Current technologies for post-tanning wastewater treatment: A review

Advanced treatment of tannery effluent from Fez City (Morocco) using a sequence of aerobic and sono-photo-Fenton processes

This work aims to purify real tannery wastewater (TWW) after a physicochemical characterization. A pretreatment using air stripping (aerobic pretreatment; AP) was first applied and compared to anaerobic pretreatment (ANP). The COD and BOD5 were highly removed by AP, reaching 86% and 88% compared to ANP, which only achieved 48% and 55%, respectively. Following the AP, the sono-photo-Fenton (SPF) process was applied as post-treatment. The optimal conditions pH = 3, [H2O2] = 1834 mg/L, and [Fe2+] = 1281 mg/L improved the COD, color and BOD5 removal of 96%, 98%, and 98%, respectively. Turbidity, N-NO3-, and N-NO2- were completely removed (100%) by the combined processes (AP+SPF), while Cr, Cl-, and N-NH4+ were reduced to 99%, 97%, and 99%, respectively. Finally, phytotoxicity tests were performed to confirm the efficiency of the sequential processes. The highest germination percentage, germination rate index, and seedling vigor index for the grains wheat and Medicago sativa were observed using the TWW treated by the AP+SPF, followed by those treated by AP alone. In contrast, no germination indicators were noticed in raw TWW. These findings highlight the significant purification effectiveness of the sequential processes of AP and SPF post-treatment, which suggests the potential use of this combination for the efficient treatment of real liquid effluents.

Experimental design for assessing the degradation of tannery azo dyes and real-time effluent

Tannery wastewater (TWW) is highly complex and is characterised by high contents of organic, inorganic, and nitrogenous compounds, sulphides, chromium, dissolved solids, and suspended solids. Therefore, our novelty lies in identifying the microbes which are used to degrade harmful azo dyes present in tannery effluent. Based upon the rising problems in tannery industries, the untreated effluent is discharged; to achieve zero effluent, the organisms are isolated from tannery effluent identified as Aeromonas hydrophila (OQ690635) and screened against the degradation potential against the azo dyes and further processed the azo dye-degrading organism for 16S rRNA sequencing. The optimisation was done in various parameters, which resulted in the highest 94% degradation at 37 °C of 7 pH at the 60th hour in 10% of inoculum concentration, which influenced azo dye degradation and confirmed the degradation profile by FT-IR secondary alcohol, alkyne group, alcohol and nitro compounds, isothiocyanate, amine salt, alkyne had been removed and confirmed, also the treated Real-time effluent by novel bacteria which has shown 93% of degradation and also degradation profile by FT-IR and proven toxic free confirmed by GC-MS analysis. Thus, the bacteria isolated in this study can be used as eco-friendly biological expedients for the remediation and detoxification of azo dyes. This could be considered an efficient treatment method for various industrial effluents, as it provides zero sludge disposal during the treatment of industrial effluents.

Modulating the Interactions of Peptide-Polyphenol for Supramolecular Assembly Coatings with Controllable Kinetics and Multifunctionalities

Polyphenols and peptides represent two fundamental building blocks in the kingdom of supramolecular assembly (SA) coatings, which have recently attracted considerable interest. Regulating the assembly kinetics of SA coatings is critical to controlling the performance of SA coatings, but this area is still in its infancy, especially in the SA coating of peptide-polyphenol. Herein, a library of oligopeptides with rich diversity, numerous polyphenols, and modulators are explored to reveal their roles in the formation and regulation of SA coating. Citric acid (CA) is an effective regulator of interaction between the polyphenols and peptides to produce peptide-polyphenol coatings, TCP. The electrostatic interaction between tannic acid (TA) and cationic peptide drives the formation of TCP, while the multiple hydrogen bonds between CA and TA and peptide dominate the assembly kinetics. With optimized assembly pH and the mass ratio of TA, CA, and peptide, the thickness of TCP coating deposits onto diverse substrates (glass, silica, titanium, polystyrene) is ≈400 nm with controllable kinetics. The multifunctional TCP coatings are endowed via peptide-coupled functional units, including enhanced cellular adhesion, elevated osteogenic capacity, anti-protein adsorption, and antimicrobial. This work contributes to the understanding of the assembly kinetics and functionalization of peptide-polyphenol coatings.

