Content: It is acknowledged that conventional chrome tanning in leather processing discharges significant amounts of chromium, dissolved solids and chlorides. The recycling technology is one of the effective solutions to reduce the environmental impact of chrome tanning waste water at source. In this work, a novel closed recycling technology of chrome tanning wastewater was applied in the tanning process of the goat skins at a pilot scale level. The properties of chrome tanning liquors obtained by the recycling technology and the resultant crust were analyzed. The results show that this close recycling process works well. The contents of Cr2O3, total organic carbon, ammonia nitrogen and chloride ion in the waste water tend to accumulate with the increase of recycling times, and finally reach a balance after 5 times of recycling. The obtained leather sample is full, soft and having a shrinkage temperature comparable to that of conventional chrome tanned leather. SEM images indicate that the resulting leather samples by this recycling technology show fine and clean grain and well-dispersed fibrils. TG and DSC results show that the thermal stability of wet blue leathers tanned by the circular process are similar to those tanned by conventional chrome tanning process. Compared with conventional chrome tanning technology, water, salt and chrome tanning agent are saved in this process, and the zero emission of chrome tanning wastewater is realized. The cleaner production technology exhibits promising application prospect for its economic and environmental benefits. Take-Away: 1. A novel closed recycling technology of chrome tanning wastewater was applied in the tanning process of the goat skins at a pilot scale level. 2. The chrome tanning liquors obtained by the recycling technology and the resultant crust were analyzed. 3. Water, Sodium chloride and chrome tanning agent are saved by the closed recycling technology, and the zero emission of chrome tanning wastewater is realized.

Content: As it is known in the tanning sector, in recent times, the so-called wet-white and/or metal-free concepts have had a certain increase. For example, in the automotive sector, the wet-white tanning system, carried out with glutaraldehyde and tannins, has been widely diffused. In fact, car manufacturers offer, for interior furnishings, leather not only for high-end cars but increasingly also in the lower segments. The components on which the leather upholstery is applied are mainly steering wheel, seats, dashboard and panels. Therefore, the use of leather also in this context must be able to meet both the aesthetic/performance criteria and the environmental ones; environmental criteria should also consider the air quality of the interior of a motor vehicle. In practice, the interior furniture consisting of finished leather must be able to release a few volatile substances and, at the same time, provide a typical smell of leather. Considering, therefore, the diffusion of alternative chrome tanning systems for the different uses, in this work, wet-white (glutaraldehyde and tannins) will be investigated, both from the point of view of the performance characteristics and from the ecotoxicological ones. and leathers deriving from the latest generation of metal-free tanning. For the characterization of Volatile Organic Compounds (VOC) the GC-MS will be used coupled with the 'Purge and Trap' technique with the aim of obtaining information on the new substances used in the wetwhite / metal free production process and then avoiding undesired effects during use (eg bad smell, SVHC substances, etc.) Take-Away: metal-free automotive VOC

Content: Surfactants are used as auxiliaries in every wet processing process of leather production and discharged into wastewater, which would cause potential ecological risks. In this paper, fresh luminescent bacillus liquids were employed to evaluate the ecological toxicity of six surfactants, including anionic, cationic and non-ionic surfactants, and mixture of two typical ionic and nonionic surfactants after a 15-min exposure period. Non-ionic surfactants AEO and Tween80 showed slight light inhibition ie.10-35% to luminescent bacteria. The toxicity of anionic surfactants with polar sulfonic group was: penetrant T(EC50=406.81mg/L) ＞SDBS(EC50=573.37mg/L). The toxicity of cationic surfactants was: DTAB（EC50=10.68mg/L）＞SKC （EC50=73.96mg/L）. The addition of nonionic surfactants reduced the toxicity of ionic surfactants. 1-1 mixture of SKC and AEO: EC50=80.17mg/L, 1-1 mixture of SDBS and AEO: EC50=624.34mg/L. These results provided ecological parameters for the selection of surfactants in the process of ecological leather production. Take-Away: 1. The toxicity measurement by luminescent bacteria, which is simple and convenient, was used to evaluate the toxicity of surfactants, and the reproducibility was improved in our study. 2. The toxicities of six different surfactants was evaluated by EC50 which provided ecological parameters for the selection of surfactants in the process of ecological leather production.

Content: Chamois leathers are basically oil tanned leathers, usually requires 10 to 15 days to process from raw skins. In chamois making, air oxidation plays a major role, free radicals initiate the oxidation process in oil, which oxidizes the double bond of the fatty acid and then the oxidized oil interacts with collagen to stabilize the skin by coating the fibers (Fig 1). In the present study an attempt has been made to reduce the time for chamois leather processing. A common oxidizing agent (Benzoyl peroxide (BPO) was utilized to enhance the oxidation of oil and reduce the time duration. It has been observed that the oxidation of oil in the presence of benzoyl peroxide has significantly reduced the duration of process from 15 to 4 days. Strength properties such as tensile, percentage elongation and organoleptic properties were found to be on par with control leather. The water absorption values of the experimental leathers improved by 1-26 %, compared with control leather. Microscopic analysis (SEM) was employed to study the fiber alignment of the chamois leathers. Take-Away: 1. Time reduction in chamois leather processing 2. Inexpensive and common oxidising agents were employed 3.Improved water absorption of chamois leather

