A PRODUCTION-SCALE ECOLOGICAL ENGINEERING FOREST SYSTEM FOR THE TREATMENT AND REUTILIZATION OF MUNICIPAL WASTE-WATER IN THE INNER-MONGOLIA,CHINA

This paper introduces the first production-scale ecological engineerin g slow-rate infiltration land treatment system (SR-LTS) with dominant covering vegetation of forest for the treatment and reutilization of w astewater in China. Vegetation includes larch (Larix principis rupprec hetii Mayr.), pine (Pinus sylvestris L. var mongolica Litv.) and popla r (Populus xoeichenesis Bal Lin II) besides primary grasses growing or iginally and naturally and a small area of fruit trees for comparative studies. Operation results and process design with emphasis on hydrau lic loading rates are presented after 3 yr successful operation. The s ystem is located north of Huolinguole city, in Inner Mongolia, China, where water is in serious shortage due to much less precipitation (389 mm yr(-1)) than evaporation (1495 mm yr(-1)) and where trees can not grow normally without irrigation. The reutilization of wastewater as a n important water resource for irrigation and forestation must be achi eved simultaneously in the course of wastewater treatment in the area. The SR-LTS was therefore designed and operated as a utilization type in order to irrigate a maximum area of land. It occupied a field area of 880 ha for a daily treatment flow of 10 000 m(3) of municipal waste water from the whole city of about 50 000 people. The system consists of five sub-systems with the main technological treatment process of ' wastewater --> primary treatment --> LTS' and 'wastewater --> primary treatment --> (winter) storage in reservoir --> LTS'. Under an average hydraulic loading rate of 41.5 cm yr(-1), the system performed well. Concentrations of BOD5, COB, total nitrogen and total phosphorus in pe rcolation water were in the range of 1 to 3, 20 to 30, 0.5 to 1.5 and 0.03 to 0.06 mg l(-1) and their removal rates were greater than 86, 65 , 85 and 84%, respectively. (C) 1997 Elsevier Science B.V.