The Influence of Temperature on the Denitrification Rate

Denitrification can be performed in the temperature range 5 °C - 35 °C. Many of the denitrifying species are adaptive to temperature changes. It is, therefore, important to realize that there is a difference between long-term and short-term temperature influences on the denitrification process.

The growth rate of the organism and removal rate of nitrate are both affected by temperature. To show the effect of temperature on growth and denitrification rates, the results at 20 °C from the literature are summarized in Fig.4.3. Denitrification proceeds at a reduced rate, at temperatures as low as 5 °C. Above 20 °C, the data indicates that the denitrification rates are constant. Murphy et al. (1973) showed that attached growth systems are less affected by low temperatures than are suspended growth systems. It is important to distinguish between two types of temperature

Table 4.7 Oxygen concentration in denitrification experiments, and literature concerned with the technical importance of oxygen concentration.

Oxygen concentration in experiments (mg/i)

Reference

< 0,5

Ludzack and Ettinger (1962)

0,5/10,0

Ruffer (1964)

< 0,5

Pasveer (1965)

0,5

Schuster (1970)

0,2 - 5,0

Dholakia et al. (1970)

0,0 - 0,2

Carlson (1971)

0,0 - 1,5

Matsche (1971)

1,5 - 1,8

Smith etal. (1972)

0,0 - 2,5

Jones (1972)

0,0 - 2,0

Haltrich (1972)

0,15 - 0,72

Toit and Davies (1973)

< 0,2

Christensen (1973)

0 - 0,3

Drews and Greef (1973)

< 1,5

Parker etal. (1975)

Source: Henze Christensen and Harremoes (1977).

responses during denitrification, as described in Section 3.8 on the influence of temperature on nitrification.

The first type of response is an immediate (rapid) temperature response, which is much smaller than the long-term (slow) temperature response. The second type is the most interesting one; the former is the one often encountered in laboratory experiments. The long-term temperature response is a mixture of an immediate temperature response and adaptation of the microorganisms (Henze and Harremoes 1978).

Very little is known about the relationship between long-term and short-term temperature dependencies.

180 160

% of denitrification at 20 °C

Symbol Reference

Dawson and Murhy (1973)

Figure 4.3 Temperature dependence of the denitrification process.

Mathematically, the dependence on temperature can be described by the following exponential expression:

where: Y is the temperature coefficient in Table 4.8.

The expression is valid only within the range from 5 0 C to about 35 °C. As the temperature in most cases changes slowly, long-term temperature dependencies are the most important for practical purposes.

In table 4.8, the long-term temperature constants k, and 6 for various denitrification processes are listed.

The following temperature expression is proposed by Hultmann (1971):

According to Table 4.8 the literature shows that the temperature dependency for attached growth is smaller than that for suspended growth.

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