Co-composting of hair waste from the tanning industry with de-inking and municipal wastewater sludges

Abstract

Production of waste hair in the leather manufacturing industry is increasing every year due to the adoption of hair-save unhairing techniques, leaving the tanners with the problem of coping with yet another solid by-product. Numerous potential strategies for hair utilisation have been proposed. However, the use of hair waste as agricultural fertiliser is one of its most promising applications due to the high nitrogen content of hair. Agricultural value of hair can be increased by composting. This paper deals with the composting of hair from the unhairing of bovine hide. Results indicated that hair cannot be either composted on its own or co-composted with de-inking sludge, a chemical complementary co-substrate. However, good results were obtained when co-composted with raw sludge from a municipal wastewater treatment plant at hair:raw sludge weight ratios 1:1, 1:2 and, 1:4 in lab scale and pilot plant scale composters. In all cases, a more stable product was achieved at the end of the process. Composting in the pilot plant composter was effectively monitored using Static Respiration Indices determined at process temperature at sampling (SRI(T)) and at 37 degrees C (SRI(37)). Notably, SRI(T) values were more sensitive to changes in the biological activity. In contrast, Respiratory Quotient (RQ) values were not adequate to follow the development of the process.