Treatment of water

Kishor Datar

From the earlier chapters we know that, with the difference in types and degree of contaminants present in water, different types of water required for different process, it is essential to have water treated so as to take care of these variations and assuring “Consistency in quality of water produced”

It is clear that consistency in quality of water produced is the key criteria for pharmaceutical water treatment. Probably the word ‘consistency’ is forgotten many a times and users get carried away by few high tech systems described by consultants like us or vendors, irrespective of the source water and the requirement. People forget to ask questions like whether this high tech system is required and can it be maintained etc. and ultimately the users runs in to problem.

Let us try and understand some of the treatments used currently. I will be presenting few things in subsequent articles which are guidance-oriented and not specific. However, I am sure that the information will help users a lot in understanding and mainly avoiding getting carried away by consultants or vendors.

We will go through the types of treatments we discussed earlier. We will just run through them quickly to have summarised information regarding these types of treatments used in the industry.

However, the details of each system will be discussed in the subsequent articles.

The system in any pharma industry is always considered as vulnerable and people continue making statement that the “system is bad.”

However, I am sure that after going through this entire series of articles, which will start from defining properly what is the source of water and what I need, the view of the users will change.

Let us differentiate between ‘want’ and ‘wish’. Wants are must to be addressed, wishes can follow if everything permits. Most of the time I have seen that wishes take over wants and put the operating staff in difficulties.

Physical treatments

The treatment process using physical parameters of contaminants to isolate it from water. Thus these type of processes will use physical properties of contaminants like size, shape, weight etc. to remove them from the water.

With this basic concept, it is clear that these treatments will have many physical aspects which will need to be maintained / monitored.

Major process used today that fall under this type of treatment are:

Filters: Normally these are depth filters. The filter media will have porosity of designated size. Water is forced through this medium using pressure to isolate particles bigger in size of porosity.

Reverse osmosis and ultra filtration: This also is a process of filtration, but normally using cross flow. The porosity of this type of filtration, normally referred as membrane filters, ranges between 20 and 100000 molecular weight cut-off (MWCO). This makes it clear that higher pressure is essential to be applied to ensure that water is forced through these membranes and at the same time a flow is maintained on other side to reject the concentrate.

At the same time, it is clear that since the porosity is ultra low, these filters are not meant for suspended particles, but to remove micro and macro molecules, which includes dissolved ions as well as bacteria.

Distillation: Distillation is a process of converting the phase of water as follows: Liquid Ü Vapours ÜLiquid.

Since water boils at 1000C, when water is converted to vapour form, most of the dissolved contaminants don’t get converted into vapour phase and hence when these vapours are converted to liquid phase, contaminants gets isolated.

Chemical treatments: The treatment process using chemical parameters of contaminants to isolate them from water. Thus this type of processes will use chemical properties of contaminants like charge, affinity, reactivity, etc. to isolate it from water.

It is clear from above concept that these type of treatments will use chemicals to complete the process or to enhance the process.

Major process used today that fall under these type of treatments are:

Softener: As the name suggests, this is a process of softening the water. It is a known fact that salts of ions like Ca and Mg, form very hard scaling / deposition. These scales are difficult to remove. Hence these ions are referred as hardness building ions. The chemical process of replacing these ions is referred to as softening and the unit that does this is called a softener.

Demineralisation/ Deionisation (DM/DI): The process of removing minerals / ions from water using chemical method is referred as demineralisation/deionization. As we know minerals /ions present in water have +ve and -ve charges. For e.g, calcium, magnesium, manganese, iron, zinc are +ve ions, chlorides, sulphates, are –ve ions. In the process of DM/DI, the particles are charged with H/OH ions, the H being +ve charged will attract –ve charged ions and OH being –ve charged will attract +ve charged ions. Thus this process will remove the ions with chemical treatment.

Chlorine/ Ozone dosing: Chlorine/ozone are highly oxidising agents. These chemicals oxidise the compound. The oxidation process, oxidises vital compounds in the cells, thus bacteria, and other microbes get killed. This process is also used to oxidise and remove the iron contaminants from water. In case of chlorine, either Cl2 gas is dosed directly or by dosing the chemical which will release Cl2.

In case of ozone, it is generated using the same water and dosed directly. This is the general principle used to control microbial contamination in water used in the pharma industry.

In the past few years ClO2 dosing has found its way in treatment of water. This is more lethal when it comes to pathogens and hence is more popular in this subcontinent as the surface water used will normally have a very high contamination of pathogens and they vary as the seasons change.

You will find them highest just before and after first few showers of monsoons.

Electrical treatments: The treatment process using chemical parameters of contaminants along with use of electricale energy to accelerate/improve efficiency of the process of isolation of contaminants or improving the efficiency of removal of contamination.

Major process used today which fall under this type of treatment are:

Electro-Deionisation (Continuous Deionisation): As the name indicates, it is a process of de-mineralisation / deionisation using electrical power. As understood in previous slides, the DM/DI process has +ve / -ve charged H/OH ions, which attract the –ve / +ve charged ions from water. When an electric field is applied across this process, the +ve and -ve poles impart additional force to remove the ions from water.

From the information gathered about the types of treatments, we understand the importance of each such treatment. Also it indicates the treatment type and what type of contaminants it can handle. The chart given summarises the treatments and the contaminants an individual treatment can handle

The major issues of the users are:

• How to select the type of treatment?
• For the given requirement, flow, source water analysis, economical considerations, which methodology is suitable?

All these can be answered, provided the salient features of each type of treatment and its advantages/disadvantages are known. These will be discussed in subsequent articles.