Synergistic impact of Fe-Zr in novel hybrid aminoclay catalytic TFC membrane for ultrafast emerging pollutant remediation

Finding new class of materials to overcome limitation in conventional membranes is a challenging task. Use of naturally stable and sustainable alternative materials stock is an emerging task. In this direction, a novel iron-zirconium hybrid aminoclay (FZ-AC) has emerged as a promising catalyst effectively employed to alleviate fouling concerns within the framework of a biopolymer-based thin film composite (TFC), constructed on a cellulose acetate (CA) support. Notably, FZ-AC exhibits remarkable catalytic activity in the degradation of foulants through potential free radicals generated from Fe and Zr active centres in synergy with oxidising agent. The optimised catalytic membrane (FZ-TFC-1) exhibited an ultrafast degradation of congo red (CR), eriochrome black-T (EBT), crystal violet (CV), methylene blue (MB), red-brown dye (RBn), bisphenol-A (BPA), azithromycin (AZC), and Cr(VI) within 4 min. The cooperative action of redox centres of Fe and Zr metal ions synergistically accelerated the swift production of reactive species and facilitated the efficient degradation of pollutants within a notably short timeframe. Furthermore, >95% of above dyes rejection was achieved with >67 L m-2.h-1 of flux. The results of a long-term study demonstrated that FZ-TFC membranes exhibit exceptional stability, retaining their performance for a duration up to 150 h. This extended period of stability underscores the superiority of these membranes over alternative counterparts, suggesting their robustness and reliability for sustained operation in various applications. This strategic utilization of FZ-AC representing a promising avenue for enhancing the efficacy and longevity of nanofiltration membranes, thereby advancing the frontier of membrane-based separation technologies.

One-step approach to fabricating amphoteric polymer fatliquors for chrome-free tanned leather eco-manufacturing

The leather manufacturing industry is increasingly embracing chrome-free tanning methods to promote environmental sustainability. However, the transition to chrome-free tanning systems presents a notable obstacle: the incompatibility of traditional anionic wet finishing materials with chrome-free tanned leather due to differences in surface electrical behavior. Herein, an amphoteric polymer, referred to P(AA-co-DMAEMA-co-DA), was synthesized through a simple one-step free radical copolymerization using acrylic acid (AA), dimethylaminoethyl methacrylate (DMAEMA), and dodecyl acrylate (DA). Notably, the isoelectric point of P(AA-co-DMAEMA-co-DA) is 7.7, which contributes to improving the leather's positive electric property and enhancing the binding between the amphoteric polymer fatliquors (APF) and collagen fiber. The APF achieves a remarkable absorption rate of 96.2% and a dyeing uptake rate of 94.3% for anionic dyes, resulting in a uniformly bright surface color of the dyed leather and further significantly reducing the dye usage. Overall, the comprehensive properties of APF align with the electrical origins of organic chrome-free tanning leather, exhibiting a pronounced fatliquoring effect while reducing the dye content in the waste liquor. This contribution holds promise for advancing chrome-free tanning technology toward greener environmental practices.

Compound Similarity Network as a Novel Data Mining Strategy for High-Throughput Investigation of Degradation Pathways of Organic Pollutants in Industrial Wastewater Treatment

Identification of degradation products and pathways is crucial for investigating emerging pollutants and evaluation of wastewater treatment methods. Nontargeted analysis is a powerful tool to comprehensively investigate the degradation pathways of organic pollutants in real-world wastewater samples but often generates large data sets, making it difficult to effectively locate the exact information on interests. Herein, to efficiently establish the linkages among compounds in the same degradation pathways, we introduce a compound similarity network (CSN) as a novel data mining strategy for LC-MS-based nontargeted analysis of complex wastewater samples. Different from molecular networks that cluster compounds based on MS/MS spectra similarity, our CSN strategy harnesses molecular fingerprints to establish linkages among compounds and thus is spectra-independent. The effectiveness of CSN was demonstrated by nontargeted identification of degradation pathways and products of organic pollutants in leather industrial wastewater that underwent laboratory-scale activated carbon adsorption (ACD) and ozonation treatments. Utilizing CSN in interpreting nontargeted data, we tentatively annotated 4324 compounds in the untreated leather industrial wastewater, 3246 after ACD, and 3777 after ACD/ozonation. We located 145 potential degradation pathways of organic pollutants in the ACD/ozonation process using CSN and validated 7 pathways with 15 chemical standards. CSN also revealed 5 clusters of emerging pollutants, from which 3 compounds were selected for in vitro cytotoxicity study to evaluate their potential biohazards as new pollutants. As CSN offers an efficient way to connect massive compounds and to find multiple degradation pathways in a high-throughput manner, we anticipate that it will find wide applications in nontargeted analysis of diverse environmental samples.

