Physical, Chemical and Biological Processes in a Wwtp and Its Applications

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Moalajah is a leading wastewater operations and maintenance company situated in the UAE. Moalajah was established in 2006 as a joint venture between the 2 major companies, BESIX and Veolia. BESIX is a leading Belgian construction group and Veolia is an international environmental management company. Moalajah was initially founded to perform the complete operation & maintenance of Ajman Sewerage, Moalajah quickly grew to become a recognised service provider in the region proposing its expertise to different clients.

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The aim of Moalajah is to work efficiently and cost effectively without disturbance to it’s clients’ businesses and environmental policies. This approach helps Moalajah make sound judgments and well-thought decisions in further strengthening the relationship made with its clients.

Moalajah holds fast to the virtues of hard work, integrity, transparency and modesty. They are always on the lookout for opportunities to grow in quality and innovation. They are always open to the idea of a clear, open and respectful communication with its clients.

In their own words, they aim to deliver reliable wastewater services and solutions across the region to serve the community, safeguard its health and contribute to a clean and green environment.

Natural resources are getting depleted by the day due to high rates of urbanisation. Moalajah aims to educate the community on the importance of preservation of such resources and to raise awareness of the importance of such an act. Moalajah works towards a cleaner and greener environment to safeguard the health of the community.

Contribution to the community

  • Educate the community schools and colleges.
  • Offer internships
  • Holding awareness campaigns by explaining the importance of conservation and by distributing devices for the same
  • Implementing sustainability of resources by reusing effluents for various purposes
  • Annually organising World Environment Day with their clients
  • Optimizing chemical and power usage to control their impact on the environment.

Moalajah offers a wide variety of services. They are:

  1. Cleaning
  2. Inspection
  3. Rehabilitation, installation, engineering, procurement and construction (EPC)
  4. Operations and Maintenance (O&M)
  5. Over-pumping. Let’s look into each of these in detail.

Periodic cleaning is required for sewerage networks to avoid blockages that would damage the pipes or cause unfavourable outcomes. Moalajah offers a wide range of cleaning services related to wastewater. Some of them are:

Cleaning of sewerage pumping stations, wet wells, sump pits, chambers and holding tanks.

Moalajah uses a specialised combination tanker and mini-combination (low height) truck that performs vacuum suction and hydro-jetting with 100% reused wastewater. In this way, the environment isn’t affected, and very high mobility is achieved as size restriction doesn’t have a large effect. This quickly allows access to difficult and troublesome locations such as underground parking areas. The benefits are that manual cleaning is very inferior to this superior mechanised system which allows for quick and mobile cleaning.

Cleaning of sewerage treatment plants, clarifiers, grid chambers, sludge tanks, tse tanks, aeration tanks and grease tanks.

Sewerage treatment plants (STP) require regular, mandatory cleaning. If not performed periodically, there are high chances of accumulation of undesirable solids (mostly waste and debris) which can lead to health and safety risks and higher operations cost. Moalajah offers a specialised truck and teams trained to work in confined spaces to contribute to the environment and the public’s wellbeing. The benefits of this is to reduce the chances of over-flooding and public health risks.

Cleaning of grease traps

Restaurants, hotels and hospital kitchens are required to install and maintain grease traps in compliance with the local laws. They need a municipality certified contractor such as Moalajah to fulfil this requirement.

Cleaning of irrigation pumping stations, wet wells, chambers and holding tanks.

Irrigation systems require continuous cleaning and inspections and failure to do so will result in over flooding and risks to public health. Moalajah provides for the cleaning of irrigation systems by deploying a well-trained team to work in small spaces to make sure that clogs formed from waste and debris are eliminated. This leads to a safer and higher quality of water in irrigation systems.

Hydro-jetting and cleaning of sewage and storm-water pipelines

Utilities which are present underground require regular cleaning and inspections to avoid blockages, over-flooding and health risks. Services by Moalajah help assess the pipes and schedule preventive maintenance and hydro-jetting.


Moalajah offers a variety of inspections to study and assess many kinds of underground utilities. Moalajah offers three kinds of inspection services:

CCTV inspection assessments and surveys for drains, sewer and storm

Water networks CCTV cameras are used to provide a visual inspection of sewage networks or storm water pipes. This is used to detect leaks, groundwater infiltration and blockages. Standard equipment used by Moalajah to observe underground utilities like sewer and storm-water pipes are Pan-and-tilt conventional cameras with crawlers and built-in inclination measurements with 300 m cable length. The benefits of this are to get an early detection of issues and to pinpoint their location in the system so that appropriate measures can be taken to resolve the problem as soon as possible.

