Designers should consider the odor and aerosol/humidity control of all thickening techniques. Regardless of where the Thickener Tank is installed, special consideration should be given to the need for sludge pretreatment in the form of sludge grinding to avoid clogging of pumps, piping and thickening equipment. In addition, where ventilation is required, adequate ventilation and odour control is required to comply with all applicable codes.
Sludge has several characteristics, including industrially derived components, which may adversely affect attempts to achieve solid-liquid separation. The presence of colloidal particles increases the specific resistance of the sludge and adversely affects the settling process. Most of the sewage sludge exhibits a net negative charge that tends to repel the particles to each other, thereby resisting aggregation into larger particles. The sludge granules have a combined water content which, if retained, results in a low cake solids after solid-liquid separation. Sludge conditioning operations attempt to alter one or more of the above sludge characteristics to increase the efficiency of the solid-liquid separation process.
Sludge concentrates that reduce sludge volume should be considered to reduce the required biogas tank capacity. Thickeners (gravity, dissolved air flotation, centrifuges, gravity belt thickeners, drum screens, etc.) should be designed to take into account the type and concentration of sludge, downstream sludge stabilization processes, dewatering and storage requirements, and final sludge. Treatment methods, chemical requirements and operating costs.
For most thickening operations and belt filter press dewatering operations, the most common conditioning chemical is a polymer. For dehydration by vacuum filtration, iron salts are most often used and are usually used with lime. Chemical conditioning using polymers is most common in centrifugal dewatering, avoiding the use of metal salts primarily due to corrosion problems. For dewatering by a filter press, high molecular weight polymers have been successfully used for sludge conditioning in place of lime and ferric chloride.
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