Industrial Wastewater Efficiency Assessment of Al-Dora Refinery Plant in Baghdad by Decreasing BOD 5 and COD Concentrations

Abstract


Introduction
Water pollution is the presence of chemical, physical, and biological constituents above the acceptable limits set by standards.Pollution can occur when a large amount of any foreign substance (solid, liquid, or gas) is found in a specific area (Abed, 2008).Thus, oil refineries are significant sources of water pollution due to their high water consumption and discharge of contaminated wastewater into rivers or the sea (Mohammed, 2018).Petroleum refineries use a variety of complex refining procedures to convert crude oil into refined products such as gasoline, liquefied petroleum gas, aviation fuel, and kerosene .As a result of the extensive water consumption involved in refining processes, the petroleum refining sector produces a significant amount of wastewater.Concern has increased among nearby communities about the potential environmental risks associated with oil refineries (Barbooti et al., 2010).Water scarcity has become more acute in Iraq due to the improper use and untreated discharge of water (Planning, 2022;Hashimi et al., 2018).Upon the introduction of petrochemical effluent into the water body, it instigates water pollution, alters the local ecological environment, leads to the demise of aquatic organisms, and imposes significant detrimental effects on water supply resources, biological resources, aquaculture, and tourism (Yang, 2020).Because of their chemical and industrial content, liquid industrial residues are considered to have dangerous effects on the properties of the aquatic environment (Hassan, 2016).
Industrial wastewater is typically contaminated with dangerous compounds, posing a significant environmental and health risk.As a result, it must undergo adequate treatment before being discharged into aquatic bodies .Efficient treatment of contaminant removal, breakdown, and conversion into lowrisk compounds is done through several methods during the processing phases of the mechanical phase, the physiochemical phase, and finally the biological phase (Hassan, 2016).Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD) are crucial in regulating the overall pollution levels and managing the aquatic environment.Both indicators assess the level of water contamination and serve as a comprehensive measure of the relative concentration of organic substances (Prambudy et al., 2019).
Al-Dora Refinery Wastewater comprises a range of pollutants, such as phenols, suspended particles, sulfides, oxygen demand, bearing material, and other detrimental contaminants.A treatment facility was built and put into operation in the year 1980.However, it was observed that on certain occasions, the quality of the effluents discharged from the refinery surpassed the water quality limits set by Iraq, resulting in detrimental environmental consequences for the Tigris River (Abed, 2008).
The analysis examines wastewater from crude oil and fuel refining in Iraq, including petroleum refinery effluents.It highlights the significant impacts of this pollution, focusing on the handling of wastewater in refineries and the treatment methods used.Oil refineries face challenges in meeting commitments, neglecting atmospheric regulation, and regarding environmental protection schemes.The government lacks commitment to minimum environmental legislation, affecting livelihoods and agriculture (Biddinger et al., 2021).To manage the water environment and control the overall content of pollution, BOD5 and COD are crucial.Both of them serve as a thorough indicator of the proportionate amount of organic matter in the water and show the level of pollution in the water (Qiong et al., 2009).For respiration needs, aquatic creatures rely on dissolved oxygen (DO), or oxygen found in water.The temperature of the water, the amount of silt in the body, the amount of oxygen removed from the system, and the amount of oxygen added back to the water all affect the DO in a body of water.Oxygen is removed from the system by respiration and the decomposition of living things.Water is then replenished with oxygen through photosynthetic organisms, aeration, and stream flow (Panawala, 2017).BOD5 measures the amount of oxygen bacteria will consume while decomposing organic matter under aerobic conditions (Khazraji and Nasser, 2012).High BOD5 waste output can result in significant dissolved oxygen depletion and fish mortality in receiving water bodies, among other issues with water quality (Penn et al., 2003;Bhateria and Jain, 2016).A sample's oxygen consumption over five days is assessed in a highly regulated and standardized environment (Brenniman, 2006).Samples often must be diluted before incubation or the bacteria will deplete all of the oxygen in the bottle before the test is complete (Khazraji and Nasser, 2012).COD measures the oxygen requirement for organic matter chemical oxidation to take place via the assistance of a strong chemical oxidant (Popoola, et al., 2019).COD is not related to a specific compound; rather it is considered a parameter to measure the degree of contamination in effluents (Mousazadeh et al., 2021).
A comparative study was conducted to evaluate pollution in five sites on the Tigris River in Baghdad.Among the study sites was Al-Dora Refinery.The documented information revealed that the five plants in the search region had BOD5 concentrations ranging from 42 to 90 mg/l in 2021 compared to 62-120 mg/l in 2020, and COD concentrations ranging from 114-221 mg/l in 2021 compared to 114-342 mg/l in 2020 (Wadeea et al., 2022).Sultan and Sultan (2021) conducted a study to reduce the BOD and COD in the final wastewater of Najaf Oil Refinery in western Iraq.They used two strains of gramnegative bacteria for this purpose.The COD removal rate achieved was 60% for both isolates, while the removal rate for B was 53.13% and 42.34% for the two isolates respectively.An investigation was carried out to evaluate the toxicity of both treated and untreated liquid waste from the Al-Dora refinery by algae, and the outcomes demonstrated that According to this study, algae can be used to produce water quality criteria, identify potential environmental concerns in contaminated sites, and evaluate how well the industrial liquid waste treatment works ( Lami, 2014).(Abdulkareem, et al., 2021) conducted a study on the performance and characteristics of liquid waste at the Al-Dora refinery treatment plant.The study found that the removal efficiency of BOD5 and COD was 98.96%.These results show that Al-Dora industrial wastewater treatment plant effectively removes pollutants according to Iraqi specifications and EPA regulations.(Hamadi, 2011) conducted an investigation and evaluation of the environmental conditions related to the water quality used in Al-Dora refinery.Time models of the final drain water were taken from the water treatment unit during the water quality assessment.The analysis showed that the treated water meets environmental quality standards.(Obiad and Al-Sultan, 2020) using the Canadian Wastewater Quality Index (CWWQI), evaluated the wastewater quality from the Al-Dora Refinery's Industrial Wastewater Treatment Plant (DWWTP).The outcomes demonstrated that CWWQI obtained this treated water from 80.19, indicating good quality.
The purpose of the current study is to evaluate the effluent discharges from the Al-Dora refinery's treatment facility, both before and following treatment.By carrying out these investigations, the quality of treated industrial wastewater released into the Tigris River is periodically monitored, protecting both humans and other living things as well as the water quality.

