Navigating Clean Waters: Sewage Treatment Vacuum Pumps on Vessels

Sewage treatment on board vessels is a crucial aspect of maritime operations, ensuring that wastewater is properly managed and disposed of in an environmentally responsible way.

Example of sewage vacuum pump

One integral component of this system is the sewage treatment vacuum pump, often coupled with a macerator, which plays a pivotal role in maintaining hygiene and safety. In this blog post, we will delve into the correct operation, maintenance, and troubleshooting of these pumps and macerators, emphasizing the indispensable role of onboard marine engineers.

Operating the Sewage Treatment Vacuum Pump and Macerator

Operating these components correctly is imperative for the efficient treatment of sewage on vessels. Here’s how to do it:

  • Start-Up: Initiate the system carefully, ensuring that all valves are in the correct position, and that the pump’s power source is secure. The vacuum pump should be started only after the sewage treatment plant is in operation. Always follow the manufacturer’s instructions.
  • Control Parameters: Maintain the required vacuum level and flow rate. The suction and discharge pressure gauges should be checked for rated pressure. Incorrect settings can lead to overloading or inefficient treatment.
  • Monitoring: Regularly monitor the vacuum pressure and macerator operation. Abnormal sounds or performance may indicate a problem.The prime mover motor ampere should be checked and compared with rated current
  • Proper Disposal: Ensure that the treated sewage is discharged in accordance with international and local regulations, avoiding any harm to the marine environment.The vacuum pump should be stopped only after the sewage treatment plant is stopped.

Maintenance of Sewage Treatment Vacuum Pump and Macerator


Proper maintenance is the key to the longevity and reliability of these components:

  • Routine Inspections: Conduct regular inspections to check for wear and tear, leaks, and loose connections. Any issues should be promptly addressed.
  • Lubrication: Ensure that all moving parts are adequately lubricated to prevent friction and overheating.
  • Cleaning: Keep the macerator clean and free from debris, which can cause clogs and damage. Regular cleaning prevents malfunctions.
  • Spare Parts: Maintain a stock of essential spare parts to minimize downtime in case of component failure.

Sewage vacuum pump troubleshooting

In the event of issues with the sewage treatment vacuum pump and macerator, onboard marine engineers must be prepared to troubleshoot effectively:

  • Diagnosing Problems: Identifying the root cause of issues, such as reduced vacuum pressure or abnormal noises, is crucial. For example:
    • If the vacuum pump fails to start, check the power supply and wiring connections.
    • If the vacuum pump fails to stop, check the solenoid valve and wiring connections.
    • If the vacuum pump is noisy, check for loose parts or worn bearings.
  • Leak Detection: Leaks can compromise the system’s performance. Use leak detection methods to pinpoint and repair them.
  • Clog Removal: Clogs in the macerator or piping can disrupt the entire system. Carefully disassemble and clean the affected areas.
  • Electrical Faults: For electrical issues, marine engineers should be well-versed in troubleshooting and repairing motor, control, and sensor problems.

The Role of Marine Engineers

Marine engineers are the unsung heroes of onboard sewage treatment systems. Their knowledge and expertise are essential for maintaining these systems in peak condition. They must undergo specialized training to understand the unique challenges of maritime sanitation and wastewater management. Moreover, their contribution extends to:

  • Regularly inspecting and maintaining the sewage treatment system to prevent emergencies.
  • Quickly responding to any system malfunctions, ensuring the safety of the vessel and its occupants.
  • Staying updated on regulations and standards to ensure compliance with environmental laws.

In conclusion sewage treatment vacuum pumps and macerators are vital components of maritime hygiene and environmental responsibility. The correct operation, maintenance, and troubleshooting of these systems are pivotal, and onboard marine engineers play an indispensable role in this process. By following proper procedures and addressing issues promptly, vessels can sail the seas while preserving the marine environment.

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Video source and credit: Shrimp to Shark Youtube channel


Sewage Air Blower: A Vital Component Onboard – Operation, Maintenance, and Troubleshooting

Onboard marine vessels, sewage treatment is a critical aspect of environmental responsibility and operational efficiency. One key component that plays a significant role in this process is the sewage air blower.


