Comparative Study of Static Pile Composting Using Natural, Forced and Passive Aeration Methods

Abstract

Poultry manure slurry amended with sphagnum peat was composted by natural aeration (NA), forced aeration (FA) and passive aeration (PA). Compost piles were built in trapezoidal shape with a volume of 5 m3. A total of nine replicates, three for each treatment method, were built. A total of 231 thermocouples were used to establish a three-dimensional temperature regime in each pile.The results showed that, for the selected configuration of aeration pipes and aeration schedule, temperature drop occurred almost two weeks sooner in PA and FA process than NA process. Also, temperature inside PA and NA processes stayed above 55°C for a longer time than FA process. Both FA and PA methods were effective in providing more oxygen. Low O2 concentrations were measured at the bottom and middle of NA pile and middle of PA pile during the early stages of the process which is an indication of anaerobic conditions. A total mass reduction of 32 percent and volumetric reduction of 16 to 22 percent were observed. The mass reduction was mainly due to water evaporation, around 550 liters of water per each pile. C/N ratio dropped from the initial value of 21.9 to 18.9, 19.8 and 20.9 for NA, PA and FA, respectively.The influence zone of aeration pipes in FA and PA composting was determined using a statistical procedure involving the verage of absolute differences (AAD) of temperature readings and two-way ANOVA. By comparing analogous thermocouple locations between PA with NA as well as FA with NA piles, it could be established whether inclusion of the aeration pipes affected the temperature at that location. A three-dimensional influence zone was mapped for PA and FA composting. Results indicate that for the selected configuration of aeration pipes and aeration schedule, PA pipes influenced temperatures in the bottom half of the PA pile while FA pipes affected the interior part of the pile. Near the pile surface, aeration was predominantly by diffusion, as these positions were not influenced by the aeration pipes. The results obtained were also verified by Cluster analysis.