Brain L. Benham, C. Roland Mote 1
Dairy lagoon supernatant treatability was evaluated using ten laboratory-scale (1.5 m by 0.45 m) constructed wetlands. Select design and operational variables were examined. Tested treatments were combinations of three organic loading rates (waste strength levels: high, medium, and low) and three types of microbial attachment sites (vegetated, plants; inert, wooden dowels; and none, no microbial attachment site). Five combinations of organic loading rate and microbial attachment site were tested. Removal efficiencies were based on analysis of influent/effluent waste constituent levels. Dominant nitrogen removal mechanisms were determined from an examination of influent/effluent nitrogen speciation. An analysis of waste utilization kinetics provided insight as to the applicability of a widely used design model.
Results showed consistently high nitrogen removal efficiencies (65 to 81 percent) for all treatments. Nitrogen speciation results indicate that nitrification/denitrification was the dominant nitrogen removal mechanism. Carbon removal was less efficient (6 to 39 percent) and varied with influent strength. Waste utilization kinetic rate-constants from the five treatments were not statistically different (alpha=0.05). The evaluated design model uses microbial attachment site parameters like specific surface area to modify a base reaction rate-constant (i.e., a rate-constant for a system with no microbial attachment sites). In this case, the rate-constant for the control (treatments with no microbial attachment site) was not statistically different from either the vegetated or inert treatments. This result illustrates short comings with the evaluated design model.
