Advanced Digestion – from Concept to Commissioning
Powell, C.1 and Plaza M.2., GHD, UK
(free)
Abstract:
A review and discussion of the design processes and challenges encountered to develop an advanced
digestion project at an existing WwTW from client concept through tender stage, detailed design,
construction and commissioning. Managing change within the design and the implications for
programme and costs.
Following the client’s decision to proceed with an advanced digestion solution sized for 11.5tds / day,
and to provide an enhanced product, GHD were engaged by the Framework Construction Partner as
Civil & MEICA designers to ensure that the proposed solution could be engineered, designed and
constructed to overcome a number of challenges;
• Regulatory date to be achieved.
• Less detailed client scope document than previous projects.
• A novel, containerised Thermal Hydrolysis Plant.
• A restricted site footprint, congested with operational infrastructure above & below ground.
• An existing sludge digestion and dewatering process to be re-engineered for changing sludge
consistency, composition and rheology.
• Existing assets that the client wished to reuse / convert.
• Management of additional liquor flows, solids and nutrient load.
• Management of changes to scope, client requirements and design elements.
Under the clients’ procurement model, the client provides a basis of design, a project scope and takes
process responsibility for the proposed solution and process throughputs. Leading the detailed design
from front end mass & energy balances, to construction stage MEICA & Civil design with extensive use
of 3D modelling, GHD ensured that robust, cost effective design was delivered on time. GHD were
responsible for specifying and integrating numerous vendor packages into the scheme including the
THP plant & steam boiler, new sludge thickening & storage, existing CHP system, Ultra Violet (UV)
Disinfection of Final Effluent service water, Dissolved Air Flotation (DAF) clarification for liquors
treatment and chemical dosing.
Effective collaboration between stakeholders was achieved with regular design reviews, site inspections
and participation in the detailed HAZOP / ALM process ensured safe construction, operation and
maintenance.
Introduction:
The project comprised the installation of a new Thermal Hydrolysis Plant (THP) plant at a large WwTW
(P.E. 100,000) with the main driver to produce an enhanced digested sludge cake by a set regulatory
date.
The THP plant selected by the client was a CAMBI B2-4 modular, skid mounted system, believed to be
the first installation of this type in the UK. In addition to the THP plant, new sludge processing assets
were required and some existing assets converted to accommodate the works.
The capital value of the project was approx. £20million and the initial construction programme as follows
• Client scoping design 2013
• Tender design Dec 2013 – Apr 2014
• Order placed with construction contractor Jun 2014
• Design start up July 2014
o Delete air blast cooler July 2014
• Coding issue MEICA design Aug – Dec 2014
• Coding issue civil design Jan – Mar 2015
• Start on Site Sep 2014
o Change design for 3% s/s raw sludge Apr 2015
o Delete UV for dewatering Apr 2015
o Layout changes Mar 2015
o Delete LTP, add DAF Unit May 2015
• Wet Commissioning & start up Dec 2015
• Project In use Jan 2016
