Efficacy Of Phosphorus Removal By Biological Filter And The Enhancement By Micro-flocculation

BAF (Biological aerated filter) is an emerging wastewater treatment process with the advantages of small area occupation and steady effluent quality. However, the deficiency that there is no condition for biological phosphorus removal in BAF will lead to poor biological phosphorus removal capability in the system. To achieve the effluent standards in phosphorus, pre-chemical phosphorus removal systerm, synergistic phosphorus removal systerm and post-chemicalphosphorus removal system in BAF are in need. Which not only extend the wastewater treatment plant process, increase investment cost, but also weaken the advantage of area small.This subject is based on the post-denitrification BAF process, according to filtration of grainy filtering media, combined with the principle of micro-particle flocculation and microbe assimilation. This paper presented strategies on improving the effecacy of dephosphorization in BAF. This paper mainly worked as follows:First, this paper studied the influence factors of phosphorus removal in the post-denitrification BAF system. The results show that the phosphorus removal by the biologica filter relies mainly on the physical interception and biological assimilation, and it occurred mainly at the middle-lower part of filling. The average treated volume of TP by C/N column is 1.48mg/L, and DN column can remove TP 0.69mg/L. While the air-to-water ratio is 5:1~7:1, BAF had high efficiency in phosphorus removal. Lengthened the work cycle of filter appropriately and reduced the hydraulic loading are good for phosphorus removal. The increasing of hydraulic load did reduce the removing ability of phosphorus from the BAF. When the water phosphorus concentration is no more than 1.32 mg/L. the density of TP in the effluent water will be under 0.5 mg/L. Furthermore, the size of ceramsite and changing of the seasons had a little effect on biological phosphorus removal.Secondly, this paper studied the efficiency of micro-flocculation phosphorus removal. The results show that among AlCl 3 , PAC, FeCl 3 and PFC, AlCl3 is the ideal chemical agent. The best position of adding chemical is the water-in of DN filter. When the dosing of AlCl3 achieved 50mg/L, the concentration of phosphorus of the effluent water will be under 0.5 mg/L. High doses of chemicals can inhibit the microbial nitrification in C/N filter, and the largest decrease of the removal rate of NH3-N is up to 20%~30%. There was no influence on denitrification adding the AlCl3 to DN filter, but the cycle of DN filter operation would changed from 3~4 to 2 days.Finally, an optimal proposal is presented through the above research, and pilot scale experiments were employed. The running state of the system shows that: with the AlCl3 50mg/L to the water-in of the DN filter, the air-to-water ratio 6:1, and the hydraulic loading 0.45m3/(m2·h), the quality of water being processed was nice. The concentration of the effluent phosphorus met the emission standards at the national level A. Meanwhile, the filters could availably remove SS, COD and TN, saving the area place. All of those had made a base for the further design of this object.