Combined anaerobic/aerobic digestion: effect of aerobic retention time on nitrogen and solids removal

A combined anaerobic/aerobic sludge digestion system was studied to determine the effect of aerobic solids retention time (SRT) on its solids and nitrogen removal efficiencies. After the anaerobic digester reached steady state, effluent from the anaerobic digester was fed to aerobic digesters that were operated at 2- to 5-day SRTs. The anaerobic system was fed with a mixture of primary and secondary sludge from a local municipal wastewater treatment plant. Both systems were fed once per a day. The aerobic reactor was continuously aerated with ambient air, maintaining dissolved oxygen level at 1.1 +/- 0.3 mg/L. At a 4-day or longer SRT, more than 11% additional volatile solids and 90% or greater ammonia were removed in the aerobic digester, while 32.8 mg-N/L or more nitrite/nitrate also was measured. Most total Kjeldahl nitrogen removal was via ammonia removal, while little organic nitrogen was removed in the aerobic digester.     

Treatment of food industry waste by bench-scale upflow anaerobic sludge blanket-anoxic-aerobic system.

An upflow anaerobic sludge blanket (UASB)-anoxicaerobic system was used for treatment of tomato and bean processing wastewater. At various hydraulic retention times, ranging from 0.7 to 5 days, excellent removal of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total suspended solids (TSS), ammonia-nitrogen (NH4-N), and total Kjeldahl nitrogen was achieved with final effluent BOD/TSS/NH4N concentrations of less than 15/15/1 mg/L. Biogas yield in the UASB reactor varied from 0.33 to 0.44 m3/kgCODremoved. The kinetics of anaerobic treatment were investigated. The yield coefficient was 0.03 gVSS/gCOD; maximum specific growth rate was 0.24 day(-1); Monod half velocity constant was 135 mgCOD/L; and specific substrate utilization rate was 3.25 gCOD/gVSS x d. Nitrification and denitrification kinetics were studied in batch experiments, and the rates were comparable with those in the continuous flow system.     

Treatment of high-strength pet food wastewater using two-stage membrane bioreactors.

A two-stage membrane bioreactor was used to treat dissolved-air-flotation pretreated, high-strength pet food wastewater characterized by oil and grease concentrations of 50 000 to 82 000 mg/L and total chemical oxygen demand (COD) and five-day biochemical oxygen demand (BOD5) concentrations of 100 000 and 80 000 mg/L, respectively, to meet stringent surface discharge criteria (i.e., BOD5, total suspended solids [TSS], and ammonium-nitrogen [NH4(+)-N] of < 10 mg/L at an overall hydraulic retention time of 6.3 days). Organic contaminants were removed primarily in the first stage, followed by almost complete removal of ammonia in the second stage. Despite a rise in poorly biodegradable COD in the second stage, overall removal of TSS, BOD5, COD, and ammonia was 100, 99.9, 95.2, and 99.7%, respectively, thus readily achieving the required criteria. Consistent nitrite accumulation over a period of more than 100 days, even at dissolved oxygen concentrations of more than 2.5 mg/L, was remarkable. A residual alkalinity requirement for nitrification was quantified. Membrane performance was extensively studied in this work.     

Slaughterhouse wastewater treatment in a full-scale system with constructed wetlands.

This work evaluated the performance of a full-scale system with wetlands for slaughterhouse (abattoir) effluent treatment in the State of Hidalgo, México. The treatment system consisted of a primary sedimentation tank, an anaerobic lagoon, and a constructed subsurface-flow wetland, in series. The wetland accounted for almost 30% of the removal of organic matter. In general, the treatment system achieved satisfactory pollutant removals, but the final effluent could not meet the Mexican environmental regulations for fecal coliform counts, five-day biochemical oxygen demand (BOD5), and total suspended solids (TSS). Overall, removal levels were 91%, 89%, and 85% for BOD5, chemical oxygen demand, and TSS, respectively. However, BOD5 in the final effluent (137 mg/L) was higher than the maximum level of 30 mg/L allowed by the regulatory agency. Although organic nitrogen removal levels were approximately 80%, the nitrogen persisted in oxidation state -3 as ammonia-nitrogen, the removal of which was only 9% in the wetland stage. On average, phosphorus removal was null, and, on occasion, the phosphorus concentration in the treated effluent was higher than that of the influent. Coliform reductions in the overall system were high (on the order of 5 logs on average), whereas the coliform removal in the wetland was between 2 to 3.5 logs. The treatment system was also effective at removing pathogens (Vibrio cholerae, Salmonella, and Shigella). Further laboratory tests with the wetland effluent suggest that post treatment in a sand filter stage followed by disinfection with sodium hypochlorite (NaOCl) could help meet the Mexican discharge regulations, particularly the criteria for coliforms and total BOD5.     

