6.
With reference to sewage treatment plants:(a)
state the purpose of the vent, and explain why it is fitted with a gauze;(3)
(b) explain the difference between aerobic and anaerobic micro organisms;(3)
(c) explain why air is bubbled through the effluent in the aeration tank;(2)
(d) explain why calcium hypochlorite is added to the treated sewage before discharge overboard.(2)
Sewage treatment plants
Sewage treatment plants onboard a vessel are specialized systems designed to process and treat wastewater generated by the crew and passengers. They play a crucial role in preventing marine pollution and ensuring compliance with environmental regulations, specifically MARPOL Annex IV.
1. Sewage treatment – Wikipedia
2. Prevention of Pollution by Sewage from Ships – International Maritime Organization
Purpose:
- To remove or reduce pollutants and pathogens from wastewater before it’s discharged into the sea. 1. Sewage Treatment Plant (STP) on ship – Naval Architecture – YouTube www.youtube.com
- To protect marine ecosystems and human health by minimizing the environmental impact of sewage discharge.
Types of Sewage Treatment Plants:
- Biological Treatment Plants: These are the most common type, utilizing aerobic bacteria to break down organic matter in the wastewater. 1. MARINE ENGINEERING KNOWLEDGE BY RAJAN – SEWAGE TREATMENT PLANT – Google Sites sites.google.com
- Physical/Chemical Treatment Plants: These systems rely on physical processes like filtration and chemical treatments to remove pollutants. They may be used in combination with biological treatment or as standalone systems for specific applications. 1. Different chemical, physical, and biological wastewater treatment methods, modified from (Singh et al., 2018). – ResearchGate www.researchgate.net
- Electrolytic Treatment Plants: These utilize electrolysis to disinfect the wastewater and reduce pollutants. 1. Electrolytic Sewage Treatment Plant – BT Water Treatment btwatertreatment.com
Basic Components of a Biological Sewage Treatment Plant:
- Collection Tank: Receives wastewater from toilets, sinks, showers, etc. 1. Sewage treatment plants for ships and offshore platforms. – Wärtsilä www.wartsila.com
- Screening/Comminution: Removes large debris and grinds solid waste into smaller particles for easier treatment.
- Aeration Tank: Aerobic bacteria break down organic matter in the presence of oxygen, supplied by aeration systems. 1. Why is Aeration Important for Wastewater Treatment? – OxyMem www.oxymem.com
- Sedimentation Tank: Solids settle to the bottom for removal, while clarified water flows to the next stage. 1. The Role of Primary Sedimentation Tanks www.robuschi.com
- Disinfection: The treated water is disinfected, usually with chlorine or UV light, to kill remaining pathogens before discharge. 1. Comprehensive Guide to Marine Sewage Treatment Plants: Ensuring Clean Seas separatorequipment.com
Benefits of Onboard Sewage Treatment Plants:
- Environmental Protection: By treating wastewater before discharge, they help maintain water quality, protect marine life, and prevent the spread of waterborne diseases.
- Regulatory Compliance: They enable ships to comply with MARPOL Annex IV and other environmental regulations, avoiding penalties and detentions.
- Reduced Reliance on Holding Tanks: Treatment plants reduce the need for large holding tanks, freeing up valuable space on board.
- Cost Savings: In some cases, treating sewage onboard can be more cost-effective than discharging it to shore-based facilities. 1. Sewage treatment plants for ships and offshore platforms. – Wärtsilä www.wartsila.com
Challenges:
- Space Constraints: Onboard space is limited, requiring compact and efficient treatment systems. 1. Sewage Treatment Plant (STP) on ship – Naval Architecture – YouTube www.youtube.com
- Maintenance: Regular maintenance and monitoring are essential to ensure proper operation and effectiveness.
- Crew Training: Crew members need to be trained on operating and maintaining the treatment plant.
Conclusion:
Sewage treatment plants are crucial for minimizing the environmental impact of ship operations. By effectively treating wastewater, they help protect marine ecosystems, safeguard public health, and ensure compliance with international regulations.
The purpose of the vent, and gauze
In a sewage treatment plant on board a vessel, the vent serves two primary purposes:
- Pressure Equalization:
- The vent allows for the equalization of air pressure within the treatment plant and the surrounding atmosphere. This prevents the buildup of excessive pressure or vacuum, which could cause structural damage to the tanks or disrupt the flow of wastewater through the system.
- During filling and emptying of tanks, air needs to be displaced or drawn in to maintain atmospheric pressure inside. The vent facilitates this exchange of air, ensuring smooth operation.
- Odor Control:
- The vent also allows for the release of gases generated during the sewage treatment process, which can include unpleasant odors and potentially harmful gases like methane and hydrogen sulfide.
- Venting these gases prevents their buildup within the treatment plant, improving the working environment and minimizing potential health risks to the crew.
