Water Treatment

When we mention water supply in a building, the normal thought will be the domestic water supply for washing, sanitary, and drinking. The systems for these water supplies are quite straightforward, using pumps, tanks, and pipes to distribute to wash basins, toilets, and taps. These will be covered in the section on domestic water supply.

There are other users of water in a building. The air-conditioning cooling towers normally consume a lot of water. They have separate storage tanks to take care of shortages of water. There are also water tanks for the fire fighting systems. The details of these arrangements will be covered at the section on Fire Systems

In the following pages, we will be looking at a specialized type of water, the DI water. They are used in high technology industries. In the process of manufacturing, very often there is a need to treat the wastewater so that it will not be harmful to the environment. We will also be exploring the processes of wastewater treatment.

DI Water

DI water is De-ionized Water, or pure water that is free from contaminants. Ordinary raw water contains dissolved minerals and suspended solid particles. Although the raw water can be used for a lot of cleaning applications, it is not suitable in environments where even traces of contamination are unacceptable.

From raw water, DI water is obtained by passing the former through processes of filtration, reverse osmosis, UV radiation and resin ion exchange. Depending on how stringent the requirement for purity, the raw water may be processed into Low DI or High DI. Typical DI water may have these specifications:

Pure DI Water

Resistivity > 10 Mohm-cm at 25°C
Particle < 50 Counts/ml for particles of 0.45 mm
Bacteria < 100 Colonies/ml
TOC < 300 ppb
Water temperature 15 ~ 30°C
Pressure 2.5 ± 0.5 Kg/cm2

Ultra Pure DI Water

Resistivity > 18 Mohm-cm at 25°C
Particle < 5 Counts/ml at 0.1 mm
Bacteria < 0.1 Colonies/ml
TOC < 200 ppb
Water temperature 25 ± 3°C
Pressure 2.5 ± 0.5 Kg/cm2

Waste Water Treatment

In the area of wastewater treatment, it must be understood that there are some waste which are normally not treated by the ordinary factory or building. Some wastes are only produced in small quantities. Some may be difficult or too expensive to treat. It would be more feasible to send them to a licensed scheduled waste treatment facility for treatment. These wastes are called Scheduled Waste. Some of the scheduled wastes include mineral oil waste, organic chemicals or solvents containing halogen and sulfur, mercury waste, pesticide waste, inorganic waste, and other miscellaneous wastes.

Waste that can be treated in-situ at the owner’s premises can be divided into 2 main types:

  • Chemical Waste
  • Biological Waste

Chemical Waste

The function of the Waste Treatment Plant is to ensure that all the effluent being discharged to the environment can comply with the minimum requirement of the Environment Quality Regulations. Several parameters are monitored: Temperature, pH, BOD at 20°C, COD, Suspended Solids, various different concentrations of heavy metals, Phenol, Free Chlorine, Sulfide, oil and grease. A most basic chemical treatment plant will have facilities to neutralize acid or alkali, and to remove heavy metals.

The control of pH is quite straightforward. Acidic waste is neutralized with alkaline Sodium Hydroxide, while alkaline waste can be neutralized with Sulfuric Acid.

Converting the heavy metal soluble salts to insoluble salt to form floc usually does removal of heavy metals. The addition of coagulant neutralizes the charges of the ions and flocculent is added to clump the small floc to form bigger flocs.

The large flocs are allowed to settle to form sludge. These are collected and de-watered. The dried sludge are collected and sent to the scheduled waste treatment facility for further treatment.

Biological Waste

Many wastes are organic in nature. The usual method of treatment is to allow aerobic bacteria to feed on the waste and digest them. The bacteria need oxygen in order to grow. These types of systems have blowers that supply air into aeration tanks. Sewage treatment systems are typical biological treatment.

When the system is working well, there is no foul smell. The treated wastewater is usually sterilized to kill off any harmful bacteria at the final discharge point.