Effluent Management in Oil and Gas Extraction

: The oil and gas industry is characterized by petrochemical industrial wastewater known basically as effluent, which typically contains various organic and inorganic components, naturally present or added during oil and gas processes. Thus, proper management or treatment is needed for reuse, discharge, or final disposal requiring complexity of the wastewater composition needing stringent discharge procedures, standards requiring combinations of treatment methods. Effluent being a complex mixture of different organic and inorganic compounds (mostly salts, minerals, gas and oils), is majorly generated during oil/gas production. The volume of effluent is increasing around the world, and as a consequence, its discharge to the environment is one of the global concerns. The various methods of effluent management have their own advantages and disadvantages when used for offshore or onshore units. However, comprehensive and deep-understanding of each issue can provide a guideline for better and more practical solutions to its management. In this work, various physical and chemical treatment methods are reviewed and the most effective recommended to proper effluent management that meets all international standard and enhances sustainability. In this study the Pre-treatment, treatment and post treatment approaches employed reduced the amount of impurities present in the effluent with varying pH of 7.2 and 7.8, COD of 30 and 60mg/L, BOD value of 45 and 54 respectively, TSS value of 80 and 60mg/L and TDS of 5200 and 4800.


Introduction
Nigerian oil was discovered in 1956, and the country's production commenced in the late 1950s.Oil exploration became available to international businesses in the ensuing ten years, and by that time, the oil industry had grown steadily to become a global behemoth, with a few exceptions owing to economic conditions.The Nigerian National Petroleum Company (NNPC) was established in 1977.The state-owned company's objectives are to oversee and take part in the nation's oil industry.Nigeria now produces the majority of the oil in Africa.Nigeria is the world's eleventh-largest oil producer in 2020, with 18 operational pipelines and an estimated 1.8 million barrels of oil produced daily on average.Nearly 90% of Nigeria's export value and 9% of its GDP are attributed to the petroleum industry (Doris Dokua Sasu, 2023).
Oil and Gas Extraction is the exploration and exploitation of petroleum and natural gas from wells.The industry generates wastewater from the water extracted from the geological formations and from chemicals used during exploration, well drilling and production of oil and gas.The oil and gas industry produces approximately 14 billion bbls of effluent annually (Rodriguez and Soeder, 2015).These waste water varies greatly in quantity and quality and in some cases the water can be a useful byproduct or even a salable commodity.The majority of this effluent is currently managed by injecting it underground, where it can no longer be accessible or utilised.In some cases, the limitations of injection are clear, necessitating other strategies.Several states and stakeholders are debating whether it makes sense to keep wasting this water, especially in regions of the country where there is a shortage of water, and what efforts would be required to purify and replenish it for other uses.Effluent has always been considered a waste, but in recent times, the industry is beginning to consider this material as a potential profit stream.Whether waste or commodity, effluent has management implications that need to be kept in-line with each specific production project and region or it could adversely affect the life of the well, thereby leaving substantial recoverable reserves in the ground.It could also have tremendous adverse impact on the environment, the drainage and aquatic system and on the health of humans and animals (Lofrano et al., 2016).Wastewater from industries principally involved in refining crude oil, producing fuels and lubricants, and producing petrochemical intermediates (Harry et al., 1995) is known as petroleum wastewater and is a significant cause of aquatic pollution in the environment.According to Coelho et al. (2006), the quantity of petroleum effluent produced during processing is 0.4-1.6 times that of the treated crude oil.The amount of dissolved oxygen needed by bacteria for normal survival declines if crude effluent with a significant amount of organic matter is released onto water bodies.Unpleasant colors and scents are produced in water in anaerobic processes by the byproducts of chemical and biological reactions.In order to lessen that, water's oxygen availability is crucial (Attiogbe et al., 2007).Effluent water handling practices must be environmentally protective and the methodology used in treating it depends on the composition of produced water, location, quantity and the availability of resources (Judd, 2016).

