Electrochemical oxidation using MMO (Mixed Metal Oxide) titanium anodes is an environmentally friendly technology for treating sulfide-containing wastewater. Such wastewater—generated in sectors including oil and gas extraction, petrochemical refining, non-ferrous metal smelting, textile printing and dyeing, leather tanning, pharmaceuticals, and landfill leachate management—contains pollutants such as S²⁻, HS⁻, H₂S, mercaptans, thioethers, and polysulfides. Wstitanium has developed a comprehensive range of titanium anode products featuring various coating systems and structural designs. These anodes are optimized for catalytic activity, resistance to sulfur-induced passivation, and overall stability, making them suitable for diverse operating conditions involving varying concentrations, pH levels, and salinity.
This page provides a systematic overview of the technical principles, coating systems, specifications, industry applications, selection guidelines, and project case studies regarding MMO titanium anodes used for sulfide catalysis.
MMO Titanium Anodes for Catalytic Treatment of Sulfide Wastewater
MMO titanium anodes facilitate the catalytic oxidation of sulfides through a synergistic combination of direct and indirect oxidation pathways. Sulfides are oxidized in stages—first to elemental sulfur and sulfites, and finally to non-toxic, harmless sulfates.
Direct Oxidation: Sulfide species (S²⁻, HS⁻) in the wastewater diffuse to and adsorb onto the catalytically active sites of the MMO coating, where they undergo direct electron transfer and oxidation.
Indirect Oxidation:Anode catalyzes the decomposition of water molecules to generate hydroxyl radicals (•OH) and active chlorine species (Cl₂, HClO, ClO⁻). These reactive species then engage in homogeneous oxidation reactions with the sulfides.
MMO Titanium Anode Coating for Sulfide Catalysis
The coating determines the anode’s catalytic activity, operating conditions, service life, and treatment performance. Specifically for the catalytic oxidation of sulfides, Wstitanium has developed four proven coating systems, precisely tailored to handle varying water qualities and specific reaction requirements. All coatings are produced using high-temperature thermal decomposition technology. A process involving multi-layer application and gradient sintering creates a uniform, dense, and porous catalytic layer, ensuring strong adhesion to the titanium substrate and an abundance of active sites.
RuO₂
The ruthenium coating utilizes ruthenium dioxide (RuO₂) as its active component. Its key characteristics include an extremely low chlorine evolution overpotential and excellent direct oxidation activity toward sulfides, making it suitable for treating sulfur-containing wastewater with high chloride concentrations. The molar ratio of RuO₂ to TiO₂ ranges from 30:70 to 40:60. The chlorine evolution overpotential is 1.13 V (vs. SHE), and the coulombic efficiency for sulfide oxidation reaches 60%. Applications include the treatment of sulfur-containing wastewater with high chloride levels—such as seawater, high-salinity produced water, and textile dyeing wastewater—as well as indirect sulfide oxidation systems dominated by the chlorine evolution reaction.
This is a specialized coating formulation developed by Wstitanium, optimized for the advanced treatment of high-concentration sulfide wastewater. The typical molar ratio is Ru:Sn:Ir = 50:30:20. SnO₂ serves to refine the coating’s grain structure and increase its specific surface area, thereby enhancing porosity and the number of active sites. IrO₂ significantly improves the coating’s oxidation resistance and boosts its oxygen evolution performance. Under operating conditions of 200 A/m² current density, an initial sulfide concentration of 300 mg/L, and a salt content of 2.5%, the RuO₂-SnO₂-IrO₂ titanium anode achieves a 92.7% sulfide removal rate after 60 minutes of operation. Applications include high-concentration sulfide wastewater and high-salinity, sulfur-containing wastewater. It is the preferred cost-effective coating solution for industrial sulfide wastewater treatment.
IrO₂ is the active phase, and Ta₂O₅ is the stable phase. The classic molar ratio is Ir:Ta = 70:30. Ta₂O₅ significantly improves the structural stability of the coating under strong oxidizing environments. The coating has a low oxygen evolution overpotential (approximately 1.25V vs SHE at 10mA/cm²) and excellent stability in acidic media. The University of Queensland, Australia, has demonstrated that IrO₂-Ta₂O₅ is the most stable system among all electrodes. Applicable scenarios: acidic sulfur-containing wastewater, high current density conditions, large-scale projects with long service life, and oxidation systems dominated by oxygen evolution reactions.
