CH₄Emission Characteristics Research Of Wastewater Treatment Processes In Municipal Wastewater Treatment Plant

This work studied and calculated CH4emissions of wastewater treatment processes from A/O, A2/O, Oxidation Ditch (OD), SBR processes of wastewater treatment plants in China.In order to express the characteristic of CH4emissions from different units of those four processes, CH4emission flux, dissolved CH4concentration, CH4emission production pre ton wastewater and CH4emission law of main units were studied. CH4emission fluxes of aeration units of each process were the highest. As the strongly aeration, the disturbance of aerated water surface is more sharply than that of non-aeration surface. It is certain that strongly aeration is better for CH4emission. That the primary processing unit is of the high dissolved CH4concentration proved that the influent contained a number of dissolved CH4. There was a series of complex treatment process in the secondary treatment unit, so the dissolved CH4was emitted and conserved in wastewater treatment process, causing a lower dissolved CH4concentration. The main CH4emission site of each processing was the aerated unit or aerated phase:the CH4emission of oxic tank in A/O process accounted for75.54%of all A/O wastewater treatment process; the CH4emission of oxic tank in A2/O process accounted for64.96%of all A2/O wastewater treatment process; the CH4emission of ditch in oxidation ditch process accounted for82.43%of all oxidation ditch wastewater treatment process; the CH4emission of feeding and aeration phase in SBR process accounted for98.91%of all SBR wastewater treatment process.CH4emission characteristics of four processes were compared after clear those. The CH4emission from the primary treatment units, the secondary treatment units and the whole processes was compared. CH4emissions from the primary treatment units and the secondary treatment units were different from each other, but the difference of secondary treatment units was the main reason that caused the whole processes difference. The order of the whole CH4emission from each process is SBR>OD>A2/O>A/O, and the values were0.681,0.440,0.238,0.228gCH4/ton wastewater, respectively. According to the CH4emission and conversion comparison of four processes’secondary treatment units, the results showed that in A/O, A2/O and OD processes, the oxidized CH4quality of secondary treatment unit was more than that produced CH4quality and the percent of net CH4oxidation rate was73.6%,72.7%and52.7%respectively; in SBR process, the oxidized CH4quality of secondary treatment unit was less than that produced CH4quality and the percent of net CH4production rate was16.7%.CH4emission influencing factors were exploded and the result was that the CH4emission was concerned with aeration rate. In A/O and A2/O processes. CH4emission per ton wastewater was positive correlation with aeration of the front of oxic tank and negative correlation with the internal reflux ratio. In SBR process, CH4emission per ton wastewater was positive correlation with aeration of feeding and aeration phase and CH4emission quality under model of feeding following aeration was less than that of feeding and aeration simultaneously. In OD process, CH4emission per ton wastewater was positive correlation with rotating brush speed and the number of rotating brush.