Bioremediation of aquaculture waste and degraded waterways using finfish
Project leader: Wayne Knibb
Principal investigator: Paul Palmer, Dan Willett, Catriona Morrison, Bruce Rutherford and Dirk Erler
Research centre: Bribie Island Aquaculture Research Centre (BIARC)
Funding body: National Heritage Trust (NHT), South Burdekin Water Board (SBWB), Aquaculture Industry Development Initiative (AIDI) and Burdekin Rangelands Reef Initiative (BRRI)
Date: July 2001 to June 2004
The Bribie Island Aquaculture Research Centre “bioremediation” team is developing cost-effect, even profitable options for treating nutrient-rich aquatic wastes in both salt and freshwaters. Treatment systems are being developed for aquaculture (eg. prawn farms), agriculture (eg. cane farms) and domestic wastewaters (eg. sewerage). Stringent wastewater discharge quotas limit current production in many commercial aquaculture ventures, while high nutrient loads in rural and domestic wastewaters can have serious consequences that range from human health issues to ecological damage on offshore reefs.
Our research is showing that natural biological processes can be used to remediate nutrient-rich water by converting and trapping nutrients in forms that can be more easily removed. The technology is conceptually simple and relies on actively promoting nutrient processing by bacteria into forms suitable for uptake by aquatic plants or animals. These plants or animals in turn act as an easily harvested “sink” for nutrients that would otherwise be discharged – and if they have commercial value, profits can be made. The challenges lay in finding appropriate species to act as the “nutrient sink”.
Ph.D student Dirk Erler conducted preliminary research into a prawn farm effluent treatment system with funding from the NHT. This research evaluated detritivorous macrofauna and bacterial biofilms associated with vertically deployed artificial substrates to process effluent nutrients. Results demonstrated that artificial substrates improved settlement of suspended organic matter and promoted bacterial processing of nitrogenous compounds within the effluent stream. Nutrient processing was boosted by detritivorous mullet, Mugil cephalus, and banana prawns, Penaeus merguiensis. These grazersaid nutrient cycling by converting some organic nutrients within the sediment into body mass whilst excreting waste nutrients in a form readily assimilated by bacteria and algae. These animals also showed promise as a value added treatment option for prawn farmers, which led to a further NHT grant to evaluate the efficacy of banana prawns to assimilate nutrients in farm effluent ponds. The results of this trial demonstrated that high quality food grade banana prawns can be produced in these wastewater treatment systems.
Current research draws on our past learnings of the interactions among animals, plants and bacteria, and assesses at pilot scale the profitability of producing prawns in fully recirculated systems where waste is treated with algae and mullet. This work is supported by the AIDI grant “Towards zero water discharge”.
Domestic and Rural Wastewater:
With grants from the SBWB, BRRI and support from the Burdekin Shire Council, researchers from BIARC have shown that aquaculture bioremediation technology can be used to improve degraded waterways in the Burdekin caused by irrigation run off and municipal sewage effluent discharge. This work has focused on using aquatic plants as the major nutrient sinks for treating effluent, aided by artificial substrates and native freshwater herbivorous fish. Trials have shown that greater than 50% reduction of incoming Nitrogen and Phosphorous is achievable from Burdekin irrigation water by a self-regulating algae/fish treatment system after a 14-day retention time.
Our work in the Burdekin also investigated biological approaches to treat municipal wastewater. We used native duckweed (Spirodela sp.) for this purpose due to its ability to efficiently accumulate nutrients, its ease in harvesting and its usefulness as a by-product. Results demonstrated that duckweed was capable of removing the majority of dissolved nitrogen from the effluent. Harvested duckweed then provided a highly nutritious diet for jade perch (Scortum barcoo), a local aquaculture species, suggesting potential for large-scale fish production using by-products from the effluent treatment process.
Last reviewed 18 February 2004