Biologically Active Filter + The O <sub> 3 </ Sub> Depth Treatment Of Citric Acid Wastewater Experimental Study

With the development of environmental pollution and shortage of water resource, wastewater reclamation has become of increasing importance. China is the largest production and export country of citric acid in the world. The production of citric acid will bring large quantity of wastewater with high density of organic pollutants and poor appearance. Although the wastewater could match the discharging standard of the country, it do causes a severe problem to the environment. So according to the chemical and hygienic problems in the wastewater reclamation of citric acid, a combination process of biological aerated filter and ozone was constructed in this study, the middle and final productions could be identified with the help of chromatogram, the degradation pathway of citric acid during oxidation was speculated, and the pollutant removel efficiency, the stabilization of the system and the safety of treated water were evaluated over long-term test. The results are summarized as follows.(1) The characteristics of secondly effluent of wastewater treatment system of citric acid.The quality of effluent was quite sable: 150—250mg/L COD, 80—100mg/L BOD, 80 cu chroma, 5—10mg/L NH₃-N, 30—60mg/L SS, 6.8—8.0 pH, BOD/COD 2=0.3(2) BAF—O₃ system for wastewater reclamation.The best filtering velocity of BAF was 15m/h, the EBCT was 2h, the ratio of gas and water was 3. The best dosage of ozone was 40 mg/L, the react time ≥10min. Under these conditions, the removal rate of COD, chroma and UV₂₅₄ surpassed 76%, 93%å'Œ 27% respectively. The COD and chroma of the effluent were less than 50 mg/L and 5 cu. The effluent conformed to the request of the plant and could be reused in the fermentation process of citic acid production. (3) Microorganism safetyThe number of total bacteria and E.coli were 1.03× 10⁷MPN/ml and 8.9 × 10⁴MPN/ml. The conventional treatment can not remove the microorganism effectively and ensure the safety of wastewater reclamation.When the dosage of ozone was 10 mg/L, the react time ≥5min, the removal rate of bacteria and E.coli were 99% and 99.99%.The inactivation efficiency of E.coli increased with the increasing dosage of ozone. Complete inactivation of E.coli required an ozone dosage at least 15mg/L.(4) The mechanism discussion of citric acid wastewater during the ozonation. With the help of HPLC and certain dynamics information, the middle and finalproductions could be identified, the degradation pathway of citric acid during oxidation was speculated.(5) Analysis of microbial communities in the BAFAfter the biofilm forming, the main part of biofilm was zoogloea through the observation of SEM, there were also large quantity of Cocci and Bacilli, small amount of protozoan in the BAF. The microbial community in the BAF was very similar over the space spans.(6) The technical and cost assessment of the mediaIn terms of pollutant removal and safety insurance, pottery media demonstrated excellent performance as well as wide adaptability, and the price was relatively low.(7) The analysis of economic benefit of the applicationAfter the combination process of BAF and ozone, the wastewater of citric acid could be reused in the fermentation process of the production. The average cost was lower than IRMB/ton. The application of this technology will not only decrease the diacharge fee and production cost for the plant, but also convert the wastewater into resource.Compared with UF, UF+RO, the BAF—O₃ process is cheaper and more adaptable, so it is an effect way for the wastewater reuse.