Field tests on phosphorus removal in greenhouse effluentIn common practice, water is multi-fold recirculated in greenhouses. By doing so, the concentration of some minerals, suchs as Na+, Cl- and SO42- increases to such an extent that the water needs to be discarded at a given time. Nutrient concentrations in this effluent exceeds the standards of 50 mg nitrate/l and 1 mg total P/l. Obviously, further treatment is needed before this effluent can be discharged in surface water.
In the field demonstration performed by PCS Ornamental Plant Research and KU Leuven in Belgium, P removal was tested by the use of iron coated sand. The latter is a side product of drinking water production. A dual filter system was set up on the premises of a floristry with pot plants. Each filter has a volume of 1 m³ and was filled for 70% with iron coated sand. Effluent was stored in a silo and pumped (500 l/h) over the filter system. More than 99% P removal could be attained resulting in less than 0,1 mg/l of P in the filtrate.
Meanwhile, the filter system is operational for more than 2 years time. P concentrations in the filtrate suddenly increased after more than a year, denoting that the iron coated sand was saturated with P. A nearly complete P removal could be realized again after replacement of the saturated iron coated sand with virgin iron coated sand.
Iron Coated Sand Granules
The grower confirmed the suitability of this technology being robust, low-tech and easy to operate. He will continu to use this filter technology to be able to discharge his effluent to the environment.