Vertical flow reed bed with aeration
Highland Spring’s Blaen Twyni site in the Brecon Beacons produces flavoured drinking water supplying numerous retail outlets including supermarket chains.
Borehole water is drawn from the ground, processed, and bottled prior to distribution. Flavourings and preservatives are added during production. Acids, alkalis and oxidising agents are used for plant cleaning. The waste water collected on site is therefore a combination of product, cleaning fluids, raw water and acid / alkali for pH balancing.
The existing effluent treatment plant had been installed in 2011 and comprised eight sequential ponds or lagoons. Unused borehole water was used to dilute the final effluent.
The system had been struggling to achieve reliable performance and maintain discharges within consent. As a result effluent was being tankered away from site at significant cost. ARM Ltd was approached by Highland Spring to assess the existing wastewater treatment system.
ARM conducted a site and data survey to establish the key treatment issues. Potential predicted increases in production were also taken into consideration.
The waste stream was characterised as follows:
Average flow: 60m3/d (350m3/d peak)
Average BOD: 400mg/l
Average TSS: 21mg/l
Average COD: 570mg/l
Significant variation in loads were seen (between 0 and 1,500mg/l COD). This variation was, in part, due to the minimal upstream flow balancing and the position in the treatment stream of the pH adjustment system, which was often stretched beyond its limits leading to plant shut-downs.
Once the flows and loads had been determined, a reed bed treatment system could be designed and installed.
To make maximum use of the existing pond assets, one of the ponds (pond 3) was converted into an aerated vertical flow system with a total area of 180m. The two ponds upstream would provide additional balancing and the downstream ponds additional polishing treatment.
Plant and operational alterations were also made upstream to provide additional balancing of the acid and alkali wash waters so that the pH adjustment system received a more consistent and manageable load.
The aerated reed bed provides Highland Spring's Blaen Twyni site with a much more secure wastewater treatment system, eliminating the costs associated with tankering effluent off site on a daily basis whilst making the most of their existing assets.
Upstream adjustments undertaken by ARM provide additional balancing and optimisation of the pH adjustment system making the water management system more robust.