污水地下渗滤系统脱氮效果及动力学过程

Efficiency and kinetic process of nitrogen removal in a subsurface wastewater infiltration system(SWIS)

建立了模拟污水地下渗滤过程的中试系统,重点考察了水力负荷对系统脱氮效率的影响情况,建立了描述地下渗滤系统微生物脱氮过程的动力学模型。结果表明:地下渗滤系统脱氮效果好,抗水力负荷冲击能力强,处理最佳水力负荷0.125m.3m-.2d-1,出水中氮浓度低于《城市污水再生利用——景观环境用水水质》标准(GB/T 18921—2002)。地下渗滤系统硝化过程符合一级动力学模型NE=N0e-0.4812t,温度是影响硝化速率的主要因素,两者的关系是KT=0.2218×1.035(T-20);出水硝态氮浓度与水力停留时间之间呈负指数关系,可描述为C=16.3475e-0.2548t,碳源是引起反硝化速率变化的主要因子。在基质层垂直深度65 cm处二次补加生活污水,反硝化速率常数由0.0355提高到0.0488。强调地下渗滤系统的污水净化功能而忽视其生态服务功能,是系统运行中普遍存在的认识误区,过高的水力负荷不利于硝化-反硝化反应的顺利进行。地下渗滤系统运行应采取适宜的水力负荷方式,促进硝化-反硝化作用。

As a kind of eco-treatment system,the subsurface wastewater infiltration system（SWIS） is made on the principles of recycling and reusing the wastewater,harmonious with the environment,unified and differencing with the positions.SWIS is an efficient and economic technology for small scale decentralized sewage（SCDS） treatment.Compared with the conventional activated sludge treating process,SWIS has more advantages,such as low construction and operation costs,easy maintenance.Subsurface infiltration technology can not only remove most of the pollutants in wastewater,but also propose high water reclaiming rates.The dominant pollutant removal efficiencies of a SWIS are generally satisfactory in terms of biochemical oxygen demand（BOD）,chemical oxygen demand（COD） and suspended solid（SS）.However,there still remain problems with nitrogen removal usually due to the complicated interior environment of SWIS,e.g.,the oxygen reduction potential（ORP） in different depth of the SWIS varies obviously,which affects the nitrogen removal process（nitrification-denitrification） directly.Hydraulic loading rate is an important factor affecting the nitrogen removal efficiency,especially the nitrification and denitrification processes,because different hydraulic loading rates can result in different ORP.The higher hydraulic loading rate hinders the nitrification process,which is proved by the increasing nitrogen concentration in the effluent.In order to promote the innovation of this kind of wastewater eco-treatment system and its wide application,provide a scientific and technical basis for the system implementation,a research on the nitrogen removal and kinetic process was made.This study conducted two pilot scale SWISs,analyzing the influence of hydraulic loading rates on nitrogen removal effect.A total of four major operational phases were tested during the experimental period： hydraulic loading rate 0.040,0.085,0.125 and 0.20 m3 · m-2 · d-1,respectively.And also,dynamic models for the nitrification and denitrification process were studied.The results showed that,as for the nitrogen removal efficiency,the optimal hydraulic loading rate was 0.125 m3 · m-2 · d-1.As such,NH3-N and TN concentrations in effluent were 3.5 and 13.6 mg/L,respectively,lower than the standard of water quality for scenic environment use（GB/T18921—2002）.The first order kinetic model NE=N0e-0.4812t fit the nitrification process well.Temperature was the main factor affecting the nitrification rate withKT=0.2218×1.035（T-20）.With respect to the denitrification process,NO-3-N concentration in effluent was in negative exponent correlation C=16.3475e-0.2548t with the hydraulic retention time.Carbon source was the major factor causing the changes of denitrification rate.With the shunt method applying at 65 cm depth,the denitrification rate rose from 0.0355 to 0.0488.Finally,the study pointed that the SWIS system should be operated under an optimal hydraulic loading rate mode,ensuring the nitrification-denitrification process going successfully.This study will guide the decision on a potential full-scale SWIS application and reuse of the treated wastewater.