ELECTROCOAGULATION TREATMENT OF PULP AND PAPER INDUSTRY WASTEWATER AND ITS RECYCLING POTENTIAL

Abstract

The pulp and paper industry (PPI) is well known for the consumption of tremendous volume of fresh water and subsequent generation of large volume of wastewater. The wastewater consists of significant amount of degraded lignin products, intense color, chlorophenols and several other toxic contaminates with limited biodegradability. These toxic organic compounds are not easy to treat with conventional treatment processes. Henceforth, wastewater treatment technologies require improvements in order to meet the strict effluent discharge standards and to make it cost effective processes. Electrocoagulation (EC) method is a versatile, clean and an advanced oxidation process can be a promising and effective treatment option for the reduction of organic contaminate present in the industrial wastewater. As India is a tropical country and having enormous solar energy potential this can be easily utilized as a source of power for the treatment of wastewater operated by EC method. In this study, pulp and paper industry wastewater (PPIW) after primary treatment was subjected to physicochemical and environmental characterization in terms of biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), color, solids, and chlorophenolics prior and after the treatment. Four types of electrodes such as aluminum, mild-steel, stainless steel (SS)-304 and SS-316 were used to treat the effluent. The electrodes metal coupons were prepared for immersion test according to ASTM standard method to detect the effect of corrosion on the electrodes surface. These coupons were immersed in PPIW for a long time about 185 day’s exposure. The corrosion rate were observed in decreasing order as mild steel > aluminum > mild steel > SS-304 > SS-316. For the determination of optimum treatment conditions for EC treatment, the influences of various process variables i.e. pH, current density, treatment time, a dose of electrolytes were observed on the basis of maximum COD and color removal. The reduction efficiency for the parameters such as BOD, TOC, total dissolved solids and chlorophenols were determined under optimum conditions. Extraction and derivatization of chlorophenols compounds from wastewater has been performed prior and post EC treatment and finally analyzed by GC-MS. Qualitative and quantitatively estimation were done on the basis of retention time and peak area respectively of particular compound. The EC treatment method was found to be highly effective for color removal with all four electrodes. In case of Al, MS, SS-304 and SS-316 electrode color was removed 98%, 94%, 99.8% and 99.6%. Reduction in COD, color, BOD/COD ratio and chlorophenolics were observed in decreasing order according to electrode material such as SS-304 > SS-316 > aluminum> mild steel. COD reduction was observed 70%, 68% 82% and 81% in respect of Al, MS, SS-304 and SS-316 3l3cctrodes. The biodegradability ii index of the effluent improved up to (0.4-0.55) after the EC treatment in respect of all electrodes. The generated sludge was characterized for various physicochemical parameters using analytical techniques such as field emission scanning electron micrograph coupled with energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and to understand the physical, chemical and elemental nature of sludge, and find out proper management option. The sludge was found to be non-hazardous and could be used as low cost alternative for several applications such as land application, industry and wastewater treatment. Furthermore, when aluminum electrode was applied for the treatment of wastewater, it was generated considerable amount of Al in the sludge. This Al content was successfully recovered near about 70 % from sludge by using digestion method. Recycling of treated water has been performed in the bleaching process in the laboratory to reduce the freshwater input in PPI. The OD0EpD1 sequence was used for the production of effluent in the laboratory. The produced wastewater was treated under optimum condition. This EC treated water was collected for further use as wash-water in the washing of virgin pulp and in between bleaching stages. In recycling study, two parallel experiments have been done using ODED and DEpD sequences with fresh water and RC_ODEPD and RC_DEpD with EC treated water to examine the recycling potential of EC treated water. To achieve the target brightness of pulp, kappa factor was increased up to (0.25-0.27) in recycling stage and the effect of increased chemical dose was observed on brightness, paper properties and generated effluent quality. The wastewater generated by recycling stage was characterized in terms of BOD, COD, and color and after the re-treatment pollution load was within permissible limit prescribed by central pollution control board on India