COMPOSTER, fit-for-purpose Lab-scale bio-reactors able to reproduce static pile composting with forced areation

The increase in environmental consciousness is pushing more and more towards sustainable systems for the management of cities and agricultural area. Organic waste can be converted into good soil amendments by composting, which is therefore recognized as an eco-friendly process. Recently, CNR-ISAFOM developed a simplified static composting method, easy to be carried out at farm level, for olive mill waste recycling; in order to analyze and model the impacts of such a method, an air-forced automated apparatus including two 35-liters bioreactors has been designed, built and set up.Once put under controlled composting conditions raw organic waste, properly added with bulking agents to ensure ideal macro and micro porosity of the biomass, the system is resulted able to analyze in real time the emissions derived from the respiration activity of the in situ microbiota.The air flow is managed by an automated mass flow controller able to keep the oxygen concentration in the exhausted air within a pre-fixed optimal aerobic value. An accurate monitoring of temperature in the biomass, as well as in the inlet and outlet airflow, is carried out all along the composting trials. In addition, the apparatus records the progressive weight loss of the two bio-reactors while the concentrations of oxygen, carbon dioxide, ammonia and hydrogen sulfide are gathered in the exhausted air by means of separate specific detectors. The equipment is managed by custom National Instruments LabVIEW software for signals acquiring and manifold switching. All parameters under control are recorded every fifteen minutes and promptly displayed in tables, graphs and spreadsheets, thus showing in real time the mass balance of the waste under composting. Moreover, GC analyses of the exhausted air periodically sampled is performed to evaluate emissions of Greenhouse Gases (GHG), as methane and nitrous oxide. The apparatus has been tested by composting olive mill waste with hygroscopic additives, such as straw and waste wool. The trial ended when a steady state had been reached for the parameters under control, which signified a sensibly reduction of the microbial activities. Monitoring at a Lab-scale the amount of emissions from composting, may led to optimize those parameters which influence the release of GHG emissions. This may help composting companies in comply the even more restrictive rules imposed by Regulators for reducing its environmental impact.