S. Speer and P. Champagne (Canada)
Constructed wetlands, Climate, Canada, Agriculture
There are many different methods of treating the rural wastewater, which include: solid-liquid separation (a manure management option), aeration (reduction of ammonia and BOD5 concentrations), digestion (odour reduction, and pathogen destruction with the advantage of methane production as an energy source), and composting (volume reduction with a high nutrient fertilizer as a by product). Some of these treatment options can be very costly ($15 per head of cattle, $10 per pig) [1]. Most of the practices involve intensive labour, which is much more than is already available at, often-understaffed, farms. Since farmers have no control over the price of the products that are produced, they often cannot recuperate the costs associated with conventional treatment technologies, or the added labour. The agricultural industry is an important part of the Canadian economy, and the waste generated by this industry has a large impact on the environment surrounding the farmland. The farmers do not control the price of agricultural products; therefore there is no way to recuperate the costs of wastewater treatment. For many farms the only feasible method to treat the agricultural wastewater is though passive systems, namely constructed wetlands. The use of these natural, passive treatment systems can be limited by many environmental factors (precipitation, temperature, sunlight, etc…), and the Canadian climate contains many features, which can impact the efficiency of constructed wetland operation. The Canadian climate consists of a shortened plant growth season, and hence a shorter operating season for the constructed wetlands. Often inconvenient solutions for farmers are passive treatment systems. These systems can be easily operated, and the capital, as well as the operation and maintenance costs, are lower than most active treatment methods. Active treatment systems for agricultural wastewater streams typically involve the addition of chemicals or mechanical works to produce an effluent that meets regulatory discharge standards. The costs associated with these types of systems can be high. The chemical additives must be purchased, and since they are used up in the process, they must be constantly replenished. The equipment that is involved in the different stages of the treatment process must also be purchased and maintained. The design of the facility must include extra flow channels in each step of the treatment process so that some channels can be taken off-line for maintenance purposes, while maintaining treatment objectives. On-site operation and maintenance staff must also be employed. The costs associated with a constructed wetland include: the purchase of the land, labor to build the wetland, and staffing for the monitoring of the influent and effluent to ensure that the treated effluent complies with discharge guidelines. Systems can be setup such that all of the components are electronically controlled and there is only a need to verify the operation, or the control can be setup such that only a pump needs to be started and stopped at regular intervals (a task that will not take much labour).
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