改良型Carrousel氧化沟工艺生物脱氮除磷效果研究

为了提高改良型Carrousel氧化沟工艺污水处理厂的脱氮除磷效果,结合某污水处理厂3年的运行实践,讨论了该工艺的处理效果,生物脱氮除磷原理及影响出水效果的因素.分析表明将DO控制在0.3～0.7 mg/L范围内,能够使出水中的TN浓度低于20 mg/L;在氧化沟中发生的同步硝化反硝化反应(SND)对总氮的去除的贡献占总系统脱氮的66%;该系统剩余污泥的含磷率为3.0%,生物细胞中平均含磷量可达细胞干重的4.2%;总磷去除率与污泥龄具有很好的线性关系,加大污泥排放量可以提高除磷效果.     

Effect of operational parameters on the removal of particulate chemical oxygen demand in the activated sludge process.

The removal of particulate material in the aeration basin of the activated sludge process is mainly attributed to bioflocculation and hydrolysis of particulate substrate. The bioflocculation process in the aeration tank of the activated sludge process occurs only under favorable conditions in the system, and several common operational parameters affect its performance. The principal objective of this research was to observe the effect of mixed liquor suspended solids, solids retention time (SRT), and extracellular polymer substances on the removal of particulate substrate by bioflocculation. A first-order particulate removal expression, based on flocculation, accurately described the removal rates for supernatant suspended solids and colloidal chemical oxygen demand. Based on the results presented in this investigation, a mixed liquor concentration of approximately 2200 mg/L, an SRT of at least 3 days, and a contact time of 30 minutes are needed for relatively complete removal of the particulate substrate in a plug-flow reactor.     

Advanced extraction and lower bounds for removal of pollutants from wastewater by water plants.

The capacity to reach lower bounds for extraction of pollutants from wastewater by four floating aquatic macrophytes--water hyacinth (Eichhornia crassipes), water lettuce (Pistia stratiotes), salvinia (Salvinia rotundifolia), and water primroses (Ludvigia palustris)--is investigated. It is shown that the following lower bounds can be established for wastewater purification with water hyacinth: biochemical oxygen demand (BOD), 1.3 mg/L; chemical oxygen demand (COD), 11.3 mg/L; total suspended solids (TSS), 0.5 mg/L; turbidity, 0.7 NTU; ammonia, 0.2 mg/L; and phosphorus, 1.4 mg/L. Also, the following lower bounds can be established for wastewater purification with water lettuce: BOD, 1.8 mg/L; COD, 12.5 mg/L; TSS, 0.5 mg/L; turbidity, 0.9 NTU; ammonia, 0.2 mg/L; and phosphorus, 1.6 mg/L. These lower bounds were reached in 11- to 17-day experiments that were performed on diluted wastewater with reduced initial contents of the tested water quality indicators. As expected, water hyacinth exhibited the highest rates and levels of pollutant removal, thereby producing the best lower bounds of the water quality indicators. Given the initially low levels, BOD was further reduced by 86.3%, COD by 66.6%, ammonia by 97.8%, and phosphorus by 65.0% after 11 days of a batch experiment. The capacity of water plants to purify dilute wastewater streams opens new options for their application in the water treatment industry.     

Ammonia removal from facultative pond effluents in a constructed wetland and an aerated rock filter: performance comparison in winter and summer.

The effluent from a facultative pond loaded at 80 kg BOD ha(-1) day(-1) was treated in a subsurface horizontal-flow aerated rock filter (RF) and a subsurface horizontal-flow constructed wetland (CW) planted with Typha latifolia. Over a 12-month monitoring period BOD and TSS removals were higher, and effluent ammonia concentrations lower, in the RF than in the CW (> 75% vs. 25-75%, and 3.6 mg N L(-1) vs. 6 mg N L(-1), respectively). However, the ammonia concentration was lower in the CW effluent than in the aerated RF effluent during mid-July to mid-September (1.1 mg N L(-1) vs. 2.2 mg N L(-1)), but in winter it was higher than the influent concentration. Overall the performance of the aerated RF was better and more consistent than that of the CW.     