Example of sewage air blower

This article will delve into the correct operation, maintenance, and troubleshooting of sewage air blowers, emphasizing their importance and the role of onboard marine engineers.

The Importance of Sewage Air Blowers

Sewage air blowers are essential for aerating wastewater in sewage treatment systems. They provide the necessary oxygen for the aerobic bacteria to break down organic matter, ensuring the effluent is treated effectively. Properly functioning sewage air blowers are crucial for adhering to environmental regulations, reducing environmental impact, and maintaining the overall well-being of the marine environment.

Example of air blower installed on sewage treatment plant

The following are some guidelines for the correct operation, maintenance, and troubleshooting of sewage air blowers.


Source and Credit: Victor Marine Ltd.

  • Start-Up Procedure: The correct operation of sewage air blowers begins with a well-defined start-up procedure. Marine engineers should ensure that the blower is started and stopped following the manufacturer’s recommendations.
    • The blower should be started before the sewage treatment plant is put into operation.
    • This usually involves gradually increasing air pressure and monitoring various parameters.
    • The blower should be kept clean and free from any obstructions.
    • The blower should be stopped only after the sewage treatment plant has been shut down.
  • Airflow Control: Maintaining the right airflow is vital. Marine engineers must adjust the blower’s speed and air pressure to ensure that oxygen levels in the sewage treatment tanks remain within the optimal range for microbial digestion.
  • Monitoring and Data Collection: Continuous monitoring of air blower performance is crucial. Modern vessels are equipped with monitoring systems that record essential data, enabling engineers to detect issues early. Regularly analyzing this data can help prevent problems before they escalate.


Source and Credit: Sean Lentze

  • Scheduled Inspections: Regular inspections are the cornerstone of maintenance. Marine engineers should follow a well-defined inspection schedule, checking for leaks, blockages, or any signs of wear and tear.
  • Lubrication: Ensure proper lubrication of the blower’s moving parts according to the manufacturer’s recommendations. Lubrication helps reduce friction, heat, and wear, extending the blower’s lifespan.
  • Air Filter Maintenance: The air filter is essential for keeping the blower’s intake air clean. Regularly clean or replace air filters as needed to prevent blockages and maintain airflow efficiency.
  • Impeller blades condition: Check the shape and condition of the blower impeller blades. Repair or replace as found necessary.


  • Unusual Noises: If unusual noises emanate from the blower, it’s an indication of potential issues, like worn-out bearings or a damaged impeller. Investigate the source of the noise and address it promptly.
  • Reduced Airflow: A drop in airflow could signify blockages, damaged components, or issues with the blower itself. If the blower is not providing enough air, it could be due to a clogged filter or a worn-out V-belt. Marine engineers should identify and rectify the problem to restore normal operation.
  • Vibration: Excessive vibration can cause damage to the blower and its mounting. Balancing and aligning the blower can resolve this issue.
  • Temperature Fluctuations: Sudden temperature changes may indicate a malfunctioning blower. Marine engineers should investigate and repair the blower or its associated systems to maintain stable operation.

The Role of Onboard Marine Engineers

Onboard marine engineers play a pivotal role in ensuring the correct operation, maintenance, and troubleshooting of sewage air blowers. Their responsibilities encompass routine checks, preventive maintenance, and immediate response to issues. Engineers should work closely with manufacturers to understand the specific requirements of the blower installed on the vessel and have the necessary tools and spare parts readily available.

It is important to note that proper operation and maintenance of sewage air blowers are critical to ensure that the sewage treatment plant functions efficiently. 

In conclusion, sewage air blowers are integral to the proper functioning of sewage treatment systems on marine vessels. Their correct operation, maintenance, and troubleshooting are essential for environmental compliance and overall operational efficiency. Onboard marine engineers hold the key to the effective and reliable performance of sewage air blowers, and their diligence in these aspects is paramount to safe and eco-friendly maritime operations.

If you have any questions regarding above, please feel free to use our existing forum Seafarer’s World, Telegram Chief Engineer’s Log Chat or Instagram and will try to answer to all your queries. You can use the feedback button as well!