IrO₂-Ta₂O₅-SnO₂
Wstitanium is a modified iridium-based coating optimized for sulfide treatment, designed to balance catalytic activity and stability. SnO₂ increases the electron-hole concentration in the coating, enhancing the efficiency of hydroxyl radical generation and strengthening its indirect oxidation capacity for sulfides and organic pollutants. Under the same experimental conditions, this coating achieves a sulfide removal rate of 89.6% in 60 minutes, slightly lower than the ruthenium-iridium-tin system, but with a lower long-term operating loss rate. Applicable scenarios: recalcitrant organic wastewater containing sulfides, highly acidic and high-salt wastewater, and treatment systems requiring long-term maintenance-free operation.
Platinum-coated titanium anodes possess irreplaceable value in specialized and precise sulfide treatment applications. Prepared using electroplating or thermal decomposition techniques, the platinum-coated titanium anode exhibits a uniform, dense coating with strong adhesion. Its chemical properties are extremely stable, being virtually insoluble in any acid or alkali. It can catalyze both chlorine and oxygen evolution, operating stably across a wide pH range and in complex media. Platinum-coated titanium anodes exhibit strong resistance to poisoning, making them suitable for low-concentration, high-precision sulfide treatment applications, such as food-grade water treatment, sulfur-containing wastewater from pharmaceutical intermediates, and precision electrolysis equipment in laboratories.
MMO Titanium Anode Comparison
To compare the performance and applicability of different coating systems, we have compiled parameters for four core coating types in catalytic sulfide scenarios. All data are from the Wstitanium laboratory and publicly available authoritative literature, serving as a reference for the selection and design of MMO titanium anodes. Disclaimer: All data were obtained under constrained conditions and are not universally applicable.
| Performance Item | Ru-Ir-Sn | Ir-Ta | Ir-Ta-Sn | Pt |
|---|---|---|---|---|
| Active Components | RuO₂, IrO₂, SnO₂ | IrO₂, Ta₂O₅ | IrO₂, Ta₂O₅, SnO₂ | Pure Pt |
| Molar Ratio | Ru:Ir:Sn = 5:2:3 | Ir:Ta = 7:3 | Ir:Ta:Sn = 6:2:2 | 100% Pt |
| Coating Thickness | 8~15 μm | 10~20 μm | 12~22 μm | 2~10 μm |
| Chlorine Evolution Overpotential (10mA/cm², vs SHE) | ~1.12V | ~1.30V | ~1.26V | ~1.18V |
| Oxygen Evolution Overpotential (10mA/cm², vs SHE) | ~1.32V | ~1.25V | ~1.23V | ~1.45V |
| Operating Current Density | 50~1500 A/m² | 50~2000 A/m² | 50~2000 A/m² | 10~1000 A/m² |
| Sulfide Removal Rate (60min, 200A/m², initial 300mg/L) | ≥92% | ≥85% | ≥89% | ≥82% |
| pH Operating Range | 1~12 | 0~14 | 0~14 | 0~14 |
| Max Working Temperature | 80℃ | 90℃ | 90℃ | 100℃ |
| Max Tolerable Chloride Concentration | ≤100g/L | ≤80g/L | ≤80g/L | ≤120g/L |
| Max Tolerable Fluoride Concentration | ≤10mg/L | ≤20mg/L | ≤20mg/L | ≤30mg/L |
| Annual Coating Consumption Rate | 2~4 mg/A·year | 0.5~1.5 mg/A·year | 0.8~2 mg/A·year | 0.5~1 mg/A·year |
| Design Service Life | 3~8 years | 5~12 years | 5~10 years | 8~15 years |
| Anti-Sulfur Passivation Capacity | Good | Excellent | Excellent | Excellent |
| Core Advantages | Highest desulfurization efficiency, optimal cost-performance | Extreme stability, longest service life | Balanced catalytic activity & stability | Optimal chemical stability, high cleanliness |
| Applicable Scenarios | High-salinity high-concentration sulfide wastewater, textile printing & dyeing | Acidic sulfur-containing wastewater, high-load long-cycle projects | Refractory sulfur-containing organic wastewater, general working conditions | Food & pharmaceutical grade, precision laboratory applications |
| Relative Cost Level | ★★★☆☆ | ★★★★☆ | ★★★★☆ | ★★★★★ |
MMO Titanium Anodes for Catalytic Sulfide Applications
Sulfur-containing wastewater from different industries varies significantly in concentration, pH, coexisting pollutants, and treatment requirements. Wstitanium has developed tailored anode solutions for the specific water quality and treatment needs of various industries.
