| | Criteria for land application (wastewater irrigation) | Snowfluent treatment of food processing wastewaters
Food processing is a significant opportunity for development and diversification in rural areas of Alberta. However, small rural communities have difficulty handling wastewaters from food processing plants. Wastewaters must be collected and treated to meet the standards set by Alberta Environment before authorized release into the natural environment.
Food processing wastewaters are unsuitable for release to water bodies without extensive treatment. Prairie water bodies are typically shallow and low in volume making them particularly sensitive to increases in nutrient loads and increases in biochemical oxygen demand. Food processing wastewaters have high concentrations of organic material resulting in high biochemical oxygen demand (BOD), and high concentrations of nitrogen and phosphorus nutrients.
The typical treatment strategy in Alberta is to store the wastewater in lagoons and then combine it with municipal wastewater and irrigate cropland. This is a cost-effective method of treatment, which recycles plant nutrients and water through crops. However, for food processing plants that produce large volumes of high nutrient wastewater, storage and odour are significant problems, economically and environmentally.
Criteria for Land Application (Wastewater Irrigation)
Wastewater irrigation requires a permit from Alberta Environment, the issuance of which is decided on criteria presented and discussed in draft Guidelines for Municipal Wastewater Irrigation (Alberta Environment, 1997). Criteria are based on conditions described in the Procedures Manual for Land Classification for Irrigation in Alberta (Alberta Agriculture Food and Rural Development, 1992). Considered are:
- Soil type with consideration of the capacity to retain moisture and nutrients
- Local topography with respect to the potential for off-site runoff
- Crops with respect to water and nutrient requirements
- Local groundwater conditions with respect to the potential for impact from the wastewater.
The Guidelines for Wastewater Irrigation also set limits for:
- Nutrient loads applied - limited to single season nutrient uptake by crop.
- Water volumes - limited to moisture requirement of the crop
- Times of application - limited to growth periods of crops, which fall between May 1, and September 30; creating the requirement for facilities to store at least 7 months of wastewater.
Prolonged storage of food processing wastewater does present a problem. The high BOD of the wastewater quickly depletes the dissolved oxygen, causing the wastewater to become anaerobic. Under anaerobic conditions, proteins and sulphate decompose and the nitrogen and sulphur contained in them are reduced to malodorous amines and sulphides. These compounds are volatile and create an odor problem where the storage lagoons are located. When wastewaters are stored under ice through the winter, these compounds build up and are released en masse in the spring following melting of the ice cover and isothermic turnover in the lagoon.
Snowfluent Treatment of Food Processing Wastewaters
Snowfluent is a technology that offers a solution to the problem of winter storage of wastewaters. Treatment of wastewaters with Snowfluent is an effluent treatment/land application process developed by Northern Watertek Corporation (White and Frere, 1994), which has been successfully used in the treatment of municipal wastewater since 1985 (Huber and Palmateer, 1985). The process, involving the conversion of wastewater to man-made snow, is an attractive alterative to winter storage of wastewaters. The equipment and technology are very similar to those used to make snow at ski resorts. The process involves production of a fine aerosol of the effluent - propelled at high pressure from the nozzle of the snow gun. The cooling of the water droplets, from the surrounding air and evapouration of water, results in the rapid crystallization (freezing) of the water droplets to form snow (Netterville et al, 1997). All of the nonvolatile constituents of the effluent remain in the snow while there is some loss of volatile components and water. Use of Snowfluent to treat freshly produced wastewaters without extended storage in lagoons should reduce the odour problems caused by the amines and sulphides that are formed during extended storage.
Snowfluent opens an new treatment window, winter, to continue land application of wastewaters, provided the application site and wastewater meet the land application criteria listed in draft Guidelines of Municipal Wastewater Irrigation (Alberta Environment, 1997). The field site should be landscaped to ensure that surface runoff will not leave the site.
The volume of wastewater that should be processed with Snowfluent is limited to volumes that do not exceed the nutrient uptake and moisture requirement of the crop on the site. The extended snow cover resulting from the application of Snowfluent limits agricultural uses to crops that do not require spring seeding. These include pasture, forage crops for hay and fall seeded crops. |
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