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Biodegration And Translation Property Of Pollutants From Faeces In Aerobic Composting Reactor

Posted on:2012-07-21Degree:DoctorType:Dissertation
Country:ChinaCandidate:F BaiFull Text:PDF
GTID:1221330338998650Subject:Municipal engineering
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This dissertation is component of the the National Natural Science Foundation of China(Grant No. 50621140002) focusing on the sanitary disposal and fertilization utilization of human feces. The aerobic composting experiments were conducted using a closed aerobic composting reactor with sawdust as the bulky matrix to simulate the condition of a bio-toilet for sanitary disposal of human feces. Attention was paid to the biodegration of feces, mainly the characteristics of biodegration and translation of organic matters, nitrogen and phosphorus in aerobic composting reactor.In this study, a closed aerobic composting reactor was designed and maded, the tempreture of reaction controlled by water bath, the aerobic condition by air pump, and the moisture of compost by a water cooled condensing unit and initial moisture of compost. Batch experiments were conducted using the closed aerobic composting reactor with sawdust as the bulky matrix under a controlled condition of temperature - thermophilic (60℃) and methepholic(35℃), moisture content at 60%, continuous air supply 0.4m3.h-1.Kg-1, feces/sawdust at 1:4 on dry weight and the composting period for 14 days. The biodegradation of organic matter and transnation of organic nitrogen was studed, including: Dissment of decrease of feces by total solids(Stot)、organic solids(Sorg) and inorganic solids(Sino) change; Biodegradation charactration of organic matters in feces by change of Sorg、total organic carbon (TOC) and chemical oxygen demand (CODCr); The transformation characteristics of nitrogen by change of total nitrogen content (Ntot)、its organic parts Norg and inorganic parts Nino(nitrites NO2--N、nitrates NO3--N and ammonium NH4+-N、Gaseous ammonia(NH3-N) exhausted from the reactor); Assessment of biomass by Phospholipid fatty acid (PLFA) and microbial community by fluorescence in situ hybridization(FISH); Biodegradation of organic matter in feces by mathmatic modling in the composting process under an aerobic condition.Under aerobic composting condition controled well with moisture at 50%~60% and pH about 7, the mainly results in the study show that:(1) Decrease effect of the composting reactor was very abvious: the removal of Stot reached above 50% both at 60℃and at 35℃, and the former more abvious than the.(2) The biodegradetion of organic matter was well in the composting reactor: Under a controlled conditions of temperature at 60℃and at 35℃, degradetion of organic matter in feces was above 70% of CODCr and TOC and the former more than the during aerobic composting; there was common change trend of ecrease quickly during first 6~8 days and reduction slowly until the end of composting. Under a controlled condition of temperature at 35℃, degradetion of organic matter in feces during aerobic composting was above 64% of CODCr、TOC and Sorg in feces during composting; there was common change trend of decrease quickly during first 10 days~12 days and reduction slowly until the end of composting. This was that well biodegradetion of organic matter in feces during composting, compost period shortened to 6th8th d at 60℃from 10th d12th d at 35℃.(3) The holding of nitrogen as fertilizer in feces was abviously effected by aerebic composting temprature: Ntot decreased quickly in the first 24 hours of composting and the trend of variation of Ntot was similar to that of Nino, while the Norg was almost unchanged in the whole composting period, removal about 17% of Ntot and mainly Nino by NH4+-N into NH3-N, Norg had not change almost in the aerobic thermophilic composting process. While the loss of Ntot was about 31% with the loss of Norg more than that of the aerobic thermophilic composting, NH3-N exhausted abviously in first 4 days of composting at 35℃. Norg were mainly involved in the nitrogen loss process of feces by Norg into NH4+-N, finally into NH3-N in the aerobic mesophilic composting process. The loss of Ntot was equal to the accumulation of NH3-N exhaused under the thermophilic and mesophilic condition. It almost was regarded the holding of Norg was abvious characteristic of the aerobic composting reactor under the thermophilic condition.(4) By Phospholipid fatty acid (PLFA) analysis, assessment of biomass in the microbial community was conducted and found that: the biomass of feces was very high, and had the trend of changed including decreased in initial some days and increased quickly, it shown that microorganism proliferated after needing to adapt to the environment. reached maxium after about 56 days under thermophilic composting but reached maxium after about about 1112 days under mesophilic composting, and the time reached maxium in keeping with the time finished biodegradation of organic matters. After maxium reached, the biomass decreased slowly, it demonstrated that the use of biochemical degradable organics led to the proliferation of biomass. The maxium peak of biomass under thermophilic composting was higher that of biomass under mesophilic composting, and this was in accord with higher biodegradation of feces under thermophilic condition.(5) Based on assumptions that the organic matter of feces was invided into two parts included degradation and undegradation, the organic matter’s biochemical degradation of similar level 1 dynamics model can build. Using the experimental data of composting reaction under thermophilic composting and mesophilic composting conditions, calculated out two conditions respectively reaction kinetics constants 0.4413 and 0.2684, the organic matter degradation rate under thermophilic composting was 1.65 that of under mesophilic composting.(6) By fluorescence in situ hybridization(FISH) and Image-Pro Plus 6.0 analysis, It found that ammonium oxidation bacteria(AOB) and Nitrite oxidation bacteria (NOB) decreased quickly under the aerobic thermophilic condition,but AOB and NOB decreased sllowlly during composting under mesophilic composting. It show that ammonification may have been hindered under the thermophilic condition due to lack of ammonifying bacteria activity. As a result, almost all the Norg in the feces were well held in the composts without almost biodegradation.(7) In aerobic composting reaction, the phosphorus concentration of feces basically don’t change, as results, nutrients phosphorus was well held in the compost.The results of the study reveals rule of organic decomposition and nutrients transformation during aerobic composting, reasonable controling of the composting reaction temperature is effective way to hold nutrients N、P of the compost, the organic nitrogen losses can effectively be avoided under the conditions of thermophilic composting. therefore thermophilic composting can be considered as a method to improve the nitrogen holding property of the composts. The research has important theoretical significance and practical value.
Keywords/Search Tags:feces, sawdust, aerobic composting, thermophilic, bio-chemical degradation, Fate and holding property of nitrogen of faeces
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