Comparative Nutrient Profiling of Kitchen Food Waste, Cow Dung, and Their Bio-slurries in Kilifi County, Kenya

Abstract

Kitchen food waste and cow dung are potential feedstocks for anaerobic digestion, but their comparative physicochemical characteristics and the nutrient properties of their resulting bio-slurries require direct evaluation. This study determined the physical and chemical properties of kitchen waste and cow dung feedstocks and assessed the effects of anaerobic digestion on the corresponding bio-slurries. The study was conducted at the Pwani University Integrated Biogas Research Unit in Kilifi County, Kenya, during the 2021/2022 and 2022/2023 growing seasons. Kitchen waste and cow dung were digested separately in a Flexi biogas system after each feedstock was mixed with water at a 1:1 ratio. Seventeen physical and chemical parameters were evaluated, including bulk density, dry matter, moisture content, pH, ammonium, nitrate, bicarbonate, electrical conductivity, and exchangeable macro- and micronutrients. Kitchen waste and cow dung feedstocks showed a very strong positive correlation (r = 0.999977) and no significant difference (t(16) = 1.0155, p = 0.325). Their bio-slurries were similarly strongly correlated (r = 0.999983), with no significant difference (t(16) = 1.0288, p = 0.319). Anaerobic digestion did not significantly alter kitchen waste or cow dung properties relative to their raw feedstocks. The findings indicate that both feedstocks produced bio-slurries with comparable physicochemical characteristics, supporting the potential use of kitchen waste as an alternative or complementary feedstock where cow dung is limited.