Chromium Discharge Research Articles

Advances in adsorption technologies for hexavalent chromium removal: Mechanisms, materials, and optimization strategies

In the realm of environmental engineering and water treatment, significant attention has been devoted to the removal of hexavalent chromium Cr (VI) from wastewater. Delving into the mechanisms of adsorption reveals a complex interplay of ion exchange, surface complexation, and electrostatic interactions dictating the binding of Cr (VI) to various adsorption materials. Utilizing diverse adsorbents like 2-D materials, metal oxides, and bio-based substances is driven by their exceptional absorptive capacity and specificity. Key parameters such as pH, temperature, initial concentration, and dosage are scrutinized to optimize the efficiency of adsorbent removal and ascertain the absorptive nature of the adsorbate. Beyond natural sources, human activities have exacerbated chromium contamination across ecosystems, posing a threat to food chains due to chromium's non-biodegradable nature and persistence. Chromium affects a wide range of life forms, including humans, aquatic organisms, and terrestrial species, through the accumulation and repercussions of chromium discharge. The leaching of chromium into ground and surface water triggers various health issues such as dermatitis, allergic reactions, skin ulcerations, bronchial carcinoma, asthma, and gastroenteritis. This review intended to list different treatment technologies for chromium removal along with their mechanism. Different types of sensors used for chromium detection have also been explored.

Fe(III) transporter OsYSL15 may play a key role in the uptake of Cr(III) in rice (Oryza sativa L.)

Due to the widely discharge of chromium (Cr) by mining and smelting industries, etc., contamination of paddy soils and rice has become serious problems. Therefore it is crucial to explore how rice takes up Cr. Cr(III) is the most common Cr form in the long-term water flooding paddy soils. Here, we demonstrate that OsYSL15, a key gene for Fe(III) uptake, is equally applicable for Cr(III) uptake in rice. Firstly, the antagonistic effect of Cr(III) and Fe(III) in the uptake process was found. Rice could accumulate more Cr(III) under Fe-deficient conditions. And the Fe(III) content in the protoplasts of rice root cells gradually decreased with the increase exposure of Cr(III). Knockdown of OsYSL15 in rice significantly reduced the Cr(III) uptake rate. Compared with wild type rice, the accumulation of Cr(III) in OsYSL15 mutant was decreased by 40.7%− 70.6% after gene editing. These results indicate that OsYSL15 is a key gene responsible for Cr(III) uptake in rice, which can guide the screening or genetic modification for low-Cr-accumulation rice varieties.

Biorreducción in vitro de cromo hexavalente utilizando consorcios microbianos

Constant industrial development has increased the chromium use, resulting in chromium discharge into wastewater. The implementation of microbial bioremediation has been proposed as an ecological, efficient and economical alternative for the implementation of microorganisms to reduce chromium to a less toxic form. Our objective was to evaluate the Cr (VI) removal capacity of microbial consortia at different concentrations. Accordingly, an activation and identification of microorganisms from chromium-containing wastewater was carried out. Seven microbial consortia were established and their synergy, individual and consortium growth curves were evaluated. Subsequently, a scaled adaptation of the consortia was carried out with eight concentrations of Cr (VI). Reciprocal regression models and growth curves were used to identify the consortium with the highest removal. Synergy was found in the consortia evaluated; growth curves of consortia showed higher absorbance than individually, with higher absorption in the Candida famata-Serratia sp. Consortium. However, in the scaled adaptation, greater Cr (VI) reduction capacity was demonstrated in Candida tropicalis-Serratia sp. with 79.20% at a concentration of 100 ppm with a total chromium reduction of 31.12%. At the same time, a greater adaptation of the consortia to high concentrations of Cr (VI) was identified. This is the first research to report C. tropicalis-Serratia sp. microbial consortium with a positive interaction and higher metabolic reduction capacity, which will have a positive impact on bioremediation of chromium-containing wastewater.