Content: Unhairing process is usually considered as the most polluted process in leather production. The conventional method of unhairing which using lime and sodium sulfide produces a large amount of sludge and waste water. In order to reduce pollution, we developed a novel unhairing enzyme and named as WB600-KerT, which possesses low collagen-degrading ability and high keratin-degrading ability in previous study. The objective of this study is to study the properties and effect of WB600-Kert to replace traditional chemicals in unhairing process. It found that the protease of WB600-Kert exhibited optimum keratin activity at 40°C. Compared with commercial unhairing enzyme and conventionally sodium sulfide methods, WB600 exhibited better unhairing effect and higher efficiency. The results indicated that goat skin unhaired with WB600 achieve enough softness, shrinkage temperature and tear strength as well as conventionally sodium sulfide methods Furthermore, if adding a small amount of sodium sulfide, the unhairing process could be accelerated while the unhairing effect was further improved. Generally speaking, this enzyme showed good application potential in unhairing process and was effective for reducing pollution which may promote the development of leather industry. Take-Away: 1. The protease of WB600-KerT was firstly applied to hair removal. 2. The addition of little sodium sulfide in WB600-KerT could enhance unhairing efficiency.

Content: This paper briefly introduced the process of leather manufacture and the potential pollution sources of soil in tannery sites. Pollutants are mainly derived from the use of a large number of various chemicals and organic matter decomposed by raw skin. The characteristics of typical pollutants in tannery sites soil were summarized, including tannery site soil pH, organic and inorganic compounds, and heavy metals, etc., especially the status of chromium contamination were reviewed. The pH of soil in the tanning workshop (6.65-7.8) is generally lower than tannery sludge dumping site (7.94-8.40). The main organic pollutants contained in the tannery site soil include nitrogen compound, grease, petroleum hydrocarbon. In tannery sludge dumping site soil, the content of nitrogen compound (10cm depth) is 28400 mg/kg, which is similar to tannery sludge. The content of petroleum hydrocarbon is 5-700 mg/kg, which partially exceed the limits of China agricultural land quality standard(<500 mg/kg). In tanning workshop soil, the content of grease is 220-62000 mg/kg. The main inorganic pollutants contained in the tannery site soil include sulfide, high concentration of salt, lime. The high salt content of tannery sludge (99000 mg/kg) leads to high salt content in soil (5500-17500 mg/kg). Total hardness (>450mg/L), total dissolved solids (>1000mg/L), sulfate ions (>250mg/L), nitrite nitrogen (>0.02mg/L) partially exceed the limits of China groundwater quality standard, which are found in groundwater below the tannery site. Heavy metal pollutants in the tannery sites soil have many characteristics and large differences in content, due to the different tanning processes. Among them, chromium (Cr) is the most used heavy metal and the highest content of pollutants. Cr content in tanning process wastewater, dyeing process wastewater and chromiumcontaining sludge are about 2000-3000 mg/L, 30-40 mg/L and 8500-25800 mg/kg, respectively. Total Cr content in the partial tannery sites soil are higher than 800 mg/kg, which exceed the limits of China agricultural land quality standard(<150mg/kg). Surprisingly, Cr(VI) appears in tannery sites soil and the contents are partly higher than 40 mg/kg, which exceed the limits of China development land quality standard(<3.0mg/kg). Furthermore, the more effort needs to be directed toward the chemistry of chromium-organic complex pollutants, and an understanding of the speciation of Cr in highly organics contaminated tannery site soil is essential for the development of suitable remediation strategies for contaminated soil. Take-Away: 1. The pH of soil in the tanning workshop (6.65-7.8) is generally lower than tannery sludge dumping site(7.94-8.40). 2. Total Cr content in the partial tannery sites soil are higher than 800 mg/kg, which exceed the limits of China agricultural land quality standard(<150mg/kg). 3. Cr(VI) appears in tannery sites soil and the contents are partly higher than 40 mg/kg, which exceed the limits of China development land quality standard(<3.0mg/kg).

Content: Microwave is a fast, efficient and energy-saving thermal resource, hence an attempt has been made for applying this technology in the combination tanning using titanium (III) and tannin extracts. In this work, the microwave effects on the complex reaction of Ti (III) with tannin extracts and leather products properties were investigated. The precipitation condition was used to characterize the complexation degree between Ti (III) and tannin extracts. And the shrinkage temperature, tear strength, SEM, DSC, TG, FT-IR, and histological structure were used to characterize the changes in the physical and chemical properties of the combined tanned leather. Take-Away: The results showed that microwave irradiation can accelerate the complex reaction of Ti (III) with tannin extracts. At the room temperature, the mixture of tannin and titanous sulphate kept stable at pH 3-4. In addition, microwave could increase the shrinkage temperature, tear strength, thermal stability, and fibrage of Ti (III)-tannin tanned leather, and it would not change the combination mode of the skins with tanning agents as well as the hierarchical structure of collagen. Therefore, these results inferred that microwave could promote the reaction between Ti (III) and tannins and the combination of tannins with collagen, which may provide a theoretical basis for the application of microwave in Ti (III)-tannin combination tanning technology.

