| | Background and objectives | Findings | Conclusions | Recommendations
Background and Objectives
Snowfluent is a new Canadian technology that uses specially modified snowmaking equipment to treat wastewater. It has the potential to be a useful wastewater treatment system for the food processing industry in rural Alberta. Pilot scale trials in 1997 and a production scale trial in 1998 were conducted to evaluate the performance of Snowfluentin the treatment of malting plant effluent. The specific goals of the study were to determine:
1. The degree of treatment achieved by applying the Snowfluent system to a food processing wastewater.
2. How the treatment is achieved during snowmaking and the subsequent aging of the snowpack.
3. The effects of the Snowfluent-treated wastewater on the soil and shallow water table
4. The concentration and distribution of bioaerosols produced during the snowmaking process.
Findings
The 1998 production scale test represented worst-case conditions. The food processing wastewater had been stored anaerobically under ice for three months and had high levels of odour. Neither the wastewater’s salt content nor the site met Alberta’s draft guidelines for effluent irrigation. Consequently, the impacts on air, soils and groundwater represent the extreme and are not typical of Snowfluent treated wastewater. However, these conditions were optimal for evaluating the risk to the public.
Separation of soluble and insoluble salts from the bulk of the Snowfluent -processed wastewater occurred as the snow piles aged and melted. Highly soluble salts like sodium and potassium were concentrated in the initial meltwater draining from the snow piles, with over 80% of the soluble salt load in the first 20% of the meltwater. Less-soluble material, including precipitates of phosphorus and nitrogen compounds, remained in place after the snow had melted, resulting in a residue rich in plant nutrients.
Increased concentrations of soluble constituents of the processed wastewater were found in shallow groundwater at and downslope of the snow piles as the snow melted. Concentrations in shallow groundwater downslope of the snow pile returned to pretrial levels by the end of the snowmelt but concentrations of sodium and potassium remained higher in groundwater directly beneath the site of the snow piles.
Snowfluent was found to be an effective means of eliminating pathogens. Reductions in fecal coliforms, from wastewater to Snowfluent meltwater, were 4 to 5 log units. Many samples showed significant reductions at snowmaking. However, our tests found that the major reductions occurred as the snow piles aged and melted. Aersol counts of bacteria at snowmaking were high enough to warrant that operators should wear breathing protection when working in or around the snow plume during snowmaking. Since bioaerosol levels returned to background levels 100 metres downwind of the snowguns, off-site impacts can be controlled.
Only the aesthetic guideline for Total Dissolved Solids for the Canadian Drinking Water Quality Guidelines was exceeded in the groundwater during this worst-case test. This exceedance is attributable to the wastewater’s high salt concentrations and the highly permeable soils at the test site and is not a result specific to Snowfluent treatment.
A strong odour plume travelled up to a kilometre off-site during snowmaking in 1998. In contrast, in 1997, when fresh wastewater from the same malting plant was processed, significant odour was limited to the area where the snow plume was falling. Both the 1997 and 1998 tests confirmed that Snowfluent is effective in stripping odours from wastewater. Snow piles and meltwater had odours significantly less than the wastewater in both tests. The 1998 test showed that odour plumes will travel off-site at snowmaking when a pungent wastewater is being treated during mildly freezing conditions with high winds.
Notable increases in sodium concentrations occurred in groundwater at and immediately downslope of the Snowfluent snow piles. Very small increases in potassium concentrations were also observed. No changes in groundwater concentrations of Total Kjedahl Nitrogen (TKN) or dissolved phosphorus could be attributed to the effects of the Snowfluent -processed wastewater. High pre-existing concentrations of nitrogen and phosphorus in surface soils throughout the study area may have masked some minor effects of Snowfluent. Elevated concentrations of dissolved organic carbon, with accompanying increases in biochemical oxygen demand, were also found in a pattern analogous to that of sodium. No exceedences of drinking water guidelines for humans or livestock for these parameters were attributable to Snowfluent treatment.
Increased soil concentrations of sodium and potassium were observed in soil under and immediately downslope of the Snowfluent -processed wastewater snow piles. Sodium was evenly distributed through the soil profile to a depth of 0.9 m but concentrations of potassium decreased with depth, indicating binding in the upper soil layers. Concentrations of sodium and potassium decreased after the snow melted and returned to pretrial levels.
Native pasture and alfalfa hay both benefited from Snowfluent -processed wastewater. Better crop growth and fewer weeds were observed in the area of the snow piles after melting. This is probably the result of increased soil moisture as ample plant nutrients were present in surface soils throughout the study area. Areas of natural snow and water accumulation outside the snowmaking area also displayed the same effects.
Conclusions
When land application guidelines derived from wastewater irrigation criteria (Alberta Environment, 1997) are met, Snowfluent is a safe, environmentally sustainable winter treatment method for high nutrient, high organic matter wastewaters. Moisture and plant nutrients remain in place until snowmelt and are available as the piles melt through the growing season. Snowfluent -processed wastewater provided substantial benefit to an alfalfa hay crop, increasing growth and reducing weeds. In a site with very permeable soils and a high watertable, impact on shallow groundwater was limited to increases in sodium, potassium and dissolved organic carbon in the immediate area of the snow piles.
Recommendations
Alberta does not have specific criteria for land application of wastewater with Snowfluent systems. However, elements of wastewater irrigation criteria (Alberta Environment, 1997) are reasonable standards to use initially for a Snowfluent system when it is used to apply food-processing wastewater to land. When wastewaters meet wastewater irrigation criteria for Electrical Conductivity and Sodium Absorption Ratio, Snowfluent is an effective and environmentally safe treatment and land application system. Since there is significant treatment of total coliforms, fecal coliforms and Biological Oxygen Demand (BOD) during snowpack aging, it is recommended that wastewater irrigation guidelines for these parameters be applied to the snowpack meltwater, not the wastewater at snowmaking.
It is recommended that the benefits of land-applying wastewater fresh from the food processing plant be considered in developing criteria for Snowfluent; treatment systems. The 1997 tests showed that Snowfluent trade; treatment on fresh wastewater did not produce significant odours. Wastewater with high nutrients and BODs needs additional treatment (aeration or enzyme treatment) during lagoon storage to minimize odour production. Snowfluent; systems need lagoons for storage during system shutdowns due to warm weather and other factors. However, treating wastewater fresh from the food processing plant has the potential to divert and treat significant volumes of fresh wastewater before it goes to lagoon storage and needs odour treatment. Since odours from anaerobic decomposition will always be a problem with lagoons with food processing wastewater (as the 1998 test showed), the opportunity with a Snowfluent system is to reduce storage times and wastewater volumes in lagoons during the winter. These tests showed that wastewater fresh from a food processing plant can be applied to land through a Snowfluent; system without risk to air, soil, surface water and groundwater quality.
Snowfluent can be applied as a pretreatment to wastewaters that do not meet the criteria for land application or conventional treatment. Pre-treatment can desalinize and reduce nutrient and organic concentrations in saline, nutrient-rich wastewater to produce an improved effluent that can be handled by conventional treatment systems. |
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