Petroleum Refinery Wastewater Treatment

Water, as the universal solvent, is essentialfor all living things from tiny organisms such as cyanobacteria to giant blue whales and the environment as 71% of the surface of the earth is water covered. Water is widely used in various industry activities such as fabrication, processing,dilution, cooling and transportation,etc.

Nowadays, rapid industrialization and urbanization contributed a lot to economic growth, however a quick increase in population and development consumed large amount of water,  both municipal and industrial wastewater discharged tens of million tons of wastewater into the environment.

Amongst industries generated huge amount of waste water, the petroleum industry is growing rapidly as petroleum and diesel are the major enegry for most of the people to launch vehicles, generate electricity and the petroleum industry is expected to accelerate in the coming dacates. Wastewater from petroleum companies contains many pollutants, including petroleum hydrocarbons, oil, grease, phenol, ammonia, sulfides, and other organic compounds, all pollutants are hazardous to human health and the environment.

Conventional wastewater treatment process for refinery industry got some disadvantage such as stubby handling efficiency, incapacity to degrade biological pollutants which containing persistent and toxic pollutants.

Chemical oxidation was introduced to degrade biological pollutants with much higher treating efficiency, chemical oxidation can treat wastewater through conventional methods and advanced oxidation processes (AOPs). AOPs are very effective for oil and gas wastewater as they produce hydroxyl radicals which are highly reactive molecules that break down organic pollutants.
AOPs generate hydroxyl radicals through various means to oxidize and degrade nearly all organic compounds into water, carbon dioxide, and inorganic ions through reactions like hydrogen extraction, radical addition, or electron transfer. Hydroxyl radicals have stronger oxidizing power than chemicals like potassium permanganate or hydrogen peroxide.
Common AOPs for treating organic pollutants use hydrogen peroxide and iron ions (Fenton’s reagent), UV radiation (photo-Fenton process), or semiconductors (photocatalysis) to produce hydroxyl radicals. These oxidize organic molecules into carbon dioxide and water.

Anodic oxidation, or electrochemical incineration, generates hydroxyl radicals on electroactive anodes without hazardous chemicals. It is easy to scale up, requires little labor, and is environmentally friendly, using mainly electrons. The anode material affects oxidation rates. Boron-doped diamond electrodes are promising, having a wide potential window, producing weakly adsorbed hydroxyl radicals for fast and efficient oxidation, and highly stable and chemical-resistant.

Le’t take a look at the removal mechanisms of macro pollutants via electrochemical oxidation process based on BDD anodes prepared by Boromond during the primary test and experiment with samples from Liaoning XXX Petrochemical Company.

Main reaction to produce OH:

H20→ 0H+ H+ +e-

Main reaction to remove color:

BDD + H20 → BDD(OH + H+ +e-

BDD(OH)+ R → BDD +mCOz+ nH0

Ammonia surface oxidation:

BDD(OH)3 + NH4一 BDD + NO +3H+ +e
Side reaction in high current intensity:

BDD(OH) → BDD +1/202+ H+ +e
2CI- → Cl 2+ 2e-

In this experiment, anodic oxidation with a boron-doped diamond electrode reduced chemical oxygen demand (COD) from 970 mg/L to 65 mg/L, a 93% decrease, in 90 minutes at 30°C and pH 3.