Effect And Mechanism Of Intermittent Aeration On Oxygen Supply/consumption And Main Gaseous Emissions During Livestock Manure Composting

Aerobic composting has been widely used in the recovery,stabilization and volume reduction of manure.Conducting systematic study on aeration strategies,GHG emission and its impact factors during composting was significant for developing a composting industry with environment protection,high efficiency,high quality,and low consumption.Based on the mainstream trough composting pattern in China,this study developed a real-time monitoring system for temperature and oxygen concentration during lage-scale aerobic composting,and conducted trough composting experiment to investigate the spatial and temporal distribution of pore gas concentrations and dynamics of oxygen supply and consumption.Intermittent aeration was applied and optimization and effect of the aeration interval were investigated using small and medium reactors to propose an appropriate aeration strategy for solving the problem that the pores were extremely lack of oxygen and large amount of pollutant gases were accumulated in the pores,which would give theoretical support for saving energy,reducing emission,promoting quality and increasing effect in composting process.The main innovation and achievements and conclusions were obtained as follow:The real-time monitoring system developed in this study for temperature and oxygen concentration during large-scale aerobic composting with high integration and easy portability consists of temperature acquisition module,oxygen concentration acquisition module,signal processing module and data display and storage module.The results of performance experiments showed that the relative standard deviation(RSD)of temperature monitoring was inferior to 3.02%and the response time was less than 45 seconds;the RSD value and the response time of oxygen concentration was inferior to 2.96%and 40 seconds,indicating that the system has good performances such as high accuracy,good stability and fast response speed.The temperature,pore CO2 and CH4 concentrations in the center of the pile was obviously higher than that in the side of the pile The top layer exhibited highest pore O2 concentration and lowest CO2 and CH4 concentrations,and the bottom layer was on the contrary.Effective O2 diffusion occurred at most in every two contiguous layers Therefore,mixing the center and the side of the pile when mechanical turning,and adjusting the height of the pile according to the physical properties of bulking agents are suggested to optimize the oxygen distribution and promote the composting process during large-scale trough composting.In active phase(OUR>0.02 mol O2 kg-1 OM h-1),oxygen was consumed at a stable respiration rate to a concentration of 5%in 12～49 min after each mechanical turning and remained anaerobic in the subsequent static condition.The daily percentage of time under aerobic condition was no more than 6.84%of a single day.Therefore,improving free air space(Fas),adjusting aeration interval or combining turning with forced aeration was suggested to provide sufficient oxygen during composting.Although O2 was sufficiently supplied during aeration period,it could be consumed to<10%only when the aeration interval was 50 min,indicating that an aeration interval more than 50 min would be inadvisable.Specifically,both the total CH4 and N2O emissions as well as the total GHG emission equivalent were inversely proportional to the duration of aeration interval(R2>0.902),suggesting that lengthening the duration of aeration interval to some extent could effectively reduce GHG emission.Compared to continuous aeration,reductions of the total CH4 and N2O emissions as well as the total GHG emission equivalent by 22.26～61.36%,8.24～49.80%and 12.36～53.20%,respectively,was achieved through intermittent aeration.Comprehensive analysis of the oxygen dynamics and GHG emission equivalent,an aeration interval of 30 min on the basis of 30 min aeration at 500 mL/min was thought to be optimal.The degradation rate of organic matter,removal of dry matter and total carbon loss were almost the same during both continuous and intermittent aeration.The removal of moisture,total nitrogen loss and degradation rates of cellulose,hemicellulose and lignin during intermittent aeration were a bit lower than those during continuous aeration.Compared to continuous aeration,reductions of the CH4 emissions,N2O emissions,NH3 emission,total GHG emission equivalent and energy consumption by 14.92%,96.03%,78.45%,60.02%and 51.65%respectively,were achieved through intermittent aeration,during which the O2 utilization efficiency was doubled.