Why the Vent is Fitted with a Gauze:
The gauze fitted on the vent serves several crucial functions:
- Preventing Insect and Debris Entry:
- The gauze acts as a physical barrier, preventing insects, rodents, or other debris from entering the sewage treatment plant through the vent.
- This helps maintain the cleanliness and hygiene of the system, preventing blockages or contamination that could disrupt the treatment process.
- Flame Arrestor (in some cases):
- In certain designs, the gauze may also act as a flame arrestor. This prevents flames or sparks from entering the vent and igniting any potentially flammable gases that might be present within the treatment plant.
- This is particularly important if the plant handles sewage containing flammable liquids or gases.
- Minimizing Splash and Aerosol Release:
- The gauze can help reduce the release of splash or aerosol droplets from the vent, particularly during turbulent flow or aeration processes within the treatment plant.
- This helps maintain hygiene and prevent the spread of potentially harmful microorganisms.
Overall, the vent and its gauze play an essential role in the safe and effective operation of the sewage treatment plant. It ensures proper pressure equalization, odor control, and prevents contamination while minimizing potential safety risks.
Difference between aerobic and anaerobic micro organisms
In the context of sewage treatment plants, aerobic and anaerobic microorganisms play distinct roles in breaking down organic matter and purifying wastewater. The key difference lies in their oxygen requirements and metabolic processes:
1. Aerobic vs. Anaerobic: What to Know About Biological Wastewater Treatment – Aquacycl
2. Anaerobic vs. Aerobic Wastewater Treatment Systems: What’s the Difference?
Aerobic Microorganisms:
- Oxygen Dependence: These microorganisms require oxygen to survive and function. They utilize oxygen in their metabolic processes to break down organic matter and convert it into simpler substances, such as carbon dioxide, water, and biomass. 1. Bacteria – Temperature, Oxygen, pH | Britannica www.britannica.com2. Degradation of organic matter | Processes in Microbial Ecology – Oxford Academic academic.oup.com
- Role in Sewage Treatment: Aerobic bacteria are crucial in the secondary treatment stage of sewage treatment plants, where they are responsible for oxidizing and removing a significant portion of the organic pollutants present in the wastewater.
- Examples: Common aerobic bacteria used in sewage treatment include Pseudomonas, Bacillus, and Nitrosomonas. 1. WO2014186856A1 – A natural wastewater treatment system that uses pseudomonas-type bacteria, and treatment method – Google Patents patents.google.com
Anaerobic Microorganisms:
- Oxygen Independence: These microorganisms thrive in the absence of oxygen and can even be killed by its presence. They utilize different metabolic pathways to break down organic matter, producing methane, carbon dioxide, and other byproducts.
- Role in Sewage Treatment: Anaerobic bacteria play a crucial role in the sludge digestion process, where they decompose the settled solids (sludge) from the primary and secondary treatment stages. This process reduces the volume of sludge and generates biogas (primarily methane), which can be used as a renewable energy source. 1. Primary treatment of sewage and anaerobic treatment of sludge – YouTube www.youtube.com
- Examples: Common anaerobic bacteria involved in sludge digestion include Methanobacterium and Clostridium. 1. Methanobacterium – Wikipedia en.wikipedia.org
Key Differences:
| Feature | Aerobic Microorganisms | Anaerobic Microorganisms |
|---|---|---|
| Oxygen Requirement | Require oxygen for survival and function | Thrive in the absence of oxygen |
| Metabolic Processes | Utilize oxygen to break down organic matter (aerobic respiration) | Break down organic matter without oxygen (anaerobic respiration or fermentation) |
| Byproducts | Carbon dioxide, water, and biomass | Methane, carbon dioxide, and other gases |
| Role in Sewage Treatment | Primarily involved in secondary treatment (oxidation of organic matter) | Primarily involved in sludge digestion (decomposition of solids) |
| Examples | Pseudomonas, Bacillus, Nitrosomonas | Methanobacterium, Clostridium |
Export to Sheets
Both aerobic and anaerobic microorganisms are essential components of a sewage treatment plant, working together to effectively treat wastewater and reduce its environmental impact. Aerobic bacteria primarily focus on removing dissolved organic matter, while anaerobic bacteria play a key role in breaking down solid waste and generating valuable biogas.
1. Aerobic vs. Anaerobic: What to Know About Biological Wastewater Treatment – Aquacycl
Why air is bubbled through the effluent in the aeration tank
In sewage treatment plants, air is bubbled through the effluent in the aeration tank to provide oxygen to the aerobic microorganisms responsible for breaking down organic matter in the wastewater.
Aerobic bacteria require oxygen for their metabolic processes, where they utilize it to oxidize organic pollutants and convert them into simpler substances, such as carbon dioxide, water, and biomass. By bubbling air through the effluent, the dissolved oxygen concentration in the water is increased, creating a favorable environment for these bacteria to thrive and effectively decompose the organic matter.
