Sourcing phosphorus for agriculture: Life cycle assessment of three options for India

Abstract

Life cycle assessment of three sources of phosphorus (P) to agriculture is presented, comprising a conventional source, namely a chemical fertilizer (DAP, or diammonium phosphate), and two alternative sources, namely P recovered from septic tank liquor (decentralized system) and that recovered from sewage sludge (centralized system). Impacts of each option on the following aspects were measured using the ReCiPe methodology, in addition to the total impact: global warming, formation of particulate matter, terrestrial acidification, eutrophication of freshwater, and consumption of non-renewable resources (fossil fuels and minerals). The cumulative energy demand of each option was also estimated. The three options differed in terms of their impact on environmental externalities. The energy demand of DAP production was the lowest, and its impact on global warming was 38% of decentralized system and 37% of the centralized system. Production of DAP was associated with maximum mineral resource consumption because of extraction of rock phosphate. The decentralized system had the least impact on eutrophication of freshwater and most on particulate matter formation. Overall, the centralized system had the highest impact score – 2.3 times that of DAP production – followed by decentralized process, its impact being 1.4 times that of DAP production. If the phosphogypsum waste produced in manufacturing DAP is landfilled, DAP production had highest overall impact. The decentralized system was better than the centralized system – impacts lower by 40%. Change of source of energy from coal to solar power makes the centralized system most favourable option and is thus recommended for implementation.