WASTE TREATMENT METHODS
Purpose :
▪ Reducing Toxicity
▪ Minimizing the waste volume
▪ Altering the state so that is suitable for disposal option.
TREATMENT METHODS
Treatment of Treatment of Air
Treatment of Solids
Water Emissions
Removal of Removal of Removal of Removal of
Suspended HCs Dissolved HCs Suspended solids Dissolved solids
TREATMENT METHODS
Treatment of Treatment of Air
Treatment of Solids
Water Emissions
Removal of HCs Removal of water
REMOVAL OF SUSPENDED H/C
1) Gravity separation – When a
free oil or unstable oil is present so
the effective method is separator
tanks with skimmers. Example –
Free Water knockout, wash tanks,
settling tanks and gun barrel.
• Plate separators can reduce oil
concentration to 2-25 mg/l and
can remove oil droplets down to
about 20-20 micrometers in
diameter.
Fig:
Schematic of
Plate
Separator
Hydrocyclones:
➢ Hydrocyclones is also a standard method
to remove suspended particles .
➢ In hydrocyclone a high velocity stream is
injected tangentially into the conically
shaped hydrocyclones creating a vortex.
➢ The radial accelerations forces the more
dense water to the outer edge of the
hydrocyclone and less dense oil to the
center.
➢ Hydrocyclones can reduce oil
concentration to 10 ppm but 30 ppm is a
common average.
➢ Centrifuges can remove oil droplets to
about 2 micrometer in diameter.
2) Heater Treater:
• The crude which is produced contains
considerable amount of water in it
which has to be removed or treated
before crude is supplied to the
refinery.
• It is used for treatment of emulsion.
• This is a method to destabilize the
stable emulsion reducing the
interfacial tension between the
phases allowing the oil and water to
separate faster.
• Heater treater uses a high voltage
potential on the electrodes for
coalescing of the water droplets in the
final stage of processing.
3) Gas floatation:
• Gas bubbles are passed through an
emulsion of oil in water, the oil
droplets will attach to the bubbles
and can be carried to the top of the
mixture where they can be easily
removed.
• It is aided by using chemical
coagulants.
• Carbon di oxide floatation
techniques is the most common
and widely used floatation
techniques.
• It reduce the oil concentration to
15-100 mg/L with a typical average
of 40 mg/L
4) Filtration:
• This is a process through which water is passed through water wet filters or
membranes.
• These filter media use capillary pressure to trap oil and prevent it from passing
out of the filter.
• Advanced filtration process uses hydrophilic membranes where the filter media
passes the water not oil through a capillary bundle tubes.
• This process is called ultrafiltration or microfiltration.
5) Chemical Coagulants:
➢ Coagulants typically overcome the electrostatic repulsion charges on the individual
droplet allowing them to coagulate to larger drops.
➢ Aluminium Sulfate (alum) is the most common coagulant used for water purification.
Other chemicals, such as ferric sulfate or sodium aluminate, may also be used.
6) Electrostatic Separation:
➢ Separation of water is done either by passing DC or SC current supply.
➢ When a DC current is applied to the water containing such an emulsion, the oil will
migrate to the positive electrode. The migration velocity is 1mm/min.
➢ This can be used only with saline water.
7) Filtration Coalescence:
➢ This is a process in which the water is passed through oil wet filters.
➢ The oil droplets attached to the filter matrix and coalesce into larger ones.
➢ Eg: Sand , Gravels and Glass Fibres are used.
REMOVAL OF DISSOLVED H/C
1) Adsorption :
➢ This is a method to remove the low level of dissolved HC by using a packed bed
process.
➢ The packed bed consists of an activated carbon.
➢ This activated carbon effectively adsorbs the oil droplets from the medium.
➢ All free oil must be removed prior to the use of activated carbon to prevent the oil
from clogging.
➢ Natural and Synthetic Resins are also used nowadays to adsorb oil through packed
bed adsorption process.
2) Biological Process:
➢ It consists of mixing oxygen and nutrients with the water in a tank.
➢ The bacteria then degrade the organic compounds.
➢ Disadvantages is because of eutrophication leads to oxygen demand and
corrosion.
3) Volatilization :
➢ Volatile Organic Compounds (VOC) can
be removed from water by lowering the
partial pressure of the compound in the
vapour phase in contact with the water.
➢ When the partial pressure of the
dissolved VOC’s in the water exceeds
that of its vapor pressure the compounds
will come out of the solution and enter
the vapor phase.
➢ The most common process in the air
stripping.
➢ In this process air and water are passed
through a containment vessel in
countercurrent flow where VOC’s
evaporate into the air.
➢ The removal of VOC’s can be enhanced
by heating the air or by using the stream.
