Sludge settling processes in SBR-related sewage treatment plants according to the Biocos method.

This paper describes the investigations in a sedimentation and circulation reactor (SU-reactor) of a three-phase Biocos plant. The aim of these investigations was the determination of the temporal and depth-dependent distribution of suspended solid contents, as well as describing the sludge sedimentation curves. The calculated results reveal peculiarities of the Biocos method with regard to sedimentation processes. In the hydraulically uninterrupted (pre-)settling phase, a sludge level depth was observed, which remained constant over the reactor surface and increased linearly according to the sludge volume. The settling and the thickening processes of this phase corresponded to a large extent to the well-known settling test in a one-litre measuring cylinder. During the discharge phase, the investigated settling rate was overlaid by the surface loading rate and the sludge level changed depending on the difference between those two parameters. The solid distribution of the A-phase indicated a formation of functional zones, which were influenced by the surface loading. The formation was comparable to the formation of layers in secondary settling tanks with vertical flow. The concentration equalisation between the biological reactor and the SU-reactor proved to be problematic during the circulation phase, because a type of internal sludge circulation occurred in the SU-reactor. A permanent sludge recirculation seems to be highly recommendable.     

Removal of endocrine-disrupting chemicals by ozonation in sewage treatment.

Treatment experiments by two laboratory scale semi-batch reactors and a demonstration scale process were both carried out to evaluate endocrine disrupting chemical removal characteristics by ozonation in sewage treatment. In the semi-batch mode experiments, secondary effluent and primary effluen of sewage treatment plants were ozonated respectively. Behaviour of brominated by-products was also evaluated. The results based on these studies indicated that estrogenicity in wastewater can be removed by ozonation effectively. The condition of ozonation until dissolved ozone concentration increased to 0.1 mg/L, which corresponded to 1 mgO3/mgC and 0.4 mgO3/mgC of ozone consumption per initial DOC for secondary effluent and primary effluent, respectively, is proposed as an appropriate operational condition for efficient removal of EDCs as well as UV254 and SUVA without production of brominated by-products.     

Phosphorus recycling in sewage treatment plants with biological phosphorus removal.

In this paper, phosphorus balances are calculated for the wastewater purification and sludge treatment stages for wastewater treatment plants (WWTPs) applying Enhanced Biological Phosphorus Removal (EBPR). The possible P-recovery potential is then estimated and evaluated regarding different locations along the process of wastewater purification and sludge treatment, taking the different phosphorus bonding forms into account. Caused by the more favourable bonding forms in the excess sludge as well as possibly also in the sludge ash a recovery of the phosphorus seems especially favoured for WWTPs with EBPR. The processes available for a P recycling are named, and special regard is given to the Phostrip-process, which is a possible recycling process already tested in practice. Further R&D demand consists in basic research regarding disintegration, fermentation or acidic total digestion of excess sludge followed by phosphorus precipitation including separation of the precipitates, MAP-precipitation and separation from digested sludge and on the ability to extract phosphorus and heavy metals from sewage sludge ash. These investigations are a precondition to enable purposeful process developments. At the present state the cost of recycled phosphorus earned from wastewater, sludge and ash, respectively, are a multiple higher than the costs for raw phosphate taking into account the suitable processes. Thus, up to now no phosphorus recycling with a defrayal of costs is possible. The future importance of phosphorus recycling will depend on the market price for raw phosphate, the recycling costs and, furthermore, on the general political framework.     

Integrated odour modelling for sewage treatment works.

