Improving the homogeneity of a sewage sludge-based phosphorus fertilizer by Monte Carlo simulation of the production chain

Sewage sludge mono-incineration with subsequent phosphorus (P) recovery from the ash is becoming increasingly important in many European countries. Plant operators are facing the challenge to produce a homogeneous P output which needs to conform to fertilizer standards (including trace elements levels) upon processing. This needs to take into account (i) the compositional variability of municipal sewage, (ii) design of incinerator and phosphorus recovery unit, and (iii) logistical and management aspects. In this study, those challenges were considered in Monte Carlo simulations based on a discretized sewage sludge input. To propagate the uncertainty along the entire process chain of thermal sewage sludge treatment and P-recovery, a simulation model was implemented using MATLAB. Specifically, logistical factors, different management options along the treatment chain, technical boundary conditions were investigated and the distribution of the P2O5 concentrations in the output (fertilizer/ash) was calculated. The results show how appropriate handling and treatment of sewage sludge helps to reduce the width product properties (e.g. P2O5 distribution, trace metal distribution in the output. From the options tested, storage management (including automated crane operation) had the strongest homogenization effect and could be easily implemented at incinerator sites.