Petroleum Refinery Wastewater Treatment: Case Study of Shandong XXX Petrochemical Company

Background

Water covers about 71% of the earth’s surface and supports every form of life, from single-celled organisms to the largest animals on the planet. Industry depends on it just as heavily — as a raw material, a solvent, a coolant, and a transport medium across fabrication, processing, and dilution processes.

That dependence has a cost. As industrialization and urbanization have accelerated, both municipal and industrial sources now discharge tens of millions of tons of wastewater every year. Petroleum refining is one of the largest contributors. Refined fuels remain the primary energy source for transportation and power generation worldwide, and refining capacity continues to expand to meet that demand — which means refinery wastewater volumes are growing along with it.

Refinery effluent is a difficult matrix to treat. It typically carries petroleum hydrocarbons, free oil and grease, phenols, ammonia, sulfides, and a range of other organic compounds, most of which are toxic to aquatic life and harmful to human health even at low concentrations.

Conventional treatment trains — screening, gravity separation, biological treatment — struggle with this matrix for a simple reason: many of the pollutants in refinery wastewater are persistent and resistant to biodegradation. Biological treatment works by feeding pollutants to microorganisms; if the pollutant is toxic to the organisms doing the work, or simply doesn’t break down at a biologically useful rate, conventional treatment plateaus well short of discharge standards.

Why Electro Oxidation

Chemical oxidation was adopted specifically to address that gap. Within chemical oxidation, advanced oxidation processes (AOPs) stand out for refinery-grade wastewater because they generate hydroxyl radicals — short-lived, highly reactive species that attack organic pollutants directly, breaking them down through hydrogen abstraction, radical addition, or electron transfer until the end products are water, carbon dioxide, and simple inorganic ions.

Hydroxyl radicals are a stronger oxidant than most of the chemistries used in conventional treatment, including potassium permanganate and hydrogen peroxide on their own. That’s what makes them effective against the recalcitrant fraction of refinery wastewater that biological treatment can’t reach.

AOPs generate hydroxyl radicals through several routes: Fenton’s reagent (hydrogen peroxide with an iron catalyst), photo-Fenton (the same chemistry driven further by UV light), photocatalysis using semiconductor materials, and anodic oxidation.

Anodic oxidation — also called electrochemical oxidation, or electrochemical advanced oxidation processes (EAOPs) — generates hydroxyl radicals directly at an electrode surface, using electrical current rather than added chemicals. It scales up in a straightforward way, needs little operator intervention once running, and avoids the chemical handling and secondary waste streams that come with reagent-based EAOPs.

The anode material determines how efficiently that oxidation happens. Boron-doped diamond (BDD) electrodes have become the preferred anode material for this kind of duty because of a specific electrochemical property: BDD has an unusually wide potential window, which lets it generate hydroxyl radicals that stay weakly adsorbed to the electrode surface rather than binding tightly to it. A weakly adsorbed radical is a more reactive one — it’s available to attack pollutant molecules instead of being consumed in side reactions at the electrode. BDD is also chemically and mechanically stable under the current densities this kind of treatment requires, which matters for electrode life in continuous operation.

Reaction Pathway

The results below come from bench-scale testing performed on real refinery effluent from Shandong XXX Petrochemical Company, using a BDD electrode system built by Evoaeo. The following is the reaction pathway observed during that test program.

Hydroxyl radical generation at the anode:

H₂O → •OH + H⁺ + e⁻

Color removal:

BDD + H₂O → BDD(•OH) + H⁺ + e⁻

BDD(•OH) + R → BDD + mCO₂ + nH₂O

Ammonia oxidation at the electrode surface:

BDD(•OH)₃ + NH₄⁺ → BDD + NO₃⁻ + 3H⁺ + e⁻

Side reactions at high current density:

BDD(•OH) → BDD + ½O₂ + H⁺ + e⁻

2Cl⁻ → Cl₂ + 2e⁻

The side reactions matter operationally: at excessive current density, part of the applied charge goes into oxygen evolution and chlorine formation instead of pollutant destruction, which lowers current efficiency. Keeping current density within the right window is one of the main levers for getting good removal performance without wasting energy on these side pathways.

Test Results

Running the BDD anodic oxidation system on the Shandong XXX Petrochemical Company sample at 43°C and pH 5, chemical oxygen demand (COD) dropped from 11450 mg/L to 362 mg/L in 172 minutes — a 96.84% reduction.

Parameter	Value
Initial COD	11450 mg/L
Final COD	362 mg/L
COD reduction	96.84%
Treatment time	172 minutes
Temperature	43°C
pH	5

Takeaway

For refinery wastewater carrying persistent organic load that conventional biological treatment can’t fully break down, BDD-based electrochemical oxidation offers a chemical-free path to a substantial COD reduction in a short treatment window. The mechanism — direct hydroxyl radical attack at the electrode surface — is what allows it to reach pollutants that resist biodegradation, and the operating conditions used here (mild acidic pH, moderate temperature) are practical to hold at full scale.

The next step from this bench result is pilot-scale validation under continuous flow, to confirm electrode life and current efficiency hold up outside a controlled lab run.