The Environmental Impact of Wasting Recoverable Nutrients From Treated Sewage Sludge for Agricultural Use: A Life Cycle Assessment For a Circular Economy

This study assesses the environmental advantage of the recirculation of valuable nutrients available in treated sewage sludge (SS) to enhance fodder plant growth, embracing a cradle to cradle philosophy through Circular economy (CE) . Within the CE context, LCA is applied to evaluate the environmental savaging in utilizing recovered nitrogen (N), phosphorus (P), and potassium (K), or NPK nutrients in treated SS as opposed to the synthetic virgin counterparts while maintaining fodder needs and health and safety standards. The LCA for the three scenarios, fertilizer use, landfilling and incineration of SS, is constructed using consequential modelling and an open-loop system based on ISO 14044 (2006). Analysis by substance shows that a significant amount of natural gas and crude oil could be saved when N is obtained from SS as opposed to virgin sources. Savings on virgin N alone account for more than 95% of the total environmental burden. Nitrous oxide (N2O), for N production is responsible for 58% of the CT impact, 38% of the adverse impact on MD is due to the use of extensive Copper for N production. 42% of the HT impact is due to Manganese use for N production. This all highlights the urgency of recovering nutrients from treated SS as opposed on consuming virgin materials. Regression models were constructed to predict annual NPK consumption, and a metamodel is used to calculate he total savings in Carbon dioxide of treated SS used as fertilizer. The study have also emphasized the potential recovery of organic P as it is declared among list of critical raw materials in EU (COM No. 297, 2013; EC, 2017). The results indicated that P from phosphatic rock had almost three times the burden borne by the current treatment of sludge at the WWTP and 1.6 the burden of ssewage sludge ash (SSA). SSA approach could be particularly relevant for countries, agricultural reuse of SS is not generally accepted by the general public. Especially, in light of the EU Fertilizer regulation (2019/1009) which although promotes the use of fertilizers from recycled biowaste but, excludes wastewater sludge from the list of sources amended. Treated SS needs to be tested for microbiological agents (viruses, bacteria, parasites and helminths), chemical substances and heavy metals to avoid risks to public and occupational health via direct or indirect exposure.