“FROM CONVENTIONAL DRYING BEDS TO HIGH RATE, HIGH CAPACITY VACUUM DEWATERING BEDS”
Abstract:Minimal draining, decanting, and evaporative drying have been the predominant factors determining performance of the well known lagoon, conventional sand drying bed and evaporation bed process. Previously, the “rule of thumb” design procedure determined the sizing of these beds. Fortunately, more rational design factors were established from experience and published in “MOP 20, l983”, resulting in facilities with proper capacity.
Efforts to improve the under drainage in the bed type device have been made over the years, but none have been made as durable as the rigid, porous, epoxy- bonded, aluminum oxide surface which is guaranteed for 20 years.
Attempts at increasing the dewatering rate by applying pressure to the beds have been attempted but only vacuum has proven to be feasible. Early generations of the vacuum bed have applied 8 - l0" Hg, but the current design allows for 24 - 26" Hg vacuum. This has resulted in higher capacities and dryer cakes, in a shorter cycle time.
Case studies will be presented for this low energy, simple technology system that has over 18 years experience on various types of sludges at over 180 locations.
Prior thickening of water plant residuals and biosolids digestion is also addressed as being important for any type of drying bed and mechanical dewatering. Consideration must be given to the final disposition of the resulting cake, be that land filling or beneficial use.
Document Type: Research Article
Publication date: January 1, 2000
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