Afan WwTW, Digester Degrit and Tank Inspection

Afan WwTW, Digester Degrit and Tank Inspection

Afan WwTW, Digester Degrit and Tank Inspection

Dŵr Cymru Welsh Water (DCWW) engaged Marches Biogas to manage the decommissioning, pump down, grit removal, tank inspection, future proof tank with foam relief systems and re-commissioning of the two digesters on site at Afan WwTW, Port Talbot. The digesters contained high levels of grit which was affecting the operation of the mixing system, the biological stability of the digesters and caused the reduction in their operational capacity. 

The digesters were removed from service consecutively to ensure that sludge processing capacity was maintained throughout the project.  Marches Biogas performed the role of Principal Contractor managing SludgTEK and Celvac, the main sub-contractors used to dewater tank liquors and empty and cleanout of the tanks.

Prior to removing the digester contents, Marches Biogas purged each digester with Nitrogen before setting up forced air ventilation fans to ensure that the head space composition was continually managed and safe  SludgeTEK were then contracted to pump down the contents of the digester via a mobile centrifuge; this was followed by the removal of the heavier material by Celvac, which was passed over their degritting screens. The digester was fully cleaned including the mixer lances and recirculation pipework.

Marches Biogas were then able to carry out a visual conditional internal and external tank survey using a drone-mounted camera alongside civil engineers from Pebble Engineering.  The use of a drone saved significant time and expense associated with full tank scaffolding, traditionally used for structural surveys. 

Once any remedial works were completed the discharge of the operational digester was diverted into the newly cleaned tank to reseed the digester.  The headspace was Nitrogen purged back into service and the feed rate was gradually increased to full output before taking the other digester offline to repeat the process. 

Marches Biogas had a dedicated Site Manager throughout the works who co-ordinated the project with all sub-contractors and worked closely with DCWW Site Operators to ensure that the project ran smoothly and efficiently.


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