Biology Reference
In-Depth Information
method for simultaneously reducing effl uent nutrient loading (especially
nitrate and ammonia) and for reducing organic loading (especially BOD
5
)
of shrimp culture effl uents. Throughout the experiment, high values in
oxygen concentrations (8 mg/l) were achieved. This was probably due
to photosynthetic oxygen production by microalgae and cyanobacteria
of the mat. The photoautotrophic (top of the mat) and heterotrophic
community was dominated by diatoms (
Nitzchia
sp. and
Navicula
sp.) and
fi lamentous forms of cyanobacteria (
Microcoleus chthonoplastes
,
Spirulina
sp.,
Oscillatoria
sp.,
Schizothri
x sp.,
Calothrix
sp. and
Phormidium
sp.) as
well as green algae as comprised by
Chlorella
sp. and
Dunaliella
sp. Mixed
microbial mats containing fi lamentous cyanobacteria (
Oscillatori
a sp.) as
the dominant species have been shown to remove nitrogenous compounds
and other toxic chemicals from polluted sites (Bender and Phillips, 2004;
Zachleder et al., 2002). In summary, marine bioremediation by constructed
microbial mats systems could represent an effi cient and environmentally
sound alternative for the improvement of the environmental conditions of
coastal sensitive regions and overall effl uent water discharges (Paniagua-
Michel and Garcia, 2003).
Aerobic and Anaerobic Sludge Treatments
Most smolt hatcheries are fl ow-through plants with water and energy
demands of up to 700,000 m
3
and 105-245 MW h per 100,000 smolts
produced. The anaerobic treatment of sludge from salmon smolt hatchery
in a continuous stirred tank reactor at mesophilic temperature (35°C) and
55-60 d HRT (hydraulic retention time) was investigated (Gebauer and
Eikebrokk, 2006). The main components of treated sludge with 1.5-3.3%
total (dry) solids were 32% nitrogen, 8.5% phosphorous, 1.2% potassium,
acceptable concentration of heavy metal apart from zinc and high levels of
volatile fatty acids (VFA). The treated sludge was in liquid form and could
be used as a liquid fertilizer on cultivated land and meadows; however,
requirements for special means of application were needed. Furthermore,
the methane content in biogas was stabilized at 59.4-60.5% vol., methane
yield was 0.14-0.15 l/g COD, nitrogen mineralization increased to 70%,
and 44.8-53.5% COD removed. The potential of the sludge for energy
production was also exploited. The net energy production from the biogas
was 43-47 MW h/year and could cover 2-4% of the energy demand in fl ow-
through hatcheries, and at least twice as much in recirculation hatcheries.
(Arvanitoyannis and Kassaveti, 2008).
Lanari and Franci (1998) examined the potential of biogas production by
fi sh farm effl uents in a small-scale close system with partially recirculated
water. The system consisted of two fi sh tanks with a recirculation rate of
60% and a rainbow trout daily feeding allowance of 1%, 1.5% and 2% of
live weight, an up-fl ow anaerobic digester connected with a sedimentation
