| Nitrobenzene compounds are an important chemistry in industry. It's widely used for national defense, weaving, printing, dynamite, pesticide and medicine etc.. The wastewater in these industries with great quantity of nitrobenzene will do great harm to all kinds of water bodies and human being after discharging, and it's one of the 58 poisonous chemicals which need priority-controlled in China.There are many techniques to treat wastewater with nitrobenzene compounds, mainly including extraction, biochemistry, adsorption and oxidation. These methods have their own advantages and disadvantages: extraction has not so good treatment efficiency so it's not wildly used; biochemistry will be inhibited and can't show the advantages when the concentration of nitrobenzene in wastewater is high, because microorganisms are likely to get poisoned in the condition; adsorption usually uses active carbon alone, and it makes a sacrifice of much wood; oxidation can't treat nitrobenzene to the core, and takes second pollution easily at the same time. Therefore, the study of economical and practical new techniques to treat these kinds of organic wastewater is still popular. Recently, the study of inner electrolysis/ micro-electrolysis is very hot in the treatment of this organic industrial wastewater, and has been applied in practical engineering. It has quite high removal rate of chroma to this kind of wastewater, and can enhance the biodegradability of wastewater. Moreover, the technique has many other advantages, such as having wide sources, convenient, economical and practical, so people get more and more interested in this technique as pretreatment of biological techniques.At present, the study on the treatment of nitrobenzene is focused on industrial and surface water. But in the process of producing, groundwater may be partly polluted because of leakage, operation wrongly or accidents etc.. Therefore, the protection of groundwater should be met with much recognition as the same. Since 90th, the remediation of contaminated soil and groundwater has gained great attention, and becomes one of the hot problems in international environmental science and engineering. The remediation technologies have also become PRB―― permeably reactive barrier technology which has great developing potential from conventional pump and treat technology. The technology has many advantages such as having lower investment(1/5 of pump and treat technology's), less disturbance to ground, long treatment of pollutants, almost no consume of energy as a passive technology and easily-combination with other treatment techniques, and so on. Therefore, it has been developing rapidly in recent 10 years.Therefore, the study combined iron inner electrolysis with PRB technology, with scrap iron as active fillings, to treat groundwater contaminated by nitrobenzene. But PRB is an installation for long time use, during the time, specific groundwater condition will make significant influence to the efficiency and lifespan of scrap iron, which is rarely reported yet. What's more, the study of iron inner electrolysis is usually focused on mechanism and general influence factors, and there are few reports on the influence of groundwater condition to the technology. Based on this, a series of static parallel experiments were designed to invest the influences of main irons in groundwater, such as Cl-, NO3-, hardness, SO42- and alkalinity, to the treatment of nitrobenzene with scrap iron, and to find out which groundwater conditions were fit for the method, which may be helpful to practical engineering. In the study, it also invested the influences of pH and iron diameters to the removal rate in order to seek the fitting conditions to treat nitrobenzene with scrap iron. Meanwhile, it also discussed the removal rate after adding copper as catalyzer, to understand the mechanism in more depth. The results showed that: (1) Scrap iron can remove nitrobenzene from groundwater effectively, and the process of degradation conformed to the kinetics of 1st-order, pH values and scrap iron diameters strongly influenced the degradation rate. The degradation rate of nitrobenzene achieved to 91.8% by scrap iron in 4 hours, and the rate increased with the decline of pH values. In the experimental range of pH values, the reaction rate constant decreased in the following order: strong acidity﹥slight acidity﹥neutral﹥slight alkaline. The efficiency is highest when the diameter is between 1 to 2 millimeters, and it lowered as the diameter decreased or increased. (2) Cl- can enhance the reaction rate of nitrobenzene reduction by scrap iron. In the experiment, the transform rate of nitrobenzene reached 100% in the presence of Cl- while the rate was less than 80% in the presence of NO3- in 4 hours. (3) The deoxidizing process of nitrobenzene by iron was inhibited in lower concentrations of SO42- but was accelerated in higher concentrations. (4) Hardness would inhibit the deoxidizing of nitrobenzene by iron. (5) Two kinds of alkalinity had different effects to the deoxidizing of nitrobenzene, CO32- would inhibit the process while HCO3- would accelerate. (6) Electrode reaction would be strengthened and the deoxidizing rate of nitrobenzene by iron would be accelerated after adding copper as catalyzer.
|
PDF Full Text Request