Integrated treatment of shrimp effluent by sedimentation, oyster filtration and macroalgal absorption: a laboratory scale study

Effluent water from shrimp ponds typically contains elevated concentrations of dissolved nutrients and suspended particulates compared to influent water. Attempts to improve effluent water quality using filter feeding bivalves and macroalgae to reduce nutrients have previously been hampered by the high concentration of clay particles typically found in untreated pond effluent. These particles inhibit feeding in bivalves and reduce photosynthesis in macroalgae by increasing effluent turbidity. In a small-scale laboratory study, the effectiveness of a three-stage effluent treatment system was investigated. In the first stage, reduction in particle concentration occurred through natural sedimentation. In the second stage, filtration by the Sydney rock oyster, Ž . Saccostrea commercialis Iredale and Roughley , further reduced the concentration of suspended particulates, including inorganic particles, phytoplankton, bacteria, and their associated nutrients. Ž . In the final stage, the macroalga, Gracilaria edulis Gmelin Silva, absorbed dissolved nutrients. Pond effluent was collected from a commercial shrimp farm, taken to an indoor culture facility and was left to settle for 24 h. Subsamples of water were then transferred into laboratory tanks stocked with oysters and maintained for 24 h, and then transferred to tanks containing macroalgae Ž . Ž . for another 24 h. Total suspended solid TSS , chlorophyll a, total nitrogen N , total phosphorus Ž . q y 3y P , NH , NO , and PO , and bacterial numbers were compared before and after each treatment 4 3 4 Ž . Ž . Ž . Ž at: 0 h initial ; 24 h after sedimentation ; 48 h after oyster filtration ; 72 h after macroalgal . absorption . The combined effect of the sequential treatments resulted in significant reductions in the concentrations of all parameters measured. High rates of nutrient regeneration were observed ) Corresponding author. Department of Botany, The University of Queensland, Brisbane, Qld 4072, Australia. Tel.: q61-7-3365-4132; fax: q61-7-3365-7321. Ž . E-mail address: [email protected] A.B. Jones . 0044-8486r01r$ see front matter q2001 Elsevier Science B.V. All rights reserved. Ž . PII: S0044-8486 00 00486-5 ( ) A.B. Jones et al.rAquaculture 193 2001 155–178 156 in the control tanks, which did not contain oysters or macroalgae. Conversely, significant reductions in nutrients and suspended particulates after sedimentation and biological treatment Ž were observed. Overall, improvements in water quality final percentage of the initial concentra. Ž . Ž . Ž . q Ž . y Ž . 3y tion were as follows: TSS 12% ; total N 28% ; total P 14% ; NH 76% ; NO 30% ; PO 4 3 4 Ž . Ž . Ž . 35% ; bacteria 30% ; and chlorophyll a 0.7% . Despite the probability of considerable differences in sedimentation, filtration and nutrient uptake rates when scaled to farm size, these results demonstrate that integrated treatment has the potential to significantly improve water quality of shrimp farm effluent. q 2001 Elsevier Science B.V. All rights reserved.