Scenario-based techno-economic analysis of pumped denitrification bioreactors

Abstract

Pumped denitrification bioreactors are currently being assessed in the field to extend the use of traditional, subsurface drainage bioreactors. Pumped bioreactors for the treatment of drainage ditches, surface waters, and cisterns intercepting drainage were evaluated to provide a basis of the unit cost of bioreactor operation ($ kg NO₃–N removed⁻¹) under a variety of scenarios. The unit costs were modeled using a techno-economic analysis. The variables assessed in the analysis included nitrate removal rate, bioreactor lifespan, and operating periods, which were assumed. To evaluate the impact of these variables on the unit cost, a sensitivity analysis was conducted where one variable was adjusted (e.g., lifespan) while the other variables were kept the same as a traditional bioreactor. The cistern and supplemental surface water bioreactors were larger in size and had similar unit costs ranging from ∼$5 to $27 kg NO₃–N removed⁻¹ for all scenarios except for the low mass removal and worst-case scenarios. The smaller, ditch diversion bioreactor had unit costs in the best- and worst-case scenarios in the range of $24 to $619 kg NO₃–N removed⁻¹, respectively. A breakeven analysis indicated increasing the mass removal rate of the bioreactors and ensuring an operating period greater than 6-months had the greatest impact on reducing the unit cost compared to a traditional bioreactor. Overall, the larger-scale surface water and cistern bioreactors had comparable, but slightly higher, unit costs than traditional bioreactors under most scenarios evaluated. This information can be used to optimize and inform of the potential of pumped bioreactor systems.