Study On Biological Pretreatment Process During The Raw Water Switch Between Micro-polluted Water And Heavy-polluted Water

For the 2010 Asian Games, and in order to solve the issues of water supply during the urban development, the government of Guangzhou City decided to build the West River Diversion Project, with the West River which is micro-polluted as a common drinking water source, and the original heavy-polluted Pearl River in Guangzhou section as a standby water source, adding the biological pretreatment process in response to the original water pipe burst, water pollution and other sudden emergencies that may occur in the West River Diversion Project.Based on this background, this issue examined effects of the pretreatment process with biological aerated filter (BAF) respectively treating micro-polluted and high-polluted sources; meanwhile it focused on purifying effects during the influent switch. The results showed that:(1) BAF process had a good pollutants removal effect in the pretreatment of simulated slightly polluted West River water. The removal ratio of ammonia, nitrite, CODMn and turbidity respectively reached an average of 87.04%, 83.33%, 18.54% and 39.52% in an operating condition of 16m/h filtration rate and air/water ratio 0.1 to 0.2. Besides, BAF showed good nitrification performance when treating with high polluted Pearl River water. In an operating condition of 16m/h filtration rate and air/water ratio 0.5 to 0.6, the average influent ammonia concentration was 3.49 mg/L, while the average effluent was 0.30 mg/L. The water purification results of two sources showed that,"BAF+General"combined technique could substantially remove ammonia nitrogen, organic compounds and other pollutants, improving water quality and ensuring the effluent up to the new national standard"drinking water health standards"(GB5749-2006 ).(2) In a condition of 16m/h filtration rate and air/water ratio 1 to 1, when the average influent concentrations of ammonia were some 3.0 mg/L, 4.5 mg/L, 6.5 mg/L respectively during the Pearl River's wet, moderate and dry period, the final effluent ammonia nitrogen reached 0.5 mg/L (limitation of"drinking water health standards"GB5749-2006) in 18 hours, 35 hours and 74 hours after the raw water switch. When purifying raw water in the Pearl River's wet period,"BAF+General"combined process achieved the objective that nitrogen concentration of the final effluent was less than 0.5 mg/L within 24 hours after the raw water switch in an operating condition of 16m/h filtration rate and air/water ratio 1 to 1. However, it didn't achieve the objective in either moderate or dry period tests.(3) In an operating condition of 16m/h filtration rate, the final effluent ammonia of the combined process could basically achieve under 0.5 mg/L within 24 hours after the raw water switch when adjusting the air/water ratio from 1:1 to 2:1 in the Pearl River's moderate period. But as for raw water of the dry season, the final effluent ammonia concentration still needed 61 hours after the raw water switch to achieve under 0.5 mg/L when adjusting the air/water ratio from 1:1 to 2:1.(4) With the gas/water ratio 2:1, the average influent ammonia 6.5 mg/L during dry period, when the filtration rates of BAF were reduced to 14.4 m/h, 12.8 m/h, 11.2 m/h and 9.6 m/h, the final effluent ammonia nitrogen of"BAF+General"respectively required for 55 hours, 38 hours, 26 hours and 20 hours to reach 0.5 mg/L after the raw water switch. It showed that with the gas/water ratio 2:1, decreasing the BAF's treating load to 70% of its design load, which was reducing the filtration rate from 16m/h to 11.2m/h, could basically ensure the final effluent ammonia nitrogen under 0.5 mg/L limitation.