Statement of Research Problem
The management of effluent in the oil and gas industry is both a herculean and risky task.Industrial waste water from this industry is a hazardous process but essential for successful operation of the industry.The sources of water pollution can be categorized as point source and non-point source.Waste water pollutants from oil and gas wells are classified as point sources.Polluted water originates from physical, biological or chemical change in water quality which adversely affects living organisms or makes the water unsuitable for the desired use.Thus the need to understand the most appropriate treatment technique for effluent in the oil and gas industry.It is notable that while water is used in numerous oil and gas industry activities, not all of them necessitate raw or treated water.While some leftover water from the oil and gas refinery can be recycled or reused repeatedly inside the same facility, a significant amount needs management.

Objective of the Research
Ascertain the most sustainable effluent treatment approach.

Literature Review
The generally accepted definition of effluent is that of the United States Environmental Protection Agency (2006) as wastewater -treated or untreated -that flows out of a treatment plant, sewer, or industrial outfall.Generally refers to wastes discharged into surface waters (Fogler and Gurmen, 2015) The Compact Oxford English Dictionary defines effluent as "liquid waste or sewage discharged into a river or the sea (Mason et al., 2016).
Effluent in the artificial sense is in general considered to be water pollution, such as the outflow from a sewage treatment facility or the wastewater discharge from industrial facilities.
The extraction of petroleum-based substances, that is an intricate combination of naturally occurring substances named crude oil and natural gas, and the production of hydrocarbon effluent are significant challenges because of the rising worldwide need for energy, which is projected to increase by 44% over the course of the next two centuries (Aljuboury et al., 2017).
The purity of crude affects what is found in refining effluent.According to the operational circumstances (Benyahia et al., 2006), it changes.Non-hydrocarbon compounds are eliminated in the refinery, where the crude oil is separated into its constituent components and combined to create products that are beneficial.Because of this, refineries that process petroleum generate large amounts of effluent, such as crude oil water generated from and restored on the outside during the extraction of petroleum, which is challenging to cleanse naturally and frequently contains compounds that are resistant (Vendramelet al., 2015).
The quality of the crude affects the effluent in refinery wastewater.It varies depending on the circumstances.Some of the treatment methods for effluent in the oil and gas industry include: Chemical techniques, physical techniques and biological techniques.The oil and gas industries produce both liquid and gaseous pollutants.Gaseous pollutants are easier to manage as liquid pollutants are more complicated.
Over time, the vast oil exploration in Nigeria's Niger Delta has resulted in a number of environmental problems.In addition to oil spills, inadequate treatment of wastewater at oil refineries and the effluents that are emitted are now another potential cause of pollution that the government and the general public have not given sufficient consideration to (Osin et al., 2017).According to the processing facility layout, how it operates, and the kind of oil that is processed, petroleum effluent might vary significantly (Aljuboury et al., 2017).Production processes such as vapor condensation, used caustic, and process water are the sources of effluents.Additionally, effluents may be produced by a cooling tower, surface runoff, or treatment of spilt petroleum products.Treatment of effluent and other liquid pollutants can be done using the following techniques as divided into 5 (five) categories as below (Fakhru et al., 2009;Brindle 1994;Kirk et al., 2002;Van et al., 1998;Glaze, Kang and Chapin, Preparatory or preliminary treatment: to remove coarse suspended and floating matters, oil or grease; primary or physical treatment: to remove settle able and suspended solids; secondary or biological treatment: to remove organic solids through a biological process; tertiary or advanced treatment: to achieve additional removal of suspended solids, colloidal particles, nutrients, and refractory organics and further reduction of fecal coli.Use of nanotechnology has demonstrated its ability to remove persistent organic pollutants (POPs) or transform harmful components into environmentally beneficial derivatives, it has also been suggested as a potential upgrade to existing treatment approaches as reported by Osin et al.,(2017).

Sources of Waste Water in Oil and Gas Industry
The availability of water is crucial to the procedures used in the oil and gas sector.The intricacy of the process, plant size, oil type, and products and chemicals used for treatment are just a few of the variables that can affect how much water is needed.A significant amount of wastewater is created during the refining process, and this wastewater gets into close proximity with hydrocarbons, producing pollution by some hydro-soluble oil components.Waste water can be categorized into a number of major classes as a result (Eldos et al., 2022).