4) Precipitation :
➢ The solubility of many organics molecules decreases as the pH decreases.
➢ By lowering the pH some organic molecules can be precipitated.
➢ Precipitation will however not remove all dissolved hydrocarbons and will acidify the
water.
5) Ultraviolet Irradiation:
➢ In this process, high energy short wavelength photons are used to break the chemical
bonds of dissolved hydrocarbons.
➢ When combined with heating to high temperature e.g. by solar panels virtually complete
destruction of hazardous hydrocarbon molecules in water has been observed.
➢ Disadvantages is time consuming and costly.
6) Oxidation:
➢ Dissolved oil can also be destroyed through oxidation.
➢ Few examples of the test is done by ozone ,peroxide chlorine or permanganate.
➢ But in oil field treatment process this is not used as per OISD standards.
REMOVAL OF SUSPENDED SOLIDS
1) Gravity Separation:
➢ Fluids can be discharged into pits or tanks, where the solids settle to the bottom. For fine
particles gravity settling is not effective.
2) Filtration:
➢ The water passes through the filter while the solids are retained.
3) Coagulation
REMOVAL OF DISSOLVED SOLIDS
1) Reverse Osmosis:
➢ This is widely used process in water treatment plant but is least applicable in waste
water oil field practices.
➢ By this process membrane filter is used to selectively bypass the water molecules
allowing the larger dissolved solids (like salt and metals) to hinder back.
➢ Fouling is a problem if arises then reverse osmosis techniques should be incorporated
in oil-filed brines ETP plant for desalination.
2) Ion Exchange:
It is a process of exchange of divalent ions with monovalent cations. The removal of
hardness ions is necessary for many processes because these ions radially precipitate and
form a hard scale that can foul equipment.
Strong Acid Resins: Sulfonic Acid – regenerated process is by using concentration solution
NaCl.
Weak Acid Resins – Carboxylic Acid – regenerated process is by using – flushing with a
strong acid- like HCl or Sulphuric acid and then neutralizing with NaOH.
3) Evaporation/Distillation
4) Biological Process
5) Neutralization:
Many aqueous wastes is either acidic or alkaline. Hydration is a process to neutralize the pH
of the content before refusal or disposal.
TREATMENT OF SOLIDS (REMOVAL OF H/C)
1) Washing:
➢ This method uses a fluidized bed of upward flowing high velocity water. These stream agitates the solids and
opens the pore system to release the oil.
➢ The efficiency of the system can be enhanced by adding a surfactant to the water to lower the IF holding the
oil to the solids.
➢ Washing is more effective in sandy soil containing low amounts of clay.
➢ Reducing the toxicity is also another process by mixing the hydrocarbon content with low toxic H/C like
diesel oil.
2) Adsorption
3) Heating :
In this process the sludge are heated above the boiling point of water and allowed to flash to vapor. This
separates the light H/C from heavier H/C.
4) Incineration: (Incineration is the process of burning hazardous materials at temperatures high enough to
destroy contaminants. Incineration is conducted in an “incinerator,” which is a type of furnace designed for
burning hazardous materials in a combustion chamber.
This is a process to burn the mixture in an incinerator. Incinerator generally removes 99% of the H/C from the
solids.
5) Biological Process: (All biological waste treatment processes involve the decomposition of biodegradable
wastes by living microbes (bacteria and fungi), which use biodegradable waste materials as a food source for
growth and proliferation.) Bioremediation is also one process.
TREATMENT OF SOLIDS (REMOVAL OF WATER)
1) Evaporation:
The method to dewater solid wastes in arid climate is to put them in open pit or on concrete
pads and allow the free water to evaporate.
2) Sprinkling:
Method is generally used to enhance the vaporization process.
3) Percolation:
This ponds have permeable sides and bottoms allowing the water to percolate into the
surrounding soil leaving the solids at the bottom of the pond.
4) Mechanical Methods using Sieve Analysis, Shale Shaker and Hydrocyclones.
SOLIDIFICATION
➢ One way to treat contaminated solids is to solidify the mixture so that the contaminants
become part of the solid.
➢ Solidification reduces pollutant mobility and improve handling characteristics. Two types of
solidification have been used:
1) Adding materials to absorb free liquids.
2) Adding Materials to chemically bind and encapsulate the contaminants.
➢ Absorbants are typically used to dewater reserve pits in areas where the evaporation rate is
low. Materials that have been added to the pits to absorb free water include fly ash, straw
and kiln dust.
➢ The best solidification methods are those that chemically bind the contaminants. These
methods are based on primarily Portland cement, calcium silicate , or alumino silicate
reactions. These materials unlike kiln dust and fly ash, can reduce the leachability of heavy
toxic metals, asbestos , oils and salts.
