Sustainable management of water hyacinth via gasification: Economic, environmental, and toxicity assessments

Water hyacinth gasification, which generates syngas and biochar, is a promising thermochemical approach for bioenergy production and greenhouse gas mitigation. We investigated the economic feasibility, life-cycle greenhouse gas emission and human toxicity impact of two different water hyacinth gasification approaches: water hyacinth with and without wood chips. The safety of biochar horticulture and agriculture application was evaluated based on the heavy metal analysis results and 3 different biochar standards. Among 9 potential heavy metal contaminants, only the Ni of water hyacinth mono-gasification biochar was found 2.45 ppm higher than the Singapore Compost Standard. Both the water hyacinth mono-gasification and the co-gasification of water hyacinth and wood chips were shown to be economically feasible and carbon negative. However, the water hyacinth mono-gasification will become carbon positive and be resulted in a higher human toxicity impact if implementing additional CaCl2-based Ni extraction treatments. The carbon tax revenue based on Singapore policy is considered in the economic assessment. The optimal 15-year net present value was found to be 12.25 million SGD for the co-gasification of water hyacinth generated from a 45-ha water body.