An integrated approach for tannery effluent treatment with ozonation and phycoremediation: A feasibility study

Unlocking the potential of parboiled rice mill effluent: From microalgae cultivation to bioelectricity production for sustainable development

Rice is a staple food in many Asian countries, and parboiling is a crucial process to reduce grain breakage and improve head rice yield during milling. However, this process generates substantial amounts of nutrient-rich effluent, which, if inadequately treated, leads to environmental issues such as eutrophication. The present review critically examines the parboiling process, highlighting that wastewater contains high concentrations of nitrogen, phosphorus, and organic matter with Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD). These nutrients, when utilized effectively, can support sustainable practices such as microalgae cultivation for food and biomass, biofertilizer production, and bioenergy generation, including biofuel and bioelectricity through microbial fuel cells (MFCs). Around 94 % reduction in COD levels and 90 % removal in nitrogen and phosphorus is achieved on effective utilization of nutrients in wastewater for biomass cultivation. Strategies for odor management in parboiling units are also discussed, leveraging techniques such as activated carbon adsorption and advanced oxidation processes adapted from municipal wastewater treatments. The manuscript emphasizes a circular economy approach, proposing integrated solutions for effluent reuse to minimize environmental impact and support sustainable agricultural and energy practices. Future research directions focus on scaling these technologies and optimizing their cost-effectiveness.

Assessment and monitoring of leather effluent discharge from Dewas and Ranipet and their computational approach

The swift pace of industrialization, urbanization, and burgeoning populations propel the surge in demand for manufactured goods and infrastructure. The wastewater produced during leather processing comprises a cocktail of organic and inorganic chemical contaminants that have the potential to affect the environment. This study focuses on conducting a comparative physico-chemical, analytical, in vitro, and in silico toxicity assessment and monitoring of leather effluent discharged from two different areas, namely, Dewas and Ranipet. The physicochemical analysis of collected effluents revealed higher levels of biochemical oxygen demand, chemical oxygen demand, total dissolved solids, total suspended solids, and heavy metals than the permissible limit fixed by the Central Pollution Control Board (CPCB). The X-ray powder diffraction analysis of both samples identified the existence of crystalline and amorphous phases. The functional composition of compounds was identified through the analysis of Fourier-Transform Infrared Spectroscopy, which revealed the existence of C-H, O-H, N-H, C = O, C=C, and C≡C stretching vibrations. A variety of compound derivatives, including amines, organic acids, organometallic compounds, alcohols, hydrocarbons, esters, aldehydes, ketones, aromatic, and organogermanium, were identified by Gas Chromatography-Mass Spectrometry. An assessment and monitoring of the phytotoxicity of effluent on the germination of Vigna radiata seeds reveals that (100%) of both Dewas and Ranipet leather effluents inhibited seed germination by 33.34% and 100%. The incorporation of Absorption-Distribution-Metabolism-Excretion-Toxicity (ADMET) analysis improved comprehension of the toxicity profiles of the GC-MS-identified compounds. Moreover, the result of docking studies revealed that cytochrome P450 showed the highest binding affinity towards 1,3-benzodioxol-2-one, hexahydro-cis with an affinity score of - 7.1 kcal/mol. The overall research revealed that the leather effluents from Dewas and Ranipet exhibit significant toxicity, highlighting the necessity of better wastewater management. In the future, innovative treatment methods and environmental friendly processes can be developed to minimize the detrimental effects of leather effluents.

