Need

Lamerton Wastewater Treatment Works (WwTW) near Tavistock in Devon, serves 590 people and consists of a primary settlement tank, trickling filters and a humus tank. The Environment Agency (EA) tightened the phosphorous discharge consents from X mg/l to X mg/l to aid the prevention of algal growth and subsequent eutrophication of the River Tamar the receiving water. reduce the level of acceptable phosphorus found in wastewater. Phosphorus is essential for the growth and health plant life, but too much of it in a watercourse can promote excessive algae growth; this in turn depletes the water’s quality and oxygen levels, harming plant and water-based life.

The previous bed would require an upgrade to meet the Environment Agency’s new standards. When planning the bed’s refurbishment, it was noted that the system could not be expanded outward; any treatment method would need to accommodate this space restriction.

Solution

ARM’s ARMPhos™ wastewater treatment was selected because of its previous effectiveness at treating phosphorus in Wilmington. Part of the civil engineering works saw the secondary containment system being raised by 1000mm to reduce flood risk.

This bed is situated lower than the main treatment works and is optimised to reduce size and costs; high-concentration, low-flow sewage will pass through the ARMPhos bed for phosphate removal, while high volumes of low-concentration wastewater will bypass the bed and mix with treated water in the level control chamber before discharge.

The bed is regularly inspected, and ARM’s recommendation for refurbishment is every 7 years.

Performance

Upon its successful installation, the bed provided excellent treatment; the phosphorus level dropped from 7.06mg/l to 0.355mg/l, a 95% reduction. This level of phosphorus was far below the maximum treatment level of 2.5mg/l, ensuring that it could handle larger loads of phosphorus if the population it served expanded.

Additionally, the bed was able to drastically reduce the levels of other contaminants in the influent; BOD (biological oxygen demand, or how much oxygen is needed to begin the reedbed process) was reduced by 35% to 11mg/l, lead was reduced by 81% to 0.0007%, and magnesium by 56% to 0.0555.

Benefits

The ARMPhos™ solution is an innovative development of SVF treatment wetland technology

incorporating a processed reactive media to ensure consistent, long-term P removal to meet new and increasingly stringent regulatory treatment requirements.

  • Consistent long-term P removal/capture

  • No elevation of pH, typical of alternative reactive medias

  • Passive operation and low maintenance requirements

  • No chemical dosing or routine sludge management requirements

  • Saves up to 80t CO2 equivalent over 40-year operating period compared to chemical dosing

  • Green solution creating habitat with high biodiversity value

  • Potential for P recovery to create a more sustainable circular economy