A common operational problem with advanced AD plants is high loading of digesters, and indeed partial overloading in some cases. A high concentration of dry solids and high viscosity can result in gas entrapment.
This, in turn, increases the associated GHG emissions – and direct emissions contribute a major share of a WwTP’s carbon footprint. The methane emissions exceed the total indirect emissions from a WwTP.
Utility company Dwr Cymru Welsh Water and water technology firm Eliquo Hydrok have partnered to test a new approach to tackling these kinds of operational problems with AAD. They installed an EloVac®-P Pilot Plant at Five Fords WwTW near Wrexham. The EloVac pilot scale trial ran for around 12 weeks over April-June.
The main motivation for the trial was to mitigate the excess foaming present in the digesters of the AAD plant.
To mitigate the problems caused by foam generation, they varied the operating conditions of the plant.
Despite the inconsistency of the digestate density, the group said the sludge discharged from the EloVac® was consistent in quality and high density, with virtually no foam present.
The EloVac®-P Pilot Plant can process up to 20 m3/hour of digested sludge. By removing entrapped gas bubbles and dissolved gas, it is possible to increase digestate density, and avoid or reduce the use of expensive anti-foam chemicals. This, in turn, improves digester mixing efficiency.
Dwr Cymru Welsh Water says the results of the pilot EloVac®-P trial are being assessed for possible incorporation into the process at Five Fords and other AAD sites run by the utility.
