Surface World February 2020 Surface World February 2020 | Page 126

WATER & EFFLUENT TREATMENT WE ARE AT SURFACE WORLD LIVE 2020 Dam good river management By Xavier Mear, Product Manager, Lhoist UK “Water is not a commercial product but a heritage to be protected.” Increasing levels of European legislation, led by the Water Framework Directive, is putting great pressure on companies involved with wastewater treatment. Nutrient removal and reduction technologies will continue to be at the centre of efforts on water protection. The presence of nutrients, especially nitrogen and phosphorous in wastewater effluents and their impacts on natural water bodies, continue to be a major concern for companies involved with wastewater treatment. Phosphates, like nitrates, are responsible for eutrophication, causing a deterioration of an aquatic ecosystem by the proliferation of certain plants, including algae. Industrial emissions, but also urban waste streams, contain these pollutants. Eutrophication – keeping the industry awake at night The presence of phosphorous in rivers and lakes is responsible for eutrophication, resulting in the uncontrolled proliferation of algae and excessive consumption of dissolved oxygen in the body of the water. It is thereby less available for other living species, and in particular fish, making it necessary to restrict phosphorous discharges into natural water courses. Strategies The removal of Phosphorous can take place successfully through a process called enhanced biological phosphorous removal. Specific bacteria are selectively enriched and accumulate large quantities of phosphorous within their cells (up to 20% of the mass). When the biomass enriched in these bacteria is separated from the treated water, these biosolids have a high fertiliser value. A well-buffered system maintains the pH where biological activity is optimised and allows for a more efficient use of oxygen, leading to reduced energy costs. Treating wastewaters using lime-based reagents increases the wastewaters’ buffering capacity and helps the phosphorous removal step. Phosphate precipitation Chemical precipitation is used to remove inorganic forms of phosphate by the addition of a coagulant and a mixing of wastewater and coagulant. The multivalent ions most commonly used are calcium, aluminium and iron. The formation of calcium phosphate salts in aqueous solutions takes place following the development of supersaturation, with excess calcium ions reacting with the phosphate to precipitate hydroxyapatite. Aluminium and Iron Calcium Alum is widely used precipitating phosphates, as are ferric chloride and sulfate. For both reagents however, the resulting AlPO4 precipitates need to be removed by flocculation via the excess addition of a metal hydroxide, and typically lime is added to enhance this treatment step Calcium is usually added to the process as hydrated lime Ca(OH)2. It is reported that addition of lime makes it possible to remove 85-90% of the inorganic orthophosphates present in wastewater. For more information on Neutralac please contact Xavier Mear, Product manager at Lhoist UK on 07968 755590 or [email protected] Separating phosphate from aqueous solutions exist and the physico- chemical processes utilised are based on precipitation phenomena by use of salts of calcium, iron or aluminium, or adsorption phenomena. Phosphate removal may also be achieved by biological processes. 124 SHOW GUIDE 2020 twitter: @surfaceworldmag