Oil & Gas
Oil & gas is one of the industries with the highest concentration and greatest difficulty in treating sulfide pollution. In produced water from oil and gas fields, the concentrations of hydrogen sulfide, mercaptans, sulfides, and sulfides are typically 100-500 mg/L. These pollutants are characterized by high salt, high oil content, and suspended solids. Mineralization can reach tens of thousands of mg/L. In refining wastewater, the concentrations of various pollutants such as sulfides, volatile phenols, ammonia nitrogen, and petroleum hydrocarbons are typically 50-200 mg/L. In desulfurization wastewater, especially in wet desulfurization processes, the concentrations of sulfides and thiosulfates are extremely high.
Wstitanium Solutions
For acidic smelting wastewater, Ru-Ir-Sn mesh titanium anodes are recommended. High-chloride ion environment generates active chlorine, which is then directly oxidized to achieve efficient desulfurization. In produced water from a 1200 m³/d gas field, the original sulfide concentration was 300 mg/L. After treatment, the effluent sulfide concentration was consistently below 10 mg/L, achieving a removal rate of 92%.
For refining wastewater containing phenols and sulfur, Ir-Ta-Sn plate titanium anodes are recommended, simultaneously achieving sulfide oxidation and phenolic organic matter degradation. After application in a 200 m³/d petrochemical project, the sulfide removal rate reached 96%, the phenol degradation rate 96%, and the effluent COD consistently remained below 50 mg/L.
Mining and Metallurgy
The mining and metallurgical industries are another major source of sulfide pollution. Wastewater generated from sulfide ore flotation contains residual sodium sulfide, xanthate, and other beneficiation reagents. Sulfide concentrations are typically 20-100 mg/L, and the wastewater also contains heavy metal ions and suspended solids. In smelting wastewater, acidic wastewater from copper, lead, zinc, and other mineral processing processes contains pollutants such as sulfides, arsenic, and heavy metals. It has high acidity (pH 2-5) and is highly corrosive. Sulfur-containing solutions are also found in hydrometallurgical leaching solutions produced during the leaching of sulfide ores.
Wstitanium Solutions
For acidic smelting wastewater, Ir-Ta titanium anodes are recommended. They achieve sulfide oxidation and partial heavy metal valence state control. The “Technical Specification for Copper Smelting Wastewater Treatment Engineering” has listed electrochemical oxidation as a recommended treatment technology.
For alkaline mineral processing wastewater, ruthenium mesh titanium anodes are recommended. They efficiently oxidize sulfides and mineral processing reagents such as xanthates, improving wastewater reuse rates. All electrodes feature a thickened titanium substrate and corrosion-resistant sealing design.
Dyeing and Textile Industry
Sulfur dyeing requires the use of large amounts of sodium sulfide as a reducing agent. This results in wastewater with high concentrations of sulfides, typically ranging from 100-300 mg/L. The wastewater has extremely high color, high COD concentration, and strong alkalinity (pH 9-11).
Wstitanium Solution
We recommend Ru-Ir coated mesh titanium anodes. These utilize chloride ions in the wastewater to generate active chlorine, achieving sulfide oxidation and decolorization. For example, a 500 m³/d dyeing plant had influent sulfides of 180 mg/L and a color intensity of 800 times. After electrochemical treatment, the sulfide removal rate reached 94%, and the decolorization rate reached 95%. The mesh structure effectively improves mass transfer efficiency and reduces electrode clogging caused by elemental sulfur deposition.
Pharmaceuticals and Fine Chemicals
In the pharmaceutical and fine chemical industries, sulfur-containing wastewater has a complex composition. Wastewater generated during the production of pharmaceutical intermediates such as sulfonamides, thiols, thioethers, and disulfides typically contains large amounts of recalcitrant organic sulfides. This wastewater is highly biotoxic and can inhibit the activity of microorganisms in biological systems.
Wstitanium Solution
We recommend Ir-Ta-Sn titanium anodes, which utilize a synergistic effect of direct oxidation and indirect oxidation via hydroxyl radicals to mineralize and decompose sulfides in wastewater into sulfates, carbon dioxide, and water. As a pretreatment technology, it breaks down the structure of toxic sulfides, improving the biodegradability of the wastewater. It can also be used as an advanced treatment technology to ensure that effluent COD and other pollutants meet discharge standards. It does not leach heavy metal ions into the wastewater.
