CompostManager's Latest Worldwide Orders
SITA UK Ltd, Arkwright IVC, Derbyshire, UK
Remondis, New South Wales, Australia
Cowbridge Compost, South Wales, UK
Cherries Tasmania, Australia
The Green Waste Company, Hayle, Cornwall, UK
Amey UK, Waterbeach, Cambridgeshire, UK
Willen Biogas, Enfield, Hertfordshire, UK
Casella Organics, Portland, Maine, US
St Louis Composting, Missouri, US
Wasatch Integrated Waste Management District, Layton, Utah, US
DEMZ, Agadir, Morocco
Collier Environnemental, Chertsey, Surrey, UK
Viridor Waste Management - Temperature Mapping Sytem UK
Progressive Waste Solutions - Winnipeg, Canada
City of Winnipeg, Canada
University of St. Thomas, St. Paul, Minnesota, USA
Eco Sustainable Solutions Christchurch, UK
ELEPHANT VERT - MALI, WEST AFRICA
W2R BRINGELLY - SYDNEY, AUSTRALIA
Measuring Oxygen In Compost
Composting is, by definition, a predominantly aerobic process. Failure to provide sufficient oxygen for aerobic degradation by microbes results in slow maturation rates and excessive odors. For industrial composting activities, supplying oxygen costs money. This may be through extra land use for low passively ventilated windrows, or power and equipment for forced ventilation systems. Therefore, carefully monitoring oxygen levels to optimize the composting process while minimizing odor pollution is necessary.
Progressive operators may already be using commercial or home-built probes to check the supply of oxygen in composting windrows or tunnels. That is an important step forward, but to get full value from these measurements, the influence of temperature needs to be considered. First, there is an inbuilt error in the oxygen measurements that increases at higher temperatures. This can be corrected using Dalton’s Law, courtesy of English Victorian chemist, John Dalton.
Second, microbes live in the water layer coating composting particles, not in air. The limited amount of oxygen that can dissolve in water is further reduced at high temperatures. Soluble oxygen levels can be calculated using Henry’s Law, developed by another Victorian chemist, William Henry.
This article explains each of these calculations and provides simple methods for assessing the availability of oxygen. A compost operator is then in a much better position to judge the health and productivity of the site’s composting system.
Dissolved Oxygen Levels
Data collected using the CompostManager system from several sites in the United Kingdom have been analyzed with a view to determining the minimum required levels of dissolved oxygen in order to avoid excessive odor. By selecting data from well-performing sites without significant odor problems, it appears that if dissolved oxygen levels in windrows are above 1 ppm most of the time, there are unlikely to be major odor problems. By contrast, data from failing sites with significant odor problems consistently showed dissolved oxygen levels below 0.5 ppm.
As these results do show a significant difference between odorous and nonodorous conditions and the dataset is large (over 100,000 individual readings), this would certainly suggest that dissolved oxygen levels are an invaluable tool for monitoring and reducing odorous conditions in compost. Indeed, trends in this value have successfully been used to identify potentially problematic batches on sites that are otherwise performing well.
However, it is difficult to argue that this inductive approach alone provides the basis for a conclusive threshold limit for dissolved oxygen. Additional research is needed into the link between dissolved oxygen levels and scientifically measured odor emissions from composting materials and systems.