Activated carbon filters 

Abrah Co's Activated Carbon Filters are Designed for larger commercial and industrial water filtration applications with multi-tank parallel systems common for high flow rates. Epoxy lined and prime exterior finished carbon steel pressure vessels. high working pressures (up to 8 bar). the sand bed is fully utilized, and the trapping of dirt is prevented. This allows for reaching good results with a higher filtration speed. Perfect backwashing can be achieved, whereby all the captured dirt is washed out of the filter media. New manhole system for easier inspection without the trouble of corrosion in accessing the inside media that save time in the process. The filter is provided with enough manholes to allow for easy inspections and sand changes.

Activated carbon adsorption

As water passes through an activated carbon filter, organic particles and chemicals are trapped inside through a process known as “adsorption”.Activated carbon's big internal surface makes active carbon ideal for adsorption. Adsorption is a process where a solid is used to remove a soluble substance from the water.

Active carbon comes in three variations:  Active Carbon Filter Block, Powder Activated Carbon (PAC), and Granular Activated Carbon (GAC). The GAC version is mostly used in water treatment, it can adsorb the following soluble substances:

  • Adsorption of organic, non-polar substances such as:
    • Mineral oil
    • BTEX
    • Poly aromatic hydrocarbons (PACs)
    • (Chloride) phenol
  • Adsorption of halogenated substance: I, Br, Cl, H en F
  • Odor
  • Taste
  • Yeasts
  • Various fermentation products
  • Non-polar substances (Substances which are non soluble in water)

 Factors that influence the performance of active carbon in water:

Activated carbon filters are generally employed in the process of removing organic compounds and/or extracting free chlorine from water and are common methods in water and wastewater treatment systems

1. Chlorine Removal: Activated carbon may be used to remove chlorine with little degradation or damage to the carbon. Dechlorination occurs rapidly and flow rates are typically high. However, this process requires an extensive amount of surface area, and organics in the water will eventually fill up and block the pores of the carbon. Ultimately, the activated carbon filter will need to be replaced as its ability to dechlorinate the water will slowly decline. Spent carbon can be re-activated; however, re-activated filters should only be used in waste-water treatment applications. One advantage to using AC is its low operating cost and virtual “fail safe” operation once installed. One disadvantage is that as the chlorine is removed from the topmost layer of the media, the AC provides a damp environment ideal for the growth and proliferation of bacteria. Bacteria can cause problems in medical applications, or when using carbon as a pretreatment to reverse osmosis.

2. Removal of Organic Matter: . The adsorption process depends upon 5 key factors:

1)The type of compound to be removed. Compounds with high molecular weight and low solubility are better absorbed and the physical properties of the activated carbon (surface area and pore size distribution); the Presence of other organic compounds which will compete for the available adsorption sites. 

2) the chemical makeup of the carbon source (amount of hydrogen and oxygen)

3) the chemical makeup and concentration of the contaminant, The higher the concentration, the higher the carbon consumption.

4) water pH and temperature, The pH of the waste stream. For example, acidic compounds are better removed at lower pH

5) the length of time the water is exposed to the activated carbon filter (called empty bed contact time or EBCT). 

Applications:

  • Pre-filtration of disinfection equipment
  • Pre-filtration of Reverse Osmosis treatment systems
  • Preparation for micro and ultrafiltration
  • Recirculation systems
  • Cooling water processes
  • Irrigation systems
  • Swimming-pool filtration
  • Basin water filtration
  • Groundwater purification

Activated carbon filters backwash Process: 

Over time the pressure drop over the filter rises while the flow remains the same, due to the adhered suspended solids. Eventually, the filter media needs to be cleaned, a process called backwashing.

In drinking water treatment, backwashing is a routine practice for AC maintenance. The purpose of backwashing is to reduce clogging, head loss, and unwanted organisms in AC. Meanwhile, backwashing is an efficient method to maintain the proper biofilm on AC, because inadequate backwashing leads to the formation of thick biofilm, which can hinder the access of substrates to the microorganisms. On the other hand, a thin biofilm may decrease the performance of GAC because most of the microorganisms will be dislodged by backwashing

A backwash should be performed when the differential pressure exceeds 0,1-0,2 bar over the differential pressure of a clean filter. A backwash should be performed at least once a week to prevent clumping of the media. With a setup of valves, the flow direction over the filter reverses. At a velocity of 35m/h (depending on the type of media) the filter bed expands. The particles detaches of the filter media grains due to the raised velocity. The expanded gaps between the grains make sure it can exit the vessel. When the velocity exceeds the maximum design specifications the filter bed expands to much which will result in losing media out of the top during backwash.