Inquiry And Characteristic Study On Biological Pretreatment Of Municipal Solid Waste In Dalian

With the rapid development of the urbanization, the problem of the municipal solid waste (MSW) becomes more and more serious. At present, a lot of waste was dumped to landfill. In some developed cities, MSW incineration power plants are constructed one after another. Now Dalian city is building a garbage incineration power plant. Though incineration can deal with rubbish effectually, there are many shortcomings of waste incineration. We should look for the waste disposal method which is suitable for China's national conditions.This paper is divided into two parts. In the first part, we investigated and monitored refuse situation of three towns in Dalian for six months. The results are as follows:(1) MSW can not be ignored for its serious environmental pollution. It has aroused people's complaints and grievances and the Government has begun to attach importance to garbage disposal problem.(2) Plant and kitchen waste are the main components. For example, perishable rubbish are accounted for 63.68%, 52.68%, 54.70% in Taiping Industrial Park, Pikou town and Jingxi town. These wastes have higher moisture content and lower heat value. The moisture contents of waste are 53.62%, 51.87%, 50.74% respectively and the heat value of waste are 2486.2 kJ/kg, 3384.5kJ/kg and 3666.6kJ/kg respectively in these 3 towns.(3) Refuse collection system is backward, sanitation is poor, Innocent treatment rate of MSW is 0. Refuse is directly dumped to landfill without treatment. There is a landfill which is far less than 200m from residential area. It is a health threat for people.(4) Rural refuse don't merged to municipal solid waste collection system. It doesn't meet the requirements of building new countryside.(5) We put forward waste disposal program to these 3 towns: The waste of Taiping town is taken to Pulangdian waste treatment system, they don't need a independent refuse treatment plant for avoiding redundant construction, because it is very close to Pulandian city; Pikou town should establish a refuse treatment plant, and select integrative processing technology including biological pretreatment, incineration and landfill, what's more, they can combine nearby Yangshufang town to invest it; Jiangxi town may set up a refuse transfer center, refuse is transfer to other big refuse treatment plant after pre-sorting there. In the second part, I designed a drum bioreactor for the city solid waste characteristic in china. Drum bioreactor is the biggest advantage of uniform materials, and better ventilation, so it is propitious to treat organic waste of high content. With the bioreactor I carry out MSW intermittent biological pretreatment experiment in lab scale. The results show that:(1) The drum bioreactor works well, the mechanical system and ventilation systems is in normal.(2) In different conditions, drum reactor biological pretreatment process has achieved satisfactory results of the reduction, volume decreased by 60-75%, weight decreased by 30.58-71.34%, moisture decreased by 41.20-74.29%.(3) When ventilation quantity is 0.75-2.5 m³/h, the pretreatment process can proceed well. However, small ventilation quantity is conducive to heating up clearly, it promote the degradation of organic matter, so it raised the weight loss rate, on the contrary, superfluous ventilation is beneficial to moisture volatilizes thought it is: not good for degradation of organic matter.(4) To these refuse which have high organic matter, initial moisture content is not a constraints for biological pretreatment process of drum bioreactor. However, the lower initial moisture content, the bio-drying effect more obvious.(5) Small particle size is conducive to biological pretreatment process, but in the initial stage of pretreatment process, small size isn't conducive to ventilation, it will reduce heating up rate. Proposed particle size 30-60mm is suggested.(6) Through the analysis of oxygen concentration during pretreatment, we find out the oxygen consumption is significant change during the entire reaction cycle, oxygen consumption rate is the largest in the initial stage of pretreatment process.(7) In addition, we take analysis of the leachate. The leachate pH gradually increased with reaction progress, which suggests the process is in normal. The leachate is high concentrated organic wastewater due to the concentration of COD_cr and NH₄⁺-N.After biological pretreatment, the refuse is easy to further treatment and disposal, (l)it can reduce the amount of garbage into landfill and extend the life of landfill, reducing the landfill's leachate quantity and reducing environmental pollution in the landfill; (2)the moisture content will get lower and the heat value higher after biological pretreatment. Pretreated refuse will improve combustion efficiency of waste incineration plant.