Petroleum Wastewater Treatment

*Ali Aghababai Beni, Mohammad Saleh Samie Adel, Mojgan Zaeimdar, Arezoo Ghadi, Vahid Hassani, Kiarash Jalalvandi and Sayed Asaad Abdollahi*

#### **Abstract**

Petroleum hydrocarbons in refinery wastewater are considered the main cause of pollution. Wastewater from oil refineries contains large amounts of oil and fat in the form of suspended particles, light and heavy hydrocarbons, phenol, and other dissolved organic substances, which cause environmental pollution if they are discharged into the environment without treatment. Usually, conventional methods of treating petroleum wastes have a lot of costs; due to the existence of sufficient area for the construction of solar distillation ponds and suitable sunlight, as well as a large number of sunny days near the equator, the solar distillation method can be used. Membrane bioreactors based on biological decomposition and biological transformation of oils and waste oil materials have provided new solutions for the biological treatment of these wastewater. In addition to these methods, Fenton's advanced oxidation methods, electrochemical coagulation method, and membrane filtration method are mentioned in this chapter.

**Keywords:** petroleum wastewater, solar evaporation, membrane bioreactor, advanced oxidation Fenton, electrocoagulation, membrane filtration

#### **1. Introduction**

Water is one of the most important resources in the development of countries. During the twentieth century, the world's population tripled, and water use increased six-fold. The world's available water is only sufficient for the current population with minimal access to clean water [1]. Improper distribution in terms of space and time and an increase in population and per capita consumption of water have aggravated this problem. The world's population is increasing, and drinking water resources are decreasing, so the world may face the problem of water shortage in the future. Destructive activities and inefficient use of water resources, along with the increase in population and increase in water demand, have severely limited water resources in the last few decades. The United Nations states that the lack of water resources has caused the reduction of agricultural land, and the production of food in recent decades has been extremely risky. The lack of water resources is a serious threat to human life [2].

Climate change and the reduction of rain forests and the reduction of the thickness of the ozone layer all aggravate the water shortage. Lack of water also has side and

indirect effects, such as increasing poverty and hunger, ecosystem destruction, desertification, climate change, and even world peace [3].

The per capita standard of drinking water consumption in different countries rarely exceeds 200 liters per day. But the results of researchers'studies show that per capita water consumption is much higher than the standards set in the countries [4]. That is because besides the direct consumption of water, humans consume water through the consumption of food, fruits, and even services and goods, and its amount is on average about 3400 L per day per person in the world, which is called virtual water [5]. Climatic conditions, place and time of production, management and planning, and culture and habits of people are some of the effective factors in the amount of virtual water [6].

The security of water resources has become another challenge with increasing demand. Harvesting and purifying water from surface and underground sources, as well as treating wastewater produced in underground aquifers, in addition to polluting aquifers, will also disrupt the natural water cycle [7]. On the other hand, due to the possibility of the spread of many diseases caused by the contamination of water and sewage, in order to preserve the health of human societies and prevent disruptions in the water cycle, sewage must be properly collected, treated, and returned to the natural water cycle [8]. The most important goals are to build urban and industrial wastewater treatment systems, maintain public health, protect the environment, prevent the pollution of water sources, and reuse treated wastewater in industry and agriculture [9].

Wastewater provides a valuable source of recoverable water. Although this source can contain dangerous compounds that endanger public health and the environment, at least 90% of the wastewater is water [10]. New technologies to treat wastewater and return it to water supply networks are an important factor in increasing limited water resources. Water treatment plants are an important part of the water recovery process. The main goal of water purification processes is to reduce the concentration of water pollutants by separation, destruction, and disinfection [11]. Many efforts have been made to maintain the quality of treated industrial wastewater, recover them, and prevent them from jeopardizing public health [12].

From another point of view, the disposal of untreated effluents from factories and industries creates many health risks for human societies [13]. In order to reduce these risks, wastewater treatment plans for factories must also be developed. Therefore, the use of water obtained from sewage treatment in agriculture can not only make an important contribution to the water supply of the society but is also considered a solution for environmental preservation and sustainable development [14].

