Material Mixing And Ventilation Strategy On Aerobic Composting Of Chinese Medicine Herbal Residues

With the continuation of COVID-19 and the support of national policies,the Chinese medicine industry continues to develop,accompanied by the rising yield of Chinese medicine herbal residues,which can cause huge pollution as well as waste of resources when landfilled or directly discharged into the environment,while it is difficult to continue the extraction of resource-based substances and the preparation of some high value-added products due to the wide variety of Chinese medicine herbal residues and their complex composition.As solid waste mainly from farmland,composting of Chinese medicine herbal residues is one of the more realistic and effective methods,but after the extraction of active ingredients to produce Chinese medicine herbal residues（such as steamed medicine herbal residues）,generally,the nitrogen and phosphorus content is difficult to meet the requirements of composting products.The sewage sludge is rich in microorganisms and nitrogen and phosphorus,so adding a suitable proportion of sewage sludge to the Chinese medicine herbal residues for aerobic composting not only enriches the microbial community structure of the pile,but also enhances the nitrogen and phosphorus content of the pile and enables to adjust the material structure of the pile.In this study,experiments were conducted to investigate the effects of different residual sludge addition ratios（material ratios）and ventilation control methods（ventilation intervals）on the aerobic composting of Chinese medicinal herbal residues.The experiments were conducted to analyze the changes of physical and chemical parameters such as temperature,oxygen concentration,p H,electrical conductivity（EC）and nutrient content,as well as ammonia release and enzyme activity during the aerobic composting process,supplemented by spectral analysis and seed germination index to evaluate the degree of decay.Finally,the appropriate sewage sludge addition ratio and ventilation control method were determined,and the change pattern of the microbial community of the pile under continuous ventilation mode was analyzed,in order to provide a basis for the regulation of aerobic composting of Chinese medicine herbal residues and the development of bacteriological agents.The experiment set 0%,5%,10%and 20%sewage sludge addition ratios for the aerobic composting of Chinese medicine herbal residues and found that the addition of sewage sludge could effectively promote the temperature rising of the pile,with the peak temperature of the four groups reaching 59.9℃,64.6℃,66.9℃and67.8℃respectively.The final cumulative ammonia release was 191.8,400.7,775.9and 1386.3 mg·kg^-1 respectively;by the end of composting,the total nutrient content of the four groups was 4.45%,4.67%,5.19%and 5.86%respectively,the addition of sewage sludge increased the nitrogen and phosphorus content of the pile,and the concentration effect due to organic carbon consumption made the compost product more concentrated.The relative nitrogen and phosphorus content of the compost product was enhanced by the concentration effect,and the addition of 10%and 20%sewage sludge resulted in the composting product with a total nutrient content of>5%,meeting the requirements of the Organic Fertilizer（NY 525-2012）and other relevant standards.The 10%sewage sludge addition was considered to be appropriate in terms of temperature rising,ammonia release and total nutrient content of the product.At 10%sewage sludge addition ratio,intermittent ventilation experiments were carried out at intervals of 0,10,20 and 40 min,and it was found that at a ventilation rate of 1 L·min^-1,the increase in ventilation intervals extended the time to reach the maximum pile temperature and reduced the maximum pile temperature.The maximum pile temperatures were 66.4℃,66℃,64.9℃,61.7℃ and above 50℃ for more than 10 d.In addition to the continuous ventilation group,the three groups of intermittent ventilation all had oxygen concentrations<5%,and the 40 min ventilation interval group lasted for more than 10 d,the anaerobic condition occurred for a longer period of time.Intermittent ventilation could effectively reduce the ammonia release from the piles,and the cumulative ammonia release from the piles to the end of the composting.The cumulative ammonia release was 733.1,363.3,206.61 and 99.4 mg·kg^-1for each pile,decreasing with increasing ventilation intervals.The final seed germination index for each pile was 95%,93%,93%and 90%respectively.A ventilation interval of 10 min was found to be appropriate,taking into account the temperature rising,oxygen concentration,ammonia release and final total nutrient content.Finally,the succession of bacterial communities in the composting pile during continuous ventilation was analyzed,which would provide a basis for the development of relevant bacterial agents.