A critical review on environmental risk and toxic hazards of refractory pollutants discharged in chlorolignin waste of pulp and paper mills and their remediation approaches for environmental safety

Agro-based pulp and paper mills (PPMs) inevitably produce numerous refractory pollutants in their wastewater, including chlorolignin, chlorophenols, chlorocatechols, chloroguaiacol, cyanide, furan, dioxins, and other organic compounds, as well as various heavy metals, such as nickel (Ni), zinc (Zn), chromium (Cr), iron (Fe), lead (Pb), arsenic (As), etc. These pollutants pose significant threats to aquatic and terrestrial life due to their cytogenotoxicity, mutagenicity, impact on sexual organs, hormonal interference, endocrine disruption, and allergenic response. Consequently, it is crucial to reclaim pulp paper mill wastewater (PPMW) with high loads of refractory pollutants through effective and environmentally sustainable practices to minimize the presence of these chemicals and ensure environmental safety. However, there is currently no comprehensive published review providing up-to-date knowledge on the fate of refractory pollutants from PPMW in soil and aquatic environments, along with valuable insights into the associated health hazards and remediation methods. This critical review aims to shed light on the potential adverse effects of refractory pollutants from PPMW on natural ecosystems and living organisms. It explores existing effective treatment technologies for remediating these pollutants from wastewater, highlighting the advantages and disadvantages of each approach, all in pursuit of environmental safety. Special emphasis is placed on emerging technologies used to decontaminate wastewater discharged from PPMs, ensuring the preservation of the environment. Additionally, this review addresses the major challenges and proposes future research directions for the proper disposal of PPMW. It serves as a comprehensive source of knowledge on the environmental toxicity and risks associated with refractory pollutants in PPMW, making it a valuable reference for policymakers and researchers when selecting appropriate technologies for remediation. The scientific community, concerned with mitigating the widespread risks posed by refractory pollutants from PPMs, is expected to take a keen interest in this review.

Hetero-catalytic hydrothermal oxidation of simulated pulping effluent: Effect of operating parameters and catalyst stability

In the present study, activated carbon (AC) supported bi-metallic catalyst (3.3Cu/2.2Ce/4.4AC) was subjected to catalytic wet oxidation (CWO) of simulated pulping effluent at moderate operating conditions (temperatures = 120-190 °C and oxygen partial pressures = 0.5-1.2 MPa). The oxidation reaction was performed in a high pressure reactor (capacity = 0.7 l) with catalyst concentration of 1-5 g/l for 3 h duration. During CWO at 190 °C temperature and 0.9 MPa oxygen pressure, the chemical oxygen demand (COD), total organic carbon (TOC), lignin and color removals from the wastewater were 79%, 77%, 88% and 89%, respectively, while the wastewater biodegradability was enhanced to 0.52 from an initial value of 0.16. TOC mass balance suggested that nearly 86-97% of the degraded TOC was mineralized whereas copper and cerium leaching from the catalyst were in the range of 1-15% and 0.7-1% with respect to their initial amounts. Metal leaching was reduced with increase in the reaction temperature. Global kinetic rate model was also developed using TOC degradation data and the activation energies of two step (rapid followed by slower TOC removal) CWO reaction were determined as 34.2 kJ/mol and 28.5 kJ/mol, respectively.