Research Of Strengthen Control Characteristics And Integrated Application Of Process Of Improved Zero-valent Iron (ZVI) Technology For Nitrophenol

The nitrophenol pollutants (Nitrophenols, NPs) can do serious damage to the environment for the characteristics of variety, refractory and toxicity. There is an urgent need to seek practical processing methods both in industrial water treatment and the groundwater remediation. Zero-valent iron (ZVI) reduction technology is the core of this paper, theory and technology research of the pure ZVI system, iron/copper bimetal catalytic ZVI system as well as ZVI-enhanced coagulation process of degradation of NPs were systematically carried out in the paper.4-nitrophenol (4-NP) and 2,4-dinitrophenol (2,4-DNP) were optimized as the target characteristics of the pollutants for these NPs figured into a "priority control pollutants list" by countries such as China and the United States environmental protection departments. ZVI reduction reaction system was builded to the research of the reduction conversion efficiency and process mechanism of two kinds of NPs. ZVI efficiency can be promoted by Mass concentration, temperature, reaction speed, etc. The influence of pH to the reaction is obvious, acid condition is good to the reaction for the optimal pH of 2.0. The degradation rate of pure ZVI system for 4-NP and 2,4-DNP is 92.8%,58.7% under the optimal condition,respectively.The order of influence to ZVI degradation efficiency by different electrolytes is:NaCl> NaSO4> no electrolyte> Na3PO4> NaNO3.Periodic acid pickling has an significant effect on improving the reactivity of passivated ZVI. HPLC and LC-MS analysis results show that the degradation path for 4-NP:first,nitrophenol was transformed to aminophenol, part of aminophenol continue to be oxidated to hydroquinone and benzoquinone.Series of Fe/Cu bimetal catalysts were designed and prepared, Various methods such as SEM-EDS, XRD, XRF were used to characterize the material and its preparation of success was verified based on microscopic and chemical structure. Galvanic coupling was constituted by cathode metal Cu and anode metal Fe,which can make the electrons liberating to the cathode Cu surface from anode Fe at a faster speed, therefore the NPs has higher rate of reduction. In the cathodic reduction process, the H adsorpted by cathode surface has reducing action for the pollutant. Loading capacity of Cu, pH, temperature, etc are the main factors of the effects of Fe/Cu for the NPs degradation efficiency. The degradation rates of 4-NP and 2, 4-DNP were as high as 98.8% and 98.8% respectively in the optimal pH of 2.0, the optimal temperature condition of 30℃, the initial concentration of 200 mg/L, the ZVI dosage of 4.0 g/L, increased by 7.4% and 40.4% compared with the pure ZVI system,respectively. TOC removal rates for the 4-NP and 2,4-DNP wastewater by Fe/Cu bimetal catalytic system reached 20.54%,16.38%, increased 3.7,4.2 times compared with the pure ZVI system respectively, which was remarkable for the mineralization effect. Excellent acid resistance and reliability of the Fe/Cu bimetal material were proved by 9 batches of stability experimental results.Conventional water quality indicators (TOC,COD), particular pollutants and biological toxicity indicators were used to evaluate and optimize the ZVI-coagulation integrated process. The order of coagulation efficiency of Neutralizing agent is: calcium hydroxide> sodium hydroxide> ammonia. The order of effect of three kinds of high polymer coagulant for NPs enhanced coagulation is:PFS> PAFC> PAC. The removal rate of 4-NP and 2,4-DNP for residual pollutants of the waste water reached 90.12%,85.37% respectively with the PFS dosage of 200 mg/L. ZVI mixed and stirred reactor was manufactured to proceed NPs wastewater treatment pilot tests on the basis of comparing to fixed bed, fluidized bed, mechanical agitation type and other various types of ZVI equipments. The results proved that removal rate of 4-NP and COD reached 100%,50.8% respectively by ZVI-coagulation process. Under the condition of optimized processing, BOD5/CODCr of the effluent reached up to 0.41, as well as the toxic unit (TU) to 1.6 with the raw water of 5.2. Therefore, ZVI-coagulation integrated process can strengthen the pollutant control process effectively, at the same time improve the biodegradability observably, reduce the comprehensive biotoxicity of wastewater greatly.