Even where fine screens are installed in the head works of wastewater treatment plants, some debris will always end up in the sludge. Plastic parts and fibrous materials can severely disturb the operation of thickeners, digesters and dryers. Such solids impair the operation of pumps, heat exchangers, mixers, dewatering systems, pelletizers, etc. Hair and fibers often lead to the formation of tresses and grease balls. Where biosolids are land-applied, plastic parts should be removed.
In the early 1980s, engineers of the Swiss company Picatech-Huber AG invented and developed an inline sludge screen, the Strainpress. The Strainpress is manufactured by Huber SE and is supplied and serviced by Huber Technology Inc. in North America.
Sludge is pumped into the Strainpress’ perforated tube and flows through the perforations into a casing while debris is retained within the tube. An internal screw pushes the retained screenings along the tube’s axis into a conical dewatering and compressing section that is provided with a smaller perforation compared to the screening section.
A pneumatically operated cone, installed at the press zone’s discharge end, keeps the discharge opening closed and generates a back pressure. After a screenings plug has formed, preventing sludge flow towards the discharge end, and has been sufficiently pressurized by the screw’s movement, it pushes the cone back, and some dewatered and compressed screenings are discharged and drop into a container or bag. The screw’s flights keep the screen clean. No wash water is needed.
Huber Technology Inc.