advantages over single-stage mesophilic treatment in terms of COD and VS removal. At a thermophilic temperature of 60 degrees C, the plant achieved 35% VS reduction, representing a 46% increase compared to the single-stage mesophilic digester. This is a significant level of degradation which could make such a process viable in situations where there is no primary sludge generated. The fate of the biologically stored phosphorus in this BNR sludge was also investigated. Over 80% of the incoming phosphorus remained bound up with the solids and was not released into solution during the WAS digestion. Therefore only a small fraction of phosphorus would be recycled to the main treatment plant with the dewatering stream.     

Sludge-sludge interaction in the enhanced biological phosphorus removal process.

Metabolisms related to enhanced biological phosphorus removal (EBPR) were found to be affected when two activated sludges with different EBPR activities were mixed together. In the present study, two laboratory scale EBPR processes were operated in parallel, one of them with higher and another with lower EBPR activities. The activated sludges from the two reactors were mixed together at different mixing ratios. The supernatant was made the same for all mixing ratios, anaerobic-aerobic batch experiments were performed, and acetate uptake rate and phosphate release rate under anaerobic conditions and phosphate uptake rate under aerobic condition were determined. The metabolic rates measured were expected to be linear to the mixing ratios, as the supernatant was the same for all mixing ratios, whereas the metabolic rates were either promoted or inhibited by mixing of sludges. As an indicator for the sludge mixing effect on the metabolic rates, mixing effect intensity (MEI) was introduced. Chemical substances that are produced by microorganisms in activated sludge are proposed to be one of the possible causes of the sludge mixing effect.     

A membrane bioreactor for the removal of dimethyl sulphide and toluene from waste air.

In biotrickling filters, mass transfer of hydrophobic compounds is the limiting factor. Biofilters are static systems, and so control and regulation of operational parameters such as pH and nutrient supply can be a problem. In membrane bioreactors, these drawbacks can be avoided. The hydrophobic membrane separates the waste air from the aqueous phase, thus avoiding mass-transfer limitation, while pH and nutrient supply can be directly controlled. In this contribution, an overview will be given of results obtained during a four-year project. First, the physical chemical characteristics (solubility, permeability, diffusivity) and microbial adhesion of different membranes were tested. This led to the selection of a composite membrane consisting of a porous polyvinylidenefluoride (PVDF) support layer coated with a thin (1 or 2.5 microm) dense polydimethylsiloxane (PDMS) top layer. This membrane was mounted into a module provided with four parallel rectangular channels for gas flow (in contact with the porous layer) and nutrient solution (in contact with the dense layer) respectively. After inoculation, a biofilm developed on the dense layer. Experiments were performed with dimethyl sulphide and toluene as target VOCs. Operational characteristics such as elimination capacity as a function of the volumetric load and residence time, effect of nutrient supply, long-term performance) were determined. Mass transfer was studied by measuring concentration profiles along the channels of the module in different conditions.     

Effect of a suspended carrier on membrane fouling in a submerged membrane bioreactor.

In an attempt at membrane fouling control, a kind of cylindrical plastic suspended carrier was added in a submerged membrane bioreactor (SMBR) and its effect was investigated in this study. According to the transmembrane pressure (TMP) profiles and the sludge characteristics in comparative runs with and without suspended carriers, it was found that the suspended carriers added in SMBR had two effects on membrane fouling: one was the positive effect of mechanically scouring the membrane surface and the other was the negative effect of breaking up sludge flocs. Sludge particle size distribution change was mainly responsible. It was suggested to apply the suspended carrier at higher MLSS concentration and lower carrier dose based on the consideration for retarding sludge breakage caused by the carrier. The experiment was conducted under higher MLSS (8 gL(-1)) and lower carrier dose (carrier volume/total volume = 10/). The TMP increase was effectively retarded by added suspended carriers compared to the system without addition of the carriers. The effect of suspended carriers on membrane fouling at high MLSS concentration was verified.     

UNITANK系统生物——化学联合除磷工艺中试研究

以诸暨市水样进行的中试研究表明,采用生物—化学联合除磷工艺对UNITANK系统进行常规改进得不偿失。但可以考虑采用生物—化学联合除磷工艺作为UNITANK系统应对TP冲击负荷的应急处理工艺。     

Treatment of winery wastewaters in a membrane submerged bioreactor.