Reducing chromium discharge in tanning: The salt-free chrome tanning process

Nowadays, there is increasing concern about environmental protection in global industrial activities. The sustainable leather industry is currently focusing on cleaner processing methods to promote a greener environment. However, the discharge of waste streams containing several pollutants poses a significant social threat to the leather sector. The conventional pickling and chrome tanning process is particularly problematic due to the enormous amounts of chlorides and chromium emissions, which have been a longstanding issue that has not been satisfactorily resolved. In order to minimize the emissions of chromium and chloride integrately, a salt-free and high exhaustion chromium tanning method was designed and optimized. The study's results demonstrated that the chrome tanning process could be improved by conducting it in a salt-free environment, resulting in a smooth process and a chromium absorption rate increase to 99% compared to 75% in the conventional process. Moreover, the dosage of Chrome required was minimized from 1.5% to 0.8%, resulting in a significant reduction of residual Chromium concentration in the spent liquor from above 1150 mg/L to 40 mg/L. The novel chrome tanning process significantly decreases the amount of chromium-containing sludge generated and facilitates the disposal of spent liquor with a reduced amount of chrome and chloride. The novel process effectively addresses long-standing problems and meets the requirements of the modern sustainable leather industry.

Reducing chromium discharge in tanning: The salt-free chrome tanning process

Reducing chromium discharge in tanning: The salt-free chrome tanning process

An approach on chromium discharge reduction: Effect and mechanism of ketone carboxylic acid as high exhaustion chrome tanning agent

Chrome tanning agent is the most widely used tanning agent with the best performances of finished leather, but the traditional chrome tanning process poses severe challenges because of the serious chromium pollution, thus the upgrading of cleaner chrome tanning process is imminent. In order to reduce the residual chromium in wastewater and increase the utilization rate of chrome tanning agent, 4-acetyl-heptanediate (AHA), a high exhaustion chrome auxiliary, was developed and applied in chrome retanning process. The results showed that AHA chrome retanning processes (AHA-6 and AHA-4) significantly reduced the chromium content in wastewater by 48.14% and 47.57%, and increased the chromium content in leather by 102.14% and 82.43%. COD and TDS values decreased by 43.82% and 31.46% with AHA-4 method. The addition of AHA obviously reduced the chromium concentration of wastewater, improved the chromium absorption rate, and promoted the cleaner chrome retanning process, which satisfied with the overall requirements of modern sustainable leather industry. The formation of AHA and chromium (III) was discussed using Gaussian 16 program to explain the high exhaustion chrome tanning agent mechanism. The work will guide on design and preparation of new high exhaustion chromium tanning agents for clean leather production.

Removal of recalcitrant trivalent chromium complexes from industrial wastewater under strict discharge standards

Various industries produce large amounts of wastewater containing chromium complexes, such as tanning, electroplating, printing and dyeing. The complete removal of chromium complexes through traditional precipitation and coagulation processes is difficult, which is a great challenge in meeting strict chromium discharge standards. To date, a large number of literature reviews on chromium ions removal processes have been published, but none on the removal of chromium complexes. To tackle the challenge and provide reference for future research, this review summarized the difficulties of chromium complex removal and systematically explores the research status of chromium-complex-removal technologies. The researches on chromium complex removal are mainly focused on the precipitation, biotechnology, adsorption and redox process. These technologies are reviewed in detail in terms of their technological mechanisms, main advantages and shortcomings. In general, the researches available are still not sufficient to solve this problem to date. And finally, the future research directions of chromium complex removal have been proposed.

Melamine-Based Polymeric Crosslinker for Cleaner Leather Production.

