BioWin modelling to reduce the Avonmouth digester commissioning programme from 6 months to 6 weeks

Forgacs, G.1, Smyth, M.1, Law, I.2 and Arnot, T.3, 1 Aqua Enviro, UK, 2 Wessex Water Enterprises trading as GENeco, UK, 3Water Innovation & Research Centre, University of Bath, UK


In this study a novel accelerated restart strategy has been developed for a two stage anaerobic digestion
system, involving acid phase digestion of sewage biosolids, followed by mesophilic digestion. The strategy
involves start-up of the acid phase process, and then restart of the secondary mesophilic digesters, following a feed starvation period, and without re-inoculation. Process simulation with BioWin 4.1 software was coupled with continuous lab-scale trials to inform a full sized trial, which in turn defined the full plant restart schedule.

Biosolids feed shut down period, and feed loading and feed acceleration rates were explored via lab-scale
trials and simulation. The lab and simulation trials lead to the proposal of a 21 day restart profile for start-up and recovery of the two-stage anaerobic digestion process at Avonmouth. This profile involved an initial feed load of 39% of the normal steady-state flow, and a 5% daily feed flow ramp up rate, following a 3 week
starvation period. This accelerated restart strategy was successfully deployed on a 24,500 m3 anaerobic
digester system in the UK. During restart the concentration of VFAs remained less than 1,500 mg L -1, whilst pH and alkalinity were stable around 7.8 and 5,000 mg L-1, resulting in a stable recovery.

Start-up is considered as a most sensitive, challenging and critical stage in the operation of anaerobic
digesters. During start-up the delicate balance between the different groups of microorganisms can be easily disrupted, because the microbial population varies in relation to pH optima, growth rates, inhibition levels etc. [1]. Moreover, a poorly executed start-up can lead to foaming, low treatment efficiency, or microbial death due to acid accumulation [2].

The main objective of this study was to develop a restart strategy for a two-stage anaerobic process, which
required some maintenance of the first stage. For this purpose, process simulation, continuous lab-scale
experiments, and full-scale trials were carried out. The result of these tests was used to determine an optimal restart profile for a full-sized AD plant at Avonmouth, UK.

Please fill in your details to download the proceedings

For more information about how Aqua Enviro
can help you, contact us...

8 Appleton Court, Calder Park, Wakefield, WF2 7AR, UK

Consultancy and Laboratory services: + 44 (0)1924 242255

Conferences and Training enquiries: +44 (0)1924 257891


  • By submitting this form, you agree that we may use the data you provide to contact you with information related to your request/submission and other relevant Aqua Enviro services. You can unsubscribe from Aqua Enviro marketing emails at any time by clicking the unsubscribe link in the email. To learn more, see our Privacy Policy