The amount of oxygen required or requested by aerobic bacteria to break down the organic matter contained in a specific sample of water at a specific temperature and during a specific time period is known as biochemical oxygen demand (BOD).
Water bodies have a specific amount of dissolved oxygen on which aquatic life relies for its respiratory needs. When organic matter is present in a water body, aerobic microbes consume the dissolved oxygen in the water to break down the organic matter, limiting the amount of oxygen available to aquatic life. Water contains molecular oxygen, which is either a result of photosynthesis in aquatic plants or air oxygen in dissolved form. The higher the BOD of a water body or sample, the more polluted it is. Organic matter levels are rising due to a variety of sources, the most of which are human in nature, such as pollution. BOD is a metric for assessing the quality of water. Water quality management includes determining the amount of organic matter in a body of water and its impact on the environment and aesthetics of the body of water.
Biochemical Oxygen Demand Measurement
The Biochemical Oxygen Demand of a water sample is determined using a Bioassay process that analyses the oxygen required by bacteria as a result of organic matter breakdown over a five-day period at a temperature of 20°C. The amount of BOD in a litre of water is measured in milligrammes. Despite the fact that this is not an exact quantitative test, it is extensively used to determine the polluting potential of water. Sawyer and McCarty administered this test in 1978.
BOD Typical Values and Indications:
Below 1 mg/L– Pristine water quality.
2-8 mg/L- Moderately contaminated water.
Above 8 mg /L- Severely contaminated water.
Factors Affecting BOD
1.Temperature
2.The pH of the water
3.The growth of aerobic bacteria is influenced by the presence of specific microorganisms.
4.Type of inorganic compounds.
5.The amount and type of organic matter present in water.
The Importance of BOD
The importance of biochemical oxygen demand can be found in a variety of professions. These are the following:
1.Sewage treatment plants are where BOD is most useful. The respiration rate of sewage, sludge, soil, and rubbish is calculated.
2.It is responsible for determining the rate of breathing in living things.
3.The COD, or Chemical Oxygen Demand, of inorganic compounds is determined by measuring BOD.
4.It demonstrates how contaminated water can be.
5.The oxygen consumption of cell cultures is measured using BOD in the medical and pharmaceutical industries.
BOD’s sources
Sources that boost biological oxygen levels Water demand is both natural and man-made. Pollution contributes significantly to the increase in BOD in water bodies. A healthy lifestyle is linked to the daily use of a lot of water, which results in a lot of wastewater with organic content. Pollution levels are skyrocketing as the world becomes more industrialised. Large amounts of wastewater are generated in factories. Paper mills, food processing factories, jute mills, and other sectors produce large amounts of wastewater. Surface runoff, floating debris, dead animals and plants, soil erosion, and other environmental variables all contribute to an increase in BOD. The BOD of drinking water is influenced by a small number of substances. Phosphate is one of these, and it raises the BOD of water when it is present in large proportions.
Usage of BOD in Sewage Treatment Plants
In secondary sewage treatment or biological sewage treatment, biochemical oxygen demand is applied. The primary effluent is delivered to aeration tanks where it is constantly agitated and air is injected into it after primary treatment, in which the floating debris is removed by sequential filtering and sedimentation. Heterotrophic microorganisms are rapidly growing into flocs in aeration tanks. Flocs are bacterial swarms that cling to fungal filaments.
The organic stuff in the main effluent is consumed by these microorganisms. The water is treated until the BOD level falls below a certain threshold. The activated sludge is what it’s currently known as. This aeration tank effluent is pumped into settling tanks, where bacterial flocs settle and are then treated with anaerobic microorganisms and physicochemical processes before being discharged into bodies of water.
High BOD has a negative impact on the aquatic ecosystem.
The effects of increasing BOD are similar to the effects of dissolved oxygen depletion. A considerable increase in a water body’s BOD has a negative impact on aquatic life. Microbes that break down organic waste lower the amount of oxygen consumed by aquatic species for respiration and metabolism. Fish and aquatic plants die as a result, and the aquatic environment is completely disrupted. Even low oxygen organisms like catfish and carps are at risk when oxygen levels fall below 5ppm (parts per million). Freshwater fish such as Catla and rohu cannot thrive at these levels. The water body’s overall appearance and beauty have been harmed.
The Impact of Pollution on Biochemical Oxygen Demand
The water quality of the water bodies is deteriorating as a result of increased pollution and urbanisation. The proper ecological functions require proper water quality control. As a result of urbanisation, substantially higher amounts of sewage are produced. The number of sewage treatment plants available was insufficient to handle the massive amounts of sewage. Untreated sewage was frequently released straight into bodies of water, resulting in significant contamination and an increase in the BOD of the bodies of water. This resulted in an upsurge in water-borne illnesses such as cholera, dysentery, and jaundice, among others.
The increased levels of BOD and pollution resulted in severe pollution of India’s two major river systems, the Ganga and the Yamuna. To safeguard these country’s important rivers, the Ministry of Environment and Forests launched the Ganga Action Plan in 1985 and the Yamuna Action Plan in 1993. These plans prompted the construction of a huge number of sewage treatment plants in order to allow only treated sewage to be discharged into waterways.
Methods to Reduce BOD in Water
The biological oxygen demand of water can be lowered using the methods listed below.
1.H2O2/UV, O3/UV, Fenton’s reagent (H2O2+FeSO4), and other Advanced Oxidation Processes (AOP)
2.Using alum or cationic polymers to coagulate
3.Flocculation and sedimentation (e.g., chitosan, isinglass, polyelectrolyte).
4.Activated charcoal adsorption method
5.Electro flocculation.
6.Using an anaerobic sludge blanket reactor with up-flow (UASB).
7.Reverse osmosis.
8.Dissolved air floatation technique.
All life forms on the planet require water to survive. As a result, it is critical that we conserve water and do not contaminate it. Polluted water causes direct harm to all living creatures, including humans and other kinds of life. Rising biochemical oxygen demand levels in water are wreaking havoc on the ecosystems of water bodies, which, in turn, is wreaking havoc on the ecology of the entire biosphere. It is our responsibility to ensure the survival of these ecosystems. Other forms of life have the same level of access to natural resources that humans have. We must put our avarice aside and work toward the conservation of water bodies and the lowering of BOD levels inside them.
Biochemical Oxygen Demand is a measurement of the amount of dissolved oxygen consumed by aerobic bacteria while digesting organic materials in stream water.
Factors that Influence BOD
The following are the elements that influence biological chemical demand:-
The amount of dissolved oxygen in streams and rivers is affected by biological oxygen demand. pH, temperature, microbes, and organic and inorganic elements all influence the rate of oxygen consumption.
Higher types of aquatic life consume less oxygen. The effects of a high BOD are similar to those of a low dissolved oxygen level.
Biological oxygen requirement has a variety of applications, as follows:
1.Biological oxygen demand is utilised in studies to determine a stream’s self-purification capacity.
2.It’s a significant sanitary analysis method for determining industrial waste, sewage strength, and polluted water.
- It also acts as a source for testing the effluent quality that is discharged into the stream water.
CONCLUSION
BOD is defined as the quantity of molecular oxygen necessary for biological oxidation of organic matter in water, and it is also used to describe the average amount of oxygen required for the degradation of organic waste materials that are aerobically degradable.