摘要
随着社会的发展，国家对城市污水排放的要求越来越高。为改善双沟镇的水体环境，使双沟镇的污水能够得到全面的收集和完善的处理，拟建设一污水处理厂，设计中污水厂服务的人口为近期5万人，远期11万人。设计管网服务的面积为1712.13公顷,工程总造价为10950.15万元。排水管网设计时，根据城镇的地形趋势，将整个城镇划分成了四个排水区域，然后通过提升泵站将各区的污水提升至污水处理厂。
污水厂设计规模为：近期2万吨/d，远期6万吨/d。设计进水水质为：悬浮物（SS）：239mg/L；五日生化需氧量（BOD5）：317mg/L；化学需氧量（CODcr）：221mg/L；总氮（TN）：32mg/L；总磷（TP）：4mg/L；氨氮（NH3-N）：30mg/L。设计出水标准达到《城镇污水处理厂污染物排放标准》（GB18918-2002）一级A标准，即：悬浮物（SS）≤10mg/L；五日生化需氧量（BOD5）≤10mg/L；化学需氧量（CODcr）≤50mg/L；总氮（TN）≤15mg/L；总磷（TP）≤0.5mg/L；氨氮（NH3-N）≤5mg/L。
为达到出水标准，本设计采用A2/O-MBR工艺处理双沟镇的污水。与传统活性污泥工艺相比，MBR对含碳有机物的去除有以下特点：去除率高，一般大于90%，出水达到回用水的指标；污泥负荷（F/M）低；所需水利停留时间（HRT）短，容积负荷高，刚冲击负荷能力强。而膜生物反应器用膜组件替代了传统的二沉池进行固液分离，由于膜的高截留率并将浓缩污泥回流到生物反应器内，而使生物反应器内具有很高的微生物浓度和很长的污泥停留时间，所以MBR法可以在比传统活性污泥法更短的水力停留时间内达到更好的去除效率。本设计的理念是利用MBR膜池代替传统工艺中的二沉池，在A2/O生物池对污水进行脱氮除磷的基础上，膜池达到进一步深度处理的效果。为解决出水中总磷的含量不太稳定的问题，在膜池的进水端进行加药除磷。
设计中主要构筑物包括粗格栅、提升泵房、细格栅、旋流式沉砂池、A2/O生物池、MBR膜池、接触消毒池、贮泥池、脱水机房等。市政污水管网收集的污水经中格栅拦截较大的悬浮物和漂浮物后，由污水泵房提升至细格栅和旋流式沉砂池去除比重较大的无机颗粒，在经过生物池脱氮除磷后再通过膜池对污水中剩余的有机物质及氮磷进一步降解去除，处理后的污水经氯消毒后排放。在整个处理工程中，污泥回流比为100%，其余的由污泥脱水机房浓缩脱水后外运。
在该处理工艺下，最终排放的污水达到国家一级A标准，符合设计要求。
关键词：污水处理，A2/O-MBR工艺,一级A标准
ABSTRACT
With the development of our society, the standard of the urban sewage discharge that the state requires are higher and high. To improve the environment shuanggou town ‘s water , collect this water comprehensively and deal with it comprehensively,the state plans to build a sewage treatment plant.In this design the wastewater treatment plant services a population of 5 million people recently and 11 million long-term . The pipe network services 1,712.13 hectares and the total cost of the project is 109.5015 million dorall. During the design of the pipe network, we divide the entire town into four drainage areas according to the urban terrain, and then upgrade the sewage to the sewage treatment plant by pump.
The design scale of this wastewater treatment plant is 20,000 tons / d for recent and 60,000 tons / d for long-term. Design quality of enter water are: suspended solids (SS): 239mg / L; the oxygen demand for biochemistry in the 5 days (BOD5): 317mg / L; oxygen demand for biochemistry in the 5 days (BOD5): 317mg / L; oxygen demand for chemistry (CODcr): 221mg / L; total nitrogen contents (TN): 32mg / L; total phosphorus contents (TP): 4.0mg / L; ammonia nitrogen contents (NH3-N): 30mg / L. The designed effluent standards can achieve to grade A standards ,which comes from "Municipal Wastewater Treatment Plant’s Emission Standards of Pollutant " (GB18918-2002).Namely: suspended solids (SS) ≤ 10mg / L; the oxygen demand for biochemistry in the 5 days(BOD5) ≤ 10mg / L; oxygen demand for chemistry (CODcr) ≤ 50mg / L; total nitrogen contents (TN) ≤ 15mg / L; total phosphorus contents (TP) ≤ 0.5mg / L; ammonia nitrogen contents (NH3-N) ≤ 5mg / L.
To achieve the effluent standards, the design uses A2/O-MBR Process to treat the urban sewage water of shuanggou . Compared with conventional activated sludge process, MBR process has the following characteristics on the removal of organic carbon :Removal rate is high that can be generally greater than 90% and the effluent water can reach the target of reuse water; sludge loading (F / M) is low; hydraulic retention time (HRT) that required is short. What’s more, it has high-volume load and strong –capability of shock load. Membrane Biological Reactor replaces the traditional secondary separation of solid with membrane in order to separate solid and liquid. As the film has high retention rate and it can return the concentrated sludge back to the bioreactor so that the bioreactor can have microorganism with high concentration and a long sludge retention time. Compared with conventional activated sludge process the MBR process can achieve better removal efficiency with shorter hydraulic retention time. The concept of this design is replacing the secondary settling tank in the traditional process with MBR membrane pool. On the basis of the A2 / O biological sewage pool’s removal for nitrogen and phosphorus, membrane pool has the further treatment function. To solve the problem that the content of total phosphorus in effluent is not stable, we add specific pharmaceutical to the intake department of membrane pool for removing phosphorus.
The main structures of the treatment process include medium bar screen, sewage pumping station, thin bar screen, Vortex-type grit chamber, A2 / O biological pool, MBR membrane pool, Chlorine concentration tank, Storage basins ，sludge dehydration shop etc. In preliminary treatment, the original water enters medium screening in order to remove heavy solids and floatable materials, in case that it influences the working of the following devices and the pipelines. Then it enters vortex-type grit chamber, which is used to remove bigger inorganic sand of heavy density after the wastewater is pumped into the thin screening. Afrer this the wastewater goes to the A2 / O biological pool for organics, nitrogen and phosphorus removal .Then the wastewater goes to MBR membrane pool for the remaining organic matter , nitrogen and phosphorus to treat deeply. At last the wastewater enters Chlorine concentration tank and is discharged.100% of sludge are recycled to the oxidation ditch and the rest are pumped to sludge dehydration shop to discharge after thickening and dehydration.
Under this process for wastewater treatment, the effluent standards can reach grade A.
Keywords: Sewage treatment, A2/O-MBR process，Grade A standards
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