Wine production is seasonal, and thus the wastewater flow and its chemical oxygen demand (COD) concentrations greatly vary during the vintage and non-vintage periods, as well as being dependant on the winemaking technologies used, e.g. red, white or special wines production. Due to this seasonal high variability in terms of organic matter load, the use of membrane biological reactors (MBR) could be suitable for the treatment of such wastewaters. MBR offers several benefits, such as rapid start up, good effluent quality, low footprint area, absence of voluminous secondary settler and its operation is not affected by the settling properties of the sludge. A pilot scale hollow fibre MBR system of 220 L was fed by adequately diluting white wine with tap water, simulating wastewaters generated in wineries. The COD in the influent ranged between 1,000 and 4,000 mg/L. In less than 10 days after the start up, the system showed a good COD removal efficiency. The COD elimination percentage was always higher than 97% regardless of the organic loading rate (OLR) applied (0.5-2.2 kg COD/m3 d), with COD concentrations in the effluent ranging between 20 and 100 mg/L. Although the biomass concentration in the reactor increased from 0.5 to 8.6 g VSS/L, the suspended solids concentration in the effluent was negligible. Apparent biomass yield was estimated in 0.14 g VSS/g COD.     

Nitrogen removal from piggery waste using the combined SHARON and ANAMMOX process.

Nitrogen removal in piggery waste was investigated with the combined SHARON-ANAMMOX process. The piggery waste was characterized as strong nitrogenous wastewater with very low C/N ratio. For the preceding SHARON reactor, ammonium nitrogen loading and conversion rates were 0.97 kg NH4-N/m3 reactor/day and 0.73 kg NH4-N/m3 reactor/day, respectively. Alkalinity consumption for ammonium conversion was 8.5 gr bicarbonate utilized per gram ammonium nitrogen converted to NO2-N or NO3-N at steady-states operation. The successive ANAMMOX reactor was fed with the effluent from SHARON reactor. Nitrogen loading and conversion rates were 1.36 kg soluble N/m3 reactor/day and 0.72 kg soluble N/m3 reactor/day, respectively. The average NO2-N/NH4-N removal ratio by ANAMMOX reaction was 2.13. It has been observed that Candidatus "Kuenenia stuttgartiensis" were dominated in the ANAMMOX reactor based on FISH analysis.     

Application of PTFE membrane for ammonia removal in a membrane contactor

The feasibility of a membrane contactor system for ammonia removal was studied. The mass transfer coefficient was used to quantitatively compare the effect of various operation conditions on ammonia removal efficiency. Effective removal of ammonia was possible with a Polytetrafluoroethylene (PTFE) membrane contactor system at all tested conditions. Among the various operation parameters, contact time and solution pH showed significant effect on the ammonia removal mechanism. The overall ammonia removal rate was not affected by influent suspended solution concentration unlike other pressure driven membrane filtration processes. Also the osmotic distillation phenomena which deteriorate the mass transfer efficiency can be minimized by preheating of influent wastewater. A membrane contactor system can be a possible alternative to treat high strength nitrogen wastewater by optimizing operation conditions such as stripping solution flow rate, influent wastewater temperature, and influent pH.     

Simultaneous removal of organic and strong nitrogen from sewage in a pilot-scale BNR process supplemented with food waste.

As the sewerage system is incomplete, sewage in Korea lacks easily biodegradable organics for nutrient removal. In this country, about 11,400 tons of food waste of high organic materials is produced daily. Therefore, the potential of food waste as an external carbon source was examined in a pilot-scale BNR (biological nutrient removal) process for a half year. It was found that as the supply of the external carbon increased, the average removal efficiencies of T-N (total nitrogen) and T-P (total phosphorus) increased from 53% and 55% to 97% and 93%, respectively. VFAs (volatile fatty acids) concentration of the external carbon source strongly affected denitrification efficiency and EBPR (enhanced biological phosphorus removal) activity. Biological phosphorus removal was increased to 93% when T-N removal efficiency increased from 78% to 97%. In this study, several kinds of PHAs (poly-hydroxyalkanoates) in cells were observed. The observed PHAs was composed of 37% 3HB (poly-3-hydroxybutyrate), 47% 3HV (poly-3-hydroxyvalerate), 9% 3HH (poly-3-hydroxyhexanoate), 5% 3HO (poly-3-hydroxyoctanoate), and 2% 3HD (poly-3-hydroxydecanoate).     

