Monitoring of Organic Matter During Composting

The composting of town refuse is an interesting tool for waste management: compost is a major source of organic matter and fits completely into the framework of the recycling of organic waste. However, in order to be able to spread compost on different soils and to meet the various agricultural requirements, it is necessary to know perfectly the evolution of organic matter and the characteristics of the end-product. The composting process can be divided into two major stages: a rapid degradation of the easily degradable insoluble components into water-soluble compounds, and subsequently the metabolization by microorganisms of the latter and of the less degradable compounds. Many tests and criteria have been experimented for the long term monitoring of organic matter during the composting process as a whole whereas a less attention has been paid to monitoring merely the first stage of the process. Butyric, propionic and acetic acids are water-soluble intermediate compounds formed as organic matter are broken down. A better follow-up of the first stage of the process is necessary to avoid the presence of these phytotoxic compounds (DeVleeschauwer et al., 1981; Cocucci et al., 1989) in the end-product. Whereas volatile fatty acid (VFA) concentration is a parameter which has been widely used to monitor the anaerobic digestion (Azinari di San Marzano et al., 1981; Henson et al., 1986, Mata-Alvarez, 1990) of organic waste, it has rarely been used for the evaluation of the composting process evaluation (Saviozzi et al., 1992). In this work, it is proposed to use the VFA as the means to monitor organic matter during the first stage of composting while, for the characterization of the maturation level, a new index of maturity, based on rapid spectrophotometric measurements, has been proposed in previous works (Prudent et al., 1994, 1995).