Recycling and Sustainable Development Characteristics, Treatment Techniques, and Operational Limitations for Refinery Wastewater: Review

Received 13 March 2021 Accepted 17 June 2021


Introduction
Petroleum consists of oil and gas. Refinery is one of the sources of producing enough quantity of wastewater that is related to the source of hydrocarbon. Refinery can be defined as storage for producing petrochemical materials from crude oil. Petrochemical materials are possibly more than 2,500 products which include kerosene, gasoline, diesel, fuel oil, liquefied gas, and oil lubrication to use in industrial for variety purpose. The consequences of these petrochemical materials is the production of tremendous amounts of wastewater (Mustapha, 2018). The quantity and characteristics of produced wastewater are based on the configuration of the process. There is a high amount of wastewater produced during recycling of cooling water that is about 3.5-5 m 3 /ton. Refinery is a kind of source of producing polluting wastewater that includes chemical oxygen demand (COD), biochemical oxygen demand (BOD), oil and grease, phenol, benzene, and heavy metals (such as lead, and chrome). However, Large quantities of wastewater generate from refineries in the process of crude oil usage, distillation, and cooling systems. The wastewater samples need to be treated before disposing into the environment. Disposal of the untreated refinery wastewater causes problems for the water sources and environment. The aim of this work was to study the characteristics, treatment techniques, and limitations of refinery wastewater treatment. A number of tables were prepared to summarize and review wastewater characteristics, treatment process, and the operational limitations. Results revealed that values of some parameters such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), phenols, oil and grease, and total suspended solids (TSS) were 40.25 mg/L to 8,000 mg/L, 80 mg/L to 21,000 mg/L, 3.5 mg/L to 128 mg/L, 12.7 mg/L to 50,000 mg/L, and 22.8 to 2,580 mg/L, respectively. Numerous treatment technologies were used for the treatment of refinery wastewater. Treatment techniques have benefits, weaknesses, and operational limitations. Most amount of the TSS, oil and grease, organic materials are eliminated in the primary and secondary treatment units. Tertiary/Advanced treatment units are necessary for removal of the remaining portions of the contaminants, heavy metals, nitrogen compounds, and phosphorus. Combination of physical, chemical and biological treatment techniques increase removal efficiency of the contaminants. www.rsd.tfbor.bg.ac.rs

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Online ISSN 2560-3132 Print ISSN 1820-7480 refinery produces soft and solid waste that ranges between 3-5 kg/ton of petrochemical. In addition, about 80 % of this waste material is considered as a hazardous due to presence of some toxic heavy metals (Benyahia et al., 2006). Modifications and novelty in the treatment of petroleum refinery wastewater have been conducted by researchers. A three-step modification including ZnO nano particle loading, UV irradiation, and Polyether sulfone coating on membranes studied by Ratman et al. (2020). Authors reported that treatment technologies increased the rejection of organic matter from 16 % to 54 %. Jafarinejad et al. ( 2019) stated that membrane separation was low cost and efficient for the treatment of the refinery wastewater and petrochemical plants. Radelyuk et al. (2019) studied effluent quality of three refinery wastewater treatment plants in Kazakhstan. The authors reported that characteristics of treated wastewater exceeded the disposal standards. In another research, powdered activated carbon augmented with the sequencing batch reactor (SBR) process for improving Kawergosk oil refinery wastewater treatment in Erbil City, Kurdistan Region-Iraq was studied (Aziz and Fakhrey, 2017). Rahi et al. (2021) studied thirteen refinery wastewater treatment plants in Iraq and they stated that effluent impacted the environment and water sources. The use of Microbial Fuel Cells for simultaneous degradation of pollutants in the refinery wastewater with electricity generation was studied by Sheela (2020). Recent global issue in some developing regions and countries is a contamination of land and water by petrochemical products. Furthermore, the ecosystem is polluted by untreated refinery products released into the environment. Consequently, refinery wastewater needs treatment before disposing to natural environment. Additionally, efficiency of various treatment technologies and operational limitations for treatment of refinery wastewater are other issue.
Subsequently, the objective of this research was to describe and discuss refinery wastewater quality, various treatment techniques and studying operation limitations of petroleum refinery wastewater based on the study and results of other researchers.

