Apilot Study On The Continuously Batch Feeding For Aerobic Composting Human Feces Using A Rotating Drum Reactor

The pyriform rotating drum reactor for aerobic composting human feces wasdeveloped to solve the problems of low treatment efficiency, bad movability and largeinitial quantity of batch feeding of material. Also, the novel reactor might be used toeffectively treat the non-centralized human feces, which could be as a resource offertilizer. The former research had elucidated that the optimum stirring frequency was5min/h, the optimum ventilation rates of intermittent and continuous batch feedingcompost were1.5L/min and3.0L/min, respectively. Accordingly, this thesis aims todetermine the best feces-sawdust ratio in dry weight and to optimize the system forcontinuous compost of the reactor, also to further improve the efficiency of aerobiccomposting human feces using the novel reactor.Regarding the experimental parameters when the human feces were compostedunder the different feces-sawdust ratio in dry weight are shown as follows. Thefeces-sawdust ratios of the batch feeding experiment were respective1:4,1:3,1:2.5,1:2and1:1.5. The initial moisture contents were all60%when the feces-sawdust ratioswere1:4,1:3and1:2.5, respectively. The initial moisture contents were65%and70%when the feces-sawdust ratios were1:2and1:1.5respectively. The initial quantities ofbatch feeding were all5.0kg. The results demonstrated that the best compost efficiencywas obtained under the dry weight ratio of1:2.5. At this time, the compost temperaturerose to58℃and maintained within1day. After15days of compost, the degradationrate of COD and TOC reached68.71%and66.15%, respectively. The GI was96.52%.On the basis of the results of heat balance calculation, it was clear that the compostquantity was only3.3kg feces in15days and the compost efficiency was only7.86 g/(L d) under the reactor volume of28L. The result might be attributed to the lessinitial batch feeding quantity of compost, which led to the shortage of heat resource.The initial quantity for compost feeding was also5.0kg,1.0kg of the compostedmaterial was taken out and1.5kg of raw compost was fed in every36hours when thecontinuous batch feeding compost was carried out. The result showed that the limitingstep of the entire reaction process might be the organic molecule hydrolysis. Thetemperature of compost heap rose slowly after each feeding, the cycle of temperaturerising and falling was36hours. In30days, i. e.,3periods in theory, the degradation rateof COD and TOC in the first period was quite low, only46.68%and42.57%, whichwere lower than efficiencies of batch feeding. However, from the fifth day of secondperiod (the15th day from the start of compost) to the end, the degradation rate of CODand TOC stably reached more than66%, which were equivalent to the efficiencies ofbatch feeding. In another word, during the continuously batch feeding for aerobiccompost, the first14days (the whole first period and the early second period) was themicrobial acclimation stage. Subsequently, the compost entered the stabilization stage.During this stage, a sustainable high temperature for human feces compost could beobserved, the composting efficiency was23.81g/(L d), which was3times higher thanthe batch feeding. It showed that microbe inoculation might be more favorable toimprove the efficiency of the aerobic compost, since a steady resource of the compostmicrobe for the acclimation stage were cultured in advance during the stabilizationstage.The effects of inoculation on the efficiency of continuous batch feeding aerobiccompost were investigated by means of inoculating aboriginal bacteria, baciuus subtilisand saccharomyces, in order to further improve the compost efficiency of human fecesin the novel reactor. The experimental result revealed that compost characteristics ofhuman feces was significantly improved, including:(1) The compost efficiency was35.71g/(L d), which was4.5times higher than the batch feeding;(2) The cyclicduration of temperature rising and falling decreased to24hours, the highest temperaturereached about60℃;(3) Acclimation stage decreased to8days, the degradationefficiencies of COD and TOC were respective65.28%and55.03%during this stage;(4)Compared to the TN loss of56.68%in non-inoculation compost, it markedly decreased to25.75%after inoculation compost, indicating that the duration of compost andacclimation largely reduced more than50%;(5) Compared with the duration of21daysfor GI to110%of non-inoculation, it only took9days of inoculation compost,demonstrating that microbe inoculation was favorable to the rapid maturity of compost.(6) Based on the quantities change of inoculated microbes during the compost process,it could be known that the ammonifier was one of the main microbes in aerobic compostreaction. The quantities of ammonifiers, actinomyces and biomass presented a cyclicchange of decreasing and increasing with the temperature cycle of rising and falling.The fluctuation was relatively intense during the acclimation stage and significantlyweak during the stabilization stage;(7) The high temperature compost played animportant role on the activity inhibition of denitrifying bacteria and the deactivation ofE. coli, nitrobacteria and fungi; and (8) The function of inoculated microbes in compostreactor was not persistent, the inoculation should be performed synchronously with thecompost materials feeding.Compared with the intermittent batch feeding composting reactor, the pyriformrotating drum reactor for aerobic compost could treat the human feces more rapidly. Thecompost efficiency increasing and energy consumption reduction could be over50%bythe synchronous inoculation of aboriginal bacteria; thus, the compost cost could besignificantly reduced.