Monitoring the biological activity of the composting process: Oxygen uptake rate (OUR), respirometric index (RI), and respiratory quotient (RQ)

Abstract

Composting of several organic wastes of different chemical composition (source-separated organic fraction of municipal solid waste, dewatered raw sludge, dewatered anaerobically digested sludge and paper sludge) was carried out under controlled conditions to study the suitability of different biological indexes (oxygen uptake rate, respirometric index, and respiratory quotient) to monitor the biological activity of the composting process. Among the indexes tested, oxygen uptake rate (also referred to as dynamic respirometric index) provided the most reliable values of microbial activity in a compost environment. On the other hand, values of the static respirometric index measured at process temperature, especially in the early stages of the composting process, were significantly lower than those of the dynamic index, which was probably due to oxygen diffusion limitations present in static systems. Both static and dynamic indexes were similar during the maturation phase. Static respirometric index measured at 37 degrees C should not be used with samples obtained during the thermophilic phase, since it resulted in an underestimation of the respiration values. Respiratory quotient presented only slight variations when changing the process temperature or the waste considered, and its use should be restricted to ensure aerobic conditions in the composting matrix.

In search of a reliable technique for the determination of the biological stability of the organic matter in the mechanical–biological treated waste

“…Among them, BOD 5 is universally used in the wastewater treatment field, whereas the rest of parameters (generically called respiration index) are commonly used in the composting field (Adani et al, 2003;Gea et al, 2004). The reduction results obtained for these indices showed a high efficiency of the biological treatment used in the MBT plant when compared to reductions calculated from chemical data ( Table 2).…”

“…Although some authors present partial comparisons between static and dynamic respirometric approaches or some correlations between indices used for biodegradable organic matter determination (Adani et al, 2003;Gea et al, 2004;Barrena et al, 2005), this is, to our knowledge, the first study where a massive comparison of indices and methods is P r e -p r i n t carried out. The objectives of this research are therefore: i) to study the suitability of the methods proposed by different authors or institutions for the determination of the biological stability in samples from a MBT plant, which were obtained at different stages of their biodegradation; ii) to compare the two main groups of methods proposed (aerobic and anaerobic), iii) to determine the correlations among the methods studied and iv) to determine the efficiency of the treatment of biodegradable organic matter in the MBT studied, based on some selected indices.…”

Determination of the energy and environmental burdens associated with the biological treatment of source-separated Municipal Solid Wastes

“…42 The degree of biological stability of waste materials can be directly measured by means of respirometric indices. 26,28,43 In the European legislation drafts 44 'stabilization' means the reduction of the decomposition properties of biowaste to such an extent that offensive odors are minimized and that the Dynamic Respiration Index (DRI) is below 1.0 g O 2 kg -1 OM h -1 .…”

Prediction of temperature and thermal inertia effect in the maturation stage and stockpiling of a large composting mass

“…In the experiments presented, respirometric measures were obtained at the same temperature of the pile in the moment of sampling to ensure the same conditions of the pile (Gea et al, 2004). Prior to the assays, samples were incubated for 4 hours.…”

“…Respiration indices have been routinely used in the monitoring of composting process to quantify the global biological activity or to determine the stability of compost (Ianotti et al, 1993;Scaglia et al, 2000;Adani et al, 2003;Gea et al, 2004). However, the use of these indices as a measure of heat generation is, to our knowledge, very limited (Cronje et al, 2003).…”