طرق معالجة مياه الصرف الصناعى الناتج من ابار الغاز الطبيعى والبترول ومصانع البتروكيماويات

oil and gas production wastewater (OGPW)

1. Introduction

During oil and natural gas production, so-called “produced water” comprises the largest byproduct stream.

In addition, many oil and gas operations are augmented via injection of hydraulic fracturing (HF) fluids into the formation.

Both produced water and HF fluids may contain hundreds of individual chemicals, some known to be detrimental to public health and the environment.

the effects of oil and gas production wastewater (OGPW) on groundwater and surface water quality and on soil chemical, physical, and biological properties

Wastewater Industrial Process

Wastewater Process wastewater and other wastewaters, which may be contain dissolved hydrocarbons, oxygenated compounds, and other contaminants, should be treated at the onsite wastewater treatment unit (WWTU).

Recommended process wastewater management practices include:

Prevention and control of accidental releases of liquids through inspections and maintenance of storage and conveyance systems, including stuffing boxes on pumps and valves and other potential leakage points, as well as the implementation of spill response plans;

Provision of sufficient process fluids let-down capacity to maximize recovery into the process and to avoid massive process liquids discharge into the oily water drain system;

Design and construction of wastewater and hazardous materials storage containment basins with impervious surfaces to prevent infiltration of contaminated water into soil and groundwater.

Specific provisions to be considered for the management of individual wastewater streams include the following:

· Amines spills resulting from the carbon dioxide alkaline removal system downstream of the Gasification Unit should be collected into a dedicated closed drain system and, after filtration, recycled back into the process provided the amine did not become contaminated as a consequence of being spilled and/or collected;

· The water effluent from the stripping column of the FischerTropsch (F-T) Synthesis Unit, which contains dissolved hydrocarbons and oxygenated compounds including alcohols, organic acids and minor amounts of ketones, should be re-circulated inside the F-T Synthesis Unit in order to recover the hydrocarbons and oxygenated compounds;

· Acidic and caustic effluents from demineralized water preparation, the generation of which depends on the quality of the raw water supply to the process, should be neutralized prior to discharge into the facility’s wastewater treatment system;

· Blow-down from the steam generation systems and cooling towers should be cooled prior to discharge.

Cooling water containing biocides or other additives may also require dose adjustments or treatment in the facility’s wastewater treatment plant prior to discharge;

· Hydrocarbon-contaminated water from scheduled cleaning activities during facility turn-around (cleaning activities are typically performed annually and may last for a few weeks), hydrocarbon-containing effluents from process leaks, and heavy-metals containing effluents from fixed and fluidized beds should be treated via the facility’s wastewater treatment plant.

Process Wastewater treatment Techniques for treating industrial process wastewater in this sector include source segregation and pretreatment of concentrated wastewater streams.

Typical wastewater treatment steps include:

grease traps, skimmers, dissolved air floatation, or oil / water separators for separation of oils and floatable solids; filtration for separation of filterable solids; flow and load equalization; sedimentation for suspended solids reduction using clarifiers;

biological treatment, typically aerobic treatment, for reduction of soluble organic matter (BOD);

chemical or biological nutrient removal for reduction in nitrogen and phosphorus;

chlorination of effluent when disinfection is required; and dewatering and disposal of residuals in designated hazardous waste landfills.

Additional engineering controls may be required for

(i) containment and treatment of volatile organics stripped from various unit operations in the wastewater treatment system,

(ii)advanced metals removal using membrane filtration or other physical/chemical treatment technologies,

(iii) removal of recalcitrant organics, cyanide, and non biodegradable COD using activated carbon or advanced chemical oxidation,

(iii) reduction in effluent toxicity using appropriate technology (such as reverse osmosis, ion exchange, activated carbon, etc.),

(iv) containment and neutralization of nuisance odors.

Storm water:

Storm water may become contaminated as a result of spills of process liquids.

Natural gas processing facilities should provide secondary containment where liquids are handled, segregate contaminated and non-contaminated storm water, implement spill control plans, and route storm water from process areas into the wastewater treatment unit.

Cooling water:

Cooling water may necessitate high rates of water consumption, as well as the potential release of high temperature water, residues of biocides, and residues of other cooling system anti-fouling agents.

Recommended cooling water management strategies include:

· Adoption of water conservation opportunities for facility cooling systems as provided in the General EHS Guidelines;

· Use of heat recovery methods (also energy efficiency improvements) or other cooling methods to reduce the temperature of heated water prior to discharge to ensure the discharge water temperature does not result in an increase greater than 3°C of ambient temperature at the edge of a scientifically established mixing zone that takes into account ambient water quality, receiving water use, assimilative capacity , etc.;

· Minimizing use of antifouling and corrosion-inhibiting chemicals through proper selection of depth for placement of water intake and use of screens;

selection of the least hazardous alternative with regards to toxicity, biodegradability, bioavailability, and bioaccumulation potential; and dosing according to local regulatory requirements and manufacturer recommendations;

· Testing for the presence of residual biocides and other pollutants of concern to determine the need for dose adjustments or treatment of cooling water prior to discharge.

