BIOWASTE HOME COMPOSTING: EXPERIMENTAL PROCESS MONITORING AND QUALITY CONTROL

At local territorial levels, the combined option of segregating domestic biowaste at the source and directly destining it to home composting may be seen as a valuable prevention action contributing to reduce the generation of household waste. However, although the alternative and predominant recovery option of centralized composting of organic waste has been widely studied and developed at the industrial level and well addressed in international waste/biowaste management handbooks, biowaste home composting has only recently begun to be analyzed from a technical and scientific perspective. Therefore, the objective of the present study was to contribute to the knowledge of the process evolution and compost quality that can be expected and obtained, respectively, in this decentralized option. In this study, organized as the research portion of a provincial project on home composting in the territory of Pesaro-Urbino (Marche Region, Central Italy, Adriatic Sea side), four experimental composters were first initiated and temporally monitored. Second, two small sub-sets of selected provincial composters (directly operated by households involved in the project) underwent quality control on their compost products at two different temporal steps. For a realistic evaluation of the monitoring and control of biowaste home composting, the obtained results were compared with available reference limits for several of the characterized parameters. The monitored experimental composters showed overall decreasing profiles versus composting time for moisture, organic carbon, and C/N, as well as overall increasing profiles for electrical conductivity and total nitrogen, which represented qualitative indications of progress in the process. Comparative evaluations of the monitored experimental composters also suggested some interactions in home composting, i.e.: high C/N ratios limiting organic matter decomposition rates and final humification levels; high moisture contents restricting the internal temperature regime; nearly horizontal phosphorus and potassium evolutions contributing to limit the rates of increase in electrical conductivity; and prolonged biowaste additions contributing to limit the rate of decrease in moisture. The measures of parametric data variability in the two sub-sets of controlled provincial composters showed decreased variability in moisture, organic carbon, and C/N from the seventh to fifteenth month of home composting, as well as increased variability in electrical conductivity, total nitrogen, and humification rate, which could be considered compatible with the respective nature of decreasing and increasing parameters during composting. The modeled parametric kinetics in the monitored experimental composters, along with the evaluation of the parametric central tendencies in the sub-sets of controlled provincial composters, all indicate that 12-15 months is a suitable duration for the appropriate development of home composting in final and simultaneous compliance with typical reference limits. Ideally, the derived duration of 12-15 months places the decentralized home composting approach near the upper limit of the total duration generally expected in the simplest of centralized composting approaches (i.e., the windrow process).