A pilot scale bioreactor using EMMC for carbon and nitrogen removal

A pilot scale (100 l reactor) of an entrapped mixed microbial cell (EMMC) process was fabricated and tested for simultaneous removal of carbon and nitrogen. Process performance, operational stability, and maintenance requirements were all determined. Two sources of actual agricultural processing wastewater containing a high concentration of chemical oxygen demand (COD) (about 800–1,000 mg/l) and domestic sewage containing a low concentration of COD (about 150–200 mg/l) were investigated in this study. Various HRT (hydraulic retention time) and aeration schedules were operated. It was found that soluble COD (SCOD) and soluble total nitrogen (STN) could be removed in the range of 40–70% and 20–90%, respectively, for domestic sewage depending on the operational conditions provided. For agricultural processing wastewater, removal efficiencies of SCOD and STN are 89–91% and 60–75%, respectively, depending on the HRTs and aeration schedules applied. Economic evaluation for the application of domestic sewage was conducted. It was found that at an HRT of 6 h with 24 h of aeration it costs U.S.$1.75 for the treatment of 1,000 gal/day (3.8 m³/day). It is apparent that the EMMC process is technically feasible for simultaneous removal of carbon and nitrogen under the operation of an alternated schedule of the aeration in one single bioreactor. Ultimately, it can replace or upgrade the existing conventional wastewater treatment plant by combining the secondary and tertiary wastewater treatment plant in one bioreactor and provides simple maintenance and operation. This will also assist in providing the high quality of treated effluent meeting current and future environmental regulation for reuse. Electronic Publication     

Integrating entrapped mixed microbial cell (EMMC) technology for treatment of wastewater containing dimethyl sulfoxide (DMSO) for reuse in semiconductor industries

Solvents containing dimethyl sulfoxide (DMSO) are widely used in the rinse process of stripping photoresistors in semiconductor manufacturing industries. The disposal/reuse of wastewater containing DMSO is a serious problem because of its high concentration of organic carbon and the need to suppress the odor from its sulfur contents. An entrapped mixed microbial cell (EMMC) process was used to investigate the effectiveness of removing DMSO from a synthetic wastewater in a once-through up-flow fixed-bed bioreactor. Both cellulose triacetate and cellulose acetate were used to prepare the EMMC carriers. Various hydraulic retention times (HRTs) (based on the void volume) of 3, 4, 5, 6, and 12 h were investigated when the concentration of DMSO was 500 mg/l and 1,000 mg/l. It was found that the addition of 50 mg/l of sucrose was needed to serve as the carbon source for possible co-metabolism of DMSO. Based on the result of the impact of various dilution rates (1/HRT) on the TOC (total organic carbon) removal efficiency and TOC remaining, a dilute curve for this relationship was plotted. Thus, an optimal operational criterion was developed, i.e., it must be operated at a dilution rate of less than 0.15 h⁻¹ or at an HRT of higher than 6.66 h, in order to achieve more than 95% of TOC (or more than 99% of DMSO) removal efficiency when using the cellulose triacetate as the EMMC carriers. This process performance was compared to the bio-contact filter (BCF) process conducted in Japan. It was found that the present study is capable of producing much less effluent nitrogen (including NH₄-N and NO₃-N) content than the BCF process under similar loading conditions. It is possible that integrating the unit process of EMMC as pretreatment with microfiltration (MF) and reversed osmosis (RO) processes is promising for the reuse and recycling of semiconductor wastewater. Thus, higher quality (less organic carbon and inorganic nitrogen content) pretreated water can be further treated by another physical chemical process, such as MF and RO, for the production of superpurity water for reuse in the semiconductor manufacturing industry.     

淹没式MBR去除有机物动力学模型及其应用

针对淹没式MBR的工艺特点,以反应器内物料衡算为基础,建立了有机物去除的动力学模型——ROM模型,得出淹没式MBR对有机底物的去除速率Uy不仅与进、出水中的有机底物质量浓度S0、Sc和水力停留对间tH有关,还与膜组件去除的有机底物质量浓度Sm、污泥停留时间ts有关．利用ROM模型,可以预测反应器内活性污泥浓度X,确定污泥停留时间ts和不排泥条件下反应器内的最大活性污泥浓度Xmax,试验中以啤酒厂废水为例,对模型进行了验证,试验结果与模型计算结果基本一致．     

