Potential and limitations of phosphate retention media in water protection: A process-based review of laboratory and field-scale tests

Abstract

The application of phosphorus (P)-sorbing materials offers a possible solution for treating municipal wastewater and agricultural runoff. In this paper we discuss P retention and release mechanisms, and review studies on the P retention of different materials and their use as reactive media in filter beds. The main mechanisms for P retention are sorption on metal (mostly Fe or Al) hydroxide surfaces and, in alkaline conditions, the formation of Ca-P precipitates. The retention of P is strongly affected by the chemical composition of a material, its particle size and pH-related effects on sorption and precipitation both during testing and in practical operation. Laboratory tests are sensitive to solution chemistry (pH, alkalinity, ionic strength and composition, P concentration) and affected by material-to-solution ratio, contact time and agitation. Moreover, due to deviations from realistic field conditions, laboratory tests may produce imprecise estimates of the retention capacity and retention kinetics. In particular, materials that contain soluble substances (e.g., CaO) that elevate the pH of the ambient solution to high levels may in batch tests suggest a high capacity for P retention, but will most probably show much lower retention in field settings. On the other hand, materials containing metal oxides also retain P via slow reactions, and their retention capacity may be underestimated in short equilibrations. Appropriate laboratory test procedures will depend on their intended applications and material properties. Long-term field-scale tests are few in number, but some of them have shown promising results. Field-scale tests have, however, highlighted the design of the filters as a critical factor in their efficiency.

Comparisons Study of Phosphate Removal in Unaerated and Aerated High Calcium Steel Slag Filter System of Different pH Feed

“…Therefore, adsorption might be more significant phosphate removal mechanism in aerated systems since no white precipitates were visible in the filters. The adsorption follows inner-sphere ligand exchange mechanism [15] where they reacted by forming monodentate and bidentate complexes which were determined by how they were coordinated [16].…”

Can limestone, steel slag or man-made sorption materials be used to enhance phosphate-phosphorus retention in treatment wetland for peat extraction runoff with low phosphorous concentration?

“…Thus treatment wetlands are also often constructed on drained 47 such as slags have been frequently tested, because they are widely available and cheap 73 materials. However, based on Klimeski et al (2012) review, P sorption tests are usually 74 conducted using water with a high P concentration, whereas the average P concentrations 75 in peat extraction runoff are 80-90 μg Ptot L -1 and 25-30 μg PO4-P L -1 (Postila et al, 2014; 76 Tuukkanen et al, 2012). 77 78 Addition of Fe, Al and Ca can increase PO4-P retention due to their sorption capacity 79 (Richardson, 1985;Seo et al, 2005).…”

Using Chemically Treated Organic Recycling Materials to Enhance Freshwater Purification

“…The materials may also be classified according to their chemical composition as follows: those containing metals (mostly Fe and Al), those containing soluble divalent earth metals (Ca, Mg), and mixtures of the two [12]. Several studies have shown that some materials are capable of removing P from household wastewater or agricultural runoff, but more studies are needed to optimize the design of filter beds intended for field conditions [12].…”

“…While P appears in inorganic and organic forms under field conditions, laboratory experiments mostly use inorganic P. Secondly, sufficient contact time between the filter material and the flow solution is likewise a crucial point in developing P filters [12].…”

“…The use of phosphate retention media is one method employed to remove phosphorus pollution. Different materials and chemical compounds can be used for this purpose, for example natural materials (snail shells, tree bark, limestone), industrial by-products (fly ash, acid mine drainage residuals) and manufactured materials (including Fe, Al, and Ca salts) [12][13][14][15][16]. Binding phosphorus in the sediments of lakes and reservoirs is a common and easy technique to prevent algal blooms, but this solution has a high cost of use and needs large quantities of compounds [17][18].…”