THE REUSE OF SPENT BLEACHING EARTH - A FEASIBILITY STUDY IN WASTE MINIMIZATION FOR THE EDIBLE OIL INDUSTRY

Spent bleaching earth, a solid waste from the edible oil industry can be converted to a clay-carbon adsorbent for potential reuse in the adsorptive cleansing vegetable oils. Commercial and laboratory-prepared adsorbents were screened for their ability to remove coloured pigments, impurities and trace contaminants from rapeseed and crude coconut oils. Activated spent bleaching earth demonstrated efficient removal of benzol[a]pyrene from crude coconut oil reducing the concentration from 12.8 mug kg-1 in the crude oil to 1.3 mug kg-1 (89.8% w/w removal) in the treated product at a 2.0% w/w adsorbent dose. Soybean and rapeseed process wastes activated under identical conditions exhibited similar removal efficiencies of 89 and 86% w/w, respectively. This compared with a reduction in benzo[a]pyrene concentration to 10.8 mug kg-1 for virgin bleaching earth (15.6% w/w and to less than 0.1 mug kg-1 for commercial powdered activated carbon (> 99.2% w/w). Activated spent bleaching earth exhibited limited removal of chlorophyll derivatives (27% w/w) and negligible uptake of the beta-carotenoids and phosphorus from degummed rapeseed oil compared with the virgin bleaching earth which showed effective bleaching of chlorophyll derivatives (98% w/w), the beta-carotenoids and removal of phosphorus (71% w/w). Adsorptive differences between these materials are interpreted with reference to interactions at the surfaces of acidulated montmorillonite and activated carbon. Processing incentives for the recovery and reuse of spent clay are discussed.