Integrated ozone and biotreatment of pulp mill effluent

Abstract

In this study, the effluents from the biggest pulp and paper plant in Turkey that having amultistage chlorine bleaching process were treated by an integrated process consisted ofozonation and activated sludge processes to enhance the biodegradability and increase the quality of effluent.In the first part of the study, ozonation process was applied to CEHDED and CEH stagebleaching effluents. The effects of fibre type, pH, H2O2, and ozone dose were investigated ontreatment performance of ozonation process. Significant COD and color removals wereachieved by increasing ozonation pH of combined bleaching effluents to a value of 12. The highest treatment efficiency was achieved by the O3/H2O2/pH=7 process with 1632 mg/Lozone dose for CEHDED effluent. While 41 per cent COD removal was obtained by applyingO3/pH=7 process to CEHDED effluent, COD removal was increased to 57 per cent by the addition of 15 mM H2O2. Although ozonation of CEHDED effluent at pH=7 resulted in only amoderate alteration in BOD5/COD ratio, O3/H2O2 /pH=7 treatment increased the BOD5/CODratio from 0.2 to 0.4. Almost complete color removal was also achieved by O3/H2O2 /pH=7treatment. In the second part of the study, activated sludge process was applied to pulp milleffluent. While for the raw effluent overall CODs removal efficiency of biological processwas 61 per cent, it was 77 per cent for the pulp mill effluent, which contained the pretreated(O3/H2O2/pH=7) CEHDED effluent. Furthermore, AOX removal rate was increased from 39 to 70 per cent by the pretreatment of combined bleaching effluent.