Biological treatment processes for saline organic wastewater and related inhibition mechanisms and facilitation techniques: A comprehensive review

Owing to its profound pollution-inducing properties and resistance to biodegradation, saline organic wastewater (SOW) has unavoidably emerged as a predominant focal point within the wastewater treatment domain. Substantial quantities of SOW are discharged by diverse industries encompassing food processing, pharmaceuticals, leather manufacturing, petrochemicals, and textiles. Within this review, the inhibitory repercussions of elevated salinity upon biological water treatment systems are subject to methodical scrutiny spanning from sludge characteristics, microbial consortia to the physiological functionality of microorganisms have been investigated. This exposition elucidates the application of both anaerobic and aerobic biological technologies for SOW treatment, which noting that conventional bioreactors can effectually treat SOW through microbial adaptation, and elaborating that cultivation of salt-tolerant bacteria and the design of advanced bioreactors represents a promising avenue for SOW treatment. Furthermore, the mechanisms underpinning microbial acclimatization to hypersaline milieus and the methodologies aimed at amplifying the efficacy of biological SOW treatment are delved into, which point out that microorganism exhibit salt tolerance via extracellular polymeric substance accumulation or by facilitating the influx of osmolarity-regulating agents into the bacterial matrix. Finally, the projections for future inquiry are proffered, encompassing the proliferation and deployment of high salt-tolerant strains, as well as the development of techniques enhancing the salt tolerance of microflora engaged in wastewater treatment.

Microalgae: A green eco-friendly agents for bioremediation of tannery wastewater with simultaneous production of value-added products

Tannery wastewater (TWW) has high BOD, COD, TS and variety of pollutants like chromium, formaldehydes, biocides, oils, chlorophenols, detergents and phthalates etc. Besides these pollutants, TWW also rich source of nutrients like nitrogen, phosphorus, carbon and sulphur etc. that can be utilized by microalgae during their growth. Direct disposal of TWW into the environment may lead severe environmental and health threats, therefore it needs to be treated adequately. Microalgae are considered as an efficient microorganisms (fast growing, adaptability and strain robustness, high surface to volume ratio, energy saving) for remediation of wastewaters with simultaneous biomass recovery and generation of value added products (VAPs) such as biofuels, biohydrogen, biopolymer, biofertilizer, pigments, bioethanol, bioactive compounds, nutraceutical etc. Most microalgae are photosynthetic and use CO₂ and light energy to synthesise carbohydrate and reduces the emission of greenhouse gasses. Microalgae are also reported to remove heavy metals and antibiotics from wastewaters by bioaccumulation, biodegradation and biosorption. Microalgal treatment can be an alternative of conventional processes with generation of VAPs. The use of biotechnology in wastewater remediation with simultaneous generation of VAPs is trending. The validation of economic viability and environmental sustainability, life cycle assessment studies and techno-economic analysis is undergoing. Thus, in this review, the characteristics of TWW and microalgae are summarized, which manifest microalgae as potential candidates for wastewater remediation with simultaneous production of VAPs. Further, the treatment mechanisms, various factors (physical, chemical, mechanical and biological etc.) affecting treatment efficiency as well as challenges associated with microalgal remediation are also discussed.

Management of tannery waste effluents towards the reclamation of clean water using an integrated membrane system: A state-of-the-art review

Tanning and other leather processing methods utilize a large amount of freshwater, dyes, chemicals, and salts and produce toxic waste, raising questions regarding their environmental sensitivity and eco-friendly nature. Total suspended solids, total dissolved solids, chemical oxygen demand, and ions such as chromium, sulfate, and chloride turn tannery wastewater exceedingly toxic for any living species. Therefore, it is imperative to treat tannery effluent, and existing plants must be examined and upgraded to keep up with recent technological developments. Different conventional techniques to treat tannery wastewater have been reported based on their pollutant removal efficiencies, advantages, and disadvantages. Research on photo-assisted catalyst-enhanced deterioration has inferred that both homogeneous and heterogeneous catalysis can be established as green initiatives, the latter being more efficient at degrading organic pollutants. However, the scientific community experiences significant problems developing a feasible treatment technique owing to the long degradation times and low removal efficiency. Hence, there is a chance for an improved solution to the problem of treating tannery wastewater through the development of a hybrid technology that uses flocculation as the primary treatment, a unique integrated photo-catalyst in a precision-designed reactor as the secondary method, and finally, membrane-based tertiary treatment to recover the spent catalyst and reclaimable water. This review gives an understanding of the progressive advancement of a cutting-edge membrane-based system for the management of tanning industrial waste effluents towards the reclamation of clean water. Adaptable routes toward sludge disposal and the reviews on techno-economic assessments have been shown in detail, strengthening the scale-up confidence for implementing such innovative hybrid systems.