Hydrostatic testing water:

Hydrostatic testing of equipment and pipelines involves pressure testing with water (generally filtered raw water) to verify their integrity and to detect possible leaks.

Chemical additives (typically a corrosion inhibitor, an oxygen scavenger, and a dye) may be added. In managing hydro-test waters, the following pollution prevention and control measures should be implemented:

· Using the same water for multiple tests to conserve water and minimize discharges of potentially contaminated effluent;

· Reducing the use of corrosion inhibiting or other chemicals by minimizing the time that test water remains in the equipment or pipeline;

· Selecting the least hazardous alternative with regards to toxicity, biodegradability, bioavailability, and bioaccumulation potential, and dosing according to local regulatory requirements and manufacturer recommendations.

If discharge of hydro-test waters to the sea or to surface water is the only feasible alternative for disposal, a hydro-test water disposal plan should be prepared considering location and rate of discharge, chemical use (if any), dispersion, environmental risk, and required monitoring.

Hydro-test water disposal into shallow coastal waters should be avoided.

Hazardous Materials Natural gas processing facilities use and manufacture significant amounts of hazardous materials, including raw materials, intermediate / final products and by-products.

The handling, storage, and transportation of these materials should to be managed properly to avoid or minimize the environmental impacts from these hazardous materials.

Recommended practices for hazardous material management, including handling, storage, and transport, are presented in the General EHS Guidelines.

Wastes Non-hazardous Waste Non-hazardous industrial wastes consist mainly of exhausted molecular sieves from the air separation unit as well as domestic wastes.

Other non-hazardous wastes may include office and packaging wastes, construction rubble, and scrap metal.

General recommendations for the management of nonhazardous waste, including storage and disposal, are presented in the General EHS Guidelines.

Hazardous Waste Hazardous waste should be determined according to the characteristics and source of the waste materials and applicable regulatory classification.

In GTL facilities, hazardous wastes may include bio-sludge; spent catalysts; spent oil, solvents, and filters (e.g., activated carbon filters and oily sludge from oil water separators); used containers and oily rags; mineral spirits; used sweetening; spent amines for CO2 removal; and laboratory wastes.

General recommendations for the management of hazardous waste are presented in the General EHS Guidelines.

Spent catalysts:

Spent catalysts from GTL production are generated from scheduled replacements in natural gas desulphurization reactors, reforming reactors and furnaces, Fischer-Tropsch synthesis reactors, and reactors for mild hydrocracking.

Spent catalysts may contain zinc, nickel, iron, cobalt, platinum, palladium, and copper, depending on the particular process.

Recommended waste management strategies for spent catalysts include the following:

· Proper on-site management, including submerging pyrophoric spent catalysts in water during temporary storage and transport until they can reach the final point of treatment to avoid uncontrolled exothermic reactions;

· Return to the manufacturer for regeneration; and

· Off-site management by specialized companies that can recover the heavy or precious metals, through recovery and recycling processes whenever possible, or who can otherwise manage spent catalysts or their non-recoverable materials according to hazardous and non-hazardous waste management recommendations presented in the General EHS Guidelines.

Catalysts that contain platinum or palladium should be sent to a noble metal recovery facility.

Heavy ends:

Heavy ends from the purification section of the Methanol Synthesis Unit are normally burnt in a steam boiler by means of a dedicated burner.

-Production of conventional oil and gas and coal bed methane is often accompanied by production of large volumes of produced water.

In certain geologic strata substantial volumes of oil and natural gas are present, yet they experience poor recovery rates due to low permeability of local strata.

This is especially true for shales, tight sands, oil sands, and coal beds .

In hydraulic fracturing (HF) (“fracking”), a specially tailored mixture of fluids is pumped into recovery wells under high pressure to fracture low permeability formations and enhance gas and oil production .

Extraction of hydrocarbon resources using HF is commonly referred to as “unconventional production.”

Unconventional wells include those drilled horizontally, allowing the borehole to bend 90 degrees and penetrate the target formation laterally up to thousands of meters .

Within the past two decades the combination of HF with horizontal drilling has opened immense new oil and gas reserves worldwide which were previously considered inaccessible or unprofitable and brought large-scale drilling to new regions .

Hydraulic fracturing is performed at depths between 5,000 and 10,000 feet and requires 2,500,000–4,200,000 gallons of water per well.

