Reducing nitrogen pollution
The main aim of the process is to provide a more energy efficient way of breaking down the ammonia present in liquors from sludge treatment plants.

When sewage sludge is treated by digestion or drying, the liquid left over, known as return liquor, is usually recirculated back into the main treatment works. However, this liquor is very high in ammonia content, which presents an energy consuming, additional load for the works to process and often risks effluent consent failure.

The SHARON process involves diverting this liquor into an additional tank for treatment before it is re-circulated back to the works.

Energy efficient
In this tank, the liquor is kept at temperatures of 30°C to 40°C, which promotes the growth of the bacteria nitrosomonas that break ammonia (NH4) down into nitrite (NO2). This nitrite is then broken down into its components nitrogen and oxygen, enabling the nitrogen to be removed. The elevated temperature is not a problem because the liquors are frequently warm, or a low grade heat source is available and furthermore the process itself produces heat.

The temperatures in the SHARON process also reduce the activity of a competing bacteria called nitrobacter, which when present will turn the nitrite into nitrate (NO3). Nitrate requires a more energy intensive process for the works to remove. The formation of nitrate absorbs more oxygen and in being broken down into nitrogen and oxygen it requires more feed chemicals such as methanol or glycerol.

Uptake in UK
Commenting on the implementation of the United Utilities plant, Gordon Thomas, Principal Engineer at Grontmij, said, “With the increasing amount of sludge being processed in the UK there is a need for more return liquor to be treated.

“With this initial project now underway in the UK, we expect to see the technology spread throughout the country, because by treating the sludge liquors separately with an efficient process the loads on the main treatment works are considerably reduced.“

Technology developed by Grontmij
Grontmij began developing the SHARON technology in the early 1990s in partnership with Delft University of Technology and the Dutch water industry, following the introduction of the Urban Waste Water Treatment Directive in Holland, where all surface waters were defined as ‘sensitive’.
The EU Urban Waste Water Treatment Directive was adopted by member states in May 1991 and transposed into legislation across the UK by the end of January 1995. It sets treatment levels on the basis of sizes of sewage discharges and the sensitivity of waters receiving the effluent.

Environmentally friendly
Incorporating a SHARON plant reduces energy usage by 25% and carbon dioxide emissions by 20%, while converting to nitrite uses 40% less carbon source in the process than conversion to nitrate.