Monitoring of the evolution of an industrial compost and prediction of some compost properties by NIR spectroscopy

Sewage treatment plants produce wastes resulting from the organic matter concentration in the form of sludge. A way of jointly treating and exploiting these increasing wastes jointly is the composting. Composting makes it possible to reduce volumes and the masses of wastes all while developing them in a product usable like organic soil enrichment. In this work, the composting process of an industrial sewage sludge composting plant was monitored to study the evolution of different physico-chemical parameters (temperature, moisture, pH, organic carbon, organic and inorganic nitrogen, organic carbon/organic nitrogen ratio, humic substances) and biochemical parameters (soluble fraction, hemicellulose, cellulose, lignin). Because these analyses are expensive and time consuming, we wanted to develop an alternative method to determine the maturity of compost related to compost properties with raw samples. Acceptable predictions were found for moisture, temperature, pH, organic carbon, organic carbon/organic nitrogen ratio, total-, organic- and ammoniacal nitrogen, fulvic- and humic acids and fulvic acids/humic acids ratio, but the error values were too high for the compost age to consider a quantification model. With regard to the biochemical parameters, this study is rather a preliminary test which shows the interest of the approach, but requires to be continued. Finally, the age of compost can be evaluated with Principal Component Analysis applied to NIR spectra.