Content: Microwave was used as a thermal source to extract collagen acid from the cattle hide in the present work. The effects of microwave on collagen extraction yields were studied under different microwave temperatures, time and hide-liquid ratio. The optimal extraction process was obtained by an orthogonal experiment, and the composition, structure and properties of the extracted collagen were characterized by amino acid analysis, SDS-PAGE, FTIR, UV-Vis, CD, FL, and VP-DSC. The results showed that the extraction rate of collagen was positively correlated with temperature, time and hide-liquid ratio. Under the condition of 35 °C, 6 h and 1:30 of solid-liquid ratio, the extraction proportion of collagen extracted under microwave was the highest, reaching to 13.40 %. The extracted collagen was identified as type I collagen by Amino acid analysis, and the graphic pattern of SDS-PAGE, FTIR and UV-Vis showed that the extracted collagen was similar to the standard type I collagen. Also, the results suggest that the triple helical structure exists still in the extracted collagen. The transition from triple helix to random coil of the extracted collagen was 41 ℃. These results provide a scientific basis for microwave technology for the extraction of collagen. Take-Away: The results showed that the extraction rate of collagen was positively correlated with temperature, time and hide-liquid ratio. Under the condition of 35 °C, 6 h and 1:30 of solid-liquid ratio, the extraction proportion of collagen extracted under microwave was the highest, reaching to 13.40 %. The extracted collagen was identified as type I collagen by Amino acid analysis, and the graphic pattern of SDS-PAGE, FTIR and UV-Vis showed that the extracted collagen was similar to the standard type I collagen. Also, the results suggest that the triple helical structure exists still in the extracted collagen. The transition from triple helix to random coil of the extracted collagen was 41 ℃. These results provide a scientific basis for microwave technology for the extraction of collagen.

Content: In leather making processes, the thermal and non-thermal effect of microwave, especially non-thermal effect, strengthen the combination between collagen and chemicals. Although tanning under microwave makes the leather have better thermal stability, the tanning process and leather properties have not been studied in detail. For illustrating the influence of microwave on chrome tanning process, pickled skin was tanned for 6h as penetration procedure and then basified for another 4h as fixation procedure. The tanning under microwave heating (MW) was experimental sample and under water bath heating was control. UVVis, ICP-OES and pH meter were used to measure the changes of tanning effluent during tanning, and Shrinkage temperature meter, DSC, TG, FT-IR, SEM, XRD and XPS were applied to determine the differences between MW and WB in aspect of leather property and structure. The results indicated microwave accelerated chrome tanning agent penetration and had better promotion effect on chromium complex hydrolysis and olation. The leather tanned with microwave assisting had special effect on improve tanning effect which led better thermal stability and resistance of leather, but the collagen structure, including triple helix structure, stayed as WB and the combination mechanism between collagen and chromium was also same with conventional. In sum, microwave had positive effect on accelerating tanning rate and resulting in better leather without any negative effect on leather structure. Therefore, microwave would be a potential for achieving clean and sustainable chrome tanning by making tanning much faster and more efficiency. Take-Away: Microwave promotes chrome tanning agent penetration and combination Microwave has positive effect on tanning effect further as the leather tanned by microwave assisting has higher thermal stability. Although microwave promotes chrome tanning process, the collagen structure and tanning mechanism remained as normal.

Content: Pre-treatments are widely used during tanning processes as to improve the performance of the main tannage. Synchrotron small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) were used to study four common types of pre-treatments, viz. monodentate complexing agent (sodium formate, SF), chelating agent (disodium phthalate, DSP), covalent cross-linker (glutaraldehyde, GA) and nanoclay (sodium montmorillonite, MMT) about their effects on chromium-collagen cross-linking reaction during tanning. Based on the results, the performance of chromium-collagen cross-linking with and without pre-treatments was presented considering five aspects: cross-linking, the level of hydration, hydrothermal stability, uniformity through leather cross-section and the uptake of chrome. Comparing to the original ThruBlu chrome tanning, at the same chrome offers, leather pre-treated using SF, DSP and MMT showed improved hydrothermal stability, uniformity and the level of hydration, while GA showed decreased hydration. All of the pre-treatments reduce surface fixation by decreasing the reactivity of chromium with collagen. Changes in the reaction performance can influence the properties of the leather products as well as the efficiency of the leather manufacturing processes. Insights into the structural changes of collagen during tanning with varied reaction conditions can guide the design of novel, benign tanning processes to reduce environmental impact. Take-Away: 1. Uniformity of the hydrothermal stability through leather cross-section were improved by all of the studied pre-treatments. 2. Reactivity of chromium to cross-link with collagen was reduced as a result of the complexing, covalent cross-linking, or preferential adsorption. 3. Complexing agents and nanoclay pre-treatments tend to retain collagen bound water, while covalent cross-linker causing decrease in the level of hydration of collagen.