Comparison of the water purification efficiency of two different flocculation-sediment-filtration (FSF) processes in Chaohu Lake in China

Abstract

A novel biofilter (BF) with the potential to improve pollutant removal when used as a substitute for sand filters in water purification processes is presented. To investigate BF's pollutant removal performance, a flocculation-sediment-biofiltration (FSBF) process was compared with a flocculationsediment- sand filtration (FSSF) process on a lab scale, with water collected from Chaohu Lake. The results showed that, during the stable period, the average removal efficiencies of CODMn, NH3-N, NO2--N and UV254 of the FSSF process were 31.7, 29.9, 33.3, and 21.1%, respectively, while 42.7, 92.7, 90.3, and 27.8% of CODMn, NH3-N, NO2--N, and UV254 were removed by the FSBF process, respectively. In the BF, microorganisms in the biofilm on granular activated carbon appeared to play an important role in pollutants removal. Moreover, the FSBF process was more efficient at removing compounds from each organic content molecular weight fraction than the FSSF process, particularly for the removal of fractions with a molecular weight less than 10 KD, and especially for fractions less than 3 KD, which predominated the organic contents in raw water. Gas chromatography-mass spectrometry (GC-MS) indicated that the FSBF process could reduce more species than the FSSF and tended to produce or induce more kinds of new organic chemical simultaneously. Ultimately, the total organic species in the effluent of the FSBF process was less than that in the effluent of the FSSF process.