Technical-economic evaluation of nutrient removal filters
P filter box
Ghent University and Inagro demonstrated that the P filter box removes 60 to 90% of dissolved phosphorus from drainage water. The capital investment of the P filter box is about € 635 and a life time span of 15 years was assumed. Yearly operational costs are about € 80. The average cost to remove P from drainage water was calculated to be € 1.264/kg P. However, the final cost strongly depends on the P concentration in the drainage water being € 4.938, 409 and 85/kg P for drainage water having a P concentration of 0,12; 0,46 and 10 mg P/l, respectively.
Average P removal efficiencies up to 95% could be attained in horticulture. PCS constructed a do-it-yourself P filter for which the investment cost is € 690 and the operational cost is € 95 per year. As such, the average cost to remove P from greenhouse effluent was calculated to be € 85/kg P.
Nitrates are biologically ‘removed’ via conversion into nitrogen gas in a Moving Bed BioReactor (= MBBR). MBBRs have been configurated and demonstrated in several ways. MBBRs operated via the grid or via solar panels, were installed above or under ground and treated low (1 m³), medium (8 m³) or high (15 m³) flows. Both drainage water and greenhouse effluent have been tested. Depending on the configuration, the investment cost ranges between € 3000 and € 46 000 whereas the operation cost fluctuates between € 1 300 and € 6 000. The average cost to remove nitrates amounts up to € 100 to € 135/kg N.
Filter technologies are cost-effective
The cost to remove 1 kg P or 1 kg N with these nutrient filter technologies has been compared with current existing measures. This comprises amongst others green covers, stricter fertilization standards, buffer strips, deployment of municipal wastewater treatment infrastructure and deployment of individual wastewater treatment infrastructure. The comparison revealed that the filter technologies are very cost-effective, far more cost-effective than the deployment of large infrastructures. When it comes to the excess of nitrates in water, source measures are still the most efficient. It comes down to fertilizing judiciously, being in the right place, at the right time, with the right technique and the right dose. In locations where no improvement is observed despite the efforts made, the MBBR can offer a solution.