Chlorination Tips

• Liquid chlorine (usually sodium hypochlorite) oxidizes everything it can in water -iron, manganese, sulfur, sulfur dioxide (rotten egg smell), etc. -and kills bacteria as well. Put enough chlorine in the water and it will oxidize and kill everything it can, leaving a residual that can be measured with a test kit. Any level of measurable residual chlorine means that the oxidation and kill have occurred.
• Most chlorinators use common household bleach, which is typically 5.25% sodium
hypochlorite. Look for a generic bleach that isn’t contaminated with additives.
• Commercial swimming pools should turn their volume over for treatment at least every 6 hours, so figure 4 or more turns per day to size a pump.
• Commercial bleach, which is readily available from swimming pool suppliers, is usually 12.5% sodium hypochlorite. One gallon of 12.5% chlorine bleach is approximately equivalent to one pound of dry chlorine gas in treatment capacity.
• The half-life of a chlorine solution is approximately 30 days, depending upon its
concentration, temperature, etc. A 5.25% solution will deplete over 30 days to a strength of about 2.5%.
• The amount of chlorine solution you’ll need to feed will be a measure of the chlorine demand required for the oxidation/kill and the chlorine residual (the amount extra put in to be able to measure with a test kit). An easily measurable, yet consumer-acceptable, residual is 0.5 parts per million (PPM). If the user objects to the residual chlorine, a carbon filter can be used as a following treatment stage to remove the chlorine.
• Contact time is an important part of achieving an effective chlorine oxidation and kill. The chlorine solution you inject needs time to thoroughly mix with and treat your water supply. The hypochlorite ions need to make physical contact with the bacteria and oxidizable matter present to react with and nullify them. Hence contact time, or retention time. As a rule of thumb, a 5 PPM residual after 5 minutes of contact, or a 1 PPM residual after 30 minutes of contact, will accomplish an effective oxidation and kill.

DMI FILTER DESIGN CONSIDERATIONS

(lifted from an Article entitled “Design Recommendations for Water Treatment Plant using DM 65 Filter Media: Flow, Pressure, Water Velocity” by Quantum Filtration Medium)


The DMI-65 is the most sophisticated catalytic water filtration media that has extremely high capabilities of removing both Iron (Fe) and Manganese (Mn) simultaneously through low cost catalytic oxidation and retention of precipitate. The DMI-65 will also remove arsenic from a water supply given the correct conditions.

The DMI-65 is one of the fewer catalytic water filtration media in the world developed to remove iron and manganese that is certified to NSF/ANSI 61 for drinking water applications.

With regards as to how DMI 65 works, this is a catalytic filter media boosting oxidation capacity of low cost oxidant such as NaOCl. The oxidant is injected before water reach the filter.

Iron and manganese in solution are in the form of lower valence oxi-hydroxides (example, ferrous hydroxide). Higher valence oxi-hydroxides (ferric hydroxide, red color) are not soluble in water around neutral pH. When the water with iron and manganese in solution and oxidant reaches the filter bed, the low valence hydroxides oxidize to high valence; insoluble form and precipitated particles are retained in the filter bed. This process would take place normally in a matter of days to weeks. The catalytic filter media makes this happen in minutes accelerating the reaction a few hundred times.


DMI 65 is easy to use and provides flexibility when upgrading old water treatment systems. DMI 65 can be used for modification of existing systems by just replacing ordinary sand or multimedia filter used for mechanical filtration, or for removal of iron and manganese through catalytic oxidation.

DMI 65 Filters have three cycles of operation, the same as other media filters:
1. Filtration mode,
2. Backwash mode, and
3. Rinse mode.



1. Filtration mode
Pressure drop for an initially CLEAN filter depends on the depth of the filter media bed and water velocity. Below is a chart showing the pressure drop for 1 meter bed depth. For other bed depth, the pressure drop can be determined linearly. Thus, to find out the pressure drop for 0.6 m bed depth we multiply the value for pressure drop found in the chart by 0.6.

We relate the pressure drop to velocity of the water through the cross sectional area of the filter because its usefulness and simplicity of relating the data to flow rate. We can calculate the flow rate “Q” in cubic meters per hour by multiplying the velocity ‘v” in meters per hour by the filter area “A” in square meters.

Q = v x A

Water temperature during test for the data in the graph was 24º C.


