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The secure and harmless disposal for Cr-bearing tannery sludge (Cr-TS) has attracted an increasing concern, due to potentially adverse effect on ecosystem and human health. A greener alternative method about "waste treatment with waste" for thermally stabilizing real Cr-TS was developed via employing coal fly ash (CA) as dopants in this research. The co-heat treatment of Cr-TS and CA was carried out at the temperature range of 600-1200 °C to investigate the oxidation of Cr(III), immobilization of chromium and leaching risk of the sintered products, and the mechanism of chromium immobilization was further explored. The results indicate that the doping of CA can significantly inhibit the oxidation of Cr(III) and immobilize chromium by incorporating chromium into spinel and uvarovite microcrystal. At the temperature higher than 1000 °C, most of chromium can be converted into stable crystalline phases. Furthermore, a prolonged leaching test was conducted to study the leaching toxicity of chromium in sintered products, indicating that leaching content of chromium is much less than the regulatory limit. This process is a feasible and promising alternative for immobilization of chromium in Cr-TS. The research findings are supposed to offer a theoretical foundation and strategy choice for thermal stabilization of chromium, as well as safety and harmless disposal of Cr-containing hazardous waste., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Graphene Oxide (GO) has wide applications in many fields which has caused a large expected quantity of the graphene-based wastes. It is necessary to understand the toxic effects of the GO on the activated sludge (AS) considering its inevitable discharge to the wastewater treatment plants as the ultimate repositories for these wastes. In this study, the acute exposures of the multilayer Nano-graphene oxide (MNGO) at different dosages were conducted in order to investigate its integrated effects on the formation of the biofilm, mature biofilm and the microbial activity of the activated sludge. Raman spectroscopy and laser scanning confocal microscopy (LSCM) were adopted for the in-situ characterization of the biofilm with the exposure of the MNGO. The results showed that the activated sludge was tolerable to the acute exposure of the less than 100 mg/L of the MNGO, especially for the mature biofilm, and only a subtle decrease was found in the size and thickness during the formation of the biofilm, while the amount of 300 mg/L of the MNGO caused the sever deterioration on the activated sludge system. The microbial metabolic activity, viability, and the biological removal of the nutrients were significantly affected with the more than 100 mg/L of the MNGO. It was also demonstrated by the microbial cytotoxicity tests that the increase in the exposure of the MNGO was related to the increase in the reactive oxygen species (ROS) and the damaging degree of the cell membrane., (Copyright © 2020 Elsevier Inc. All rights reserved.)

As a hazardous waste, the disposal of chromium enriched tannery sludge has attracted increasing public concern due to its potential adverse risks towards the environment. And incineration is considered to be an effective method to stabilize heavy metals, like Cr, in solid phase during tannery sludge treatment. In this study, real chromium enriched tannery sludge without pre-treatment was incinerated at 300°C-1200 °C under air atmosphere to investigate the transformation of chromium speciation. Here detailed thermal behavior, phase transformation and chromium speciation were characterized by TG-DSC, XRD and XPS, respectively. Experimental results show that content of Cr(VI) increases gradually with the increase of temperature from 300 °C to 500 °C and reaches a maximal level of 46% total Cr at 500 °C, with different Cr(VI) species of CaCrO 4 , MgCrO 4 and Cr 5 O 12 . However, the content of Cr(VI) decreases gradually with the further increase of temperature, with only about 5% Cr(VI) at high temperature of 1200 °C, due to formation of Cr(III) species of Cr 2 O 3 crystallite and MgCr 2 O 4 spinel. Besides, a growing number of hexagonally shaped flake-like crystallite Cr 2 O 3 can be discovered from characterization results of XRD and SEM. Finally, the reduction of CaCrO 4 to Cr 2 O 3 in the presence of SiO 2 is thermodynamically feasible over 700 °C, indicating possible transformation of Cr(VI) to Cr(III) through controlled incineration temperature., Competing Interests: Declaration of competing interest The authors declare that we have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