固定化菌藻系统对污水处理厂出水的深度处理

将海藻酸钠固定化活性污泥和小球藻制成颗粒小球,以自制的流化床反应器对重庆市某污水处理厂出水进行深度处理,探讨了系统对氨氮、TP、COD的去除效果,实验结果表明:在HRT=12 h,溶解氧浓度为3.0 mg/L左右,pH值为6.2至8.0之间,环境室温条件下,系统对氨氮、TP、COD均有较好的去除效果,系统稳定运行后对氨氮、TP、COD去除率基本维持在60%、60%和30%以上,出水氨氮、TP、COD浓度基本维持在8、0.5和40 mg/L以下,出水浓度达到了《城镇污水处理厂污染物排放标准》(GB 18918-2002)的一级A标准。这项研究显示固定化菌藻胶球系统在污水处理厂出水的深度处理中具有潜在的应用前景。     

Optimization of circular plate separators with cross flow for removal of oil droplets and solid particles

A circular gravity-phase separator using coalescing medium with cross flow was developed to remove oil and suspended solids from wastewaters. Coalescence medium in the form of inclined plates promotes rising of oil droplets through coalescence and settling of solid particles through coagulation. It exhibits 22.67% higher removal of total suspended solids (TSS) compared to separators without coalescing medium. Moreover, it removed more than 70% of oil compared to conventional American Petroleum Institute separators, which exhibit an average of 33% oil removal. The flowrate required to attain an effluent oil concentration of 10 mg/L (Q(o10)) at different influent oil concentrations (C(io)) can be represented by Q(o10) x 10(-5) = -0.0012C(io) + 0.352. The flowrate required to attain an effluent TSS concentration of 50 mg/L (Q(ss50)) at different influent TSS concentrations (C(iss)) can be represented by Q(ss50) x 10(-5) = 1.0 x 10(6) C(iss)(-2.9576). The smallest removable solid particle size was 4.87 microm.     

低温条件下硝化污泥的驯化

为了在低温13～14％下取得较好的硝化效果，分3个温度阶段25℃，16～17℃，13—14℃对活性污泥进行了驯化培养，研究了进水氨氮浓度和混合液COD对硝化污泥的影响。实验结果表明，硝化污泥经过驯化培养后，氨氮去除率可达80％以上，且在DO浓度为2ing／L，pH为6．7～7．5，进水氨氮为300mg／L，混合液COD为80mg／L条件下，硝化污泥能取得较快的增长，氨氮平均去除率可达89％。     

Degradation of 2,4-dichlorophenol by combining photo-assisted Fenton reaction and biological treatment.

The photo-Fenton reaction effect on the biodegradability improvement of 100 mg/L solution of 2,4-dichlorophenol (DCP) has been investigated. Biochemical oxygen demand (BOD) at 5 and 21 days, BODn/ chemical oxygen demand (COD) and BODn/total organic carbon (TOC) ratios, average oxidation state, and inhibition on activated sludge were monitored. For 50 mg/L hydrogen peroxide and 10 mg/L iron(II) initial concentrations and 40 minutes of reaction time in the photo-Fenton process, the biodegradability of the pretreated solution, measured as BOD5/COD ratio, was improved from 0 for the original DCP solution up to 0.18 (BOD21/COD = 0.24). At that point, all DCP was eliminated from the solution. To study the effect of the pretreatment step, the biological oxidation of pretreated solutions was tested in two semicontinuous stirred tank reactors, one operated with activated sludge and one with biomass acclimated to phenol. Results showed that more than 80% TOC removal could be obtained by codigestion of the pretreated solution with municipal wastewater. Total organic carbon removals of approximately 60% were also obtained when the sole carbon source for the aerobic reactors was the pretreated solution. The hydraulic retention times used in the bioreactors were of the same order of magnitude as those used at domestic wastewater treatment plants (i.e., between 12 and 24 hours). Kinetic studies based on pseudo-first-order kinetics have also been carried out. Constants were found to be in range 0.67 to 1.7 L x g total volatiles suspended solids(-1) x h(-1).     

