How Hamilton’s Woodward Avenue WWTP Reduced Struvite Damage in Sludge Dewatering
Struvite can turn a routine sludge-dewatering process into a costly maintenance problem. Deposits can obstruct centrate lines and ports, accumulate inside centrifuges and contribute to damage on high-value rotating equipment. At the City of Hamilton’s Woodward Avenue Wastewater Treatment Plant, those impacts had become frequent and expensive.
A three-month HydroFLOW evaluation was undertaken to determine whether physical water treatment could reduce hard struvite accumulation and make any remaining deposits easier to manage. The reported operating results led the plant to retain the trial unit and expand treatment to additional centrifuges.
Key result Hard struvite no longer accumulated sufficiently to block the treated centrifuge’s ports and piping. Material that remained was reported to be substantially softer and removable with power washing. |
Why struvite is a serious wastewater maintenance issue
Struvite is magnesium ammonium phosphate hexahydrate. In wastewater facilities, the combination of magnesium, ammonium and phosphate can become supersaturated, particularly in and downstream of anaerobic digestion. Changes in pressure, turbulence, pH and carbon dioxide concentration can encourage precipitation around pumps, valves, centrifuges and centrate piping.
The problem is not only the presence of mineral solids. It is where those solids form and how strongly they adhere. Hard crystalline deposits can restrict flow, interfere with dewatering equipment and require mechanical or chemical cleaning.
The challenge at Woodward Avenue WWTP
Woodward Avenue is a large conventional activated-sludge facility with sludge digestion and dewatering. Its digester complex processes primary sludge and thickened waste activated sludge through multiple anaerobic digesters. Dewatering was performed using four Alfa Laval G2 centrifuges.
According to the project case study, struvite created several recurring problems:
- Blockage and buildup in centrate discharge piping and centrifuge ports.
- Deposits inside the centrifuges after as little as approximately 400 operating hours.
- Abrasive interaction between hard deposits and metal surfaces, damaging the slot ring and centrifuge barrel.
- Labour-intensive shutdowns, hand cleaning and power washing.
- Periodic off-site barrel rebuilding, reported to cost more than $70,000 per rebuild and require weeks of downtime.
HydroFLOW installation and trial design
A HydroFLOW i160 unit was installed on a six-inch stainless-steel sludge feed pipe approximately six feet upstream of one centrifuge. The clamp-on installation did not require cutting the pipe or adding treatment chemicals.
The evaluation ran for three months. Plant personnel used existing electronic monitoring and regular physical inspections. Success was assessed primarily through the amount, density and operational impact of struvite accumulation. Polymer optimization was not part of this trial.
Reported operating results
The case study reported a material change in the character and impact of the deposits after HydroFLOW was installed:
- Struvite no longer accumulated to the point of blocking the treated system’s ports and piping.
- Remaining material was substantially softer and could be removed more readily with a power washer.
- The centrifuge could operate for longer periods before maintenance was required.
- Damage to the slot ring and centrifuge barrel was largely eliminated.
- Annual maintenance and repair savings were estimated by the project team at more than $50,000 per centrifuge, with an estimated payback of less than one year per unit.
After the trial, the City purchased the evaluation unit and subsequently purchased additional HydroFLOW i160 units. The intent was to protect all four centrifuges as they returned to service.
“I put my backside on the line to try this technology and I am very pleased with the results; it has done what we were told it would do.” — Mechanical Supervisor, City of Hamilton (as quoted in the project case study)
What the Hamilton result means for other wastewater facilities
The project provides a useful operating precedent for facilities experiencing struvite in anaerobically digested sludge, centrifuges and centrate systems. It also illustrates an important technical point: successful scale control may mean changing hard, adherent deposition into softer material that can pass through or be removed with less labour—not necessarily removing the dissolved mineral constituents from the process.
Every plant has different chemistry and hydraulics. Phosphate, magnesium, ammonium, pH, alkalinity, temperature, chemical dosing, sludge characteristics and equipment configuration should all be reviewed before selecting a unit or installation point.
A practical evaluation approach
For facilities with parallel dewatering trains, a treated-versus-untreated comparison can provide a practical trial structure. Useful measures include:
- Operating hours between cleaning events.
- Location, thickness, hardness and mass of deposits.
- Centrate flow, pump performance and differential pressure where available.
- Cleaning labour, chemical use and maintenance downtime.
- Wear, repair and replacement costs for affected components.
Discuss your wastewater scaling application
HydroFLOW Canada evaluates struvite, calcium carbonate and other mineral-deposition problems in municipal and industrial wastewater systems. Our team can review process flow, water chemistry, piping and operating history to identify whether a controlled evaluation is appropriate.
Contact HydroFLOW Canada at info@hydroflow.ca or 1-877-477-3569 to discuss an application.
Source and evidence note
This article is based on the HydroFLOW Canada case study “HydroFLOW Canada Struvite Reduction Study — Woodward Avenue WWTP, Hamilton, Ontario.” The results are specific to this installation and should not be interpreted as a guaranteed result for every facility. Site-specific engineering review and trial design are recommended.