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.
Raw Material and Process Efficiencies with the Powell Sodium Hypochlorite Filtration
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
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
- 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.
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.
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.
Sodium Hypochlorite Production Systems
Skid Mounted Batch
Sodium Hypochlorite System
Skid Mounted Continuous
Sodium Hypochlorite Production System
Sodium Hypochlorite Filter
Hypochlorite Dilution System