Collected Data
Data were collected from published works of other researchers and arranged in Table 1 that illustrated the characteristics of refinery wastewater. Refinery wastewater contains many impurities such as BOD5, COD, total organic carbon (TOC), phenol, oil and grease, heavy metals, pH, Turbidity, Total suspended solids (TSS) etc.

Characteristics of Refinery Wastewater
Petroleum wastewater properties are different from a refinery to another refinery and from country to country that is based on drilling of crude oil, crude oil types, composition of crude oil and treatment strategy. It is dramatically influenced by the quantity and character of the material that causes the contamination by refinery (Aljuboury et al., 2017). Table 1 showed the different organic material types that found from petroleum. BOD refers to the quantity of organic substances in the water which causes the increase of pollution. When BOD is high then the pollution level is high. BOD is usually determined after 5 days at temperature 20 °C.
TOC represents the quantity of the organic carbon in the waste water which can be determine from the oxidation of carbonaceous (Catalytic combustion) and it measures the carbon dioxide (CO2) production. Suspended solid is a type of the physical contamination.
The high ratio of the suspended solid makes biological alteration and aesthetic which increases the nutrients, metal quantity, fish kills and pesticide that goes in the water. Both nutrients such as nitrogen and phosphorous have the ability to make depletion of the oxygen. Ammonia (NH3) refers to the ration of the nitrogen parts in the pollutant of the refinery wastewater that is highly harmful and toxic to the human health and aquatic life.
Other pollutants of wastewater are called heavy metals that include Iron (Fe), Copper (Cu), Cadmium (Cd), Vanadium (V), Nickel (Ni), Arsenic (As), Zinc (Zn), and Mercury (Hg). These have high ratio of toxic which leads to health problem to the human body (Abdelwahab et al., 2009). Wastewater from petroleum is composed of the pollutants composed of different organic materials and most of that material contains grease and oil which can make a barrier for oil pipes which has odors and is sticky (Mustapha, 2018). The compounds of phenolic has harmful influence to the environment because it has high toxicity and ability for long time to remain in the environment. Both sulphur and nitrogen are producing hydrogen sulphate and ammonia, respectively (Altas and Buyukgungor, 2008). The demand on the petroleum and products of petrochemical will increase fluid waste and its discharge to the water that leads to environmental pollutant (Zhao et al., 2006;Diya'uddeen et al., 2011).
The influence of this water discharge consists of toxic material accumulation, eutrophication, dissolved oxygen in to the sediment and water (Paul et al., 2021). The source contamination of drinking and ground water influences the health life in the community (Yuliwati et al., 2011). Shpiner et al. (2009) mentioned that the wastewater from petroleum included organic and inorganic materials. The organic wastewater from petroleum had grease, oil and dispersed oil, heavy oil, aromatic hydrocarbon, and phenols. The inorganic wastewater from petroleum had, for example, heavy metals and ammonia. Therefore, there are some small quantities of metals inside the crude oil which needs to be treated with a specific tool to separate it. Furthermore, hydrocarbon contains both carbon dioxide and sulphur which needs to be cleaned before going to the market marketing. The toxicity depends on many factors, such as volume, variability, and quantity of the discharge (Nwanyanwu and Abu, 2010). Table 1 illustrated that values of some parameters such as BOD, COD, phenols, oil and grease, and TSS were 40.25 mg/L to 8,000 mg/L, 80 mg/L to 21,000 mg/L, 3.5 mg/L to 128 mg/L, 12.7 mg/L to 50,000 mg/L, and 22.8 to 2,580 mg/L, respectively. Refinery wastewater contains high concentrations of the contaminants and they exceeded the disposal standards (Aziz et al., 2020).
Direct disposal of the refinery wastewater causes problems for the people, animals, and the environment.
Consequently, proper treatment is essential for the refinery wastewater prior disposal to the environment.
Different treatment techniques for the refinery wastewater is illustrated in Figure 1. There are three types of wastewater treatment from hydrocarbon which are biological, chemical, and physical. Therefore, petroleum wastewater represents a complicated problem that requires a specific technique.
The conventional method needs a several steps to treat the process. First step, consists of before treatment that includes physicochemical and mechanical treatment. Second step is a more modern treatment for previous wastewater.
Different treatment methods and the removal efficiency of the pollutants for petroleum refinery wastewater are shown in Table 2.
Details and discussion for the treatment techniques are shown in the following section.   This treatment method is a process that is free from biological and chemical changes to treat the wastewater. Course screening is an example for removing large particle and sediment. Currently, physical technique for example sedimentation method is used for treatment to remove fine grains rather than biological method. Sedimentation method is used for separating both water and oil that is obtained. The process of changing liquid to solid state was used for reduction fine grains. Physical process was effective for treatment wastewater from petroleum due to their complexity and the other process can do better (Mikhak et al., 2019). Wang et al. (2016) reported that the maximum reductions for total naphthenic acids and aromatic naphthenic acids using physicochemical processes were 16 % and 24 %, respectively. While in the biological process the removal efficiencies were 65 % and 86 %, respectively.