The depth of filter media needed shall be dependent on the required residual iron and manganese in the filtered water. Filter media depth needed increases with the as the required amount of residual iron and manganese allowed in the filtered water decreases. Maximum bed depth could be just over 1 meter and relates also to the flow capacity of the system and effective height of available filters.

Water velocity through the filter should be selected in accordance with the usage of the filtered water, size of water treatment plant, water quality and other factors.

For large drinking water treatment plants the depth of the bed should be selected towards the maximum and the water velocity around 5 m/hr, and in any case, be not more than 10 m/hr. This maximizes performance in removing iron and manganese, reduces the frequency of backwashing, reduces power consumption because average pressure drop is lower, and could provide redundancy in case one of the filters is out of order and higher flow rate has to be put through the remaining filters.

The upper limit of velocity, up to 30 m/hr should be used for small bed depth and larger allowed amount of residual iron and manganese in the filtered water.


2. Backwash mode
Total pressure drop through the filter before backwashing is recommended to be maximum 100 kPa. The granules of DMI 65 filter media are porous. The larger the pressure drop, the larger compaction forces are applied to the filter media. The interaction between filter media particles during alternated compaction under normal service and expansion of the bed during backwashing leads inevitably to deterioration of granules.

Backwashing the filter when the pressure drop has increased by 50 kPa from the initial clean filter pressure drop is a good reference. Higher or lower values could be set depending on the application and how long the filter media has to last before changing it. Note that during filtration cycle, the filter media would not loose significantly its effectiveness in removing the iron and manganese, but the pressure drop through clean filter bed will increase.

Water velocity for backwashing the filter is limited to 80 m/hr. This is the same as recommended for ordinary sand filtration. Although it is possible to use not filtered water for backwashing in general this is not a good idea unless the water is relatively clean and the system is set up with a rinse operating mode in addition to filtration and backwashing. At low backwashing velocity, longer backwashing time is needed. In general backwashing velocity should be twice the filtration velocity.

Backwashing time should be determined on the backwash discharge line, devise a way to observe when the backwash water discharged is satisfactorily clean. Backwashing time could vary from a few minutes to 15 minutes.


3. Rinse mode
This mode follows backwashing to remove the contaminant solids that would exit the filter before the filter bed is compacted back and operates normally. This mode is not necessary to be implemented in all water treatment systems.

Iron and Manganese Removal Filter

DMI-65 is a catalytic filter media boosting oxidation capacity of low cost oxidant such as NaOCl. It is necessary to inject chlorine before the filter to activate the filter.

The DMI-65 is one of the fewer catalytic water filtration media’s in the world developed to remove iron and manganese that is certified to NSF/ANSI 61 for drinking water applications.

Iron and Manganese
Iron can be removed by many different methods to achieve a certain level. These methods are regarded as old technology in world standard, expensive in chemical and labor costs, energy and ongoing costs and Maintenance costs.

Manganese however is much more difficult to remove and expensive using traditional methods.

The DMI-65 is the most sophisticated catalytic reaction media in the world and has a very high ability in removing iron and manganese. The DMI-65 will also remove arsenic from a water supply given the correct conditions.

The DMI-65 is the lowest cost method of removing Iron – Manganese from a water supply. All other processes are expensive to operate and difficult to maintain. The DMI-65 has a life span of at least 5 years before needing to be replaced if the plant is maintained correctly.

Catalytic Filter Media
Iron and manganese in solution are in the form of lower valence oxi-hydroxides (example, ferrous hydroxide). Higher valence oxi-hydroxides (ferric hydroxide, red color) are not soluble in water around neutral pH. When the water with iron and manganese in solution and oxidant reaches the filter bed, the low valence hydroxides oxidize to high valence; insoluble form and precipitated particles are retained in the filter bed. This process would take place normally in a matter of days to weeks. The catalytic media makes the reaction to take place in minutes accelerating the reaction a few hundred times.

The DMI-65 is a similar filtration media to other iron and manganese removal media, however the DMI-65 does not need to be regenerated.

Comparison of Different Disinfection Technologies

CHLORINATION

Advantages:

- Lower capital cost needed

- Residual persists in the water for an extended period of time. This feature allows the chlorine to travel through the water supply system.

- More suitable for system wherein residual disinfectant is needed.

- Good color removal

- Can also be used to oxidize iron bacteria in water, but with sufficient contact time.

Disadvantages:

- Reacts with naturally occurring organic compounds found in the water supply to produce dangerous compounds, known as disinfection byproducts (DBPs). The most common DBPs are trihalomethanes (THMs) and haloacetic acids.

