Analysis of heavy metals and toxicity level in the tannery effluent and the environs

Tannery effluent treatments with mangrove fungi, grass root biomass, and biochar

Tannery effluents contain high amounts of polluting chemicals, such as salts and heavy metals released often to surface waters. New economic and eco-friendly purification methods are needed. Two adsorbing materials and five salt-tolerant fungal isolates from mangrove habitat were studied. Purification experiments were carried out using the pollutant adsorbents biochar and the biomass of vetiver grass (Chrysopogon zizanioides) roots and the fungi Cladosporium cladosporioides, Phomopsis glabrae, Aspergillus niger, Emericellopsis sp., and Scopulariopsis sp., which were isolated from mangrove sediment. They efficacy to reduce pollutants was studied in different combinations. Salinity, turbidity, total dissolved solids, total suspended solids, phenols, nitrogen, ammonia. Biological and chemical oxygen demand (BOD, COD) and several heavy metals were measured. The adsorbents were efficient reducing the pollutants to 15-50% of the original. The efficiency of the combination of biochar and roots was generally at the same level as the adsorbents alone. Some pollutants such as turbidity, COD and ammonium were reduced slightly more by the combination than the adsorbents alone. From all 14 treatments, Emericellopsis sp. with biochar and roots appeared to be the most efficient reducing pollutants to < 10-30%. BOD and COD were reduced to ca 5% of the original. The treatment was efficient in reducing also heavy metals (As, Cd, Cr, Mn Pb, Zn). The fungal species originating from the environment instead of the strains present in the tannery effluent reduced pollutants remarkably and the adsorbents improved the reduction efficiency. However, the method needs development for effluents with high pollutant concentrations to fulfil the environmental regulations.

Evaluating hydrogeochemistry and heavy metal contamination of groundwater at Ranipet environs: employing multivariate statistics, agricultural indices, and health risk assessment

Water plays an essential role in sustaining life on Earth as an indispensable natural resource. In recent decades, dependence on groundwater for domestic and industrial purposes has become inevitable. The Ranipet industrial environs (RIE) has many tanneries and chemical industries, which affects the groundwater quality. This study assessed groundwater quality and its suitability for domestic, agricultural, and human health risk assessments. 40 groundwater samples (28 open wells and 12 bore wells) were collected during pre-monsoon 2022 and analyzed by employing multivariate statistics, standard scatter plots, irrigation indices, and health risk assessment. The results of hydrogeochemical analysis and multivariate statistics affirmed that electrical conductivity (EC), total dissolved solids (TDS), calcium (Ca2+), and magnesium (Mg2+) have controlled the hydrochemistry of RIE. Cadmium (Cd) at 46% and chromium (Cr) at 33% have contaminated the groundwater in the study area, making it unsuitable for human consumption and irrigation. The agricultural indices analysis results show groundwater quality ranging from very poor to unsuitable making it unsuitable and also affects crop productivity. Hazard index (HI) results infer that Cr and Cd severely contaminated the RIE's groundwater, encompassing 14 villages, making the groundwater unfit for drinking, domestic use, and irrigation. Hazard quotient (HQ) and incremental lifetime cancer risk (ILCR) analysis revealed that 2 in 100 infants and 3 in 1000 people over the age of 63 are likely to develop cancer due to Cr and Cd in the REI. This is a need-of-the-hour problem, addressing this issue with preventive measures to ensure the protection of groundwater sources will lead to achieving the Sustainable Development Goal 6 (Clean Water and Sanitation).

Improving Tannery Wastewater Treatments Using an Additional Microbial Treatment with a Bacterial-Fungal Consortium

Environmental pollutants such as toxic heavy metals and oxygen-demanding solids are generated by leather manufacturing. In most tanneries, wastewaters are treated with physico-chemical methods but overly high levels of pollutants remain in surface waters. The efficiency of tanning wastewater treatment with conventional techniques was evaluated in four tanneries in Saudi Arabia. It was observed that the wastewaters contained high amounts of pollutants, needing further treatment. We isolated microorganisms from the wastewaters and carried out experiments to treat the effluents with different bacteria, fungi, and their consortia. We hypothesized that a consortium of microorganisms is more efficient than the single microorganisms in the consortium. The efficiency of five single bacterial and five fungal species from different genera was tested. In a consortium experiment, the efficiency of nine bacterial-fungal consortia was studied. The bacterium Corynebacterium glutamicum and the fungus Acremonium sp. were the most efficient in the single-microbe treatment. In the consortium treatment, the consortium of these two was the most efficient at treating the effluent. The factory wastewater treatment reduced total dissolved solids (TDS) from 1885 mg/L to 880 mg/L. C. glutamicum treatment reduced TDS to 150 mg/L and Acremonium sp. to 140 mg/L. The consortium of these two reduced TDS further to 80 mg/L. Moreover, the factory treatment reduced BOD from 943 mg/L to 440 mg/L, C. glutamicum to 75 mg/L, and Acremonium sp. 70 mg/L. The consortium reduced BOD further to 20 mg/L. The total heavy-metal concentration (Cd, Cr, Cu, Mn, and Pb) was reduced by the factory treatment from 43 μg/L to 26 μg/L and by the consortium to 0.2 μg/L. The collagen concentration that was studied using hydroxyproline assay decreased from 120 mg/L to 39 mg/L. It was shown that the consortium of the bacterium C. glutamicum and the fungus Acremonium sp. was more efficient in reducing the pollutants than the single species. The consortium reduced almost all parameters to below the environmental regulation limit for wastewater discharge to the environment in Saudi Arabia. The consortium should be studied further as an additional treatment to the existing conventional tannery wastewater treatments.