Odours from sewage treatment works are a significant source of environmental annoyance. There is a need for tools to assess the degree of annoyance caused, and to assess strategies for mitigation of the problem. This is the role of odour modelling. Four main stages are important in the development of an odour problem. Firstly, the odorous molecules must be formed in the liquid phase. They must then transfer from the liquid to the gaseous phase. They are then transported through the atmosphere to the population surrounding the odour source, and are then perceived and assessed by that population. Odour modelling as currently practised tends to concentrate on the transportation of odorants through the atmosphere, with the other areas receiving less attention. Instead, odour modelling should consider each stage in an integrated manner. This paper describes the development of integrated odour models for annoyance prediction. The models describe the liquid-phase transformations and emission of hydrogen sulphide from sewage treatment processes. Model output is in a form suitable for integration with dispersion models, the predictions of which can in turn be used to indicate the probability of annoyance. The models have been applied to both hypothetical and real sewage treatment works cases. Simulation results have highlighted the potential variability of emission rates from sewage treatment works, resulting from flow, quality and meteorological variations. Emission rate variations can have significant effects on annoyance predictions, which is an important finding, as they are usually considered to be fixed and only meteorological variations are considered in predicting the odour footprint. Areas for further development of integrated odour modelling are discussed, in particular the search for improved links between analytical and sensory measurements, and a better understanding of dose/response relationships for odour annoyance.     

Energy saving system with high effluent quality for municipal sewage treatment by UASB-DHS

An up-flow anaerobic sludge blanket (UASB) - down-flow hanging sponge (DHS) was applied to Japanese municipal sewage treatment, and its treatability, energy consumption, and sludge production were evaluated. The designed sewage load was 50 m(3)/d. The sewage typically had a chemical oxygen demand (COD) of 402 mg/L, a suspended solids (SS) content of 167 mg/L, and a temperature of 17-29 °C. The UASB and DHS exhibited theoretical hydraulic retention times of 9.7 and 2.5 h, respectively. The entire system was operated without temperature control. Operation was started with mesophilic anaerobic digested sludge for the UASB and various sponge media for the DHS. Continuous operational data suggest that although the cellulose decomposition and methanogenic process in the UASB are temperature sensitive, stable operation can be obtained by maintaining a satisfactory sludge volume index and sludge concentration. For the DHS, the cube-type medium G3-2 offers superior filling rates, biological preservation and operational execution. The SS derived from the DHS contaminated the effluent but could be removed by optional sand filtration. A comparison with conventional activated sludge (CAS) treatment confirmed that this system is adequate for municipal sewage treatment, with an estimated energy requirement and excess sludge production approximately 75 and 85% less than those of CAS, respectively.     

MBR处理生活污水的效果研究

采用设计流量为120 m3/d的一体式膜生物反应器处理北京某小区的生活洗涤废水,出水回用于该小区冲厕.通过3个月的水质监测结果表明:工艺出水稳定,水质良好,无色无味,CODCr≤50 mg/L,BOD5≤10 mg/L,TN≤10 mg/L,TP≤1 mg/L,细菌总数≤100个/L,符合<城市污水再生利用城市杂用水水质(GB/T 18920-2002)的要求.整个系统的抗冲击负荷能力强,其容积负荷为0.38～2.23 kgCODCr/(m2·d),污泥负荷在0.08～1.48 kgCODCr/(kgVSS·d).     

Dynamics in maximal settling capacity in an activated sludge treatment plant with highly loaded secondary settlers.

Secondary settling dynamics at maximal capacity were investigated at a full scale wastewater treatment plant which utilizes a unique process solution incorporating pre-denitrification with post-nitrification in nitrifying trickling filters. Since nitrogen removal is greater when more secondary effluent is recirculated to the trickling filters, the secondary settlers generally operate at close to their maximal capacity. The settling and flocculation properties of the activated sludge are therefore a major capacity-determining factor for plant operation. Due to the short sludge age, the flocculation properties, with respect to both thickening and clarification, can change quickly. The dynamics in these changes were studied and the factors that determine the maximal settling capacity were assessed. Solids flux curves were constructed from batch settling tests and compared with the actual maximal settling capacities.     

