Composting under controlled conditions

Abstract

Three cylindrical reactors, each with a working capacity of approximately 200 litres, were used to investigate composting. The process was optimised and conditions were controlled so that composting on a laboratory-scale thermally resembled that occurring in the core of large open heaps. A baseline flow of humidified air aerated the reactors in five-minute bursts. The reactors operated as closed systems with facilities to analyse the composition of the off-gas for ammonia, oxygen and carbon dioxide. Temperature was used to monitor the progress of the process. Heat loss from the reactor surface was compensated for with an external heat source. A basic model of radial conductive heat losses showed that 53 watts per square-metre would be the maximum heat flux needed to keep the temperature difference across the reactor to within a degree when running at 60 degrees C. A heating cable was used, which could supply 150 watts per square-metre, and the radial temperature difference was reduced to within a degree in more than 60% of the recorded temperatures in the case studies presented. The temperature of the composting material was held at 60 degrees C using a high flow rate 'cooling' aeration with temperature feedback. This, however, led to a mean vertical temperature difference of at least 10 degrees C. The aeration strategy resulted in a well-aerated material, which favoured aerobic microbial activity and the temperature increased as a result of the internally generated heat associated with composting. Three-quarters of the ammonia was emitted in the first week.

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

“…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). RI is the amount of oxygen consumed by a compost sample per gram of organic matter, and it is well known that during aerobic oxidation, 4 moles of electrons must be transferred for each mole of oxygen reduced.…”

Effect of temperature and aeration rate on co-composting of olive mill wastewater with olive stone wooden residues

“…The term efficiency of co-composting process is defined as the carbon dioxide produced by the biological reactions to the total carbon available (both from wastewater and bulking material) to the microorganisms. The composting of various feedstocks under controlled conditions has been studied thoroughly in the literature (Cronjé et al 2003;Gomes and Pereira 2008;Liang et al 2003;Petric and Selimbašić 2008;Richard et al 2006;Wang et al 2006). Form this literature survey, the parameters that were selected to be examined were temperature and oxygen partial pressure, given that the composting mixture was specified.…”

Environmental impact of mushroom compost production

“…10 During this process it is essential to control the different factors that ensure proper microbial growth and consequently an adequate organic matter mineralisation. 11 Equally, it is important to control the compost pile's parameters such as temperature, moisture, oxygen content and pH levels, as a variety of microbial populations grow as a result of these parameters. 12 The composting process is the intermediate stage of the mushroom production process, subsequent to the mycelium cultivation stage and prior to the fruiting bodies cultivation stage.…”

“…During this process it is essential to control the different factors that ensure proper microbial growth and consequently an adequate organic matter mineralisation . Equally, it is important to control the compost pile's parameters such as temperature, moisture, oxygen content and pH levels, as a variety of microbial populations grow as a result of these parameters …”