The anammox (anaerobic ammonium oxidation) process has been one of the most innovative developments in biological wastewater treatment in recent years. With its discovery in the 1990s a completely new way of ammonium removal from wastewater has become available. Side-stream deammonification, a process based on anammox activity, can significantly lower the energy consumption and overall operation costs related to the removal of high loads of ammonium nitrogen (~1000 mg-N/L) from biosolids dewatering centrate. The application of Main-Stream Deammonification is likely to be the next biological innovation in the wastewater industry. Watercare has been evaluating the feasibility and benefits of incorporating these processes and have started the development of a viable New Zealand anammox ‘inoculum’ for wider use. Anammox based technologies have yet to be implemented in New Zealand. One constraint has been the non-availability of anammox cultures to seed full-scale reactors. Biosecurity restrictions by EPA and MPI (Environmental Protection Agency and the Ministry of Primary Industry) have complicated the importation of anammox enrichments from overseas. Watercare have set about the task of developing a culture of our own indigenous anammox biomass, using a combination of molecular biology and bioprocess control techniques. The first step in this process was the confirmation of the presence of small quantities of anammox bacteria in activated sludge samples from the Mangere and Rosedale WWTPs using high-throughput meta-genomics and qPCR techniques. The analysis showed that, although in small quantities, anammox bacteria are present in the activated sludge and mesophillic anaerobic digester reactors at both of these plants.
The second phase of work involved the development of laboratory scale reactors to isolate and enrich the anammox microbes. The bioreactors were seeded with sludge from the activated sludge RAS streams at the Mangere and the Rosedale WWTPs. Ammonium depletion under complete anaerobic conditions started after 110 days of reactor operation. After more than 270 days of continuous operation the bioreactors developed sufficient quantities of anammox culture to take the process ‘out of the lab’. So far the ammonium removal rates are in the range of 15-20 mg-N L-1 d-1. These rates need to be increased four times (e.g. to achive 100 mg-N L-1 d-1 or 0.1 kg-N m-3 d-1) before the activity would be sufficient for the next stage of ‘pilot scale sidestream treatment’. Much of the technical development has focussed on staged scaling up of cultures and optimizing influents characteristics to build-up more anammox biomass and simultaneously increase ammonium removal rates. Pilot scale facilities are currently under design and will be established at the Mangere WWTP ‘Wastewater Innovation Centre’.