Design of Oil Containing Wastewater Treatment
Introduction
Oil containing wastewater (OCWW) is a kind of wastewater containing suspended organic and inorganic compounds, which is generated from oil and gas production activities in oil field. In addition, the OCWW might contain oil, gas, mineral salts, heavy metal, alcohol, surfactant, and relatively high concentrations of suspended solids. Due to its complex composition, it is difficult to treat and has a significant environmental impact. Therefore, in order to reduce the pollutant concentration to meet the requirements of wastewater discharge, it is necessary to carry out comprehensive treatment of this kind of wastewater.
Treatment objective
Oil containing wastewater is often generated during oil and gas operations. As a result, it is necessary to identify the specific properties of OCWW to ensure that the appropriate treatment process is used to meet the water quality requirements. The treatment objectives of OCWW include the following:
1. Removal of oil and grease to meet the requirements of the local governing body.
2. Achieve biodegradable organic removal and reduce biochemical oxygen demand (BOD) and chemical oxygen demand (COD).
3. Reduce the concentrations of suspended solids and settleable solids to reduce the turbidity in the treated water.
4. Achieve the necessary pH adjustment to recover process water.
5. Remove heavy metals, if required.
6. Disinfection to achieve a pathogen-free effluent.
Treatment strategy
The most common treatment strategies for oil containing wastewater include physical, chemical and biological treatment processes. The physical methods remove oil, grease, settleable and suspended solids from the wastewater. Chemical methods are used to break down the organic components in the wastewater while biological methods are employed to remove the remaining organic components. In addition, additional components such as pH adjustment and disinfection processes may be incorporated depending on the requirements of the local governing body.
Physical treatment
Physical treatment methods are commonly used to remove oil and grease, settleable and suspended solids from the wastewater. This involves the use of filtration and coalescence units which use activated carbon, sand, or membranes to remove oil droplets and other suspended solids. In addition, this process is often used in combination with floatation and flocculation to remove oil droplets and other settleable solids from the wastewater.
Chemical treatment
Chemical treatment processes involve the addition of chemicals such as caustic soda, Aluminum sulphate, ferric chloride and polymers to break down the organic components and also to improve the settleability of the wastewater. Along with coagulation, these processes can be used to enhance the removal of grease, oil and other suspended solids from the wastewater.
Biological treatment
Biological treatment process is used to reduce the concentrations of organic components such as COD and BOD in the wastewater. This process involves the use of aerobic and anaerobic bacteria that break down organic molecules into simpler compounds. Aerobic treatment involves the use of oxygen to facilitate the degradation of organic compounds while anaerobic treatment processes involve the conversion of organic compounds into methane gas and carbon dioxide.
Final treatment
The final treatment process of OCWW is often used to adjust the pH of the treated water and to disinfect the effluent. Depending on the requirements of the local governing body, the pH of the effluent is adjusted with the addition of lime or other chemicals to achieve the desired pH. In addition, chlorine or ultraviolet light can be used for disinfection, depending on the effluent requirements.
Conclusion
Oil containing wastewater is a complex wastewater that requires comprehensive treatment to meet the requirements of wastewater discharge. The common treatment processes include physical, chemical and biological methods, as well as final treatment such as pH adjustment and disinfection. With the implementation of these processes, the oil and grease, suspended solids and other contaminants can be effectively removed to meet the requirements of the local governing body.