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.

Integrated strategies for robust growth of Chlorella vulgaris on undiluted dairy farm liquid digestate and pollutant removal

Undiluted dairy farm liquid digestate contains high levels of organic matters, chromaticity and total ammonia nitrogen (TAN), resulting in inhibition to microalgal growth. In this study, a novel cascade pretreatment with ozonation and ammonia stripping (O + S) was employed to remove these inhibitors, and was compared with single pretreatment approach. The optimum parameters for ozonation and ammonia stripping were obtained and the mechanisms of inhibition elimination were investigated. The results show that ozonation contributed to the degradation of non-fluorescent chromophoric organics through the direct molecular ozone attack, which mitigated the inhibition of chromaticity to microalgae, while ammonia stripping relieved the inhibition of high TAN to microalgae. After cascade pretreatment, TAN, total nitrogen (TN), COD and chromaticity were reduced by 80.2 %, 75.4 %, 20.6 % and 75.8 % respectively. When C. vulgaris was cultured on different pretreated digestate, it was found that cascade pretreatment was beneficial for retaining high PSII activity and synergistically improved microalgal growth. The highest biomass increment and productivity achieved 5.40 g L^-1 and 900 mg L^-1 d^-1 respectively in the integration system of cascade pretreatment with microalgae cultivation (O + S + M). After O + S + M treatment, the removal efficiencies of TAN, TN, COD and total phosphorus (TP) were 100 %, 92.8 %, 46.7 % and 99.6 %, respectively. This work provided a promising strategy (O + S + M) for sustainable liquid digestate treatment, along with nutrient recovery and value-added biomass production.

Advancements of sequencing batch reactor for industrial wastewater treatment: Major focus on modifications, critical operational parameters, and future perspectives

Industrial wastewater discharge has increased manifolds over the last few decades. Efficient industrial wastewater treatment is mandatory to meet stringent discharge regulations. Biological treatment systems, such as the sequencing batch reactor (SBR) are generally employed for domestic wastewater treatment. However, low infrastructure and energy requirements, as well as low footprint, make SBR a prominent technique to treat industrial wastewater. In the present review, the feasibility of SBR to treat wastewater generated from industries, such as textile, pulp and paper, pharmaceutical, tannery, etc., has been discussed. The factors affecting the treatment efficacy of the SBR in terms of organics and nutrient removal have also been investigated. It has been observed that the SBR system is effective for industrial wastewater treatment as it is easy to operate, resistant to shock loads, and can retain high biomass concentrations. The modifications to the conventional SBR, such as sludge granulation, the addition of bio-film carriers, and the incorporation of adsorbents, salt-tolerant microbes, and coagulants have been discussed. Further, various novel combinations of SBR with the other advanced treatment technologies, such as Fenton, membrane-based process, and electrochemical process have shown enhanced removal of various conventional and recalcitrant pollutants. The current review also accentuates the sustainability aspects of SBR technology to treat industrial wastewater which may be beneficial for researchers and engineers working in this field.

Comparison of degradation kinetics of tannery wastewater treatment using a nonlinear model by salt-tolerant Nitrosomonas sp. and Nitrobacter sp

Conventional biological treatment has been reported to be ineffective for pollutant removal in tannery wastewater due to high salinity. To overcome it, this work used salt-tolerant bacteria (STB) isolated from a membrane bioreactor to evaluate the organic and nutrient removal through a series of batch experiments. Compared with the control, the STB reactor enhanced the reduction of persistent organics by 11% based on the double exponential decay model. Besides, the removal of NH₄⁺-N is 26% higher, satisfying the first-order decay model. The nitrification was inhibited entirely in control during 48 h, whilst the assimilation process involved 55% of total nitrogen removal. In the STB reactor, nitrification occurred after 12 h, resulting in significantly increased NO₂^--N and NO₃^--N concentrations according to the logistic function. Although nitrification was successfully activated, C/N ratios and free ammonia were identified as limiting factors for STB activity, requiring mitigation strategies in further studies.