Leather and Fur Processing
The wastewater generated during the liming and dehairing process has extremely high sodium sulfide concentrations, reaching thousands of mg/L, and also contains large amounts of protein, oil, and suspended solids. Sulfide concentrations in tanning wastewater are typically 100-500 mg/L, with high COD.
Wstitanium Solution
We recommend pretreatment with plate titanium anodes to oxidize the high-concentration sulfides into elemental sulfur for recovery. For combined wastewater, a mesh titanium anode electrochemical system is used to completely oxidize the sulfides into sulfates, while simultaneously removing some COD and color. Compared to traditional air oxidation methods, electrochemical oxidation is several times faster, requires less space, has no waste gas emissions, and is more environmentally friendly.
Landfill Leachate
Leachate and anaerobic treatment effluent commonly contain sulfides. This causes pipe corrosion and foul odor. In landfill leachate, anaerobic fermentation produces large amounts of hydrogen sulfide and mercaptans, accompanied by high ammonia nitrogen, high COD, and high salinity, resulting in significant water quality fluctuations. In municipal wastewater anaerobic effluent, sulfate reduction produces sulfides.
Wstitanium Solution
Iridium-tantalum coated titanium anodes are recommended. They operate stably in complex water conditions with high ammonia nitrogen and high salinity, simultaneously achieving sulfide oxidation, ammonia nitrogen removal, and COD degradation. This effectively solves the problems of hydrogen sulfide corrosion and foul odor in wastewater pipe networks, improves the environmental quality of the plant area, and extends the service life of pipelines.
Custom Titanium Anode Specifications
To help you quickly understand Wstitanium’s custom-manufactured titanium anodes, we have compiled the standard and custom parameters for mainstream anode types.
| Titanium Anode Type | Titanium Substrate | Standard Sizes | Custom Sizes | Coating Thickness | Connection Mode |
|---|---|---|---|---|---|
| Plate Anode | Gr1 / Gr2 Titanium Plate | Thickness 0.5–3mm; Length & Width ≤ 1200×2000mm | Thickness 0.3–10mm; Extra large sizes available by splicing | 8–20 μm | Titanium conductive lugs, titanium conductive rods, threads |
| Mesh Anode | Gr1 / Gr2 Expanded Titanium Mesh | Thickness 0.5–1.5mm; Mesh opening 3×6 ~ 6×12mm | Thickness 0.3–3mm; Custom special mesh apertures | 8–18 μm | Titanium frame, conductive rod, welded terminals |
| Tubular Anode | Gr1 / Gr2 Seamless Titanium Tube | Pipe diameter Φ10–Φ60mm; Length ≤ 3000mm | Pipe diameter Φ3–Φ200mm; Extra-long tubes can be connected in series | 10–20 μm | Threads, flanges, welded conductive rods |
| Rod Anode | Gr1 / Gr2 Titanium Rod | Diameter Φ3–Φ50mm; Length ≤ 2000mm | Diameter Φ1–Φ100mm; Customizable length | 8–15 μm | External threads, internal threads, welded terminals |
| Strip Anode | Gr1 / Gr2 Titanium Strip | Thickness 0.2–1mm; Width 10–100mm | Thickness 0.1–2mm; Customizable width | 5–12 μm | Welded terminals, crimp terminals |
| Basket Anode | Gr1 / Gr2 Titanium Mesh + Titanium Frame | Diameter Φ50–Φ300mm; Height 100–500mm | Any dimensions customizable on demand | 8–15 μm | Central conductive rod, top wiring terminal |
Customized Solutions for High-Sulfur Operations
For operations with sulfide concentrations >500mg/L and a tendency for elemental sulfur deposition under alkaline conditions, an anti-sulfur passivation modified coating is recommended. Mesh or grid structures are preferred to enhance water flow scouring and improve self-cleaning performance.
High-Fluoride Wastewater Solutions
A fluoride-resistant coating is used to increase coating density and resist fluoride ion corrosion. A high-purity titanium substrate prevents localized corrosion caused by impurities. Optimized operating parameters, controlling current density and pH, reduce fluoride ion activity.
Long-Life Customized Solutions
For large-scale projects requiring unattended operation and maintenance-free operation for over 5 years, a high-load iridium-tantalum thickened coating is used. A thickened titanium substrate and conductive structure prevent substrate corrosion and joint overheating.
Coating Repair
Wstitanium offers professional coating repair services. The titanium substrate undergoes surface treatment and coating sintering, achieving performance identical to new products. Repair costs are only 50%-70% of new product costs.