A systematic review on the current situation of emerging pollutants in Mexico: A perspective on policies, regulation, detection, and elimination in water and wastewater

Emerging pollutants (EPs) emerged as a group of new compounds whose presence in the environment has been widely detected in Mexico. In this country, different concentrations of pharmaceutical compounds, pesticides, dyes, and microplastics have been reported, which vary depending on the region and the analyzed matrix (i.e., wastewater, surface water, groundwater). The evidence of the EPs' presence focuses on the detection of them, but there is a gap in information regarding is biomonitoring and their effects in health in Mexico. The presence of these pollutants in the country associated with lack of proper regulations in the discharge and disposal of EPs. Therefore, this review aims to provide a comprehensive view of the current environmental status, policies, and frameworks regarding Mexico's situation. The review also highlights the lack of information about biomonitoring since EPs are present in water even after their treatment, leading to a critical situation, which is high exposure to humans and animals. Although, technologies to efficiently eliminate EPs are available, their application has been reported only at a laboratory scale thus far. Here, an overview of health and environmental impacts and a summary of the research works reported in Mexico from 2014 to 2023 were presented. This review concludes with a concrete point of view and perspective on the status of the EPs' research in Mexico as an alert for government entities about the necessity of measures to control the EPs disposal and treatment.

Bacterial cell immobilized packed bed reactor for the elimination of dissolved organics from biologically treated post-tanning wastewater and its microbial community profile

In conventional, the biologically treated tannery wastewaters are rich in dissolved organics and the application of reverse osmosis (RO) to biologically treated tannery wastewater was challenged with fouling and failure of RO membrane due to existence of lingering dissolved organic compounds. In present investigation the bacterial cell immobilized packed bed reactor (CIPBR) was operated to remove the dissolved organic compounds in biologically treated post-tanning wastewater to avoid membrane fouling in RO. The efficient microbial syndicate to eliminate dissolved organics in post-tanning wastewater was isolated and immobilized on to the carbon silica matrix (CSM) in the range of 2.98 ± 0.2 × 10⁷ cells gm^-1 of CSM and the same was used as a carrier matrix in the packed bed reactor. The CIPBR established the COD_tot, COD_dis and BOD removal efficiency by 61 ± 4%, 57 ± 4% and 87 ± 3% respectively with COD_tot, COD_dis and BOD remained in the treated wastewater as 236 ± 21 mg/L, 228 ± 21 mg/L, and 12 ± 3 mg/L under continuous operation. The removal of dissolved organic compounds from the post-tanning wastewater was confirmed using UV-Visible and FT-IR spectroscopic studies. Among the total microbial community, the phylum Proteobacteria played most abundant role with 48.47% of relative abundance for the removal of dissolved organics in biologically treated post-tanning wastewater. The significance of the study is to replace the tertiary treatment unit operation in the conventional ETP/CETP to remove dissolved organics in wastewater.

Wastewater generation and treatment by various eco-friendly technologies: Possible health hazards and further reuse for environmental safety

The discharge of untreated wastewater as a result of various developmental activities such as urbanization, industrialization and changes in lifestyle poses great threats to aquatic ecosystems as well as humans. Currently, ∼380 billion m³ (380 trillion liters) of wastewater is generated globally every year. Around 70% of freshwater withdrawals are used for agricultural production throughout the world. The wastewater generated through agricultural run-off further pollutes freshwater resources. However, only 24% of the total wastewater generated from households and industries is treated before its disposal in rivers or reused in agriculture. The most problematic contaminants associated with ecological toxicity are heavy metals such as Cd, Cr, Cu, Ni, Zn, Fe, Pb, Hg, As and Mn. One of the most important issues linked with wastewater generation is the residual presence of pathogenic microorganisms which pose potential health hazards to consumers when they enter into the food chain. It is estimated that in India almost USD 600 million (48.60 billion INR) is spent per year to tackle waterborne diseases (WBD). In light of this, immediate action is needed to effectively treat wastewater and develop safer reuse prospects. Various wastewater treatment technologies have been established and they work well to provide an alternative water source to meet the growing demand. The main concern towards treating wastewater is to eliminate inorganic and organic substances and lower the nutrient concentration, total solids, and microbial pathogens to prevent freshwater pollution and health risks.