The production fluid of oil wells is usually a combination of gas, oil, and water. Water with oil can be observed as free water or fine suspended droplets or both in the fluid. Since the production of excess water is an integral part of the production and preliminary processing of crude oil, in order to prevent environmental pollution, maintain reservoir pressure, and increase extraction from oil production wells, these waters, after preliminary treatment in the treatment systems of desalination units, are again sent to disposal wells that are intended to be injected for this purpose [15].

The production amount of salt water along with oil in desalination units from crude oil is significant. These effluents have created a big problem for the environment due to their specific quantitative and qualitative characteristics, which include soluble salts, the presence of petroleum substances, volatile and non-volatile organic substances, and other hazardous pollutants in large volumes [16]. Due to the presence of supersaturated soluble salts and suspended particles and corrosive agents, these

wastewaters have a strong tendency to deposit, and if they are injected into the well without preliminary treatment, it may cause clogging of the flow path in the underground flow pipes and/or the opening of the well or cause the corrosion of the flow pipes as a result of the effluent leaks into the environment.

Oil refineries, as one of the complex process industries, consume significant amounts of water based on the size and configuration of the process for multiple operations (65 to 90 gallons of water per barrel of crude oil) and a large volume of wastewater with diverse natures from 1.6 to 0 [17]. They produce 4 times the amount of processed crude oil. The recycling and reuse of this significant amount of wastewater for various purposes, including the supply of water needed for cooling systems, process units, irrigation, and firefighting after the implementation of purification based on quality standards in oil refineries, is a significant matter [18]. Several postrefining approaches, depending on the nature of the type and size of process units in oil refineries, have evolved over the past decades with the aim of improving water and wastewater management [19]. These approaches include the investigation and implementation of traditional techniques such as distillation, evaporation, active carbon filtration, sand filtration, and chemical oxidation and advanced cases such as membrane separation under pressure, electrodialysis, ion exchange, and advanced oxidation processes [20].

The necessity of treatment includes engineering investigations and the use of appropriate technology, measuring the quantitative and qualitative parameters of wastewater in the outlet pool of the treatment plant, comparing with the declared standards, the fate of excess sludge, and ensuring the absence of unpleasant odors and floating objects in the outlet wastewater and no change in the color and turbidity of receiving water at the place of discharge [21].

### **2. The treatment of crude oil desalination unit wastewater with the solar evaporation method**

Effluents from crude oil desalination units due to their specific qualitative and quantitative characteristics, which include highly soluble salts of 50 grams per liter, and the presence of petroleum substances, volatile and non-volatile organic substances, and other hazardous pollutants for the environment, as well as a large volume, create a big problem in the vicinity of oil units and the environment around them. At present, these wastewaters are usually re-injected into operating wells or abandoned wells without treatment or after initial treatment, including the removal of suspended particles and major associated oil substances, with the aim of increasing harvest or preserving the environment. Also, these wastewaters are sent to the evaporation ponds adjacent to these units after degreasing the crude oil desalination units to protect the environment, so that over time, with the solar evaporation method, their amount is reduced, and the volume of the pond to enter the production wastes is emptied again.

This method creates the risk of pollutant leakage into groundwater and release to air and harm to humans, birds, and other creatures around the pond. Considering the sufficient temperature and the high intensity of radiation most days of the year, the use of solar energy seems appropriate. Solar distillation is a relatively simple solution for brackish water sources. Distillation is one of the processes used to purify water, and for this purpose, any heat source can be used. In the solar distillation method, using the energy of the sun, evaporated water and pure water vapor after condensation are used as pure water. The use of solar distillation method is a solution for water supply in remote areas that face a shortage of drinking water and common resources such as heat and electricity grid.

The possibility of building in small capacities, no need or minimal need for fuel and electricity, and the absence of environmental pollution caused by fuel consumption are among the advantages that make the use of this system in areas with significant renewable energy potential and, at the same time, where electricity and fuel transmission is difficult justifiable. The first and simplest solar device built is a single pond solar still (solar still). The building of this device consists of a wooden pond whose floor is blackened by safe pigments.