Fracturing operations inject highly pressurized fluids, that is, between 2,000 and 12,000 psi, at an average flow rate of 2000 gpm (47 bbl/min) .

The water is mixed with 0.5–2.0% (by volume) of selected chemical additives to increase water flow and improve deposition efficiency.

Approximately 1,000 chemicals are known to be used in the HF process .

2. Hydraulic Fracturing Fluids

Oil and gas production chemicals can be pure compounds or mixtures containing active ingredients dissolved in a solvent or cosolvent and used to serve numerous processes

Common classes of hydraulic fracturing compounds.

The broad categories of HF fluids in routine use consist of

(1) viscosified water-based fluids

(2) nonviscosified water-based fluids

(3) gelled oil-based fluids

(4) acid-based fluids

(5) foam fluids.

For many hydrocarbon reservoirs, water-based fluids are most suitable due to the historic ease with which large volumes of mix water can be acquired.

Hydraulic fracturing fluids contain approximately 98 to 99.5% water plus a specially prepared mixture that helps optimize the fracturing process .

Typical additives include proppants (propping agents), gelling and foaming components, friction reducers, cross-linkers, breakers, pH adjusters, biocides, corrosion inhibitors, scale inhibitors, iron controlling compounds, clay stabilizers, and surfactants .

Composition of oilfield produced water.

.1. Production Chemicals

Production chemicals, that is, HF fluids, enter produced water in traces and sometimes significant quantities and vary from platform to platform.

Active ingredients partition themselves into all phases present depending on their relative solubilities in oil, gas, or water.

.2. Dissolved Minerals

Flow back water tends to have extremely high concentrations of total dissolved solids (TDS); this is due to dissolution of constituents from the formation following injection of HF fluids .

High salinity may also originate from release of in situ brines (formation water)

Levels of TDS can be 5–10 times the concentration in seawater .

Na+ and Cl− are responsible for salinity and range from a few mg/L to 300,000 mg/L .

For comparison, seawater and salt lakes are defined as having an upper limit of 50,000 mg/L .

Ions such as Cl−, , , , Na+, K+, Ca2+, Ba2+, Mg2+, Fe2+, and Sr2+ affect conductivity and scale-forming potential.

High levels of organic carbon also occur in substantial levels in flow back fluids and produced water .

Fluid chemical composition is dependent, in part, upon its interaction time with the shale play.

It has been found that TDS levels in produced water and late flow back can increase four-fold over that of early flow back.

Similarly, total suspended solids (TSS) concentrations increase over 100-fold between early and late flow back.

.3. Metals

Oilfield produced water contains heavy metals such as mercury and lead, as well as metalloids such as arsenic, in varied concentrations depending on formation geology and age of the well .

Metal concentrations in produced water are usually higher than those found in sea water .

The most commonly studied metals are Ba, Cd, Cr, Cu, Pb, Hg, Ni, Ag, and Zn

Produced water contains other trace metals including Al, B, Fe, Li, Mn, Se, and Sr.

Certain metals are of particular environmental concern as they may bio accumulate and/or be toxic .

.4. Dissolved and Dispersed Oil Components

Dispersed and dissolved oil components are derived from the source rock and chemical additives in HF fluids, and their concentrations may be very high at some oilfields .

BTEX, phenols, aliphatic hydrocarbons, carboxylic acid, and low molecular weight aromatics are classified as dissolved oil, while the more hydrophobic PAHs and heavy alkyl phenols are present in produced water as dispersed oil

Produced water contains predominantly C6–C16hydrocarbons, while Eagle and the highest concentration in the C17–C30 range.

The structures of saturated hydrocarbons identified generally follow the trend of linear > branched > cyclic.

Heterocyclic compounds, fatty alcohols, esters, and ethers have also been identified.

The presence of various fatty acid phthalate esters produced water may be related to their use in HF fluids .

No polyaromatic hydrocarbons (PAHs) were observed .

.5. Produced Solids

Produced solids include clays, precipitated solids, waxes, microbial biomass, carbonates, sand and silt, corrosion and scale products, proppant, formation solids, and other suspended solids .

The primary objectives for treating produced water include desalinization; removal of dispersed oil and grease, suspended particles and sand, soluble organic compounds, dissolved gases, and naturally occurring radioactive material; disinfection; and softening (i.e., to remove excess water hardness)

The optimal wastewater treatment technologies available are not able to strip all toxic chemicals from OGPW and are often selectively implemented due to cost

A range of dedicated and combined physical, biological, and chemical treatment processes have been developed to treat OGPW. Some popular technologies are reviewed here.

. Membrane Processes for Removal of TDS

(1) Membrane Filtration.

Membrane separation processes available for treating OGPW include microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) .

