Approach towards zero discharge tanning: role of concentration on the development of eco-friendly liming–reliming processes

Beam house processes¹ in leather processing are known for their uncleanness. More than 60% of the total pollution is emerging from the liming–reliming processes. The use of lime and sodium sulphide is purely empirical without quantification. Lime has a potential to drive swelling in a gradual manner due to its low solubility; however, the use of lime is currently creating a lot of environmental concern. Huge amounts of lime sludge and total solids formation are the main drawbacks of lime. Sulphide plays a detrimental role in effluent treatment plants. This is mainly due to the application of lime, sulphide, water and other chemicals without any rationalization. An approach has been made to apply the beam-house chemicals with optimal requirement. This is based on the fact that swelling requires only 20 to 40% water (based on raw skin weight before soaking) for conventional opening up. This would, in principle, make possible the use of only one tenth of the chemicals conventionally used in liming–reliming processes maintaining the same concentration gradient. The process employs 40% water, 0.35% sodium sulphide and 1% lime for liming and 40% water and 1% lime for reliming, with conventional process time in a drum. Commercial post-reliming processes and operations were adopted. A control experiment was run parallel using conventional liming–reliming processes. It has been found that the dehairing is complete and the extent of opening up of fibre bundles is comparable to that of the control. This has been substantiated through scanning electron microscopic, stratigraphic chrome distribution analysis and softness measurements. Performance of the leathers is shown to be on par with conventionally opened up leathers through physical and hand evaluation. Especially, softness of the leathers is numerically proven to be comparable with that of control. The process also enjoys reduction in chemical oxygen demand and total solids load on environment by 85 and 12%, respectively compared to the conventional process. The total dry sludge from the liming–reliming processes is brought down from 152 to 6 kg for processing 1 ton of raw skins, which has been demonstrated for the first time.     

Cleaner tanning practices for tannery pollution abatement: Role of enzymes in eco-friendly vegetable tanning

Concern about pollution related problems in the global scenario are persuading all the processing industries to adopt cleaner manufacturing practices. Thus, the leather industry is also under pressure to look for effective alternative tanning materials for chromium. Natural products like vegetable tannins are regaining importance. However, there are limitations in the use of vegetable tanning materials because of its high organic load in the effluent, which are difficult to degrade leading to high chemical oxygen demand (COD). Moreover, conventional vegetable tanning process requires partial pickling that involves the use of sodium chloride, to suppress osmotic swelling. This results in very high amount of total dissolved solid (TDS) content in wastewaters. In this investigation, an attempt has been made to design an eco-friendly vegetable tanning process combining pickle-free tanning and application of proteolytic enzymes to improve the exhaustion of vegetable tannins. Such an approach has resulted in more than 95% tannin exhaustion in the case of the experimental process, an increase of 10% compared with the conventional vegetable tanning process. The tanned leathers showed slight improvement in hydrothermal stability. Physical and tactile evaluation of experimental leathers has been better than conventionally tanned leathers. Surface colour values illustrated negligible variation in colour and shade between control and experimental leathers. The resultant leather showed opened up, split compact fibre structure that has been well coated, indicating that the enzyme assisted tanning process did not bring about any major change or destruction on the fibre structure of the leathers. The optimized system has been field tested in a commercial tannery. The results showed that the enzyme assisted tanning process is efficient in terms of improved quality of leather and also led to reduction in total solids (TS), chlorides and COD loads. The enzyme assisted tanning system presented appears to be a viable option for combating pollution arising from the conventional vegetable tanning system.     

Recouping the wastewater: a way forward for cleaner leather processing

Leather processing employs copious amounts of water. This leads to the generation of enormous amounts of liquid effluent. The high effluent volume requires huge investments for effluent treatment plants in order to meet the required specification for the discharge of liquid effluents to various water bodies. Increasingly therefore, water use minimization in leather processing assumes greater significance due to increased treatment costs. End-of-pipe treatment methods alone do not meet the requirements and hence, in-plant control measures are gaining importance. The new era of cleaner technology has begun in leather processing. Pre-tanning and tanning operations contribute about 57% of the water consumption in leather processing and the washings about 35%. The proper adoption of integrated cleaner technologies provides a viable solution to the conservation of water in leather processing. This paper presents an integrated approach for water use minimization through recycling and optimization in leather processing. The integrated approach provides considerable reduction in the use of process water.     