Titanium Anode Selection Guide for Catalytic Sulfide Treatment
Correct selection is the prerequisite for ensuring efficient and long-life operation of anodes. Based on experience from hundreds of projects, Wstitanium has summarized a scientific selection method to help you choose the most suitable titanium anode product for your specific operating conditions.
Selection Principles
Based on the target processing efficiency and throughput, select a coating and area that matches the catalytic activity and current carrying capacity to avoid insufficient or excessive performance.
Optimal Life Cycle Cost Principle: Do not only look at the purchase price; comprehensively evaluate the total life cycle cost by considering service life, energy consumption, and maintenance costs.
Operating Parameters
Before selecting a model, you need to clarify the following core parameters. The more detailed the parameters, the more accurate the selection will be:
- Sulfide concentration (S²⁻, HS⁻, etc.)
- pH value and fluctuation range
- Cl⁻, SO₄²⁻, F⁻, etc. concentration
- COD, heavy metals, oils, suspended solids, etc.
- Inlet water temperature
- Designed treatment capacity
- Target effluent sulfide concentration
- Current density and voltage
- Expected design life
- Continuous operation / Intermittent operation
- Electrolyzer dimensions
- Electrolyzer spacing design
- Anode installation
- Matching rectifier
Coating System
Coating selection is the core of the selection process, primarily based on the media environment and the main reaction type.
Alkaline high-chlorine sulfur-containing wastewater (pH > 7, Cl⁻ > 1000 mg/L): Ruthenium-iridium-tin coating is preferred. It utilizes high chloride ions to generate active chlorine for synergistic oxidation, resulting in the highest desulfurization efficiency and best cost-effectiveness. Typical scenarios: gas field produced water, dyeing and printing wastewater, leather tanning wastewater.
Acidic sulfur-containing wastewater (pH < 5): Iridium-tantalum coating is preferred. It exhibits excellent stability in strongly acidic environments, has a long lifespan, and avoids the rapid dissolution of ruthenium-based coatings in strong acids. Typical scenarios: mining and smelting wastewater, acidic desulfurization waste liquid.
Neutral/weakly alkaline, complex sulfur-containing wastewater: Iridium-tantalum-tin coating is preferred. It offers a balanced activity and stability, adapts to water quality fluctuations, and has strong versatility. Typical scenarios: petrochemical wastewater, pharmaceutical wastewater, landfill leachate.
Food/pharmaceutical grade wastewater with high cleanliness requirements: Platinum-coated titanium anode is selected. It exhibits the strongest chemical stability and poses no risk of heavy metal leaching.
Note: When the fluoride ion concentration in the wastewater is >5 mg/L, a fluoride-resistant modified coating must be used. Ordinary MMO coatings are strictly prohibited, as fluoride ions will damage the passivation film on the titanium substrate. This will lead to coating blistering and peeling, and rapid anodic failure.
Effective Anode Area Calculation
Effective Area (㎡) = Total Processing Current (A) ÷ Design Current Density (A/㎡)
The total processing current needs to be calculated based on the treated water volume, sulfide concentration, and current efficiency. Wstitanium technical engineers can assist you with the calculation. Recommended design current density for sulfide treatment: 100-300A/m² for normal operation, 300-500A/m² for high concentration operation. Long-term operation exceeding 1000A/m² is not recommended.
Quantity and Installation
Determine the size of a single anode and the total number of anodes based on the electrolytic cell size and electrode spacing. A electrode spacing of 3-10cm is recommended. Smaller spacing results in lower energy consumption, but increases installation difficulty and short-circuit risk.
Service Life Estimation
Formula: Design Lifespan (Years) = Precious Metal Load (g/㎡) ÷ (Annual Loss Rate (g/A・Year) × Operating Current Density (A/㎡)). The annual loss rate is closely related to the coating and operating conditions. We will provide an accurate reference value for the loss rate based on your specific working conditions.
