Last week and today I met some Water Treatment Plant vendors to discuss about technical clarification. Some engineers and my boss have discussed the possibility to reduce the money to purchase water treatment package and make the system more simple. The main purpose the technical clarification meeting was to inform vendors what we want in our Water Treatment Plant, to ensure that is possible, and to ask for quotation, of course.
My boss is a very intelligent chemical engineer therefore I learn much about Water Treatment Plant from him. The vendors also told us about technical consideration in their water treatment plant configuration so that we understand a bit the reason behind their configuration selection. Of course we want to choose vendor who can offer best price and acceptable water quality (mainly for boiler feed water).
The more I met those people, the more I am eager to learn. I have a plenty questions on my mind but I don’t know who to ask. I am lucky some vendor answered several of our questions satisfactorily, but I also want to make sure they answered something true. For that reason, I write this post. Hopefully, I will undestand the reasons behind the configuration of water treatment plant, what is very necessary, and what is not.
Check the characteristics of your water
The configuration of water treatment plant at least depends on the application of the water and the characteristics of water source. For example, water output characteristics from water treatment plant for steam power plant is more stingent than water characteristics to produce medium pressure steam. Another example is, the configuration of water treatment plant will be different if iron content in the feed water is high/low. Therefore, the first thing you need to do is to check the characteristics of the water. You also need to make sure that you prepare the sample well by considering the easily-oxidized component, such as iron (you need to add something to your sample to prevent iron to oxidize).
Clarifier to reduce Iron content
A vendor reccomended us to use clarifier to reduce iron and manganese in well water. I’ve never think about the idea before so I browsed some information concerning this matter. I found that if the iron and manganese in raw water greater than 6 ppm, it is recommended to install clarifier in the upstream (for example after deep well). It will remove a large percentage of solid, so that filtration in multimedia filter will be performed easily (the load is also lower so than backwash will be performed not so often).
Iron exists in ground water and usually poses no problem. However, when it is found in process water, iron can cause a problem.
Manganese is always found in combination with iron. Oxidized manganese is always black in color. When manganese is present itself, it cause a problem at level over 0.05 ppm. When manganese and iron are present, the combined total should not exceed 0.3 ppm.
In addition to clarifier, we may need to add flocculant (such as alumina chloride) to create flocs thus accelerate solid sedimentation. We can also use pH adjustment (by increasing pH to certaion number so that flocs will be formed). Floc particles can be separated from the water using inclined plate separator.
Methods to Remove Taste and Odor
Odor and taste from water supply has several causes. In some cases bacterial activity in relation to mineral matter are the chief causes of tastes and odor. For example, iron bacteria have been responsible for tastes and odors in groundwater as well as in water distribution system (for more information, see this source).
Odor and taste can be originated from chemicals. List below presents some of chemicals which cause the most common taste and odor problem in water.
| Criteria | Reciprocating compressor | Centrifugal compressor | Axial-flow compressor |
|---|---|---|---|
| Application | Low-flow, high pressure service | ||
| Flow range | 10-5000 acfm (inlet) | 500-200,000 acfm (inlet) | 75,000-600,000 acfm (inlet) |
| Pressure range | 60,000 psia for small machine. 3000 psia for large machine | 10,000 psia for small machine. 100 psia for large machine | 10-100 psia |
| Pressure ratio | Max 3:1 to 4:1 per stage | ||
| Mechanical design limit | 350-450 deg F or lower | 400-450 deg F | 600 F |
| Overall adiabatic efficiency | Typically 0.75-0.85 |
The choice of methods to remove taste and odor in water treatment plant depends on the cause of the problem. Water treatment plant may involve air stripping, oxidation and adsporption.
- Air stripping is primarily used in water treatment plant to remove Volatile Organic Chemicals (VOCs), oxidizing contaminants, such as iron and manganese, improving taste, and removing odors. In air stripping process, air and packed column are contacted in packed column to maximize the contact surface area between water and air (click here for more information).
- Oxidation is the best method to control taste and odor in most cases. It can be done by adding chemicals, such as potassium permanganate, ozone, or chlorine.
- Adsorption. Adsorption using activated carbon provides safe and economical choice to control odor and taste. Activated carbon is very porous with a very large surface area. Certain contaminants collect on the surface of activated carbon so that it’s called adsorption.
Video about water treatment plant using activated carbon.
[youtube=http://www.youtube.com/watch?v=YaVkZSVehT4&w=500&h=300]
Commercial video about air stripping.
[youtube=http://www.youtube.com/watch?v=-vwn0pXy2CY&w=500&h=300]