Efficient phosphate removal from contaminated water using functional raw dolomite powder

Phosphate, when present in water, forms one of the basic nutrients that lead to eutrophication and its associated negative impacts. The use of raw dolomite powder as an adsorbent was found to be very effective in the removal of phosphates from various waters and wastewater matrices. Ayoub and Kalinian (Water Environ Fed 78:353–361, 2006) reported phosphate removals, amounting to 100%, over more than 300 bed volumes at inflow concentrations between 0.30 and 0.40 mg/L. This marked achievement led to the present study with the objective of defining the effects of the various parameters involved in the process and determining the optimal operating condition to achieve effective and sustainable removal efficiencies. Experimental work was conducted by passing three types of influent water and two types of wastewater jacked with a phosphate salt (KH2PO4) through a fluidized column bed of dolomite powder, where the effect of various parameters, including system operation mode, adsorbent particle size, rate of flow through the bed (contact time), initial phosphate concentration, influent pH, and the presence of competing anionic solutes on the adsorption of phosphate was evaluated. The results asserted that the most effective mode of operation for the system was the fluidized bed configuration. Results further showed that the smaller-sized dolomite powder (< 0.074 mm) sustains better adsorption. Also, higher contact time and lower feed phosphate concentration result in increased adsorption. Adsorption capacity was found to decrease with increased influent pH values. Competitive adsorption with existing anions was noted to occur, leading to reduced efficiency in phosphate removal. The Thomas and Yoon–Nelson models were deemed to agree best with the experimental data, while the Thomas model was determined to be the most descriptive of the column runs and to produce the most accurate predictive results. The use of dolomite as an adsorbent in the removal of phosphates, considering its wide availability, ease of application and regeneration capability, if operated under optimal conditions as determined by the present study, will present a highly sustainable process with added advantages over the more complex and costly adsorbents.