颗粒物质控制膜污染的增强型膜生物反应器工艺的研究

用于废水处理的膜生物反应器工艺(MBR),是指通过膜过滤实现活性污泥与产水的分离的新型生化法处理废水技术.由于MBR具有占地面积小和出水水质好的优点,膜生物反应器成功应用到废水处理中的案例正在迅速增加.膜污染是MBR废水处理工艺面临的主要问题之一.膜污染会导致膜的渗透性能降低,为此必须通过化学清洗才能恢复膜的性能.为了实现无化学清洗的MBR工艺,研究使用持续物理冲刷去除膜污染层的方法.在活性污泥中加入颗粒物质(粉料),通过这些颗粒物质的持续冲刷作用实现去除膜污染层的目的.经过8个多月的实验,膜组件的渗透性能保持不变,通量可以达到40 L/(m2.h)以上.系统安装了在线的浊度仪作为产水质量的检测,在试验过程中,浊度始终没有变化.作为对比,同时也进行了一个参照实验(MBR标准工艺,没有加入颗粒物质),实验结果表明,传统的MBR工艺的膜组件渗透性能会不断下降导致通量下降,需要进行化学清洗.新型MBR工艺高通量和无需化学清洗的优势,将极大地提高MBR工艺的成本效益.     

Integrating an anaerobic Bio-nest and an aerobic EMMC process as pretreatment of dairy wastewater for reuse: a pilot plant study

A large dairy farm located on the island of Oahu, Hawaii was the site for an investigation for the potential integration of the existing facultative lagoon system with a cost effective pretreatment unit process. Based on the results from a laboratory study, a pilot plant was installed with two anaerobic bioreactors (10 m3 each) and one aerobic reactor (3.8 m3). Two layers of media “Bio-nest,” providing a void volume of 98%, were placed into each anaerobic bioreactor with 19% space-based on the bioreactor water volume. For better performance and reduction of shock-load, the equalization/settling tank was employed prior to the first anaerobic Bio-nest reactor. The intermediate holding tank settled effluent suspended solids from the Bio-nest reactor and adjusted the loading rate in order to improve the performance of the aerobic EMMC (entrapped mixed microbial cell) bioreactors. Based on the start-up operation of the Bio-nest system at an organic loading rate of about 1.5 g TCOD/l/day, the production rate of biogas from the first and second Bio-nest reactors was 0.64 and 0.15 l/l/day, respectively. This indicates that the anaerobic degradation of organics occurs mainly in the first Bio-nest reactor due to the low loading rate. The removal efficiency from the Bio-nest system shows TCOD removal of about 70%. The EMMC process provided further treatment to achieve a removal efficiency of TCOD at about 50% and a TN of about 35%. The cost for these pretreatments in order to be integrated with the existing lagoon system is US $1.1 per 1,000 gallons (3.8 m3) for dairy wastewater and $1.1 per 1,000 gallons (3.8 m3) for dairy wastewater and 91 for each ton of TCOD removal. This integration system provides a sustainable improvement of environment and agricultural production.     

A/O MBR处理城市污水回用的中试研究

采用中试规模(36 m3/d)的缺氧-好氧膜生物反应器(A/O MBR)对城市污水处理回用进行了试验研究.试验结果表明,该工艺处理效果优良,系统对COD、氨氮、浊度、细菌的平均去除率分别为94%,98.3%,99.6%,lg6,出水浓度分别为18 mg/L,0.65 mg/L,0.06 NTU,4个/mL.出水水质优于城市杂用水水质标准(GB/T 18920-2002).该系统具有较强的抗冲击负荷能力.     

Fate of copper in submerged membrane bioreactors treating synthetic municipal wastewater

This paper assesses the impact of copper on the performance of two membrane bioreactors (MBR) treating municipal wastewater at a hydraulic retention time (HRT) of 4h, and solids residence times (SRT) of 20 days, at influent copper concentrations of 0.2-8 mg Cu/L. The addition of copper resulted in a significant increase in soluble microbial products (SMPs), and a predominance of >100 kDa molecular weight SMPs. The study showed that in well-buffered wastewaters, complete nitrification was achieved at total copper concentrations as high as 840 mg/L or 10% of the mixed liquor volatile suspended solids. MINTEQ simulation showed that most of the copper (99.8%) in the MBR was in the form of inorganic copper precipitates, with free Cu2+ and total soluble copper in the range of 0.0-0.11 and 0.1-0.82 mg/L, respectively.     