Analysis of the Capacity of the Fenton Process for the Treatment of Polluted Wastewater from the Leather Dyeing Industry

In this work, the capacity of the Fenton oxidation process for the degradation of color and organic matter contained in the wastewater generated in the leather dyeing stage (WWDS) of an industrial tannery was evaluated. The wastewater characteristics included, among others, high toxicity (lethal concentration for Artemia salina, 24 h test, 50% of population = 93.71 ppm), high dye concentration (36 mg/L, yellow color), high chromium concentration (3.34 mg/L), and low biodegradability index (BOD₅/COD ratio = 0.083). From an experimental design, the response surface methodology, and the multiobjective optimization analysis, the following optimal operating conditions were established: initial pH = 3.15, [Fe²⁺] = 0.981 mM, and [H₂O₂] = 5.38 mM. After 10 min of oxidation (determined from kinetic studies), it reached approximately 97% decolorization, COD reduction of approximately 82%, and TOC mineralization of approximately 92%. A synergistic effect of Fenton's reagents for TOC removal (S _TOC = 0.8) and decolorization (S _CN = 0.28) of the WWDS under study was confirmed experimentally. An increase in the biodegradability index, to a value of approximately 0.3, was confirmed. The cost of the treatment was estimated at 0.0112 USD/m³. Thus, the Fenton oxidation process allowed compliance with current Colombian environmental regulations and considerably improved the biodegradability and toxicity characteristics of the studied industrial effluent. It can be considered as an efficient alternative, easy to carry out on an industrial batch scale, and economically viable for the treatment of wastewater from the leather dyeing stage of an industrial tannery.

Phytoremediation of chromium, iron and nickel by Indian Rice Plant (Oryza sativa L.): An opportunity for management of multi-metal contaminated tannery wastewaterPhytoremediation of chromium, iron and nickel by Indian Rice Plant (Oryza sativa L.): An opportunity for management of multi-metal contaminated tannery wastewater

India is the largest producer of leather and leather products. Tannery industries use a large number of synthetic chemicals for the processing of leather and generate a huge amount of wastewater containing a large amount of potentially toxic heavy metals (PTHMs) making them problematic for next-door soil and water system. Currently, phytoremediation is an inexpensive green technology used to move, eradicate, and stabilized heavy metal contamination from contaminated sludge, soil, and wastewater. In this study, the accumulation and distribution of PTHMs found in tannery wastewater and their physio-biochemical effects on Oryza sativa L. have been studied by ICP-MS, GC-MS, and biochemical analysis. The plant was grown in the soil spiked with a mixture of metals (Cr, Fe and Ni) and their five-level of treatment T1 (25mg/kg); T2 (50mg/kg); T3 (100mg/kg); T4 (200mg/kg) and T5 (400mg/kg). During the experiments, various morphological attributes, oxidative stress, enzymatic activities, chlorophyll, and protein content at the different stage was measured. Further, metal accumulation pattern in different parts of plants was also measured. Results of the study revealed that plant root, shoot length, chlorophyll content, and enzymatic activities were significantly reduced after the treatment with 200 mg/kg PTHMs; whereas oxidative stress was increase compared to control levels.  Further, treatment of PTHMs suggested that the rice plant (Oryza sativa L.) is well adapted to tolerate and accumulate a high level of heavy metals (up to 200mg/kg) in the root and shoot of the treated plants. If it is treated above this, then seeds were also affected and not safe for human consumption.

The noteworthy chloride ions in reclaimed water: Harmful effects, concentration levels and control strategies

Chloride ions (Cl^-), which are omnipresent in reclaimed water, can cause various problems in water reuse systems, especially during water transmission and at end use sites. Although reverse osmosis (RO) is considered as an effective technology to reduce chloride, its high investment and complex maintenance requirements hinder its application in many water reclamation plants (WRPs). Recently, several technologies bringing new options to better deal with chloride have gained increased attention. This review provides detailed information on the harmful effects, concentration levels, and sources of chloride in reclaimed water and summarizes and discusses various chloride removal technologies, including non-selective methods (e.g., membrane filtration, adsorption and ion exchange, oxidation, and electrochemical methods) and selective methods (e.g. precipitation and specially designed electrochemical methods). Among these, Friedel's salt precipitation and capacitive deionization showed attractive development potential. This review also proposes a holistic framework for chloride control from aspects of "Fit-for-Purpose" planning, technical system development, and whole process optimization, which could facilitate the planning and operation of long-term sustainable water reuse practices.

