Shafted Screw Conveyors for Transferring Biosolids City of Holland, MI
End User or OwnerHolland Board of Public Works
Holland, Michigan
Fishbeck, Thompson, Carr & Huber, Inc.
Grand Rapids, Michigan
Davis Construction
Lansing, Michigan
Holland WWTP
Holland, Michigan
General Description
The Holland Board of Public Works (BPW) provides electricity, water filtration/supply and wastewater collection/treatment for nearly 28,000 customers in and around Holland, MI. The system has grown tremendously in size, technology and reliability. The Holland BPW maintains all of the sanitary sewer collection system south of Lake Macatawa and the Macatawa River. This system contains nearly 190 miles of sanitary sewer pipe and 34 sewage lift stations. While the system is mostly within the City of Holland, it also includes portions of Park, Laketown, Fillmore and Holland Township.
The Holland Wastewater Treatment Plant (WWTP) has a hydraulic loading capacity of 12 million gallons per day (MGD). On an average day, about 9 million gallons per day (MGD) of wastewater is processed by the plant. Once in the facility, the influent is treated in several stages. The primary stage includes routing the wastewater to primary treatment clarifiers where about half of the pollutants in the wastewater are removed. The next step, secondary treatment, includes using biological and gravity treatments to bring the level of pollutants removed to over 85-percent. This meets all discharge permits issued by the EPA and DNRE and allows the treated wastewater to be released to Lake Macatawa.
The City of Holland required a new dewatering and truck loading facility. Screw presses were selected as the dewatering technology. Four screw presses were required to meet the capacity requirements. KWS Environmental interfaced directly with the screw press manufacturer and provided shafted screw conveyors to transfer dewatered biosolids from the screw presses to two progressive cavity pumps. The pumps then transferred the biosolids to one of four dumpster loading bays.
Design Parameters
- Product Type: Dewatered Biosolids
- Material Density: 55 to 60 Lbs. per Cubic Foot
- Solids Content: 23-Percent Total Solids
- Capacity: 105 Cubic Feet per Hour (per Screw Press)
- Duty: 24 Hours per Day, 7 Days per Week
KWS Advantages
KWS Environmental worked directly with the consulting engineer to develop a solution that met the Customer’s primary design objectives; redundancy, reliability and minimal maintenance. The complete system needed to be automated with minimal operator intervention for daily operation and housekeeping. As a custom manufacturer of engineered equipment, KWS Environmental provided experience and design expertise to ensure that all of the Customer’s needs were fulfilled.
KWS Environmental supported the installation, commissioning and training by providing a qualified and registered engineer familiar with the project, design requirements and equipment delivered.
Special Features
The shafted screw conveyors were located near the ceiling with very limited access for maintenance. KWS Environmental designed the shafted screw conveyors to be reliable with minimal maintenance downtime and direct access to maintainable components. Shafted screw conveyors were chosen because of their superior reliability when compared to shaftless screw conveyors. Shaftless screw conveyors require maintenance and replacement of trough liners and there was no room to access the conveyor for this type of maintenance. Each shafted screw conveyor was mounted on an oversized center pipe to reduce the number of intermediate bearings. Only two KWS Tor-Ri-Flex intermediate bearings were required.
The intermediate bearings were accessible through a door for periodic inspection and maintenance. The intermediate bearings and end bearings were automatically lubricated by a central lubrication pump system with reservoirs located at floor level with easy access. The automatic lubrication system provided grease to all bearings at timed intervals and was controlled by the KWS supplied control panel.
Engineers from KWS Environmental worked closely with the consulting engineer to locate the hanging supports for the screw conveyors. The area around the screw conveyors was very congested with piping and other equipment.
Each shafted screw conveyor was equipped with an automatic wash-down system for cleaning out residual biosolids. The wash-down system could be initiated at the local control station at floor level.
KWS Environmental also supplied a control system that integrated with the screw press and pump systems for seamless continuity of essential interlocks and sequencing control logic. Continuous monitoring information is provided to operators that facilitate operation and maintenance.
