Study On The Resource Utilization Of Excess Sludge From Lanzhou Area In Sintered Brick Manufacture

The production of sludge from five sewage treatment plants in Lanzhou was 203,600 tons in 2013,and they were disposed by the land-fill method. By the end of 2015, the sewage treatment plants in normal operation will be increased to nine in Lanzhou. The daily sewage treatment capacity will increase by 75,000 tons. The production of sludge will continue to rise. They will make enormous holding pressure on the existing landfills in Lanzhou. Soil and groundwater contaminated by the landfill leachate will cause huge environmental risks.This paper is a study of the preparation of sintered brick with excess sludge, fly ash and Lanzhou loess as material, in order to find a resource utilization of excess sludge which is simple and easy to spread in Lanzhou area. Firstly, the characteristics of Lanzhou excess sludge were analyzed by test, then carried out the research of drying to find a relatively fast economic and practical sludge conditioning program reducing the moisture content of sludge by using methods of natural drying, lime drying, lime and fly ash joint drying. Secondly, drying sludge, fly ash and Lanzhou loess was used as the materials to produce sintered bricks, the properties of which were tested. At last, it was a simple analysis of economy for this process.The experimental study of excess sludge from the Qilihe-Anning wastewater treatment plant in Lanzhou showed 95.51% of moisture content, pH 7.4, 26.6% of organic matter content, 29.7% of loss on ignition of dry sludge, metal arsenic 11.76 mg/kg, metal chromium 189.75 mg/kg, and under 0.04 of fecal coliform. According to the relevant requirements of the control indicators in GB "The disposal of sludge from municipal wastewater treatment plant-The quality of sludge used in making brick", the most of the test results meet the standards except that the moisture content and value of fecal coliform exceed targets. In order to further study the forming of bricks, the excess sludge need to be dehydrated and done harmless treatment to meet the requirements of forming bricks. Another test showed average calorific value of dry sludge was 12560.65 kJ / kg, reflecting a heat energy utilization value of the dry sludge.Through a series of preliminary tests of the excess sludge by natural drying, lime drying, lime and fly ash joint drying, the research shows that the natural conditions of Lanzhou was good for natural drying; the drying mud field should be set up away from residential areas, in order to reduce odor pollution; the lime drying effect of the excess sludge was remarkable, when added 15% quick lime, the moisture content of the sludge reduced to less than 60% on the third day, which fit for the requirements of sanitary landfill, and the moisture reduced to less than 40% on the eighth day, which fit for the requirements of mud brick; lime bactericidal and deodorizing effect was obvious; equal proportions of lime and fly ash added to the sludge, had a significant effect which significantly reducing the moisture content and eliminating E.coli, when added 7.5% each of lime and fly ash, the moisture reduced to 46% on the eighth day, which had equal effect with separate adding 10% of quick lime. Due to the cost of lime was higher than fly ash, and fly ash was an industrial solid waste, the method of joint added lime and fly ash was more suitable.Excess sludge, fly ash and Lanzhou loess was used as the materials in a certain proportion to produce sintered brick in the process of drying, screening, ready-mixed, aging, forming, drying and firing. It had some tests to find the effects of the sintering temperature. Based on compressive strength and the maximized using ratio of sludge, the most suitable sintering temperature was 1150 ℃, and the proportion of excess sludge, fly ash and Lanzhou loess was 2:3:5. Heavy metal can be well solidified during the sintering process. The result of water extraction test was much lower than the relevant standards in “Identification standards for hazardous wastes-Identification for extraction toxicity”.Through the economic analysis showed that the process of producing sintered bricks with excess sludge is simple, easy to spread, in accordance with national industrial policy, and have good environmental, social and economic benefits, it was a suitable way for resource utilization of excess sludge in Lanzhou Area.