Studies in green hydrolysis of waste wool

A large amount of raw wool, practically unserviceable for textile uses, is generated in Europe from sheep shearing and butchery; this is a byproduct that is either dumped, burned or sent to landfill. Following the European Commission regulations on animal by-product control, unserviceable raw wool is classified as a category 3 special waste materials, and its collection, storage, transport, treatment, use, and disposal is subject to European Union regulations because of a potential risk source to human and animal health. Raw wool has a noticeable chemical potential to conceive and generate a broad category of products, spreading from protein-based scaffold tissues to fertilizers. Considering all these points, raw wool has potential to create a circular economy rather than just wasted as an unserviceable material. In general, raw wool finds its application in insulation panels, composites, carpets, etc., but needs a complete pre-treatment before use. The problems begin with the use of raw wool is that; it cannot be used as a fertilizer without any previous pretreatment such as washing because of the potential risk of infection and its slow degradation process in the soil environment. For these reasons, fertilization with untreated greasy wool is forbidden by the EU legislation, which strictly provides guidelines for raw wool storage, transportation, and disposal. These costs heavily weigh on the profit of sheep farmers. The primary objective of this study is to develop the cost-effective, sustainable process to use raw wool prior to any pretreatment. This study aims at • Converting waste wool into nitrogen fertilizers at a commercial scale for grassland management and cultivation purposes. • Development of potential novel applications of hydrolyzed wool In order to achieve the desired aim of fertilizer, the chemical breakdown of wool needs to be done using sustainable way, i.e., chemical-free process. In general, hydrolysis process is performed using acids, bases, and enzymes. The literature survey on existing hydrolysis processes, their limitations, industrial scale-up viability, sustainability, cost-effectiveness, etc., lead towards the process where chemical transformation is based on a green economically sustainable hydrolysis treatment using only green solvent superheated water. The other the advantage of green hydrolysis is that it sterilizes the wool at high temperature, which indirectly overcomes the problem of pretreatment prior to use and infection problem in the application phase.In order to understand the extent of degradation and industrial viability of the superheated water hydrolysis process with the aim of fertilizer; the development the process implies two steps: the first one at laboratory scale (batch process) and the second at semi-industrial scale (continuous process). A set of experiments on batch scale reactors was performed to monitor process parameters and extent a degree of hydrolysis on raw wool; to establish the ground for designing and construction of semi-industrial scale reactor. The green hydrolysis process optimization was carried out in batch and semi-industrial scale reactors by varying parameters such as temperature, wool density, material to liquor ratio, time, depending on the extent of degradation of the final hydrolyzed product. Controlled treatment with superheated water converts wool keratin into simpler compounds. At the end of the process, it is possible to obtain a hydrolyzed product in either solid or liquid phase depending on the extent of hydrolysis parameters implemented. The presence of amino acids, primary nutrients, and micronutrients in wool hydrolyzates, along with a concentration of heavy metals below the standard limit, confirm the possibility of using wool hydrolyzates as nitrogen based ecologically sound fertilizer. On the way to find the possible application of keratin hydrolyzate other than fertilizer, which overcomes the environmental problem of wool waste and byproducts were found to be a foaming agent for dyeing. The foam-forming the behavior of the keratin hydrolyzate along with its application in dyeing was studied to develop sustainable and green dyeing process. The surface tension, foam stability, blow ratio, bubble size of the keratin hydrolyzate in aqueous solutions with and without dyeing auxiliaries were determined. The dyeing influential parameter such as wet pickup was studied to identify their effect on dye fixation and color strength. The foam dyeing was compared with conventional cold-pad batch and pad-steam processes for cotton and wool, respectively. The combination of green hydrolysis and the biodegradable keratin hydrolyzate resulted in the sustainable green dyeing process