Petroleum refinery stripped sour water treatment using the activated sludge process

A pilot study was performed over 91 days to determine if the activated sludge process could treat a segregated stripped sour water (SSW) stream from a petroleum refinery. The study was performed in two periods. The first period was terminated after 19 days, as a result of excessive sludge bulking. The elimination of sludge bulking during the 70-day second period is attributed to operational changes, which included aerating the influent to oxidize reduced sulfur, adjusting the influent pH, and adding micronutrients to satisfy biological requirements. The pilot plant provided a chemical oxygen demand (COD) removal of up to 93%. Nitrification was achieved, with effluent ammonia values < 1 mg-N/L. These results indicate that direct treatment of SSW with the activated sludge process is possible and has direct application to full-scale petroleum refinery wastewater plant upgrades.     

Activated sludge deflocculation in response to chlorine addition: the potassium connection.

Chlorination is often used to control filamentous bulking in activated sludge systems. Pure culture and mixed-liquor experiments showed that soluble potassium (K+) concentrations increased by 2.4 mg/L (80%) and 1.5 to 3.6 mg/L (11 to 30%) in the bulk liquid phase of pure and activated sludge cultures that were exposed to chlorine, relative to unchlorinated controls. Effluent turbidity and total suspended solids from settled mixed liquor increased significantly in both short-term batch and sequencing batch reactor experiments when chlorine mass load increased above 6 milligrams of chlorine per gram mixed liquor volatile suspended solids (mg Cl2/g MLVSS) in a single dose, which correlated with a localized chlorine concentration at the dose point of 10 mg/L as Cl2 or greater. The results support the hypothesis that the glutathione-gated potassium efflux (GGKE) bacterial stress response may contribute to increased effluent turbidity associated with high doses of mixed-liquor chlorination. It is suggested that potassium is a useful parameter to monitor at full-scale facilities when determining chlorine mass doses that should be used to control filaments and minimize increases in effluent turbidity.     

不同运行模式对同步脱氮除磷CAST工艺快速启动及其稳定维持的影响

以实际生活污水为处理对象,考察了传统进水/曝气和改良型分段进水的交替缺氧-好氧(A/O)2种运行模式对CAST工艺的快速启动及脱氮除磷性能稳定维持的影响。结果表明,传统进水/曝气运行模式下,系统达到最佳营养物去除性能所需启动时间30 d,稳定运行阶段TN平均去除80.66%,磷的去除率维持在66.30%左右;采用改良型交替运行模式,反应器达到稳定运行状态仅需18 d,系统稳定运行时TN平均去除81.36%,磷去除率稳定维持在90%以上,出水磷浓度在0.3 mg/L以下,出水水质达到国家污水综合排放标准一级A(GB8978-2002)。研究还发现,传统运行模式下,由低温引起的污泥沉降性能变差导致系统污泥严重流失,反应器几乎丧失污染物去除性能;而低温对交替运行模式下的反应器除磷性能几乎没有影响,总氮去除则因氨氮不完全硝化而大大降低。     

低温下ZCS工艺和改进式ZCS工艺脱氮效率研究及微生物特性分析

考察冬季低温下沸石联合生物吸附再生工艺和改进式沸石联合生物吸附再生工艺对城市污水的脱氮效率,结果表明在HRT为3.5 h下,ZCS工艺出水氨氮为11.65 mg/L,总氮高于20 mg/L.而相同条件下MZCS工艺氨氮出水为5.45 mg/L,总氮去除率比原ZCS工艺提高了11%,均值为16.8 mg/L.通过聚合酶链式技术,变性梯度凝胶电泳和电镜扫描技术发现两工艺微生物多样性、丰度高于传统活性污泥法,兼具活性污泥法和生物膜法的微生物特性.     

高氨氮污泥脱水液短程硝化反硝化的启动及稳定

采用A/O-CSTR工艺处理高氨氮污泥脱水液。进水氨氮浓度浓度约为375 mg/L，C/N比小于1.0，反硝化碳源明显不足。A/O反应器完成短程硝化反应，CSTR定期投加初沉污泥作为碳源进行反硝化。两者联合达到总氮去除的目的。实验研究短程硝化反应的启动过程，以及CSTR出水回流对短程硝化和系统脱氮效果的影响。实验结果表明系统具有良好的硝化反硝化效果。A/O反应器亚硝酸盐积累率迅速提高并稳定在90%以上。CSTR有效利用初沉污泥实现了稳定的反硝化。出水回流有利于提高总氮去除率，在回流比为200%时，系统平均总氮去除率达到85%以上。     

Removal of organic and nitrogen and molecular weight distribution of residual soluble organic from entrapped mixed microbial cells and activated sludge processes.

