Effects of air-dry pretreatment on maturity and odors during composting of pig manure and corn stalks

Abstract: Under the guiding thought of closed loop agriculture, the agriculture industry is becoming more intensified and specialized in China. Large scaled pig farms increased dramatically in China recently, which led to an enormous increase in pig manure. However, unlike in the US, the lagoon is not widely used to store swine manure in China because of the lack of land. Moreover, for some pig farms, it is hard to find enough land to consume all the manure nearby. Therefore, in some area, manure need to be transported to a specialized composting plant for treatment. Air-dry is a good process to decrease the volume of fresh manure for transporting. Meanwhile composting is a good way to treat pig manure as well as produce high-quality fertilizer. So it is meaningful to compare air-dried manure and fresh manure composting. In this study, composting reactors were used to conduct continuous aerated composting of air-dried pig manure and fresh pig manure. The dry matter of dry manure and fresh manure was controlled equally in each reactor. Same amount of 1～3cm corn stalks was used as a bulking agent for different treatments. Water was added into the feedstocks for the same initial moisture. Temperature, CO2, pH, electrical conductivity and germination index were measured to compare the maturity of two treatments. NH3 and eight kinds of sulfur odors were measured to compare the odor emissions of treatments. Specialized gas chromatograph was used for the measurement of sulfur odors. The result showed that mature compost product could be obtained from both of dry manure composting and fresh manure composting according to the result of temperature, pH, electrical conductivity and germination index. The electrical conductivity of dry manure composting product was significantly lower than fresh manure. It took less time for dry manure composting to start the curing phase. NH3, dimethyl sulfide and dimethyl disulfide emissions of dry manure composting were 71.09%, 66.11% and 9.66% less than those of fresh manure composting, respectively. Dimethyl sulfide and dimethyl disulfide are the main odors (>96%) among H2S, COS, CS2, dimethyl sulfide, diethyl sulfide, dimethyl disulfide, methyl mercaptan and ethyl mercaptan. The emissions of other sulfur odors of dry manure composting were all less than fresh manure too. There was no ethyl mercaptan detected in two treatments. The moisture of dry manure and fresh manure was 28.53% and 70.27%, respectively. Transporting fresh manure may cause more fly-tipping and odor issue than dry manure. The result of mass balance showed that the volume of manure was reduced by 1/3 after the air-dry process. And dry manure composting could produce 60% more product than fresh manure composting based on dry matter. The total carbon and total nitrogen of dry manure composting were higher than those of fresh manure composting. Therefore, composting manure after air-dry process could reduce the consumption of transporting, shorten the composting time, reduce the emission of odors, as well as increase the amount of composting product. The air-dry pretreatment process is a good choice for operators who have the demand for transporting manure to minimize the environmental impacts and maintain income in composting practice.