Technological-economic optimization of enzymatic hydrolysis used for the processing of chrome-tanned leather waste

Abstract

Chrome-tanned solid waste generated in large quantities by the leather industry poses a major threat not only to the environment, but also to living organisms including humans because of its potential toxicity. The crucial issue determining viable industrial processing and valorisation of this waste is the process economy. In this work, a mathematical model that enables technological simulation of complete process for chrome shavings utilization by alkali-enzymatic hydrolysis was developed and incorporated into an economic optimization model. The model includes experimentally verified quantitative description of the dependence of reaction rate on enzyme concentration, an important factor which so far has not been addressed in this context. The simulation calculation showed that the enzyme optimal concentration usually lies in a relatively narrow area between 0.2 and 0.4 % wt. of the feedstock dry matter at standard reaction conditions. Such optimization can save considerable portion of the processing costs – as much as 43 % at given calculation parameters – and improve the plant capacity and annual profit leading to the reduction of payback period from initial 4.7 years to final 1.5 year. The results obtained through this engineering approach are valuable not only for the processing plant operation, but also for the overall process design including the design of process control algorithms, and therefore are applicable and adjustable for a wide range of cases, from individual waste producers to centralized leather waste processing. © 2021 Institution of Chemical Engineers