the saturation value. Dissolved oxygen measurements are given as a percent of
saturation (%) or in units of milligrams per liter (mg/l) [22]
The oxygen content of natural waters can vary widely depending on the physical,
chemical, and biological processes in the water body as already indicated. Running
waters generally have higher oxygen content than stagnant waters. As explained, the
major source of oxygen in natural waters is the atmospheric air. Oxygen enters water
by the process of diffusion and higher the mixing of air and water due to surfacewater agitation, such as by wave action and turbulence in running water or due to
artificial process of aeration by compressed air diffusers and use of agitators, in
aquaria and ponds, the higher the oxygen saturation. Apart from diffusion from the
air, water bodies gain oxygen through photosynthesis of chlorophyll-bearing aquatic
organisms, i.e., higher plants, phytoplankton, and photosynthetic bacteria. Oxygen is
lost from the water body by the respiration of animals and plants and also by
decomposition of organic matter. Excess oxygen will also be released from water
to air by diffusion.
The four commonly recognized profiles described are indicated in Fig. 3.10.
Stratification of lakes with reference to temperature and physico-chemical conditions, though mainly recognized in temperate conditions, are also seen in tropical
water bodies in a modified form; these are of special importance for aquaculturists
working to stock open waters, which is also part of the present course.
3.2 Biochemical Decay of Organic Waste Materials
Natural organic detritus and organic waste from waste water treatment plants, failing
septic systems, and agricultural and urban runoff, act as food sources for water-borne
bacteria. Bacteria decompose these organic materials using dissolved oxygen. Biochemical oxygen demand (BOD) is a measure of the amount of oxygen that bacteria
will consume while decomposing organic matter under aerobic conditions. The main
focus of wastewater treatment plants is to reduce the BOD in the effluent discharged
to natural waters. Wastewater treatment plants are designed to function as bacteria
farms, where bacteria are fed oxygen and organic waste [23].
The BOD test can be used to investigate the controls on consumption of dissolved
oxygen in the water column and to derive decay rates for water quality models.
BOD t ¼ BOD u 1 À e
Àkt
À
Á
ð3:16Þ
Where, BOD t is the exerted biochemical oxygen demand (mg/L of O 2 ) at time t,
BOD u is the ultimate BOD (mg/L of O 2 ), k is the first-order decay rate (1/day), and
t is the time (days).
The Streeter-Phelps equation is used in water pollution as a water quality modeling tool. The model describes how dissolved oxygen (DO) decreases in a river or
stream along a certain distance by degradation of biochemical oxygen demand
96
H. A. Aziz et al.
saturation (%) or in units of milligrams per liter (mg/l) [22]
The oxygen content of natural waters can vary widely depending on the physical,
chemical, and biological processes in the water body as already indicated. Running
waters generally have higher oxygen content than stagnant waters. As explained, the
major source of oxygen in natural waters is the atmospheric air. Oxygen enters water
by the process of diffusion and higher the mixing of air and water due to surfacewater agitation, such as by wave action and turbulence in running water or due to
artificial process of aeration by compressed air diffusers and use of agitators, in
aquaria and ponds, the higher the oxygen saturation. Apart from diffusion from the
air, water bodies gain oxygen through photosynthesis of chlorophyll-bearing aquatic
organisms, i.e., higher plants, phytoplankton, and photosynthetic bacteria. Oxygen is
lost from the water body by the respiration of animals and plants and also by
decomposition of organic matter. Excess oxygen will also be released from water
to air by diffusion.
The four commonly recognized profiles described are indicated in Fig. 3.10.
Stratification of lakes with reference to temperature and physico-chemical conditions, though mainly recognized in temperate conditions, are also seen in tropical
water bodies in a modified form; these are of special importance for aquaculturists
working to stock open waters, which is also part of the present course.
3.2 Biochemical Decay of Organic Waste Materials
Natural organic detritus and organic waste from waste water treatment plants, failing
septic systems, and agricultural and urban runoff, act as food sources for water-borne
bacteria. Bacteria decompose these organic materials using dissolved oxygen. Biochemical oxygen demand (BOD) is a measure of the amount of oxygen that bacteria
will consume while decomposing organic matter under aerobic conditions. The main
focus of wastewater treatment plants is to reduce the BOD in the effluent discharged
to natural waters. Wastewater treatment plants are designed to function as bacteria
farms, where bacteria are fed oxygen and organic waste [23].
The BOD test can be used to investigate the controls on consumption of dissolved
oxygen in the water column and to derive decay rates for water quality models.
BOD t ¼ BOD u 1 À e
Àkt
À
Á
ð3:16Þ
Where, BOD t is the exerted biochemical oxygen demand (mg/L of O 2 ) at time t,
BOD u is the ultimate BOD (mg/L of O 2 ), k is the first-order decay rate (1/day), and
t is the time (days).
The Streeter-Phelps equation is used in water pollution as a water quality modeling tool. The model describes how dissolved oxygen (DO) decreases in a river or
stream along a certain distance by degradation of biochemical oxygen demand
96
H. A. Aziz et al.