Hagerstown WWTP Biosolids Upgrade Phase 1B – DAFT Rehabilitation

Key Accomplishments

Johnston Construction Company

• Removed major portions of the existing thickening infrastructure before reconstruction, including flotation-thickener equipment and piping, digester-feed pumps and pads, HVAC equipment, chillers, air-scrubber equipment and pads, building-entrance concrete, handrails, gratings, miscellaneous concrete and masonry.
• Installed the new thickened-sludge pumping and process-piping systems, including two plunger pumps designed for thickened primary and waste-activated sludge service at approximately 210 gpm and 40.6 feet total dynamic head, together with pump pads, piping, a sump beneath the dismantling joint, valves, supports and associated process connections.
• Installed and coordinated odor-control and HVAC improvements, including odor-control ductwork, supports and expansion joints, floor-drain piping, fans, heaters, louvers, motor-operated dampers, registers and associated ventilation components serving the rehabilitated DAFT area.
• Integrated the final gas-detection system into the rehabilitation, with the project specifications originally requiring methane detection within the flotation-thickener area. JCC’s accepted value engineering revised the design to two sensors/transmitters and a Gasgard XL controller, reducing the original specified sensor quantity while retaining combustible-gas monitoring for the renovated process area.
• Managed rehabilitation within an operating wastewater treatment plant while maintaining continuity of biosolids processing. The existing dissolved-air-flotation system could not be taken offline until the temporary thickening system was operational, and the DAFT outage was limited to 90 days under the specifications. JCC coordinated temporary sludge conveyance, facility outages, sequencing and access while Synagro provided and operated the temporary thickening equipment.
• The project rehabilitated the plant’s existing dissolved air flotation thickening process used for biosolids treatment. The new DAFT system was designed to co-thicken primary sludge and waste activated sludge on a continuous basis, receiving approximately 194,500 gallons per day and approximately 19,037 pounds per day of solids. The process was designed to produce approximately 4% thickened solids while achieving a specified 90–95% solids capture rate with chemical flotation aids.
• JCC coordinated installation of the new DAFT equipment supplied through Synagro. The complete system incorporated thickener internals, a surface skimmer, bottom and settled-sludge collection systems, sludge-underflow pumping, a pressurization system, motors, controls and associated accessories. The installation specification assigned JCC responsibility for coordinating, scheduling, unloading, storing, installing, testing, training and startup of the furnished equipment.
• Process improvements extended beyond the thickener itself. JCC’s subcontract included new flotation-thickener piping, thickened-sludge pumps and pads, sump work, flow measurement, ultrasonic level sensing, gas detection, odor-control ductwork, handrails and grating. Two thickened-sludge plunger pumps were specified for approximately 210 gpm each at 40.6 feet of total dynamic head for handling thickened primary and waste-activated sludge.
• JCC’s overall subcontract also carried coordination of the electrical package required to support the process rehabilitation, including the 600A, 480V MCC-DAFT, GP-DAFT and PP-DAFT panels, GT-DAFT transformer, disconnects, lighting and conduit/wiring for power, HVAC and instrumentation. Detailed electrical trade work will be documented separately under the ESD job sheet, while the JCC sheet reflects JCC’s contractual responsibility for integrating those systems with the civil, mechanical and process work.
• Maintaining plant operations was a major construction constraint. The existing DAFT system could not be removed from service until Synagro’s temporary thickening system was tested and operational. The specifications limited the planned DAFT outage to 90 days and required continuity-of-service planning, temporary conveyance of sludge, coordinated shutdowns and prompt return of the rehabilitated system to operation.
• Testing and startup were integral to project completion. JCC coordinated preliminary field tests, functional testing, PCS/SCADA programming support, system demonstration testing and startup with GHD, the City, Synagro and the DAFT equipment supplier. Final performance verification included TSS testing and demonstration of long-term operating performance in accordance with the DAFT specifications.
• The Project Was Completed On 28th August, 2019