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Waht you need to know about marine sewage effluent testing

To reduce sewage’s contribution to marine pollution, the IMO spearheaded the very first global environmental project. Changes in both technology and policy have been steadily accruing over the past century, and this trend will only accelerate. Raw sewage being dumped into the ocean poses a health risk to marine life. Oxygen depletion and visual pollution caused by sewage are particularly problematic for countries that rely on tourism. Most human waste is disposed of in onshore facilities, like municipal sewers and treatment plants. Yet another source of maritime contamination is the dumping of raw sewage overboard by ships.

Sewage effluent can have disastrous consequences on ecosystems and human and marine health if not thoroughly screened.
Sewage discharge regulations, including those for ships’ equipment and systems for controlling sewage discharge, port reception facilities for sewage, and survey and certification requirements, may be found in Annex IV.
The oceans are thought to be able to process and deal with raw sewage on the high seas through natural bacterial action. Consequently, unless otherwise indicated, discharging sewage into the sea within a certain distance from the nearest land is prohibited by the provisions in Annex IV of MARPOL.
When sewage effluent is improperly released in coastal areas, it can deplete the oxygen in the water, killing off fish, coral, seaweed, and vital microorganisms that are important to the ecosystem’s survival.

Discharging raw sewage into the ocean is illegal unless the vessel is equipped with a functioning sewage treatment plant or is discharging comminuted and disinfected sewage using a permitted system more than three nautical miles from the nearest shore. It is permissible to release untreated sewage at sea, provided it is discharged more than 12 nautical miles from the nearest shore and the ship is moving at a speed of at least 4 knots, and the rate of untreated sewage release must be allowed by the administration per resolution MEPC.157(55).

Sewage testing on board is an easy way to spot problems before they become major headaches. If you wait until an issue arises, your system may be down for repairs, which is a waste of time and money.

It is acknowledged that the performance of sewage treatment plants may vary considerably when the system is tested ashore under simulated shipboard conditions or on board a ship under actual operating conditions.

Sampling should be carried out in a manner and at a frequency which is representative of the effluent quality. Figure below provides a suggested frequency for sampling, however, the frequency should take account of the residence time of the influent in the sewage treatment plant. A minimum of 40 effluent samples should be collected (over 10 days) to allow a statistical analysis of the testing data (e.g. geometric mean, maximum, minimum and variance).

Suggested hydraulic loading factors and sampling frequency for testing sewage treatment plants. May be modified as necessary to take account of characteristics of individual sewage treatment plants

MARPOL ANNEX IV – RESOLUTION MEPC.115 (51) entered into force on 27th September 2008. It applies to ships on international voyages which are either 400gt and greater or less than 400gt when certified to carry more than 15 persons, which includes passengers and crew.

As set out in Annex 22 Resolution MEPC.227(64) adopted on the 5th October 2012, sewage treatment plants installed prior to 1st January 2010, on ships other
than passenger ships operating in MARPOL Annex IV special areas and intending to discharge treated effluent into the sea, should comply with resolution MEPC.2(VI) adopted on 3rd December 1976.

As set out in Annex 22 Resolution MEPC. 227(64) adopted on the 5th October 2012, sewage treatment plants installed prior to 1st January 2016 and on or after
1st January 2010, on ships other than passenger ships operating in MARPOL Annex IV special areas and intending to discharge treated effluent into the sea, should comply with resolution MPEC.159(55) adopted on 13th October 2006.

As per MEPC.2(VI):

    • Coliforms – up to 250 CFU/100ml
    • Total Suspended Solids (TSS) – up to 100 mg/l
    • Biological Oxygen Demand (BOD) – up to 50 mg/l

As per MEPC.159(55):

    • Coliforms – up to 100 CFU/100ml
    • Total Suspended Solids (TSS) – up to 35 mg/l
    • Biological Oxygen Demand (BOD) – up to 25 mg/l
    • Chemical Oxygen Demand (COD) – up to 125 mg/l
    • Chlorine (Free) – up to 0.5 mg/l
    • pH – between 6.0 – 8.5

For exemplification purpose, we will describe the “Martek Marine” test kit. There are different testing kits,  produced by different companies for sewage, but the required testing is quite similar.

      The Permanganate Value test is used for indicating the general quality of final effluents as to its acceptability for discharge. You simply fill your sample containers and add Acidifying SE tablets. After a short 30 minute wait you read the result from the following table.

