In 2018, the Capital Programmes of Irish Water received planning permission from Carlow County Council to construct Sludge Drying Reed Beds (SDRBs) at five of their Waste Water Treatment
Plants (WWTPs), as follows:
- Ballon WWTP
- Clonegal WWTP
- Fenagh WWTP
- Myshall WWTP
- Raheendoran WWTP
Irish Water aim to commence the construction of the SDRB systems in March 2019, followed by a 12 month proving / validating period where the optimum sludge loading rate will be established for each site.
A large number of existing WWTPs do not have facilities for on-site sludge treatment, hence the requirement of hauling off-site, which is expensive, requires significant logistics and management resources and is not sustainable in the long-term. SDRB systems offer a sustainable and affordable solution for the long-term treatment of wastewater sludge, providing in situ treatment and stabilisation, minimising quantities of material requiring disposed offsite, where primary sludge and excess activated sludge is reduced to a stabilised product. SDRBs have strong ecological and environmental benefits due to the use of vegetation and the significant reduction in greenhouse gasses associated with the reduction in sludge transport and processing.
The design of the sludge drying reed bed system includes a retaining structure, liner, distribution and collection pipework, filter bed material and reed vegetation. The technology of the sludge reed beds is based upon the ability of the Common Reed (Phragmites australis) to reduce the volume and biomass loading of sludge over time. Common Reed has the advantage of being a native plant with high evapotranspiration capabilities, low maintenance requirements and a long vegetation period. Sludge reduction takes place within the SDRBs due to the dewatering process, via draining and evapotranspiration, and the mineralisation of the organic solids in the sludge. Yellow Iris (Iris pseudacorus) would also be planted, to increase the biodiversity value of the system.
As part of the planning process, Panther Environmental Solutions Ltd. carried out Stage 1 Screening for Appropriate Assessment for each of the five WWTP sites, to ascertain if the projects had the potential to affect the integrity of the Natura 2000 network, in particular upon the River Barrow and River Nore Special Area of Conservation (SAC) (Site Code 002162) and the Slaney River Valley SAC (Site Code 000781). The screening studies for four of the sites determined that there would be no potential for significant effects on the Natura 2000 network as a result of the proposed SDRB systems. For Clonegal WWTP, given the proximity of the Slaney River Valley SAC to the proposed development, a Natura Impact Statement was prepared, which detailed recommended control measures and standard practice during the construction phase to ensure that the development would have no significant impacts upon the integrity of the Slaney River Valley SAC.