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Testing the effectiveness of the SKIM foam fractionator to reduce nutrient levels in prawn farm effluent

Palmer, P.J., Morrison, C., Willett, D.J. and Rutherford, B.W. (2005) Testing the effectiveness of the SKIM foam fractionator to reduce nutrient levels in prawn farm effluent. In: Project Report QO04018. Wastewater remediation options for prawn farms. Aquaculture Industry Development Initiative 2002-04. Department of Primary Industries and Fisheries, pp. 75-93.


Article URL: http://era.deedi.qld.gov.au/2080/


To experimentally investigate the effect of the “SKIM” mechanical foam fractionator on suspended material and the nutrient levels in prawn farm effluent, a series of standardised short-term treatments were applied to various effluent types in a static 10,000-litre water body. Prawn pond effluents were characterised by watercolour and dominance of phytoplankton species. Three effluent types were tested, namely 1) particulate-rich effluent with little apparent phytoplankton, 2) green mircoalgal bloom predominately made up of single celled phytoplankton, and 3) brown microalgal bloom with higher prevalence of diatoms.

The effluent types were similar (P>0.05) in non-volatile particulate material, and nitrate/nitrite but varied from each other in the following ways:
1) The particulate-rich effluents were lower (P<0.05) in volatile solids (compared to brown blooms), total Kjeldahl nitrogen, dissolved organic nitrogen, dissolved organic phosphorus and chlorophyll a (compared to both green and brown blooms).
2) The brown blooms were higher (P<0.05) in ammonia (compared to green blooms), total nitrogen and total phosphorus (compared to both green and particulate-rich effluent), but were lower (P<0.05) in inorganic phosphorus (compared to both green and particulate-rich effluent).
3) The green blooms were higher (P<0.05) in dissolved (both organic and inorganic) phosphorus (compared to both brown and particulate-rich effluents).

Although the effluent types varied significantly in these aspects the effect of the Skim treatment was similar for all parameters measured except total phosphorus. Bloom type and Skim-treatment period significantly (P<0.05) affected total Kjeldahl phosphorus concentrations. For all effluent types there was a continuous significant reduction (P<0.05) in total Kjeldahl phosphorus during the initial 6-hour treatment period.

Levels of total suspended solids and volatile suspended solids in all effluent types were significantly (P<0.05) reduced in the first 2 hours but not thereafter. Non-volatile suspended solids were also significantly (P<0.05) reduced in the first 2 hours (30 to 40 % reduction) and a further 40% reduction occurred in the particulate-rich effluent over the next 2 hours. Mean values for total ammonia, dissolved organic nitrogen, total Kjeldahl nitrogen, total nitrogen, chlorophyll a and dissolved organic or inorganic phosphorus levels were not significantly (P>0.05) affected by the Skim unit in any bloom type during the initial 6 hours of testing. Nevertheless, non-significant nitrogen reductions did occur.

Foam production by the Skim unit varied with different blooms, resulting in different concentrate volumes and different end points for separate experiments. Concentrate volumes were generally high for the particulate-rich and green blooms (175 – 370 litres) and low for the brown blooms (25 – 80 litres). This was due to the low tendency of the brown bloom to produce foam. This generated higher nutrient concentrations in the associated condensed foam, but may have limited the treatment efficiency.

The results suggest that in this application, the Skim unit did not remove micro-algae as effectively as was anticipated. However, it was effective at removing other suspended solids. Considering these attributes and the other uses of this machinery documented by the manufactures, the unit’s oxygenation mixing capacities coupled with inorganic solids removal may provide a suitable mechanism for construction of a continuously mixed bioreactor that utilises the filtration and profit making abilities of bivalves.

Item Type:Book Section
Corporate Creators:Department of Employment, Economic Development and Innovation (DEEDI), QPIF, Agri-Science, Fisheries and Aquaculture
Business groups:Agri-Science, Fisheries and Aquaculture
Additional Information:© The State of Queensland (Department of Employment, Economic Development and Innovation). © The State of Queensland, Department of Primary Industries 2005. Copyright protects this publication. Except for purposes permitted by the Copyright Act 1968, reproduction by whatever means is prohibited without prior written permission of the Department of Employment, Economic Development and Innovation. Enquiries should be directed to Commercialisation Unit: http://www.dpi.qld.gov.au/77.htm . Email: SAFTRSCopyright@deedi.qld.gov.au . Phone: the Business Information Centre on 13 25 23 (Queensland residents) or +61 7 3404 6999. Published electronically August 2011.
Keywords:Prawns; nutrient levels; prawn farm effluent; settlement ponds; Skim treatment; wastewater.
Subjects:Aquaculture and Fisheries > Aquaculture > Mariculture
Science > Science (General)
Deposited On:04 Aug 2011 05:31
Last Modified:08 Jun 2015 15:57

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