DryVac in Municipal Wastewater Treatment

We have over 40 DryVac installations worldwide handling a wide range of municipal and industrial slurries. In municipal wastewater applications the units are typically fed with sludge between 0.5% and 4% dry solids. This is mechanically dewatered in stage one of the process to between 20-30% dry solids. The mechanical dewatering process typically requires chemical treatment. Low-pressure steam (14 psi; 240 deg F) is then applied to the DEEM’s while a vacuum is applied to the filtrate ports, and the drying phase proceeds. The remaining moisture is "boiled" off in a process that can be halted at the desired moisture level. Depending on the type of sludge making up the feedstock a 40% dry solids cake can be achieved with a drying time of approximately 1.5 hours. To achieve 90% dry solids requires a drying time of between 3.5 to 4 hours. Pathogen kill is achieved during the drying cycle.  At the conclusion of the drying phase the DryVac equipment is opened up and the dried sludge drops to a conveyor/auger or into a skip below. Discharge of the press and preparation for the next cycle normally takes less then 30 minutes.
 
Activated Sludge
 
The processing of activated sludge is a common problem in wastewater treatment as it is difficult to dewater. Often it is mixed with other sludge prior to processing in an effort to improve its digestion and dewatering characteristics but this can result in an overall drop in sludge handling efficiencies.
 
By treating activated sludge in the DryVac process separately from other sludge it is possible to dry it to a level that makes economic sense. If required, the activated sludge can then be blended back with other sludge for the disposal route of choice e.g. incineration or land spread.

DryVac vs. Lime
DryVac can compete favorably with and overcome many of the negatives associated with the liming of sewage sludge.

The process is virtually odorless
From a health and safety viewpoint, the process is relatively simple with little risk
Dried product can be stored indefinitely
The potential to achieve higher dry solids means less cost of transport and disposal
Enhanced treatment is achieved with pathogen kill
Flexibility of disposal routes
Potential for CHP & sludge combustion applications with DryVac providing an excellent heat sink
Low temperatures and pressure eliminate health and safety concerns of other drying technologies