Raw water can be pre-treated to remove contaminants (such as particulates, calcium and magnesium salts, heavy metals, organics and bacteria) through different steps.
Pretreatment of feed water is important in a total system approach for continuous and reliable operation. Improperly designed or operated pretreatment system leads to issues with the downstream water systems; resulting in poor product water quality, frequent breakdowns, and high-maintenance activists
The proper treatment scheme for feedwater depends on:
- Feedwater source
- Feedwater composition
- Application
The type of pretreatment system depends to a large extent on feedwater sources (i.e., well water, and surface water). In general, well water is a consistent feed source that has a low fouling potential. Well water typically requires a very simple pretreatment scheme such as acidification and/or antiscalant dosing and a 5-µm cartridge filter.
Surface water, on the other hand, is a variable feedwater source that is affected by seasonal factors. It has a high-fouling potential, both microbiological and colloidal. Pretreatment for surface water is more elaborate than pretreatment for well water. Additional pretreatment steps often include chlorination, coagulation/flocculation, clarification, multimedia filtration, dechlorination, acidification, and/or antiscalant dosing.
Once the feedwater source has been determined, a complete and accurate analysis of the feedwater should be made. based on the feed water analysis & application of product water, a suitable pretreatment process shall be selected
Why pretreatment systems are important in the pharmaceutical industry?
The pharmaceutical industry requires water of very high purity for manufacturing processes, formulation, and cleaning operations. Water pretreatment systems are designed to remove impurities such as ions, organic compounds, bacteria, and particulates that could interfere with the manufacturing process or compromise the quality of the final product.
Failure to provide adequate pretreatment can lead to :
- Higher Operating Cost
- Poor efficiency
- Short equipment life
- Variable water quality
What are the steps involved with pretreatment of water?
The pretreatment of water typically involves several key steps to remove impurities and contaminants and to prepare the water for its intended use. Here are the common steps involved in water pretreatment:
- Screening: The initial step where large solids and debris are removed from the water using screens or filters.
- Sedimentation: In this step, water is allowed to sit in large tanks where heavier particles settle at the bottom due to gravity. This process helps remove suspended solids from the water.
- Coagulation and Flocculation: Chemicals called coagulants are added to the water to neutralize the electrical charges of suspended particles, allowing them to come together and form larger particles called flocs. Flocculants can also be added to enhance this process.
- Clarification: After coagulation and flocculation, the water is passed through a clarifier where the flocs settle to the bottom, and the clear water is separated.
- Filtration: The water is then passed through a filter to remove any remaining suspended particles. Filters can be made of sand, activated carbon, or other materials depending on the type of impurities to be removed.
- Softening: This process is used to remove hardness from water caused by calcium and magnesium ions. Softening is typically done using ion exchange resins or lime softening.
- Disinfection: This is a critical step to kill any remaining bacteria, viruses, and other microorganisms in the water. Disinfection can be achieved through chemical methods (e.g., chlorination, ozonation) or physical methods (e.g., ultraviolet (UV) light, membrane filtration).
- Adjusting pH: The pH of the water may need to be adjusted to meet the requirements of the end use. This can be done by adding acid or alkali to the water.
- Deionization: This process is used to remove dissolved ions from water using ion exchange resins. Deionization can produce water of very high purity, often required in pharmaceutical and other high-precision industries.
- Reverse Osmosis: This is a membrane filtration process that removes dissolved salts and other impurities from water by forcing it through a semi-permeable membrane.
The specific combination of pretreatment steps will depend on the quality of the source water and the requirements of the end use. In many cases, a combination of these processes will be used to ensure the water meets the necessary quality standards.
What chemicals may be added during pretreatment?
- Coagulants: Coagulants, such as aluminum sulfate (alum), ferric chloride, and ferric sulfate, are added to neutralize the electrical charges of suspended particles, causing them to clump together and form larger particles called flocs. This process is known as coagulation.
- Flocculants: Flocculants, such as polyacrylamide and other synthetic polymers, are added to enhance the flocculation process by promoting the aggregation of flocs, making them larger and more easily settleable.
- Lime: Lime (calcium oxide or calcium hydroxide) is often used for softening hard water by precipitating calcium and magnesium ions as calcium carbonate and magnesium hydroxide.
- Soda Ash (Sodium Carbonate): Soda ash is used to adjust the pH of the water and to precipitate hardness ions.
- Sodium Hydroxide (Caustic Soda): Sodium hydroxide is used to raise the pH of the water, which can aid in coagulation and flocculation processes.
- Chlorine: Chlorine is commonly used for disinfection to kill bacteria, viruses, and other microorganisms in the water.
- Ozone: Ozone is a powerful oxidizing agent that can be used for disinfection and the removal of certain contaminants, such as iron and manganese.
- Hydrogen Peroxide: Hydrogen peroxide is used as an oxidizing agent and disinfectant.
- Polyphosphates: Polyphosphates are used to sequester hardness ions and prevent scale formation on equipment.
- Antiscalants: Antiscalants are chemicals that inhibit the formation of scale deposits in equipment such as boilers and reverse osmosis membranes.
- Corrosion Inhibitors: Corrosion inhibitors are added to prevent corrosion of metal surfaces in the water treatment equipment.