Water treatment - carbon filtration process

1. What is carbon filtration?

The pharmaceutical carbon filtration unit is usually designed in the pretreatment process, is set after the softening process, before the water enters the reverse osmosis membrane, multi-effect or vapor compression distillation of the pharmacopoeia water treatment unit, the filter is usually made of stainless steel material, the activated carbon filter media is carbon particles of various sizes, ranging from 10 to 50 mesh, the activated carbon particles are made of coconut shells, usually in an atmosphere containing nitrogen or other inert gases, burned under oxygen-free conditions, and then this charcoal is activated by steam or chemical methods, in steam activation, This charcoal is heated to 750-950°C in the presence of steam. Vapor activated carbon contains very fine pore sizes that are ideal for adsorbing components in water. In the chemical activation of charcoal, it is mixed with zinc chloride paste and heated at 600-800°C. Chemically activated carbon has a large pore size, making it ideal for adsorbing larger molecules in water.

2. Why install carbon filtration?

This starts with the removal of chlorine and chloramine, bacteria or microorganisms are the key factors to be considered in the process of pharmaceutical water treatment, and the water system pretreatment unit is no exception. However, chlorine inhibits microorganisms and poses two main risks to downstream treatment unit equipment:

1. Erosion of reverse osmosis (RO) membranes. The Pharmacopoeia water treatment unit uses RO membranes, which are very thin semi-permeable materials that act as filters. This membrane is sensitive to chlorine. Over time, chlorine can break down the membrane, compromising its filtration capabilities.

2. Dangerous to hemodialysis treatment. Chlorine oxidizes red blood cells, just like it does to bacterial molecules. When cells are oxidized, potassium inside the cells is released. Potassium turns blood reddish – it's actually used in lethal injections to stop your heart from beating, which is why it has to be filtered for hemodialysis, so the final production water with excessive chlorine levels poses a risk to patient safety.

It is obvious that chlorine or chloramines need to be removed from the water, and the removal of chlorine or chlorine amines is to prevent membrane degradation or chlorine stress corrosion cracking in the reverse osmosis system, which ensures the continuous stability of the final treatment membrane filtration unit and at the same time meets the pharmacopoeia requirements for final water use, including chlorine.

3. The role of carbon filtration

1. Dechlorination

Granular activated carbon water filters are effective in removing free chlorine. Carbon particles reduce hypochlorous acid (HOCL) to chloride ions. Over time, the reaction of chloride ions will be degraded, and new carbon ions chloramines will be produced, and the residual chlorine production of activated carbon filter water is set to no more than 0.1ppm.

2. Remove chloramine

Monochloramine in particular is not well absorbed by the body. Reactions with activated carbon are not so easy to occur. Catalytic activated carbon can provide a faster reaction rate than traditional charcoal.

3. Physical adsorption

Activated carbon also has physical adsorption function, which can adsorb organic matter, water odor, colloids and pigments.

4. What factors affect the efficiency of carbon filtration?

Factors such as the contact time between water and the charcoal bed, the concentration of pollutants, the temperature and pH of the water affect the filtration efficiency of the carbon filter. At high temperatures, activated carbon filters are not as effective as at low temperatures. The pH of the water also affects the adsorption of pollutants. When we increase the pH by one unit from 7, we need to increase the activated carbon surface by 20%.

5. Disinfection method

Activated carbon filter is also a potential unit of microbial contamination, which may be related to the possibility of "regenerated coconut shell activated carbon" in the filter material, low-quality filter material is more likely to cause large-scale bacterial infection after adsorption and saturation, so the activated carbon filter should be designed with steam disinfection function, and the disinfection of the carbon bed by cyclic steam can avoid the microorganisms exceeding the standard of the carbon filter in this province.

6. Filter material replacement

Preventive filter media replacement is also a key activity to maintain the stability of pretreated water quality, iodine adsorption value in the industry is one of the important parameters to judge the adsorption capacity of activated carbon, high iodine adsorption value helps to prolong the effective working time of coconut shell activated carbon, under normal circumstances, the iodine adsorption value of new coconut shell activated carbon should not be less than 1000mg/g, and it should always be greater than 500 mg/g during the working period; Regular replacement of activated carbon filter media based on water quality data is an important activity to maintain water quality, but qualified enterprises can determine the adsorption capacity of coconut shell activated carbon by regularly measuring its iodine adsorption value, and use this to judge the replacement time node.