Research On Physio-chemical Characteristics Of Spent Mushroom Substrate And Its Environmental Impact During Recycling Process

Spent mushroom substrate (SMSs) is a kind of typical agricultural wastes, which refers to the residue after harvesting of edible mushroom. Due to high amount of residue generation, the disposal of SMSs has become a worldwide issue and attracted researchers'attention. Conventional disposal methods include incineration and landfills, both of which might cause environmental pollution problems. A comprehensive utilization technique consisting continuous cultivation and composting process could not only reuse the remaining nutrients from SMSs, but also avoid any negative environmental impacts.Based on the PCMs-SMSs-PE-SMSs-PO-SMCs comprehensive utilization, prepared cultivation materials (PCMs), spent Pleurotus Eryngii substrates (SMSs-PE), spent Pleurotus Ostreatus substrates (SMSs-PO) and spent mushroom composts (SMCs) were selected as the periodical samples. Nutrient analysis, characterizations as well as heavy metal analysis was conducted in order. The results showed that the moisture content of material decreased by 13.8% during continuous cultivation while polysaccharide and protein increased by 2.4% and 3.8%, respectively. Moreover, humic acid content of material increased by 2.2% during composting process while BDM index, polysaccharide and protein decreased by 12.5%,7.7%, and 11.2%, respectively. In addition, lignin contents didn't show a significant difference during both processes. Characterization suggested that there were interspaces and pores on SMSs-PE and SMSs-PO surfaces, while the surface of SMCs was found to be rougher. Heavy metal analysis revealed that the content of arsenic, mercury, lead, chromium, cadmium and other harmful elements in materials were within the permissible limits of standards.SMCs were found to be used as organic fertilizer once returned to the fields. For this purpose, an incubation test was designed to investigate the fertilizer response of SMCs by measuring ammonium and nitrate concentrations in soils. Experimental results showed that application of SMCs could improve the mineral nitrogen content in soil, and a content of 157.35 mg N/kg was reached after 42-day incubation. In order to investigate the releasing characteristics of SMSs/SMCs, a soil column test was conducted to compare with chemical fertilizers (urea and calcium superphosphate). As a result, the SMCs-applied group showed a less leaching loss in N, P (N with a less leaching of 65%). However, the CODCr of SMCs leachate was found to far exceed chemical fertilizer, which may cause groundwater pollution. Mixed application of SMCs and chemical fertilizers could reduce the leaching loss of CODCr and the nutrient releasing was well fitted with the first/first order mixed model.To solve the excessive loss of CODCr, biocharl (550-600?), biochar2 (650-700 ?) and biochar3 (750-800?) were prepared according to a pyrolysis-steam activation process using SMSs-PO as precursor. The application of biochar could promote the nutrient-maintaining ability, which ranked in the sequence of biochar3> biocharl> biochar2. Overall, biochar3 showed a strongest nutrient-maintaining ability in N, P and CODcr in the mix application with SMCs.Considering the disadvantages during the comprehensive utilization, a preliminary design was conducted on aerobic composting project of SMSs in Li Shui. Warehouse was chosen as the fermentation equipment to shorten the decomposing time, and to improve the health conditions in the meantime.