In a general and apparent classification, pond solar desalination plants can be divided into two groups with a one-way slope and a two-way slope liquefaction surface (**Figure 1**). According to the investigations, the solar distillation pond with a liquefaction surface with a one-way slope has a higher efficiency, because the incoming radiation is more.

The main problem of this type of water desalination plant, like most solar water desalination plants, is the relatively low production of desalinated water. One of the other obstacles of desalters using the solar distillation method is the absorption of less solar energy in areas far from the equator, because in these areas, the liquefaction surface of the device is parallel to the horizon and the oblique radiation of solar rays, and hence, the absorption of solar energy is very low. After the desalination of sea water by the solar distillation system, researchers have performed chemical analyses to check the possibility of using the water produced by this system as drinking water and compared the results with drinking water. The results showed that the resulting distilled water could be mixed with well water to obtain drinkable water, and the quality of this water was acceptable. The results showed that impurities such as nitrate, chloride, iron, and solids soluble in water were removed by solar distillation method. Most of the research related to this topic is often reported for seawater desalination; the treatment of petroleum effluents with this method is a new topic. One of the parameters affecting the efficiency of pond solar desalination plants is the optimal depth of salt water. Research has been done on the effect of water depth inside the pond. In addition to the geometrical parameters of the pond, in recent years, most researchers have focused on the construction of solar energy absorbent beds and heat transfer to increase evaporation.

Zhang et al. [22] reported that highly polluted saline wastewater was treated by carbonized lotus seedpod with the solar evaporation method (**Figure 2**). In their research, COD was removed by more than 84%.

**Figure 1.**

*Pond solar desalination plants with a one-way slope (a) and a two-way slope, and (b) liquefaction surface.*

#### **Figure 2.**

*Lotus seedpod-based solar steam generation. Digital photograph of a lotus seedpod (a) before and (b) after carbonization; (c–j) SEM images of the flower disc, receptacle, and petioles of the lotus seedpod after carbonization, respectively [22].*

#### **Figure 3.**

*Image of the ultra-light substrate based on a chitosan/bamboo fiber matrix and temperature rise in 40 min [23].*

Sun et al. [23] synthesized a new photothermal substrate based on a chitosan/ bamboo fiber matrix with high efficiency for use in water evaporators. According to **Figure 3**, this ultra-light substrate had the ability to increase the local temperature up to 37°C in less than 40 min. The evaporation rate in their research was 6.72 kg m<sup>2</sup> of purified water with a removal efficiency of 85%.

### **3. The treatment of petroleum wastewater with the membrane bioreactor**

Membrane bioreactor technology or MBR refers to technologies in which wastewater is biologically treated, and then, the resulting biomass is physically separated from the mixed liquid using membrane processes. All these steps are performed in a single bioreactor (**Figure 4**). Therefore, in this method, the secondary sedimentation basin is removed from the system. Among the other advantages of this system we can mention the small amount of space they need, the lack of sludge production, and the high quality of the output effluent. These systems are used for purification; so far, urban and domestic wastewater as well as industrial wastewater such as food, pharmaceutical, oil and petrochemical industries have been used. A lot of research has been done on the treatment of petroleum industry wastewaters by MBR and methods of improving its performance. One of the most important wastewaters from oil

**Figure 4.**

*Configurations of membrane bioreactor with the submerged membrane [9].*

industries, which has many adverse effects on the environment, is the water produced in oil fields, which contains large amounts of salt and oil.

Soltani et al. [24] used a submerged MBR with a hollow fiber membrane to treat this wastewater. Due to the fact that this wastewater contains large amounts of salt, due to the increase in osmotic pressure, it destroys the cell wall of the normal microorganisms in the MBR system. In this study, the purified bacteria that were obtained from the areas of oil deposits in the sea, after exposure to the main sewage, were able to decompose 50% of phenanthrene, which is a complex and difficult-to-decompose aromatic compound with three benzene rings, after 45 days. Based on these results, these bacteria can break down other compounds in crude oil. By reducing the salt concentration in this experiment, contrary to expectation, the performance of bacteria purified from the environment with high salt concentration did not decrease. This confirms that these bacteria belong to the halotolerant group.

