Treatment Of Rural Sewage With Low Carbon/Nitrogen By Hydrolysis Acidification-SNAD Biofilter Process

Owing to the much more serious situation of pollution problems derived from rural sewage, more attention has been focused on more efficient nitrogen removal process. There are some existing problems in the traditional biological nitrogen removal processes, such as complicated system, requirement of external carbon source, large footprint, high investment and operating cost, especially for the rural sewage with low C/N ratio and dispersal discharge. However, the new promising biological nitrogen removal process "SNAD", in which partial nitrifition, anaerobic ammonia oxidation and denitrification could occur in one reactor, can accomplish simultaneous organic and nitrogen removal for the wastewater with low C/N ratio.In this study, a process combined hydrolysis acidification-SNAD was developed to treat the low C/N rural sewage. Firstly, the organics in rural sewage were converted into VFAs in an anaerobic hydrolysis acidification unit, which could be the favour substrate for denitrification and have no inhibition to ANAMMOX. Then, the sewage was flowed into the SNAD unit for simultaneous organic and nitrogen removal. In the biofiler SNAD reactor, after ANAMMOX bacteria attached onto the carriers, the nitrite bacteria and denitrifying bacteria was inoculated. The effluent from the hydrolysis acidification unit was induced the SNAD biofilter for nitrifition, anaerobic ammonia oxidation and denitrification after biofilm attachment.The main experimental results are as follows.1. During the biofilm attachment of ANAMMOX bacteria, with the influent ammonia and COD concentrations of152.2mg/L and97.1mg/L, the maximum removal efficiencies of ammonia nitrogen, TN, COD was76.5%,71.6%, and53.4%, respectively.2. The SEM (scanning electron microscopy) observation of biofilm in SNAD reactor during biofilm attachment shows that:the outer layer of the biofilm was mostly spherical bacteria, and most of the inner layer was the aggregation of similar cauliflower bacteria.3. The experimental results of hydrolysis acidification-SNAD process in treating artificial rural wastewater show that, in the hydrolysis acidification unit, with the influent C/N ratio of2:1, the removal rate of COD reached69%, and the main components of volatile fatty acid was acetic acid, propionic acid and butyric acid, and the average content of88.4%,6.5%and5.1%, respectively. The effluent VFAs/COD and C/N ratio were0.74and3:5, respectively. In the subsequent SNAD-biofilter unit, by the coupling effect of nitrification, denitrification and anaerobic ammonium oxidation, the removal efficiencies of COD, ammonia nitrogen and total nitrogen were76.7%,94.4%and84.1%, respectively. The COD and total nitrogen removal rates for the whole system reached92.8%and84.1%, respectively.