Study On Micro-electrolysis, Activated Sludge Process In Simulated Nitrobenzene Wastewater Treatment

Nitrobenzene is a kind of chemical material which has been applied in chemical industry market widely and which mainly aims at dyestuff, spice, agrochemical and explosive industry etc. The washes are one of the greatest pollution sources, the concentration of which reaches 2000 mg/L or so. Fish and aquatic organisms will die if the concentration of nitrobenzene in the water is more than 33 mg/L.Nitrobenzene is a common persistent organic pollutant, and its processing methods can be divided into three categories, namely, the physical, chemical and biological methods. However, because Nitro is a passive matrix, and its high stability, the effect of a single method is not good. The three methods are often combined in practical application of nitrobenzene processing.This paper first conduct a simulation study on the ratio of nitrobenzene wastewater. Nitrobenzene and water were mixed in accordance with the volume ratio of 1/1000, and the mixed solution can only be used after three days att room temperature. The concentration of nitrobenzene is 270mg/L, COD=700 mg/L, pH=7 for this simulation wastewater. Microelectrolysis - activated sludge process is chosen for this simulation wastewater. Cheap microelectrolysis process can initial be used to remove nitrobenzene and COD in the wastewater, and raise the biodegradability of the wastewater. Then the activated sludge process can be used to remove nitrobenzene again.Parameters influencing treatment effect include pH value,residence time, and ferrous-carbon ratio. Accordingly, the orthogonal experiment with three factors and three levels was designed. The result demonstrates that residence time is a significant factor, while the ferrous-carbon ration and pH value are fewer significant ones.For cost reasons, parameter settings are as follows: pH = 7, ferrous-carbon ratio =1.5/1. The retention time ranges from 24 hours to 180 hours. Microelectrolysis reaction trough filled with 18L ferrous powder and 12 L activated carbon. Microelectrolysisreaction lasted for 70 days. At first 30 days of the microelectrolysis reaction, the COD value of the effluent did not exceed 100 mg/L, and nitrobenzene content was not more than 5 mg/L. COD removal rate at this stage was between 88 to 98 percent. The effect of the COD removal will better if the retention time is longer. But it is not linear relationship between the two. As the retention time extended, the COD removal increases slowly.At the last 40 days of the microelectrolysis reaction, the retention time was almost the same with the previous stage. The COD value of the effluent was still less than 100 mg/L, nitrobenzene content was not more than 6 mg/L, respectively. COD removal at this stage was between 87 to 96 percent. The COD removal rate in the second stage was low 1% ~ 2% than that in the first stage under the same condition. This shows that: the COD removal rate will decline slowly as the reaction lasted even if the retention time keeps the same. In other words, run-time is also a parameter influencing treatment effect. The COD removal rate will be high if the retention time is long and run-time is short, and the COD removal rate will be low if the retention time is short and run-time is long.In the micro-electrolysis reaction, the iron is oxidized in the original battery reaction. The iron adsorbed the particles in the water, and flocculation occurred. The flocculation increased the effect of pollutants removal, and it also had a flocculation of iron, which blocked gaps between the iron and carbon. This flocculation of iron called iron mud. When the iron mud blocked all the gaps, soil hardening of iron-carbon occurred, and water can not be passed. Even if the production of iron mud did not reach the degree of soil hardening, iron mud will still precipitate in the surface of iron and carbon, and isolate iron-carbon from the original battery reaction to some extent. This phenomenon was known as passivation. This is the main reason for decline in treatment effect after continuous operation of micro-electrolysis process.The aeration of glucose solution method was used to train activated sludge at the first 30 days of microelectrolysis reaction. Then adequate sewage sludge was added to accelerate the growth of the activated sludge. The diluted effluent of microelectrolysis was used in the activated sludge domestication process. The effluent of microelectrolysis comes into bioreactor after 30 days training and domesticationAs microelectrolysis effluent COD value is too low, not suitable for the growth of activated sludge in the bioreactor, diluted solution of the beer was added to bioreactor, and the COD value reached 400 mg/L. The COD removal rate in activated sludge bioreactor was between 87 to 93 percent, and the concentration of nitrobenzene at the same time declined from 6 mg/L to 5 mg/L.On the whole, the effect of microelectrolysis process was considerably good because the retention time was long. But the effect of activated sludge process was not very good because exclusive degrading bacteria were not added in the bioreactor.