This aeration process is crucial for several reasons:
- Enhanced Biological Activity:
- Increased Oxygen Availability: The continuous supply of oxygen through aeration ensures that the aerobic bacteria have sufficient oxygen for their metabolic processes, promoting their growth and activity.
- Faster Degradation of Organic Matter: With ample oxygen, the bacteria can efficiently break down the organic pollutants present in the wastewater, reducing its biochemical oxygen demand (BOD) and chemical oxygen demand (COD).
- Improved Treatment Efficiency:
- Enhanced Solids Removal: Aeration also helps in the formation of flocs, which are clumps of bacteria and other suspended solids. These flocs settle more readily in the subsequent sedimentation tank, improving the removal of suspended solids from the wastewater.
- Nitrification: Aeration also supports the growth of nitrifying bacteria, which convert ammonia (a toxic byproduct of organic matter decomposition) into less harmful nitrates. This is an essential step in removing nitrogenous pollutants from the wastewater.
- Odor Control:
- Aerobic Conditions: Maintaining aerobic conditions in the aeration tank helps prevent the growth of anaerobic bacteria, which can produce foul-smelling gases like hydrogen sulfide.
Overall, the aeration process in the sewage treatment plant is critical for:
- Providing essential oxygen for the aerobic bacteria responsible for organic matter degradation
- Enhancing the efficiency of the treatment process by promoting bacterial activity and solids removal
- Controlling odor and preventing the generation of harmful gases
By creating an oxygen-rich environment, aeration ensures the optimal functioning of the biological treatment process, leading to effective wastewater treatment and environmental protection.
Why calcium hypochlorite is added
Calcium hypochlorite is added to the treated sewage before discharge overboard primarily for disinfection. It acts as a powerful oxidizing agent that effectively kills or inactivates harmful microorganisms, such as bacteria, viruses, and protozoa, that may still be present in the treated effluent.
This disinfection process is crucial for several reasons:
1. CALCIUM HYPOCHLORITE – Ataman Kimya
- Public Health Protection:
- Preventing Waterborne Diseases: Discharging inadequately disinfected sewage can contaminate water bodies and pose a significant health risk to people who may come into contact with the water, either directly or indirectly through consumption of contaminated seafood. Calcium hypochlorite helps eliminate harmful pathogens and ensures the safety of recreational waters and the marine environment.
- Protecting Marine Life: Untreated or partially treated sewage can introduce pathogens into the marine ecosystem, potentially harming marine life and disrupting the delicate balance of the ecosystem. Disinfection with calcium hypochlorite helps to mitigate this risk. 1. What is Blackwater? • Cruise Ships – Friends of the Earth foe.org
- Regulatory Compliance:
- MARPOL Annex IV: The International Convention for the Prevention of Pollution from Ships (MARPOL) Annex IV mandates the treatment and disinfection of sewage before discharge. Calcium hypochlorite is a commonly used and approved disinfectant for complying with these regulations. 1. Ship’s sewage and garbage (MARPOL Annex IV-V) – deutsche-flagge.de www.deutsche-flagge.de
- Local Regulations: Many coastal states and port authorities have their own specific regulations regarding sewage discharge, often requiring disinfection to protect local water quality and public health.
- Odor Control:
- While not the primary purpose, chlorination with calcium hypochlorite can also help control odors associated with sewage effluent. It oxidizes organic compounds that contribute to unpleasant smells. 1. Calcium hypochlorite – Wikipedia en.wikipedia.org
Advantages of Calcium Hypochlorite:
- Effectiveness: It’s a powerful disinfectant that effectively kills a wide range of pathogens. 1. What is the Purpose of Calcium Hypochlorite Granules? – McWane Ductile – Iron Strong www.mcwaneductile.com
- Stability: It’s relatively stable and can be stored for longer periods compared to other disinfectants like chlorine gas. 1. Calcium hypochlorite – Wikipedia en.wikipedia.org
- Ease of Use: Available in granular or tablet form, it’s relatively easy to handle and dose in sewage treatment plants.
Considerations:
- Dosage Control: Proper dosage control is essential to ensure effective disinfection while avoiding over-chlorination, which can be harmful to aquatic life.
- Dechlorination: In some cases, excess chlorine may need to be removed (dechlorination) before discharge to protect the environment.
- Safety: Calcium hypochlorite is a strong oxidizer and can be hazardous if mishandled. Proper safety precautions must be taken during storage and use. 1. OSHA Hazard Information Bulletins Calcium Hypochlorite (CaCl 2 O 2 ) www.osha.gov
In summary, the addition of calcium hypochlorite to treated sewage before discharge overboard serves as a crucial disinfection step, protecting public health, safeguarding marine ecosystems, and ensuring compliance with environmental regulations.Sources and related content