Flocculants for the High-Concentration Activated Sludge Method and the Effectiveness of Urban Wastewater Treatment

In this paper, the three inorganic flocculants polymeric chloride PAC, FeCl3, and Al2(SO4)3 and two organic flocculants anionic polyacrylamide APAM and cationic polyacrylamide CPAM were screened to determine the most efficient flocculants and the optimal dosage, optimizing the flocculation operating conditions through the orthogonal test and then proving the experimental effect according to a comparison study of the high-concentration method and the traditional activated sludge method. The results show that the addition of CPAM achieves the best flocculation for high-concentration activated sludge suspension, and that the sludge interface descent rate, sludge volume index, and sludge settling ratio are better than those of other flocculants. The orthogonal test was used on the sludge volume index to perform evaluations and analyses: mixing section mixing intensity > Flocculation Stage 1 section mixing intensity > Flocculation Stage 2 section mixing intensity > mixing section residence time > flocculation section hydraulic residence time. In the comparison test, the settling performance of the high-concentration method was higher than that of the traditional activated sludge method. In terms of pollutant removal, the removal rates of COD, ammonia nitrogen, and total nitrogen of the traditional activated sludge method were 90.85%, 95.74%, and 71.6%, respectively. The average removal rates of COD, ammonia nitrogen, and total nitrogen of high-concentration activated sludge method were 92.24%, 97.28%, and 80.97%—higher than that of the traditional activated sludge method.