Paihia WWTP, Innovative in pond removal of ammonia using bioshells®

Andrew Springer (WSP), William Down (Far North District Council).

Situated in the Waitangi Forest in the Bay of Islands, Paihia WWTP has a discharge that feeds
into the sensitive Waitangi wetlands, home to the Northland Mudfish. To improve this
habitat, it has been necessary to upgrade the plant that serves Paihia, Opua, Waitangi and
Haruru to meet a 2 mg/l ammonia consent. Like many wastewater systems in New Zealand,
Paihia WWTP is a pond based system built in the 1980s. not intended to meet nitrogen
removal requirements.
To meet the tight standards the innovative technology of Bioshells® has been adopted to
provide an in pond treatment system within the existing assets. With over 550 Bioshells®
operating, this is the first NZ nitrifying plant and the largest of its kind outside of the USA.
Performance monitoring over more than 1 year of operation has demonstrated that ammonia
concentrations have been reduced from typically 50 mg/l to less than 2 mg/l. Total nitrogen
has been reduced by 40% and additional benefits to BOD, TSS and E coli concentrations have
been recorded.
Alkalinity has been identified as a major issue within pond treatment, resulting in the need
for chemical addition to ensure full ammonia removal occurs and to maintain acceptable
discharge ph.
By adopting this Innovative approach on a space restricted site, FNDC have achieved all
required performance outputs at an affordable cost to the community in a tight capital
programme. A capital saving of over $18m against a conventional solution has been realised.