Produced Water
The majority of oilfield wastewater generated during the oil extraction or deep well injection process is known as produced water.Total soluble solids (TSS), chemical oxygen demand (COD), total organic carbon (TOC), hydrocarbons, and heavy metals are the most frequent pollutants found in generated water Al-Ghouti et al., 2019;Dawoudet al., 2021).

Desalter effluent
In an oil refinery, a desalter is often the initial step in the process when hot crude oil is washed with feed water and chemical additives to remove the salt.The desalter effluent is the water produced during the washing process that desalinates the crude oil.Total Suspended Solid (TSS), Chemical Oxygen Demand (COD), hydrocarbons, ammonia, and sulfides are the most frequent pollutants in desalter water.whichever is the type of feed water in the desalter unit, the levels vary (Bineset al., 2017).

Stripped sour water
In order to reduce the petroleum portion of the pressure, heat is used in a variety of refining operations as a diluent in catalysis cracking and additional procedures along with an extraction carrier in distilling.The aqueous phase formed when the heated air condenses is removed as sour water.Hydrocarbons comprising hydrogen sulfide (H2S) and ammonia (NH3) get absorbed into the sour water at levels that often require treatment due to this steam compresses with the presence of these substances (Coelho et al., 2006).The pollutants that are frequently found in sour water are COD, phenols, cyanide, sulfides, and ammonia.The origin of sour water used to make stripped sour water has a significant impact on the makeup of that water (Bastos et al., 2020).

Tank bottoms water
When crude oil is retrieved from wells, water and sediments are frequently encountered in the raw form.This is referred to as bottom water and sediment.The bottom sediment and water that collect when oil is kept in large tanks must be constantly removed to prevent accumulation and a reduction in storage capacity.Typically, the sludge in these bottom tanks is moved for separation or to the wastewater treatment facilities.Water from tank bottoms frequently contains impurities such COD, hydrocarbons, TSS, and sulfides.Given that water comes into touch with crude oil in its unprocessed form, it frequently has high COD and organic contents (Hochberget al., 2022).

Spent caustic effluent
When acidic elements from hydrocarbon streams are removed, spent caustic is created.These acidic substances include phenol, cyanide, organic acids, residual H2S, and CO2.The most frequent pollutants found in used caustic are sulfides, phenols, cyanide, H2S, and RSH (mercaptans).The composition of used caustic effluents varies depending on the production process (Rita et al., 2022).

Quality of Effluents from Oil and Gas extraction
Diverse levels of harmful substances, which include inorganic and organic contaminants such as petroleum hydrocarbons and heavy metals, are present in petroleum effluents.The primary effluent variables used to assess the water quality are total dissolved solids (TDS), total suspended solids (TSS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total petroleum hydrocarbons (TPH), oil and grease (O&G), total organic carbon (TOC), and total metals and ions including ammonia, nitrates, sulfides, and others.More precise criteria, including cadmium, lead, and mercury, as well as some organics, including benzene, toluene, ethylbenzene, and xylene (BTEX), and inorganics, including phosphates, chlorides, and other micropollutants are also used.Physical characteristics of effluents, including pH (acids, alkalis), turbidity, color, and odor, are occasionally utilized as a sign of the water quality (Haneen et al., 2022).pH One of the crucial factors that directly impacts how treatable petroluem effluents are is pH.It also affects the leachability of heavy metals and the dispersion of other contaminants.The proteinaceous matter content and ammonia compound discharge of petroleum effluents are revealed by their pH level.When using wastewater for agriculture, the ideal pH range ranges from 6.5 and 8.4.The amount of some compounds in the environment can alter as a result of a slight pH variation.Anions become more soluble in alkaline solutions, whereas cations become more soluble in acidic solutions (Qaseem et al., 2021).Additionally, acidic effluents alter the composition of the microbial ecosystem by reducing diversity of bacteria and altering microbial population dynamics (Kr´ol et al.,2020).

