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2. CONTINUOUS CULTURES
In continuous culture, since this technique serves to check the concentrations
of all the nutritive elements at all times, and to adjust these
concentrations to limit thresholds, thus closely approaching conditions
encountered at sea, we attempted to quantify the nitrogen, phosphorus
and oxygen requirements for the biodegradation of given quantities of
hydrocarbons present in ALC 240+ .
The following operating conditions were used:
• Dilution rate D = 0.04 h~
• Temperature 20°C
• Reactor volume 2 liters
• Agitation 520 rpm
• Ph of culture 8.1
• GHSV 1
(except for quantification of the oxygen requirements, where the GHSV
was varied from 1 to 0.25).
• ALC 240 concentration
entering reactor
always about 2.5 g.l -
For a given concentration of an element (nitrogen, phosphorus or oxygen)
entering the reactor, the experimental time was about one week.
Upon each alteration in operating conditions, it was necessary to wait
another week for equilibrium to be re-established.
When the residual concentration of nitrogen was in excess, the bacterial
consumption of this element per mg of hydrocarbons degraded ranged from
0.1 to 0.11 mg. However, when the nitrogen reached a limit with residual
contents around 1 mg/liter, the nitrogen requirements dropped to 0.07 mg.
The same occurence was observed with phosphorus. In conditions of nonlimitation,
the biochemical consumption of phosphorus, around 0.012 to
0.013 mg/mg of hydrocarbons consumed, declined to only 0.005 mg/mg of
hydrocarbons consumed when the residual concentration of elemental P
reached a limit ( C 1 mg.l - -'-).
With respect to oxygen, microorganism requirements fluctuated between
1.4 and 1.9 mg oxygen per mg of biodegraded hydrocarbons, for residual
dissolved oxygen concentrations between 50 and 7 % of the saturation
value.
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