Sodium Hypochlorite Filtration

Sodium hypochlorite - commonly called bleach in the US - is made by reacting chlorine in a solution of sodium hydroxide (caustic soda). The resultant product, due to the nature of the process and other factors, usually has a significant amount of contamination from metal ions and/or substantial amounts of suspended solids. These conditions adversely affect the quality of the bleach and significantly shorten its shelf life. In order to meet the tough specifications drinking water treatment facilities and other industries mandate for high purity sodium hypochlorite, the metal ions and suspended solids must be removed from the bleach in additional process steps. This critical step is achieved with a complete filtration process that removes heavy metals, suspended solids, and other contaminants.

Powell has developed the technology and equipment for a complete filtration process for high quality sodium hypochlorite. When properly deployed, the Powell Sodium Hypochlorite Filtration Process not only removes suspended solids and metal ions such as iron, nickel and copper from the bleach - it also ultimately reclaims liquid waste streams created in the production and storage processes for reuse in subsequent sodium hypochlorite manufacture. The equipment components of the process are each designed to specific parameters and made from appropriate materials of construction. The system can be expected to provide remarkable results and years of reliable service. The block flow diagram below illustrates the process.

Continuous Sodium Hypochlorite Production Process Ideal for applications where air or nitrogen are readily available. Requires 90 psig to operate. Fail-closed design operates even if AC power or air pressure is lost. Powell gas detection systems integretate with Powell Valve Closure Systems.Pressurized railcars of chlorine frequently require additional pressure to facilitate the railcar unloading operation at user production facilities. This practice - often called pressure padding - introduces air or nitrogen into the vapor space above the liquid chlorine in the car to force the liquid chlorine out of the liquid angle valve at the top of the car. Typically air, as opposed to nitrogen, is used as the pad gas. The Powell ProVent Equipment Scrubber is designed to evacuate transfer hoses, piping, and vaporizers used for chlorine or sulfur dioxide process systems. The Powell ProVent, which can be sized for your specific needs, recirculates a caustic soda solution through an eductor to safely neutralize any chlorine remaining in the hoses or piping. In case of power failure, the scrubber can still neutralize chlorine or sulfur dioxide under pressure.Chlorine Tank Car:  Powell offers a full inventory of chlorine line equipment, unloading equipment, and motion detection systems.  Powell UniPro Valve Closure Systems can be integrated with the Powell Railcar Motion Detection System which will trigger the valves to be closed in the event railcar movement is detected.Chlorine Control Module:  The Powell Chlorine Control Module is designed for the offloading of chlorine from railcars. Powell has combined high quality, chlorine-rated components with the latest design recommendations from The Chlorine Institute, Inc. Pamphlet 57 into a single unit.  Sodium Hypochlorite (Bleach) Continuous System:  The Powell Continuous Sodium Hypochlorite Process System is designed to manufacture sodium hypochlorite with greater efficiency and higher quality than previously obtainable with batch or continuous methods.  The process, which uses liquid or vapor chlorine and caustic, is versatile and has the design capability of making any concentration of sodium hypochlorite solution from 20 to 200 grams per liter available chlorine.Sentry 2000 Chlorine Scrubber:  The system is a 4-stage, single-pass scrubber with a horizontal packed bed of high efficiency packing material. The Sentry 2000 can achieve virtually any stack emission performance desired. Thus, it is possible to control performance of the system based on any inlet and outlet concentrations and flow rates.Chlorine Padding System:  The Powell Railcar Padding System provides an independent source of clean, oil free, dry air in accordance with The Chlorine Institute, Inc. Pamphlet 66 guidelines for chlorine tank car pressure padding. This separate chlorine padding system is completely isolated from other air supplies to prevent chlorine vapors from accidentally mixing into the instruments and equipment.Filtrate Water Dilution System:  designed to reduce or eliminate liquid water discharge from a bleach production process.Unfiltered Bleach TanksSodium Hypochlorite (Bleach) Filter System:  The Powell Sodium Hypochlorite Filter System provides the highest quality sodium hypochlorite available in the market and can be used with any quality caustic to yield sodium hypochlorite that can be packaged for the household market using sealed bottles, the drinking water industry, or any other application required.Sodium Hypochlorite (Bleach) Dilution System:  The Powell Sodium Hypochlorite (Bleach) Dilution System combines water and sodium hypochlorite to produce a high quality diluted strength bleach product.  An optional caustic stream can be provided to add sodium hydroxide as needed, increasing the amount of excess caustic of the diluted bleach. This provides the ability to produce very specialized bleach products to meet a wide variety of customer specifications.Filtrate Water TanksSodium Hypochlorite Filter Backwash:  Powell offers a plate and frame filter press for de-watering backwash discharge from filter-aided filter systems. Plastic wetted parts eliminate the need for neutralization. Water washing and air drying produce a pH balanced dry cake ready for disposal. Wastewater Process TankBleach Storage TanksWaste Dry Cake DischargeTransportation TruckBleach Loading Pump

