Research On Application Of EBF Equipment For Sewage Treatment In Highway Service Area

With the rapid development of China’s highway industry,its affiliated service areas provide convenience for people to travel,but also bring a certain degree of pollution to the surrounding environment.Sewage treatment equipment selecting,high operating costs,and high operational management requirements have become disposal difficulties for wastewater treatment in service areas.In order to promote the building of"resource-saving and environment-friendly"modern transportation industry and promote the sewage treatment and utilization in expressway service area,a small integrated equipment with high processing efficiency,low operating cost and high degree of automation--EBF（Expanded bed combined biofilters）integrated equipment is researched in this paper.This equipment is applied to the sewage treatment in Zhongxin Service Area of the Guanghe Highway.In view of the characteristics of high NH₄⁺-N and high organics in the inlet water quality,the"down-flow denitrification filter（A）--up-flow aerobic expansion bed filter（O）--down-flow aerobic expansion bed filter（O）"multi-stage filter is applied in series.The experiment first studied on the biofilm culturing feature of EBF integrated equipment,the equipment’s biofilm formation method,and the backwash mode,strength and cycle of various filters.Then the influence of factors such as alkalinity,inlet hydraulic load,reflux ratio and gas-water ratio on the removal effect of COD_crr and NH₄⁺-N is analyzed to obtain the optimal operating condition.Running equipment stably at the best operating conditions and then discuss the removal of organics,NH₄⁺-N,TN,SS and turbidity.Finally studied the biological phosphorus removal and adding polymeric ferric sulfate（PFS）phosphorus removal agent to enhance the effect of micro flocculation phosphorus removal.Based on above tests and the analysis of the removal effect of the equipment on various pollutants in rush hour,sewage reuse and discharge schemes are designed to provide a reference for this service area.The experimental conclusions are as follows:The experiments were performed on the natural biofilm start-up.After 30 days of biofilm culture,the removal rate of COD_cr、NH₄⁺-N can reach above 70%、90%.Under the test conditions,when Na₂CO₃ was added at 100-150 mg/L,the total removal rate of NH₄⁺-N in the system was up to 95.75%.After the addition of alkalinity,the concentration of NH₄⁺-N in the effluent does not decrease immediately,but will lead to a lag period of about one week.With the increase of influent hydraulic load,the concentration of COD_crr and NH₄⁺-N decreased.The recovery ability of the system was strong when it was subject to the large water shock.When the reflux ratio was 150%,the removal rate of COD_crr and NH₄⁺-N was the highest.With the increase of gas water ratio,the concentration of COD_crr increased first and then decreased,the concentration of NH₄⁺-N increased.when the water hydrauli load was 3 m³/（m²·h）and reflux ratio was 150%,together with gas water ratio was2:1,under this running condition,the removal rate for COD_cr、BOD₅、NH₄⁺-N、SS and turbidity could respectively achieve 88.57%、94.96%、96.29%、96.21%and 98.05%.The effluent water quality could stably reach the comprehensive water quality standards of"urban miscellaneous water quality standards"and"urban sewage recycling-water quality for landscape environment".The average removal rate of TP in the equipment relying only on biological phosphorus removal was 65.29%.After adding PFS phosphorus removal agent,TP removal rate increased with the increase of PFS dosage.When the dosage of PFS was 40 mg/L,the average removal rate of TP was 84.94%,and the effluent could reach the secondary standard of"comprehensive sewage discharge standard".The removal rate of COD_cr,NH₄⁺-N,SS,turbidity by equipment in rush hour could still maintain a high level.The dosage of PFS should be increased to 50 mg/L to strengthen phosphorus removal,so that the effluent water quality could meet the reuse and discharge standards.In view of the situation of water volume doubling and rising,it was suggested to add an integrated 60m³/d EBF equipment in the later operation.The sewage partial reuse and discharge scheme or the sewage total reuse scheme could be selected to ensure the effluent quality reaching the standard in the rush hour.