Pole camera inspection

For a quick visual analysis of the conditions of the underground systems, pole camera inspections are carried out by Moalajah Services. Moalajah uses Quick-view zoom camera as their standard equipment. With the help of powerful zoom optics, Quick-view quickly and accurately analyses manholes and tanks and can assess the sewer lines from adjoining manholes. The benefits of this are to provide a quick inspection of any problems and to find their exact location to help come up with appropriate solutions as soon as possible.

Manhole inspections

Moalajah provides services to inspect manholes and to report any anomalies that are present within the manhole that are of concern. This inspection helps assess and prevent the accumulation of debris and blockages. These different inspections can be seen in the pictures provided below.

Operation and maintenance (O&M) of sewerage networks, pumping stations and sewage treatment plants

Moalajah operates and maintains many sewerage networks, pumping stations and sewage treatment plants which treats a capacity of 130,000 cubic meters/day, all within the United Arab Emirates. They maintain long-term contracts with clients and are confident in offering a full range of O&M services which aren’t limited to asset management, sampling and analysis and health and safety improvements.

Commissioning and rehabilitation of sewage and irrigation pumping stations

Moalajah acts as a contractor involved in small to medium-sized mechanical, electrical and instrumentation works relating to the commissioning and rehabilitation of sewage, storm water and irrigation pumping stations.

Supply, installation and maintenance of odour control units and other waste

Water related equipment

Moalajah also acts as a contractor involved in the supply, installation and maintenance of odour control units and other related equipment for sewerage pumping stations, lifting stations and sewage treatment plants.

Over-pumping, plugging and flow diversion

Moalajah provides for different flow diversion needs with a range of plugging equipment that spans from 70mm to 2,400mm in diameter. They also provide pumps which has a capacity of 5,400 cubic meters/hour. Their services have three components:

Sewerage flow diversion

Diversion of the flow of sewage is required for the repair and maintenance of the sewer systems. To provide for this, Moalajah provides a range of flow diversions that include isolation, plugging, over-pumping and controlling of sewage flows.

Over-pumping arrangements

Moalajah offers services over-pumping arrangements that include the installation of pipes and pumps of up to 5,400 cubic meters per hour. They also provide for the operation of pumps and level control for the required period.

Pneumatic pipe plug installation

Moalajah offers plugging solutions by offering plugs ranging from 70mm to 2,400 mm diameters in pipes. They install, rent, check and remove inflatable plugs.


Moalajah focusses on digitalising their services to provide a quick, accurate and user-friendly way to keep track of all things that are important for their clients. To accomplish this, Moalajah created an app which their clients can use to keep track of progress, make payments and to provide feedback among other services.

Mini-combination truck

It is a very mobile vehicle that causes no hindrance to traffic and is used to Clean in locations that are difficult to access like underground parking, restricted areas and places of the kind. It is used for grease trap cleaning, internal drainage works etc.

Occupational health and safety policy

Health and safety is an integral part of Moalajah. They ensure that training is provided to all employees to maintain safety and health requirements when on and off the job. Listed below are some policies as stated by Moalajah, in their own words.

To study the physical, biological and chemical processes – To study the applications of the three processes in the preliminary, primary, secondary and tertiary treatment stages in a WWTP. This report will cover the physical, chemical and biological processes involved in a WWTP and their applications in the preliminary, primary, secondary and tertiary treatment stages in a WWTP.

Most information provided in the report was obtained from our mentors and the staff present at Moalajah. Some information was obtained through means of the internet. There are 3 different processes that occur in a wastewater treatment plant (WWTP). These are physical, chemical and biological processes. Each of these processes are fundamental to run a WWTP efficiently because each of these processes occur at different stages of treatment. The different stages of treatment are preliminary, primary, secondary and tertiary stages. This project will provide a detailed study into each of the processes and the different stages present in a WWTP such as Moalajah. Physical processes are processes where no gross chemical or biological changes are carried out, and only physical changes or processes are used to treat the wastewater. The physical processes that are carried out at Moalajah are:

  • Screening
  • Comminuting
  • Aeration
  • Sedimentation or clarification
  • Flotation and skimming
  • Degasification
  • Deep bed filters.