Recommended Table for Sulfide Wastewater Treatment
To help you quickly make a decision, we have compiled selection recommendations for typical sulfide treatment scenarios. Disclaimer: This table is for reference only and should not be used as the sole basis for decision-making. The final interpretation right belongs to Wstitanium.
| Application | Sulfide Concentration | pH Range | Recommended Coating | Recommended Anode Shape | Recommended Current Density |
|---|---|---|---|---|---|
| Oil & Gas Produced Water | 100–500 mg/L | 7–9 | Ru-Ir-Sn | Mesh / Plate | 150–300 A/m² |
| Refinery Comprehensive Wastewater | 50–200 mg/L | 6–8 | Ir-Ta-Sn | Plate / Mesh | 100–250 A/m² |
| Acid Metallurgical Wastewater | 20–100 mg/L | 2–5 | Ir-Ta | Plate | 200–400 A/m² |
| Textile Printing & Dyeing Sulfide Wastewater | 100–300 mg/L | 9–11 | Ru-Ir-Sn | Mesh | 100–200 A/m² |
| Tannery Comprehensive Wastewater | 100–500 mg/L | 8–11 | Ru-Ir-Sn | Mesh / Grid | 150–250 A/m² |
| Pharmaceutical Sulfur-Containing Wastewater | 50–300 mg/L | 4–10 | Ir-Ta-Sn | Mesh | 200–400 A/m² |
| Landfill Leachate | 20–150 mg/L | 6–9 | Ir-Ta-Sn | Mesh | 200–500 A/m² |
| High-Concentration Desulfurization Waste Liquid | >1000 mg/L | 8–12 | Sulfur Passivation Resistant Ru-Based Coating | Plate | 300–500 A/m² |
Misconception 1: Higher current density is always better
Many customers deliberately increase the design current density and reduce the anode area to reduce anode procurement costs. In reality, exceeding the optimal current density leads to a sharp increase in oxygen evolution side reactions. Current efficiency drops significantly, energy consumption rises dramatically, and coating wear increases exponentially. Anode lifespan is drastically shortened.
Misconception 2: Choosing the cheapest ruthenium coating
While ruthenium-based coatings are cheaper per unit, their wear rate is much higher than iridium-based coatings in acidic, high-oxygen environments. For acidic wastewater, high current density, and continuous operation scenarios, ruthenium-based coatings may need replacement every 1-2 years, while iridium-based coatings can last 5-8 years. The overall cost of iridium-based coatings is actually lower.
Misconception 3: Ignoring fluoride ions
Fluoride ions are a “killer” of titanium anodes. Even a few mg/L of fluoride ions can damage the passivation film on the titanium substrate over long-term operation. This causes coating blistering and peeling. Before selection, it is essential to confirm the fluoride ion concentration; if it exceeds the limit, a fluoride-resistant coating must be used.
Misconception 4: Ignoring Sulfur Passivation
High concentrations of sulfides electrolyzing under alkaline conditions readily generate elemental sulfur, which deposits on the electrode surface. When selecting a coating, the passivation risk must be assessed based on the sulfide concentration, and an anti-passivation coating should be chosen.
Misconception 5: Ignoring Precious Metal Content
The lifespan of a coating depends primarily on the loading and composition of precious metals, not simply its thickness. All Wstitanium products clearly indicate their precious metal loading.
Project Cases
Wstitanium’s MMO titanium anodes for catalytic sulfides have been successfully applied in hundreds of projects across dozens of industries worldwide. Below are a few representative project case studies. All data is from actual project operation records.
Case Study 1: Sulfide Treatment in Produced Water from a Gas Field
The produced water contained excessive levels of sulfides and COD, failing to meet reinjection and discharge standards. The client required a stable and reliable pretreatment technology to efficiently remove sulfides.
- Sulfides: 280 ~ 320 mg/L
- Chloride: 12000 ~ 15000 mg/L
- Petroleum hydrocarbons: 30 ~ 50 mg/L
- Mineralization: 25000 ~ 30000 mg/L
- COD: 400 ~ 500 mg/L
- pH: 7.5 ~ 8.5
- Temperature: 30 ~ 40℃
Wstitanium Solution
- Ru-Ir-Sn mesh titanium anode.
- Total effective area: 480㎡
- Design current density: 200A/m²
- Cell voltage: 3.0-3.5V
Results
- Effluent sulfide concentration ≤ 10mg/L
- Power consumption per ton of water: 3.2kWh
- Sulfide removal rate > 92%
- COD removal rate > 30%
Case Study 2: Advanced Treatment of Refining Wastewater
The wastewater from a large integrated refining and chemical plant in Indonesia still failed to meet emission standards for COD, sulfides, and volatile phenols. The existing Fenton advanced treatment process consumed large quantities of reagents and generated significant amounts of hazardous iron sludge. The client sought an electrochemical alternative to Fenton to achieve stable compliance with standards while reducing costs and increasing efficiency.
