The Effect Of Different Initial Temperature On Aerobic Composting Of Human Feces

As an important factor in aerobic composting, temperature has a direct effect onthe organic decomposition and microbial communities. To study the effect of differentinitial temperature on aerobic composting of human feces, four different temperatures(25℃,35℃,45℃,55℃) were selected as initial experimental temperature, and theexperimental period was set to20days. A sequencing batch aerobic composting reactorwas used for feces composting with sawdust as the bulky matrix, the moisture contentwas maintained at55%～60%, and air was supplied continuously. Main attentionswere paid on the change of temperature, pH, EC, phosphorus, E．coli and germinationindex, especially on the transformation of nitrogen, degradation of organic matter. Themain research results are as follows：（1）when the initial temperature were25℃and35℃， the temperatures of thepile began to rise and reached the maximum for34.5℃and37.1℃at the end of1dayand1.5days, respectively, and then gradually reduced. While at the conditions of45℃and55℃, temperatures declined rapidly after the end of the heating, thetemperature of the pile were almost comparable to the ambient temperature at the firstfew days of experiment until the6thday there was a phenomenon of temperature rising,the maximum temperature appeared at7.5thdays and6.5thdays, were35.8℃and35.6℃, respectively, then gradually declined. Under the initial thermophilicconditions, the time of composting temperature began to rise was significantly delayedthan at the conditions that initial temperature were25℃and35℃, which indicated that excessive initial temperature (>45℃) could inhibit composting reaction.（2）The moisture of the composting process could be basically maintained at50%～60%, which may ensure aerobic composting to carry out smoothly.（3） The initial temperature had a significant effect on the changes of pH duringcomposting. The initial temperature was higher, hydrolysis was more significant in theearly days of composting, which lead to pH decreased more under the initialthermophilic conditions than under the mesophilic conditions, meanwhile, the time ofpH decreasing lasted longer. As the temperature increases during the reaction, pHgradually increases to a steady. At the end of composting, pH of different initialtemperature were8.5～9.（4）The initial high temperature would make lots of microbial in the pile inactive,however, the duration of thermophilic was not long enough that thermophilic bacteriacould not multiply enormously, so there was a phenomenon that the beginning of thecomposting process was suppressed. Then as the temperature dropped, after about fivedays to adapt, a large number of mesophilic microbial began to multiply, organicmatter was gradually decompose.（5）At the end of composting, the removal rates of soluble COD at four differentinitial temperatures were88.2%,89.3%,92.0%,89.6%, respectively. Because theinitial thermophilic condition was beneficial for hydrolysis of organic matter, resultingin removal rates of soluble COD under the initial thermophilic conditions were slightlyhigher than under the mesophilic conditions during aerobic composting. The contentsof TOM almost did not change significantly throughout the reaction. At the end of theexperiment, the contents of TOM in final composting product under different initialtemperature were more than95%.（6）In aerobic composting process, under the initial mesophilic conditions, NH3released rapidly at the first two days of the reaction, while under the initialthermophilic conditions, NH3didn’t release enormously until the7thday of the reaction,which was delayed for about five days compared to the initial mesophilic condition.However, the total cumulative release of NH3was not significantly affected by theinitial temperature, were12.08g/kg,13.62g/kg,11.07g/kg,12.80g/kg respectively. The content of TKN and NO3--N reduced as the reaction proceeded. Theinitial concentration of NO3--N concentration during composting was very low, andalmost completely disappeared at the end of composting.（7）The content of total phosphorus in solid sample hardly changed in thecomposting process, while the change of water-soluble phosphorus was closely relatedto pH, the content of water-soluble phosphorus decreased with increase of pH. At theend of the composting, the contents of water-soluble phosphorus under four differentinitial temperature conditions were2.13g/kg,2.35g/kg,2.35g/kg,2.46g/kg,respectively, and no significant difference appeared.（8）When the reaction started, the number of E. coli in the pile was about3×103cfu/g, with the progress of the reaction all of the E. coli were inactivated becausethey could not adapt to the change of environmental. The higher initial temperaturecould play a better role inactivation of E. coli during aerobic composting, E. coli couldbe inactivated rapidly in a short time.（9）The initial temperature not only inhibited the degradation of organic mattersbut also affected the seed germination index, the seed germination rates were higherunder the initial mesophilic conditions compared to thermophilic conditions. But at theend of compost reaction all of the germination rates were between100%and150%,indicating the final composting products were mature, and were not toxic to plants.However, the maturity period of composting was delayed because of initialthermophilic condition.