In the treatment of leather factory wastewater, the selection of coal-based or wood powder Activated carbon requires comprehensive consideration of factors such as adsorption performance, cost, and process adaptability. The following is a detailed analysis:
Main pollutants in leather factory wastewater:
1. Organic pollutants (accounting for about 60–80%)
Protein and fat
Source: Raw leather dehairing, liming and other processes, containing a large amount of hair degradation products (keratin) and animal fat.
Hazards: COD (chemical oxygen demand) as high as 3000–8000 mg/L, easy to ferment and produce odor.
Tanning agent residues
Chrome tanning agent: Trivalent chromium (Cr³⁺) concentration 50–200 mg/L, highly toxic and easy to accumulate.
Vegetable tanning agent: Tannic acid substances, resulting in deep color (dilution multiple 500–2000 times) and difficult to degrade COD.
Dyes and auxiliaries
Contains azo dyes, sulfur dyes, etc., with significant color (pH sensitive), and some contain carcinogenic aromatic amines.
2. Inorganic pollutants
Sulfide (S²⁻)
Comes from the unhairing process (Na₂S or sodium hydrosulfide), with a concentration of 50–300 mg/L, highly toxic and corrosive to pipes.
Chloride (Cl⁻) and sulfate (SO₄²⁻)
Brought in by washing salted hides, with a concentration of up to 2000–5000 mg/L, inhibiting microbial activity.
Ammonia nitrogen (NH₃-N)
Produced by protein decomposition, with a concentration of 100–300 mg/L, aggravating eutrophication of water bodies.
3. Suspended solids (SS) and special substances
Leather scraps: particle size 0.1–2 mm, SS concentration 800–1500 mg/L.
Surfactant: Residues from the degreasing process, easy to produce foam, interfering with the treatment process.
Emerging pollutants: Perfluorinated compounds (PFCs, from waterproofing agents) were detected in some factories.
5. Summary of water quality characteristics
Parameter Typical range Exceeding the standard multiple (GB 8978–1996)
pH 8–12 (mainly alkaline) 1.5–3 times
COD 3000–8000 mg/L 10–20 times
BOD₅ 1500–4000 mg/L 8–15 times
Total chromium 10–50 mg/L 20–100 times
V. Difficulties and trends in treatment
Chromium recovery: Advanced technology has achieved 90% chromium recycling (such as membrane separation + precipitation method).
Deep decolorization: Ozone oxidation and activated carbon adsorption are required (refer to the previous activated carbon selection suggestions).
Low-carbon treatment: From 2025, the EU will require leather factories to use biogas for power generation (COD energy conversion rate ≥ 30%).
How to choose a suitable activated carbon?
1. Comparison of adsorption performance
Coal-based powder Activated carbon
Advantages: The pore structure is mainly microporous, with a large specific surface area (usually 800–1200 m²/g), strong adsorption capacity for small molecular organic matter (such as dyes, phenols) and heavy metal ions, and suitable for treating leather wastewater with complex components (including tanning agents, dyes, oils, etc.).
Limitations: The adsorption efficiency of larger molecules (such as some high-molecular tanning agents) is low.
Wood powder Activated carbon
Advantages: The mesoporous structure is more developed, suitable for adsorbing large molecular organic matter (such as lignin, protein residues), and performs well in decolorization and COD removal.
Limitations: The specific surface area is usually low (500–900 m²/g), and the adsorption of heavy metals is weaker than coal-based carbon.
2. Economic efficiency and source
Coal-based charcoal: The raw material is coal, which is relatively cheap (about 5,000–8,000 yuan/ton), but due to the limitation of coal resources, it is less environmentally friendly (high energy consumption in production).
Wood-based charcoal: The raw material is wood or coconut shell, which is highly renewable, but the cost is relatively high (about 8,000–12,000 yuan/ton), and is suitable for scenarios with strict environmental protection requirements.
