Modeling compartmentalized lagoon systems under cyclic operation

Aerated lagoon systems have been widely used for municipal wastewater treatment because of their simplicity and low maintenance costs, but many have subsequently required upgrading due to increased wastewater volume and stricter environmental regulations. To improve performance and increase capacity with minimal capital infusion, Hawkins (1997, United States Patent No. 5,624,563) developed a process wherein the lagoon basin is compartmentalized and selected compartments are cycled to separate and recycle biosolids. Simulation would be useful to assess the process and to evaluate alternative plant modification schemes. The hydraulic behavior of the system is complex, however, due to the interconnected and cyclic nature of the compartments and their operation. This paper describes the development of a hydraulic modeling approach for compartmentalized lagoon systems, and discusses its implementation using AQUASIM (EAWAG, Dubendorf, Switzerland). The modeling approach was implemented for a specific configuration and several operating conditions. Simulated tracer tests indicated that the oscillatory nature of the system makes its behavior difficult to simulate with commonly used non-ideal reactor models. Biotreatment simulations using Activated Sludge Model No. 1 suggest that conversion into a compartmentalized lagoon system could effectively upgrade the performance and capacity of a conventional aerated lagoon.