Development of novel low-cost sewage treatment system applicable to developing countries

由于缺乏基本的城市污水处理设施，大多数发展中国家的城市地区正面临着水环境的严重恶化。由于财政资源有限，确实需要一种符合成本效益的污水处理系统适当技术。在这种实际限制下，厌氧工艺可能是最有吸引力的污水处理，因为它具有优于传统好氧工艺的优点，例如不需要曝气和通过生物气生产回收能量。然而，厌氧过程具有一些弱点。厌氧工艺的出水水质往往不能与活性污泥工艺的出水水质相比。提出了一种新的UASB出水处理工艺，该工艺由UASB预处理单元和后续DHS（Downflow Hanging Sponge-curtains）反应器组成，无需外加曝气即可对UASB出水进行精处理。我们提出的系统安装在一个城市污水处理厂的网站，其可行性进行了评估，进行了长期的实验与实际污水作为饲料。整个系统不仅具有上级的有机物去除能力，而且在HRT为8小时的条件下具有良好的硝化作用。微生物分析和DO微电极测试结果表明，DHS反应器具有保持高密度生物量和良好的吸氧性能。在两年的整个实验期间内，在我们的系统中没有污泥排出。一个简单的模型解释了新系统中没有剩余污泥的产生。

Most of urban areas of developing countries are facing severe deterioration of aquatic environment due to shortage of facilities for basic municipal sewage treatment. Because of the limited financial resources, there is a definite need of a cost-effective appropriate technology for sewage treatment system. Under this practical constraint, anaerobic process could be the most attractive for sewage treatment, since it has advantages over conventional aerobic processes, in such points as no need of aeration and energy recovery benefit through bio-gas production. However, anaerobic processes possess some weak points. Effluent quality of anaerobic process is often not comparable with that from activated sludge process. That is why anaerobic process sometimes requires post-treatment for removal of residual organics and nutrients.A novel process, which consists of a UASB pre-treatment unit and the following DHS(Downflow Hanging Sponge-curtains)reactor for polishing up the UASB effluent without external aeration input, was proposed in this study. Our proposed system was installed at a municipal sewage treatment plant site, and its feasibility was evaluated by conducting a long-term experiment with actual sewage as a feed. The proposed whole system verified to perform not only superior organic removal but also excellent nitrification at an overall HRT of 8hrs. Microbial analysis and DO microelectrode showed that the DHS reactor had a function of retaining highly density biomass and excellent oxygen-uptake from atmosphere. Over the whole experimental duration of two years no sludge withdrawal was made in our system. A simple model accounted for no excess sludge production in the new system.