Recycling of leather industrial sludge through vermitechnology for a cleaner environment—A review

Abstract In the last few decades, an enormous number of industrial sectors have been developed particularly, leather industries. The leather industries consume a large quantity of freshwater and various chemical substances during the leather making process and eject different solid waste materials, hides, buffing dust materials, and wastewater sludge. Besides, leather industrial wastes contain a significant amount of hazardous substances like heavy metals (e.g. cadmium, chromium, lead, nickel, and cobalt), aluminum sulfate, and magnesium oxide. Insecure disposal of wastewater sludge creates serious environmental problems in soil and groundwater. This situation warrants the easiest way to rationalize such conflicts through urgent environment-friendly disposal technologies. The main objective of the present review is to highlight the remediation of leather industry wastewater sludge through eco-friendly vermiremediation employing earthworms. Additionally, earthworms and microorganisms can eliminate toxic chemical substances. The present review also addresses earthworm species employed in a polluted environment, factors (i.e., pH, humidity, and temperature) and amendment materials essential for the stimulation of earthworm activity. In the hope of moving past this state, the earthworms are used for in-situ and ex-situ remediation of leather waste materials. The present review points to the real significances of vermi-treated leather wastes as plant growth-promoting medium that is useful in the field of sustainable agriculture. Furthermore, the fastidiously gathered evidence proves that vermi-treatment would be a potential alternative strategy to our surroundings with improved agroecosystems.