Rapid on site assessment of a compost chemical stability parameter by UV and fluorescence spectroscopy coupled with mathematical treatment

Abstract

Sewage sludges are problematic due to the constant increase of urban population. The high level of organic matter in sludges can be valorized by co-composting with green waste. Many chemical changes occur in the compost maturation process, resulting on stabilized organic matter by humification which is recoverable as soil amendment. In this way, the knowledge of organic matter stability and maturity of compost is essential. However, estimation of chemical parameters allowing the management of compost quality usually need complex time consuming laboratory measurements. Indeed, there is not yet rapid, simple and robust method for their on site assessment at the moment. Among usual parameters used to monitor compost evolution, the C/N 2 ratio is a fundamental chemical parameter. The aim of this work is the estimation of the C/N ratio using a Partial Least Squares regression based on UV and fluorescence spectroscopic data and pH from compost water extracts at various steps of composting process and measured on site. A mathematical linear model is established based on selected data (pH, spectroscopic indices) resulting on average relative error for C/N estimation of 5.26 % (range between 0.5 % min. and 9.5 % max.). This tool leads to a rapid and simple on site estimation of the compost stabilization, allowing qualification of the end-product resulting on a global spectroscopic index of stability.

Application of Near-Infrared Spectroscopy for Monitoring and/or Control of Composting Processes

“…Taking into account that dissolved organic matter not only represents the biochemical change of organic matter during the decomposition process but also assesses the composting humification degree, Abaker et al [103] efficiently estimated the C/N ratio during sludge composting using PLS regression models based on UV and fluorescence data, while Tai et al [104], Fuentes et al [105], and Mouloubou et al [106] monitored organic matter degradation using UV-Vis and Fourier transform infrared spectroscopy. Similarly, the application of FTIR spectroscopy and differential scanning calorimetry for monitoring biodegradation during olive mill residue composting was also described in the literature [107].…”

Treatment of Sewage Sludge Compost Leachates on a Green Waste Biopile: A Case Study for an On-Site Application

“…The spectra were performed on a Shimadzu UV-1800 spectrometer over a wavelength range of 200 to 1000 nm using a 10 mm quartz optical cell-3 mL volume. We calculated two spectroscopic indices to evaluate the evolution of the organic matter contained in the water extracts, representing WEOM (water-extractable organic matter) [16,21,22].…”