Other Abstract | The environmental carrying capacity has become increasingly saturated in china,requiring the sewage treatment plants implementing stricter discharge standards.However, current technology for deeply removing nitrogen pollutants, as represented by heterotrophic denitrification filter, suffers from high operating costs and sludge yield, and is difficult to balance the COD reaching standards. A hydrogen rich solution is to obtain by dual champers MFCs, which usually is directly discharged .The present study aims at demonstrating t he dissolved hydrogen can be feasibly applied in iron assisted autotrophic denitrification to accelerate the nitrate reduction during ZVI corrosion. If the hydrogen rich water was re cycle d for iron assisted denitrification , it could a chieve further hydrogen recovery and purification of wastewater. Meanwhile, t his project proposes a novel reactive filter for deeply removal of nitrate with low cost element sulfur and siderite as the bio carrier in order to replace traditional adding carbon sources . The composition principle of elemental sulfur and siderite for the removal of N, as well as the effects brought from the change of influent criteria will be investigated to understand the optim ized status of the composite system and the potential advantages compared to the existing technologies. In addition, the fate of each relevance element and the biological information in the system will be analyzed to clarify the correlated synergistic mech anism of elemental sulfur and siderite during the removal of N. This project is expected to technologically and theoretically support the deeply removal of nitrogen pollutants in sewage treatment plants more cost effective, integrated and stable.
Firstly,H 2 producing by ZVI corrosion process plays an important role in the iron assist ed nitrate reduction process, which determines the nitrate reduction rate and the end product. The present study aims at demonstrating t he dissolved hydrogen can be feasibly ap plied in iron assisted autotrophic denitrification to accelerate the nitrate reduction during ZVI corrosion. It was observed that a continuous dissolved hydrogen supply with electrolysis promoted and stabilized the performance of iron assisted autotrophic denitrification. The average nitrate removal was 47.3% 0.2% in ZVI reactors with dissolved hydrogen rich water (DH reactor), and 30.2% 0.3% in the ZVI reactors without dissolved hydrogen rich water (control Moreover,the concentration of nitrite w as 0.0 4 mg/L in DH reactor compared with 0.50 mg/L in the control reactor No other intermediate s (e.g. N 2 O) were found in both the autotrophic denitrification reactor s. Finally, the hydrogen rich water enriched the denitrifying bacteria and increased the abundance of f unctional genes specific ,resulting in the promotion of h ydrophobic denitrification during the iron assisted nitrate removal process.
Secondly,in order to investigate the feasibility of sulfur coupled with iron(II) carbonate ore (SICAD) to drive deeply removing nitrogen and phosphorus pollutants of wastewater, this study selected the optimal size of 1.0 1.5 mm from different sizes of sulfur and iron(II) carbonate ore to construct a SICAD system . The packed bed (SICAD system) is used to treat wastewater containing nitrogen and it is highly efficient for deepl y removing nitrogen and phosphorus pollutants. At a HRT of 0.5 h, the TN load ing is as high as 720.35 g∙N / m 3 d SICAD could decrease N2O or NO2 accumulation and produce less sulfate products. The acid produced through sulfur driven denitrification was found to promote the Fe(II) leaching from the ore and likely extend the reaction zone from the surface to the liquid. As a result, more biomass was accumulated in the SICAD system compared with the controls (sulfur,iron(II) carbonate ore and SLAD systems Moreover, iron(II) carbonate might promote the electron transfer by enrichment of FeOB in order to enhance the nitrogen removal efficiency . SICAD might bring out t he redox cycling of Fe in order to promote the transfer of electrons between two solids (ie. S ulfur and iron(II)carbonate particles ) or two bacteria by electron shuttles.
Further, we study the effect of sulfur and siderite mixed principle and the water quality on the SICAD process . It was necessary to focus on the characteristics of the filter material consumption, the optimization of the filter material and the ability to treat the secondary effluent. The results show ed that the SICAD 1/1 system ha s the highest TN removal efficiency which was higher than that in SICAD 2/1 and SICAD 1/2 system, when the ratio of sulfur and siderite was 1:0, 1:1, 2:1 and 1:2 . This result was attributed to that the main process of autotrophic denitrification is carried out in this layer of biofilm. Therefore, t he specific surface area of sulfur is an important factor on nitrate removal efficiency . In addition, the addition of siderite provide d a site for microbial attachment on sulfur, and it act as electron donor for autotrophic denitrification. I n this study t he TN removal efficiency of was not affected by the influent nitrate.
Finally, the effect of SICAD system on phosphorus removal was investigated. It was found that the phosphorus removal mechanism in SICAD sys tem was consistent with that of siderite . I t achieved higher phosphorus removal efficiency in SICAD than ICAD system . It wa s mainly attributed to t he ferric phosphate precipitate was filtered and trapped in the filter. These substances c ould adhere to the surface or gap of siderite , which will further affect the nitrate removal efficiency . However, the acid produced through sulfur also could help sedimentation not accumulate on the surface of sul f ur/siderite . It can provide a reaction interface for the deni trification process and ensure high er TN removal efficiency. The SLAD process also has a certain removal effect on phosphorus. It mainly relies on the hydrogen ions generated by denitrification could promote limestone to release Ca 2+ which react with H 2 PO 4 and HPO 4 2 to form precipitates. However, this form of precipitation is not stable. This study revealed both the feasibility and mechanism of SICAD, offering greater potential and feasibility for practical applications for secondary effluent purification. |
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