改进型合并净化槽处理生活污水的影响因素

通过设置改性复合填料和微电解铁屑床对合并净化槽进行工艺改进,采用厌氧(缺氧)好氧(A2/O)工艺处理生活污水。为优化该装置处理生活污水的效果,分别选取水力停留时间、有机负荷、污泥回流比作为运行条件进行试验室中试研究。结合试验结果和经济效益,得出最佳运行条件:水体停留时间为8 h,此时系统对COD、TN和TP的去除率分别为95%、63%8、7%;COD有机负荷为2.7 g/(L.d),该条件下出水COD、TN和TP平均去除率分别可达到90%、74%、88%;污泥回流比为75%,此时净化槽出水COD、TN和TP平均去除率分别达到95%、70%、94%。     

梯田式人工湿地处理生活污水的初步研究

针对山丘坡地的自然环境特点,提出构建梯田式人工湿地处理生活污水的方法,并通过实验装置对梯田式人工湿地处理生活污水的效果进行了初步研究。结果表明:当CODCr、NH4+-N、TP的进水质量浓度变化范围在182.3~286.7 mg/L、32.91~59.28 mg/L、1.23~3.05 mg/L时,其平均去除率分别为86.52%、80.5%、96.16%,出水质量浓度分别低于30mg/L、10mg/L、0.1mg/L;湿地基质中硝化菌、反硝化菌数量变化范围分别为1.5万~420万MPN/g、30万~1 860万MPN/g。与常规人工湿地相比,梯田式人工湿地具有较强的污染物去除能力,特别是具有高效的脱氮除磷效果。     

Evaluation of virological quality of sewage from four biological treatment plants by a nested-PCR technique.

In order to determine the virological quality of sewage from four biological treatment plants in Greece (two in the city of Athens and two in the city of Patras), 92 raw sewage samples were analysed for the presence of enteroviruses and adenoviruses during the period from October 2000 to February 2003. A nested-PCR method was used in order to increase the sensitivity of virus detection. Enteroviruses were detected in 43 samples (47%) and adenoviruses in 75 samples (81.5%) of raw sewage by nested PCR. The more frequent isolation of adenoviruses in raw sewage indicated their stability as virological indicators of the pollution of the environment and their increased persistence in sewage.     

Simultaneous treatment of sewage sludge and food waste by the unified high-rate anaerobic digestion system.

This study aimed to evaluate the performance of the unified high-rate anaerobic digestion (UHAD) system treating co-substrate of sewage sludge and food waste. A 24-hr operating sequence consisted of four steps including fill, react, settle, and draw. The effects of co-substrate and organic loading rate (OLR) on the performance were investigated to verify the system applicability. In each OLR, the UHAD system showed higher CH4 recovery (> 70%), CH4 yield (0.3 L CH4/g VSadded) and CH4 production rate (0.6 L CH4/L/d) than the control system. In the specific methanogenic activity (SMA) tests on thermophilic biomass of the UHAD system, the average SMA of acetate (102 mL CH4/gVSS/d) was much higher than those of butyrate (85 mL CH4/g SS/d) and propionate (42 mL CH4/gVSS/d). It was demonstrated that the UHAD system for co-digestion resulted in higher methane yield and methane production rate due to sequencing batch operation, thermophilic digestion, and co-digestion. The enhanced performance could be attributed to longer retention time of active biomass, faster hydrolysis, higher CH4 conversion rate, and balanced nutrient conditions of co-substrate in the UHAD system. Consequently, this optimized unification could be a viable option for the simultaneous treatment of two types of OFMSW with high stability.     

