| Compared with physical or chemical methods, biological technologies are more cost-effective in sewage treatment. Anaerobic processes for treating wastewater can have lower costs but more environmental friendly. However, the toxicity of high concentration industrial wastewater may inhibit the microbes in biological processes decreasing the performance in terms of organic removal and mineralization ratio. Producing dye is a typically fine chemical production process. Because of dyes diversity and their complex reactions, complicated composition is frequently involved in dye wastewaters, leading to the poor biodegradability and low treating efficiency using biological methods. The combination of advanced oxidation and anaerobic digestion technology is expected to improve the removal of toxic refractory organic pollutants in the wastewaters. ZVI has been proven effective to maintain the anaerobic atmosphere in anaerobic processes, promoting anaerobic hydrolysis acidification and improving anaerobic treating capacity. Till now, few reports have been focused on the impacts of ZVI in methanogenesis of the two-phase anaerobic process for treating high-concentration dye wastewater, especially in anaerobic process following Fenton oxidation. Therefore, ZVI was added into the methane-producing phase of the two-phase anaerobic process for treating a high-concentrations dye wastewater was investigated in this study. Prior to the anaerobic treatment, this wastewater was pretreated by Fenton.Based on the above consideration, the following conclusions were made:1. Optimized Fenton oxidation conditions were as follows:Fenton reagents were added according to the mass ratio as COD:H2O2:Fe2+=1:0.3:0.2. After the Fenton, the biodegradability of the dye wastewater increased from 0.0808 to 0.3350, creating a good condition for the subsequent biological treatment.2. Enhancement of zero-valent iron added into anaerobic methane reactor was investugated. Compared with conventional anaerobic reactors, COD removal efficiency increased from 60% to 87%, methane production increased from 0.17 L/h increased to 0.26 L/h. These results indicated that zero-valent iron added had significantly improved the performance of the anaerobic reactor.3. As a reducing agent, ZVI reduced the redox potential in the reactor to optimize the anaerobic environment. The reaction of zero-valent iron with organic acids reduced H+content in the reactor, which effectively enriched hydrogen-consuming methanogens, improved the utilization of H2, reduced the partial pressure of H2, promoted the organic acid catabolism, and improved the mineralization of organic matters in the wastewater. 4. ZVI generated iron ions in the anaerobic reactor during the reaction. As nutrients, the iron ions might be used by microorganisms to improve the iron content of the sludge in anaerobic reactor. At the same time, the oxidation product of anaerobic microorganisms consumed zero-valent iron surface to maintain the degradation of organic pollutants.5. Adding the Fe3+ into the anaerobic reactor increased the activity of iron-reducing bacteria in anaerobic sludge. By electron transfer, the organic matter is oxidized and degraded with the reduction of Fe3+. It also improved the removal of COD. Therefore, as industrial waste, rusty iron could be directly added into anaerobic reactor with no need of removing its surface rust. The iron oxides on the surface of iron might be depleted, and then the fresh zero-valent iron inside could play the role in the anaerobic process. |
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