Effect of corn stalk and biochar aerobic fermentation combined with biogas slurry spraying

Abstract: At present, the demand for the quantitative reduction and resources recovery of biogas slurry is increasing rapidly. In this study, an aerobic fermentation experiment of biogas slurry with biochar and corn stalks after adsorbing and filtering the biogas slurry, was conducted to investigate the effect of biogas slurry spraying to the fermentation, and the effect of co-fermentation with corn straw and biochar was also analyzed. The results indicated that crushed corn straws had better water absorbing ability and suspended matter filtering ability. Moisture content of crushed corn straws, after adsorbing and filtering the biogas slurry of pig manure and chicken manure, increased from 5.92% to 76.35% and 85.72%, and the carbon nitrogen ratio increased from 42.4 to 50.2 and 51.7, respectively. Due to the effect of corn stalks adsorption filtration, total suspended matter and total phosphorus in the biogas slurry of pig manure and chicken manure decreased 34.42%-43.78% and 20.00%-41.01%, respectively. The adsorption and filtering effects of crushed corn stalks to the total phosphorus and total potassium were not significant in slurry. After adsorption saturation, carbon nitrogen ratio of corn stalks was not suitable for aerobic fermentation, indicating amendments were important assistant materials in the composting process. Biogas slurry spraying and compost turning could prolong the duration of high temperature phase more than 2 times during fermentation. The addition of biochar to the compost could shorten the temperature raising period and prolong the high temperature period, which could be benefit of utilizing biogas slurry. The content of nitrogen, phosphorus and potassium were found to increase constantly in the composting process. After aerobic fermentation, organic matter content of fermentation materials with slurry spraying decreased by 10.42%-18.63% and the total contents of nitrogen, phosphorus and potassium increased by 6%~21.5% compared to other treatments without slurry spraying. The compost maturity of fermentation materials with slurry spraying was also improved. The test results demonstrated that the technology of corn stalk and biochar aerobic fermentation combined with biogas slurry spraying could be feasible to make use of quantitative reduction and resources recovery of biogas slurry to produce organic fertilizer, which had better environmental, social and economic benefits. Meanwhile, there are some further studies are needed to conduct. Firstly, process parameter optimization of the technology in the paper will be needed. Secondly, the effect of different amount of biochar added to the compost still needs further study. Thirdly, the technology in the paper is more suitable for gutter fermentation process, and the related process parameters worth in-depth study.