Study On The Treatment Of Water From Yellow River Reservoir By The Technology Of Biological Pre-treatment In Pilot Test

This subject was supported by "The research and demonstration of biological pretreatment technology",which led by the major science and technology projects of national water pollution control and management. The Aerated Biological Fluidized Tank and the Biological Aerated Filter were seperately used in pre-treatment of micro-polluted water derive from Yellow River, and these two kinds of water treatment technology were optimized.The optimal elements and index were selected by pilot-scale test, including hydraulic condition、the most suitable padding、the influence of temperature. the optimal hydraulic condition in low temperature、the influence of phosphorus and ammoniac nitrogen concentration made to nitrification, and coagulation effect the biological pre-treatment made to the water.The results of the pilot-scale test show that:(1) The optimal operating condition of ABFT was selected as the water temperature was16-20℃, the optimal HRT and the aeration intensity are separately60min and2.7m3/(m2·h), and the air water ratio is0.6:1. As to BAF, the optimal filtering velocity and aeration intensity are separately6.4m/h and3.2m3/(m2-h), the air water ratio is0.5:1.(2) The metabolic activity of heterotrophic and nitrifying bacteria are restricted as the water temperature below5℃in ABFT and BAF. The restriction was relieved as the temperature raised. The removal potential of ammoniac nitrogen and CODMn were enhanced as temperature rose from6℃to20℃.(3) Water temperature was below5℃in winter. Considering of this factor, the optimal HRT and aeration intensity of ABFT were separately100min and2.2m3/(m2-h), the air water ratio was0.8:1. And the optimal filtering velocity and aeration intensity of BAF were5.1m/h and2.5m3/(m2·h) separately, the air water ratio was0.5:1.(4) In the operation of ABFT, comparing to the fluidized degree, the LT-100padding behaved better than the LT-50padding. And it was better as filling rate reaching50%than30%.In the operation of BAF, three grain sizes of volcanic was compared according to their removal rate of ammonic nitrogen、CODMn、turbidity and UV254. As influent ammonic nitrogen concentration0.2mg/L, the filtering velocity7.6m/h, gas water ratio0.5:1, water temperature 16-20℃, the reactor with1-3mm volcanic obtained higher removal rate in ammonic nitrogen、CODMn and turbidity than volcanic with the grain size of3-5mm、8-10mm.(5) The removal process of ammoniac nitrogen could be restricted in ABFT if the phosphorus concentration in the influent water is too low. But the restriction in BAF behaved not so obvious. As water temperature became16-20℃, influent ammoniac nitrogen concentration was0.2mg/L, the phosphorus concentration of influent rose from5μg/Lto20μg/L, the removal rate of ammoniac nitrogen in ABFT was improved from26.2%to86.2%. And the removal rate of ammoniac nitrogen in BAF was improved from55.3%to89.6%. When phosphorus concentration of influent in ABFT reached20μg/L, its restriction to the removal of ammoniac nitrogen could be relieved. In this condition, the phosphorus concentration of effluent was9-13μg/L. When phosphorus concentration of influent in BAF reached10μg/L, the removal rate of ammoniac nitrogen could keep at over80%-90%. The restriction of phosphorus to the removal of ammoniac nitrogen could be relieved. With the increasing of ammoniac nitrogen concentration of influent, the consumption of phosphorus increased.(6)Comparing to coagulation process alone, the ABFT/Coagulation combination process could improve CODMn、TOC and UV254removal rate of about6%-9%,1.5%-6%and2%-14.4%. The BAF/Coagulation combination process could improve CODmn、TOC and UV254removal rate of about8%-11.8%,4.6%-8.5%and2%-9%. Adding into the effluent the coagulant as its concentration was5mg/L. Adding the coagulant with the concentration of5mg/L into effluent of biological treatment, the removal rate of CODMn、TOC、UV254in ABFT were separately22.1%、18.0%、22.2%, the removal rate in BAF were separately24.0%、23.8%、27.7%. The coagulation effect was the same as the coagulation with10mg/L coagulant in raw water. Coagulation effect could be greatly improved after ABFT、BAF process. The coagulant dosage in the subsequent coagulation process could be reduced. The combination process can reduce the environmental load and save the cost. The effluent of BAF behaved better than ABFT in coagulation process.