Recycling the nutrients from pāua aquaculture effluent into a fresh seaweed feed

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dc.contributor.advisor Jeffs, Andrew Greig
dc.contributor.author Jang, Incheol
dc.date.accessioned 2021-10-28T22:29:16Z
dc.date.available 2021-10-28T22:29:16Z
dc.date.issued 2021 en
dc.identifier.uri https://hdl.handle.net/2292/57151
dc.description.abstract This is the first study to test the potential of macroalgae to grow and remove nutrients from New Zealand pāua farm effluent. Three different macroalgae culture systems were compared for the treatment of aquaculture effluent and macroalgae production: a suspended macroalgal culture system – representing a high rate algal pond, and two algal turf scrubber (ATS) culture systems with attached macroalgae (i.e., a typical land-based system and a novel floating system). A series of consecutive experiments were conducted for batch, semi-continuous, and nutrient spiked semi-continuous culture using these three culture systems. The suitability of the Ulva spp. cultured in the effluent was then tested as a feed supplement for pāua. Four different feeding treatments were tested, with replacement of formulated abalone feed with different amounts of fresh effluent-grown Ulva spp.In the batch culture experiment, macroalgae grew well and removed ammoniacal-N (from ~1.5 to 0 mg NH3-N L-1) from the pāua aquaculture effluent during 0 – 3 days in both ATS culture systems and 1 – 6 days in the suspended culture system. However, the nitrate concentration (~2.4 mg NO3--N L-1) was not reduced below 1 mg NO3--N L-1 in any of the culture systems and dissolved reactive phosphorus (DRP) was too low to measure. The highest growth rates measured in each culture system were 12.5 g m-2 d-1 (suspended), 8.3 g m-2 d-1 (floating ATS), and 1.6 g m-2 d-1 (land-based ATS), but these growth rates were highly influenced by the amount of biomass initially present. In the semi-continuous culture experiment, the macroalgae also grew well and removed ammoniacal-N (from 1.23 to ~0.06 mg NH3-N L-1) from the pāua aquaculture effluent (with 94, 98, and 99% removal achieved by the suspended culture system, floating ATS culture system, and land-based ATS culture system, respectively) even at a 1-day HRT (hydraulic retention time). However, the ~2.4 mg NO3--N L-1 inflow nitrate concentration was not reduced below 1 mg NO3--N L-1 in any of the culture systems. The inflow DRP concentration was still below detection. The highest growth rate measured in each culture system when operated at a 1-day HRT was 6.3 g m-2 d-1 (suspended culture system), 7.7 g m-2 d-1 (floating ATS culture system), and 16.2 g m-2 d-1 (land-based ATS culture system). In the spiked semi-continuous culture experiment, the pāua aquaculture effluent nutrient concentration was increased to ~30 mg NH3-N L-1 and ~3 mg DRP L-1. The land-based ATS culture system showed the most potential for phycoremediation of aquaculture effluent and production of macroalgal biomass. The land-based ATS had the highest ammoniacal-N removal and macroalgal growth rate (16.2 g m-2 d-1) but became contaminated by nitrifying bacteria, which led to an accumulation of nitrate-N (up to 13 mg NO3--N L-1). Also, the land- based ATS culture system may be susceptible to contamination by colonial cyanobacteria which may outcompete the macroalgae. In contrast, the suspended culture system consistently showed lower (and less consistent) ammoniacal-N removal and had the lowest macroalgal growth rate (6.3 g m-2 d-1), although it was not contaminated by nitrifiers it was often contaminated by phytoplankton at the high inflow nutrient concentrations. Therefore, the land- based ATS culture system and to a lesser extent, the suspended culture system warrants further evaluation at both mesocosm scale and commercial large scale. Complete removal of ammoniacal-N (0 mg L-1) and near-complete nitrate-N removal (~1 mg L-1) from the drum filter backwash effluent produced by Moana Ltd’s pāua aquaculture facility could be achieved in all three macroalgal culture systems with a surface area of 1,280 m2 (100 × 12.8 m). The land-based ATS culture system alone or the integration of both the land-based ATS and suspended culture systems could provide the highest nutrient removal and macroalgal production. Effluent-grown Ulva spp. was found to be an excellent feed supplement for pāua with no difference in the survival or growth of juvenile pāua when up to 20% of a formulated diet (Abfeed®) was replaced with fresh Ulva spp. in a 38-day feeding trial. A 20% substitution of Abfeed® is economically beneficial given that this feed costs NZ$3.60 kg-1. It was estimated that sufficient Ulva spp. could be produced to supply 20% of the feed requirements for Moana Ltd’s entire pāua farm from a macroalgal culture system covering an area of 7,230 m2 (100 × 72.3 m) and using 100% of the drum filter backwash effluent (259,200 L d-1) and 10% of the drum filtered effluent (1,290,087 L d-1). The present preliminary study has demonstrated the potential of land-based macroalgae culture systems to remove nutrients from New Zealand pāua farm effluent whilst also producing Ulva spp. as a suitable feed for cultured pāua.
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof Masters Thesis - University of Auckland en
dc.relation.isreferencedby UoA en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.
dc.rights.uri https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm en
dc.rights.uri http://creativecommons.org/licenses/by-nc-sa/3.0/nz/
dc.title Recycling the nutrients from pāua aquaculture effluent into a fresh seaweed feed
dc.type Thesis en
thesis.degree.grantor The University of Auckland en
thesis.degree.level Masters en
dc.date.updated 2021-09-20T11:55:50Z
dc.rights.holder Copyright: the author en
dc.rights.accessrights http://purl.org/eprint/accessRights/OpenAccess en


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