To augment sustainable tanning, less chrome input, high functional quality leather processed via no restricted substance in processing, and ease to treat the inevitable protein waste generated are the key challenge, and currently, they have become the active part of leather research. Our work covers the synthesis of a formaldehyde-free chromium-incorporated polymeric tanning agent (FF-CIPTA) and its application in a reformed leather processing route which ensures near zero discharge of chromium containing solid waste. The preliminary characterization of FF-CIPTA reveals that the developed product is stable up to pH 5.2, and the particle size distribution ranges from 955 to 1450 nm with 12% Cr2O3 content. The present work significantly reduces the tanning agent input without compromising the thermal stability (103 °C) of the leather because of its multicrosslinking nature. Since the product exhibits a polymeric character, it provides tanning-cum-filling action which in turn reduces the retanning agent consumption in subsequent processes. Scanning electron microscopic study, porosity analysis, and hand assessment results clearly indicate the significant improvement in organoleptic properties. In addition, the process also enjoys the benefits of zero chromium containing solid waste generation, 71.4% reduction in chromium input, and high chromium transfer efficiency (92%) than the conventional process (36%), and 74.4% reduction in total dissolved solids generation. Furthermore, the water consumption and chemical input are reduced by 51.6 and 17%, respectively. Reduction in wastewater treatment cost and a high economic value of chromium-free leather scraps leads to a cumulative gain of US$ 39.84 per ton of raw material processing. Overall, a potential and practical applicability for cleaner and sustainable tanning is well established.

Optimization studies on aqueous two-phase extraction of hexavalent chromium from contaminated aqueous solutions

Chromium has wide applications in industry and its resources are limited. The total chromium discharge to the environment needs to be monitoredand regulated. The extraction of chromium to PEG offers its reuse in pure form. The present study focuses on the optimization of hexavalent chromium extraction to PEG 1500 using ammonium salt. The effect of independent parameters as to the initial salt solution pH and initial salt phase metal concentration on the extraction efficiency has been studied experimentally. Second-order polynomial models have been used to fit the dependent variables in the experimental range of parameters.Central composite rotatable design in Minitabstatistical software version 16is used as the optimization tool. The maximum efficiency that is achieved through the optimization studies is 29.8%at an initialsalt solution pH of 6.5 and initial metal concentration 24.4 ppm. The corresponding distribution coefficient at the optimum conditionshas been found to be 1.14. The results of the optimization studies have been validated by conducting experiments at the optimum conditions.

Biosorption of chromium from tannery effluent using carbon-activated algae granules of Chlorella vulgaris and Scenedesmus obliquus

The discharge of chromium into the environment has become a problem of great concern all over the world including Pakistan for a few decades. The present research was conducted to study the bioremediation effect of carbon-activated granules (CAAGs) of two algal strains as a novel biosorbent for chromium from tannery effluent in addition to improvement of different water quality indicators. Effect of sorbent dose (5, 7 and 9 g L−1) and contact time (0–140 h with interval of 20 h) on chromium removal was evaluated. Maximum chromium removal (9.33 mg L−1 and 7.60 mg L−1) from raw tannery wastewater (WW) was reached after 120 h using 9 gL−1 of Chlorella vulgaris and Scenedesmus obliquus biomass, respectively. Rate of Cr removal was found directly proportional with dose of granulated algae and incubation period. Carbon-activated granules of Chlorella vulgaris as a biosorbent (9 g L−1) exhibited 19.47% more chromium removal in 10 times diluted WW compared to raw WW. The CAAG of both isolates reduced COD (38.08% and 34.72%), BOD (37.04% and 13.60%) and TSS (34.01% and 36.30%) for Chlorella vulgaris and Scenedesmus obliquus, respectively. Meanwhile, both CAAG types decreased TSS by around 85% while resulting in a slide increase in pH compared to initials. The CAAG of both isolates proved to be promising candidates for environmental bioremediation by reducing chemical and biological oxygen demand and total suspended solids of tannery WW by developing cost-effective and ecofriendly process in the prevalence of sunlight.

Comparing chromium phyto-assessment in Brachiaria mutica and Leptochloa fusca growing on chromium polluted soil

