What are the process steps present in a typical water treatment plant?

Although each water treatment facility is different and will have its own process, the steps you would typically see at a plant are outlined below.

  • Screening: To protect plant equipment and aid in efficient plant operation. Both coarse and fine screening can be used to remove materials such as leaves, twigs, rags, paper, and other debris that could obstruct water flow.
  • Aeration and/or Prechlorination: Water is aerated by passing over a series of steps to take in oxygen from the air. This can help expel organic or soluble gases as well as provide for oxidation of iron and manganese for removal later on in the process. Prechlorination with chlorine gas or bleach which also aids oxidation of iron and manganese as well as provide bacteria and odor control.
  • Coagulation (Fast Mix Zone): The addition of a chemical coagulant which is designed to remove fine particles through charge neutralization. Chemical coagulant usually impart a positive or cationic charge to the very fine particles which are negatively charged for charge neutralization. The coagulant is added in a fast mix zone to allow for the coagulant to contact as many of the fine solid particles as possible to form a visually small solid in the water called “pin” floc.
  • Flocculation (Slow Mix Zone Flocculators): As Pin Floc grows larger, the water enters a slow mix zone which is usually paddle type flocculators which turn very slowly allowing particle size to grow. At this point, a chemical flocculant or settling aide can beaded to assist in forming a very large particle size for settling purposes in the next step of the process (Sedimentation).
  • Sedimentation (Settling): This part of the process provides a long retention time for settling of solids to the bottom of a tank or a piece of equipment called a clarifier. The settled solids accumulating/ compacting on the bottom of the tank or clarifier is referred to as sludge.
  • Filtration: The clear portion of the water on the top of the tank now flows to a filter which most of the time is composed of sand for removal of any fine particles which did not settle in the Sedimentation area.
  • Disinfection (Chlorination): This part of the process is to remove any pathogenic micro-organisms from the water making it safe for human consumption and use. Chlorine is the most common chemical used for disinfection which can be in a gas form  or bleach  as well as chlorine dioxide.

What chemicals are used for wastewater treatment?

There are several types of chemicals that can be used in wastewater treatment depending on the type of plant and wastewater process. Some normal chemicals and their use are as follows:

  • Flocculants – Chemical Flocculants or settling aides can be used to enhance settling especially if the biological plant is overloaded which can make settling difficult. Flocculants are also used in wastewater sludge dewatering.
  • Magnesium Hydroxide and/or Caustic – These can be used for pH control. Magnesium Hydroxide provides a safer handling alternative to caustic. Magnesium Hydroxide also can provide a cost performance savings over caustic as well as reduced potential for exceeding pH limits. Magnesium Hydroxide can also provide reduced sludge volume, improved settling, and actually provides some nutrient benefits as well.
  • Sulfuric or Hydrochloric acid – Used for pH control where effluent coming to wastewater plant is highly alkaline and potentially above discharge permit limitations.
  • Defoamer or Antifoam – Used to control foaming in the plant and on effluent.
  • Coagulant – Used as needed to provide charge neutralization forimproved settling or compaction. Sometimes used to aid in precipitation of nutrients prior to wastewater discharge.
  • Precoat chemicals – Precoat chemicals for precoating some specific types of equipment in sludge dewatering such as recessed chamber presses or Rotary Drum Vacuum Filters.
  • Bioaugmentation – Specific bacteria added to improve health of the wastewater plant biomass.
  • Specialty Cleaners – Chemicals used to clean specific plant equipment or surfaces. Egs. Cleaners for cleaning wastewater belt press belts or clean plates in a recessed chamber filter press.
  • Urea and or Phosphate – These are nutrients that can be used to enhance bacterial growth and health.

If you operate a water treatment plant and want to know how Aries Chemical can benefit your water treatment process, please give us a call at (315) 346-1489 or send us a note.

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