Experimental Study On Refined Cotton Black Liquor Degraded By Acid Precipitation And Electrical Fenton Combined Process

The black liquor ?BL? is generated from refined cotton process production, which is a type of special industrial wastewater and difficult to deal with. It is characterized of high chrome, high concentrations of organic matter, biological toxicity and other hazards. In this study, samples of the wastewater were collected from a refined cotton plant of Jiangsu Province. The acid precipitation - Fenton or Electro-Fenton?EF? combined process for pollutants removal from BL was chosen as a treatment measurement and the operating parameters of respective units were optimized. At last, the overall optimal treatment process was proposed.The best result of acid precipitation was obtained under the condition of pH=3, reaction temperature= 25?, concentration of sulfuric acid =25%, the acid addition rate =1 ml/L. After 10 min of treatment, the removal rate of chemical oxygen demand ?COD? and chroma of black liquor were 34.53% and 48.59%, and the precipitation of lignin was 11.88 g/L.Fenton and EF were compared as the next treatment process after the acid precipitation,The best result of Fenton was obtained with a combination of H₂O₂ dosage =102 ml/L,nFe²⁺/nH₂O₂ = 0.1,initial pH =3, reaction time= 30 min, precipitation pH= 8, dosing frequency= 1,The best result of EF was obtained with a combination of H₂O₂ dosage 45 ml/L,at a current density of 22 mA/cm² , initial pH 3, electrodes placed at 2 cm distance, reaction time 25 min. Under the best optimal conditions, the COD removal rate were 69.53% and 76.18% in the Fenton and EF, respectively. EF was better than Fenton through the comprehensive evaluation, so EF was chosen as the next process after acid precipitation . To reduce the amount of acid dosage in acid precipitation process, the effects of microbial acidification to pH of black liquor was studied, the results showed that microbial acidification affected by microbial inoculation and temperature, the pH of black liquor after microbial acidification could be reduced to 10.04.From the above research, microbial acidification - acid analysis - EF combined process was presented, And the operating parameters of each units were optimized, the best operating parameters as following: Microbial acidification stage were microbial inoculation 30%,culture temperature 37?; acid precipitation stage were pH 3, reaction temperature 25 ?; EF stage were H₂O₂ dosage 15 ml/L, current density 22 mA/cm², pH 3, distance between the electrodes 2 cm. After the treatment, the final concentrations of COD and chrome in the effluent were 3168 mg/L and chrome 500, the removal rates reached to 91.43% and 93.75%,respectively.