Abstract
Sorption by active filter media can be a convenient option for phosphorus (P) removal and recovery from wastewater for on-site treatment systems. There is a need for a robust laboratory method for the investigation of filter materials to enable a reliable estimation of their longevity. The objectives of this study were to (1) investigate and (2) quantify the effect of hydraulic loading rate and influent source (secondary wastewater and synthetic phosphate solution) on P binding capacity determined in laboratory column tests and (3) to study how much time is needed for the P to react with the filter material (reaction time). To study the effects of these factors, a 22 factorial experiment with 11 filter columns was performed. The reaction time was studied in a batch experiment. Both factors significantly (α = 0.05) affected the P binding capacity negatively, but the interaction of the two factors was not significant. Increasing the loading rate from 100 to 1200 L m−2 d−1 decreased P binding capacity from 1.152 to 0.070 g kg−1 for wastewater filters and from 1.382 to 0.300 g kg−1 for phosphate solution filters. At a loading rate of 100 L m−2 d−1, the average P binding capacity of wastewater filters was 1.152 g kg−1 as opposed to 1.382 g kg−1 for phosphate solution filters. Therefore, influent source or hydraulic loading rate should be carefully controlled in the laboratory. When phosphate solution and wastewater were used, the reaction times for the filters to remove P were determined to be 5 and 15 minutes, respectively, suggesting that a short residence time is required. However, breakthrough in this study occurred unexpectedly quickly, implying that more time is needed for the P that has reacted to be physically retained in the filter.
Highlights
It has been suggested that filters for the removal and recovery of phosphorus (P) from wastewater would be beneficial for on-site wastewater treatment e.g. in constructed wetlands
Many filter materials have been investigated [1,2] but it is still uncertain how well they would work in full-scale installations
There is a need for a robust test method that can be used to investigate filter materials and that gives reliable estimates of how well and how long they will function under given conditions
Summary
It has been suggested that filters for the removal and recovery of phosphorus (P) from wastewater would be beneficial for on-site wastewater treatment e.g. in constructed wetlands. To speed up the laboratory testing, parameters such as influent source (real wastewater or synthetic P solution), hydraulic loading rate, residence time, P loading and temperature do not match field conditions. These parameters vary substantially between different studies it has been shown that the method used to test the materials influences the measured P binding capacity and the predicted performance of the filters as well as their predicted lifetime [3]. There is a need for a robust test method that can be used to investigate filter materials and that gives reliable estimates of how well and how long they will function under given conditions. It needs to be investigated as to which parameters can be altered in the laboratory to determine P binding capacity in a reasonable amount of time whilst assuring that the binding capacity determined in the laboratory resembles the one expected under field conditions
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