Research On Enhancing Denitrification And Phosphorus Removal Of Urban Wastewater With Low-Carbon

With the development of economy, the contradiction between water pollution problems and rapidly increasing water demand become more serious. At the same time, large amounts of nitrogen and phosphorus from domestic sewage and industrial wastewater were discharged into rivers and lakes, so the nitrogen and phosphorus content of water grow rapidly and result in a lot of issues. Dongjiang River is the mother river of Shenzhen and Hong Kong. As a source of drinking water, its water quality was highly valued by our nation and local governments in Dongjiang River Basin. During the period of Twelfth Five-Year Guideline,water quality of upper reaches of Dongjiang River Basin should meet the Class III water standards of Surface Water Environmental Quality Standard（GB3838-2002）. As a typical urban wastewater treatment plant in the upper reaches of the Dongjiang River, the effluent of Heyuan Chengnan Domestic Wastwater Treatment Plant should meet the Class III water standards of Surface Water Environmental Quality Standard（GB3838-2002）.The main Treatment Process of this Plant is A/O Biofilm Reactor. The main Sewage Indexes of Influent and Effllunt showed that it was a typical Low-carbon Sewage Plant in South China and the effluent of TN could not meet the Standard stablely.To achieve the standard, PAC was dosed to the effluent of A/O Biofilm Reactor. While, this strategy need high costs and will have a problem of high sluge production.What’s more, the effluent can not meet the standard either and the sluge can plug the microfilter.So in this article, we want to seek an economical and effective way to remove nitrogen and phosphorus in this Plant. The use of Coupling body of Ferrous Salts and Organic Carbon to treat low carbon wastewater was first proposed.SBR reactor and A/O biofilm reactor were used to inspect the effection of denitrification and phosphorous removal by adding coupling body of Ferrous Salts and Organic Carbon, and the impact factors and mechanisms of using coupling body to enhance denitrification and phosphorous were preliminarily studied.The experimental results are as follows:（1） Different levels of FeSO₄(5⁶0mg·L^-1) and 50mg·L^-1CH₃ OH were dosed to several SBR reactors and the efficiency of denitrification and phosphorus removal were recorded. The results showed that adding FeSO₄ to the rector can promote the removal efficiency of nitrogen and phosphorous. And the efficiency was increasing with the increasing addition of FeSO₄.（2） Different kinds of Ferrous Salts（FeSO₄, FeCl2, FeS） and organic carbons（CH₃OH,CH₃CH2 OH, CH₃COONa） were selected through a series of parallel experiments. FeSO₄ coupled with CH₃ OH was chosen to be the most suitable coupling due to its high removal efficiency of both nitrogen and phorsphorous. The conditions of using coupling body to enhance removal efficiency of denitrification and phosphorous removal were further investigated by an orthogonal experiment. Results showed that appropriate conditions ofusing coupling body were Fe/P=2.4、T=33℃ and pH=7 when the C/N was 2.5 and the dosage of CH₃ OH was 100mg·L^-1. And in this condition, the effluent water could meet the Class III water standards of Surface Water Environmental Quality Standard（GB3838-2002）.（3） The mechanism of coupling body enhancing the efficiency of nitrogen and phosphorous removal was studied too. And results showed that the addition of FeSO₄ can promote biological activity.（4） For low-carbon source wastewater, using arrange mud law can achieve rapid and stable biofilm for A/O Biofilm Reactor.（5） Considering of the quality of influent, the dosage of CH₃ OH was fixed to 50mg·L^-1.When the FeSO₄ was dosed as [Fe] = 5mg·L^-1, the removal rate of COD, TN, TP and NH₃-N had been significantly improved compared to previous in a period of SRT. Their removal rate increased by 5%, 36%, 66.7%, 13.06% respectively and COD, TN, NH₃-N could meet the Class III water standards of Surface Water Environmental Quality Standard（GB3838-2002）and the removal rate of TP can reach the ‘urban sewage treatment plant pollutant discharge standard’（GB18918-2002） 1A discharge standard. The effluent pH decreased slightly by adding Coupling body.（6）In order to increase the removal rate of TP, different amounts of FeSO₄ were dosed to the A/O Biofilm Reactor. The results showed that increasing [Fe] could increase the removal rate of TP effectively. When the [Fe] = 20mg·L^-1, the effluent TP could meet the Class III water standards of Surface Water Environmental Quality Standard（GB3838-2002）.However, when the [Fe]=8mg·L^-1 and 20mg·L^-1, the removal of TN had been severely affected. This is mainly due to the excessive dosing of FeSO₄, which could make severe iron accumulation in biological membrane.