Membrane Process
According to Malamis et al. (2019) and Razavi and Miri (2015), membranes were basically divided in two main types, i.e. synthetic and biological membranes. Both ultra-filtration and electrodialysis are tools of membrane technology that are increasingly applied. This technology was found as a useful for organic matter treatment and in terms of economic efficiency it is more acceptable for treating (Jyoti et al., 2013;Kulkarni and Goswami, 2014). Razavi and Miri, (2015) showed that the average removal efficiencies of COD, BOD5, TSS, volatile suspended solids (VSS), and turbidity using hollow fiber membrane bioreactor were obtained 82 %, 89 %, 98 %, 99 %, and 98 %, respectively. The interactions between the membrane surface and suspended solid constituents in refinery wastewater strongly influenced the membrane in polyvinylidene fluoride hollow fiber membranes, which was approved by Yuliwati et al. (2011).

Coagulation/Flocculation
This process is one of the most popular methods for treatment of wastewater to remove the material such as turbidity, COD, color, TSS (Farajnezhad and Gharbani, 2012). This treatment belongs to the pre-treatment that is used before membrane and biological treatment. This process can be also used in the final process treatment to eliminate the organic matter of non-biological origin in hydrocarbon (Farajnezhad and Gharbani, 2012). The flocculation method is used for treatment of wastewater from petroleum to bring the large removable material that includes the total phosphate, TSS, and COD. On the other hand, this process is not accurate to remove full wastewater treatment caused by level of efficiency to eliminate the organic matter (Hassan et al., 2012).
Applied the ferric chloride and aluminum chloride are used to remove wastewater from petroleum (Farajnezhad and Gharbani, 2012). They noticed that from two above parameters the aluminum chloride was more effective than ferric chloride. The changing of the pH was significant for the removal of color of the hydrocarbon while the effect of the COD was based on the properties of the petroleum and coagulant types that included metals of inorganic origin, such as ferrous sulfate and aluminum sulfate. El-Naas et al. (2009b) achieved 30 % of COD reduction at the ambient temperature, whereas at 60 °C, 53 % of COD reduction was reached.

Adsorption
The main advantages of using adsorption process are affordable cost, adaptability, and simplicity (Kulkarni & Goswami, 2013). Cavalcanti et al. (2012) studied analysis of adsorption by used organ clay for eliminating liquid waste from petroleum wastewater. They mentioned that the organophilic clay had significant effective adsorption for reducing the material with maximum toxicity for example phenols and compounds of BTEX. Technology of adsorption refers to the activated adsorption of carbon that is mainly used for ammonium, toxicity and organic compounds in petroleum treatment wastewater (Wang et al., 2007).
Activate carbon is highly influencing the reducing remain organic compounds after treatment from biological method. Therefore, pollutant of the low molecular weight is highly adsorbed (Wang et al., 2007).
This process has limited work due to consumption of carbon activated columns (Renou et al., 2008;El-Naas et al., 2009a).