Electrical Services Division

• Electrical Services Division, LLC performed the major electrical trade package for the Hagerstown WWTP Biosolids Upgrade Phase 1B – DAFT Rehabilitation. ESD furnished the labor, materials, tools, equipment and supervision required for electrical construction in accordance with the project’s Division 16 specifications and electrical drawings E-001 through E-015.
• Furnished and installed the electrical power-distribution infrastructure serving the rehabilitated dissolved air flotation thickening process, including power conduit, conductors, wiring, connections, panel GP-DAFT, panel PP-DAFT, transformer GT-DAFT, switchgear, disconnect switches, boxes, devices and associated electrical equipment.
• Installed the project's instrumentation raceways, wiring and electrical connections, providing the field-side electrical infrastructure required to connect process instrumentation and control equipment with the DAFT control architecture. ESD's subcontract specifically included instrumentation conduit, wire and connections while excluding the furnishing of the instrumentation devices themselves.
• Completed motor-control and process-equipment electrical connections for the DAFT system, coordinating local control stations, motor starters and control wiring serving equipment such as the surface skimmer, bottom scraper, sludge-underflow pumping equipment and pressurization pumps. The DAFT controls exchanged equipment run status, fault alarms, start commands, speed signals and process information through the MCC and control system.
• Worked with the new MCC-DAFT power and control system, which was specified as a 480/277-volt, three-phase, four-wire, 60-Hz system with a 600-amp horizontal bus. The MCC provided motor-control and VFD interfaces serving major DAFT process equipment and incorporated remote monitoring and control functions required by the process-control system.
• Performed substantial electrical demolition and reconstruction within the existing Operations Building, including disconnection and removal of existing DAFT motors, control panels, junction boxes, disconnect switches, conductors, raceways and lighting, together with rerouting and modification of circuits necessary for the new installation.
• Installed electrical systems serving lighting, HVAC and related building equipment, including conduit and wiring for lighting, motors, unit heaters and HVAC equipment, as well as electrical connections to equipment furnished by other trades.
• Performed electrical work in demanding wastewater-treatment environments. The Flotation Thickener Room was designated as a wet, corrosive and Class I, Division 1 hazardous location, requiring electrical equipment and installation practices appropriate for both the hazardous and corrosive operating conditions.
• Coordinated installation, inspection, testing and startup within an operating wastewater treatment facility. The specifications required electrical work and shutdowns to be carefully scheduled to minimize impacts on continuing plant operations, while ESD's subcontract included electrical permitting, inspection, testing, shop drawings/submittals and startup assistance.
• ESD's subcontract covered a substantial portion of the electrical systems required to support rehabilitation of the dissolved air flotation thickening process. The work included power conduit, conductors and connections; instrumentation conduit and wiring; GP-DAFT and PP-DAFT panels; transformer GT-DAFT; switchgear; disconnect switches; lighting; HVAC and process-equipment wiring; electrical equipment connections; permitting; submittals; inspection; testing and startup assistance.
• The Division 16 specifications required the electrical construction to provide complete operating systems incorporating power distribution, lighting, controls, instrumentation, raceways, conductors, cables, wiring devices, starters, overcurrent protection, grounding, terminations and interconnections. ESD coordinated these systems with JCC and the other project trades as the existing DAFT facility was demolished and reconstructed.
• Electrical demolition was a significant component of the work. Existing DAFT motors, control panels, junction boxes, disconnect switches, raceways, conductors and lighting were disconnected and removed or modified as necessary. Existing circuits affected by the rehabilitation were traced and rerouted, while equipment and electrical systems remaining in service had to be protected throughout construction.
• Power and motor-control work supported the new DAFT process equipment. The project incorporated MCC-DAFT and its associated motor-control and VFD functions, along with GP-DAFT and PP-DAFT panels, transformer GT-DAFT, switchgear and equipment disconnects. The specified MCC electrical system operated at 480/277 volts, three-phase, four-wire, 60 Hz and provided the interfaces required for equipment operation, protection and remote control.
• Instrumentation and SCADA/PCS integration were important elements of the rehabilitation. ESD's subcontract specifically included instrumentation conduit, wiring and connections. The process controls incorporated equipment operating status, common alarms, VFD faults, start commands, speed references and feedback, magnetic-flow-meter signals, pressure and level instrumentation, and signals associated with the existing plant PLC.