Description of the Study Area
The Midland Refineries Company (MRC) operates the Al-Dora refinery, which is located in the southeast of the Baghdad governorate.Its coordinates are latitudes 33°15'38"N and longitudes 44°25'28"E.It is only 4 km from Baghdad's city center and near the Tigris River's western bank.The refinery is 1620 meters long and 860 meters wide.Large amounts of crude oil are converted into oil products at Al-Dora refinery, which is open twenty-four hours a day and has thirty plants divided into twelve sections.The location of this refinery, which is mostly on flat land, is about in the center of Iraq Fig. 1.Fig. 2 shows the map of numerous oil fields in Iraq.Many oil fields are scattered around southern and northern Iraq, where the city of Basra is one of the largest cities in Iraq containing oil fields (Almaalei et al., 2019).Also, the map mentions the sources of crude oil sent to the Dora refinery.

Wastewater Treatment units in Al-Dora Refinery
The primary sources of hazardous aquatic pollution and wastes are thought to be the oil industry and the procedures involved in the manufacturing and export of petroleum products.Discharging of the oil refinery wastes to the aquatic ecosystems can cause hazardous and harmful effects on the water quality, biodiversity, and food chain, depending on the discharge pollutants concentrations.Therefore, if industrial wastewater is not adequately treated, it will seriously harm the ecological system due to its complex and harmful components, various suspended solids, and high concentrations of organic contaminants (Jilani and Khan, 2013).All industrial establishments, particularly those in the oil sector, are required by environmental legislation to establish units or plants for the treatment of industrial wastewater (Zaki et al., 2023).The location of the water treatment plants is shown in Fig. 3, and an overall flow diagram of Al-Dora refinery wastewater treatment plant is schematically illustrated in Fig. 4. Traditional technologies consist of three primary elements: (a) physical processes (e.g., skimmer tanks, dissolved air flotation (DAF), filtration, etc.); (b) chemical processes (e.g., coagulationflocculation, ozonation, electrochemical oxidation, etc.); and (c) biological processes (e.g., trickling biofilters (TBF), activated sludge process (ASP), rotating biological contactor, etc.) (Bhargava, 2016;Thorat and Sonwani, 2022).Various physical, chemical, and biological treatment processes can effectively treat petroleum and petrochemical wastewater (Kulkarni and Goswami, 2015).Alum and polyelectrolytes are added to the chemical treatment tank, CTT.Urea and phosphoric acid are added as nutrients within the biological treatment basin.Recycling is adopted within the biological treatment basins.The sludge from the various parts of the treatment units is finally filtered off to be treated and incinerated later.The wastewater treatment plant of Al-Dora refinery has a design capacity of disposal of 700 m 3 /hr to Tigris River (Hamadi, 2011).Three stages of treatment operations are carried out: 1-Mechanical treatment: The industrial water pumped from all over the refinery, which is in the form of emulsion water containing fats, free hydrocarbons, plankton, and mud, is collected in one tank and then enters the main separation basins (API).In the first stage, fats, floating hydrocarbons, and asphalt hydrocarbons coming from the fat section are eliminated, as well as sand and silt are eliminated, which is an obstacle to the physicochemical purification process, as it hinders the process of collecting fat minutes.The principle on which the separation process depends is (the difference in density) (Walker, 2014).2-Physical-chemical treatment: During this stage, suspended substances (organic or inorganic) and emulsified hydrocarbons are removed through physical and chemical methods such as coagulation, sintering, and flotation.The treated water formula (pH7) is also necessary for mineral deposition as oxides or hydroxides (Bhargava, 2016).Chemical treatment of wastewater can be employed as a pretreatment step before biological treatment or as a single primary chemical treatment technique.3-Biological treatment: It is considered one of the most important stages of wastewater treatment because it achieves the main purpose of water treatment before it is released into the river, which is the removal of toxic substances affecting human health and living organisms, and these substances.most of them are organic solvents used in refinery units such as (furfural, phenol, and aldehyde) by bacteria to get rid of these substances, which are food for these organisms, so they analyze, oxidize, and convert them into precipitated and non-toxic solids under certain conditions of temperature and PH, a controlled percentage of pollutants and a sufficient amount of oxygen (Al Zoubi et al., 2019).

