Study On The Co-composting Of Organic Solid Waste In Rural Areas

China is the country with the largest amount of agricultural waste in the world.With the acceleration of urbanization rate,rural living standards have been gradually increasing and the disposal of rural solid waste has become an urgent environmental issue.In this paper,composting were used to achieve the recycling of rural sludge,domestic waste,human excrement and straw.The experiment started with the control of technical point and the addition of amendment hoping to obtain the higher quality composting products and smaller environmental impacts.The experiment consists of three parts: the first one is the optimization of the mixture ratio of the three main organic solid wastes(rural sludge,domestic waste,and human excrement);the second one is the modification of sludge biochar for the purpose of nitrogen fixation and mechanism of ammonia adsorption;the third one is the impact of the addition of sludge biochar on the composting process of rural solid waste,including physical and chemical properties,nitrogen transformation and greenhouse gases emission.The main findings are as follows:(1)The response surface analysis method could obtain more systematic test results through a small number of test points,and it is feasible to optimize the mixture ratio of compost materials;The transformation of organic carbon is not complete because of excessive content of organic matter and carbon and carbon-nitrogen ratio when compost were made from domestic waste separately which is not conductive to maturity;The accumulation of water-soluble nitrogen caused by uncompletely transformation of the excessive nitrogen reduced the quality of the compost when compost were made from rural sludge or human excrement separately;The composting products reached the higher quality when raw material consisted of 50-75% domestic waste and 25-50% rural sludge and human excrement(dry weight).The six parameters(WSCorg?WSC/WSN?T?k?N H4+?NH4+/NO3-)were in the range of 7.57-8.78 mg · g-1,4.97-6.07,0.43-0.48,0.10-0.12d-1,0.62-1.31mg/g and 0.33-2.04,respectively.The composting quality is the best in this range,which C/N of corresponding raw materials is 18-24 and the expected value can reach 0.6 or more.(2)Modified sludge biochar by acid is not conducive to the adsorption of ammonia nitrogen,but to a degree,the modifiers such as hydrogen peroxide,potassium permanganate and potassium hydroxide,sodium hydroxide improve the adsorption of ammonia nitro gen.The amount of C content increased significantly after the modification of acid and alkali,while the O content was significantly lower than the original sludge biochar;There is no significant difference in the carbon content between KMn O4 or H2O2 modified sludge biochar and original sludge biochar,but the O content has increased after modification;Metal ion exchange plays an important role in the adsorption of ammonia nitrogen.Compared with the original biochar,the content of Mg,K,and Ca in the biochar modified by nitric acid has significantly reduced,which reduced the adsorption sites of ammonium ions and reduced the cation exchange capacity of biochar,resulting the reduction of adsorption of ammonia nitrogen.Other modifiers did not have a significant effect on the surface metal elements of biochar;The acid functional groups of the acid modified biochar and oxidized modified biochar were significantly higher than the original biochar,especially carboxyl group,which were beneficial to increase the adsorption site of ammonia nitrogen;Considering the actual adsorption efficiency,potassium permanganate is selected as the optimal modifier.(3)The addition of sludge biochar can effectively improve the air permeability of the reactor and provide suitable living environment for microorganisms,which promoted the metabolism of microorganisms and accelerate the degradation of organic matter.The compost can reach and maintain the thermophilic period quickly and reach the maturity standards;Compared with the original sludge biochar,the modified biochar can absorb ammonia nitrogen more effectively,inhibiting the volatilization of ammonia and increasing the nitrogen content of the fertilizer.However,the modified biochar has not been further reduced greenhouse gas emission such as methane,nitrous oxide,and carbon dioxide.