In this paper, a process combining biodegradation and Fenton oxidation was proposed for the removal of polydiallyldimethylammonium chloride-acrylic-acrylamide-hydroxyethyl acrylate (PDM) in aqueous phase. Biodegradation of PDM was investigated in activated sludge systems, and the effects of the solution pH, mixed liquid suspended solids (MLSS), salinity, co-substrate, and initial substrate concentration, were studied. The biodegradation process was well-described with the Monod model and the values of the kinetics parameters v max , k s were 0.05 h -1 and 333 mg/L. The optimal biodegradation conditions in the experimental range were determined to be: pH = 7.0, 0%-0.01% (w/v) NaCl, 4000 mg/L of MLSS, and 500 mg/L of glucose as co-substrate. FT-IR analysis indicated that PDM molecules biodegradation partly. The microbial community structures and dehydrogenase activity analysis revealed that PDM showed some toxicity to microorganisms in activated sludge. The effects of several parameters, including the pH and chemical doses, were investigated for removing PDM in Fenton oxidation process. The optimal Fenton oxidation process conditions in the experimental range were pH = 2.0, Fe 2+ concentration of 40 mg/L, and H 2 O 2 dosage of 23 mL/L. PDM was treated by biodegradation and subsequent Fenton oxidation under the optimal operating conditions. The removal efficiency was 44.5% after the biodegradation process and further increased to 85.5% after Fenton oxidation. The combined process was revealed to be a promising solution for achieving effective and economical removal of PDM., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Tannery sludge contained plenty of organic matter, and the organic substance stability had direct impact on its derived chars' utilization. In this paper, the stabilization of tannery sludge and the variation of humic acid-like (HAL) extracted by different methods were investigated in a magnetic stirring reactor under low temperature pyrolysis of 100-400 °C. Results showed that the aromatic structure of pyrolysis chars increased with the increase of temperature and time. The char contained highly aromatic structure and relatively small dissolved organic matters (DOM) at 300 °C. The similar behaviors appeared in two HAL series by different extraction methods. The N content, H/C value, and aliphatic structures of HAL decreased with the increase of pyrolysis temperature, while the C/N value and aromatic structures increased with the rise of pyrolysis temperature. The composition and functional groups of HAL were similar with the purchased humic acid (HA). The fluorescence spectra revealed that two main peaks were found at Ex/Em = 239/363-368 nm and 283/359-368 nm in each HAL series from raw and 100 °C pyrolysis tannery sludge, representing a protein-like matter. The new peak appeared at Ex/Em = 263-283/388 nm in each HAL series from 200 °C pyrolysis tannery sludge-represented humic acid-like matter. The fluorescence intensity increased strongly compared to the other two peak intensity. Therefore, the humification of organic matter was increased by pyrolyzing. Notably, the HAL from 200 °C pyrolysis tannery sludge contained simple molecular structure, and the polycondensation increased but with a relative lower humification degree compared to soil HAL and purchased HA. Therefore, the sludge needs further oxidation. The humic substance was negligible by direct extraction when the temperature was 300 and 400 °C.

Microorganism communities and chemical characteristics in sludge-bamboo charcoal composting system were investigated to find the effect of bamboo charcoal on composting. According to a plate count test, abundances of bacteria, fungi and actinomycetes in the treatment with bamboo charcoal were several times higher than those in treatment without bamboo charcoal. In addition, terminal restriction fragment length polymorphism (TRFLP) analysis indicated that the bacterial community diversity in treatment with bamboo charcoal was greater than that of the control. Both results demonstrated that amendment with bamboo charcoal can increase microorganism population and microorganism community diversity in a sludge composting system. Moreover, the results of FTIR spectroscopy disclosed that aerobic composting can promote the formation of surface acid groups on bamboo charcoal. These surface acid groups may deprotonate and react with NH4+ to form stable complexes. Therefore, the increase of functional groups accompanied with greater assimilation of nitrogen by microorganisms could reduce nitrogen loss in sludge composting.

During the leather tanning process, chromium (Cr) can interact with different macromolecular organics to generate mixed ligand complexes. The removal of organochromium complexes is one of the main difficulties in the treatment of tannery wastewater. In this study, a gelatin-gallic ac-id-Cr(III) (G-GA-Cr) mixed ligand complex was used to examine the effects of ultrasonic on chromium destabilization and removal from the dissolved complexes. To investigate organic destruction and chromium liberation, alkali precipitation or chelating precipitation assisted with ultrasound were conducted, respectively. The findings demonstrate that ultrasonic-assisted alkali precipitation and chelating precipitation, respectively, removed over 50% and 93% of Cr from the complexes. According to the data, ultrasonication weakened the bonds that bound macromolecular ligands together, and depolymerization took place to the point where Cr could interact directly with hydroxide ions or chelating agents. In addition, by applying ultrasonic-assisted chelating precipitation, the chromium concentration could meet the discharge standard and the amount of precipitation was also noticeably decreased. [ABSTRACT FROM AUTHOR]

