Study On Filtration With Four Kinds Of Media For Seasonally Polluted Raw Water With High NH₃-N Concentration

Enhanced filtration with activated anthracite was used to treat the seasonallypolluted raw water of Dongjiang River, and with anthracite, sand and activatedcarbon was compared. In the raw water the concentration of ammonia nitrogen andorganic matter rises sharply caused by seasonal pollution.Laboratory analyses were conducted to analyze the surface property of thesefour kinds of media. Scanning electron micrographs （SEMs） showed that the surfaceof the activated anthracite was finely porous similar to activated carbon, butanthracite was much smoother. The results of nitrogen adsorption analysis showedthat the pore size of activated anthracite was mainly in the range of0.45⁴.70nm,and its capacity of mesopore and macropore was slightly more than activated carbon.The removal effect of total organic carbon （TOC） and odor matters by adsorptionwas tested. It was showed that the activated anthracite and activated carbon canremove more than70%of TOC and60%⁹0%of odor matters, much better thananthracite tested.Filtration performance with activated anthracite, sand, anthracite and granularactivated carbon was tested on site. The results showed that filtration performancewith activated anthracite was similar to that with sand in the removal of turbidity,and the turbidity in effluent of each filter was below0.2NTU. Filtration withactivated anthracite and activated carbon can removal more than94%of ammonia,the concentration of ammonia in effluent reached to0.3mg/L lower. Thetransformation of ammonia in filtration with sand and anthracite was not completed,thus the nitrite concentration in effluent got accumulated, even0.58mg/L higherthan that in influent. Removal efficiency of TOC and UV₂₅₄in filtration withactivated anthracite were33.4%and43.6%on average. The filtration with activatedanthracite was also much better than that with either sand or anthracite in terms ofodor matters such as geosmin,2-MIB, and dimethyl sulfide removal.Pure oxygen aeration-biological active filtration was used to treat the waterwith high concentration of ammonia. The results showed that aeration with pure oxygen could increase dissolved oxygen concentration to25mg/L, thus significantlyimprove removal efficiency for ammonia of all four filters. When the ammoniaconcentration in influent was4mg/L and6mg/L respectively, the removal efficiencyincreased to67%and47%from40%and26%before aeration by filtration withsand and anthracite, to90%and84%by filtration with activated anthracite andactivated carbon. The nitrite concentration in effluent of sand filter and anthracitefilter got accumulated, even increased to0.8⁰.9mg/L. Filtration with activatedanthracite and activated carbon can convert most part of ammonia into nitrate, andduring this process the ratio of ammonia removal to oxygen demand was1:4.25onaverage, which a little bit lower than theoretical ratio. The quantitative ratio is ofsignificance in guiding the design and operation of bio-filtration process to removeammonia from water.