Membranes are microporous films with specific pore sizes which selectively separate components from a fluid.

MF uses the largest pore size (0.1–3 mm) and is typically employed for removal of suspended solids and turbidity reduction.

UF pore sizes are between 0.01 and 0.1 mm; this technology is employed for removal of color, odor, viruses, and colloidal organic matter .

UF is the most effective method for oil removal from produced water as compared with conventional separation methods .

UF is more efficient than MF for removal of hydrocarbons, suspended solids, and dissolved constituents from oilfield produced water

NF is a successful technology for water softening and metals removal and is designed to remove contaminants as small as 0.001 mm .

NF is selective for multivalent ions such as Ca2+ and Mg2+ .

It is applicable for treating water containing TDS in the range of 500–25,000 mg/L.

NF membranes have been employed for produced water treatment on both bench and pilot scales .

(2) Ceramic Membranes.

Ceramic UF/MF membranes have been used in a full-scale facility for treatment of produced water .

Treated product water was reported to be free of suspended solids and nearly all nondissolved organic carbon .

Ceramic UF/MF membranes have a lifespan of about 10 years.

Chemicals are not required for this technology except during cleaning of membranes

(3) Reverse Osmosis.

RO is a pressure-driven membrane processes.

Osmotic pressure of the feed solution is suppressed by applying hydraulic pressure whose forces permeate (i.e., clean water) to diffuse through a dense, nonporous membrane .

The major disadvantage of the technology is membrane fouling and scaling

A process for converting oilfield produced water into irrigation/drinking quality water consisted of air flotation, clarification, softening, filtration, RO, and water reconditioning .

RO membrane technology should be appropriate for treating oilfield produced water with appropriate pretreatment technology .

RO membrane systems generally have a life expectancy of 3–7 years .

(4) Electrodialysis/Electrodialysis Reversal.

Electrodialysis (ED) and ED reversal (EDR) are well-established desalination technologies.

These electrochemically driven processes separate dissolved ions from water through ion exchange membranes.

A series of membranes containing electrically charged functional sites are arranged in an alternating mode between an anode and a cathode to remove charged substances from feed water .

(5) Biological Aerated Filters.

Biological aerated filtration (BAF) consists of permeable media under aerobic conditions to facilitate biochemical oxidation and removal of organic constituents in wastewater.

Media do not exceed 10 cm in diameter to prevent clogging of pore spaces when sloughing occurs .

BAF can remove oil, ammonia, suspended solids, nitrogen, BOD, COD, heavy metals, Fe, soluble organics, trace organics, and H2S from produced water

Removal efficiencies of up to 70% N, 80% oil, 60% COD, 95% BOD, and 85% TSS have been achieved with BAF treatment

Water recovery is nearly 100% since waste generated is removed in solid form

The method is most effective for produced water with Cl levels < 6600 mg/L

BAF systems usually have a long lifespan; they do not require any chemicals or cleaning during normal operations.

Accumulated sludges are captured in sedimentation basins.

Solid waste disposal can account for up to 40% of the total cost of this technology

(6) Vibrating Membrane Process.

The vibrating membrane process VSEP® (Vibratory Shear Enhanced Process)limits membrane fouling, removing the main contaminants from wastewater without the addition of antiscalant chemical substances.

The design greatly reduces the fouling common to all membrane processes .

The pressure vessel moves in a vigorous vibratory motion, tangential to membrane surface, thus creating shear waves which prevent membrane fouling

RO may be implemented as tertiary treatment.

5.5. Thermal Technologies for Removing Oil and Grease Content

Multistage Flash (MSF)

MSF distillation involves evaporation of water by reducing atmospheric pressure instead of raising temperature.

Feed water is preheated and flows into a chamber with reduced air pressure where it immediately flashes into steam .

Water recovery from MSF treatment is approx. 20%; it often requires posttreatment because it typically contains 2–10 mg/L TDS .

A setback in operating MSF is scale formation on heat transfer surfaces which often requires the use of scale inhibitors and acids.

MSF is a relatively cost-effective treatment method with plant life expectancy of more than 20 years .

Multie ffect Distillation

The MED process involves application of energy that converts saline water into steam, which is condensed and recovered as pure water.

Multiple effects are employed in order to improve the efficiency and minimize energy consumption.

A major advantage of this system is the energy efficiency gained through the combination of several evaporator systems.

MED is suitable for treatment of high TDS produced water .

Product water recovery from MED systems ranges from 20 to 67% depending on design .

Despite the high water recovery, MED has not been extensively used for water production like MSF because of scaling problems associated with early designs.

Recently, falling film evaporators have been introduced to improve heat transfer rates and reduce the rate of scale formation .

