sludge drying beds
Post on 12-Jul-2015
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Environmental Engineering Project Topic Sludge Bed Drying
Topic Sludge Bed DryingPresented and created by - Shankar Mujoo12ce 047
What is sludge ?
Sludge is a residual, semi-solid by-product left from industrial or refining processes. It is a separated solid suspended in a liquid, typically containing major quantities of interstitial water between its solid particles. What is sludge drying bed ? A sludge drying bed is a common method utilized to dewater sludge via filtration and evaporation. Perforated pipes situated at the bottom of the bed are used to drain seepage water or filtrate. A reduction of about 35% or less in moisture content is expected after drying
Purpose of sludge drying beds ?Sludge drying beds are provided to allow surplus sludge that is withdrawn from the process to dry for easier handling. Sludge drying relies on an underground drainage system as well as sunshine. Liquid from the underdrains should be returned to the sewage treatment process for further treatment. Sludge drying beds are usually situated beside treatment plants to readily receive and treat incoming sludge coming from primary or secondary treatment facilities.
In brief method.
A sludge drying bed usually consists of a bottom layer of gravel of uniform size over which is laid a bed of clean sand. Open jointed the underdrains are laid In the gravel layer to provide positive drainage as the liquid passes through the sand and gravel.
Under drains are made of vitrified clay pipes or tiles of atleast 10 cm dia. Laid with open joint.
The drying beds are usually 6 to 8 mt wide and 30 to 45 mt long. The sludge should be deposited evenly to a depth of not greater than 20 cm. when digested sludge is deposited on a well drained bed of sand.The major portion of liquid drains off in a few hours after which drying commences by evapouration .this produces cracks in sludge cake.In about 2 to 3 weeks sludge cake dries up completely with 20% to 40% volume reduction and can be removed.Sand and gravel underlying bed
Sludge treatmentSludge, produced from the treatment of wastewater, basically consists of two basic forms. Raw primary sludge and Secondary sludge.Here are some methods described that are most commonly used to process the sludge produced during wastewater treatment.Thickening
The sludge produced during waste water treatment has a water content between 97 % and 99.5 %. In sludge thickening, the dry and solid content of sludge is increased by reducing the water content with low energy input. This task is usually accomplished in a tank called a gravity thickener. The process of gravity thickening is one of the easiest ways to reduce the water content of sludge with low energy consumption. The process can reduce the total volume of sludge to less than half the original volume.
Dewatering aims to reduce the water content further so that the solids content of the sludge remains about 20 %. It can then be handled like a solid material. Dewatering can either be done mechanically using a filter press or by using drying beds. Sludge drying beds, however, provide the simplest method of dewatering. In the process, digested sludge slurry is spread on an open bed of sand after which drying takes place by a combination of evaporation and gravity drainage through the sand.
This is basically a thermal drying process where thermal energy is provided to the sludge to evaporate water. The process of drying sludge reduces volume of the product, making its storage, transportation, packaging and retail easier.
This process of drying sludge comprises of two methods- direct and indirect. However, these days the indirect thermal drying is becoming more popular as a means of decreasing sludge volume by removing the moisture content and attaining a dry solids content of 90%. The process reduces the environmental impact and produces a stabilized dry granular product that is easy to store, and deliver and suitable for agricultural use.
Formation of cake
Sludge Drying Applications
Dried or treated sludge offers a wide range of applications, mainly including agricultural land application. When the drying is completed to produce biosolids, these biosolids act as a fertilizer for crop harvesting. The organic nitrogen and phosphorous found in biosolids are used quite efficiently by crops as these plant nutrients are released slowly throughout the growing season. This allows the crop to absorb these nutrients as the crop grows.Besides the application of crop harvesting, the treated sludge can also be used as top dressing on golf course fairways, soil conditioner for construction of parks, and other athletic fields, a soil substitute in final landfill cover, etc.Sludge drying beds are suitable for treatment plants serving a population ranging from 1,000 to 20,000. These facilities exhibit reliability and good process flexibility. However, during the wet season, its efficiency decreases.Performance.In terms of its efficiency, while dried sludge is not fully disinfected, the solid content is increased to 50%70% of total solids. CostAmong the available sludge dewatering methodologies, investment cost for sludge drying beds is considered the lowest. For operation and maintenance, the only item to be considered is the labor cost.AdvantagesSludgedryingbedsaresimpletooperateandenergy-efficient .It presents the least cost technologyoption for dewatering sludge.DisadvantagesTreatment is required forseepagewater. Solar power is required. Thebeds are prone to odor and insect problems.