Surface World August 2018 (Show Guide) Surface World Aug 2018 - Page 167

WATER & EFFLUENT TREATMENT Is your wastewater treatment watertight? Increasing levels of European legislation, led by the Water Framework Directive, is putting great pressure on companies involved with wastewater treatment. On top of pH, total suspended solids and tight limits on heavy metals, nutrient removal and reduction technologies 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. 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. can be used to raise pH, such as caustic soda (NaOH). Whilst effective in increasing pH, it also generates the highest dissolved solids content in an effluent stream, relying on additional chemicals and plant design to meet consent limits. Caustic soda also tends to produce a gel-like sludge, and for those sites with heavy metals in their wastewaters, the highly leachable characteristics of a sodium-based sludge can be an issue. Due to caustic soda’s cost, the use of lime is reinforced as the reagent of choice, chemically as well as financially. Phosphate precipitation Chemical precipitation is used to remove inorganic forms of phosphate by the addition of a coagulant. The multivalent ions most commonly used are calcium, aluminium and iron. Calcium 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. 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 together before. It differs extensively from the common types of lime slurries available and can compete with 50% caustic soda, whilst combating a range of wastewater pollutants for safe site discharge. Phosphate removal from wastewater in the stainless steel fi nishing industry A specialist in metal finishing and architectural metals, produces surface finishes on stainless steel and other metals. The company traditionally used a low solids content lime suspension to treat effluent which is collected in two separate sumps – one for chromic acid-based, and the other for phosphoric/sulphuric based effluent. All the effluent is dosed with an aluminium reagent before being neutralised with a strong liquid lime (Neutralac SLS45). This is a two-step process, with the final pH around 11.5, found to be the optimum pH for the formation of calcium aluminium sulphate oxide. Epofloc L1-R is then dosed to ensure heavy metals removal but it also starts the flocculation process. The effluent is then pumped to a lamella settler for separation of solids and liquids. Phosphate is finally removed by precipitation with aluminium and calcium. Key Achievements 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. 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. Strategies System Solutions with Neutralac® SLS45 2. Reduce its reagent costs by up to 20% Lhoist developed a multi-functional reagent called Neutralac® SLS45, a lime product that combines lime slurry features never seen 3. Reduce the operators’ workload considerably due to the lower number of delivery vehicles required. Many industrial processes create acidic waste streams, and a number of alkaline chemicals read online: www.surfaceworld.com Neutralac® SLS45 has proved to be easy to handle, simple to pump and dose. Depending on dosage rates, site has been able to: 1. Achieve removals of up to 99.9% for phosphates, and up to 99.7% for sulfates and heavy metals SHOW GUIDE - AUGUST 2018 165