Study on Leachate Treatment of Chengdu Landfill Site

摘要

Chengdu Chang' an Landfill Site is a unique large landfill site for disposing municipal solid waste of Chengdu, the capital of Sichuan Province, China. The landfill site was constructed in complying with the national standard related to sanitary landfill of refuse. It receives 2400 tons of refuse generated from the urban area of the city every day. Phase I of the project covers an area of 836 mu (1 mu = 1/15 hectare) and has a volume of 11.35 million m~3. Since it put into operation in 1993, now only has a remaining volume for some 2 years. Thus the Chengdu Municipal Government approved to implement the Phase Two of the project to expand the volume of 25 million m~3. Phase II Project will put into operation in 2001 according to a plan. To treat leachate of landfill site is one of the important environmental problems in the process of landfill disposal. As municipal solid wastes contain higher organic matters (30% of the total in average, >50% at maximum) and higher water content, high concentration of organic wastewa-ter, i.e. leachate, will generate in the process of fermentation as well as leaching caused by rainfall or run-off. The leachate contains not only organic substances with dark color but also pathogenic bacteria and heavy metals (partially mixing with hazardous industrial wastes) . Such leachate will cause severe water pollution, harm human health and impact negatively on the environment, and damage agriculture production if it discharges directly to surface water bodies or groundwater body. The existing Project Phase I has a wastewater treatment station with a daily treatment capacity of 500 m~3. But it operates abnormally due to the variation of wastewater quantity and quality in comparison with initiate stage. The practical operation shows that the influent from the station greatly exceeds the related standard, and causes the pollution both in surface water and groundwater and affects health of the people living nearby. In order to solve the problem of leachate that affects the residents nearby, Chengdu Environmental Protection Bureau (CEPB) and Chengdu Research Institute of Environmental Protection (CRIEP) conducted a specific bench-scale test on leachate treatment based on the instruction given by Chengdu Municipal Government. On the basis of monitoring data on existing quality of leachate and some reference concerning treatment technology of leachate both home and abroad, and combining the concrete conditions of the city, biological process combined with physical and chemical processes was adopted. The proposed treatment is of a long technological process that consists of several modules, among which biological process is the main one. The study was conducted in a laboratory from March through July 1999. Based on the results gained from the bench-scale test, a pilot test was carried out at Chang'an Landfill site from August till December 1999. The results show that aerobic plus physico-chemical process is suitable for treating the leachate of the landfill site. Effluent from such treatment process can meet the requirements specified by Class B of the leachate discharge standard, Control Standard of Refuse Landfill Contamination, GB16889-1997, During January to September 2000, a further study was conducted to tackle the problem existing in pilot-scale test, acquiring some optimized parameters of technology. The scheme has an advantage of multi-module combination. That is, through different combination of modules, the treatment process can meet the requirements of different leachate and different discharge standard.