An improved product-process for cleaner chrome tanning in leather processing

Severe restrictions imposed by the pollution control authorities on the disposal of chromium, total dissolved solids and chlorides in tannery effluents have forced the tanners to look for low-waste, high exhaust chrome tanning salts. An improved chrome syntan with more than 90% uptake of chrome has been developed. The new product serves both as tanning and retanning agent and can be applied directly to delimed pelts thus eliminating the conventional pickling stage in the leather processing. This modified process helps to reduce the chemical oxygen demand (COD), total dissolved solids (TDS) and chlorides in the spent tan liquor by 51, 81 and 99%, respectively. The product offers full, soft leathers having shrinkage temperature comparable to conventional chrome tanned skins. Since the developed product is highly reactive, it saves time and reduces the water requirement when compared to the conventional chrome tanning method. Thus the novel product/process developed not only has advantages in reducing pollution loads but also seems to be techno-economically viable.     

New findings on the generation of waste and emissions, and a modified cleaner production assessment approach-illustrated by leather production

New findings on the causes of waste and emissions, which were obtained from analysing numerous material streams in various sectors of industry, are presented in this article. It describes the implications of these findings for the vision of clean production, for formulating environmental policy concerning cleaner production targets, for the opportunities to assess to what extent the cleaner production targets have been met, and for the cleaner production assessment. A modified cleaner production assessment approach is presented, and illustrated using leather production as an example. The consequent implications for the diffusion of cleaner production are discussed.     

清洁生产技术在制革工业生产中的应用

分析了我国制革工业的污染现状 ,提出了制革工业推行清洁生产的必要性及实现清洁生产的途径。通过生产性试验研究出羊皮制革工业的清洁生产技术 ,详细分析了羊皮制革工业在生产过程中采用清洁生产技术的污染物削减情况。     

Power ultrasound in fatliquor preparation based on vegetable oil for leather application

In recent years, power ultrasound has taken a significant place in chemical and physical activities of the process industries as an effective and non-polluting method of activation. Oil in water emulsions known as fatliquors are used for the lubrication of tanned leather fibres to get softness and also to improve the strength properties. In the present study, ultrasound has been used as a tool for the preparation of fatliquor emulsion for application in leather fatliquoring process. An emulsion is a fine dispersion of one liquid in another liquid. Sulphation is one of the common methods followed to prepare fatliquor emulsion where sulphuric acid is used. In the conventional process, emulsifying agent is also added to increase the stability of oil in water emulsions. The emulsifying agents generally used are chemicals or metal soaps. The potential use of ultrasound in the preparation of stable oil in water emulsions dispensing with sulphation process and with the minimum use of emulsifying agent has been studied and reported in this paper. This process enjoys the benefit of less pollution load in the form of chemical entities. The studies included the effect of process parameters such as ultrasonic output power and amount of oil used. Fatliquor emulsion prepared using ultrasound has been applied in leather fatliquoring process and the strength properties of the leathers were assessed. Emulsion particle size, which is another important parameter for diffusion through leather, has been measured using Laser Diffraction Technique. The stability of the ultrasonically prepared fatliquor emulsion has been found to be good. The results indicate that ultrasound could be effectively utilized in the preparation of non-ionic fatliquor emulsion eliminating sulphuric acid and impart required properties in leather.     

Cleaner techniques for the preservation of raw goat skins

As the popular salt curing system is considered detrimental to the environment, a search for safer alternative systems has been a top priority research in the area of leather science. The ill-effects of sodium chloride on the environment and eco-system need no emphasis. Hence there is an urgent need for the development and adoption of a viable cleaner curing system. In the present study, a short-term preservation technique using silica gel has been studied and standardized. The possibility of using silica gel in place of salt as a curing agent alone and in combination with a suitable biocide was studied at an ambient temperature of 31°C. The preservation efficacy of the methods was assessed by various parameters such as moisture content, total extractable nitrogen, and bacterial count. The layer wise moisture content was determined using a NMR micro-imaging technique. The effect of the new curing methods on the fibre structure of treated skins was assessed using scanning electron microscopic (SEM) studies. The pollution load generated in the processing of the skins treated using the new techniques is compared with that for salt cured stock. The results show that the cleaner preservation techniques developed were as efficient as salt curing for the preservation of skins. The new curing methods did not pose any problem either in soaking or in the leather manufacturing processes. The methods developed are found to be effective and viable options for combatting the pollution problems of chloride and total dissolved solids (TDS).     