稳定塘污水处理技术的研究进展

总结了稳定塘中有机物、氮、磷的去除机理,稳定塘中的有机物主要通过微生物降解、有机物吸附、有机颗粒的沉降和截滤作用去除;硝化/反硝化、水生植物吸收、NH3挥发这3个过程为TN的主要去除机制;磷的去除涉及底泥对PO43-的吸附/解吸、有机磷氨化、磷的扩散、水生植物吸收等多种机制的共同作用。介绍了新型稳定塘技术以及塘与传统生物法组合、各类塘型组合工艺。指出今后的稳定塘将朝着强化机理、提高效率、完善设施、塘型优化组合方向发展。     

移动式污水处理系统应用于分散生活污水的试验研究

针对分散型生活污水量小面广的特点,开发出移动式污水处理系统,系统由生化预处理池和车载式移动污水处理设备组成.中试结果表明,采用该组合工艺,出水CODCr＜40 mg/L,BOD5＜10 mg/L,TP＜0.5 mg/L,TN＜10 mg/L,NH3-N＜1 mg/L,其平均去除率分别达到86.69%,94.89%,89.40%,74.35%和97.89%.出水指标均能达到＜城镇污水处理厂污染物排放标准＞(GB 18918-2002)一级A排放标准.     

Adapting UASB technology for sewage treatment in Palestine and Jordan.

High rate anaerobic technologies offer cost-effective solutions for "sewage" treatment in the temperate climate of Palestine and Jordan. However, local sewage characteristics demand amendments to the conventional UASB reactor design. A solution is found in a parallel operating digester unit that stabilises incoming solids and enriches the UASB sludge bed with methanogenic activity. The digester operational conditions were assessed by operating eight CSTRs fed with primary sludge. The results showed a high degree of sludge stabilization in the parallel digesters at SRTs>or=10 and 15 days at process temperatures of 35 and 25 degrees C, respectively. The technical feasibility of the UASB-digester combination was demonstrated by continuous flow pilot-scale experiments. A pilot UASB reactor was operated for 81 days at 6 hours HRT and 15 degrees C and was fed with raw domestic sewage. This period was subsequently followed by an 83 day operation period incorporating a parallel digester unit, which was operated at 35 degrees C. The UASB-digester combination achieved removal efficiencies of total, suspended, colloidal and dissolved CODs of respectively 66, 87, 44 and 30%. Preliminary model calculations indicated that a total reactor volume of the UASB-digester system corresponding to 8.6 hours HRT might suffice for sewage treatment in Palestine.     

ABR—好氧组合工艺对农村生活污水处理效果研究

研究了厌氧折流板反应器(ABR)分别与跌水曝气和曝气生物滤池组合工艺对农村生活污水中COD_(Cr)和氨氮的去除效果,并对两种组合工艺去除效果进行了比较。结果表明:采用ABR—好氧组合工艺处理生活污水,COD_(Cr)的平均去除率基本上稳定在84.2%左右,这说明生活污水经过ABR厌氧反应器和好氧处理后,能有效去除污水中的有机物;在后续好氧段,采用跌水曝气作为后处理,COD_(Cr)去除率比单独采用ABR提高了9.5%,采用曝气生物滤池作为后处理,COD_(Cr)去除率提高了24.9%,与ABR—跌水曝气相比,采用ABR—曝气生物滤池去除COD_(Cr)的效果较好;ABR—好氧组合工艺对氨氮的去除效果较差,达不到理想的去除效果。     

采用不确定性因素决策法确定污水处理厂布局

随着城市的不断发展,污水处理厂的规模、承受的负荷也不断增大,对小区域污水处理厂布局方案进行优化选择已越来越重要。利用不确定性多属性决策对其进行选择,既省去了烦琐的计算步骤,又减少了决策者在决策过程中承担的风险,具有较高的实用价值。     

Cost-effective solutions for sewage treatment in developing countries--the case of Brazil.

