A simple tool to help decision making in infrastructure planning and management of phytotreatment ponds for the treatment of nitrogen-rich water

In situ experimental studies were carried out aimed at the quantitative estimation of biological processes involved in nitrogen removal such as macro-algal assimilation and bacterial denitrification and their optimisation in two experimental phytotreatment ponds colonised by the macro-algae Ulva rigida in central Italy. Results from an in situ manipulative experiment estimate that Ulva carrying capacity defined as the macro-algal biomass in which the uptake of dissolved inorganic carbon (DIC) equals the production of oxygen (O sub(2)), was close to 300g times m super(-2) dry biomass (dw). At this carrying capacity the experimental assessment of Ulva growth rates and Ulva assimilation rates and their optimisation with use of a logistic model estimated that maximum inorganic nitrogen removal ( similar to 0.04 mol N times d super(-1)m super(-2)) was attained when Ulva biomass reached 150 g sub(dw) times m super(-2) and growth rate was 0.1 times d super(-1). Denitrification rates accounted for a small amount of total nitrogen removal ( similar to 150 mu mol N times m super(-2) times h super(-1)) although an intact core incubation experiment demonstrated that denitrification increased with increasing nitrate concentrations. Based on experimental results a series of calculations have been made by use of MATLAB algorithms to facilitate manipulation of easy-to-measure variables (infrastructural, chemical and biological) and subsequent gross estimates of their effect on biological nitrogen removal efficiency, thus providing a simple tool to help decision making for infrastructure planning and management of phytotreatment ponds.