Use of calcium-based materials for phosphorus removal from greenhouse wastewater
Phosphorus (P) contamination in wastewater is a major topic of discussion in the North American greenhouse industry. This study evaluated chemical treatment methods including precipitation of P as calcium phosphate and P-sorbing material filters for removing high, variable P concentrations, and provided treatment recommendations specific to greenhouse wastewater treatment. Precipitation via lime addition achieved 99% P removal at a lime : P ratio of 1.5 and a pH of 8.6-9.0. Efficiency of separation of the precipitate was improved via flocculation using guar gum or cationic starch. Material columns incorporating steel slag or concrete waste removed >99% over repeated applications, and demonstrated high phosphate retention. Both methods also removed some micronutrient contaminants, and recovered P and other nutrients in forms that could be re-used as a nutrient source for plants. Overall, this research demonstrated that these treatment methods are worthy of further research on application to a full-sized system.