Lower Mainland BC WWTP: Dry Polymer Make-Down Systems
Two dry polymer make-down systems for a large regional wastewater treatment plant in the Lower Mainland, BC: a new DAF thickening polymer system in 2019 and an upgrade of the centrifuge polymer system in 2025–26.
The application
The plant, a large regional wastewater treatment plant in the Lower Mainland of BC, thickens its sludge with dissolved air flotation (DAF) and dewaters it with centrifuges. Both steps run on polymer made down on site from dry powder.
In 2018 the plant replaced its DAF polymer system. The new system had to work like the existing centrifuge polymer system, so that each could back the other up, and it had to take 750 kg bulk bags lifted by the existing monorail hoist instead of 25 kg sacks. In 2023 the owner turned to the centrifuge polymer system itself. Archer proposed keeping most of the existing bulk bag frame and hopper and rebuilding everything below it: a new feeder, a new wetting stage on the existing mix tank, a booster pump skid and new controls, all fitted into a small room on the existing slab.
What Archer supplied
2018–2019: DAF polymer system
- Hapman bulk bag unloading frame for the plant hoist, with bag agitator paddles, a 12-inch iris valve and an access chamber so the operator unties the bag spout before powder flows
- Hapman volumetric screw feeder with a stainless extension hopper, dust sock and level sensor
- Wetting cone and stainless eductor skid with a booster pump, automatic valves and a flowmeter
- Kozegho HDPE mixing tank with a top-entry mixer, and a separate ageing / feed tank
- Local control panel, valves and instruments, shop drawings, manuals, start-up and commissioning
2024–2026: centrifuge polymer system upgrade
- New powder-coated bottom frame under the existing bulk bag frame and stainless hopper
- Schenck volumetric screw feeder with a heated barrel and a pneumatic stopper that seals the discharge when it stops
- Stainless solids-handling eductor mounted on the existing mix / ageing tank, fed through the old air-conveying line, now a vacuum line
- Booster pump skid with pressure regulation, flowmeter and motorized valve; Schedule 80 PVC service water piping
- Ultrasonic level transmitter for the mix tank, capacitance level switch for the hopper, actuated tank outlet valve
- NEMA 4X stainless control panel with a PLC, 15-inch touchscreen and Modbus TCP to the plant control system
- Bulk bag on the bag unloader frame
- Bag unloader discharge hopper (stainless)
- Volumetric screw feeder, stainless
- Feeder support frame (galvanized)
- Vacuum conveying line, 1-1/2″ stainless
- Clear wire-reinforced suction hose
- Eductor (stainless) – polymer wetting
- Polymer drop pipe into the tank (not visible in this view)
- Booster pump skid (vertical multistage pump)
- Service water line to the eductor, PVC Sch 80
- Polymer mix / ageing tank (FRP)
- Top-entry mixer (motor, gearbox, impeller)
- Tank outlet valve, actuated
- Ultrasonic level transmitter
- Local control panel
- Service water tie-in and isolation valve
- Feeder air panel (filter-regulator, solenoid)
Design basis
| Product | Polymer solution 0.1–0.5 %, made in batches from dry powder (about 700 kg/m³) |
|---|---|
| Powder supply | 750 kg bulk bags, lifted by the existing monorail hoist |
| Mixing | Two stages: eductor at G ≈ 10,000–12,000 /s, then gentle tank mixing at about 110 rpm |
| Batch time | A batch made within 15 minutes, leaving about an hour for ageing |
| 2019 feeder | Volumetric screw feeder, 28–396 L/h |
| 2019 wetting | Wetting cone and eductor, 13.4 USGPM water at 50 psig |
| 2019 tanks | HDPE mixing tank Ø1500 × 1700 mm with a 2.2 kW, 700 mm propeller mixer; separate ageing / feed tank sized for about 80 minutes at average DAF and centrifuge demand |
| Upgrade feeder | Volumetric screw feeder, polymer at 40–50 kg/h (60–70 L/h) |
| Upgrade eductor | 1-inch 316L solids-handling eductor, 220 L/h dry capacity with 10 ft vertical vacuum lift |
| Service water | 2–3 m³/h at 4–6 bar (upgrade) |
Design figures from the equipment submittals.
Engineering
- Heated feeder barrel checked with a thermal finite element model: it keeps the powder outlet warm and dry so the polymer does not cake
- Seismic assessment of the bulk bag support frame with a finite element beam model to NBC 2020 / BCBC 2024 and CSA S16-19, including the base plate anchors
- Eductor placed on the tank, away from the feeder, so warm water can be used without condensation at the screw
- Full 3D model of the room, equipment, piping and cable routing, used for the layout, the drawings and the renderings
- Bulk bag (FIBC) of dry polymer
- Bulk bag unloader frame with bag lifting frame
- Pneumatic bag massagers
- Bag discharge and volumetric screw feeder
- Wetting-cone skid: wetting cone, booster pump, actuated valves
- Solution and dilution-water lines to the mix tank (PVC Sch 80)
- Mix tank with top-entry mixer
- Transfer line to the feed tank (actuated outlet valve at the mix tank)
- Feed (storage) tank
Numbered view of the system.
Related: Polymer Systems · DAF / Dissolved Air Flotation Systems · Decanter Centrifuges · Control Panels · Municipal Water and Wastewater · All case studies