- Sulfides: 80 ~ 120 mg/L
- Volatile phenols: 50 ~ 80 mg/L
- COD: 300 ~ 500 mg/L
- Ammonia nitrogen: 30 ~ 50 mg/L
- pH: 6.0 ~ 8.0
- Chloride ions: 800 ~ 1500 mg/L
Wstitanium Solution
- Ir-Ta-Sn plate titanium anode
- Effective area: 96㎡
- Four pieces of plates in parallel
- Panel spacing: 5cm
- Current density: 250A/m²
- Cell voltage: 2.8-3.2V
- Preset COD: ≤50mg/L
Results
- Volatile phenol degradation rate ≥ 96%
- Effluent volatile phenols < 0.5 mg/L
- Sulfide removal rate > 96%
- COD 40-48 mg/L
Case 3: Sulfur Dye Wastewater Treatment
A dyeing factory in Malaysia primarily uses sulfur dyes. The wastewater has a high concentration of sulfides and a deep color. The existing “hydrolysis acidification + contact oxidation” technology had long resulted in effluent that failed to meet standards for color and sulfide content.
- Sulfide: 150 ~ 200 mg/L
- COD: 500 ~ 700 mg/L
- Color: 600 ~ 1000 times
- pH: 9.0 ~ 10.5
- Chloride: 2000 ~ 3000 mg/L
Wstitanium Solution
- Ru-Ir mesh titanium anode
- Effective area: 320㎡
- Current density: 150A/m²
Results
- Sulfide removal rate > 94%
- Effluent sulfide < 5 mg/L
- Decolorization rate > 95%
- COD removal > 40%
Frequently Asked Questions
A: An applied electric field catalyzes an oxidation reaction on the anode surface, which can be either direct or indirect oxidation. Direct oxidation occurs when sulfides are adsorbed at the active sites on the anode and lose electrons, thus being oxidized. Indirect oxidation involves the anode catalyzing water or chloride ions to generate hydroxyl radicals, active chlorine, and other strong oxidizing substances, which oxidize the sulfides. Ultimately, the sulfides are gradually oxidized into non-toxic sulfates.
**No External Reagents Required:** No oxidants such as sodium hypochlorite, ozone, or hydrogen peroxide are needed; only electricity is consumed.
**High Controllability:** The oxidation intensity and reaction rate can be flexibly controlled by adjusting the current and voltage.
**No Secondary Pollution:** No large amounts of chemical sludge are produced; oxidation is thorough and environmentally friendly.
**Low Operating Costs:** In medium-to-high concentration scenarios, the operating costs are significantly lower than chemical oxidation methods, and the treatment efficiency is higher.
A: The key factors for choosing between ruthenium and iridium-based coatings are the wastewater’s pH, chloride ion concentration, and operating conditions.
1. Scenarios where ruthenium-based coatings are preferred: alkaline or neutral wastewater, high chloride ion content (>1000 mg/L), high sulfide concentration, pursuit of maximum treatment efficiency, intermittent operation, and limited budget. Typical examples include dyeing and printing wastewater, gas field produced water, and leather tanning wastewater.
2. Scenarios where iridium-based coatings are preferred: acidic wastewater (pH < 5), high current density continuous operation, requirements for ultra-long service life, and complex wastewater composition with strong oxidizing properties. Typical examples include mining and smelting wastewater, pharmaceutical wastewater, and large-scale, long-cycle projects.
In short: Choose ruthenium-based for efficiency, iridium-based for lifespan; choose ruthenium-based for high chloride levels, and iridium-based for strong acids. If you are unsure, please provide your water quality parameters, and Wstitanium’s technical engineers will recommend the optimal solution for you.
A: Fluoride ions are highly corrosive to titanium substrates. They damage the TiO₂ passivation film on the titanium surface, causing the coating to lose its adhesion foundation and blister and peel off. Therefore, ordinary MMO titanium anodes are not suitable for fluoride-containing wastewater.
1. When the fluoride ion concentration is <5mg/L, ordinary MMO anodes can be used with caution. The current density should be appropriately reduced, and the pH should be controlled to be no lower than 2 to slow corrosion.
2. When the fluoride ion concentration is 5-50mg/L, a Wstitanium fluoride-resistant modified coating must be used. This prevents fluoride ions from contacting the titanium substrate and ensures the anode’s service life.
3. When the fluoride ion concentration is >50mg/L, it is not recommended to use titanium-based anodes. Other electrode materials, such as nickel electrodes, should be considered.
Special Reminder: Many customers have suffered huge losses because they overlooked trace amounts of fluoride ions in their wastewater, causing their anodes to fail within just a few months. Before selecting a model, be sure to test the fluoride ion concentration and inform Wstitanium in advance.