Effective arsenic removal from highly laden industrial wastewater is an important but challenging task. Here, a combined coprecipitation/nano-adsorption process, with ferric chloride and calcium chloride as coprecipitation agents and polymer-based nanocomposite as selective adsorbent, has been validated for arsenic removal from tungsten-smelting wastewater. On the basis of operating optimization, a binary FeCl (520 mg/L)-CaCl (300 mg/L) coprecipitation agent could remove more than 93 % arsenic from the wastewater. The resulting precipitate has proved environmental safety based on leaching toxicity test. Fixed-bed column packed with zirconium or ferric-oxide-loaded nanocomposite was employed for further elimination of arsenic in coprecipitated effluent, resulting in a significant decrease of arsenic (from 0.96 to less than 0.5 mg/L). The working capacity of zirconium-loaded nanocomposite was 220 bed volumes per run, much higher than that of ferric-loaded nanocomposite (40 bed volumes per run). The exhausted zirconium-loaded nanocomposite could be efficiently in situ regenerated with a binary NaOH-NaCl solution for reuse without any significant capacity loss. The results validated the combinational coprecipitation/nano-adsorption process to be a potential alternative for effective arsenic removal from highly laden industrial effluent. [ABSTRACT FROM AUTHOR]

This study examined the correlation between non-metallic organic tanning agents (NOTAs) and wastewater containing double-triazine (bistriazine). Specifically, high-throughput sequencing was used to analyze how the physical and chemical properties of the bistriazine-containing wastewater affected the microbial community. In total, 9995 operating taxonomy units (OTUs) were detected at a similarity level of 97%. According to the taxonomy results and relative bacterial richness, the non-metallic organic tanning agent (NOTA) wastewater communities showed significant differences. Clostridium sensu stricto and Turicibacter bacteria were dominant in NOTA T2, T3, and the blank control (KB) wastewater; Trichococcus and Aeromonas were dominant in NOTA T4; and Pseudomonas was dominant in T2, T4, and the blank control (KB). Thus, the addition of bistriazine ring derivatives altered the composition of the bacterial community. Furthermore, Spearman's correlation analysis revealed a substantial correlation in the composition of the communities and the physicochemical properties of the wastewater. Acidocella and norank c Cyanobacteria correlated positively with Total Phosphorus (TP) (p ≤ 0.001) and Mycobacterium showed a positively held correlation with pH (p ≤ 0.05). Conversely, norank_f__Elev-16S-1332 indicated a negative correlation with TP, Total Nitrogen (TN), and Total Organic Carbon (TOC) (p ≤ 0.05), whereas Zoogloea correlated negatively with NH3–N, TOC, and TN (p ≤ 0.05). Regarding water quality, a significant correlation between microbial communities and the physicochemical properties of bistriazine wastewater was also observed (p ≤ 0.05). We concluded that Trichococcus, Clostridium sensu stricto, Turicibacter, Pseudomonas, Intestinibacter, Acidocella, Bacillus, and Tolumonas showed a high tolerance for bistriazine wastewater, which could offer insight into its bioremediation. [ABSTRACT FROM AUTHOR]

The performances of advanced oxidation processes (AOPs) for the removal of refractory dissolved organic matter (DOM) are significantly different due to the various degradation mechanisms and competitive interactions between DOM and AOPs. This research traced the variation and removal of DOM components in tannery wastewater (TW) during conventional treatment, which includes coagulation, hydrolytic acidification/anoxic (H/A), and anaerobic/aerobic (A/O) stages. Electrochemical oxidation (EO) and ozone oxidation (OO) AOPs were conducted to treat a conventional treatment effluent based on selective oxidation and performance. The results demonstrated that the refractory DOM of the secondary effluent of the TW was mainly the hydrophilic neutrals (HIN) fraction (44.1%), which consisted of fatty acids and aliphatic compounds, and the hydrophobic acids (HOA) fraction (28.5%), which included the carboxylic-rich alicyclic molecules (CRAMs) and complex polycyclic aromatic structures. During the conventional treatment, lower molecular weight (MW) aliphatic and protein substances were preferentially removed by the H/A stage, while the A/O stage more completely eliminated hydrophobic aromatic substances of a lower MW. However, humus-like substances increased in both scenarios. With respect to the two AOPs, OO preferentially removed substances with a lower MW, and the HOA fraction converting to hydrophilic humus-like substances followed with more derived by-products. Comparing to OO, EO performed better on the removal of aromatic compounds, especially the humus-like substances (polycyclic aromatic and CRAM-like substances) in HOA fraction, therefore significantly improved the biodegradability of the effluent. The results indicate that EO has a better selectivity for humus-like substances and is suitable for the treatment of refractory DOM containing chloride. [ABSTRACT FROM AUTHOR]