Organic Waste Recycling

342 Organic waste recycling: technology and management

effluent BOD 5 concentrations is presented in Figure 7.11. In this example, the
magnitude of the winter leakage of BOD is quite high (around 30 mg/L). If the
BOD 5 loading rate is either reduced in winter in conjunction with climatically
induced reductions in bacterial metabolic rates and in bacterial support structure,
or low on a year-round basis so as to avoid overloading the system in winter,
then the effluent BOD 5 in winter would be lower than the concentrations
reported in Figure 7.11.

Figure 7.11 An example of the seasonality of effluent BOD 5 concentrations. Note:
Compiled by Stowell et al. (1980), using data from Wolverton and McDonald (1976a).
Reproduced by permission

TEMPERATURE (°C)

EFFLUENT BOD

(mg/L) 5

ZONE DESCRIPTION

Late spring to fall: active bacterial metabolism and full plant structure for

supporting bacteria; effluent BOD at

background concentrations.

Late fall to winter: diminishing bacterial activity caused by cooling temperatures:

progressive loss of bacterial support

structure as plants die off.

Winter to spring: increasing bacterial activity,

but continued loss of bacterial support structure as plants again.

Spring: increasing bacterial activity and plant

structure (regrowth).

A

B

C

D

C

B

A

D

BACKGROUND BOD

CONCENTRATION (VARIABLE)