Industrial discharge of chromium (Cr) into environment puts serious threat on living beings due to its potent toxicity. Phytostabilization, a type of in-situ phytoremediation is aimed to immobilize and stabilize the toxic elements in soil using root system of metal resistant potential plants. To evaluate the phytostabilization potential of two grass species Brachiaria mutica and Leptochloa fusca, a pot study was conducted using soil spiked with different concentrations of Cr (control, 25, 50 and 100 mg kg−1). Three plants were sown in each pot with three replications and arranged following completely randomized design. After three months of growth, the plants were harvested and above and below ground plant’s parts were analyzed for various growth and physiological parameters. Data revealed that plant biomass, chlorophylls and carotenoids reduced substantially with increasing Cr concentration. Antioxidant enzymatic activity increased significantly in L. fusca as compared to B. mutica with increasing Cr levels (up to 50 mg kg−1), then reduced at maximum Cr level (100 mg kg−1) in both grasses. Leptochloa fusca performed better with maximum root Cr accumulation 93.7 μg plant−1, shoot Cr accumulation 24.7 μg plant−1, root bioconcentration factor (BCF) 2.0, shoot BCF 0.08, shoot TF 0.06 and MTI 87%. While B. mutica showed maximum root Cr accumulation 18.4 μg plant−1, shoot Cr accumulation 7.6 μg plant−1, shoot BCF 0.03, root BCF 1.28, shoot TF 0.04, and MTI 56%. These results showed that L. fusca possessed good potential with better Cr bioaccumulation, MTI, BCF and antioxidant activities compared to B. mutica. Hence L. fusca can be used as good phytostabilizing agent for the soils contaminated with lower to moderate levels of Cr.

Chromium Pollution in European Water, Sources, Health Risk, and Remediation Strategies: An Overview.

Chromium is a potentially toxic metal occurring in water and groundwater as a result of natural and anthropogenic sources. Microbial interaction with mafic and ultramafic rocks together with geogenic processes release Cr (VI) in natural environment by chromite oxidation. Moreover, Cr (VI) pollution is largely related to several Cr (VI) industrial applications in the field of energy production, manufacturing of metals and chemicals, and subsequent waste and wastewater management. Chromium discharge in European Union (EU) waters is subjected to nationwide recommendations, which vary depending on the type of industry and receiving water body. Once in water, chromium mainly occurs in two oxidation states Cr (III) and Cr (VI) and related ion forms depending on pH values, redox potential, and presence of natural reducing agents. Public concerns with chromium are primarily related to hexavalent compounds owing to their toxic effects on humans, animals, plants, and microorganisms. Risks for human health range from skin irritation to DNA damages and cancer development, depending on dose, exposure level, and duration. Remediation strategies commonly used for Cr (VI) removal include physico-chemical and biological methods. This work critically presents their advantages and disadvantages, suggesting a site-specific and accurate evaluation for choosing the best available recovering technology.

Hexavalent chromium removal from municipal wastewater using ferrous salts

Abstract Hexavalent chromium is difficult to remove during conventional biological wastewater treatment. This is because the hexavalent form is dissolved and is only sparingly removed by adsorption onto biomass in conventional processes. Hexavalent chromium is of particular concern because of its aquatic toxicity, and an increasing number of wastewater works have effluent discharge limits to protect receiving water courses, some as low as 8 μg Cr L−1. A relatively simple improvement to the removal of chromium could be made by switching the aluminium or ferric solution dosed at most treatment works for the removal of solids, organic load and phosphorus, to a ferrous salt. Ferrous reduces hexavalent chromium to insoluble trivalent chromium, which can be readily settled out of waste streams as a particulate. In the present study, laboratory experiments using real wastewater and ferrous doses of 10 mg Fe L−1 achieve the chromium discharge consent of 8 μg L−1 from initial solution concentrations of up to 40 μg L−1. A ferrous chloride dosing system was subsequently installed at an operational sewage treatment works that has produced an average final effluent chromium concentration of 2.4 μg L−1 (with a maximum of 4.2 μg L−1), despite influent spikes >300 μg L−1.

Hydroxyl‐Terminated Dendrimer Acting as a High Exhaustion Agent for Chrome Tanning

AbstractSevere restrictions for chromium discharge and scarcity of chromium resources have forced the tanners to seek for low‐waste and high exhaust chrome tanning technology. Based on the structural traits of dendrimers, in this paper, a series of hydroxyl terminated dendrimers (HTD) with different molecules weight (Mw) was synthesized and applied in the chrome tanning of pigskin. The effect of HTD was investigated on chromium discharge in effluent, and on the shrinkage temperature (Ts), denaturation temperature (Td), mechanical properties, and microstructure of the leather. The experimental results indicated that the chromium discharge in effluent by applying HTD (A1) was reduced to 236.0 mg/L, almost one‐sixth of the conventional chrome tanning. HTD that, possesses high hydroxyl density, has endowed the obtained leather with higher chrome uptake, Ts, and mechanical properties. Specially, HTD could slow down the basification process by the forming of hydrogen bonds with collagen residues. In addition, HTD could combine more chromium and form net crosslink, notably improve the chrome uptake and hydrothermal stability. Therefore, it is conceivable that the HTD could act as a high exhaustion agent in chrome tanning process.

