Tube settlers increase the settling capacity of circular clarifiers and/or rectangular sedimentation basins by reducing the vertical distance a floc particle must settle before agglomerating to form larger particles. Tube settlers use multiple tubular channels sloped at an angle of 60° and adjacent to each other, which combine to form an increased effective settling area. This provides for a particle settling depth that is significantly less than the settling depth of a conventional clarifier, reducing settling times. Tube settlers capture the settleable fine floc that escapes the clarification zone beneath the tube settlers and allows the larger floc to travel to the tank bottom in a more settleable form. The tube settler’s channel collects solids into a compact mass which promotes the solids to slide down the tube channel.
The treatment of sewage results in the production of solids commonly referred to as sludge. Sludge that has undergone dewatering or treatment is generally referred to as treated sludge. When the treated sludge is suitable for land application, it is referred to as bio-solids.
Holding tanks and basins may be used for blending materials such as sewage sludge from primary and secondary clarifiers. Tank and basin equipment often includes an aeration system, mechanical mixers or a recycling system for mixing.
Sludge conditioning affects the solids concentration of the thickened or dewatered sludge and the solids capture efficiency. The presence of colloidal particles increases the specific resistance of the sludge and adversely affects sedimentation processes. The net negative charge exhibited by most sewage sludge tends to make the particles repulse each other and thus resist agglomeration into larger particles. Sludge conditioning operations attempt to alter one or more of the above sludge characteristics so as to improve the efficiency of the solid-liquid separation processes. Sludge can be conditioned by physical methods, such as heat treatment or addition of fly ash or by chemical methods, involving the addition of either coagulants and/or polymers.
Chemical conditioning methods involve the use of organic or inorganic flocculants to promote the formation of a porous, free draining cake structure. Chemically conditioning the sludge involves coagulation and flocculation of the sludge fine particles to produce a filterable floc structure. When considering costs such as capital equipment, conditioning agents, transportation and handling of conditioning agents. Chemical conditioning, in most cases, will prove to be the most economical and by far is the most generally used method of treatment. Commonly used conditioners for sludge treatment are: Ferric Chloride, Alum, Lime, and Polyelectrolyte.
Sludge thickening normally refers to the process of reducing the free water content of sludge whereas, dewatering refers to the reduction of floc-bound and capillary water content of sludge.