Tannery wastewater treatment: conventional and promising processes, an updated 20-year review

Mismanagement of various wastes especially waste water produced by tanning processes has caused serious environmental problems and ultimately impaired human health. Constant efforts have been making to alleviate the pollution of tannery wastewater (TWW), yet terminal treatment still takes dominance. In this review, research on TWW treatment from 2000 to 2021 was summarized, and main methods such as coagulation and flocculation, adsorption, biological treatment, membrane filtration, advanced oxidation process were briefly discussed. More detailed introduction was given to the method of electrochemical treatment since it has excellent performance such as environmental friendliness and high efficiency, hence attracting more and more research attention in recent years. In view of the harsh physi-chemical conditions of TWW, integrated or combined treatment methods are accordingly recommended with better performance and multi-function, however comprehensive studies on optimization of methods combination and cost-effectiveness are needed. The certain issues that the residue Cr in treatment sludge and high salinity in effluent still remain were put forward in this work and potential solutions were provided. Moreover, this review proposed the perspective that realizing multi-function, recycling, and intensification should be the developing direction for future TWW treatment. This review is expected to provide a general guide for researchers who aspire to ameliorate TWW pollution problems and understand various methods utilized in this field.

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Unified, simple and decentralized treatment process for synthetic and real-time dye contaminated wastewaters

The aim of this study is to develop a simple, economical and effective treatment scheme to treat effluents from small scale textile dyeing units and tanneries, which have been set up in rural areas. The physicochemical properties of real time effluents procured from these industries were analysed. The workflow required for treating these effluents were ascertained by preliminary tests carried out on synthetically created solutions. A novel treatment scheme for tannery and textile dye effluents sludge volume reduction by the use of sodium hypochlorite was identified. Effective methods for the safe disposal and recycling of all the by-products generated from different steps were discussed. The proposed scheme was successfully able to decolourize and detoxify both the tannery and textile dyeing effluent with over 90% removal of both COD and BOD. The impacts of the treatment scheme on 14 different effluent parameters were reported. The methodology developed in this study may be utilized to construct simple localized treatment units for handling effluents in isolated rural areas. This preliminary treatment at the source, will help in the reduction of the load on the local treatment plants and prevent their choking.

Microalgal-based removal of contaminants of emerging concern

The presence of contaminants of emerging concern (CECs) in the environment has been recognized as a worldwide concern. In particular, water pollution by CECs is becoming a major global problem, which requires ongoing evaluation of water resources policies at all levels and the use of effective and innovative wastewaters treatment processes for their removal. Microalgae have been increasingly recognized as relevant for wastewater polishing, including CECs removal. These microorganisms are commonly cultivated in suspension. However, the use of planktonic microalgae for wastewater treatment has limitations in terms of microbiological contamination, process effectiveness and sustainability. The use of consortia of microalgae and bacteria represents a significant advance for sustainable wastewater polishing, particularly when the microorganisms are associated as biofilms. These immobilized mixed cultures can overcome the limitations of suspended-microalgae systems and improve the performance of the involved species for CECs removal. In addition, microalgae-bacteria based systems can offer a relevant combined effect for CECs removal and biomass production enhancement. This study reviews the advantages and advances on the use of microalgae for wastewater treatment, highlighting the potential on the use of microalgae-bacteria biofilms for CECs removal and the further biomass valorisation for third-generation biofuel production.

