Upgrading of Existing Filters

The very first work that I've witnessed for the water supply works was the upgrading of existing water filter modules at Betong Water Treatment Plant, Sarawak in June 2012. The structural works was seems to be a long way behind completion. I was expecting terrible delay of the project as the works coordination on site was surprisingly very poor for an established main contractor. So, I had almost 8 months of nothing for Mechanical and Electrical (M&E) works on site. When the M&E team mobilized to site in May 2012, I was a little bit relief as I know that the M&E work would start quite soon even tough there were some incomplete paperworks by the contractor which were in the way of their commencement of works.

The water filters upgrading works finally started in June 2012. 4 units of filters were upgraded which had increased the filtration capacity of the filters.
The works sequences were as follows:
1. Removal of existing filter media.
2. Hacking of existing filter bed concrete slab and removal of existing lateral pipes.
3. Installation of new lateral pipes.
4. Concreting of new filter bed concrete slab.
5. Installation of new filter nozzles and air scour pipe.
6. Air distribution test.
7. Charge in new filter media.
8. Backwash and put the filter into service.

To tell the story of the upgrading works, I believe it is better to describe them in photos rather than in words.

1. Removal of existing filter media.

2. Hacking of existing filter bed concrete slab and removal of existing lateral pipes.

3. Installation of new lateral pipes.

4. Concreting of new filter bed concrete slab.

5. Installation of new filter nozzles and air scour pipe.

6. Air distribution test.

7. Charge in filter media.

8. Backwash and put into service.

Water Treatment Process of Betong Water Treatment Plant

Betong Water Treatment Plant is the heart of water supply for Betong and its neighbouring areas. At the moment, the treated water production capacity is at 12 million litres per day. 

The water treatment process at Betong Water Treatment Plant start with the feeding of raw water from the nearby river named Batang Layar. The delivery process is by pumping the raw water from the river to the flow split chamber. Before reaching the flow split chamber, the raw water was dosed with aluminium sulphate (alum) solution and sodium carbonate (soda) solution. Alum is added as a primary coagulant which acts as bonding agents to make the suspended particles in the raw water to stick together and create heavier particles which is called floc. Soda is added to control the acidity of the raw water within the allowable range.

Photo: Batang Layar

 

Photos: Raw Water Pumps Cages

Photo: Flow Split Chamber

The next step is to allow the formation of floc in a tank called flocculation tank. The tank was designed so that the water moves slowly and to allow the effective formation of floc. The next step is settling of floc at the sedimentation tank. At the sedimentation tank, the heavy floc will sink and will be settled at the bottom of the tank by gravity. At the end of this process, the water is called settled water and will be sent to the filters.

Photos: Flocculation Tank (top) and Sedimentation Tank (bottom)

Betong Water Treatment Plant utilize rapid gravity sand filters for settled water filtration. Filtration process will remove the remaining suspended solids in the settled water which are unable to be removed by settling process. The rapid gravity sand filters in this water treatment plant use multi graded filter media for the filters. They are commonly known as sand and gravel. The water that leave the filters is called filtered water and to be sent to a tank called clear water tank.

Photo: Rapid Gravity Sand Filter

At the entrance point to the clear water tank, the filtered water will be dosed with soda solution, chlorine solution and sodium silicofluoride (fluoride) solution before it is called the clear water. Soda is added for pH correction of the filtered water. Chlorine is for bacterial disinfection and fluoride is for tooth care purpose. The clear water or treated water will be stored in a lower level tank (clear water tank) before being pumped to the high level lank (reservoir) which will then deliver the water to the consumers by gravity feed. 

Photos: Clear Water Tank (top) and Treated Water Pumps (bottom)

Chemicals in Treated Water

This article will only discuss on the chemicals used in the water treatment process. If you would like to know more on the water treatment process, please go to http://scienceray.com/biology/ecology/water-treatment-process/.

Have you ever wonder what do they add in our tap water during the water treatment process and what are the chemicals for?

The chemicals added to the water during the treatment process is are dependent on the quality of the raw water. The area with good quality of water need less chemicals than the area with bad quality of water. The common chemicals for water treatment process are:

1. Alum
2. Soda
3. Chlorine
4. Fluoride

Alum is the chemicals for the coagulation and flocculation processes. Flocculation and coagulation is the process to separate suspended solids from the water. In this process, the suspended solids will form a colloid that will become heavier and drop to the bottom of the water. Alum is normally dosed as Aluminum Sulphate (Al2SO4). Sometimes, dependent of the quality of raw water, polymer is also added as the coagulant aid. The type of commonly used polymer is polyacrylamides.

Soda is added for pH adjustment or increase the alkalinity of the water. Soda is dosed as Calcium Carbonate (CaCO3). In some area, the water is too acidic. Therefore, soda is added in order to adjust the pH of the water so that it will be almost neutral.

Chlorine is dosed as chlorine gas into the water system. The purpose of chlorine dosing is to disinfect the water mostly from bacteria so it is safe to be drank directly from the tap. Only of after the point of chlorine dosing is the water considered as treated water. Without the chlorine, the water is known as the clear water which is after the filtration process.

Fluoride is added for the purpose of dental protection which is specifically to prevent tooth decay. Fluoride is dosed as Sodium Silicofluoride (Na2SiF6) to the water system. However, it is not applied to all water treatment plant. In other words, it is an optional dosing which is dependent on the policy of the authorities at the location of the treatment plant.

In some locations, more chemicals need to be dosed to the water system dependent on the raw water quality. It is also dependent on the regulations of the state or country which the water treatment plant is located.

Water Treatment Process

Water is consumed by every living creatures on earth. Our daily activities require us to use a large amount of water which is available easily to us by just turning the valve at the end of a pipe. The water that is being used daily by consumers is treated water that can be safely drank directly from the tap. How is the water being treated?

It start from the source where the raw water is taken. Raw water is the untreated water with a lot of unhealthy elements in it. Raw water can't be utilize directly without being treated due to the contents which will cause bad effect to the health. The raw water for example from the river will be pumped to a pond for an initial process called aeration. Aeration is a process of circulation the water which in this case to ensure more air into the water. Aeration usually done by a device called aerator which will circulate the water to the air. 

Photo: Aeration Tank 



After the aeration process, the water will flow to the flocculation tank for flocculation and coagulation process. Flocculation and coagulation is the process to separate suspended solids from the water. In this process, the suspended solids will form a colloid that will become heavier and drop to the bottom of the water. The coagulation and flocculation will only happen by the aid of chemicals which in common water treatment processes are Alum and polymers.

Photo: Colloids forms in flocculation



The next process is called sedimentation. Sedimentation is the process of settling the suspended solids or colloids formed in flocculation and collection of sludge or the suspended solids. In this process, the water will become clearer than in the previous process. The sludge in the sedimentation process will move down to the bottom of the tank and will be collected for disposal by a mechanical system.

Photo: Sedimentation tank



The final step is filtration. Filters are being used to remove the fine particles that are still present in the water. Water will flow through the filter by gravity action from top to the bottom of the filter and will be collected by an underdrain system. The water then will be stored in a tank as clear water.

Before the water is safe to be drank, some chemicals need to be dosed to eliminate biological threats such as bacteria. Some common chemicals used are chlorine solution, fluoride solution and soda solution. These chemicals are used not only to eliminate the micro organisms, but also to correct the state or condition of the water such as acidity so that is is suitable to be consumed. The information above are the basic of water treatment process. However, the process might be different for different locations on earth due to the geographical and environmental condition of the place.