Key Stages of Sewage Treatment and Their Impact on the Environment
Human health and environment are mainly suffering from direct disposal of commercial and human effluents into the natural resources with none of the treatment. The sewage treatment is important to scale back the toxicity of sewage and maintain a secure and healthy environment, also as it promotes human welfare.
Sewage Treatment Process
Sewage contains an enormous amount of organic matters which are toxic. Microorganisms are widely utilized in the sewage treatment plant for removing this toxic organic matter. Sewage or wastewater treatment plant consists of two stages:
Primary Treatment
It involves the removal of huge or small sized components within the wastewater through physical processes.
Biological Treatment
The sewage treatment plants are inoculated into Aerobic microorganisms .These organic components of these microbes utilize the sewage and reduce the toxicity which can be measured by BOD (Biological oxygen demand).
After the biological treatment, the sludge is pumped from the treatment plant into an outsized tank. This large tank consists of anaerobic bacteria which cause the digestion of sludge. During digestion, biogas is produced and it is used as an energy source. Hence, Sewage treatment plant design and sewage management play an important role within the maintenance of human welfare.
Energy Generation
Microorganisms which are involved within the production of energy are called microbial fuel cells. Microbial fuel cells are used to generate a variety of energy sources like biogas and electricity. Agricultural waste, manure, and domestic wastes are used as raw materials for the generation of biogas. Biogas generation is completed within the large concrete tank which is named as a biogas plant.
Biomasses (Biowastes) are collected at the biogas plant and therefore the slurry is fed. Biomasses are rich in organic matter. Some of the bacteria inside the biogas plant anaerobically These bacteria can digest the biomasses which are present within the slurry and sewage. During digestion, an enormous amount of mixture of gases is released inside the tank. The mixture of these gases is called biogas. Biogas is removed from the biogas plant through a separate outlet.
Electricity from wastewater can also be generated by Microbial fuel cells. From the wastewater treatment plant microbial fuel cells utilize the organic matter.During digestion, organic matters are converted into the straight molecule and release the CO2 and electrons. Those electrons are absorbed by the electrode and used as the source of electricity.
Odor Control
Odors emitted by sewage treatment are typically a sign of an anaerobic or "septic" condition. Early stages of processing will tend to supply foul-smelling gases, with sulfide being commonest in generating complaints. Carbon reactors, a contact media with bio-slimes, less doses of chlorine, or circulating fluids to biologically capture and metabolize the noxious gases at plants with large processes in urban areas are the processes that are used to fade away the foul odor. Other methods of odor control exist, including addition of iron salts, peroxide , nitrate, etc. to manage hydrogen sulfide levels. High-density solids pumps are used for minimizing the odor by conveying sludge through hermetic closed pipework.
Environmental Aspects
There are many processes that are used in the wastewater treatment plant that are designed to copy the natural treatment processes that occur within the environment, whether that environment may be a natural water body or not. Bacteria within the environment will consume organic contaminants if not overloaded,although this may lead to the reduction of the amount of oxygen within the water and should significantly change the general ecology of the receiving water. Organic contaminants work as a food for the neighbouring bacterial populations and therefore the numbers of disease-causing microorganisms are reduced by natural environmental conditions like predation or exposure to ultraviolet .
Consequently, in cases where the receiving environment provides a high level of dilution, a high degree of wastewater treatment might not be required. However, recent evidence has demonstrated that very low levels of specific contaminants in wastewater, including hormones (from farming and residue from human hormonal contraception methods) and artificial materials such as phthalates that mimic hormones in their action, can have hit or miss adverse impact on the natural biota and potentially on humans if the water is reused for drinking water. As per the law in the US and EU, uncontrolled discharges of wastewater to the environment aren't permitted under law, and strict water quality requirements are to be met, as clean water is essential. A significant threat within the coming decades are going to be the increasing uncontrolled discharges of wastewater within rapidly developing countries.