      It is possible to derive an indication of the Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) from the result of the Permanganate Value test.
      To convert the Permanganate Value (PV) for domestic sewage and effluent to probable BOD, COD and TOC values multiply by the following factors:

The probable BOD can be calculated from the result of the turbidity test using the following formula :

The Royal Commission Standard for Effluents recommends a BOD value of not more than 20 mg/l.

      The Turbidity test is designed to give a measure of the suspended solids content of the final effluent. It is also useful in following the day to day variation in the quality of sewage and effluent.
      The Turbidity test uses a specially calibrated plastic tube. This provides the simplest possible method of performing this important test. Test kit SP 304 includes a tube graduated at 30 to 500 turbidity units.

The Royal Commission Standards for Effluents recommend that the suspended solids content of sewage effluent should not be more than 30 mg/l.

    • PH TEST
      The pH test is carried out using a Universal pH test tablet in conjunction with a comparator colour wheel. The test covers the pH range 4 to 10.
      The expected pH range for raw sewage is 6 to 8.5,and the pH of final effluents
      should also fall within the 6 to 8.5 pH range unless other consent limits are specified.
      The Free Chlorine test is carried out by taking a sample of your sewage effluent, adding a crushed DPD 1 tabletvand comparing the sample effluent against the chlorine comparator disc. The corresponding number on the disc is what you record.
      A Bacteria Plate test simply involves taking a small 1ml sample of effluents and placing it onto the bacterial plate.
      You incubate the sample at 35oC for 48 hours and simply count the number of red colonies on the plates surface.
      You are looking for a result less than 100/250 CFU/ml depending on the vessel.
      The coliform test is carried out by taking a sample of your sewage effluent and adding Sodium Thiosulphate and ready cult. Once thoroughly shaken, you incubate the sample for 24 hours and 35oC. You then check for a colour change in the effluent sample, a change to blue/green indicates a presence of coliforms. Log result as present or absent.
      A check should be maintained on the temperature of effluent discharges and these should always be close to ambient temperatures. Sewage Effluent Test Kit SP 304 contains a 0 to 50°C thermometer complete in a brass protecting case.

In case that vessel requires to discharge untreated sewage, which means sewage that has not been treated by a type approved sewage treatment plant, or that has not been comminuted and disinfected, the rate of discharge should not exceed the rate described in the first table above at minimum permissible of 4 knots. Where the intended actual discharge rate exceeds that permissible at 4 knots, the actual discharge rate may need to be reduced or the speed increased.

Before undertaking a sewage discharge in accordance with this standard, the crew member responsible for sewage operations should ensure that the ship is en route, is more than 12 nautical miles from the nearest land and the navigation speed is consistent with the discharge rate that has been approved by the Administration. Ships with high discharge requirements are encouraged to keep notes of calculations of the actual discharges to demonstrate compliance with the approved rate.

If you have any questions regarding above, please feel free to use our existing forum Seafarer’s World and will try to answer to all your queries. You can use the feedback button as well!

If you like my posts, please don’t forget to press Like and Share. You can also Subscribe to this blog and you will be informed every time when a new article is published. Also you can buy me a coffee by donating to this website, so I will have the fuel I need to keep producing great content! Thank you!

Source and Bibliography:

  • Martek Marine – Innovative ship solutions
  • MARPOL Annex IV

What is sewage treatment plant and its purpose?

Sewage is defined as drainage and other wastes from any form of toilets or urinals, drainage from medical premises via wash basins, wash tubs and scuppers located in these premises, drainage from spaces containing live animals and other waste waters when mixed with drainages defined aforementioned.

The sewage treatment plant is a biological unit, which works on the aerobic activated sludge principle and constructed to meet the rules and regulations in MARPOL 73/78 Annex IV and should be approved according to IMO MEPC 2(VI) which specify the following effluent values:

  • Suspended solids <1000mg/liter
  • Coliform bacteria <200 off/100 ml
  • BOD5 < 50 mg/liter

The plant will treat black and grey water and is, in general, fully automatic in operation.

Example of a sewage treatment plant

The sewage treatment plant consists, usually of a tank with three or four main compartments: aeration/activation compartment, activation compartment, settling compartment and sterilization and discharge compartment.