Physicochemical Treatment
Physical-chemical method is combined with previous method physical techniques for example filtration and absorption and chemical techniques for example ozonation and oxidation for treatment petroleum wastewater (El-Naas et al., 2016).
After the mechanical process, the physicochemical step collected fine grains that deposited within large grains to easily reduce by the process of floatation, sedimentation and filtration.

Chemical Treatments
This treatment consists of utilities chemical reactions to enhance the quality of water. This treatment is usually used for petroleum wastewater treatment that is called neutralization. Neutralization comprises of the base or acid to change the level of the pH. The base material is lime that is used in the neutralization of acidic waste. According to Sun et al. (2008), a microwave-catalytic wet air oxidation method gained more than 90 % of COD removal and increase in BOD5/COD ratio at 30 min from 0.04 to 0.47 to treat petroleum wastewater at 150 ℃ with 0.8 MPa.

Biological Treatment
There is a number of micro-organisms used for treating wastewater to fix the last product. Part of the most microorganisms waste is changed to water, CO2 and other products (Zhao et al., 2006). There are several biological methods used for treating wastewater of the petroleum, for example soft reactors and biofilm reactors to eliminate organic compound pollutants (Melamane et al., 2007;Manyuchi and Ketiwa, 2013). Biological oxidation is based on the components of the wastewater from petroleum. However, this method has some disadvantage, such as high soft production and low space to COD removal (Jou and Huang, 2003). Biological process is divided into two types which are anaerobic and aerobic that depend on availability of oxygen dissolved (Zhao et al., 2006). In the anaerobic method, biochemical and chemical products reactions lead to change color and odor of the water. So, the availability of oxygen is very crucial to eliminate that process to change the odor and color (Attiogbe et al., 2007).

Aerobic Biological Treatment
The main objective of this process is to change organic material and refusing materials from wastewater to the CO2, water and biological product (Zhao et al., 2006). This type of reactor has the degradation efficiency of about 78 % and 94 % removal of the total organic carbon and oil, respectively from wastewater of the petroleum refinery. This method showed the enhancement of the COD reduction (Satyawali and Balakrishnan, 2008). Furthermore, higher willing for toxic and loads of organic shock and losing biomass was recorded.

Anaerobic Biological Treatment
One of the most popular methods for its economic efficiency and removal of organic component is called anaerobic biological treatment. Organic component is changed to methane (CH4), CO2 and wet material during this process. Due to high efficiency, this process is widely applied (Lettinga et al., 2001). The use of anaerobic upflow of the wet beds is dramatically increased for treatment in petroleum wastewater due to simple and clear design, easy construction with highly maintenance (Rastegar et al., 2011). According to Gasim et al. (2013), the anaerobic method could easily be used for treatment of the petroleum wastewater because it could remove about 82 % of COD. Wang et al. (2016) determined that 70 % of COD was removed, as well as 72 % of the total oil which was obtained from up-flow sludge beds of anaerobic reactor for heavy oil treatment wastewater. It contained tremendous amount of the polar organic and potential efficiency for petroleum wastewater treatment. However, up-flow sludge beds of anaerobic (UASB) reactor had to be used within few organic loads and long duration time of the petroleum wastewater treatment . Zou (2015) illustrated that removal of NH3-N, oil, and COD from the complex oil wastewater were 90.2 %, 86.5 %, and 90.8 %, respectively. The combinations of the UASB and biofilm reactor for treatment of the petroleum wastewater resulted in COD removal of 81.075 % (Nasirpour et al., 2015).

Aerated Lagoons
Biological process for the treatment of wastewater from petroleum is normally organized in wet or soft aerated lagoon environment (Tellez et al., 2002;Ma et al., 2009). The activity of being a few times aerated in lagoon does not obtain the needs in fluid treatment. They require a large area caused by small concentration of biomasses (Ma et al., 2009).

