Study On Advanced Treatment Technique Of Phosphorus Removal In Drinking Water

The biological stability of drinking water is the hot point in research field. In pipe network, the increasing of the heterotrophic bacteria is related to the nutrients that the bacterial growth needed, and phosphorus is one of the most important nutrients, being regarded as one of reasonable biological stability indexes of drinking water quality.Phosphorus exists as various forms in water. Through extensive survey of surface water fields, phosphorus contents of every form, the relativity with other indexs, the microbial availibility and the removal feasibility of them in water treatment processes are studied in this paper. The results show that the general order in concentration is: floating phosphorus> dissolvable organic phosphate> dissolvable inorganic phosphorus, and 80 percent of total phosphorus exists as floating phosphorus; phosphorus of every form is relative with other water indexes in concentration, respectively; more than one form of phosphorus is available to microbial and the model between the concentrations of microbially availible phosphorus and phosphorus of different forms is found; routine water processes present well on phosphorus removal, but advanced techniques are needed in order to achieve biological stability.Through coagulation experiments, phosphorus removal efficiency of commen coagulants is compared, the influence indicators and removal mechanism of phosphorus in coagulating are studied. The results shows that poly ferric sulphate, poly aluminum chloride and poly aluminum-ferric sulphate are three highly active coagulants in phosphorus removing and poly ferric sulphate presents best, the optimum pH values for them to remove phosphorus are 7.5, 6.5 and 6.0, respectively, the effects of pH on PAC and PAFS are remarkable while on PFS is slight; there are three mechanisms in phosphorus removing: colloid flocculating and settling function, associative adsorption, and adsorption wraping function, one of which may dominate for phosphorus of certain form; for floating phosphorus, colloid flocculating and settling function is the main mechanism while associative adsorption and adsorption wraping dominate, respectively, for dissolvable organic phosphorus and dissolvable inorganic phosphate.Through comparing experiments of manifold coagulating aids, polyacrylamide(PAM) and permanganate composite chemicals (PPC) are proved outstanding on improving phosphorus removal, and PAM presents better; optimum adding time and dosage for them exist; the combination of PAM and PPC presents even better phosphorus removal efficiency.Through dynamic simulated filtration experiments, phosphorus adsorption of common filters from water samples containing phosphorus of different form is studied.The results show that the removal efficiency for floating phosphorus of the filters used is equivalent, and the removal mechanisms of it are holding up,exterior physical and static sorption of filters; for dissolvable inorganic phosphorus, proprietary sorption is the main mechanism;activated alumina presents as an efficiency adsorbent, the proprietary mechanism of which is the iron exchange between phosphate and oxyhydrogen aluminium forming from the combining of surface molecules of activated alumina with water, but aluminium iron rising and pH adjusting after filtration are two problems to alumina's usage as drinking water filter.Through altered filters experiments, altered sand filter which has equivalent phosphorus removal efficiency with activated alumina is prepared. It is economically and technically feasible to use the altered sand as a drinking water filter. Beside routine holding up and sorption function in filtration, the formation of oxides on the alter sand is propitious to the removal of phosphorus.