Sewage plant schematic

The sewage treatment plant is located in the machinery space and sewage from the accommodations runs through pipelines to the sewage treatment plant, aided by flushing water and gravity or by vacuum generated by vacuum pumps. On the latter the sewage treatment plant is under atmospheric pressure and the vacuum is only generated in the collection pipes between the toilets and vacuum pumps. The vacuum pumps are started and stopped according to the vacuum in the collection pipes and operate on a lag/lead principle as long as they are both switched on automatic mode. Normally only one pump is in operation but, if it is unable to keep the vacuum, the stand-by one will start. There are vacuum systems with only one pump and no stand-by pump available.

Example of vacuum pump arrangement
Sewage system vacuum pump with macerator

The vacuum pipe is connected via a network of pipes to the toilet bowls throughout the ship and when a toilet is flushed the flushing valve at the back of the toilet will open to discharge the contents and the surrounding air will be drawn into the bowl. A synchronized valve will allow fresh water into the bowl for flushing and for sealing the main discharging valve. Although the system is expensive and requires a lot of maintenance and expensive parts, it provides to be effective and uses about 1 liter of water per flush. The vacuum pump macerates the waste from the sewage pipe and discharge it to the first stage of the sewage treatment plant.

After treatment in the sewage plant the effluent is pumped overboard, if permitted, by means of the discharge pumps. If the discharge is not permitted due vessel being in a special protected area or to close to the shore line, the treated effluent is stored into the sewage holding tank which can be pumped overboard at a later stage while the vessel is en route and at a distance more than 12 nm from the nearest shoreline if the effluent is not treated and disinfected and minimum 3 nm if the effluent is treated and disinfected.

Example of a sewage holding tank

All the black water from the toilets, urinals and infirmary black water are collected and discharged to the first compartment aeration (activation) chamber of the sewage treatment plant. The incoming effluent material mixes with the activated sludge already present in this compartment. Air is supplied by means of a blower and distributed though the tank by aerators. The gases produced during the bacterial action which takes place are vented to atmosphere. Oxygen is essential for the aerobic activity, the organisms require oxygen for digesting the raw sewage and it also assists in mixing the incoming sewage with the water, sewage sludge and bacteria already present in the compartment.

The grey water from washbasins and showers flow separately to the first chamber and can also be directed to the sewage holding tank or directly overboard. The grey water from the infirmary flows to the aeration chamber through a separate line and cannot be directed to the sewage holding tank or overboard.

After a period of time in the aeration chamber the bacterial action will have reduced the biodegradable organic matter to water, gas and sludge. The treated effluent is then discharged to the settling chamber where the solid sludge settles out. The sludge contain biomass (bacteria) which increases due to the bacterial action in the aeration/ activation chamber. The biomass is returned to the aeration chamber by an air lift where reacts with the incoming raw sewage. The clean effluent flows from the settling chamber into the clean water/disinfection chamber via a weir.

In the disinfection chamber the pathogens (coliform bacteria) are destroyed, generally, thru chlorination. A dosing pump, located at the front of the unit, transfers the required dose of chemical (sodium hypochlorite) to the compartment in order to sterilize the effluent prior to discharge. The compartment has float operated switches which activate the discharge pump when the high level is reached and stop the pump when the compartment is nearly empty. The dosing pump is activated when the discharge pump stops and so the necessary quantity of sterilizing chemical is added to the compartment before the water flows into it. There should be no need to adjust the dosing rate of the pump under normal circumstances. If adjustment is needed the manufacturer’s instruction manual must be consulted with respect to adjustment of the pump stroke. The amount of sterilizing chemical added to the final discharge tank must be carefully controlled in order to ensure correct sterilization, as too much chemical results in pollution of the sea and destruction of marine organisms. Some local state authorities do not allow the discharge of sodium hypochlorite.

Sewage treatment plant explained. Source and credit: Marine Insight

As mentioned above, the sewage treatment plant works automatically once it is set but periodic attention is required and the unit must be monitored for correct operation. As sludge will build up in aeration/activation and settling chamber, this must be diluted in water (fresh or sea water) and removed approximately every two months, by discharge overboard or to approved shore facilities. It is very important that you never discharge both chambers at the same time, as this will result in the loss of the biological organisms from the plant.