- Hazardous upon contact

- May raise concern on odor and tastes.

- Can cuase corrosion on metal parts and equipment

OZONATION

Advantages:

- Effective in removing viruses and bacteria

- No harmful by-products are formed; unlikely to form carcinogens

- influences pH and temperature minimally on a broad spectrum.

- Higher oxidation potential than chlorine

- No remaining tastes or odors after treatment

Disadvantages:

- Ozone is less suitable for maintenance of a residual concentration (secondary disinfectant), causing it to decompose in water relatively quickly

- solubility decreases when temperatures rise

- High capital cost

- May result in corrosion of metal parts and equipment

UV DISINFECTION:

Advantages

- Effective in removing viruses and bacteria

- No harmful by-products are formed; unlikely to form carcinogens

- No remaining tastes or odors after treatment

- Does not corrode metal equipment

Disadvantages:

- Not suitable for maintenance of a residual concentration (secondary disinfectant)

- Good only for point-of-use applications

MEMBRANE BIOREACTOR: APPLICATION OF MEMBRANE TECHNOLOGY IN WASTEWATER TREATMENT

Why do industrial plants treat their waste water? There are few important reasons:

• Conservation of natural resources


• Compliance to environmental laws

• Financial benefits

Before we go the the main topic, let us first look at the stages of a conventional waste water treatment facility:

Preliminary Treatment

It may be a physical or mechanical process which aims to remove large or coarse particles

Examples: Screens; grit chambers


Primary Treatment

A physical or mechanical process which removes Settleable Solids, Oil and Grease and about 40% of TSS and BOD

Examples: Sedimentation (primary clarifier); oil/water separator; aeration


Secondary Treatment

Physical, Biological and/or Chemical process; process to convert Dissolved Solids and Suspended Solids into a form that can be removed by physical means; removes up to 85% of TSS and BOD and a small percentage of TDS.

Examples: Sequencing Batch Reactor; Activated Sludge; Rotating Biological Contactor; Trickling Filter; chemical precipitation; flocculation; coagulation


Tertiary/Advanced Treatment

Any level of treatment, may be physical or chemical, beyond the secondary treatment focusing on the removal of nutrients and disease-causing microorganisms

Examples: Filtration; Ammonia Stripping; pH adjustment; disinfection using chemical, UV light or ozone

To understand the revolutionary potential of Membrane Bioreactor (MBR) Technology it is helpful to first consider how a conventional wastewater treatment plant operates. Each conventional plant consists of three basic parts:

This treatment process is 85-95 percent effective in removing TSS, BOD and COD but is often ineffective in terms of removing microorganisms.

Typically the discharge from a conventional plant will contain 10,000 to 100,000 microbes per milliliter.

Membrane Bioreactors, simply called MBRs offer an optimum solution:

• Membrane modules are submerged in the activated sludge to combine the biological step and the solid-liquid separation step into a single process.

• Essentially, membrane bioreactors replace the solids separation function of secondary clarifiers and sand filters in a conventional activated sludge system


• Produces effluent with much better quality than that produced by a conventional plant

Since the membrane acts as a barrier to microorganisms, the effluent quality is much better than that produced by a conventional plant. Also, the membrane barrier eliminates the need for secondary clarifier and allows the activated sludge to be more highly concentrated. This reduces the capacity needed for biological tanks, saving space and money.

MBR Plant can be configured either as internal/submerged, or external/sidestream.

• Internal/Submerged is the type where the membranes are immersed in and integral to the biological reactor


• External/Sidestream is where membranes are a separate unit process requiring an intermediate pumping step

Advantages of MBR Technology versus conventional process:

• Improved Water Quality - it meets stringent effluent requirements and filters out nearly all solids


• Allows Wastewater Reuse - as part of a treatment scheme, provides water for potable reuse; reduces wastewater discharge fees; provides water for non-potable applications where fresh water is in short supply


• Lowers Capital Costs - that is, Clarifier is not needed and biological step can be scaled down since bacteria concentration is higher


• Reduces Plant Space Requirements - Footprint is up to 50% smaller than conventional plant. It allows for easy expansion in terms of capacity within existing buildings


• Fewer Operational Problems - Bulking and floating sludge problems are minimized


• Easily Retrofittable to Existing MBRs and conventional WWTF - the system has few module connections and there is little need to modify infrastructure