Current technologies for post-tanning wastewater treatment: A review

Leather post-tanning is responsible for producing effluents that are difficult to treat due to several recalcitrant pollutants. Dyes, tannins, and fatliquoring agents are mainly related to this characteristic. This study, as the state-of-the-art, attempts to systematically review treatment technologies applied in recent years to the post-tanning effluents. The Scopus database was used to identify articles related to post-tanning pollutants removal. Through the review, Advanced Oxidation Processes (AOPs) and adsorption proved to be good alternatives to increase the effluent biodegradability when applied before biological treatment. AOPs and adsorption were also efficient for the final polishing of the effluents, to reach the regulation standards for disposal, as well as enzymatic treatment. Furthermore, Membrane Separation Processes demonstrated good applicability when the reuse of the treated effluent is aimed.

Valorization of microalgae biomass into bioproducts promoting circular bioeconomy: a holistic approach of bioremediation and biorefinery

The need for alternative source of fuel has demanded the cultivation of 3rd generation feedstock which includes microalgae, seaweed and cyanobacteria. These phototrophic organisms are unique in a sense that they utilise natural sources like sunlight, water and CO₂ for their growth and metabolism thereby producing diverse products that can be processed to produce biofuel, biochemical, nutraceuticals, feed, biofertilizer and other value added products. But due to low biomass productivity and high harvesting cost, microalgae-based production have not received much attention. Therefore, this review provides the state of the art of the microalgae based biorefinery approach to define an economical and sustainable process. The three major segments that need to be considered for economic microalgae biorefinery is low cost nutrient source, efficient harvesting methods and production of by-products with high market value. This review has outlined the use of various wastewater as nutrient source for simultaneous biomass production and bioremediation. Further, it has highlighted the common harvesting methods used for microalgae and also described various products from both raw biomass and delipidified microalgae residues in order to establish a sustainable, economical microalgae biorefinery with a touch of circular bioeconomy. This review has also discussed various challenges to be considered followed by a techno-economic analysis of the microalgae based biorefinery model.

Advanced Oxidation Processes and Biotechnological Alternatives for the Treatment of Tannery Wastewater

The tannery industry is one of the economic sectors that contributes to the development of different countries. Globally, Europe and Asia are the main producers of this industry, although Latin America and Africa have been growing considerably in recent years. With this growth, the negative environmental impacts towards different ecosystem resources as a result of the discharges of recalcitrated pollutants, have led to different investigations to generate alternative solutions. Worldwide, different technologies have been studied to address this problem, biological and physicochemical processes have been widely studied, presenting drawbacks with some recalcitrant compounds. This review provides a context on the different existing technologies for the treatment of tannery wastewater, analyzing the physicochemical composition of this liquid waste, the impact it generates on human health and ecosystems and the advances in the different existing technologies, focusing on advanced oxidation processes and the use of microalgae. The coupling of advanced oxidation processes with biological processes, mainly microalgae, is seen as a viable biotechnological strategy, not only for the removal of pollutants, but also to obtain value-added products with potential use in the biorefining of the biomass.

Effect of culture conditions on biomass yield of acclimatized microalgae in ozone pre-treated tannery effluent: A simultaneous exploration of bioremediation and lipid accumulation potential

Microalgae has huge potential towards biological nutrient removal, but the challenges are remains in maximizing the biomass yield and so nutrient/pollutant removal efficiency. In this study, a response surface methodology-central composite design was applied to investigate the significant process variables (temperature, light intensity, inoculum density and light period) and its interaction effect on biomass yield of effluent acclimatized microalgae Nannochloropsis oculata, Chlorella vulgaris and Chlorella sorokiniana in ozone pre-treated tannery effluent (OPTE). At optimum culture condition N. oculata, C. vulgaris, and C. sorokiniana have yielded 0.67 g/L, 0.85 g/L, and 1.06 g/L biomass. Besides, correlation and regression analysis revealed the strong correlation between microalgal growth and nutrient removal rate. Among the species, C. sorokiniana has shown better remediation potential, at 27.5 °C, 150 μmol m^-2 s^-1 light intensity, 30% (v/v) inoculum, 16 h light period with the specific growth rate of 0.559 day^-1 and nutrient/pollutant removal efficiency of 90% C, 90% N, 100% P, 82% COD, and 100% chromium. But, N. oculata has revealed the better lipid accumulation potential (40%) in OPTE. Thus, the present study established the appropriate strains and conditions required for OPTE treatment along with the value-added biomass production in large scale.