Re-use of winery wastewaters for biological nutrient removal.

The aim of this study was to evaluate the feasibility of the re-use of the winery wastewater to enhance the biological nutrient removal (BNR) process. In batch experiments it was observed that the addition of winery wastewater mainly enhanced the nitrogen removal process because of the high denitrification potential (DNP), of about 130 mg N/g COD, of the contained substrates. This value is very similar to that obtained by using pure organic substrates such as acetate. The addition of winery wastewater did not significantly affect either phosphorus or COD removal processes. Based on the experimental results obtained, the optimum dosage to remove each mg of N-NO3 was determined, being a value of 6.7 mg COD/mg N-NO3. Because of the good properties of the winery wastewater to enhance the nitrogen removal, the viability of its continuous addition in an activated sludge pilot-scale plant for BNR was studied. Dosing the winery wastewater to the pilot plant a significant increase in the nitrogen removal was detected, from 58 to 75%. The COD removal was slightly increased, from 89 to 95%, and the phosphorus removal remained constant.     

Intended process water management concept for the mechanical biological treatment of municipal solid waste

Accumulating operational experience in both aerobic and anaerobic mechanical biological waste treatment （MBT） makes it increasingly obvious that controlled water management would substantially reduce the cost of MBT and also enhance resource recovery of the organic and inorganic fraction. The MBT plant at Gescher, Germany, is used as an example in order to determine the quantity and composition of process water and leachates from intensive and subsequent rotting, pressing water from anaerobic digestion and scrubber water from acid exhaust air treatment, and hence prepare an MBT water balance. The potential of, requirements for and limits to internal process water reuse as well as the possibilities of resource recovery from scrubber water are also examined. Finally, an assimilated process water management concept with the purpose of an extensive reduction of wastewater quantity and freshwater demand is presented.     

A hybrid anaerobic solid-liquid system for food waste digestion.

A hybrid anaerobic solid - liquid (HASL) system was developed to enhance food waste bioconversion in comparison with the conventional two-phase anaerobic digester. The advantages of the HASL system were the higher efficiency of methane production and smaller volume of effluent from the system. The biogas, which was generated from the methanogenic phase, had an average methane content of 71-72%. Total removal of volatile solids consisted of 78-80%. The HASL system can be operated in both batch and semi-continuous modes with satisfactory performance. The addition of a submerged biofilter for ammonia removal to the HASL system further enhanced the performance of anaerobic digestion. Methane production in the enhanced HASL system was increased by 26% in comparison with the HASL system without submerged filter. This paper describes the development of the enhanced HASL system for anaerobic treatment of food waste.     

膜生物反应器长期运行条件下膜的清洗方法及机理研究

对实际工程中运行2年以上的MBR的膜使用能谱分析、傅立叶红外光谱和接触角测定等方法对膜表面的污染物特性进行了分析,对膜清洗过程中不同清洗剂的作用效果进行了探讨,并进一步对膜污染过程进行了推测.结果表明,酸性清洗剂对膜的清洗效果较好,膜表面无机污染基本被去除,但不能完全有效去除膜表面有机酸、蛋白质、多糖和多糖类物质等有机污染物;NaOH和NaClO对污染后的膜的清洗效果不佳,原因可能是由于MBR进水为混凝沉淀池出水,长期运行条件下膜污染以无机污染为主,有机污染可能起到了螯合的作用,使无机污染物和有机污染物络合,增加了碱和氧化剂去除有机污染的难度.     

SH-A节能型生物脱氮工艺处理焦化废水工程实例

采用SH-A节能型生物脱氮工艺处理氨氮含量高、有机物可生化性差的焦化废水。工程处理水量为1600m3/d。进水CODCr约2500mg/L,NH3—N约260mg/L。处理后出水各项指标均达到了《污水综合排放标准》(GB8978—1996)一级标准,其中CODCr≤100mg/L,NH3—N≤15mg/L。     

混凝-沉淀系统改造为复合生物处理系统的工艺设计

为了改善深圳河和布吉河的水质,深圳市政府决定对布吉河水质净化厂原混凝-沉淀系统进行改造.改造工艺采用短水力停留时间的强化淹没生物膜-活性污泥复合工艺.介绍了布吉河水质净化厂原混凝-沉淀系统改造工程的工艺设计参数、工艺特点、技术经济指标及设计经验.为污水处理厂的改造设计提供了一套可靠的方案.