Fertilizer demand and potential supply through nutrient recovery from organic waste digestate in California

Diversion of organic waste from landfills offers an opportunity to recover valuable nutrients such as nitrogen and phosphorus that are typically discarded. Although prior research has explored the potential for buildout of anaerobic digestion (AD) infrastructure to treat organic waste and generate energy, a better understanding is needed of the nutrient recovery potential from the solid and liquid byproducts (digestate) resulting from AD of these waste streams. We quantified the system-wide mass of nutrients that can potentially be recovered in California by integrating current and potential future AD facilities with existing nutrient recovery technologies. Based on a profitable build-out scenario for AD, the potential for nitrogen and phosphorus recovery by mass was greatest from municipal sewage sludge. The nutrient recovery (% total mass) was determined for three different end products for the combined organic waste streams: liquid fertilizer [38% of the total recovered nitrogen (TN)], struvite [50% TN, 66% total phosphorous (TP)], and compost (12% TN, 34% TP). Based on the profitable build-out scenario of AD facilities in California, the recovered nutrients would offset an estimated 11% of TN and 29% of TP of in-state synthetic fertilizer demand, whereas a scenario in which all technically recoverable biomass is collected and treated could offset 44% of TN and 97% of TP demand.