An overview on heavy metal resistant microorganisms for simultaneous treatment of multiple chemical pollutants at co-contaminated sites, and their multipurpose application

Anthropogenic imbalance of chemical pollutants in environment raises serious threat to all life forms. Contaminated sites often possess multiple heavy metals and other types of pollutants. Elimination of chemical pollutants at co-contaminated sites is imperative for the safe ecosystem functions, and simultaneous removal approach is an attractive scheme for their remediation. Different conventional techniques have been applied as concomitant treatment solution but fall short at various parameters. In parallel, use of microorganisms offers an innovative, cost effective and ecofriendly approach for simultaneous treatment of various chemical pollutants. However, microbiostasis due to harmful effects of heavy metals or other contaminants is a serious bottleneck facing remediation practices in co-contaminated sites. But certain microorganisms have unique mechanisms to resist heavy metals, and can act on different noxious wastes. Considering this significant, my review provides information on different heavy metal resistant microorganisms for bioremediation of different chemical pollutants, and other assistance. In this favour, the integrated approach of simultaneous treatment of multiple heavy metals and other environmental contaminants using different heavy metal resistant microorganisms is summarized. Further, the discussion also intends toward the use of heavy metal resistant microorganisms associated with industrial and environmental applications, and healthcare. PREFACE: Simultaneous treatment of multiple chemical pollutants using microorganisms is relatively a new approach. Therefore, this subject was not well received for review before. Also, multipurpose application of heavy metal microorganisms has certainly not considered for review. In this regard, this review attempts to gather information on recent progress on studies on different heavy metal resistant microorganisms for their potential of treatment of co-contaminated sites, and multipurpose application.

Phycoremediation coupled biomethane production employing sewage wastewater: Energy balance and feasibility analysis

In the present work Chlorella pyrenoidosa, Scenedesmus abundans and Anabaena ambigua have been evaluated for their biomass, phycoremediation efficiency and biomethane production potential by cultivating them in the primary treated sewage waste water (PTSWW) under controlled conditions. By the end of 25-day experiment, up to 52-88% reduction was observed in the nutrient concentration from the 3:1 ratio of PTSWW. Co-digestion of microalgal biomass (dry) with cow dung was performed to estimate biomethane potential. Biogas yield of 618-925 ml g^-1 VS with 48-65% of methane content was obtained employing the microalgal species cultivated in PTSWW. Microalgae appeared notably competent at nutrient sequestration from PTSWW with significant microalgal biomass productivity for biogas production. Energy balance studies revealed the feasibility of coupling the remediation with energy generation. High photosynthetic rate and biomass generation ability along with nutrient confiscation supports employment of microalgae as a potential next generation biofuel source with waste management.

Phycoremediation of Precious Metals by Cladophora fracta From Mine Gallery Waters Causing Environmental Contamination

We have presented a study to determine the possibility for the usage of Cladophora fracta as bioaccumulator of the metals (Au) and silver (Ag) both have characteristics of pollutant and precious in mine water. The highest concentrations accumulated by C. fracta were determined as 5.8 ± 0.3 and 5323 ± 75 µg/kg for Au and Ag, respectively. The results showed that the accumulation of the metals measured followed the order of Ag > Au. The Metal Pollution Index (MPI) values calculated between 39.37 × 10^-3 and 175.7 × 10^-3 were used to determine the pollution degree of C. fracta. As a result, it was determined that C. fracta highly accumulated the precious metals from the gallery water. Therefore, C. fracta was a good bioaccumulator for the remediation of Au and Ag in mine gallery waters. In this way, it is possible to minimize or eliminate the environmental risks of the precious metals in the gallery waters.