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Design of Sludge Drying Bed

Executive Summary

 Sludge drying bed (SDB) is the most widely used method for sludge dewatering.Sludge drying involves natural ways of drying to mechanical ways of removing water content.SDB is generally used for small and medium sized communities.The selection of the technology will depend upon land availability,climatic factors,the quantity and composition of the sludge.The construction of this is usually undertaken with civil structure.

               Advantages                                                             
               

    
    1.Easy to operate                                              


    2.No electrical energy required                         


    3. Organic content can be used as fertilizers      

                                                                            

                                                                            

           Disadvantages

1.Requires stabilised sludge to prevent nuisance and odours  

 2.Technology is land intensive 

 3.Climatic fluctuation may cause disturbance

 4.Clogging of sand bed  

 5.Only applicable during dry seasons.                                                                              

Design and Construction Principle


                                                           Design of a Sludge drying bed

The prediction of the drying rate is an empirical part of the designing the system.Drying of the sludge can be divided in to two different stages,namely drainage and evaporation.The design if SDB is based mainly on site specifications,as well as environmental and climatic factors.The sizing of the sludge drying beds should be done considering the worst case scenario.The loading is based on per capita basis or on a unit loading of pounds of dry solids per square foot per year.There are mainly five types of sludge drying methods viz. conventional sand beds,paved drying beds,artificial media beds,vacuum assisted and solar.The typical conventional SDB has dimensions of 6m width,6-30m length,with sand layer ranging from 230-300mm depth. The sand should have a uniformity coefficient of not over 4.0 and effective size of 0.3 to 0.75 mm. The piping to the sludge drying beds should be designed for velocity of at-least 0.75 m/s. The sludge is placed on the bed in 20-30 cm layers and allowed to dry. Sludge cake removal is manual by shovelling into wheel-barrows,trucks,scraper,or front-end loader. The drying period is 10-15 days, and the moisture content of the cake is 60-70%. Sludge loading rate is 100-300 kg dry solids/m2/year for uncovered beds. 

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