In a similar study, Xianling et al. [7] studied the purification of petroleum hydrocarbons in a membrane bioreactor by purifying different bacteria from oilcontaminated areas. In this system, it was found that COD removal efficiency was different in steady state, and despite the gradual increase of COD, the efficiency increased from 93 to 96.5%. The reason for this can be seen in the increase in MLSS concentration in these types of systems, which reached 16.2 g L<sup>1</sup> in this system.

The increase in the concentration of MLSS in such MBR systems is due to the use of a membrane that prevents the exit of the mixed liquid, and this concentration increases over time. After entering the petroleum wastewater into the reactor and physiological adaptation with it, the bacteria responsible for the decomposition begin to decompose the hydrocarbons, the final product of which is carbon dioxide and water. First, light hydrocarbons such as alkanes and aromatics with low molecular weight and then heavy hydrocarbons such as polycyclic aromatics are decomposed. This rate of decomposition of petroleum materials in an ultrafiltration bioreactor with transverse flow was observed up to 0.82 g of hydrocarbon per gram of MLVSS per day. In this study, all hydrocarbons with carbon atom numbers from C10 to C24 were removed with almost the same efficiency. Due to the complexity and diversity in the quality of petroleum wastes, in some researches, phenol has been used as a suitable indicator to investigate the removal of biodegradable compounds.

Zhou and Hong, by investigating the treatability of oil refinery wastewater by a fixed film bioreactor at a hydraulic retention time of 8 h and an initial phenol concentration of 30 mg/liter, reported a COD removal efficiency between 85 and 90% and a phenol removal efficiency of 100% [25].

The results of Viero et al. study confirm the high efficiency of phenol removal from petroleum wastewater in a submerged membrane bioreactor. In this research, which was carried out in three stages, during the operation period, a high organic loading rate was applied in the long term by mixing the flow of petroleum wastewater with phenol-rich wastewater to the bioreactor, and it was shown that the treatment of petroleum wastewater in a submerged membrane bioreactor with specific hydraulic retention time, in addition to removing organic matter, also caused high efficiency of phenol removal. The presence of a membrane in this bioreactor increases COD removal efficiency by 17% [9].

The operating conditions of a membrane bioreactor, such as the pressure applied to both sides of the membrane (Transmembrane Pressure: TMP), the amount of aeration, the speed of the transverse flow, and so on, affect the purification efficiency in this system. Increasing the transverse flow speed increases the turbulence of the liquid flow inside the reactor and increases the mass transfer coefficient in the concentration polarization layer and consequently the output flux. The relationship between the output flux (J) and the transverse flow velocity (V) in a bioreactor with transverse flow, in the treatment of petroleum wastewater in a refinery, is obtained as the following power relation [26]:

$$J = kV^{\pi} \tag{1}$$

*n* and *k* are affected by MLSS, and these two factors decrease with the increase of MLSS. The COD removal rate in this bioreactor is reported to be more than 93%. Of course, increasing the speed of the transverse flow and creating a turbulent flow removes the cake layer of organic materials on the surface of the membrane, which plays the role of an additional filter and prevents the passage of impurities, and as a result, the possibility of oil particles passing through the membrane increases. The pressure applied to the membrane also has a double effect. Although increasing TMP increases the amount of output flux, on the other hand, it causes more accumulation of oil droplets on the surface of the membrane as well as inside its pores and intensifies the clogging of the membrane. If this pressure increases, oil and oil droplets will pass through the pores of the membrane and reduce the quality of the output effluent. Aeration also causes the mixing of wastewater inside the bioreactor and provides better contact between particles and microorganisms. On the other hand, it creates a shear force that causes the biofilm flocs to break and separate from the membrane surface. Also, aeration increases dissolved oxygen in the bioreactor, which has a positive effect on COD removal.
