Mechanical Biological Treatment (MBT) is a proven technology for the treatment of municipal solid waste (MSW). The number of MBT plants is increasing significantly in recent years. In a significant number of these plants, the three major elements are a Rotary Drum Reactor (RDR) for preparation of the waste, an anaerobic digestion system for organic matter degradation and energy recovery followed by a composting step for organic matter stabilisation. Although industrial feedback exists, there is a lack of scientific results at industrial scale. For that reason, Veolia Environnement Recherche et Innovation (VERI), with the support of the Agence de l’Environnement et de la Maîtrise de l’Energie (ADEME), carried out a research project to evaluate the performance of an MBT of residual municipal solid waste (rMSW) including a 24-m RDR from the VEOLIA-operated industrial site of Champagne sur Oise, the VERI semiindustrial (21m3) dry anaerobic digester at Graincourt les Havrincourt and the VERI pilot-scale (160L) composting reactors at Limay. The objective of the project was to evaluate the impact of the retention time of the RDR, which varied between 1.5 and 4 days, on the performance of the biogas production in the mesophilic anaerobic digestion, the compostability of the digestate and the agronomic value of the final product.
A. Bellegarde, H. Olczyk, A. Covez, F. Lebrisse, R. Lecarpentier, J.A. Cacho Rivero – Veolia Environnement Recherche et Innovation;
Y. Crepel – Veolia Propreté
Two three-month experiments were conducted considering the two retention times (1.5 and 4 days) of the RDR. The incoming rMSW and both flows of the screen at 40 mm following the RDR were characterized using the MODECOMTM (MéthODE de Caractérisation des Ordures Ménagères, 1993) methodology and physical and biochemical parameters in order to determine the performance of the equipment. The comparison between the composition of the rMSW used during each test and the average composition of the French rMSW shows that the material used during both tests could be considered as classical rMSW. No real impact on the quantity of Volatile Solids (VS) was observed whereas a modification of the particle size was pointed up.
Weekly three tons of the below 40 mm fraction were fed into the anaerobic digester. It was operated at 35°C and 30 days of retention time. The anaerobic digestion performance was evaluated in terms of biogas production and quality and also in terms of process stability (NH4+, VFA, TAC, and pH). In terms of biogas production, the results obtained show that, during both experiments, around 65 % of the Biochemical Methane Potential (BMP) of the feed was expressed in the reactor. There was no significant difference between both experiments indicating that there was no significant impact of the retention time in the RDR on the amount of organic matter made available for anaerobic digestion.
In both experiments, the digestate was analyzed in order to determine its ability to be composted in terms of organic matter availability and simultaneously composting test were conducted in order to evaluate the agronomic value of the stabilised final product. The dehydrated digestate was composted alone. The results showed low VS degradation due to the degradation of most of the VS during anaerobic digestion. Nevertheless a VS stability difference seems to exist between the two experiments maybe due to a longer retention time in RDR for the second experiment.