Ultrasound-accelerated enzymatic hydrolysis of solid leather waste

The leather industry is a heavy pollution industry and looking for clean technology. The utilization of enzyme and ultrasound in the industry are potential eco-friendly technologies.Enzymes can degrade the untanned solid leather waste. According to our investigation, ultrasound (40 kHz, 0.64 W/cm²) has little effect on the activity of one alkaline protease from Bacillus licheniformis. It is the first time to use ultrasound to accelerate the enzymatic hydrolysis of the untanned solid leather waste. With the application of ultrasound, the value of k_A for the enzymatic hydrolysis of the untanned solid leather waste increases 18% and K_M is almost unchanged, compared with that obtained without ultrasound. Ultrasound improves the ultimate conversion ratio from 57.6% to 84.1%. The reason is that ultrasound can facilitate the protease through the pores of skin and impair the integrity of collagen. Amino acid analysis indicated that ultrasound can promote the breakdown of helical regions of collagen which are difficult to attack by proteases.In view of environment protection, the use of enzyme and ultrasound in combination is a promising clean technology for the disposal of the untanned solid leather waste.     

A chemo-enzymatic pathway leads towards zero discharge tanning

Leather processing has been an important industrial activity, which has gained significant economic relevance in India. The recent practices of leather manufacture cause difficulties with regard to environmental challenges. The conventional method for making the skins ready for tanning and the tanning by itself employs a wide variety of chemicals which result in an increase in chemical oxygen demand (COD), total dissolved solids (TDS), chlorides, sulfates and chromium in the tannery effluent. In this study, an integrated chemo-enzymatic methodology has been explored which would minimize or to some extent eradicate the unsafe chemicals involved in the process to provide a clean environment. The sequence involves an enzymatic dehairing, NaOH based fibre opening and a pickle-less chrome tanning. The modified process results in decrease in COD and TS (total solids) loads by 67 and 78%, respectively, as compared with control process. The process explored appears to be economically viable.     

A cleaner production method for the synthesis of bronopol – A bactericide that is useful in leather making

In leather industry environmental concern has been growing since 1980s. Increasing levels of pollutant emissions have reached saturation point in spite of the conventional technology that highly industrial countries have adopted to keep them under control. This has started a technology revolution in several industries. These critical levels of pollution may have been caused by high industrial density, by high population density or by the use of old polluting technology. This situation has boosted emerging green technology which has begun to take up a larger portion of research work in the supply and raw materials in industries. Together with consumers growing awareness of the environment, this new technology has ended up affecting the consumer good industry. In leather industry due to the sector's bad public image regarding pollution more emphasis has been given to clean technologies and waste reduction. At this time nearly every part of the tanning process has several cleaner or environmentally friendlier alternatives. In leather industry to prevent damage to the hide and skin, bactericide is added during soaking process to kill the growth of microorganism. Bronopol is used as a bactericide. The active ingredient of bronopol is 2-bromo-2-nitropropane-1,3-diol. Here we have reported simple and cleaner technology of the bronopol by using nontoxic and non-hazardous raw materials and belongs to the modern concept of environmentally friendly low waste or nonwaste technology. Bronopol was characterized by IR and Mass spectral data.     

Application of power ultrasound in leather processing: an eco-friendly approach

The paper analyses and reviews in detail the use of ultrasound as a tool to improve the cleanliness of leather production for each stage of leather processing, showing that ultrasound has the added advantages of improving the process efficiency, reducing the process time and improving the quality of leather produced. The rate of diffusion of chemicals such as dyes through the pores of the leather matrix can be enhanced by the use of power ultrasound. Thus the optimum amount of chemicals required can be employed to improve the % exhaustion of chemicals, thereby minimising the significant amount of unspent chemicals in the effluent and reducing pollution load to a large extent. Dyeing experiments carried out in the presence of ultrasound (150 W and 33 kHz) give an increase of about 40% in dye exhaustion and a decrease in dyeing time by about 55% compared with the process in the absence of ultrasound under stationary conditions. Compared with conventional drumming conditions, ultrasound increases dye exhaustion by about 28% and reduces dyeing time by 25%. Ultrasound can also function as a physical activator and reduce the use of conventional chemicals in some of the processing stages, such as soaking for cleaning the raw skin/hide, liming for loosening hair and degreasing for removing natural fat. Therefore, ultrasound can be employed effectively in leather processing to enjoy multifaceted benefits.     

Efficient synthesis of 2-(thiocyanomethylthio)benzothiazole

In the leather industry phenolic-based fungicides have been in use until recently. As a result of legislation limiting the content of pentachlorophenol (PCP) in leather, non-chlorophenolics based on 2-(thiocyanomethylthio)benzothiazole (TCMTB) have become more widely used in the leather industry for controlling the growth of fungi and sulphate-reducing bacteria. This paper reports a clean and simple method of synthesis of TCMTB, which is characterized by conventional methods, IR, ¹H NMR and mass spectral data.     