Scale inhibitors and acids may be required to prevent scaling, and pH control is essential to prevent corrosion.

MED has a lifespan of 20 years and can be applied to a wide range of feed water qualities, similar to MSF.

Vapor Compression Distillation

The VCD process is an established desalination technology for treating seawater and RO concentrate .

Vapor generated in the evaporation chamber is compressed thermally or mechanically, which raises the temperature and pressure of the vapor.

The heat of condensation is returned to the evaporator and is used as a heat source.

VCD can operate at temperatures below 70°C, which reduces scale formation problems .

Energy consumption of a VCD plant is significantly lower than that of MED and MSF.

Although this technology is mainly associated with sea water desalination, various enhanced vapor compression technologies have been employed for produced water treatment

Multieffect Distillation-Vapor Compression Hybrid

Multistage flash (MSF) distillation, vapor compression distillation (VCD) and multieffect distillation (MED) are extensively used thermal desalination technologies .

however, hybrid thermal desalination plants, that is, MED-VCD, have achieved higher efficiencies .

Increased production and enhanced energy efficiency are major advantages of this system .

GE has developed produced water evaporators which use mechanical vapor compression.

These evaporators exhibit a number of advantages over conventional produced water treatment methods including reduction in chemical use, overall cost, fouling severity, and handling .

Membrane technologies are often preferred over thermal technologies; however, recent innovations in thermal process engineering have made the latter more competitive in treating highly contaminated water.

Gradiant Corporation (Woburn, MA) is attempting to make HF a “water-neutral process” by reusing water for the HF process.

The technology, carrier gas extraction (CGE), is a humidification and dehumidification technique; it heats produced water into vapor and condenses it back to contaminant-free water.

This process yields freshwater and saturated brine .

Freeze Thaw Evaporation

The FTEw process employs freezing, thawing, and conventional evaporation for produced water management.

When produced water is cooled below 32°F but above its freezing point, relatively pure ice crystals and an unfrozen solution form.

The solution contains high concentrations of dissolved constituents and is drained from the ice.

The ice is collected and melted to produce clean water.

FTEw can remove >90% of TDS, TSS, volatile and semivolatile organics, total recoverable petroleum hydrocarbons, and heavy metals in produced water

FTE requires no chemical additives, infrastructure, or supplies that might restrict its use.

It is easy to operate and monitor and has a life expectancy of approximately 20 years .

However, the technology can only work in a climate that has a substantial number of days with temperatures below freezing and requires significant land area.

FTE technology generates a significant amount of concentrated brine and oil; therefore, waste management and disposal must be addressed.

Dew vaporation: Al tela Rain SM Process

The principle of operation of Dewvaporation is based on counter current heat exchange to produce distilled water .

Feed water is evaporated in one chamber and condenses in the opposite chamber of a heat transfer wall as distilled water.

Approximately 100 bbl/day of produced water with salt concentrations > 60,000 mg/L TDS can be processed .

High removal rates of organics, heavy metals, and radionuclides from produced water have been reported for this technology.

In one plant, Cl− concentration was reduced from 25,300 to 59 mg/L, TDS was reduced from

41,700 to 106 mg/L, and benzene concentration was reduced from 450 mg/L to nondetectable after treatment with Dewvaporation technology

Hydrocyclones

Hydrocyclones physically separate solids from liquids; hydrocyclones can remove particles in the 5–15 mm range and have been widely used for treatment of OGPW .

Hydrocyclones are used in combination with other technologies as a pretreatment process.

They have a long lifespan and do not require chemical use or pretreatment of feed water. A major disadvantage of this technology is generation of substantial slurry of concentrated solid waste.

. Gas Flotation

Flotation technology is extensively used for treatment of conventional oilfield produced water.

Flotation technology uses fine gas bubbles to separate suspended particles that are not easily separated by sedimentation.

When gas is injected into produced water, suspended particulates and oil droplets become attached to air bubbles as they rise.

This results in the formation of foam on the water surface which is skimmed off

Flotation can be used to remove grease and oil, natural organic matter, volatile organics, and small particles from produced water .

Two types of gas flotation technology are in use, that is, dissolved gas flotation and induced gas flotation, based on the method of gas bubble generation and resultant bubble sizes.

Gas flotation can remove particles as small as 25 mm but cannot remove soluble oil constituents from water .

Flotation is most effective when gas bubble size is smaller than oil droplet size.

It is expected to work best at low temperature since the process involves dissolving gas into a water stream.

The technology does not require chemical use, except for coagulation chemicals that are added to enhance removal of target contaminants.

Solids disposal is necessary for the sludge generated from this process.

Media Filtration

Filtration technology is used for removal of oil and grease and total organic carbon (TOC) from produced water .

