THE TREATABILITY OF CHROMIUM TANNERY WASTES

Leather processing industry wastewaters contain several conventional p ollutants as well as micropollutants. Conventional pollutants can be e ffectively treated although considerable treatment comprised of severa l stages is required. However, the potential of conventional methods t o remove COD and micropollutants has not been fully explored. The purp ose of this paper is to investigate the extent of COD removal by conve ntional methods. Experimental studies are conducted using raw wastewat ers of industries applying chromium tanning to cattlehides and sheepsk ins. Biological treatability after pretreatment by chemical coagulatio n is assessed using a lab-scale continuous activated sludge system. Re sults indicate that chemical coagulation produces wastewaters with a C OD of around 2000 mg/l almost independent of raw wastewater quality. A ctivated sludge operated at 0.17 g BOD5/g MLSS.d loading is found to p rovide limited nitrification and almost complete BOD5 removal while th e COD could only be reduced to around 500 mg/l. The residual COD ident ified using a newly developed experimental approach shows that it cann ot be reduced lower than 300-550 mg/l.