Biofiltration of hydrogen sulfide‐containing waste gas by entrapped mixed microbial cells

Abstract

The study demonstrates a novel attempt to use an aerobic biofiltration system containing entrapped mixed microbial cells (EMMC) for removal of hydrogen sulfide dominant waste gases. In the study, heterotrophic microflora‐immobilized cellulose was packed into an EMMC reactor to degrade hydrogen sulfide. Effects of hydrogen sulfide concentrations for continuous operation at various flow rates indicated that hydrogen sulfide removal efficiency is higher than 90% at inlet loadings below 4.31 mg‐S/min for retention time of 5.3 minutes. This EMMC biofiltration system also showed high tolerance to fluctuations in flow rates while maintaining stable removal performance. The predicted kinetic constant k and maximum mass loading are 0.018 s–1 and 8.64 mg‐S/min, respectively. Adaptability tests in response to gradual shifts up and down of inlet hydrogen sulfide loading indicated that the EMMC microbial communities were well‐acclimated to maintain long‐term operation stability for continuous treatment.     

Study on zeolite enhanced contact-adsorption regeneration-stabilization process for nitrogen removal

Utilizing preferential ion exchange of zeolite to ammonium, the conventional contact stabilization activated sludge process (CS) can be upgraded to a new type nitrogen removal process, zeolite enhanced contact-adsorption regeneration-stabilization process (ZCS). For municipal wastewater, the effluent ammonium concentration of the ZCS process was around 6.83 mg/L, indicating that ammonium removal efficiency was enhanced over 27% when the influent ammonium concentration was between 24.7 and 50.5 mg/L in the same hydraulic retention time (HRT) and sludge retention time (SRT) conditions as those of the CS process. The results of PCR-DGGE technology showed that the microbial diversity, uniformity and abundance of the ZCS process were all higher than that of the CS process. In addition, anoxic/oxic (A/O) process with the volumetric ratio of oxic tank to anoxic tank being 2:1 was preferred for the regeneration process. The pilot scale ZCS process with the capacity to treat up to 72 m(3)/d of municipal wastewater was also monitored. The test results revealed that ammonium saturated zeolite could be biologically regenerated effectively and in time. The daily zeolite powder addition was limited to the amount that made up the loss due to the sludge excluding. Furthermore, the orthogonal experiments results showed that the most significant effects on nitrogen and ammonium removal were zeolite powder dose and external recycle ratio, respectively.     

Simultaneous methane production and wastewater reuse by a membrane-based process: evaluation with raw domestic wastewater

In this study, a membrane-based process was applied to simultaneously reclaim methane and generate reused water from raw domestic wastewater. The system was comprised of up-flow anaerobic sludge fixed bed (UAFB), anoxic sink (AS) and aerobic membrane bioreactor (MBR). The hydraulic retention time of UAFB (HRT(U)) was gradually shortened from 8h to 6h, 3h and to 1h, while the HRT of AS and MBR kept at 8 h. It is found that HRT(U) of 3h was more suitable for the balancing production of biogas and volatile fatty acids (VFAs), and the VFAs served as carbon source for denitrification. The trans-membrane pressure (TMP) of the MBR kept lower than 0.04 MPa without wash or change of membrane sheet, however, the scanning electron microscopy (SEM) analysis indicated that microbes attached to the inner-surface of membrane, causing irreversible fouling after 133-day operation. The denaturing gradient gel electrophoresis (DGGE) profiles of amplified 16S rDNA gene fragments proved that more functional bacteria and higher microbial diversity emerged at HRT(U) of 3h and 1h. Most bacteria belonged to Betaproteobacteria and were responsible for carbon and nitrogen removal.     

TiO_2动态改性膜应用于MBR的研究

采用二氧化钛(TiO_2)纳米粒子对聚偏氟乙烯中空纤维膜微滤膜(PVDF MF,0.1μm)和实验室自制聚砜中空纤维膜超滤膜(PSF UF,0.05μm)进行表面亲水改性,以期提高膜的抗污染能力.采用膜接触角、纯水通量、出水TOC、膜压差和扫描电子显微镜(SEM)进行表征了TiO_2动态膜的性能.将TiO_2纳米颗粒改性后的PVDF MF和PSF UF膜应用于膜生物反应器(MBR)处理模拟焦化废水(TOC=500 mg/L),考察了其对MBR过滤性能的影响.实验结果表明,改性后膜的水接触角明显减小,亲水性增强,TMP升高速率明显降低,模拟焦化废水,TOC的去除率平均可达95%,经返洗及次氯酸钠清洗后膜表面TiO_2层外观没有明显变化.改性后的膜组件较显著地增加了MBR的膜抗污染的优势,且具有一定的稳定性.因此,将TiO_2动态改性耐污染膜应用于MBR是可行的.     