FAQs on Sewage Treatment Explained: Process, Benefits, and Solutions
1. What exactly is sewage and what does it typically contain?
Sewage is the wastewater generated from domestic and industrial sources. It is primarily water (over 99%) but contains a complex mixture of contaminants. Key components include organic matter (like human waste and food scraps), inorganic nutrients (such as nitrates and phosphates from detergents), pathogenic microbes (bacteria, viruses, and protozoa that can cause diseases), and suspended solids.
2. What is the main objective of treating sewage before its disposal?
The primary objective of sewage treatment is to remove pollutants and harmful microorganisms to make the water safe enough to be discharged back into the environment, such as rivers or seas. This process is crucial for preventing the spread of waterborne diseases, protecting aquatic ecosystems from pollution, and conserving fresh water resources.
3. What are the main stages involved in the process of sewage treatment in a Sewage Treatment Plant (STP)?
Sewage treatment is typically carried out in three main stages:
- Primary Treatment: A physical process where large floating debris and heavy solids are removed. It involves filtration to remove debris and sedimentation to allow grit and other solids to settle down.
- Secondary Treatment: A biological process where dissolved organic matter is removed. This stage uses microorganisms to consume the organic pollutants.
- Tertiary Treatment: A final polishing stage that removes any remaining contaminants, such as phosphates and nitrates, and disinfects the water (e.g., using chlorine or UV light) before it is released.
4. How does secondary sewage treatment differ fundamentally from primary treatment?
The fundamental difference lies in the method of purification. Primary treatment is a purely physical process that uses screens and gravity to remove large, visible solids and grit. In contrast, secondary treatment is a biological process that relies on microorganisms to break down and remove fine, dissolved organic matter that cannot be removed by physical means.
5. What role do 'flocs' play in the secondary treatment of sewage?
Flocs are mesh-like structures formed by masses of aerobic bacteria and fungal filaments. During secondary treatment, the sewage is pumped into large aeration tanks where these flocs vigorously consume the organic matter present in the wastewater. This biological consumption significantly reduces the pollution level. Afterwards, these flocs settle down as sediment, known as activated sludge.
6. What is Biochemical Oxygen Demand (BOD), and why is its reduction a key indicator of successful treatment?
Biochemical Oxygen Demand (BOD) is a measure of the amount of dissolved oxygen needed by aerobic microorganisms to break down the organic matter present in a water sample. A high BOD value indicates a high level of organic pollution. The reduction of BOD is a key goal because it directly signifies that the organic pollutants have been removed, making the water cleaner and less harmful to aquatic life.
7. What is activated sludge, and how is it used in the treatment process?
Activated sludge is the sediment that settles after the aeration stage in secondary treatment. It is rich in the aerobic microorganisms (flocs) that were used to break down the organic waste. A small portion of this activated sludge is recycled back into the aeration tank as an inoculum or starter. This ensures a high population of active microbes is available to efficiently treat the next batch of incoming sewage.
8. How is biogas produced during sewage treatment, and what is its practical importance?
The bulk of the activated sludge is processed in large, oxygen-free tanks called anaerobic sludge digesters. Here, anaerobic bacteria break down the organic matter in the sludge. This process releases a mixture of gases, primarily methane, carbon dioxide, and hydrogen sulphide, which is collectively known as biogas. Its practical importance is that biogas is combustible and can be used as a source of energy to generate electricity or heat for the treatment plant itself, making the process more sustainable.
9. Beyond cleaning water, what are the major benefits of installing sewage treatment solutions?
Effective sewage treatment offers several significant benefits:
- Environmental Protection: It prevents pollution of rivers, lakes, and oceans, thereby protecting aquatic plants and animals.
- Public Health: It eliminates harmful pathogens from wastewater, preventing the outbreak and spread of diseases like cholera, typhoid, and dysentery.
- Water Conservation: Treated water can be reused for non-potable purposes like irrigation, industrial processes, and landscaping, which reduces the demand on fresh water sources.
- Resource Recovery: It allows for the recovery of valuable resources like biogas (for energy) and nutrient-rich sludge (as fertiliser).
