Laboratory and field investigation on characteristics and removal mechanisms of phosphorus from wastewater via a carbonation process and apatite

Phosphorus (P) is a crucial element in the aquatic ecosystem for all livings. The removal of phosphorus from wastewater is primarily to reduce the potential for eutrophication in receiving waters. However, most P removal technologies do not represent an economically viable route and have been developed for use at larger wastewater treatment plants that have rigorous monitoring and in-house operating expertise. Smaller treatment plants often do not have these facilities, which is problematic because there is concern that P releases from small treatment systems may have a more significant environmental impact than previously believed (Bunce et al. 2018). This research is a laboratory and field project involving the investigation of a carbonation process using limestone to remove P from wastewater and include an investigation of the effectiveness of two industrial apatite media. Phosphorus removal using a carbonation process and limestone media to provide calcium ions and precipitation process experimented under various operation conditions of reaction time, carbon dioxide flow rate, aeration flow rate, solution composition, and initial P concentration during laboratory experimentation. Application of this process was designed, constructed and commissioned in West Bonvilston treatment works, a Dŵr Cymru Welsh Water site. The laboratory system of the proposed process showed effective P removal with a range of different P solution compositions and a range of initial P concentrations. The lowest P concentration left in solution was 0.6 mg/l which is lower than the Urban Wastewater Treatment Directive lower control limit of 1 mg/l. Further study on the precipitate collected from the laboratory system with XRD and total carbon analysis indicated that the form of the precipitate depends on initial P concentration and it’s a mix between calcium carbonate and calcium phosphate at high initial P concentration. The results of the laboratory study also showed that precipitation is the dominant removal mechanism. Carbonation stage has been identified as the limiting factor within the field trial. Ca concentration recorded in the field trial was lower than in the laboratory system. pH recorded during aeration stage within the field system was also not high enough to encourage precipitate to occur. Phosphorus removal by the two apatite media (pellets) in field trial was determined. Overall, the results have shown that both pellets are effective in removing almost 100% phosphate under a relatively low P loading rate. Mechanism of P removal by these pellets is likely to be precipitation as both media release high Ca concentration at high pH