Study On The Treatment Of AN Wastewater By Fenton Reagent, Micro-electrolysis And Enhanced Contact Oxidation Process

Acrylonitrile (AN) is a very important bio-chemical material which is frequently encountered in the manufacture of synthetic fiber, plastic and rubber co monomer. AN oligomer and its derivatives are also wildly used as building materials and commodity. They have big market demand. As a kind of industrial wastewater, AN wastewater have many peculiar characteristics such as complex water quality, containing organic compound, high concentration of COD_Cr and its toxicity. At present, the report about treatments of AN wastewater concentrates on the removal of AN. But the problem is that COD_Cr can′t reach the stander. AN is easy to remove and oligomer belonging to hard degrading material is molecular weight big. So oligomer is the material which leads to the indexes of COD_Cr in the effluent could not meet the national discharge standard.There are three kinds of method in the treatment of AN wastewater, such as physic-chemical method, chemical method and bio-chemical method. Traditional AN control technologies such as combustion and biological, pressurized hydrolyisis and biological, wet catalytic oxidation and biological have been commonly used to remove AN. However, all these methods could not meet the requirement of serious wastewater situation. Moreover, if the desired AN removal efficiencies are achieved, these AN control technologies may suffer from high operating cost and secondary waste stream problems. Consequently, founding an effective, practical and economical process is very essential.According to its characteristics, the author wanted to adopt pretreatment and biological treatment process. The pretreatment was to decrease toxicity of wastewater and degrade some organic. Then to biological treatment, the purpose was to made wastewater emitted reasonably. Considering economic, effective, simple operating, the combine of Fenton reagent and bio-electrolysis was used in pretreatment. Biological treatment employed contact oxidation.From the experiments, the sequence of Fenton reagent and Micro-electrolysis was not important to the result. The references usually adopted Micro-electrolysis then Fenton reagent, the reason is oxidation can make use of iron ion of Micro-electrolysis. The author analyzed the feasibility of the process. The condition in pH of both processes is about 3. Fenton reagent, pH of the solution does not change basically. PH increases from 3 to 6 in Micro-electrolysis process. So first Micro-electrolysis and then Fenton reagent needs an extra step in adjusting pH. This kind of process is complex, consequently, raising the treating cost. So the author determined the Fenton reagent and Micro-electrolysis process in pretreatment.In the pretreatment, the aim was to ascertain the optimum conditions of Fenton reagent process, containing the quantity of H₂O₂, concentration of Fe2+, times of H₂O₂ to reactors. The research had been done on the influencing factors of the action. The experiment results suggested that most of the COD_Cr can be removed from 1989mg/L to 723mg/L in the optimum conditions: 30%H₂O₂=40ml/L,[Fe²⁺]=0.4g/L ,pH=3, reaction time is 2 hour. Removal of COD_Cr ratio reached to 65%, meeting the requirement of biological treatment. The effluent had a high concentration of iron ion. Flocculation was used to reduce the concentration of iron ion. The optimum condition which was confirmed by experiment was 16mL PAM solution per liter effluent.The wastewater after pretreatment came into biological contact oxidation reactor. Contact oxidation combined with bio- ferric, it was definited as enhanced contact oxidation. Sludge was cultivated using seeding sludge. The concentration of Fe²⁺ in influent is about 17mg/L. There were many differences between common sludge and the sludge mentioned in this paper.The cultivated sludge was mission floccule. With reduction of the concentration of iron ion, the color of sludge was from deep to light and the structure of sludge was from compact to loose. The biological study was performed on the operating parameters for the process: DO=4.5 mg/L, HRT=10h then the concentration of COD_Cr in the effluent was less than 100mg/L. The reactor which operated for more than one month successively was proved feasibly.Aerobic granular sludge was cultivated to certain extent after a period of time in stable operating. The author studied the according references then gave deeper explanation to operating conditions and their theories.