| Biological flocculation and adsorption process is used to strengthen primary sewage treatment in recent years, which can quickly remove most of the organic material in the sewage and reduce the investment and operation cost. The removal rate of COD is over75%, and80%for SS. But the removal of ammonia is limited, normally the remove rate is around20%. Two biological aerated filters (BAF) are used by steps after the biological flocculation and adsorption process during the treatments for sewage. One is for the removal of carbon and ammonia (hereinafter referred to as C/N BAF), the other is for the removal of nitrogen (hereinafter referred to as DN BAF). The removal rate of COD, SS, and ammonia by the BAF are high. But shortage of carbon sources is the problem during the denitrification process. Most of the organic matter in sewage are removed in the biological flocculation and adsorption process by the activated sludge, which is discarded after the setting process. After the study of the impacts of hydrolysis and acidification of the sludge produced in the biological flocculation and adsorption process (named bio-flocculation/adsorption sludge), a special device for sludge hydrolysis and acidification was set up, where the bio-flocculation/adsorption sludge were hydrolyzed and acidified. The products of hydrolysis and acidification were used as carbon sources for denitrification, and improved the denitrification efficiency of the systems. So a new sewage treatment method was developed.The main results of this study are as follows:(1) The impacts of temperature, stirring, HRT and sewage on the sludge hydrolysis and acidification were studied. At the temperature of25℃, the organic products concentration (represented as COD) achieved a maximum value385mg/L after5hours of the sludge hydrolysis and acidification. The rising of temperature and mixing all can help the sludge hydrolysis and acidification. When main organic material in the sewage were dissolved, the organic matter in the bio-flocculation/adsorption sludge would reduced and COD value of the products were not more than100mg/L neither at25℃and35℃.(2) A special sludge hydrolysis and acidification device was set up, where the bio-flocculation/adsorption sludge could hydrolyze and acidify effectively, and the solution could be water separated from the sludge effectively. Stable operation within10days, the mean concentrations of COD, ammonia and phosphate were373mg/L,25mg/L and2.3mg/L, respectively.(3) Biological flocculation and adsorption system could remove the organic material from the sewage effectively, but not for the ammonia. The C/N BAF had a good ability to chang ammonia to nitrate. The total nitrogen removal by DN BAF was little without enough carbon sources, and it’s improved a lot by giving sugar or the products of hydrolysis and acidification of the bio-flocculation/adsorption sludge as external carbon sources.(4)With the products of hydrolysis and acidification of the bio-flocculation/adsorption sludge used as external carbon sources, when the flow rate was1to3, denitrification efficiency of DN BAF was more than70%, and the maximum value could be over80%.The ammonia in the hydrolysis and acidification solution had little impacts on the effluent of the DN BAF, but sometimes the phosphate in the solution would increase phosphate content in the effluent of DN BAF, compare with the C/N BAF effluent. |
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