Standard Presentation Australian Marine Sciences Association Annual Meeting 2023

Solving the aquaculture wastewater bottleneck - Microalgal removal using electro-flocculation (#81)

Angela Capper 1 , Shaneel Chandra 2 , Ziyad Abunada 3 , Louise Reeves 4
  1. Coastal Marine Ecosystems Research Centre, CQUniversity, Gladstone, Qld, Australia
  2. College of Science and Sustainability, School of Health, Medical and Applied Sciences, CQUniversity, Rockhampton, QLD, 4702
  3. College of Project Management, Built Environment, Asset and Maintenance Management, School of Engineering and Technology, CQUniversity, Melbourne, VIC, Australia
  4. Queensland Water Directorate, Eagle Farm, Brisbane, QLD, Australia

A primary factor limiting expansion of land-based aquaculture is the need to dispose of vast quantities of wastewater with high levels of nitrogen. For the $167 million Queensland prawn industry, located adjacent to the Great Barrier Reef, farm discharges must meet stringent water quality limits, particularly for total nitrogen (TN) and dissolved inorganic nitrogen (DIN). As such, developing new technologies to improve the management of water discharge quality, and ideally repurposing the waste material, is a key objective for the Queensland prawn industry. The current method, involving sedimentation of naturally occurring microalgae that take up the excess nitrogen, is slow. Electro-flocculation of pondwater can speed up the process and provide a flocculant that could be used as a commercial bio-product. To demonstrate the concept, different electro-flocculation configurations in stationary (60 L) and flowing water (240 L) were applied to three prawn farm pondwater samples with varying microalgal assemblages collected from a local farm in central Queensland. In 64% of trials, electro-flocculation reduced TN and DIN loads to near to or below regulatory limits. TN was reduced by 83.2% (10.93 – 1.83 mg.L-1) within 20 mins in stationary water. Whilst DIN was reduced by 90.6% (3.19 – 0.30 mg.L-1) in 50 mins in flowing water. Microalgal flocculant consisted primarily of Bellerochea, Pseudoanabaena, Gloeocapsa and Cyclotella. There is some evidence that Bellerochea promotes flocculation. This study confirmed that electro-flocculation can quickly reduce TN and DIN, improving the management of water discharge quality and producing a flocculant with potential as a bio-product.