Investigating dairy lagoon effluent treatability in a laboratory-scale constructed wetlands system

Dairy lagoon supernatant treatability was evaluated using 10 laboratory-scale (1.5 m X 0.45 m) constructed wetlands. Selected design and operational variables were examined. Tested treatments were combinations of three organic loading rates (high, medium, and low) and three types of microbial attachment sites (vegetated, inert, and none). Five combinations (two replications each) of organic loading rate and microbial attachment sites 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 specialization. In addition, an analysis of waste degradation kinetics provided insight with respect to the applicability of a widely used design model. Results showed consistently high nitrogen-removal efficiencies (65 to 81%) for all treatments. Nitrogen specialization results indicate that nitrification/denitrification was the dominant nitrogen removal mechanism. Carbon removal was less efficient (6 to 39%), and varied with influent strength. Waste utilization kinetic rate-constants from the five treatments were not statistically different (alpha = 0.05). The design model uses microbial attachment site parameters, such as 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 sites) was not statistically different from either the vegetated or the inert treatments.