We propose to bioremediate nutrient (N and P) rich brackish riverine/estuarine water of the Waihou river system using land-based high-rate algal ponds (HRAPs) stocked with a local species of seaweed, Ulva australis (sea lettuce).
Bioremediation of point source discharges is an established concept overseas both at research and commercial scales. However, this facility will be the first diffuse source seaweed bioremediation facility in New Zealand, and potentially globally as well with international commercial facilities based on point source effluents (e.g. aquaculture farm discharge outlets).
The seaweed provides dual benefits through nutrient removal, which is a product of the seaweed assimilating dissolved nutrients into its tissue during biomass growth, which when harvested is removed from the system. Thus delivering a high quality single species biomass for product development and feedstock for aquaculture farmers e.g biostimulants and animal feeds/supplements. The use of inorganic fertilizers (N & P) on farms in NZ causes coastal and riverine/estuary nutrient enrichment due to the amount of nutrient run-off during rainfall and irrigation. This causes issues within these environments, overwhelming the species found within these ecosystems. The bioremedial process buffers the impact of land-based industries on adjacent marine ecosystems supporting healthy productive coastal ecosystems and conserving natural ecosystem services e.g. fish nursery grounds and nutrient cycling. The by-product of this activity is cleaner water.
Environmental benefits and value potential
Based on the prediction of an average biomass productivity of 15g per meter2 per day, the proposed system has the capacity to produce 328 kg of dry weight biomass in a year.
In a nutrient replete system, Ulva biomass consists of approximately 4-5% nitrogen. Therefore, harvesting 328kg of biomass will remove approximately 16kg of nitrogen from the environment. Scaling this up, and using the same biomass productivity assumption of 15g of dry weight per meter2 per day, the annual biomass production is 54.8 tonnes dry weight per hectare. With a 5% nitrogen content, this equates to the removal of 2.7 tonnes of nitrogen, equivalent to 12 tonnes of nitrate per hectare of cultivation ponds per annum. Assuming nitrogen credits will come into effect in NZ nationally, and based on a value of $30 per kg of nitrogen that is permanently removed from the ecosystem, the biomass produced in one year from one hectare of seaweed production is worth approximately $ 82,000 in nitrogen credits.
Depending on the quality of the biomass, dried Ulva biomass fetches a value of $2-4/kg with a total market value of $109,600-219,200/hectare production. Furthermore, at a 5% loading (biomass: liquid ratio), this biomass also has the potential to produce over 1000 m 3 of liquid biostimulant.
Example of the system in full operation at the UoW
Partners and collaboration
Agrisea NZ Seaweed ltd
Ministry of Primary Industry
University of Waikato
Te Waka Anga Whakamua Waikato
Thames coromandel district council
Hauraki District Council
Creative Communities NZ