CONVOX® – New BNR solution from Plantwork Systems

All the UK water companies are under pressure to meet new discharge permit levels in place for AMP8 (Asset Planning Period starting April 2025) set by the Environment Agency.

Discharge Permits for many Sewage Treatment Works have been tightened over recent years and are expected to continue tightening due to the effects of climate change, population increase and public pressure.

Both Phosphorus and Nitrogen are recognised as pollutants in rivers and other water bodies as they are nutrients that encourage the growth of algae leading to depletion of oxygen in the water.

The ‘Oxidation Ditch’ was a popular design of activated sludge plant for a period in the second half of the twentieth century so there are many of these in use in the UK. However, many of these are not meeting the new required consent levels.

Alternative processes for removal of Phosphorus and Nitrogen require chemical dosing.

The problems with chemical dosing are:

· Chemical dosing is costly

· The chemicals themselves present health and safety risks, which have to be mitigated

· The chemical dosing increases the quantity of sludge produced that needs to be further treated and disposed of

· Where iron/aluminium is dosed to remove phosphorus the Environment Agency will set limits for the amount of iron/aluminium in the treated water

· There are sewage works that achieve the required level of phosphorus by dosing metal salts, but then fail their discharge permit by exceeding the permitted level of iron or aluminium

The Solution – CONVOX®

Plantwork System’s CONVOX® is the conversion of an existing activated sludge sewage treatment works to Biological Nutrient Removal.

Using CONVOX® we can remove phosphorous without any chemical dosing. Biological Nutrient Removal in activated sludge plants is a recognised way to remove both Phosphorus and Nitrogen.

There are many continuous flow activated sludge treatment plants in the UK and PWS can offer the experience we have gained developing and operating our NUTREM BNR solution, to design upgrades for these existing activated sludge works.

The Results

At South Tawton, the resulting performance very comfortably exceeds the permit level for Phosphorous. South Tawton is our first installation of CONVOX, for South West Water, and is based on an oxidation ditch. The principles of CONVOX can be applied to all types of activated sludge plants.

CONVOX® offers huge benefits:

Let Plantwork Systems help you meet your AMP8 targets…  get in touch for more information.

Article by Robert White, PWS Managing Director