Activated Sludge Process
This method is compacted and it should be considerable for the area of the building tanks and other construction of the sludge. Biotransformation of the acidic naphthenic from the sludge method was mostly under effect of the temperature. The average acidic naphthenic from the sludge during summer is higher than in the winter that is about 73 % and 53 %, respectively. It was caused by activity of the high Biotransformation microbial in the sludge system. There are some disadvantages of this method for example high amount of sludge product that needs more time and more energy (Renou et al., 2008).

Biofilm Reactor Process
This method has high efficiency for removing solid suspended materials (Rodgers et al., 2003;Vendramel et al., 2015). This method is known as a steady operated and flexible, with ability for difficult contaminants, and shock loads of the organic matters with large amount of the biomass existence (Galvez et al., 2003;Rodgers et al., 2003;Ibrahim et al., 2012). According to Vendramel et al. (2015), the removable amount of the COD and TSS that was about 91 % and 92 % respectively from anaerobic submerged fixed-bed reactor (ASFBR). The importance and quantity of the biofilm required more analysis in the reactor operations (Vendramel et al., 2015). The average efficiency for removing phenols in the petroleum wastewater is 98 % by utilities of the batch sequencing (Al Hashemi et al., 2015). Radelyuk et al. (2019) reported that the treated refinery wastewater in three treatment plants in Kazakhstan still contained surpassing concentrations of contaminants in their effluents. Rahi et al. (2021) studied effluent quality for thirteen refinery wastewaters in Iraq. The researchers stated that wastewater produced by the refineries contained high contaminants and caused problem to the people and the surrounding groundwater sources. Most suspended solids and oils, and a part of the organic matters were removed in primary treatment units. In the biological process, utmost remained parts of the organic matters are removed. For the removal of the remained organic material, nitrogen compounds, phosphorus and heavy metals further treatment techniques were required in the tertiary/advanced treatment process. Application of physical-chemical, physical-biological, and chemicalbiological enhance removal efficiencies of the pollutants are needed (El-Ashtoukhy et al., 2013;Wang et al., 2016;Aziz and Fakhrey, 2017;Jafarinejad, 2017;Mohanakrishna et al., 2020;Sheela, 2020). Type of influent wastewater and the goal of the treatment decides the selection of the treatment process.

Limitations of Operational Parameters
Several operational parameters, laboratory and pilot plant studies were performed for the treatment of oily wastewater using aerobic and anaerobic bioreactors of various configurations and different pattern. Table 3 showed the works of other researchers for the treatment of petroleum refinery wastewater with different reactor configurations and removal efficiencies.
It can be seen from Table 3 that more than 90 % of pollutants (such as COD, hydrocarbon, oil, NH3-N, and turbidity) were removed in the refinery wastewater.
Commonly, the biological treatment was efficient method for refinery wastewater treated, because it contained huge amount of organic matter and hydrocarbons.
In this paper review of petroleum refinery wastewater using different physical, chemical and biological methods was presented. Among them, conventional treatment technics had drawbacks as they produced large oily sludge during treatment processes. Biological treatments particularly constructed wetland were found to overcome the limitations to treat petroleum refinery wastewater since it was not only high efficient in removing COD, phosphate, and nitrate, but also were quite efficient in the removal of phenols and other organic compounds without producing any significant amount of oily sludge (Jain et al., 2020). Each method has its advantages, disadvantages, and operation limitations.

Conclusion
Refinery wastewater contains huge amount of TSS, BOD, COD, oil and grease, phenols, heavy metals etc. which surpass the disposal standards. Thus, treatment is essential before disposal to the environment. Several treatment techniques were applied for the treatment of refinery wastewater. Each treatment method had its advantages, shortcomings, and operational conditions. A great part of the TSS, oil and grease, organic matters was removed in the primary and secondary treatment units. Removal of the remaining parts of the pollutants, heavy metals, nitrogen compounds, and phosphorus needed further polishing in the advanced/tertiary treatment units. Combination of physical, chemical, and biological treatment processes improves removal of pollutants.