Filtration is carried out using various media such as sand, gravel, anthracite, and walnut shells.

This process is not affected by salinity levels and may be applied to any type of produced water.

Media filtration technology is highly efficient for removal of oil and grease; efficiency of >90% has been reported .

Efficiency can be further enhanced if coagulants are added to the feed water prior to filtration.

Media regeneration and solid waste disposal are drawbacks to this technology.

Adsorption

Adsorption is generally used as a polishing step in the OGPW treatment process rather than as a stand-alone technology, since adsorbents can be overloaded with organics.

Adsorption is used to remove Mn, Fe, TOC, BTEX, oil, and more than 80% of heavy metals present in produced water .

A wide range of adsorbents is available including activated carbon, organoclays, activated alumina, and zeolites .

Adsorption processes are successfully applied to water treatment regardless of salinity.

Replacement or regeneration of the sorption media may be required depending on feed water quality and media type .

Chemicals are used to regenerate media when all active sites are blocked.

Ion Exchange Technology

Ion exchange technology is in demand for numerous industrial operations including treatment of OGPW.

It is especially useful in the removal of monovalent and divalent ions and metals from produced water .

Ion exchange technology has a lifespan of about 8 years and requires pretreatment for solids removal.

It also requires chemicals for resin regeneration and disinfection .

Macroporous Polymer Extraction Technology

Macroporous polymer extraction (MPPE) is a liquid-liquid extraction technology where the extraction liquid is immobilized within polymer particles impregnated with macropores.

The particles have pore sizes of 0.1–10 mm and a porosity of 60–70%.

The polymers were initially designed for absorbing oil from water but later applied to produced water treatment .

In the MPPE unit, produced water is passed through a column packed with MPPE particles containing a specific extraction liquid.

The immobilized extraction liquid removes hydrocarbons from the produced water

In a commercial unit, MPPE was used for removal of dissolved and dispersed hydrocarbons and achieved 99% removal of BTEX, PAHs, and aliphatic hydrocarbons at 300–800 mg/L influent concentration.

It had a removal efficiency of 95–99% for aliphatics below C20 and it was reported that total aliphatic removal efficiency of 91–95% was feasible .

The hydrocarbons recovered from the MPPE process can be disposed or recycled.

Stripped hydrocarbons can be condensed and separated from feed water by gravity, and product water is either discharged or reused.

This technology can withstand produced water high in salinity and containing methanol, glycols, corrosion inhibitors, scale inhibitors, H2S scavengers, demulsifiers, defoamers, and dissolved heavy metals

