Evolution of process control parameters during extended co-composting of green waste and solid fraction of cattle slurry to obtain growing media

• Green waste and cattle slurry were composted to produce growing media.
• Different evolution of process parameters and compost features have been found.
• New parameter has been proposed (degree hour per day-DH).
• DH enables to quantify the decomposing material exposure to high temperatures.
• Nitrification during composting led to a trend change in compost alkalinity.

This study aimed to monitor process parameters when two by-products (green waste – GW, and the solid fraction of cattle slurry – SFCS) were composted to obtain growing media. Using compost in growing medium mixtures involves prolonged composting processes that can last at least half a year. It is therefore crucial to study the parameters that affect compost stability as measured in the field in order to shorten the composting process at composting facilities. Two mixtures were prepared: GW25 (25% GW and 75% SFCS, v/v) and GW75 (75% GW and 25% SFCS, v/v). The different raw mixtures resulted in the production of two different growing media, and the evolution of process management parameters was different. A new parameter has been proposed to deal with attaining the thermophilic temperature range and maintaining it during composting, not only it would be useful to optimize composting processes, but also to assess the hygienization degree.