Study On Rural Sewage Treatment Using Biological Aertion Filter With Slag As Medium

A set of relatively simple wastewater treatment process with better removal efficiency,which is designed according to the characteristics of the rural sewage, is very important to improve rural living environment and water environment quality. Biological aerated filter（BAF） has significant effects on solid-liquid separation, and nitrogen and phosphorus removal. It also has advantages of high ability for resisting shockload, high treatment efficiency, no requirement for secondary settling tanks and less land requisition. Thus,BAF is a kind of suitable treatment for rural sewage.In this dissertation, combining the merits of BAF and slag, slag was applied as a solid filling of BAF to treat rural sewage. The pre-denitrification BAF and pre-denitrification BAF- ecological filters were applied to the rural sewage treatment. The main contents are as the following: adsorption properties of slag to nitrogen and phosphates; biofilm process conditions of pre-denitrification BAF; the removal of COD, NH₄⁺-N, TN, TP, PO₄^3--P and suspended solids; the infiuence of HRT; backflow ratio on removal efficiency;, the optimum process parameters; the pre-denitrification BAF- ecological filter removal of COD, NH₄⁺-N, TN,TP, PO₄^3--P and suspended solids. Raw sewage, recycling water and tap water are used to irrigate Chinese cabbage. The effects of recycling water on crop growth and soil properties are analyzed. Experimental results are listed as follows:（1） Slag filler has a strong adsorption properties to NH₄⁺-N and PO₄^3--P, especially to PO₄^3--P, and the maximum adsorption rates were 29.7% and 54.9% respectively. Under natural conditions, when biofilm was formed by mere aeration, the removal efficiencies of COD and NH₄⁺-N by the slag filler pre-denitrification BAF were steady around 77.0% and90.0% respectively. It shows that it is effective and feasible to treat rual sewage by pre-denitrification BAF use slag as filler.（2） Under changing pollutants concentration in sewage and certain air conditions, the optimal total HRT of the pre-denitrification BAF was 18 h, the removal efficiencies of COD, NH₄⁺-N, TN, TP, PO₄^3--P and suspended solids were 69.5%, 95.9%, 34.4%, 67.2%,70.2 and 83.8% respectively.（3） Under a certain amount of aeration and water influent, the backflow improved pollutant removal; especially to TN removal. The optimal total backflow ratio of the pre-denitrification BAF was 2:1. The removal efficiencies of COD, NH₄⁺-N, TN,TP,PO₄^3--P and turbidity were 89.1%, 91.7%, 70.4%, 74.3%, 73.8 and 97.2% respectively.（4） Under optimum operating parameters of slag filler pre-denitrification BAF, the ecological filter increased pollutant removal, and the removal efficiencies of COD, NH₄⁺-N,TN,TP, PO₄^3--P and turbidity by pre-denitrification BAF- ecological filter were 89.1%,91.7%, 70.4%, 74.3%, 73.8 and 97.2% respectively.（5） Compared with the tap water, the reclaimed water can promote height, fresh weight and chlorophyll of cabbage. The contents of organic matter, TP and rapid available phosphorus in soil increased under reclaimed water for irrigate, but that of TN reduced.While activity of the urease, sucrose and catalase in the soil increased with reclaimed water for irrigation.