Centriskim A continuous process for reducing DAF skimmings Most meat and poultry processing companies have reduced their potential pollution problems from process water by installing DAF (dissolved air flotation) systems. More and more of these companies, however, also face a secondary problem – what to do with the recovered DAF skimmings. These contain fat and suspended dry matter – mainly proteins – all lost to the process water during the primary processing of meat and poultry, and recovered using various chemicals. Due to the nature of the DAF skimmings, with their high moisture content and the presence of flotation chemicals, this product waste is not very desirable. Traditional recipients reject the product due to the chemical contents, which downgrade the quality of the final product. The high fat and moisture content makes agricultural application difficult and very expensive. The Centriskim process provides an inexpensive solution for reducing DAF skimmings to recovered fat and an easily disposable water phase, as well as a wet concentrated solid phase. After this reduction process, the solid phase usually comprises less than 15% of the original weight, and fat recovery typically amounts to 10–15%. All Centriskim processes use centrifugal separation in a thermal process to extract fat and a highly concentrated solids phase. The solids can be transported to a central recycling plant, or further processing can be undertaken on site. The fat is normally recovered in the process, either by using a 3-phase decanter, or in a secondary separation process using a high-speed separator. Centriskim processes can be tailored to meet local requirements, with or without the use of chemical conditioners. Process description DAF skimmings are collected in a buffer system and then passed through a continuous steam injection heater to be heated to a temperature suitable for the centrifugal separation either by: • single-stage separation using a 3-phase decanter to extract solids, fat and water phase or • two-stage separation, which requires a 2-phase decanter for the solids/liquid split and a high-speed separator to extract the fat. Single-stage separation is preferable in cases where the composition and consistency of the DAF skimmings are fairly constant. Two-stage separation is a more versatile method, which provides the best separation performance on products with more variations in composition, quality and chemicals, etc. Two-stage separation thus normally produces a water and fat phase of greater purity. The fat (grease) complies with more demanding specifications as regards impurities, and the water phase has a lower BOD loading. The waste water separated from a single-stage system often requires further processing (returned to DAF or concentrated by evaporation), while the two-stage stickwater better complies with discharge criteria.

Recovered protein The defatted and dewatered solids can be dried for feed purposes or used in other recycling solutions. Recovered fat Depending on both the freshness of the DAF skimmings and the flotation chemicals used, the recovered fat is usually of a lower quality. However, fresher skimmings are usually acceptable as a direct feed-grade product, while lower grades are only used in technical applications. Cost-effective The cost-effectiveness of a Centriskim system naturally depends on the composition of the DAF skimmings processed. However, the value of the recovered fat combined with the...