Application of urban wastewater treatment techs

A research report of Sino-Africa wastewater treatment cooperation was released by Beijing Municipal Research Institute of Environmental Protection and Tongji University, to explore the possible wasterwater treatment technology transfer mechanism between China and African countries.

The selection of urban wastewater treatment process mainly considers economic performance, technical performance, environmental performance and social performance. From the point of view of economic performance, when the treatment capacity is less than 100,000 m3/day, infrastructure costs of SBR and oxidation ditch series are significantly lower than that of conventional activated sludge process and A2/O process.

The smaller the capacity, the greater the advantage. Besides, secondary sedimentation tank attached to the process of oxidation ditch series will increase infrastructure investment. Infrastructure investment costs of wastewater treatment plant with biofilter technology are slightly higher than that of SBR process, the structure of BAF is more complicated with deeper depth, so the earthwork workload is large. Activated sludge process has obvious capacity effect. Unit treatment cost of small-capacity wastewater treatment plant can be 40% higher than that of large-capacity treatment plant. SBR series and oxidation ditch process has the advantage of simple process, few equipment, lower energy consumption than conventional activated sludge process, A/O and A2/O.

From the technical performance perspective, the process mentioned can remove carbon-containing organic pollutants effectively with the treated effluent meeting standards demanded by the state. A2/O, SBR series, oxidation ditch series have relatively good nitrate and phosphorus removal effect. Phosphorus removal with A2/O and SBR series is better than that with oxidation ditch series; however, while denitrification effect with oxidation ditch series is slightly better than with SBR series. Phosphorus removal performance is poor with biofilter process, and usually requires chemical phosphorus removal supplement to meet phosphorus standards in the effluent. For areas which reuse the treated effluent for agriculture or watering plants rather than discharge to a water environment, this nutrient removal may not be necessary.

From the environmental performance point of view, the amount of excess sludge from biological filter and oxidation ditch series is lower than that of SBR series. The land occupation of natural treatment system is the largest among the technologies. As there is no primary sedimentation tank and sludge digesters, the land occupation of SBR series and biofilter process is lower than that of conventional activated sludge process such as A/O and A/A/O process.

From the point of view of simple operation and management, process units of SBR series and oxidation ditch series are 50% less than that of conventional activated sludge process. Besides, resistance to shock loading capacity of SBR, oxidation ditch process and biofilter series is a robust process and relatively stable operation, which is suitable for areas where there is shortage of skill professionals.