The simultaneous removal of organic and nitrogen and molecular weight distribution (MWD) of residual soluble chemical oxygen demand (RSCOD) in final effluent were investigated using entrapped mixed microbial cells (EMMC) and conventional activated sludge processes. Two different types of processes using EMMC carriers demonstrated better organic and nitrogen removal performance because of the high solids retention time (SRT) compared with the activated sludge process. Regarding the RSCOD, the longer SRT process (EMMC) was affected by reducing the hydraulic retention time, resulting in the increase of high-molecular-weight materials. On the other hand, reducing the aeration period had significantly affected the MWD in the shorter SRT process (activated sludge), resulting in an increase of low-molecular-weight materials.     

Carbon and nutrient removal from on-site wastewater using extended-aeration activated sludge and ion exchange.

The need to improve on-site wastewater treatment processes is being realized as populations move into more environmentally sensitive regions and regulators adopt the total maximum daily load approach to watershed management. Under many conditions, septic systems do not provide adequate treatment; therefore, advanced systems are required. These systems must remove significant amounts of biochemical oxygen demand (BOD) and suspended solids, and substantially nitrify, denitrify, and remove phosphorus. Many existing advanced on-site wastewater systems effectively remove BOD, suspended solids, and ammonia, but few substantially denitrify and uptake phosphorus. The purpose of this research was to design and test modifications to an existing on-site wastewater treatment system to improve denitrification and phosphorus removal. The Nayadic (Consolidated Treatment Systems, Inc., Franklin, Ohio), an established, commercially available, extended-aeration, activated sludge process, was used to represent a typical existing system. Several modifications were considered based on a literature review, and the option with the best potential was tested. To improve denitrification, a supplemental treatment tank was installed before the Nayadic and a combination flow splitter, sump, and pump box with a recirculation system was installed after it. A recirculation pump returned a high proportion of the system effluent back to the supplemental treatment tank. Two supplemental treatment tank sizes, three flowrates, and three recirculation rates were tested. Actual wastewater was dosed as brief slugs to the system in accordance with a set schedule. Several ion-exchange resins housed in a contact column were tested on the effluent for their potential to remove phosphorus. Low effluent levels of five-day biochemical oxygen demand, suspended solids, and total nitrogen were achieved and substantial phosphorous removal was also achieved using a 3780-L supplemental treatment tank, a recirculation ratio of 5:1, and a fine-grain activated aluminum-oxide-exchange media. Good results were also obtained with an 1890-L supplemental treatment tank and a recirculation ratio of 3:1. The most significant benefit of the supplemental treatment tank, in combination with the recirculation system, appears to be the low nitrogen concentration dosed to the Nayadic. By reducing the nitrogen concentration and spreading out its mass over time during no-flow periods, the Nayadic's inherent low-level denitrifying capacity was more closely matched and effective treatment was achieved.     

A／O-MBR工艺处理校园生活污水中水回用工程的设计与运行

针对Et处理量为1500m3的高校中水处理设施，论述了缺氧／好氧-MBR（A／O—MBR）处理工艺运行特性，完成了长效监测及经济性评价。系统MBR池污泥浓度（MLSS）控制在8～12g／L，缺氧池和好氧池水力停留时间（HRT）分别为3h和7h，污泥回流比为200％～300％。当进水COD、总氮、氨氮平均浓度分别为481．3、75．1和65．8mg／L时，出水COD、总氮、氨氮平均浓度分别为16．5、13．4和0．7mg／L，平均去除率分别为96．4％、81．9％和99．0％。在进行化学除磷的情况下，出水总磷的平均浓度为0．8mg／L，平均去除率86．5％。出水水质优于《城市污水再生利用城市杂用水水质》（GB／T18920—2002）中的相应水质指标要求。经济性分析结果显示，该中水站的电耗为0．58kWh／m3。