Total dissolved solids (TDS), electric conductivity (EC), and salinity
The total dissolved solids (TDS) in petroleum effluents includes both organic and inorganic salts.Electrical conductivity (EC) gauges a liquid's capacity to carry an electric charge, which is influenced by the quantity and potency of the dissolved ions.As a result, EC and TDS are connected and both serve as measures of salinity.Salinity is the salt in petroleum effluents, an inorganic substance that is representative of the TDS notion.Petroleum effluents typically have TDS concentrations of 1000-400,000 mg/L.Additionally, the salinity of petroleum effluents is substantially higher than that of saltwater, ranging from a few parts per thousand (ppt) to 300 ppt.High TDS indicates hard water, which causes scaling and fouling in the treatment system, reducing treatment effectiveness and driving up maintenance costs (Al-Ghouti et al., 2019;Ahmad et al., 2020).

Total suspended solids (TSS)
TSS stands for total suspended solids, which includes biological matter, sand, sediments, and other non-soluble particles in effluents.The streams and contaminants found in the petroleum effluents heavily influence the range of TSS in petroleum effluents.TSS levels in petroleum effluents typically vary from 5 mg/L to 5 800 mg/L (Hodgeset al., 2017).

Oil and grease (O&G)
The phrase "O&G parameter" with reference to petroleum effluents covers a wide spectrum of chemical substances including oils, waxes, and fats from petrochemical sources.The amount of dispersed O&G in petroleum effluents is a crucial criterion to consider when assessing the security and efficacy of the water.By covering plants and animals and smothering them through the reduction of oxygen, the release of petroleum effluents with a high concentration of oil and grease can have a significant negative impact on the natural habitat and creatures.Petroleum effluent contains O&G values ranging from 40 mg/L to 9000 mg/L (Eljaiek-Urzolaet al., 2019).

Total organic carbon (TOC), biochemical oxygen demand (BOD), and chemical oxygen demand (COD)
Any petroleum effluent's organic intensity may typically be determined in three ways: TOC, COD, and BOD.The organic matter from natural sources and hydrocarbons from petroleum is represented by TOC in petroleum effluents.Both dissolved and granular organic carbon are involved.Because it makes the effluent less homogeneous, high TSS can impact the validity of TOC.The COD stands for the amount of oxygen needed to oxidize all of the OM in the PWWs.COD refers to the amount of oxygen needed to break down both biodegradable and non-biodegradable materials.In other words, TOC measures the quantity of carbon attached to organic molecules, whereas COD measures the amount of organic compound that will be oxidized.As a result, TOC and COD have a direct proportional relationship.BOD is a measure of the oxygen needed for microorganisms to biologically break down the organic matter in effluent.With respect for the organic matter's biodegradability, the higher the biological contamination in the sample, the greater quantity of oxygen the organisms will require, the worse the condition of the effluents.BOD is an approximate indicator of organic contamination in the effluent.
But investigations by El-Naas et al., (2017), Janson et al., (2015) and Lahlou et al., (2020) revealed that the COD concentration in various petroleum effluents was 64 mg/L, 5300 mg/L, and 1572 mg/L, respectively.According to Kusworo et al., the COD and BOD ranges in petroleum effluents are, respectively, 750-1600 mg/L and 300-1000 mg/L.As they are directly related to the breakdown remediation by microbes, the values of BOD, COD, and TOC are crucial in establishing the effective treatment technology.Microbial degradation is not a suitable treatment if the wastewater's BOD, COD, and TOC values are very low since the microorganisms' ability to grow in such an environment will be negatively impacted, as will the efficacy of the treatment plant as a whole.On the reverse side, an excessive amount of organic matter can raise the amount of microbial biomass, posing many treatment difficulties that lower the effluent quality, such as bio-clogging and odor (Zhenget al., 2013).

Total petroleum hydrocarbons (TPH)
The term "total petroleum hydrocarbons" describes the total amount of hydrocarbons in PWWs, which mostly consist of carbon and hydrogen.
Petroleum hydrocarbons in suspended and dissolved forms make up TPH.Saturated, unsaturated, and aromatics make up the three main divisions.TPH is a mixture of volatile and extractable petroleum hydrocarbons made up of phenols, polycyclic aromatic hydrocarbons (PAHs), methyl tertiary butyl ether (MTBE), and naphthalic acids.It also contains volatile aromatic hydrocarbons such as benzene, toluene, ethylbenzene, and xylenes (BTEX) (Uddinet al., 2021).

