A new control strategy for the composting process based on the oxygen uptake rate

Up to now different control strategies to supply the oxygen requirements to the composting process have been studied. All of them seek for the biological activity optimization. In general, temperature and oxygen content are identified as the key parameters to assess the microbial activity. For this reason, the most favorable range of temperature and oxygen content for composting has frequently been studied and used as controllers' set points. On contrast, no previous works have studied the feasibility of oxygen supply according to the biological activity during the process, measured as oxygen uptake rate. In this field, a new automatic composting controller has been developed using the oxygen uptake rate measure as the measured variable. After setting up and to start-up this new technique, two pilot composting trials were undertaken with municipal solid waste. Oxygen, temperature and cyclic controllers were also implemented and tested in the composting of the same waste, in order to compare the results and to determine what the optimum system is. The four systems studied had similar temperature profiles, whereas except for the new controller, the oxygen content was constantly oscillating during most part of the process due to severe airflow changes. Through all the most relevant parameters determined, it can be observed that the new controller offers the most optimum system performance, since with low energy consumption a higher total oxygen uptake is achieved and, in consequence, the most stable end-product is obtained. Hence, the oxygen uptake rate controller is recommended for the airflow regulation in composting systems with automatic control. © 2010 Elsevier B.V.