WP 6 - Deliverable D6.2 Analysis of the Composter Results and Optimization of the Process - SUSMEDHOUSE Project

Production of five ideal mixtures of OW streams to be converted into HQ compost have been carried out using a peculiar lab-scale equipment, Composter, designed and self-made by CNR-ISAFOM, able to simulate a real static composting environment, characterized by mesophilic and thermophilic phases, and analyse in real time emissions released from the in situ microbiota that drives biodegradation of the organic waste. The airflow rate of each bioreactor is managed by separate mass flow controller able to keep the oxygen concentration in the exhausted air within optimal aerobic range (>10%). Temperature of the biomass, pressure and temperature of the inlet and outlet airflow, are monitored during composting as well as the weight loss of the bioreactors placed on scales, while the concentrations of oxygen, carbon dioxide, are recorded from the exhausted air by means of specific online detectors. Acquisition of signals, control of actuators, remote software supervision, data elaboration and monitoring are performed by means of fit-for-purpose integration of hardware and software created in NI LabVIEW environment. Parameters are recorded, plotted and promptly displayed in tables, graphs and spreadsheets, showing on video in real time patterns of biodegradation occurring in both bioreactors. During composting bioreactors are easily opened without stopping data collection, for a periodical turning of the mixture for ensuring a homogeneous biodegradation process; sample collection for chemical-physical and microbiological analysis, is performed during this phase. Composter releases a real mass balance of composting as well as Dynamic Respiration Index (DRI) values that give information on the on biological stability reached by the compost during the process. At the end of the thermophilic phase, occurring after about one month of composting, bioreactors are emptied, and compost destined to "curing" phase conducted at room temperature and ensuring an adequate moisture content (40-50%). Curing phase lasted in about 1 month and resulted in mature, biologically stable and no-phyto-toxic end-product (compost), rich in phyto-nutrients. Maturity of compost and potential residual phyto-toxicity is assessed by measuring the germination index on Lepidium sativum, according to UNI 10780:1998 standard. Biological stability is measured by determining the DRI, according to UNI/TS 11184 standard. Whatever OW stream is used, composter releases cured compost in about two months. For a complete standard chemical characterization of the end product, further significant parameters on cured compost, such as pH and EC on water extract, were determined by using standardized procedure as well as elementary analysis, performed by CHNS analyser and ICP-OES analyses.