Primary and digested sludge-derived char as a Cd sorbent: feasibility of local utilisation

Cadmium (Cd) is a highly toxic metal, occurring in municipal wastewater and stormwater as well as in wastewater from various industries. Char derived from the pyrolysis of municipal sewage sludge has the potential to be a low-cost sorption media for the removal of Cd. However, the balance between possible local char production and demand has not been assessed previously. In this study, the Cd sorption capacities of chars derived from primary (PSC) and secondary sludge (DSC), as well as the feasibility of char production for Cd sorbent purposes, and the pyrolysis energy balance were evaluated. Results showed that the sorption capacity of PSC (9.1 mg/g; 800 °C, 70 min) was superior to that of DSC (6.0 mg/g; 800 °C, 70 min), and increased with a higher pyrolysis temperature. Pyrolysis of primary sludge had a more favourable energy balance compared with the pyrolysis of digested sludge; however, when accounting for loss of biogas production the energy balance of primary sludge pyrolysis was negative. Assessment of the regional demand (Västerås, Sweden) indicated that PSC or DSC may cover the local Cd sorbent demand. However, it was estimated that large char volumes would be required, thus making the use of DSC/PSC less feasible.

New roles for Bacillus thuringiensis in the removal of environmental pollutants

For a long time, the well-known Gram-positive bacterium Bacillus thuringiensis (Bt) has been extensively studied and developed as a biological insecticide for Lepidoptera and Coleoptera pests due to its ability to secrete a large number of specific insecticidal proteins. In recent years, studies have found that Bt strains can also potentially biodegrade residual pollutants in the environment. Many researchers have isolated Bt strains from multiple sites polluted by exogenous compounds and characterized and identified their xenobiotic-degrading potential. Furthermore, its pathway for degradation was also investigated at molecular level, and a number of major genes/enzymes responsible for degradation have been explored. At present, a variety of xenobiotics involved in degradation in Bt have been reported, including inorganic pollutants (used in the field of heavy metal biosorption and recovery and precious metal recovery and regeneration), pesticides (chlorpyrifos, cypermethrin, 2,2-dichloropropionic acid, etc.), organic tin, petroleum and polycyclic aromatic hydrocarbons, reactive dyes (congo red, methyl orange, methyl blue, etc.), and ibuprofen, among others. In this paper, the biodegrading ability of Bt is reviewed according to the categories of related pollutants, so as to emphasize that Bt is a powerful agent for removing environmental pollutants.

Enabling simultaneous valorization of tannery effluent and waste plastic via sustainable preparation of Cr-BDC MOFs for water adsorption

Advanced materials undergo a complex and lengthy process of maturation for scaling up and deployment, mainly due to the high cost of their precursors. Therefore, it is highly desirable to fabricate highly valuable advanced porous solid-state materials, with proven applicability, by sustainably combining organic and inorganic waste materials as precursors. This study successfully demonstrates the preparation of Cr-terephthalate Metal-Organic Frameworks (Cr-BDC MOFs) by combining metal salt and organic linker extracted from tannery effluent and waste plastic bottles. The waste from tanneries was used as the source of Cr(III), while terephthalic acid was obtained from the alkaline hydrolysis of plastic bottles. Appropriate extraction and assembly processes led to the functional Cr-BDC MOFs, MIL-101(Cr) and MIL-53(Cr). The prepared MOFs showed similar properties (surface area, hydrolytic and thermal stability, and water adsorption performance) to similar MOFs synthesized from pure commercial-grade precursors, as confirmed by N2 sorption, XRD, TGA, and water adsorption experiments. The advancements made in this study represent significant progress in overcoming the bottleneck of MOF production cost efficiency via applying sustainability principles and pave the way for easy scaling-up and maturation of MOF-based processes, for air dehumidification and water harvesting as a case study.