Short CommunicationDehydrogenase activity as a method for monitoring the composting process
Introduction
Composting is a biotechnological process in which organic solid matter is biodegraded under aerobic conditions (Haug, 1993). As interest in composting is growing, the need of reliable methods for determination of the biological activity of the process increases.
Different methods have been used for monitoring the biological activity of the composting process. At present, the most popular methods are based on the respiration of a solid compost sample under dynamic and static conditions (Scaglia et al., 2000, Adani et al., 2003). However, these methods only provide quantitative results when are carried out at identical conditions of the process, which is not always feasible (Mari et al., 2003).
Another group of methods is based on more specific biochemical properties such as RNA content (Liwarska-Bizukojc and Ledakowicz, 2001), ATP content (Horiuchi et al., 2003) or several enzymatic activities (Wong and Fang, 2000, Tiquia et al., 2002a, Mondini et al., 2004). Among these, dehydrogenase activity (DA) is related to a group of enzymes which participate in the metabolic reactions producing energy in the form of ATP through the oxidation of organic matter, which is especially interesting in the composting process. DA has been studied in few works to monitor the biological activity of the composting process (Wong and Fang, 2000, Tiquia et al., 2002b) and has been correlated with some operational and biochemical parameters such as temperature, nitrogen content or other enzymatic activities (Benitez et al., 2005). Recent works on composting (Tiquia, 2005) have successfully correlated DA with respiration activity.
The aim of the present study is the determination of DA throughout a whole composting process (including active thermophilic stage and maturation mesophilic stage) and to correlate it with the static respiration index (SRI), a typical monitoring parameter of biological activity of composting.
Section snippets
Composted wastes
Source-selected organic fraction of municipal solid wastes (OFMSW) was selected as a substrate for composting experiments. OFMSW was obtained from a local composting plant and mixed with pruning wastes used as bulking agent in a volumetric ratio 3:1 (pruning wastes:OFMSW). Compost was obtained from the same composting plant at the beginning of maturation stage. In the composting plant studied, the beginning of the maturation stage starts when the material is extracted from a tunnel composting
Results and discussion
Fig. 1 shows the temperature profile of the OFMSW composting experiment. Temperature presented a typical pattern of a composting process (Haug, 1993), with a sharp peak of temperature at day 10 (70 °C) and a gradual decrease to mesophilic temperature from day 20. Thermophilic range of temperature (>45 °C) was maintained for more than 10 days, which ensures a complete sanitation of the material. Aerobic conditions were expected since the oxygen in the compost material was observed to be over 10%
Acknowledgement
Financial support was provided by the Spanish Ministerio de Ciencia y Tecnología (Project CTM2006-00315/TECNO).
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