2. CONTINUOUS CULTURES 



In continuous culture, since this technique serves to check the concen- 

 trations 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 oxy- 

 gen) 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 non- 

 limitation, 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. 



34 



