Explain important parameters which are required to be known for proper treatment of sewage.

Proper treatment of sewage is crucial for protecting public health and the environment. To design and operate an effective sewage treatment plant, several key parameters must be understood and monitored. These parameters help in assessing the characteristics of the sewage and determining the appropriate treatment processes. They can be broadly categorized into physical, chemical, and biological parameters.

1. Physical Parameters

a. Flow Rate

• Importance: The flow rate of sewage is critical for designing the capacity of treatment facilities. It varies with time of day, season, and local population.
• Measurement: Flow meters and weirs are commonly used to measure sewage flow rates.

b. Temperature

• Importance: Temperature affects the biological and chemical reactions in sewage treatment processes. It influences the rate of microbial activity and the solubility of gases like oxygen.
• Measurement: Regular temperature monitoring is conducted using thermometers or temperature sensors.

c. Color and Odor

• Importance: The color and odor of sewage can indicate the presence of industrial wastes or other pollutants.
• Assessment: Visual inspection and olfactory detection are used, though these are subjective measures.

d. Total Suspended Solids (TSS)

• Importance: TSS indicates the amount of suspended particles in sewage. High levels can lead to clogging and hinder treatment processes.
• Measurement: TSS is measured by filtering a known volume of sewage and weighing the retained solids.

2. Chemical Parameters

a. pH

• Importance: The pH level affects the solubility of gases and the activity of microorganisms. Most biological processes in sewage treatment work best in a near-neutral pH range.
• Measurement: pH meters are used for accurate and continuous monitoring.

b. Biochemical Oxygen Demand (BOD)

• Importance: BOD measures the amount of oxygen required by microorganisms to break down organic matter in sewage. It indicates the organic pollution load.
• Measurement: BOD is measured by incubating a sealed sample of sewage and measuring the decrease in dissolved oxygen over five days.

c. Chemical Oxygen Demand (COD)

• Importance: COD measures the total quantity of oxygen required to oxidize both biodegradable and non-biodegradable organic matter. It is a quicker measure than BOD.
• Measurement: COD is determined using strong chemical oxidants in a laboratory.

d. Nutrients (Nitrogen and Phosphorus)

• Importance: Nutrients like nitrogen and phosphorus are essential for microbial growth but can cause eutrophication in water bodies if discharged in excess.
• Measurement: Various chemical tests are used to measure concentrations of ammonia, nitrates, nitrites, and phosphates.

e. Heavy Metals and Toxic Compounds

• Importance: Heavy metals and toxic compounds can be harmful to both the environment and human health. They may inhibit biological treatment processes.
• Measurement: These are measured using advanced techniques like atomic absorption spectroscopy (AAS) and gas chromatography.

3. Biological Parameters

a. Microbial Population

• Importance: The type and quantity of microorganisms present are crucial for the biological treatment processes, such as activated sludge or biofiltration.
• Assessment: Microscopic examination and plate counts are used to analyze microbial communities.

b. Pathogens

• Importance: The presence of pathogens (bacteria, viruses, parasites) in sewage is a major public health concern.
• Detection: Pathogen levels are assessed through specific culture techniques and molecular methods.

4. Other Important Considerations

a. Oil and Grease

• Importance: High levels of oil and grease can interfere with treatment processes and lead to operational problems.
• Measurement: Extraction and gravimetric methods are used for quantification.

b. Toxicity

• Importance: The overall toxicity of sewage affects the viability of biological treatment processes and the potential harm to aquatic life post-discharge.
• Assessment: Toxicity is assessed using bioassays with specific organisms like fish or daphnia.

c. Solids Retention Time (SRT) and Hydraulic Retention Time (HRT)

• Importance: SRT and HRT are operational parameters that determine how long solids and water, respectively, are retained in the treatment system. They are crucial for process optimization.

Conclusion

Effective sewage treatment requires a comprehensive understanding of various physical, chemical, and biological parameters. Regular monitoring and control of these parameters are essential to ensure that the treatment processes are efficient and meet the required discharge standards. By effectively managing these parameters, sewage treatment plants can protect public health, preserve water quality, and contribute to sustainable environmental management.