SELECTING A THERMAL DRYER – ACHIVING CLASS A BIOSOLIDS

Sludge drying is becoming a popular process due to ascending disposal cost and more stringent regulations. The product of the drying process generally contains water content lower than 10% and with one-fifth of the original volume. The dried biosolids can be utilized as fertilizer, alternative fuel for co-generation or disposed in landfill. There are two major types of thermal dryers to achieve Class A biosolids: direct and indirect dryer. Indirect dryer operates at lower temperature than direct dryer. The heat transfer medium is not directly in contact with the sludge which reduces the risk of fire hazard. Screw type indirect thermal dryer appears to be the most desirable type of dryer which carries all the advantages of indirect dryer and is able to produce granular pellet which can be used in fertilizer industry.