Heterogeneous Photodegradation for the Abatement of Recalcitrant COD in Synthetic Tanning Wastewater

Tannery wastewater is considered one of the most contaminated and problematic wastes since it consists of considerable amounts of organic and inorganic compounds. These contaminants result in high chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total suspended solids (TSS). In this work, the heterogeneous photodegradation of recalcitrant COD in wastewater from the tanning industry was investigated, in particular the recalcitrant COD due to the presence of vegetable tannins extracted from mimosa and chestnut and from synthetic tannins based on 4,4′ dihydroxy phenyl sulfone. TiO2 Aeroxide P-25 was employed to study the photodegradation of model molecules in batch conditions under different parameters, namely initial concentration of COD, temperature, and catalyst dose. The maximum COD abatement reached was 60%. Additionally, preliminary kinetic investigation was conducted to derive the main kinetic parameters that can be useful for process scale-up. It was found to be independent of the temperature value but linearly dependent on both catalyst loading and the initial COD value.

Electro-oxidation of tannery wastewater to achieve zero discharge - a step towards sustainability

Pilot-scale electro-oxidation equipment with a functional capacity of 0.2 m³/hr, with titanium electrodes coated with TiO₂/RuO₂/IrO₂ as both anodes and cathodes, was designed. It was installed on the premises of a commercial tannery. The waste streams from all the unit processes were combined. The composite wastewater, after conventional pre-treatment was subjected to electro-oxidation. The treated wastewater was reused four times with intermittent electro-oxidation treatment, after each reuse. EO could bring about a significant reduction in pollution load. Reduction in BOD, COD, TKN and TSS was 92%, 87.5%, 96.2% and 94.6% respectively. Generation of ^oOCl radicals, during electro-oxidation, were ascertained with DMPO-spin trapping techniques using Electron Spin Resonance (ESR) spectroscopy. The characteristics of the treated wastewater indicated that the wastewater was fit for reuse. No significant change in the quality of the water after each reuse was observed. The physical properties of the leathers obtained following the reuse processes were akin to those of the control leathers, which was indicative that the reuse did not cause adverse quality deviations. This technique could provide the plausibility for minizine the discharge of wastewater to near-zero level.

Water reuse in the post-tanning process: minimizing environmental impact of leather production

Post-tanning wastewater is very diversified, as the post-tanning stage should meet the desirable properties of the leather for the final product, with low standardization of the process (compared to beamhouse and tanning). This makes post-tanning effluent reuse less feasible, and reuse in the post-tanning stage still needs to be explored. This work aims to evaluate the reuse of liquid effluents in the post-tanning process. The work methodology consisted of (i) characterization of water streams (groundwater, liquid effluent after primary treatment, and liquid effluent after secondary treatment); (ii) pilot-scale post-tanning tests using groundwater, primary effluent, and secondary effluent; (iii) characterization of the residual baths from pilot-scale tests (pH, conductivity, total solids, chemical oxygen demand, biochemical oxygen demand, chloride, hardness and oil and grease); and (iv) testing the leather obtained for total sulfated ash and organoleptic properties. Results showed that the primary effluent and the secondary effluent could be reused in pilot-scale post-tanning tests. There was an increase in the conductivity of the residual baths when liquid effluents were reused, which confirms the accumulation of salts in the effluents after their reuse.

Effects of municipal wastewater treatment plant effluent quality on aquatic ecosystem organisms

The management and quality monitoring of wastewater have an important role in sustainable development. A recent approach in environmental protection involves the ecotoxicological assessment of effluents to complement the usual chemical evaluations. This study assessed the impacts of wastewater treatment plant (WWTP) effluent quality in a location in Western Cape province, South Africa using organisms that bear different ecosystem-level function responsibilities like the Pseudokirchneriella subcapitata (microalgae), Daphnia magna (crustaceans), and Tetrahymena thermophila (protozoan) in addition to the physicochemical parameters. The effluent showed values of chemical oxygen demand (COD; 41-83 mg L^-1), dissolved oxygen (DO; 2.7-3.1 mg L^-1), Redox potential (189-265 mV), and total dissolved solids (TDS; 656-718 ppm). The protozoan Tetrahymena thermophila ecotoxicity test exhibited toxic effects of the effluents within 24-h with a mean lethal value (LC₅₀) of 1.12% for the winter season. The findings of this study revealed that analyzed physicochemical parameters are within the regulatory water quality acceptable standard thresholds with few exceptions, while the biotests were able to determine the toxicity levels and sensitivities of each test. The results showed that the WWTP whole effluent exerted toxicity to test organisms, but dilution can mitigate the effects considerably. The use of ecotoxicological assessment methods for municipal WWTP effluent may enhance existing water management strategies.