The C/N relationship decribes the quantity of organic matter, which is needed per unit of nitrate-nitrogen that is converted to nitrogen gas by denitrification.
Organic matter of many kinds (as shown in Table 4.5) can be used for the following three purposes in a denitrification plant.
1) Reduction of nitrate or nitrite into nitrogen gas.
2) Sludge production, i.e. biomass production.
3) Respiration with oxygen.
Knowing the values of the three parameters described, it is possible to quantify the C/N relationship for a denitrification plant.
If the C/N ratio is smaller than is stoichiometrically needed, the denitrification process will not proceed or be applied with reduced capacity. If there is less nitrate or nitrite it will be converted into nitrogen gas.
Monteith et al. (1980) conducted an experiment in 30 industrial waste water streams. Twenty-seven of the 30 industrial waste streams were evaluated as external sources of carbon, added to domestic waste water. Fifty per cent of the waste water tested supplied a sufficient content of carbon for a constant denitrification of domestic waste water and exhibited denitrification rates equal to or greater than those observed using methanol. The C/N ratio found in the described experiments with external sources of carbon were between 0,7 to 2,6 kg FOC/kg NOT-N removed. If methanol were used at carbon source an average of C/N ratio was found to be 1,17 kg FOC/kg NOt-N removed. FOC is the amount of fully oxidisable carbon. NOT - N er the total amount of nitrate and nitrite.
Table 4.5 Carbon sources other than methanol and internal carbon source in denitrifying experiments.
Bakery sludge Bouillon/Casein
Chemical industry waste
Cherry juice Citrate Corn starch
Adams etal. (1970)
Clayfied (1974) Edholm et a/.(1970) Ericsson et al.( 1966)
Wilson and Newton (1973)
Englehart and Haltrich (1968) Haltrich and Jager (1963, 1970)
Ide et al(1972)
Bringmann etal. (1959) Finsen and Sampson (1959) McCarty (1969) McCarty et al. (1969)
Ludzack and Ettinger (1962)
Ludzack and Ettinger (1962)
Balakrishnan (1968) Balakrishnan and Eckenfelder (1969) Barth and Ettiger (1967) Christenson etal. (1956) Clayfied (1974)
Table 4.5 (continued)
Milk solids Molasses
Nitro-cellulose waste Peptone
Sodium citrate Sugary syrup
Ide etal. (1972) McCarty (1969)
Schroeder and Busch (1967, 1968) Wuhrmann (1960)
Ide etal. (1972) Toit and Davis (1973)
Bringmann etal. (1959)
Christensen (1972) Harremoes and Christensen (1971) Parker etal. (1975) Pretorius (1972)
Aguirre and Gloyna (1967) Hermann (1962) Parker etal. (1975) Pretorius (1972)
Finsen and Sampson (1959)
Clayfied (1974) Ide etal. (1972)
Das etal. (1966) Finsen and Sampson (1959) Klotter (1969) McCarty (1969)
Dawson and Murphy (1972)
Source: Henze Christensen and Harremoes (1977)
carbon sources. The more easily degradable the carbon source, such as methanol the greater is the reaction rate. Heavily degradable endogenous carbon has a low reaction rate, especially at low temperature. (Source: Henze and Harremoes 1978)
Was this article helpful?