Effluents Levels for Natural Gas

Pollutant Units Guideline

pH -- 6-9

BOD5 mg/l 50

COD mg/l 150

TSS mg/l 50

Oil and Grease mg/l 10

Cadmium mg/l 0.1

Total Residual Chlorine mg/l 0.2

Chromium (total) mg/l 0.5

Copper mg/l 0.5

Iron mg/l 3

Zinc mg/l 1

Cyanide

Free mg/l 0.1

Total 1

Lead mg/l 0.1

Nickel mg/l 1.5

Heavy metals total mg/l 5

Phenol mg/l 0.5

Nitrogen mg/l 40

Phosphorous mg/l 3

[ltr]Treatment [/ltr]	[ltr]Description [/ltr]	[ltr]Advantages [/ltr]	[ltr]Disadvantages [/ltr]	[ltr]Waste Stream [/ltr]	[ltr]Oil and Gas Produced Water Applications [/ltr]
[ltr]*De-oiling* [/ltr]
[ltr]Corrugated plate separator [/ltr]	[ltr]separation of free oil from water under gravity effects enhanced by flocculation on the surface of corrugated plates [/ltr]	[ltr]No energy required, cheaper, effective for bulk oil removal and suspended solid removal, with no moving parts, this technology is robust and resistant to breakdowns in the field. [/ltr]	[ltr]inefficient for fine oil particles, requirement of high retention time, maintenance [/ltr]	[ltr]suspended particles slurry at the bottom of the separator [/ltr]	[ltr]Oil recovery from emulsions or water with high oil content prior to discharge. Produced water from water-drive reservoirs and water flood production are most likely feed-stocks. Water may contain oil & grease in excess of 1000 mg/L. [/ltr]
[ltr]Centrifuge [/ltr]	[ltr]separation of free oil from water under centrifugal force generated by spinning the centrifuge cylinder [/ltr]	[ltr]efficient removal of smaller oil particles and suspended solids, lesser retention time-high throughput [/ltr]	[ltr]energy requirement for spinning, high maintenance cost [/ltr]	[ltr]suspended particles slurry as pre-treatment waste [/ltr]
[ltr]Hydroclone [/ltr]	[ltr]free oil separation under centrifugal force generated by pressurized tangential input of influent stream [/ltr]	[ltr]compact modules, higher efficiency and throughput for smaller oil particles [/ltr]	[ltr]energy requirement to pressurize inlet, no solid separation, fouling, higher maintenance cost [/ltr]
[ltr]Gas floatation [/ltr]	[ltr]oil particles attach to induced gas bubbles and float to the surface [/ltr]	[ltr]no moving parts, higher efficiency due to coalescence, easy operation, robust and durable [/ltr]	[ltr]generation of large amount of air, retention time for separation, skim volume [/ltr]	[ltr]skim off volume, lumps of oil [/ltr]
[ltr]Extraction [/ltr]	[ltr]removal of free or dissolved oil soluble in lighter hydrocarbon solvent [/ltr]	[ltr]no energy required, easy operation, removes dissolved oil [/ltr]	[ltr]use of solvent, extract handling, regeneration of solvent [/ltr]	[ltr]solvent regeneration waste [/ltr]	[ltr]Oil removal from water with low oil and grease content (< 1000 mg/L) or removal of trace quantities of oil and grease prior to membrane processing. Oil reservoirs and thermogenic natural gas reservoirs usually contain trace amounts of liquid hydrocarbons. Biogenic natural gas such as CBNG may contain no liquids in the reservoir but when pumped to the surface, the water takes up lubricating fluids from the pumps. [/ltr]
[ltr]Ozone/[/ltr] [ltr]hydrogen peroxide/[/ltr] [ltr]oxygen [/ltr]	[ltr]strong oxidizers oxidize soluble contaminant and remove them as precipitate [/ltr]	[ltr]easy operation, efficient for primary treatment of soluble constituents [/ltr]	[ltr]on-site supply of oxidizer, separation of precipitate, byproduct CO2 etc. [/ltr]	[ltr]solids precipitated in slurry form [/ltr]
[ltr]Adsorption [/ltr]	[ltr]porous media adsorbs contaminants from the influent stream [/ltr]	[ltr]compact packed bed modules, cheaper, efficient [/ltr]	[ltr]high retention time, less efficient at higher feed concentration [/ltr]	[ltr]used adsorbent media, regeneration waste [/ltr]

[ltr]*Disinfection* [/ltr]
[ltr]UV light/ozone [/ltr]	[ltr]passing UV light or ozone produce hydroxyl ions that kills microbial [/ltr]	[ltr]simple and clean operation, highly efficient disinfection[/ltr]	[ltr]on-site supply of ozone, other contaminants reduce efficiency [/ltr]	[ltr]small volumes of suspended particles at the end of the treatment [/ltr]	[ltr]Microbes may exist in the subsurface reservoir or can be introduced during production or during water treatments. Disinfection may need to be done to protect potability or to or to prevent fouling of the reservoir, tubulars, and surface equipment. [/ltr]
[ltr]Chlorination [/ltr]	[ltr]chlorine reacts with water to produce hypochlorous acid which kills microbial [/ltr]	[ltr]cheaper and the simplest method [/ltr]	[ltr]does not remove all types of microbial [/ltr]
[ltr]*Desalinization* [/ltr]
[ltr]Lime softening [/ltr]	[ltr]addition of lime to remove carbonate, bicarbonate etc. hardness [/ltr]	[ltr]cheaper, accessible, can be modified [/ltr]	[ltr]chemical addition, [/ltr] [ltr]post treatment necessary [/ltr]	[ltr]used chemical and precipitated waste [/ltr]	[ltr]These technologies typically require less power and less pre-treatment than membrane technologies. Suitable produced waters will have TDS values between 10,000 and 1,000 mg/L. Some of the treatments remove oil and grease contaminants and some of them require oil and grease contaminants to be treated before these operations. [/ltr]
[ltr]Ion exchange [/ltr]	[ltr]dissolved salts or minerals are ionized and removed by exchanging ions with ion exchangers [/ltr]	[ltr]low energy required, possible continuous regeneration of resin, efficient, mobile treatment possible [/ltr]	[ltr]pre and post treatment require for high efficiency, produce effluent concentrate [/ltr]	[ltr]regeneration chemicals [/ltr]
[ltr]Electrodialysis [/ltr]	[ltr]ionized salts attract and approach to oppositely charged electrodes passing through ion exchange membranes [/ltr]	[ltr]clean technology, no chemical addition, mobile treatment possible, less pretreatment [/ltr]	[ltr]less efficient with high concentration influent, require membrane regeneration [/ltr]	[ltr]regeneration waste [/ltr]
[ltr]Electro-deionization [/ltr]	[ltr]enhanced electrodialysis due to presence of ion exchange resins between ion exchange membranes [/ltr]	[ltr]removes of weakly ionized species, high removal rate, mobile treatment possible [/ltr]	[ltr]regeneration of ion exchange resins, pre/post treatment necessary [/ltr]	[ltr]regeneration waste, filtrate waste from post-treatment stage [/ltr]
[ltr]Capacitive deionization [/ltr]	[ltr]ionized salts are adsorbed by the oppositely charged electrodes [/ltr]	[ltr]low energy required, [/ltr] [ltr]higher throughput [/ltr]	[ltr]expensive electrodes, fouling [/ltr]	[ltr]regeneration waste [/ltr]
[ltr]Electrochemical Activation [/ltr]	[ltr]ionized water reacts with ionized chloride ion to produce chlorite that kills microbial [/ltr]	[ltr]simultaneously salt and microbial removal, reduce fouling [/ltr]	[ltr]expensive electrodes[/ltr]	[ltr]regeneration waste [/ltr]
[ltr]Rapid spray evaporation [/ltr]	[ltr]injecting water at high velocity in heated air evaporates the water which can be condensed to obtained treated water [/ltr]	[ltr]high quality treated water, higher conversion efficiency[/ltr]	[ltr]high energy required for heating air, required handling of solids [/ltr]	[ltr]waste in sludge form at the end of evaporation [/ltr]

