Rapid on-site maturity and stability assessment of sewage sludge compost by mathematical treatment of UV and fluorescence spectroscopic data

• Sewage sludge composting can be monitored at high frequency on site. • Spectroscopic data can be used to quickly assess compost stability and maturity. • PLS effectively predicts C/N and ISMO from compost water extraction. Co-composting of sewage sludge with green waste is the main way of valorisation of organic wastes. The compost maturation process leads to production of humified and stabilized organic matter well-used for soil amendment due to its soil structuring qualities and nutrient richness. That is why the knowledge of product quality in terms of organic matter stability and maturity of compost is imperative. Unfortunately, there is a lack of quick and easy solutions available for composting plant managers who usually need complex and time consuming laboratory measurements for determination of biological or chemical parameters, and more robust on-site methods . Compost evolution monitoring needs actual determination of several biological and physico-chemical parameters as the C/N ratio, the ISMO (Organic Matter Stability Index), related to organic matter stability, and the germination test related to compost maturity. The aim of this work is the estimation of these three parameters using a Partial Least Squares regression (PLS1) based on UV and fluorescence spectroscopic data and pH from compost water extracts at various steps of composting process, ending to a mathematical linear model. Results show average relative prediction errors of 14.76 %, 16.35 % and 15.38 % for C/N ratio, ISMO and germination test results, respectively. These satisfactory results confirm potentiality of this approach for a rapid and simple on-site estimation of the organic matter stabilization and compost maturation, for qualification of the end-product before its use.