Comminuting means to break down larger particles to smaller sized particles. At Moalajah, an industrial scale comminuting mill breaks down larger debris and other particles into smaller particles. All inorganic and undesirable waste like stones, rubble, plastics etc. is screened out to a nearby bin and desirable and treatable waste is allowed to pass through the screener. Oxygen is pumped through the activated sludge which is in a tank called the activated sludge aeration tank. This process helps promote the very much needed microbial growth for different biological processes.

The settling of the sludge at the bottom of the tank due to gravity is called sedimentation or clarification. The heavier sludge settles down, and the clarified effluent is removed from the tank. The sludge is sent back to the aeration tank.

It is the removal of suspended particles or lower density particles and matter that floats such as oils, grease, through the physical process of skimming. This is done to improve the quality of water. A blanket of sludge that is formed due to rising gasses is also skimmed off.

The removal of harmful dissolved gasses in the wastewater is called degasification. H2S and Methane are removed out of the wastewater and are discarded out to a vaporiser. High levels of H2S and Methane are deadly to many life forms and must be eliminated.

Deep bed filters are columns packed tightly with sand. The treated water flows through 10 of these columns and filtration occurs. Very small solid and biological materials get filtered and trapped in the sand and only clear water exits the column.

Chemical processes use chemical reactions to improve the quality of water. The different chemical processes that occur at Moalajah are:

  • Coagulation
  • Neutralization
  • Chlorination

Coagulation consists of the addition of a chemical, which is usually a polymer at Moalajah, to form an insoluble end product through a bunch of chemical reactions. This polymer is added to sludge in order to make it clump together and settle down. This end product removes substances from wastewater.

This is the final process of the treatment at Moalajah. Chlorination is the addition of chlorine to the wastewater to disinfect the water by killing the bacteria and virus present within. The chlorine interferes with the biological processes of the bacteria and ends up killing the bacteria present. This occurs in the two Chlorination contact tanks present at Moalajah. After this stage, water is finally treated and is sent for irrigation purposes or to the sea.

Biological processes

It is the treatment of wastewater in such a way that it enhances the action of bacteria and other microbes to clean and treat water. Biological processes rely on mostly bacteria to simplify organic matter using regular cellular processes. It consists of aerobic and anaerobic processes based on the amount of Dissolved Oxygen (DO).

Aerobic processes

Aerobic processes occur due to the presence of oxygen. Aerobic Treatment results in a 98% removal of organic matter and produce cleaner water than anaerobic processes or treatments.

Bacterial activity in aerobic processes Aerobic treatment consists of:

Activated sludge process – activated sludge makes use of a multi-chamber reactor that uses microbes to break down organic matter to produce a purer effluent.

Aerated activated sludge – oxygen is induced to promote biological oxidation of wastewater

Anaerobic processes

Anaerobic processes occur because of the lack of oxygen. This kind of treatment is more cost-effective than aerobic processes. Anaerobic processes consist of the following: Upward Anaerobic flow Sludge Blanket – the water is passe through a sludge blanket that helps promote bacterial growth. This also creates H2S and Methane gas which is then treated or discarded appropriately.

Different stages of treatment in a WWTP

All the processes mentioned above are applied to the different stages of treatment in a wastewater treatment plant. At Moalajah, the stages of treatment are:

  • The preliminary stage of treatment or pre-treatment stage
  • Primary stage
  • Secondary stage
  • Tertiary stage

Preliminary treatment

The Pretreatment stage is necessary because all the harmful physical components of the wastewater that can damage the mechanical workings of the different machines or disrupt the processes involved are removed. Physical processes are used at this stage of the treatment. Some of these constituents that are removed consist of wood, metal, cloth, plastics, paper, garbage, heavy oils and greases and other organic and inorganic substances. First, the bigger particles are broken down into smaller sized particles through the use of a commuter. Then substances are removed by screening the water through screens that remove matter that thicker than 6mm. Then the screened matter is disposed off in adherence to environmental laws and practices. Then the screened water passes through a grit removal unit which removes matter up to 0.1mm in radius.

Primary treatment

After pre-treatment, the wastewater is taken into the primary treatment stage. Here, the wastewater undergoes anaerobic biological processes. The incoming flow is divided through 8 Upflow Anaerobic Sludge Blanket (UASB) reactors, where the influent flows upwards through sludge blankets which filter and treat the used water thanks to anaerobic microorganisms. As a result, up to 75% of all organic matter is removed. During this process, both sludge and biogas are produced. The gas is extracted safely and burned off. Excess sludge is removed from the UASB and dewatered using high-powered centrifuges, collected and disposed of.

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