Cost-effective solutions are a must in developing countries, not only regarding investment costs, but also in respect to technology and operating practices. With these two goals in mind, in Brazil a particular effort has been directed for the development and application of the Chemical Enhanced Primary Treatment (CEPT) process and of the Upflow Anaerobic Sludge Blanket (UASB) process, both followed by complementary secondary treatment. Both technologies are under current expansion in Brazil. Large CEPT plants have been designed and built, up to 3.7 m3/s average design flow, as well as large UASB reactors, up to 3.0 m3/s average design flow. The applied technologies are cost-effective: they present low investment and efficiencies of BOD removal of up to 50% to 70%. They allow the plant construction in steps, an initial phase with efficiency over the usual primary treatment, and in order to achieve best effluent quality and meet legal water quality standards, a logic upgrade post-treatment can later on be implemented. The higher initial reduction of BOD and TSS also permits savings in construction and operational costs of secondary treatment, due to lower organic load and lower energy consumption. Sludge represents a particular point of attention: in the cases when the CEPT was used, Chemical Stabilisation of the Sludge (CSS) has also been practiced, eliminating the high construction costs of the digesters, all the plant staying chemically operated. In the cases when the UASB is used preceding secondary treatment, sludge can easily return to the anaerobic vessel, the costly sludge digestion unit being avoided. UASB reactors have practically no equipment in the anaerobic vessel, no energy consumption, low sludge production, and when applied in hot climates as in Brazil, heating devices are not required. The Brazilian experience, some particular cases, special comments on design and different secondary treatment processes are presented in this paper, as a contribution to the discussion of cost and benefits, a prime point to be considered.     

Disinfection of sludge using lime stabilisation and pasteurisation in a small wastewater treatment plant.

Removal efficiency of faecal coliforms and helminth eggs was evaluated in a small wastewater treatment plant (WWTP) serving a population of 1,000. This system was formed by the association in series of a UASB reactor and four submerged aerated biofilters. The density of faecal coliforms and the count of helminth eggs were estimated in the liquid and solid phases of the system. Two different methods of disinfecting sludge were investigated: (a) chemical treatment with lime and (b) a physical treatment by pasteurisation. As expected, the association UASB + BF was very efficient at removal of helminth eggs from the final tertiary effluent, but coliforms were still present at high densities. Lime treatment and pasteurisation of sludge were very effective methods of disinfection and produced a sludge safe for final disposal.     

Nutrient reduction evaluation of sewage effluent treatment options for small communities.

Small communities that are sewered by either package sewage treatment plants or on-site sewerage facilities are finding that the ground and surface waters are being contaminated. Nitrogen, which typically is not removed in these conventional systems, is a major concern. This project evaluated the capability of four sewage treatment technologies to reduce the amount of nitrogen being discharged in the effluent to the receiving environment. The four sewage treatment processes evaluated include a recirculating sand filter, biofilter, slow sand filter and constructed subsurface flow wetland. These processes were evaluated for their capability to reduce nitrogen, phosphorus, BOD5 and TSS. The primary objective of the project was to evaluate the capability of these treatment processes to reduce nitrogen using biological processes nitrification and denitrification. This paper reports on the performance of these processes to reduce nitrogen. The study demonstrated that the biofilter was capable of removing from a primary treated influent 40% of the total nitrogen. For the same quality influent the recirculating sand filter was capable of removing 35% of the total nitrogen. Secondary treated effluent was fed to the slow sand filter and the subsurface flow wetland. There was a 52% reduction in total nitrogen through the wetland however there was virtually no reduction in total nitrogen through the slow sand filter.     

Strategy for olive mill wastewater treatment and reuse with a sewage plant in an arid region.

This study was conducted to evaluate the treatability of OMW (olive mill wastewater) with sewage and sewage sludge, which could supplement nutrients and microbes required for OMW treatment and reduce its possible toxicity. The amount of OMW added to an aeration tank was based on the loading difference between the designed and actual COD loads, while the amount added to anaerobic digestion for energy recovery was determined by CH4 production. The COD removal efficiencies were 70-85% for both systems. Compost of OMW with dried sewage sludge also showed a similar temperature profile without OMW addition. This strongly suggested that OMW can be treated at a sewage plant without pretreatment and the treated effluent can be reused in irrigation for an arid region.