Raw Material and Process Efficiencies with the Powell Sodium Hypochlorite Filtration Process

The Powell Sodium Hypochlorite Filtration Process is designed to take advantage of raw material and process cost efficiencies to produce high quality sodium hypochlorite. Some of the advantages of the process are discussed below:

  • Since virtually all contaminants are removed during final filtration, most of the plant's liquid wastes can be reclaimed and re-used in the production of sodium hypochlorite, eliminating or minimizing costly disposal.
  • High quality sodium hypochlorite can be produced using any quality of sodium hydroxide, including less expensive diaphragm cell caustic. This results in lower raw material costs and provides a wider choice of suppliers.
  • Contaminant-free sodium hypochlorite does not decompose as rapidly as standard grade, so strength of bleach can be reduced. Also, since metal ions and suspended solids that contribute to oxygen formation are filtered from the bleach, swelling due to oxygen formation in the bottled product is eliminated or greatly reduced. Similarly, costly customer complaints relating to oxygen and solids formation in storage tanks, pumps, and piping are eliminated or minimized significantly.
  • Higher quality bleach provides a competitive market advantage and often commands a higher price.

Bleach Filter System for Sodium Hypochlorite Filtration

The Powell Bleach Filter is the first step in the filtration process. Prior to filtration, sodium hypochlorite produced in any production facility can typically have metal contamination in the range of 1ppm iron, 400 ppb nickel, and 60 ppb copper. Also, significant amounts of suspended solids will be in the solution. This sodium hypochlorite is referred to as "unfiltered bleach" or "unfiltered sodium hypochlorite."

After the unfiltered bleach is processed through the Powell Bleach Filter component of the Powell Sodium Hypochlorite Filtration Process - with chemical treatment and the proper selection of filter aid and sizing, body feed amounts, pre-coat, and related process control - metal contamination will typically be less than 0.300ppm iron, 10 ppb nickel, and 10 ppb copper. Similarly, the suspended solids will be very low.

These results can be verified with the use of a test called "Suspended Solids Quality Test for Bleach Using Vacuum Filtration," a method to very quickly determine if the suspended solids of a sodium hypochlorite solution are within acceptable levels. Although this test, developed by Novachem, a sodium hypochlorite research and testing laboratory in Oxford Ohio, is not an indication the metals content of the solution is within acceptable limits, low levels of suspended solids directly correlates to low levels of metals. Specific procedures to perform the "Suspended Solids Quality Test for Bleach Using Vacuum Filtration," along with research documentation and additional information on the test procedure, can be found in the Powell Technical Information Center. There is also a listing of the laboratory equipment utilized for repetitive test results.