A: Energy consumption is related to various factors such as sulfide concentration, current efficiency, current density, and electrode spacing.
Low sulfide concentration (below 50 mg/L): Approximately 0.5-1.5 kWh per ton of water.
Medium sulfide concentration (100-300 mg/L): Approximately 2-4 kWh per ton of water.
High sulfide concentration (above 500 mg/L): Approximately 5-10 kWh per ton of water.
A: It can be treated, but direct one-step oxidation to sulfate is not recommended due to poor economic efficiency. A staged treatment scheme is recommended for high-concentration sulfide wastewater:
Primary controlled oxidation: Controlling current density and reaction time oxidizes sulfides to elemental sulfur, which is then recovered through flotation or filtration, achieving sulfur resource recovery. This step can remove 80%-90% of sulfides with low energy consumption.
Secondary deep oxidation: Completely oxidizes the remaining low-concentration sulfides to sulfate, ensuring the effluent meets standards.
The overall operating cost of this staged treatment is far lower than direct complete oxidation.
A: Absolutely. MMO titanium anodes are highly compatible with alkaline sulfide wastewater. This is currently the mainstream treatment technology for alkaline sulfur-containing wastewater.
Ruthenium-based coating: Suitable for pH 1-12, exhibiting good stability in alkaline environments. It is the preferred choice for alkaline sulfide wastewater.
Iridium-based coating: Suitable for pH 0-14, operating stably across the entire pH range. It has a longer lifespan in alkaline environments.
Under alkaline conditions, sulfides mainly exist in HS⁻ and S²⁻ forms, making them more susceptible to electrochemical oxidation. It should be noted that strong alkalinity (pH > 12) and high concentrations can easily lead to elemental sulfur deposition, requiring careful electrode cleaning design.
A: There’s no absolute “better” or “worse,” only the appropriate application. Both have their advantages.
Plate anode advantages: smooth surface for easy cleaning, uniform current distribution, high mechanical strength, suitable for high-concentration sulfides, easy passivation, and frequent cleaning.
Mesh anode advantages: high mass transfer efficiency, large specific surface area, low consumable cost, good anti-clogging properties, suitable for dynamic flow reactors, low to medium concentration wastewater containing suspended solids, and higher treatment efficiency.
The choice depends mainly on your reactor structure, sulfide concentration, and maintenance requirements. If the sulfide concentration is very high and the passivation risk is high, plate anodes are preferred. If you prioritize treatment efficiency and cost, mesh anodes are preferred. Many projects also combine both, using different structures for different sections.
A: No. Coating thickness and lifespan are not linearly related. Blindly increasing thickness not only significantly increases costs but may also have negative effects.
1. Excessive coating thickness leads to increased internal stress, reduced adhesion between the coating and the substrate, and a higher likelihood of cracking and peeling.
2. Excessively thick coatings have low internal porosity. The precious metals in the inner layer cannot contact the electrolyte, resulting in an ineffective load and wasted precious metals. Costs increase, but lifespan does not increase proportionally.
3. Coating conductivity decreases with increasing thickness, which in turn increases cell voltage and energy consumption.
Wstitanium will recommend the optimal coating thickness and precious metal load based on your design lifespan and operating conditions. For typical industrial applications, a thickness of 8-20μm is sufficient. For ultra-long lifespan applications, 20-30μm can be achieved.
A: The optimal current density for sulfide treatment needs to be determined based on the concentration, water quality, and target efficiency.
The generally recommended range is 100-500 A/m².
Low concentration, deep treatment: 50-150 A/m².
Medium concentration, routine treatment: 150-300 A/m².
High concentration, high load: 300-500 A/m².
Long-term operation above 1000 A/m² is not recommended, as excessively high current densities can lead to the following problems:
1. Decreased current efficiency: Excessively high current can exacerbate side reactions such as oxygen and chlorine evolution. A large amount of electrical energy is consumed in these side reactions, reducing the current efficiency for sulfide oxidation. This results in a significant increase in energy consumption.
2. Accelerated coating wear: Doubling the current density can increase the coating wear rate several times over, significantly shortening anode life.
3. Severe heat generation: High currents result in significant heating of the electrode and solution. Excessive temperature will accelerate coating dissolution and may even damage sealing and insulating components.
4. Accelerated passivation: If the reaction rate is too fast, the large amount of elemental sulfur generated cannot diffuse quickly enough and is more likely to deposit on the electrode surface, accelerating passivation.