Sampling
Five sampling points were selected from the industrial wastewater treatment plant at Al-Dora refinery to collect industrial wastewater samples and five duplicates were taken for each sample during the summer (27 July) and winter (18 January) seasons.Clean cans of 1L polyethene were used to collect the samples after homogenizing them with water samples several times.It was dealt with in the Department of Environment and Water at the Ministry of Science and Technology and subsequently analyzed.They have been numbered according to sampling sites and as shown below: S1-Main isolation Basin (pre-treatment), water entering the main basins.S2-Mechanical post-stage Basin, water out of the mechanical treatment basin.S3-Post-physiochemical Basin, water out of the physiochemical treatment basin.S4-Post-biological Basin, water out of the biological treatment basin.S5-Water is released into the river, final water is drained to the Tigris River.
Results of summer measurements measured at the Ministry of Environment Central Health Environment Laboratory by a Lovibond (OxiDirect) type device for BOD, sample incubation was for 5 days at 20°C in a BOD bottle, and Lovibond (Multi Direct) for COD and results of winter measurements measured at Baghdad University Faculty of Engineering Department of Environmental Engineering for the same type of devices.Statistics were conducted using Microsoft Excel 2016, and calculate the removal efficiency for each treatment unit was through the following equation: (Abduljabbar et al., 2021;Al-jobouri et al., 2013).
Where C0 is the influent BOD concentration to the treatment unit, and Ct is the effluent BOD concentration from treatment unit.

Results and Discussions
The water quality was assessed using laboratory analyses of the acid function variables Biochemical Oxygen Demand (BOD5) and Chemical Oxygen Demand (COD).It is possible to determine the removal efficiency of BOD5 and COD in each treatment phase, as well as the overall effectiveness of the Wastewater Treatment Plant.

Biochemical Oxygen Demand (BOD5)
The highest concentration of BOD in water entering basins (before treatment) was recorded at 180.8 ppm in summer and 106.8 ppm in winter, while its concentration in water emerging from treatment basins (water to the river) was 37 ppm in summer and 31ppm in winter.The total removal rate in the summer is 80% and 71% in the winter.Table 1 contains the rate for five repeaters per sample and the standard deviation and removal ratio per unit for summer and winter.Fig. 4 shows the BOD5 data graph.The reason for the high concentration of BOD5 in the first and second units (no actual process occurs in them to remove BOD5 concentrations), that is, the water entering the treatment plant in the winter, is due to the high load of organic materials contained in industrial wastewater, which are used by bacterial groups as a food source.This allows these groups to grow rapidly and increasingly, causing an increase in the biological requirement for oxygen and thus a decrease in the level of dissolved oxygen in the water.As for the water discharged into the river, the concentration of BOD5 in the summer is higher than in winter, due to high temperatures during summer and their impact on microorganisms, which lead to the degradation of organic substances and then the production of ammonia (NH3) and hydrogen sulfide (H2S) that raises BOD5 values.As time passes and oxygen dissolves, anaerobic oxidation processes and methane (CH3) production begin, which corresponds to the mentioned ( Hassan, 2016).Also, operational problems may sometimes occur in the refinery, which in turn affects the levels of pollutants in the industrial water discharged from the production units that operate in the refinery.

