Development of Integrated Biological Reactor for the Treatment of Pulp and Paper Industry Effluent

Abstract

Abstract Amidst rapid industrialization, like pulp and paper manufacturing, the resultant wastewater emerges as a pressing environmental contaminant. Effective treatment of wastewater generated by pulp and paper industry (PPI) is important to adhere to the stringent national environmental quality standards and to safeguard the ecosystem. In the present study, an integrated biological treatment system was designed for the PPI wastewater (black liquor, BL). The research was conducted in four phases. During the first phase, physicochemical characterization of the BL was carried out using different analytical methods. It was found that BL exhibited a pH of 8.2±0.15 with high chemical oxygen demand (COD) of 1750.56±35.50 mg/L and biological oxygen demand (BOD) of 1513.53± 32.35 mg/L. The other parameters such as sulfate, phosphate, total dissolved solids (TDS), total suspended solids (TSS), total nitrogen (TN) and lignin content were 4.2.21±0.117 mg/L, 3571.455±48.23 mg/L, 1890.411±57.28 mg/L, 160.911± 4.48 mg/L and 189.33±6.53 mg/L respectively which were beyond the permissible limits of EPA. In the second step, the bacterial strains were isolated from the BL samples using enrichment technique in MSM BL amended with 2 % lignin. Out of thirteen bacterial strains, three bacterial strains (TR-1, TR-2, & TR-3) were selected for their higher adoptability and lignin degradation traits. The optimum metabolic performance of these strains was found to be between pH (7-9) and temperature (37-41oC). These bacterial TR-1, TR-2, and TR-3 were biochemically identified as Bacillus subtilis, Bacillus cereus and Pseudomonas respectively. In the second phase of the research, two different bioreactors were designed i.e., gravitydriven bioreactor (GDB) and integrated vertical flow constructed wetland (IVFCW), to evaluate their performance for the treatment of black liquor. Both GDB and IVFCW were operated with an organic loading rate (OLR) of 1750 mg-COD/L-Day, flow rate of approximately 12 mL/minute, and HRT of 72 hours for ten samples (S1-S10) with a frequency of one sample per week under the natural temperature of workstation (35-40°C). The average results showed that the GDB achieved promising treatment efficiencies: 73.50% for COD, 67.46% for BOD5, 177 times increase in dissolved oxygen content, and 54.31%. for TDS, 92.29% for TSS, 57.11% for EC, 54.39% for PO4 3-, 53.94% for SO4 2-, 55.87% for TN, and 87.99% for turbidity levels. Additionally, about a 51.35% reduction in lignin content was observed and the average change in pH was 11.66% after the treatment. Similarly, the average results showed that the IVFCW achieved a notable treatment efficiency: 76.50% for COD, 73.76% for BOD5, 188-time increase in dissolved oxygen content, 66.4%. for TDS, 100% for TSS, 67% for EC, 54.7% for PO4 3-, 60.6522% for SO4 2-, 72.9% for TN, and 88.4% turbidity levels. Likewise, a 59.88% reduction in lignin content was observed with 5% change in pH after the treatment through IVFCW. xviii In phase three, the treatment efficacy of GDB and IVFCW was improved using black liquor blended with domestic wastewater. The GDB and IVFCW were operated and maintained at an average organic loading rate of 1235 mg-COD/L-Day, at a flow rate of approximately 12 mL/minute and hydraulic retention time of 72 hours, for twelve samples (W1-W12) at a weekly frequency. The entire process was conducted within the workstation's ambient temperature range of 35-45°C from June 2022 to September 2022. The performance of the both reactors were evaluated in terms of various pollution indicators, including COD, BOD5, lignin removal, TDS, TSS, EC, PO4 3-, SO4 2-, microbial load (CFU/mL and MPN index), total nitrogen and color reduction. The results showed that the GDB achieved promising treatment efficiencies: 84.5% for COD, 71.80% for BOD5, 82.8% for TDS, 100% for TSS, 74.71% for E.C., 67.25% for PO4 3-, 81% for SO4 2-, and 69.36% for TN. Additionally, about 80% reduction in lignin content and 57% color reduction were observed after the treatment. The GDB substantially reduced microbial load in CFU/mL (77.98%) and MPN (90%). Similarly, the IVFCW were proved more promising in removing different contaminants, including total suspended solids (TSS) and total dissolved solids (TDS), with an estimated efficiency of 100% and 83%, respectively. Other parameters such as COD and BOD declined by 80% and 81%, respectively. Further to this, the IVFCW reduced sulfates (SO₄-2), phosphates (PO₄⁻3), and total nitrogen by 81%, 63%, and 61%, respectively. The treatment has led to lignin degradation up to 83%. The microbial load was also downsized to CFU/mL (67.98%) and MPN (93%). In the last and forth phase, the microbial profiling of aerobic biofilm developed on stone media in GDB and rhizosphere soil of Typha latifolia roots in IVFCW confirmed the presence of different bacteria genera. The present study highlights the effectiveness of GDB and IVFCW, showed efficiency, in terms of lignin degradation, up to 83% and 81%, respectively and proved to be efficient in terms of removing COD, BOD and other pollutants from the pulp and paper industry effluent up to permissible limits approved by EPA. Therefore, GDBs and IVFCW have the potential for large-scale application for wastewater treatment as a cost-effective, environmentally friendly and efficient solution.