Performance of a hybrid-loop bioreactor system in biological treatment of 2,4,6-tri-chlorophenol containing synthetic wastewater: effects of hydraulic residence time

A hybrid-loop bioreactor system consisting of a packed column biofilm and an aerated tank bioreactor with effluent recycle was used for biological treatment of 2,4,6-tri-chlorophenol (TCP) containing synthetic wastewater. Effects of hydraulic residence time (HRT) on COD, TCP and toxicity removal performance of the reactor were investigated for the HRT values between 5 and 30 h, while the feed COD (2700+/-100 mgl(-1)), TCP (300+/-10 mgl(-1)) and the solids retention time (sludge age, SRT, 20 d) were constant. Percent TCP, COD and toxicity removals increased with increasing HRT resulting in more than 90% COD, TCP and toxicity removals at HRT values above 25 h. Biomass concentrations in the packed column and in the aeration tank increased with increasing HRT resulting in low reactor TCP concentrations and therefore high TCP, COD and toxicity removals at high HRT values. Volumetric and specific rates of TCP and COD removals decreased with increasing HRT due to increased biomass and decreased flow rates at high HRT levels. Volumetric and specific removal rates of COD and TCP were maximum at an HRT of 5 h.     

Optimizing aeration rates for minimizing membrane fouling and its effect on sludge characteristics in a moving bed membrane bioreactor

In MBR processes, sufficient aeration is necessary to maintain sustainable flux and to retard membrane fouling. Membrane permeability, sludge characteristics, nutrient removal and biomass growth at various air flow rates in the membrane and moving bed biofilm reactor (MBBR) compartments were studied in a pilot plant. The highest nitrogen and phosphorous removal rates were found at MBBR aeration rates of 151 and 85 L h(-1) and a specific aeration demand per membrane area (SAD(m)) of 1.2 and 0.4 m(air)(3) m(-2) h(-1), respectively. A linear correlation was found between the amount of attached biofilm and the nutrient removal rate. The aeration rate in the MBBR compartment and SAD(m) significantly influenced the sludge characteristics and membrane permeability. The optimum combination of the aeration rate in the MBBR compartment and SAD(m) were 151 L h(-1) and 0.8-1.2 m(air)(3) m(membrane)(-2) h(-1), respectively.     

Application of flat-sheet membrane to thickening and digestion of waste activated sludge (WAS)

The feasibility of using flat-sheet membrane for waste activated sludge (WAS) thickening and digestion was studied in this paper. The characteristics of the processes including the thickening efficiency, effluent water quality and filtration properties of the membrane for sludge thickening process (MST), digestion efficiency, effluent water quality and membrane permeability of the membrane for sludge simultaneous thickening and digestion process (MSTD) were investigated. Test results showed that good sludge thickening efficiency and superior effluent water quality were obtained in the MST process under hydraulic retention time (HRT) 0.26 and 2 d operation of each cycle, and the membrane fouling was mainly due to the increase of apparent viscosity of mixed liquors and the decrease of the cross-flow velocity (CFV) along membrane surfaces during one thickening cycle. Membranes were also selected for the processes and M1 membrane of polyvinylidene fluoride (PVDF) material with pore size 0.2 microm demonstrated better permeability compared with other three membranes. About 80% MLSS destruction rate and 73% MLVSS destruction rate were achieved under HRT 1 d, dissolved oxygen (DO) concentration 0.5-1.5 mg/L, temperature 20-28 degrees C and 15 d operation for one cycle in MSTD process, and membrane fouling of MSTD process was attributed to not only the reason of MST process mentioned above, but also the change of sludge properties such as the increase of soluble COD and microbial polymeric substances including EPS, carbohydrate and nucleic acids, etc. of the mixed liquors.     

