Study On Advanced Treatment Processes Of Tail Wastewater Discharged From The Leather Sewage Treatment Plant

As leather wastewater contains complex composition and large amounts of toxic substances, the COD concentration of tail wastewater discharged from leather wastewater treatment plant is still 300?800 mg/L. It cann't satisfy discharge standards. There are basic processes used to treat tail wastewater such as electrochemical oxidation, ozonation and fenton oxidation until now. However, these processes cause some defects, such as large energy consumption, easily produce secondary pollutants and difficult to satisfy the standards.In this study, using the practical tail wastewater of leather sewage treatment plant as the research object. Compare a variety of oxidation and reduction processes' treatment effects on the tail wastewater. Especially focus on the ozone and electric-Fe~0 anaerobic biology processes. The removal mechanism of refractory organic pollutants in tail wastewater is initially analyzed by fourier transform infrared spectroscopy, GC-MS analyzer and TOC analyzer. And study the feasibility of electric-Fe~0 anaerobic biology, ozonation and activated carbon combined process to satisfy COD discharge standards. The foremost conclusions as follows:(1) The practical tail wastewater of leather sewage treatment plant contains 552.8-756.68 mg/L CODCr and 9.8?245.5 mg/L NH3-N concentration. And it can't be emissed due to dissatisfy the standards. The tail wastewater includes amides, macromolecular benzene, ketones, long chain hydrocarbons, other organic nitrogen compounds and other refractory organics.(2) Compared with ozone oxidation, the electrochemical oxidation process has a better treatment effect on the tail wastewater. Graphite and iron respectively as anode and cathode, when the initial pH=7, a current density 1544A/m2, electrolysis time 2h, the electrochemical oxidation process to COD removal rate can reach 74%. But it would produce organic contaminants that have more complex structure, for example anthracene. When ozone dosage o10g/h, initial pH=8.5, reaction time of 150min, ozonation process to COD removal rate is only 44.4%. And some of refractory BTEX aren't yet effectively removed.(3) Compared with Fe~0-anaerobic biology process, the electrical-Fe~0 anaerobic biology process can significantly reduce the processing time. Since the micro-current promots Fe~0 dissolution, it may improve anaerobic microorganisms' activity. When the temperature, iron-carbon fillers, glucose dosage, sludge concentration and the COD removal rate respectively is 37±1?,10 g/L,1000 mg/L,3 g/L and about 45%, the processing time can be shortened from 48 h to 12 h. And electric-Fe~0 anaerobic biology process can effectively degrade organic nitrogen contents, propionic anhydride, dipropyl sulfoxide, tertiary amide groups, etc. But it is difficult to remove DEHP, long-chain alkanes,3-hexanone and other organic pollutants.(4) Utilizing electric-Fe~0 anaerobic biology, ozonation and activated carbon combined process can achieve emission that satisfy the discharge standards. Effluent COD and ammonia nitrogen concentration is separately reduced to 91.4 mg/L and below 15.0 mg/L.