Sj. Cripps et A. Bergheim, Solids management and removal for intensive land-based aquaculture production systems, AQUACULT EN, 22(1-2), 2000, pp. 33-56
This review aims to identify and examine realistic aquaculture waste solids
management strategies. The main reason for treating solids to be discharge
d from flow-through systems is to reduce potential negative impacts on the
surrounding aquatic environment. In reuse and recycle systems, solids manag
ement will be required to maintain culture water quality. In such cases, so
lids management will often be designed to be combined with other unit proce
sses. Solids concentrations in the untreated effluent from flow-though farm
s are low at around 5-50 mg l(-1), and do not appear to have altered greatl
y within the last 20 years. These solids can commonly carry 7-32% of the to
tal nitrogen and 30-84% of the total phosphorus in the wastewater. Feed qua
lity and feeding management can be manipulated to reduce the quantity of wa
ste solids produced. Decreases in the specific water consumption within a f
arm, increase the concentration of solids in the effluent, which results in
an increase in particle separation efficiency. Particles should be separat
ed from the culture stock and the primary effluent flow quickly and efficie
ntly (i.e. at high solids concentrations). This can be achieved by within-t
ank separation systems, often comprising a separate low-flow particle outle
t. Rotating microscreens are commonly used at land-based intensive fish-far
ms in Europe. Screen mesh pore sizes of 60-200 mu m are common. There is li
ttle advantage in using pore sizes smaller than 60 mu m. Low concentration
aquaculture solids usually settle discretely in sedimentation tanks, i.e. w
ith no agglomeration of particles that would increase their settling veloci
ty. Such basins are prone to many technical problems, and in most situation
s are unlikely to be suitable for the treatment of solids in the primary wa
stewater from aquaculture facilities. Sedimentation basins may be appropria
te for secondary de-watering or thickening. Overflow rates of 1.0-2.7 m(3)
m(-2) h(-1) have been reported. Bead filters and Rotation columns have been
shown to perform well for solids removal in limited flow-rate recycle syst
ems. The sludge produced by separation technology can be thickened and stab
ilised by the addition of lime, to kill pathogenic diseases and restrict pu
trefaction. The resulting sludge has been spread on agricultural land. (C)
2000 Elsevier Science B.V. All rights reserved.