Sewage tank during inspection and maintenance
View inside disinfection chamber

Rules governing the discharge of raw sewage must be complied with all times and the discharge of raw sewage overboard should be done when the sewage plant is unserviceable. The bacterial action in the sewage treatment plant requires a regular supply of raw sewage and the discharge of raw sewage overboard can impair effective bacterial action.
A sewage treatment plant should satisfy the following effluent standards when tested for its certificate of type test: Fecal Coliform Standard (the geometric mean of the fecal coliform count of the samples of effluent taken during the test period should not exceed 250 fecal coliform/100ml as determined by a multiple tube fermentation analysis or an equivalent analytical procedure); Suspended Solids Standard (where the equipment is tested on shore the samples of effluent taken should not exceed 50 mg/l; where the equipment is tested aboard ship the sample effluent should not exceed 100mg/l).

As part of the maintenance, the responsible engineer must check as following:

  • On a daily basis that the sludge is being returned to the activation chamber from the settling chamber, and that the discharge pump and blower are working and that there is sufficient liquid into the dosing tank.
  • Weekly change over the duty discharge pumps as this will avoid blockage in the discharge lines.
  • Every two months check that the air flows are correct and that the compartment vents are clear; Check the sludge content by filling a 1 litre glass container, or similar, with water from aeration chamber and allow the sediment to settle for 30 minutes. A sludge content of 300ml to 800ml is satisfactory. A sludge content in excess of 900ml requires the sludge to be discharged to the sea or to a shore facility. Check the chlorine content of the effluent being discharged using the test kit provided. The chlorine content should not exceed 2ppm.

In conclusion, every marine engineer should be aware of the following before and when operates the sewage system:

  • All crewmembers involved in operating sewage treatment plant must be familiarize with the operation and maintenance of the plant along with the requirements regarding discharge.
  • The documentation related to the plant must be kept in a relevant spot, easy to locate. and this documentations should include: Name of manufacturer, type and model, date of manufacture, any operational and installation limits, manual detailing the operational and maintenance procedures for the plant, test and certificates (type approval + International Pollution Prevention).
  • Discharge overboard should not take place within 12 nautical miles of the coast, so it need to ensure that maintenance takes place when at least 12 nm from nearest land.
  • The discharge overboard of treated sewage effluent must take place with the permission of the bridge. There must be effective communication between the bridge and engine room so that the engine room is immediately aware when the vessel enters waters where such discharge is prohibited.
  • Rules governing the discharge of raw sewage must be complied with all the times and the discharge of raw sewage overboard must be considered only when the sewage plant is unserviceable.
  • Only approved chemical cleaners must be used in lavatory and toilet bowls as biocidal cleaners will destroy the biomass in the sewage treatment plant.
  • Never discharge both tank chambers at the same time, as this will result in the loss of the biological organisms from the plant.
  • The dosing chemical contains chlorine and great care must be taken when handling the chemical. The appropriate protective clothing must be worn, including gloves and safety goggles. The manufacturer’s safety and health instructions should be read before the chemical is handled.

For vessels with only holding tank (without treatment of any kind) the engineers must ensure that a table approved by the Administration giving the maximum rate of discharge for various speed / draft combinations is available onboard ref MEPC 157 (55). This is as per the following:

DR(max) = 0.00926 V d B, where
DR(Max) = Maximum permissible rate of discharge (m3/hr); V = Ships average speed over period (Knots); d = Draft of vessel (m); B= Breadth of vessel (m)

Ensure that the maximum rate of discharge for untreated sewage for the corresponding ships speed is not exceeded. This is irrespective if a pump is used for disposal or done by gravity. Where a pump is to be used, the designated engineer officer is to ensure that the rate of discharge (rated pump capacity) is at or below the corresponding vessels speed as calculated with the above formula. When the gravity is used, the engineer in charge must adjust the discharge (by throttling the discharge valve) so not to exceed the rate corresponding to the vessels speed at that time.

When untreated or comminuted-disinfected sewage is discharged, relevant records are maintained in the engine log book. As a minimum these shall include:

  • Date / Time / Vessel Position at the Start of Discharge
  • Date / Time / Vessel Position at the End of Discharge
  • Vessels speed during discharge
  • Calculated rate of discharge (ONLY for UNTREATED SEWAGE)

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