The Powell Filtration Process to Reclaim Liquid Waste Streams

All sodium hypochlorite production processes generate liquid wastes that require disposal. Many times these liquid wastes are difficult and costly to chemically treat and neutralize for safe and legal disposal. It is not unusual for the production facility to be required to haul all liquid wastes to outside treatment systems, since in many locations even treated wastewater can not be discharged into local sanitary sewage systems.

These waste liquids typically include the following:

  • Backwash liquids from filtration
  • Sodium hypochlorite spilled in process production and tank truck loading
  • Containment water collected in outside tank containment systems
  • Sodium hydroxide liquids spilled and contained within process areas, loading areas, or storage tank containment areas
  • Backwash liquids from water softeners, water deionizers, brine deionizers, and other processes
  • Brine purge from chlorine plant brine systems
  • Other liquid wastes that can be pH adjusted above 9 such as HCl wastewater
  • Waste stream contaminants

These waste liquids have many commonalities, including low levels of contaminants such as heavy metals, iron, calcium, magnesium, and other chemicals commonly found in the wastewater streams of a sodium hypochlorite production facility. Rather than costly disposal, in subsequent process steps, all wastewater, including the backwash water with spent filter aid from the Powell Bleach Filter unit, can be reclaimed for use in sodium hypochlorite production. The liquid is pumped to a wastewater process tank along with other plant liquid wastes such as spillage, wash water, softener purge, and other liquid solutions. The wastewater is further processed through the Powell Filter Press System, resulting in a solution of water referred to as "filtrate water." Typically, filtrate water - which could be as much as 10% to 20% of the total volume of the sodium hypochlorite produced - has very low levels of iron, nickel, and copper, along with low levels of sodium chloride, calcium, magnesium and other related chemicals. This filtrate water is reused in sodium hypochlorite production.

Bleach Filter Press

The waste of the Powell Automated Filter Press is discharged as a dry cake. The dry cake is comprised of Perlite®, which contains very low levels of contaminates removed from the sodium hypochlorite and any contaminates removed from any other waste streams. Powell can supply material handling systems for discharged cake including dumpsters equipped with self-dumping forklift mounts. The dry cake has to be analyzed for hazardous wastes. With normal testing, using the typical TCLP testing, this dry cake is currently being treated as non-hazardous waste. Powell can provide additional information about dry cake testing upon request.

Equipment to Complete the Powell Sodium Hypochlorite Filtration Process

The complete Powell Sodium Hypochlorite Filtration Process includes several additional components. These include:

Filtrate Dilution System

The filtrate water from the Powell Bleach Filter may be pumped to a holding tank, neutralized and disposed of to a safe point of discharge. However, if desired, this water/trace bleach solution can be used in the bleach production. This allows the plant, in many applications, to become a zero discharge plant with regard to the bleach process liquids. The major components of the Filtrate Dilution System include a Powell two-stream Filtrate Dilution System and a filtrate water supply pump.

Dust Collection and Removal System

The filter aid used in the Powell Bleach Filter is a dust that can become airborne when handled during the filtering process. Powell can supply major components of a ventilation system designed for appropriate dust removal or collection and disposal.

Tank Level Automation and Control

Complete automated systems that offer both continuous level monitoring as well as high-point level detection are available from Powell.

For More Information

Powell would like the opportunity to put our extensive knowledge and more than 40 years experience in the production of sodium hypochlorite at the disposal of those who must produce high quality sodium hypochlorite, and must also process the waste streams of the plant safely and economically. Over the years, Powell has been able to show that when all the process equipment is considered and the savings due to wastewater reuse and diaphragm cell caustic are factored into the cost equation, the Powell Sodium Hypochlorite Filtration Process is very cost competitive.

More Sodium Hypochlorite Equipment from Powell

Sodium Hypochlorite Production Systems

Skid Mounted Batch Sodium Hypochlorite System

Skid Mounted Continuous Sodium Hypochlorite Production System

Sodium Hypochlorite Filter System

Sodium Hypochlorite Dilution System