[ltr]Freeze thaw evaporation [/ltr]		[ltr]utilize natural temperature cycles to freeze water into crystals from contaminated water and thaw crystals to produce pure water [/ltr]	[ltr]no energy required, natural process, cheaper [/ltr]		[ltr]lower conversion efficiency, long operation cycle [/ltr]
[ltr]*Membrane Treatment* [/ltr]
[ltr]Microfiltration [/ltr]	[ltr]membrane removes micro-particles from the water under the applied pressure [/ltr]	[ltr]higher recovery of fresh water, compact modules [/ltr]	[ltr]high energy required, less efficiency for divalent, monovalent salts, viruses etc. [/ltr]	[ltr]concentrated waste from membrane backwash during membrane cleaning, concentrate stream from the filtration operation [/ltr]	[ltr]Removal of trace oil and grease, microbial, soluble organics, divalent salts, acids, and trace solids. . Contaminants can be targeted by the selection of the membrane. The size distribution of the removable species for membrane filtration technologies is shown in table 9. [/ltr]
[ltr]Ultrafiltration [/ltr]	[ltr]membrane removes ultra-particles from the water under the applied pressure [/ltr]	[ltr]higher recovery of fresh water, compact modules, viruses and organics etc. removal[/ltr]	[ltr]high energy, membrane fouling, low MW organics, salts etc [/ltr]
[ltr]Nanofiltration [/ltr]	[ltr]membrane separation technology removes species ranging between ultrafiltration and RO [/ltr]	[ltr]low MW organics removal, hardness removal, divalent salts removal, compact module [/ltr]	[ltr]high energy required, less efficient for monovalent salts and lower MW organics, membrane fouling [/ltr]
[ltr]Reverse Osmosis [/ltr]	[ltr]pure water is squeezed from contaminated water under pressure differential [/ltr]	[ltr]removes monovalent salts, dissolved contaminants etc., compact modules [/ltr]	[ltr]high pressure requirements, even trace amounts of oil & grease can cause membrane fouling [/ltr]		[ltr]Removal of sodium chloride, other monovalent salts, and other organics. Some organic species may require pre-treatment. While energy costs increase with higher TDS, RO is able to efficiently remove salts in excess of 10,000 mg/L. [/ltr]
[ltr]*Miscellaneous Treatment* [/ltr]
[ltr]Trickling Filter [/ltr]	[ltr]develops film of microbial on the surface of packed material to degrade contaminants within water [/ltr]	[ltr]cheaper, simple and clean technology [/ltr]	[ltr]oxygen requirement, large dimensions of the filter [/ltr]	[ltr]sludge waste at the end of the treatment [/ltr]	[ltr]Removal of suspended and trace solids, ammonia, boron, metals etc. Post-treatment is normally required to separate biomass, precipitated solids, dissolved gases etc. [/ltr]
[ltr]Constructed wetland treatment [/ltr]	[ltr]natural oxidation and decomposition of contaminants by flora and fauna [/ltr]	[ltr]cheaper, efficient removal of dissolved and suspended contaminants [/ltr]	[ltr]retention time requirement, maintenance, temperature and pH effects [/ltr]
[ltr]SAR adjustment [/ltr]		[ltr]addition of Ca or Mg ions [/ltr]	[ltr]cheaper option [/ltr]	[ltr]chemical addition [/ltr]	[ltr]Balance high SAR and very low TDS (higher percentage of sodium salts) after membrane processes. [/ltr]

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