Evaluation Of The Maturity Of Organic Solid Waste Compost

With the sustainable and rapid development of economy in China, the organic solid waste production, including urban sewage sludge (SS), Municipal Solid Waste (MSW), agricultural residues (AR) and so on, has increased very quickly. Aerobic composting is a general treatment method for organic solid waste, which has a fast processing speed, little or no harm on environment and is economically feasible, and its` final product can be used as organic fertilizer, which received by many countries' all over the world. Organic solid waste composting, using the massive original existence of the microorganisms, carrying on the organic solid waste biodegradation under the artificial conditions, is the security and the effective processing method. Compost maturity is an important index that evaluates the compost safety and stability.If the compost that was immaturity was applied in soil, which will lead to a lack of available soil nutrients and result in poor crop growth. Therefore, that to build a fast, more accurate and suitable method for evaluating organic solid waste compost maturity is a need to improve composting process and a market objective requirement of improving the quality of products, as well as the inevitable requirement to promoting ecological cycle and increasing crop yield and raising the peasants'incomes.In this paper, the composting test was made with primary dewatered sewage sludge (SS) from Wastewater Treatment Plant of Yangling, sawdust (SD) from a wood processing plant in Yangling, and organic fraction of the selectively collected municipal solid wastes (MSW) from Xi'an MSW harmless comprehensive treatment plant as the raw materials using aerated static pile composting system and natural ventilation fermentation system. For the problem of compost maturity evaluation in aerobic composting process, it is very necessary to choose a wide suitable maturity indexes system and to establish a rapid evaluation method for compost maturity. The 3 laboratory scale composting tests were carried out, such as SS+SD, SS, MSW and went though a period of 120 d, respectively, and some maturity parameters were determined in composting process, then the correlation between some major parameters was identified. Finally, the comprehensive evaluation system of compost maturity was established through the fuzzy mathematical analysis method. The results were as follows:1. The spatial variation characteristic of the temperature of compost pile during aerated static pile composting period (0 ~ 35th day) showed that: (1) the regularity of the upper and lower pile temperature evolutionary in the different initial C/N ratio compost materials was uniform, but the trend of compost temperature change, the highest temperature and the higher temperature (≥55℃) persisting time, the range of compost temperature in the lower pile, and the time of entering into the lower temperature period were different. (2) The result indicated that the temperature variation were explained distinctly using Kriging method.2. The maturity indicators of the physical, chemical and biological monitoring indicators in the different compost materials were determined periodically during composting process. The results showed that the fluctuation between parameters and composting time was evident.3. The ultraviolet and infrared spectra analysis was carried out in compost samples from different composting time. The results showed that: (1) it seemed no rules were found in 3 composting tests based on the results of UV wavelength scan (190 ~ 400nm) in the water extraction fractions from composts sampled in different fermentation period. (2) the fat reGIon peak intensity(2925,2855nm-1)and polysaccharide reGIon peak intensity (1090 nm-1) were decreased relatively in final products which confirmed that reaction of the decomposition and the condensation was concurrent in the compost materials during composting process.The peak intensity decreased rapidly in 1643 nm-1 and absorption peaks in 1545 nm-1reGIon disappeared, which confirmed that the degradation of the aromatic structure was increased due to the mineralization of organic matter was accelerated in composting final period4. The relevant analysis results indicated that (1) GI has negative correlation significantly with CO2 release rate and ST in the composting test, respectively, and positive correlation significantly appeared between CO2 release rate and ST; (2) correlation between CO2 release rate and TOC was negative significant; (3) significant correlation was observed between ST and TOC.5. Based on the linear analysis of compost maturity indexes monitored and literatures, five indexes were raised including persisting time of high temperature composting period, degradation rate of C/N, NH4-N/NO3-N, seed germination index (GI) and degradation rate of NH4-N.Meanwhile, compost quality was evaluated comprehensively by fuzzy mathematics analysis mothod in the condition of five indexes, and the evaluation results were in accord with the practical situation.