Valorization of compost in the production of carbon-based materials for the treatment of contaminated wastewater

Abstract

The municipal organic waste is typically treated by mechanical separation and then by anaerobic digestion and composting, in order to valorise the residues in a biogas stream for energy purpose and in compost that can be used in agriculture. However, the current waste management legislation in Europe and the expected developments on the coming directives regarding the application of the “end-of-waste” criteria, are leading to barriers on the use of fertilizers resulting from waste. The current work proposes an alternative strategy to the valorisation of compost through the production of low-cost materials to be used as catalysts in the treatment of wastewaters. The compost was supplied by a waste management company located in the North Est region of Portugal, and then subjected to thermal and hydrothermal treatments. Compost was mixed with water, filtered and washed in order to remove the soluble compounds and suspended solids. Then, materials were prepared with H2SO4 (18 M) and different mass ratios of glycerol, the resulting products of reaction being calcined at 800 ºC. The material that presented the highest conversion was washed with hydrogen peroxide (H2O2), at room temperature and at 60 ºC, and HCl (1 M). The prepared materials were sieved, and the samples obtained were tested in H2O2 decomposition and in the remediation of waters containing one model pollutant with lipophilic character (4-nitrophenol) by catalytic wet peroxide oxidation (CWPO). The effluents of the CWPO and H2O2 decomposition runs were analysed in order to quantify the pollutant, oxidant, TOC and the leached iron. In this sense, it was concluded that the materials produced shows activity through the analyses, and the conversions reached had a strong contribution of leached iron. Then, the amount of leached iron could be minimized while maintaining the conversions.