In food processing, there are a number of different compounds released into the vapour space. This is especially the case when the food stuffs are able to decompose. Some Sulphides and Ammonia are present but there are also Diamines, Indoles, Dimethyl Sulphide, Skatoles, Thiols and Acrylonitriles.
There are key areas in the waste treatment process where odour is emitted. Generally the screening system is an area of turbulence that allows odour to be released. Holding tanks incorporating mixers to maintain solids in suspension. There is a process of constant drain and filling of wastewater tanks. This creates turbulence as well as air pulses during the filling cycle.
Normally the materials present in the waste streams is of a substantial strength. It is sufficiently high upfront processing. Upflow Anaerobic Sludge Blanket (UASB) reactors are commonly used to pretreat the waste. The waste stream can be high in fats and grease, Dissolved Air Flotation (DAF) processing is required to remove the Fats, Oils and Grease prior to processing.
The aeration process, if adequately arranged will operate in conditions where the average organic strength is very low and will have little residual volatile compounds present to be released. There will be some odour emitted from the aeration process and it needs to be appropriately considered. Only on very high strength waste will the aeration process require covers and extraction.
The sludge are stored in sludge holding tanks to be dewatered and thereafter for disposal. There will be odour associated with the storage and handling of these sludge. They will tend to contain Hydrogen Sulphide, Ammonia and complex Volatile Organic Carbon (VOC) and will be highly odorous. The sludge, depending on the capacity of the plant will incorporate Anaerobic Digestion. This is done generally to generate methane for energy management of the system and reduce the total solids sludge volume. The Methane will be in the form of Biogas (65% Methane, 34% Carbon Dioxide with traces of Ammonia and Hydrogen Sulphide). The biogas can be used either to operate boilers or once cleaned used for Combined Heat and Power systems (CHP). Inline Scrubbers are required to reduce the levels of Hydrogen Sulphide in the Biogas.
Biofilters are the most common approach to deal with the odorous air from dairy waste. The Biofilters are able to adapt to wide spectrum of volatile fatty acids. Where high quality emissions are required, then Activated Carbon is required to polish the treated air from the Biofilter. If the concentrations are high then BioTrickling Filters can be considered.