Three combined pretreatments for reactive gasification feedstock from wet coffee grounds waste

In this study, a new pretreatment for using wet food biomass waste as a high calorific and reactive feedstock for gasification is presented. The method involves the addition of calcium hydroxide, hot water treatment, and dewatering in vegetable oil. Hot water treatment at 230°C reduced the oxygen/carbon atomic ratio of coffee grounds waste to improve the calorific value, but this treatment also formed an inactive cross-linked structure caused by dehydration reactions. By mixing the coffee grounds waste with calcium hydroxide powder before the hot water treatment, cross-linking was suppressed and the gasification rate of the char significantly increased because of the catalytic effect. With or without hot water treatment, the time required to complete gasification for the chars of the grounds mixed with calcium hydroxide was reduced to about one-third of that for the char of the untreated grounds. After heating in vegetable oil at 150°C, moisture was completely removed from the coffee grounds and they became impregnated with a large amount of the oil. As dewatering in oil did not affect the gasification rate of the chars, a combination of these three treatments was found to efficiently convert wet food biomass waste into a gasification feedstock.