清洁生产审核在果汁企业的应用研究

中国是全球最大的浓缩苹果汁生产和出口国,年产量和出口量均占全球总量的60%左右,均位居世界第一。中国浓缩果汁行业高速发展的同时,严峻的行业环境问题严重限制了中国浓缩果汁行业的进一步发展[1]。企业实施清洁生产审核是企业实现清洁生产最有效的手段.实践表明,通过实施清洁生产审核活动,企业提高了资源能源利用效率,降低了环境污染,取得了经济和环境的同步发展,为浓缩果汁企业今后的清洁生产审核积累了经验。     

清洁生产推进机制研究

本文重点研究了清洁生产推进机制,对清洁生产运行机制、技术机制、管理机制、政策机制进行研究和分析,对清洁生产的产生理论和运行管理进行分析。结论是,政策机制的关键是成功地实施技术机制和内部管理机制,在中国清洁生产的实施应该主导的政府执法机制,辅之以必要的经济激励和支持机制应激机制。     

Convenient synthesis of methylene bisthiocyanate as microbiocide

Methylene bisthiocyanate (MBT) is used as a biocide in the leather making industry. Commercial biocidal formulations containing a blend of 10% MBT (Methylene bisthiocyanate) and 10% TCMTB (2-Thiocyanomethylthio)-benzothiazole are available. This blend of active ingredients combine the rapid antimicrobial action of MBT with the fungicidal properties of TCMTB. Such biocides are suitable for use over a wide range of tannery applications including the soaking and pickling stages. This paper reports on a simple and cleaner technology of the synthesis of MBT by using non toxic and non hazardous raw materials and belongs to the modern concept of environmentally friendly low wastes or non wastes technology (LWNWT). From the workers health and safety point of view raw materials such as sodium thiocyanate, water, phase transfer catalyst (Benzyl trithylammonium chloride) and halogenating agent (Bromochloromethane, ethylene bromide, methylene chloride) are used which are non hazardous and non toxic. MBT is characterized by conventional methods, IR ¹HNMR and mass spectral data.     

2006~2009年工业COD和SO2减排分解研究

通过运用分解模型,将工业COD和工业SO2减排分解为规模效应、结构效应、清洁技术效应和污染治理效应,并根据模型测算了2006~2009年各种效应的大小.结果表明:规模效应值为58.68%,即经济规模扩张增加工业COD和工业SO2排放,结构效应、清洁技术效应和污染治理效应效应值分别为-0.63%、-49.34%和-29.79%,即促进工业COD和工业SO2减排;分行业来看,农副食品加工业和非金属矿物制品业发展迅速,需要严格控制其发展速度;化学纤维制造业的COD产生强度和电力、热力的生产和供应业、有色金属矿采选业、石油加工、炼焦及核燃料加工业的SO2产生强度升高,需要加强清洁生产控制;燃气生产和供应业、皮革毛皮羽毛(绒)及其制品业的COD去除率和非金属矿采选业、非金属矿物制品业和燃气生产和供应业的SO2去除率降低,需要加强污染治理控制.     

某制革企业污染控制与环境管理中若干问题研究

通过对数家制革企业开展调查分析,探讨了制革企业在含铬、含硫废水分流处理和各生产环节臭气防治方面存在的若干技术与管理问题.首先,含铬废水和含硫废水收集与管理不规范统一致使后续废水预处理及生化处理受到影响;部分企业忽略了原皮存放及转运、皮革水场加工车间、污水处理设施等臭气产生环节的细节控制.最后提出针对性的对策与措施建议,包括统一规范含铬废水和含硫废水的收集与预处理范围,加强原皮仓库、水场和污水处理系统的恶臭全过程控制.     

清洁生产审核在酿造企业的应用

清洁生产审核是实施清洁生产的重要前提,也是企业实现清洁生产最成熟最有效的手段。在对桌酿造企业进行清洁生产审核中,针对行业特点,结合企业自身情况,提出并实施无／低费方案17项,中／高费方案3项。可节电1058kwh／a,节水2．26万t／a,减少废水排放2．26万t／a,减少固废（损失原料）排放45t／a,制曲室空气质量明显改善,产生效益39．4652万元／a。该企业在实现了降低单住产品（食醋）水耗和酱油原料损失率的同时,也实现了经济、环境和社会效益的统一,为酿造企业今后的清洁生产审核积累了经验。     

医药厂环境影响评价的清洁生产分析

介绍了清洁生产的涵义和评价内容,探讨并建立了医药厂环境影响评价清洁生产分析的指标体系、指标权值和评价方法,以海南某医药厂为分析对象,对该厂环境影响评价进行了有效而全面的清洁生产分析,提出了医药厂环境影响评价清洁生产分析的建议,是医药厂环境影响评价清洁生产分析的一次新尝试.