Removal And Recycling Of Agricultural Non-Point Phosphorus By Drinking Water Treatment Residuals And Zeolite Amended Media Filters

The need to develop effective means to reduce phosphate (P) inputs to surface waters remains a priority as harmful algal blooms continue to occur. However, because the excess nutrients that produce these blooms are integral to the agricultural industry for uses such as animal feeding and fertilizers, that cannot be easily altered, the need for innovative reduction methods is clear. Within this context, the use of drinking water treatment residuals (DWTRs) and zeolite amendments for P sorption as filter media have shown promise, but their efficiencies were never combined in the same system. This study investigates the use of a novel end-of-tile filter device with zeolite amended DWTRs for efficient agricultural excess P removal and suitability for reuse of recovered excess P as fertilizer; thus, reducing P inputs to surface waters while supporting economically sustainable farming practices. To do so, the efficiency for P removal of two media (DWTR-only and mixed-media, a DWTR/Zeolite mixture) was assessed in flow-through columns experiments. Columns were subjected to continuous infiltration of synthetic influent solutions mimicking agricultural field output with and without PO43-. Analyses of the effluent concentrations after 48 hours of leaching at 0.3 ml/min, helped determine the efficiency of the mixture and the effects induced by combining the two sorption materials with respect to PO43- sorption, competitive sorption and field deployment. Additionally, characterization of the media materials was conducted pre- and post- experiment to identify the sorption mechanisms responsible for PO43- immobilization and assess leaching potential of materials regarding. The objectives of this thesis are: (1) to optimize and investigate the use of combined DWTRs and zeolites as P sorption material as filter media (2) test the suitability for reuse of recovered excess P as recycled fertilizer. (3) implement filter media in-situ as a pilot study. My research shows that the use of DWTR-only media or mixed-media (DWTR-zeolite) for P sorption are both efficient, sorbing a maximum of 72% and 75% of influent PO43- respectively. I attribute this high sorption potential to the abundance of PO43- -selective sorption sites in the DWTR as little competitive sorption were observed and all sorbed PO43- was associated with the Al-rich DWTR. In our media, the unmodified zeolite did not contribute significant PO43- sorption but instead served as substrate for DWTR sorption and improved hydraulic conductivity. Prediction for use over longer time suggested that the filter mixed-media could be used for an estimated 27 precipitation days in a typical field setting with at least 50% removal efficiency. In desorption tests, I tested the potential use of the spent media as fertilizer and observed a very slow desorption of nutrients with safe levels of leaching of media material. Proof-of-concept field implementation, with 7 kg of media in a filter, captured 7 days of precipitation and showed an average of ~93% phosphate removal, however, with very low hydraulic conductivity. This initial in-situ experiment shows high potential for in-situ development of the filter media assuming enough zeolite is used to address the low hydraulic conductivity. This simple design and implementation of the device, combined with a low estimated cost of $2.12 per filter and potential reuse of the spent material indicates that optimization of this filter would provide a highly successful way to both reduce nutrient input to surface waters and recycling of PO43- and spent DWTRs.