Carbon And Nitrogen Transformation During Vegetable Waste Composting

With the rapid development of vegetable industrialization, there produce a large amount of vegetable waste during the process of production and transportation. Vegetable waste contains a great number of nutritional components, while high water content, low carbon nitrogen ratio of vegetable waste is easy to produce carbon and nitrogen loss and odor during composting. In order to study the carbon and nitrogen transformation rule during the vegetable waste composting, a 60 days composting experiment using a certain ratio of vegetable waste, mushroom residue, animal excrement and microbial agent mixing with aeration was conducted to investigate the characteristics of carbon and nitrogen transformation. There observe various forms organic carbon(total organic carbon, water soluble organic carbon, hot water soluble organic carbon, humus, etc.) and nitrogen compounds(total nitrogen, alkali solution nitrogen, ammonium nitrate nitrogen) during in the composting. The effects of biochar on nitrogen transformation were investigated during aerobic composting of vegetable wastes. A 30 days composting experiment using a certain ratio of tomato straw, corn straw and swine manure mixing with different proportions of biochar was conducted to investigate the characteristics of nitrogen transformation and loss during the fermentation. The main conclusions are as follows:⑴ Ventilation and adding microbial agents are conducive to increase the temperature of the pile body. The temperature of ventilation treatments is higher than the anaerobic fermentation. Under aerobic conditions, adding microbial agents had the highest temperature 4.13 ℃ above the treatment without microbial agents. Ventilator treatments can rapidly decrease the moisture content of compost. At the end of the composting, the moisture content of ventilation treatments were reduced by 32.90% and 37.52% respectively; the moisture content of anaerobic fermentation processing volatile rises. At the end of the composting, the moisture content increased by 4.13% and 8.68% respectively.⑵ Under the condition of ventilation, NH4+-N content was high at the early stage of the composting and gradually decreased at the late stage. Adding microbial agents promote transformation of NH4+-N to NO3--N(nitrification process) at the late stage. NH4+-N content of anaerobic fermentation processing gradually rose at the early stage and became steady at the middle and late stage. Ventilation and microbial agents were conducive to reduce nitrogen loss. At the end of composting, total nitrogen content of all treatments increased by 3.06%, 10.63%, 20.29% and 10.63% respectively. Adding microbial agents promoted complicated nitrogen compounds composed and product easy absorption of nitrogen that was utilized by microbial at the early stage. At the late stage, available nitrogen was used by microbial, results in the decrease of HN content. At the end of the composting, alkaline hydrolysis nitrogen content of anaerobic treatment without microbial agent was reduced by 5.72%, while other treatments increased by 0.23%, 0.23% and 0.23% respectively.⑶ Adding microbial agents is beneficial to decompose of organic material at early stage, promote the generation of humus, reduce carbon loss compost at late stage. At the end of the composting, under the condition of ventilation, without microbial agents and adding microbial agents, organic carbon was reduced by 18.46% and 18.46% respectively. At the end of the composting, under the condition of adding anaerobic fermentation, without microbial agents and adding microbial agent, organic carbon was reduced by 12.17%and 10.14% respectively. Under the condition of ventilation, HA/FA of without microbial agent and adding microbial agent treatments is higher than anaerobic treatments. Under the condition of adding anaerobic fermentation, HA/FA of adding microbial agent treatments is higher. Ventilation and adding of microbial agents promote the transformation of FA to HA.⑷ Addition of biochar could speed the compost to high temperature phase, extend the high-temperature duration, decrease the NH3 emission and nitrogen loss and consequently increase the total nitrogen content of the composted products. Addition of biochar could also promote transformation of NH4+-N to NO3--N(nitrification process) at the late stage and improve the content of unhydrolysable nitrogen. In addition, the present results could also showed that addition of biochar was in favor of compost maturing and the matured index of NH4+-N / NO3--N ≤0.5 was reached on 18 th day. Based on the present results, the optimum rate of biochar addition would be about 10 percent to promote nitrogen conservation and compost maturity.