Cooling Crystallization-Fenton-SBR Process Treating High Sulphate Organic Wastewater

High sulphate organic water is one of the most difficult wastewater to be treated effectively. It mainly comes from food processing industry, pharmaceutical industry, chemical industry and oil industry. For few decades, anaerobic digestion has becaming a regular method for treating this sulphate organic water. However, according to many reseaechers’result anaerobic biological system disposing sulphate effluent require a COD/SO42-ratio at least more than2and the SO42-concentration less than5000mg/L, otherwise, leading to a failure in process running. Considering that, anaerobic process is not suitable for applying to treat a stream with high COD concentration (18000mg/L), high SO42-concentration (212000mg/L, most Na2SO4) and very low COD/SO42-ratio (<0.1)And any single method alone is essentially impossible to treat this kind of wastewater with the characteristic of high sulphate and high organic concentration. Though the activated sludge method has the advantages of good effluent water quality and low cost, but it can not be used for direct treating organic wastewater with high COD and high sulphate concentration. As for physical and chemical methods, though they have a wide range for wastewater treatment, but they cost high, removal efficiency relatively low and couldn’t achieve the desirable resul. However, the combination of physical, chemical and biological methods can show a better performance when disposing the kind of water with complicated properties. In the paper, we studied the treatment of high sulphate organic water using combined cooling crystallization, Fenton oxidation and sulphate tolerant SBR process.The principle of cooling crystallization is the dissolubility of sodium sulphate would decrease when temperature decreasing, and then the glauber salt would be dissolved out. At the conditions of4℃, through two times cooling process, and each timen for150and120minutes, respectively, the raw water achieved a SO42-removal efficiency of54.8%, a total water volume decreasing of29.1%and a COD increasing efficiency of2.8%after cooling crystallization.The residual liquid separated with sulphate crystal after cooling crystallization then treated by Fenton oxidation. More than77%COD removal efficiency was achieved under the optimal conditions of room temperature (28℃in this experiments), initial pH value2, Fe2+concentration of8.0mM,30%H2O2dosage of40mL/L for60 minutes reaction. The COD concentration of effluent was around41000mg/L. And after Fenton oxidation the BOD5/COD ratio decreased from0.58to0.43, but still showed a relatively good biodegradability.When the taming of activated sludge’s tolerance to sulphate in SBR reactor was finished, a COD removal efficiency of ecxeed88%was achieved with the influent of about1000mg/L COD concentration and28.4g/L sodium sulphate. After the domestication of SBR’s tolerance to sulphate, the color of sludge became to yellowish-brown, and the sludge flocs became bigger than before, but its inner construction was tighter. Among the domestication process, the sludge index, MLSS and MLVSS showed an increasing tendency, to be more specific, they first decreased and then increased gradually. The sludge settling index, SV30、SVI also displayed a similar change.The mixture of wastewater treated by cooling crystallization-Fenton and domestic sewage at the volume ratio of1:4was finally treated by sulphate tolerance SBR. With a cycle time of12h, the SBR run for26cycles, and showed a steady organic pollutions removal performance. The average COD removal efficiency was over85%in the running cycles and the final wastewater COD concentrationk≤150mg/L, which achieved the secondary standard of Integrated Wastewater Discharge Standard.