Northern Ireland: Gulladuff WwTW

DAWSON-WAM Ltd. was appointed by Northern Ireland Water to design and construct a new wastewater treatment works on an existing site to introduce new advances in the wastewater treatment technology to an existing outdated filter-bed facility.  The works included the construction of an inlet works, primary, secondary and final treatment, plants, FE pumpaway to Knockloughrim WwTW along with sludge and storm storage facilities.

Gulladuff is a small rural treatment works for Gulladuff village, Co. Londonderry.  It serves a current population equivalent of 694which is expected to grow to 889 for the 2035 design horizon.

Solution development included:

Design of Process, MEICA and Civil works included the accurate sizing and selection of Primary Settlement, RBC Secondary Treatment Units & Final Settlement Tanks to meet both current and future flows and loads. 

Process and MEICA requirements included:

• 1nr Huber Rotamat inlet screening plant;
• 2nr ST9 Upflow primary settlement package plants with hydrostatic sludge draw-off;
• 2nr DN9 RBC package plants;
• 2nr ST11 Upflow conical final settlement package plants with hydrostatic sludge draw-off;
• Inlet pumping station complete with integral storm storage;
• Sludge handling facilities including sludge pumping station and sludge storage tank;
• Storm storage tanks which included Online, Blind and SDD storage capabilities;

Civils Works included:

• The excavation, 5mdeep, for the installation of the PSTs and FSTs tanks. Due to very good ground conditions, we were able to propose the use of open cut techniques to install all process units;
• Excavation and construction of a reinforced concrete base slab for RBC installation. RBCs where backfilled with concrete in strict staged sections due to the delicacy of the GRP housing;
• Inlet works and sludge holding tanks where both constructed in reinforced concrete;
• Sludge pumping station and associated valve chambers constructed with traditional concrete ring sections;
• We were able to propose the reuse of an existing holding tank as the structure to house the Final Effluent (FE) pumping station bringing both time and cost savings to the project;
• The FE pumping main ran for some 3.5km mainly through roads.  Pipework was installed predominantly by trenchless techniques, however a section of rising main required to be constructed in rock. 
• Interconnecting process pipework, asphalt access roads and concrete hard-standing provided site finishes.

Planning was a key element of the project as the site was located on a small footprint. To construct this works whilst still maintaining consent standards required the use of a temporary treatment plant. We proposed the use of a temporary SAFF treatment plant with a single primary and final settlement tank. We were able to utilise the existing inlet pumping station to transfer sludge to the existing sludge holding tank at the site entrance, thus removing tanker movements within our construction area.  Once operational, the existing works was taken off-line allowing unrestricted uninterrupted construction.

The works was subject to standard NIW level 1, 2 & 3 testing regimes and fully tested/commissioned. Once the works was handed over to NIW we continued to provide operational and maintenance assistance to NIW for a minimum period of 6 months.