A Chromium Discharge Minimizing Tanning Technology Assisted by O2 Low Temperature Plasma

Substantial quantities of solid and liquid wastes generate in the chrome tanning process, posing major environmental problem if not managed effectively. In order to minimize the emissions of chromium, a high exhaustion chromium tanning method was designed in this study. Low temperature plasma (LTP) technology has the characteristics of economy, pollution-free and high efficiency. The pioneering works were carried out by applying LTP to surface modification of natural leather before tanning process. The effects of different treatment time on micro-structure, chemical compositions, active groups, tanning absorption rate of leather fiber were studied. The SEM results showed that the leather surface was etched rougher. The XPS data showed that the O1s area ratios increased from 18.8 % to 27.6 % after O2 LTP treatment. The optimal O2 plasma treatment time is 10min. The results show O2 LTP treatment effectively improves the chrome tanning absorption rate from 78.68 % of conventional process to 94.47 % of the novel process, which reduces the emission of heavy metal chromium and protects the environment.

An integrated technology to minimize the pollution of chromium in wet-end process of leather manufacture

In order to minimize chromium pollution, based on tracing the life cycle of chromium in whole leather wet-end processing, an integrated technology comprising of a novel salt-free and high-exhaustion chrome tanning process, modified chrome retanning, direct recycling of tanning wastewater and highly efficient removal of Cr from post-tanning floats was developed. The results indicated that, in the novel technology, the total Cr utilization ratio reached to 98.6% (conventional 91.2%), the total chromium discharge was reduced by 84.2% from the source, and the spent tanning liquor could be completely recycled for at least 10 cycles, whilst the leather properties were not impaired. Furthermore, the remained Cr in the wastewater without reused value was removed by means of precipitation with optimized bases, and the residual Cr was at the level of 1.0–1.2 mg/L, the produced chrome-contained sludge was reduced by 28.1%. The novel technology integrating reduction at source and end treatment can reduce the total Cr discharge with effluent to 4.604 g/t salted-wet hide and the chrome concentration in mixed wastewater streams is 0.354 mg/L, and achieve near zero emission of chromium in leather processing.

A salt-free pickling chrome tanning approach using a novel sulphonic aromatic acid structure

Large discharge of chromium and chloride is a severe pollution source in conventional leather-making industry, which hinders the sustainable development of leather industry and affects human life greatly. Aiming at minimizing the emissions of chromium and chloride, novel materials rich in sulfonic acid group were synthesized and optimized in salt-free pickling and less chrome tanning process. The results showed that, the novel method would improve the chromium absorption and distribution in crust leather from 71.6% to 98.6%, in comparison with conventional pickling chrome tanning, and the concentration of residual chromium in spent liquor was decreased to 45 mg/L. The SEM indicated that the resulting leather treated with novel salt-free pickling showed clean pores and well-dispersed fibrils. Further experiment proved this novel salt-free pickling and less chrome tanning method is feasible in terms of organoleptic and physical mechanical properties. The financial assessment showed that the novel method is 46.9% cheaper than conventional approach. This novel pickling chrome tanning method can successfully solve the emission of chromium and chloride as well as obtain cleaner products in leather-making industry.