Chemical Oxygen Demand (COD)
The value of COD before treatment was very high, reaching 399.6 ppm, while its value in the water released to the river, i.e. after treatment, decreased to only 55.4 ppm in the summer.The greatest concentration of COD in the water entering the treatment basins was 324.4 ppm during the winter season, which was slightly lower than in the summer.
The concentration in the water emerging from the treatment basins, i.e. the water to the river, was 42.6 ppm with total removal ratios of 86% during the summer and 87% during the winter as shown in the data in Table 2 and Fig. 6 shows the COD data graph.From Table 2, we note that the highest percentage of removal of COD occurred during the physicochemical treatment unit in the winter at a rate of 63%.This is due to the use of treatment chemicals that are added to the basins, which is an alum (hydrated aluminum sulphate) with stirring and then the addition of Anino poly electrolyte, which works to collect Pollutants that are sintered through the flocculation process, which is the process of collecting neutral particles, agglomerating them largely and cohesively, and precipitating them to be separated in the flotation process.
Organic chemicals that are difficult for air bacteria to biodegrade or that are poisonous to microorganisms and can chemically oxidize into carbon dioxide, water, and ammonia contribute to the rise in COD values for these residues.Some of the dissolved lipid content of these liquid leftovers contributes to elevated COD ratios since one of the COD measurement limits cannot distinguish between biologically active and physiologically inactive organic compounds.In comparison with the Iraqi environmental determinants for industrial water discharged into rivers 100ppm for COD, and 40ppm for BOD5, we find that the measured concentrations are within the permissible limits.This means that the treatment plant works well in treating industrial water and that the highest percentage of removal of COD was during the physicochemical treatment stage during the winter, where the removal rate reached 63% and 61% for BOD in biological treatment, Fig. 7.In comparison previous studies conducted at Al-Dora refinery about the BOD5 and COD concentrations which were measured in the drained industrial water to the Tigris River (Table 3) and (Fig. 8), it was found that they are all within the Regulation No. 25 of 1967 Maintenance of rivers and public water from pollution (MOE, 1967).Despite the increase in their concentrations in this study, which is due to the increase in the volume of pollutants treated in the main treatment station in the refinery during the current study period but remain within the limits of industrial water drained into the river after treatment.

Conclusions
The findings of the measurement of COD and BOD concentrations in this study revealed that the treatment units that operate in the industrial wastewater treatment plant in the cycle refinery are suitable for treating liquid waste discharged from the refinery's production units.It has been demonstrated that it effectively removes BOD and COD concentrations from the water before discharge into the Tigris River, with a gross removal rate of 80% in summer and 71% in winter for BOD, and 85% in summer, and 87% in winter for COD.The bioprocessing unit had the highest BOD and COD removal ratio.BOD and COD concentrations in the water drained into the river ranged from 37 to 31 ppm for BOD and 49.2

Fig. 1 .
Fig.1.Location study, (a) the map of Baghdad province and its center (b) the location of Al-Dora refinery in Baghdad (Hassoon and Al-Dabbagh, 2023).

Fig. 7 .
Fig.7.Removal percentage for BOD and COD each treatment unit during the summer and winter seasons.

Fig. 8 .
Fig.8.Comparing the concentration of BOD and COD in treated water and released to the river with Iraqi determinants and literature.
for COD during both seasons.It is below the allowable environmental standard set by environmental determinants of industrial water discharged into the river under the River Maintenance System 1967, which included 40ppm of BOD and 100ppm of COD.

Table 1 .
The concentration of BOD5 by (ppm) in wastewater samples.

Table 2 .
Concentration of COD by ppm in wastewater samples 1 SD=Standard deviations.

Table 3 .
Comparison of BOD and COD concentration in the water discharged into the river with studies on the same study site.