Improvement of wastewater quality parameters by sedimentation followed by tertiary treatments

Kraft black liquor (KBL), the wastewater from digester house of pulp and paper industry using sodium hydroxide and sodium sulfide during chemical pulping, causes severe damage to a terrestrial ecosystem. In this study, first of all, KBL has been characterized in terms of wastewater quality parameters, i.e. total solids, BOD, COD, turbidity, etc. Sedimentation of KBL using lime and alum as coagulants was studied and the dosage was optimized. A 35.2% reduction of BOD was achieved using 17.5% alum solution after adjusting the solution pH to 9.5 using fresh lime solution. Tertiary treatment like adsorption/ultrafiltration was investigated so as to further remove the nonbiodegradable products like lignin and their derivatives. Adsorption was carried out at two different solution pHs under ambient condition using activated carbon as adsorbent. Adsorption isotherms of kraft pulp mill effluents over activated carbon at both pHs were found to be well described by Freundlich equation. Ultrafiltration was carried out using cross-flow module (Vivaflow™ 200) at three different transmembrane pressures, i.e. 1.5, 2 and 2.5 kg/cm2. The UF operation at a TMP of 2.5 kg/cm2 was seen to be a little bit more efficient in reducing COD, BOD, turbidity compared to adsorption on activated carbon.