Lethal and sub-lethal effects on the Asian common toad Duttaphrynus melanostictus from exposure to hexavalent chromium

Chromium discharged in industrial effluents frequently occurs as an environmental pollutant, but the lethal and sub-lethal effects the heavy metal might cause in animals exposed to it have been insufficiently investigated. Selecting the amphibian Duttaphrynus melanostictus, we carried out laboratory tests to investigate the effects of short and long term exposure to hexavalent chromium (Cr(VI)) in both tadpoles and adult toads. The concentrations used were 0.002, 0.02, 0.2, 1.0 and 2.0mg/L, the first three corresponding to field levels. In vitro exposures were also carried out using toad erythrocytes and Cr(VI) concentrations of 0.0015, 0.003, 0.015, 0.03, 0.15mg/L. Mortality, growth retardation, developmental delays and structural aberrations were noted in the metal-treated tadpoles, with increasing incidence corresponding to increase in Cr(VI) level and duration of exposure. Many of the sub-lethal effects were evident with long term exposure to environmentally relevant levels of the toxicant. Changes in selected blood parameters and erythrocyte morphometry were also detected in Cr(VI) exposed toads, indicating anaemic and leucopenic conditions. In the genotoxicity study, DNA damage indicated by comet assay and increased micronuclei frequency, occurred at the low Cr(VI) concentrations tested. The multiple deleterious effects of exposure to chromium signal the need for monitoring and controlling the discharge of chromium to the environment. The dose-dependency and genotoxic effects observed in this widely distributed Asian toad indicates its suitability for monitoring heavy metal pollution in aquatic systems.

A salt-free and chromium discharge minimizing tanning technology: the novel cleaner integrated chrome tanning process

Chrome tanning is the most important and widely used tanning method in leather manufacture up to now. However, simultaneously control of the severe contamination of large amount of chromium and chloride discharge, both of which are serious environmental concerns, is highly challenging with the conventional chrome tanning process. Consequently, the development of leather manufacture is being unsustainable. In order to minimize the emissions of chromium and chloride integrately, a salt-free and high exhaustion chromium tanning method was designed and optimized in both laboratory and pilot scale. The results indicated that, being superior to the conventional process, the chrome tanning process was conducted in a salt-free condition smoothly and the chromium absorbility was increased to 98% from 73% in the novel process. Then the Cr dosage was minimized from 1.16% to 0.61% and the residual Cr concentration in the spent liquor dropped below to 50 mg/L from above 1100 mg/L. The pilot-scale experiments verified that the novel method was acceptable in the aspects of organoleptic and mechanical properties of resultant leather, product style and cost. It is anticipated that the spent liquor containing a very small amount of chrome and chloride can be more easily disposed and the generation of chromium-containing sludge will be stoichiometrical much less. The established novel chrome tanning process satisfactorily solves the longstanding problems commercially and matches the integral requirements of the modern sustainable leather industry.

Selective and sensitive detection of chromium(VI) in waters using electrospray ionization mass spectrometry

From 2000 through 2011, there were 14 criminal cases of violations of the Clean Water Act involving the discharge of chromium, a toxic heavy metal, into drinking and surface water sources. As chromium(VI), a potential carcinogen present in the environment, represents a significant safety concern, it is currently the subject of an EPA health risk assessment. Therefore, sensitive and selective detection of this species is highly desired. This study reports the analysis of chromium(VI) in water samples by electrospray ionization mass spectrometry (ESI-MS) following its reduction and complexation with ammonium pyrrolidinedithiocarbamate (APDC). The reduction and subsequent complexation produce a characteristic [Cr(III)O]-PDC complex which can be detected as a protonated ion of m/z 507 in the positive ion mode. The detection is selective to chromium(VI) under acidic pH, even in the presence of chromium(III) and other metal ions, providing high specificity. Different water samples were examined, including deionized, tap, and river waters, and sensitive detection was achieved. In the case of deionized water, quantification over the concentration range of 3.7 to 148ppb gave an excellent correlation coefficient of 0.9904 using the enhanced MS mode scan. Using the single-reaction monitoring (SRM) mode (monitoring the characteristic fragmentation of m/z 507 to m/z 360), the limit of detection (LOD) was found to be 0.25ppb. The LOD of chromium(VI) for both tap and river water samples was determined to be 2.0ppb. A preconcentration strategy using simple vacuum evaporation of the aqueous sample was shown to further improve the ESI signal by 15 fold. This method, with high sensitivity and selectivity, should provide a timely solution for the real-world analysis of toxic chromium(VI).