The use of IOCS for P recovery

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IOCS or Iron Oxide Coated Sand, are grains of sand with an iron-rich layer that are used for phosphate removal from wastewater. The IOCS is a waste product from drinking water purification and can chemically bond with phosphorous. An installation for IOCS (€ 2 250) is more compact than one for biological phosphorous extraction. By using the filters up-flow and allow gravitation to transport the water (4 m³/day) from one filter to another, the contact time with the IOCS is sufficient for a good phosphorous removal. On an average ornamental nursery (4 ha greenhouses), where the drain water has a P-content of at least 10 mg/L, two filters of 1 m³, each filled for 70 % with IOC, are sufficient. The IOCS have a high adsorption capacity of 5 mg P g-1 of dry grain (load of 25 mg P per litre). Already after the first filter, the concentrations decline until < 0.1 mg/L. Advantages are the absence of chlorides in the water and the fact that there is no extra sludge, which is the case when adding iron chloride for phosphorous removal. Depending on the amount of floating material in the water, it might be interesting to create a backflush. Pathways for partially or completely saturated IOCS are being investigated. Possibilities are: use as a soil improver or recovery of useful components from the IOCS. Since the amount of IOCS is limited (< 200 tons a year in Belgium), it is being investigated if it is possible to pelletize silt to a similar product. IOCS can be combined with a constructed wetland in which most N and floating particles are removed from the water. This way both N and P can be eliminated from the water.

Ilse Delcour

Proefcentrum Voor Sierteelt (PCS), Belgium
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