Application of Titanium Anodes in the Removal of COD from Oilfield Wastewater

The composition of oilfield wastewater is complex. The organic pollutants it contains mainly consist of petroleum-based organic substances and the organic additives added for modification. However, due to the different geological conditions of the oil source areas, the nature of water injection, and the entire process of crude oil collection, transportation, and initial processing, the properties of oilfield wastewater vary greatly.

Electrical flotation is a wastewater treatment unit operation that uses electrochemical methods to remove suspended solids, oils, and organic substances such as oil hazards from water. It involves inserting multiple sets of positive and negative electrodes into the wastewater. When a direct current is applied, electrolysis, particle polarization, electrophoresis, oxidation, reduction, interactions between electrolytic products and wastewater, and other processes occur, resulting in the purification of the wastewater. According to whether the anode material dissolves, electrical flotation can be classified into electrocoagulation flotation and electrolytic flotation. When using soluble materials such as iron or aluminum as anodes, it is called electrocoagulation flotation. When using insoluble or inert materials such as platinum, ruthenium dioxide, or iridium dioxide as anodes, it is called electrolytic flotation. For the treatment of drilling wastewater using chemical coagulation methods, when COD cannot meet the standards, electrolytic flotation can effectively treat oilfield wastewater. It can remove oil and COD, with an removal rate of 80-90%.

During the electrochemical treatment of wastewater, through electrode reactions, hydrogen and oxygen are mainly produced on the cathode and anode respectively, generating very small (about 8-15 μm) and highly dispersed bubbles, which act as carriers to adsorb colloidal particles and suspended solids and float upward.

Electrocatalytic oxidation is the direct degradation of organic substances by the anode, or the degradation of organic substances through the generation of strong oxidizing agents such as hydroxyl radicals (?OH) and ozone by the anode reaction. This degradation pathway makes the decomposition of organic substances more thorough, without generating toxic intermediate products, and is more in line with environmental protection requirements. This method is usually called the electrocatalytic oxidation process of organic substances.

The removal of COD mainly relies on the oxidation reaction on the anode surface. Organic substances are directly oxidized and degraded on the anode surface. The anode potential must be higher than the decomposition potential of the organic substances. Usually, the decomposition potential of organic substances is higher than the potential for oxygen to be released in water. Therefore, the competing reactions that occur at the anode are the decomposition of organic substances and the release of oxygen. Therefore, when the water quality contains a lot of organic substances, an iridium anode should be used, which is more conducive to the decomposition of organic substances in water.