Materials and Methods
Two effluents samples were collected from a local petroleum refinery in Rivers State at different points and the samples where named PE 1 and PE 2. The samples were made to undergo different pre treatment, treatment and post treatment processes before they were further tested for pH, total disolved solids, total suspended solids, oil and greese, etc.

Sedimentation
In this process, the effluent was allowed to stand still in a beaker and this happens naturally because gravity will pull the heavier sediments down to form a sludge layer.Sedimentation is a treatment process in which suspended particles, like flocs, sand and clay are removed from the wastewater while crude oil settles at the top of the waste water The advantage of sedimentation is that it minimizes the need for coagulation and flocculation process (Chu et al. 2018).

Filtration
After sedimentation, filtration method was employed.The crude oil that settled at the top of the beaker was decanted and was allowed to pass through sand and other filters of different pore sizes to remove suspended solids.The grease found on the surface of the wastewater was also removed easily through this method.

Treatment Chlorination
Chlorination provides destructive treatments of aqueous phenols present in the effluent.35mL of 4% Solution of sodium hypochlorite was dissolved in 500mL of pre treated effluent and was allowed to stand for 30 minutes to allow disinfection and partial removal of phenolic compounds present in the pre treated effluents.

Determination of pH
A digital pH meter (Apera AI209 series PH20) was dipped in a buffer and then placed in the treated effluent for about 2 minutes to determine its pH.

Determination of Total Disolved solids
Weight of an empty beaker (Wo) was taken and treated effluent water sample was added with the weight taken again (W).The beaker containing the sample was heated to dryness to allow the water to evaporate.Once all the water is evaporated, the weight of beaker along with the residue was recorded again (Wf).

Determination of total suspended solids
The treated effluent water sample was filtered using 1.5 micron filter and the residual contents was kept inside oven at 104°C and taken out after an hour.The dried weight of filter along with dried residue was taken.After subtracting the weight of filter in this weight, the suspended solids weight was found out by dividing the weight of suspended solids by volume of water in ppm.

Determination of Biochemical oxygen demand
The Biochemical or Biological oxygen demand was determined using the BLE-9100 dissolved oxygen meter.The electrode was dipped inside the treated water and reading was taken.

Results and Discussion
The treatment methods of the effluent are reliant on the effluents generated characteristics and this can give insights on the type of treatment options available to treat the effluents generated during oil exploration to reduce the hazardous effect of the effluent when discharged into water bodies.In this study, effluents generated was treated on laboratory scale and after treatment, several parameters were tested to check the level of purity of the effluent.The effluents had a pH range of 7.2 to 7.8 as shown in the table 1 after treatment which is in conformity with the standard pH of waste water before they are dischareged in to water bodies as stated by United States Environmental standard for effluent discharge.

Conclusion
This study revealed that effluents from oil and gas extraction could pose danger to aquatic and terrestrial life if not treated before they are discharged into water bodies or probably for agricultural use because the varying results of parameters investigated showed that there are lots of impurities as well as toxic substances in the effluents before treatment and in view of this, more approaches should be employed to treat the effluents to reduce the level of impurities and toxic substances.

Table 1 . Various Parameters of the Two Different Points Of Effluents.
No TracesThe total suspended and total dissolved solids had little variation ranging from 4800mg/L to 5200mg/L without any traces of oil and greese.The biological and chemical oxygen demand varied also but they are not suitable for or useful for aquatic life until further treatment technique is employed.Lahlou et al., 2020reported that the COD of waste effluent from petroleum refinery was 10497mg/L while the BOD was 1034 for untreated effluents.Also in Tunisia,Karray et al.,reported that effluents from petroleum refinery had 6444.93mg/LCOD and 1310 BOD respectively.According to Environmental standards for effluent discharge as per the US EPA, the values of COD and BOD is 125mg/L and 15 respectively and from this study only the COD conforms with the standard.