Performance evaluation of single-sludge reactor system treating high-strength nitrogen wastewater

In the single-sludge reactor system treating high-strength nitrogen wastewater (similar to anaerobically pretreated piggery wastewater), the NH4(+)-N removal efficiencies (98-82%) are higher than total nitrogen removal efficiencies (71-43%). The mixed liquor recycle ratio only imposes a slight effect on total nitrogen removal efficiency. The alkalinity change data could be used for monitoring and control of the reactor system. To evaluate the performance of the single-sludge reactor system, a simplified nitrification-denitrification model (with nitrification capacity, denitrification capacity, and denitrification potential concepts) and a graphically analytical technique are proposed. It turns out that ammonia nitrification and total nitrogen removal efficiencies are strongly dependent on the process load and reactor configuration, and an optimal operating condition requires a proper match between nitrification and denitrification.     

A pilot plant for the treatment of lemon industry wastewater

A pilot plant with a 10-m³ airlift reactor, a settler and a 300-m³ pond were developed for the treatment of the lemon processing industry wastewater. The aim of this work is to evaluate reactor and pilot plant performance. We worked in a continuous system with activated sludge, using wastewater microorganisms and testing the most important parameters of the process (HRT, SRT, F/M, VRC, K _La). An outflow settler tube added to the reactor design increased sludge concentration in 25% at 200–500 l/h flow rates. At 600–800 l/h flow rates sludge concentration was 10–15% higher. Volumetric removal capacity of the suspended solid in the reactor was more than 6 kg BOD₅/m³ day with lesser than 17 h hydraulic retention time. Maximum BOD₅ removal was 92% with 200 l/h flow. The reactor had a good mixing performance and a satisfactory volumetric mass transfer coefficient. Efficient reactor design made foam disposal easy. The effluent came out of the pond with DBO = 50 mg/l, i.e. a total BOD removal of 99% with 600 l/h flow. The pond also had a very important function: it completely eliminated reactor produced biomass by using a natural degradation process.     

膜生物反应器运行中的膜污染及其控制

阐述了膜生物反应器(MBR)在水处理方面的优缺点及膜污染的主要影响因素,总结了国内外关于膜污染及其数学模型的研究进展,归纳出膜污染模型的几种形式,并从膜本身的理化性质改变、混合液理化特性改善、操作条件优化等方面论述了减缓膜污染的方法及措施,介绍了几种膜清洗的方法及设计和操作过程中应注意的问题,提出了今后研究的重点和方向．     

膜-生物反应器的研究及其在废水处理中的应用

综述了废水处理领域中的膜-生物反应器的基本特点、应用现状、存在的问题以及国内外研究的进展；重点阐述了膜-生物反应器运行工艺、新型膜材料与器件以及影响膜污染形成的因素与防治措施；并对今后的研究方向进行了展望．     

喷射环流反应器传质性能及应用研究

喷射环流反应器结合了喷射与环流的技术优势,具有传质效率高、水力停留时间短、容积负荷高、抗冲击负荷能力强等特点。对课题组自主研制开发的喷射环流生物反应器的传质性能试验结果表明,反应器中氧转移速率为传统曝气法氧转移速率的8～10倍。处理大庆东城区生活污水的试验结果表明,水力停留时间为0．5～1h,系统处理出水可达标排放。同时在好氧条件下,具有良好的脱氮除磷效果。     

Studies of a membrane aerated bioreactor for wastewater treatment

This study was undertaken specifically to collect engineering and process performance information on the behaviour of a membrane supported bio-film in a well-characterised bioreactor. A novel membrane aerated bioreactor has been tested in the laboratory on synthetic sewage, and also piloted for the treatment of primary effluent at a local municipal wastewater treatment plant. The reactor's design employs gas-permeable, hollow-fibre membranes that are submerged in the wastewater. Air is blown through the inside of the fibres. Aeration costs for such a reactor are likely to be lower than conventional systems because gas compression is not required. Thick bio-films grow on the outside of the fibres and effectively treat the wastewater. The bio-films grown in this manner are capable of biological oxygen demand (BOD) removal, nitrification, denitrification, and simultaneous sludge digestion. The character of the bio-film is very different from conventional bio-films grown on inert surfaces, since in this case the bio-film receives its oxygen and the wastewater components from different directions. In pilot studies, a reactor having a hydraulic residence time of 6.5 h and equipped with no sedimentation tank achieved 70–75% BOD and nitrogen removal, and produced an effluent containing less than 30 mg/l total suspended solids.