3. Process adaptability
Coal-based charcoal: More suitable for the physical and chemical treatment stage (such as adding after coagulation and sedimentation), used for deep removal of soluble pollutants.
Wood-based charcoal: Used in the later stage of biochemical treatment (such as after the activated sludge method), it can effectively degrade difficult-to-decompose organic matter and reduce sludge toxicity.
4. Other factors
pH adaptability: Both are acid and alkali resistant, but wood-based charcoal is more stable under acidic conditions (suitable for the weakly acidic environment common in leather wastewater).
Regeneration difficulty: Coal-based charcoal has a higher regeneration rate (can be reused through thermal regeneration), while wood-based charcoal has low mechanical strength and is easily lost during regeneration.
5. Comprehensive recommendations
Prefer coal-based charcoal: if the wastewater is mainly composed of small molecular pollutants and heavy metals, and the budget is limited.
Prefer wood-based charcoal: if it is necessary to focus on treating large molecular organic matter, decolorization, or the company has sustainable development requirements.
Combined use: For high-concentration wastewater, wood-based charcoal can be used to adsorb large molecules first, and then coal-based charcoal can be used to treat small molecular pollutants.
Supplementary explanation: It is recommended to conduct a small test before actual selection, and optimize the dosage (usually 50–200 mg/L) and contact time in combination with water quality test data (such as COD, BOD, chromaticity, heavy metal content).
The following is a summary of the separation and recovery methods for used activated carbon (saturated carbon) in leather factory wastewater. Combined with the latest engineering practices and environmental protection requirements in 2025, the key technologies and precautions are explained step by step:
1. Pretreatment stage: initial separation of activated carbon and sewage
Gravity sedimentation method
Applicable scenarios: powdered carbon (PAC) or granular carbon (GAC) with activated carbon particle size > 50μm.
Operation parameters: 30–60 minutes of standing time, more than 80% of suspended activated carbon can be removed.
Efficiency enhancement measures: Add 0.1–0.5 mg/L polyacrylamide (PAM) to accelerate flocculation and sedimentation.
Screen filtration
Equipment selection:
Vibrating screen (100–200 mesh) for coarse separation;
Microfiltration membrane (pore size 1–10μm) for fine recovery.
Note: Backwashing is required to prevent membrane contamination, and the recovery rate can reach 90%.
2. Core separation technology (selected according to the form of activated carbon)
A. Powdered activated carbon (PAC) separation
Centrifugal separation:
Use a horizontal screw centrifuge (speed 3000–5000 rpm), and the moisture content after separation is ≤40%.
Cost: about ￥0.8–1.2/ton of sewage (market price in 2025).
Dissolved air flotation (DAF):
Introduce microbubbles (diameter 30–50μm), PAC adheres and floats and then scrapes off, suitable for low-density carbon.
B. Granular activated carbon (GAC) separation
Multi-media filter:
Filled with quartz sand/anthracite, intercepts GAC and automatically backwashes and regenerates, extending the life by 30%.
Magnetic separation (modified carbon):
If the activated carbon is loaded with magnetic materials (such as Fe₃O₄), it can be quickly separated by a magnetic separator (efficiency > 95%).
3. Deep treatment: activated carbon regeneration and disposal
Thermal regeneration method (applicable to high-value carbon)
Process: drying (105℃) → high temperature activation (600–900℃, inert atmosphere) → screening.
Regeneration rate: coal-based carbon can reach 70%, wood-based carbon is about 50%.
Chemical regeneration
Acid/alkali washing: treatment with 1M HCl or NaOH to remove metal ions or organic matter (such as chrome tanning agent).
Fenton oxidation: H₂O₂+Fe²⁺ degrades adsorbed organic matter and restores porosity.
More information about the activated carbon please contact Joyce:
JoyceSales ManagerZhengzhou Yihang Water Purification Materials Co.,Ltd Cellphone / WhatsApp/Wechat: +86 19943903427E-mail : joyce@yihangcarbon.comWebsite: www.cnhnyihang.comwww.yihangcarbon.com
