Hydrolysis and Formation of Lower Fatty Acids by Acidogenic Bacteria

The formation rate of amino acids from proteins, glycerine and fatty acids from lipids and monosaccharides from higher hydrocarbons depends on:

• the mole mass of polymers,

• their stability during hydrolysis,

• the portion of colloids,

• the concentration of enzymes.

Normally, a high enzyme concentration is assumed in relation to the total amount of substrates, measured as COD or DOC, resulting in a first-order reaction with regard to substrate concentration:

where kH is the rate coefficient (h 1) and S is the polymer concentration (mg L 1 COD).

For most types of wastewater, hydrolysis and the formation of lower fatty acids by acidogenic bacteria are not rate-limiting for the total process. This follows from kinetic studies of hydrolysis of polymers and glucose fermentation to lower fatty acids (Table 8.2).

A relatively high amount of energy can be supplied for ATP production and an-abolism. A yield coefficient YX/S = 0.162-0.310 g MLSS (g COD)-1 has been measured. The mean value of YX/S = 0.236 is about 50% of that for the aerobic mineralization of glucose. The influence of the glucose concentration on the growth rate is described by Monod kinetics:

Values of KS = 24.1 mg L-1 COD and 73.4 mg L-1 COD were obtained for the saturation coefficient, which points to the useable range of substrate limitation. Only one KS value is very high and could be confirmed by other measurements. These degradation reactions of hydrolysis products (i.e. glucose) to butyrate and propion-ate are called fermentation. These coefficients and others from the literature are compiled in Table 8.2.

0 0

Post a comment