Decolorization of cotton pulp black liquor by pleurotus ostreatus in a bubble-column reactor

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.

Complexation modelling and oxidation mechanism of organic pollutants in cotton pulp black liquor during iron salt precipitation and electrochemical treatment

Removal behavior of organic pollutants such as lignin in cotton pulp black liquor (CPBL) was investigated in precipitation followed by electrochemical oxidation (EO) using FeCl₃, Fe₂(SO₄)₃, FeCl₂ and FeSO₄ as precipitants, electrolyte and catalysts. Based on comparison of precipitation efficacy of iron salts, spectroscopic techniques, thermodynamic equilibrium calculations and molecular dynamics (MD) simulations were used to provide insight into the interaction between iron cations and lignin. The results showed that FeCl₃ achieved the highest removal of chemical oxygen demand (COD, 76.05%), UV₂₅₄ (69.21%) and lignin (78.28%). Iron cationic complexation with lignin was identified as the key mechanism in precipitation. Fe³⁺ was more active in binding to organic ligands mainly due to charge effect compared to Fe²⁺. The strong Fe-sulphate coordination affected the complexation with lignin. MD simulations showed the formation of inner sphere complexes of iron cations with deprotonated carboxyl and hydroxyl groups via bidentate and monodentate coordination. The removal efficiency of electrochemical oxidation (EO) as a post-treatment of the precipitation was dependent on iron salts. Removals of COD, UV₂₅₄ and color can achieve 98.88%, 98.9% and 99.97% by FeCl₃ precipitation and EO processes. The effluent reached the primary discharge standard specified in Integrated Wastewater Discharge Standard of China (GB8978-1996). FeCl₃ demonstrated significant advantages in the removal of organic pollutants from cotton pulp black liquor in the combined process of precipitation and electrochemical treatment and may have practical application potential.

Preparation of a Coal-Based MoS2/SiO2/GO Composite Catalyst and Its Performance in the Photocatalytic Degradation of Wastewater and Hydrogen Production

Photocatalytic degradation of wastewater and the simultaneous production of hydrogen (H₂) is a green and efficient method to solve energy and environmental problems. In this paper, coal-based SiO₂/GO with a stable structure was prepared by a modified Hummers oxidation method, and then, a lotus-shaped composite photocatalyst, MoS₂/SiO₂/GO, was prepared by in situ loading of flower cluster MoS₂ from sodium molybdate reduction onto SiO₂/GO. Its photocatalytic degradation of wastewater and H₂ production properties were investigated while characterizing the material structure. The results show that SiO₂/GO as a carrier not only ensures adequate dispersion of MoS₂ but also enhances the visible-light response of the composite catalyst. In addition, it can also hinder the recombination of photogenerated electrons and holes in MoS₂ and act as an electron transport channel in composite catalysts. MoS₂/SiO₂/GO exhibits much higher photocatalytic degradation of wastewater and H₂ production capacity than MoS₂: after 180 min of reaction, the CODcr removal of wastewater increased from 45.6% for MoS₂ to 84.2% for MoS₂/SiO₂/GO and the H₂ yield reached 233.4 μmol. The goal of degrading wastewater while producing H₂ more economically has been tentatively achieved, although not to the extent required for industrialization.

Black liquor: A potential moistening agent for production of cost-effective hydrolytic enzymes by a newly isolated cellulo-xylano fungal strain Aspergillus tubingensis and its role in higher saccharification efficiency

In the present study, black liquor generated during mild alkali pre-treatment was evaluated as a moistening agent to produce cost effective hydrolytic enzymes using novel cellulo-xylano fungal strain Aspergillus tubingensis M7. The fungus competently produced 21.90 and 22.46 filter paper, 1004 and 1369 endoglucanase, 117 and 142 β-glucosidase and 8188 and 7981 U/g xylanase activity by using modified Mandel & weber's and black liquor medium, respectively. The crude hydrolytic enzymes from black liquor were evaluated for saccharification of pre-treated biomass. Reducing sugar yields (mg/g substrate) and the corresponding saccharification efficiency (%) from rice straw, corncob, sugarcane bagasse and banana stem were 745.50 (86.02; 18 h); 596 (74.50; 24 h); 358.15 (42.98; 24 h) and 245.70 (33.00; 24 h), respectively. Residual biomass compositional analysis revealed that reduced onset temperature, increased activation energy and pre-exponential factor in saccharified biomass as compared to pre-treated and untreated biomass, suggesting their utilization for pyrolysis to obtain value added products.

Mycoremediation of PCBs by Pleurotus ostreatus: Possibilities and Prospects

With the rising awareness on environmental issues and the increasing risks through industrial development, clean up remediation measures have become the need of the hour. Bioremediation has become increasingly popular owing to its environmentally friendly approaches and cost effectiveness. Polychlorinated biphenyls (PCBs) are an alarming threat to human welfare as well as the environment. They top the list of hazardous xenobiotics. The multiple effects these compounds render to the niche is not unassessed. Bioremediation does appear promising, with myco remediation having a clear edge over bacterial remediation. In the following review, the inputs of white-rot fungi in PCB remediation are examined and the lacunae in the practical application of this versatile technology highlighted. The unique abilities of Pleurotus ostreatus and its deliverables with respect to removal of PCBs are presented. The need for improvising P. ostreatus-mediated remediation is emphasized.

Mineralization of a sulfonated textile dye Reactive Red 31 from simulated wastewater using pellets of Aspergillus bombycis

BACKGROUND

Reactive Red 31, applied extensively in the commercial textile industry, is a hazardous and persistent azo dye compound often present in dye manufacturing and textile industrial effluents. Aspergillus bombycis strain was isolated from dye contaminated zones of Gujarat Industrial Development Corporation, Vatva, Ahmedabad, India. The decolorization potential was monitored by the decrease in maximum absorption of the dye using UV-visible spectroscopy. Optimization of physicochemical conditions was carried out to achieve maximum decolorization of Reactive Red 31 by fungal pellets.

RESULTS

Pellets of A. bombycis strain were found to decolorize this dye (20 mg/L) under aerobic conditions within 12 h. The activity of azoreductase, laccase, phenol oxidase and Manganese peroxidase in fungal culture after decolorization was about 8, 7.5, 19 and 23.7 fold more than before decolorization suggesting that these enzymes might be induced by the addition of Reactive Red 31 dye, and thus results in a higher decolorization. The lab-scale reactor was developed and mineralization of Reactive Red 31 dye by fungal pellets was studied at 6, 12 and 24 h of HRT (hydraulic retention time). At 12 h of HRT, decolorization potential, chemical oxygen demand (COD) and total organic carbon reduction (TOC) was 99.02, 94.19, and 83.97%, respectively, for 20 mg/L of dye concentration.

CONCLUSIONS

Dye decolorization potential of A. bombycis culture was influenced by several factors such as initial dye concentration, biomass concentration, pH, temperature, and required aerated conditions. Induction of azoreductase, laccase, phenol oxidase, and Mn-peroxidase enzymes was observed during dye decolorization phase. A. bombycis pellets showed potential in mineralization of dye in the aerobic reactor system. Isolated fungal strain A. bombycis showed better dye decolorization performance in short duration of time (12 h) as compared to other reported fungal cultures.Graphical abstractDegradation of RR31 dye in developed aerobic fungal pelleted reactor.