I. Main Sources and Characteristics of Palm Oil Mill Wastewater

Wastewater Sources

Mainly originate from the palm fruit pressing, shelling, cooking, and refining processes, including:

Pressing wastewater: Contains large amounts of oil, pulp residue, and sugars;

Washing wastewater: Contains sediment, peel debris, and a small amount of oil;

Refining wastewater: Contains fatty acids and alkali (generated during the neutralization process).

Wastewater Characteristics

High organic matter concentration: COD can reach 5,000-30,000 mg/L, and BOD can reach 2,000-15,000 mg/L;

Oil and suspended solids: Oil content is typically 50-500 mg/L, and suspended solids (SS) can reach 1,000-5,000 mg/L;

Acidic or alkaline: The pH value fluctuates widely (4-10);

High water temperature: During production, wastewater temperatures often reach 40-60°C, which is conducive to microbial activity, but fluctuations must be controlled. II. Core Processes of Wastewater Treatment

(I) Pretreatment: Removal of Suspended Matter, Grease, and Water Quality Conditioning

The purpose of pretreatment is to reduce the load on subsequent treatment units, avoid pipe blockage, and prevent microbial inhibition.

Screens and Grit Chambers

Screens: Intercept large impurities (such as peels, shells, and fibers) to prevent equipment blockage.

Grit Chambers: Remove inorganic particles such as silt and sand, reducing wear and tear on subsequent treatment processes.

Oil Separation and Demulsification

Grease Separators: Utilize the density difference between oil and water to separate floating oil (free oil), achieving a removal rate of 60%-80%.

Demulsification: For emulsified oil (oil that is difficult to separate naturally), demulsifiers (such as PAC or PAM) are added. This coagulation action breaks down the oil film, causing the oil to agglomerate and float.

Equalizing Tanks: Balance wastewater volume and quality (such as pH, temperature, and pollutant concentration) to avoid impact on subsequent biochemical treatment.

Aeration and agitation can prevent the sedimentation of suspended matter and provide a preliminary degradation of some volatile organic compounds. (II) Main Treatment: Degradation of High-Concentration Organic Matter (Primarily Biochemical Treatment)

Palm oil mill wastewater has high biodegradability (BOD/COD ratio typically > 0.5), making it suitable for biochemical treatment. Common combinations are as follows:

Anaerobic Biological Treatment

Principle: Anaerobic microorganisms (such as methanogens) decompose organic matter into methane, carbon dioxide, and other substances in an oxygen-free environment, significantly reducing COD (removal rates can reach 70%-90%).

Common processes include UASB (upflow anaerobic sludge blanket) and IC (internal circulation anaerobic reactor). These processes are suitable for treating high-concentration organic wastewater and can recover biogas (which can be used as energy). Aerobic Biological Treatment

Principle: Under aerobic conditions, aerobic microorganisms (such as activated sludge and biofilms) further decompose residual organic matter into carbon dioxide and water.

Common Processes:

Activated sludge process (such as sequencing batch reactors (SBRs) and oxidation ditches): Suitable for low- to medium-concentration wastewaters, with strong resistance to shock loads.

Biofilm process (such as biofilters and contact oxidation tanks): Microorganisms are attached to a carrier, resulting in high treatment efficiency and low sludge production.

Combination: An anaerobic + aerobic process is typically used in tandem, initially reducing high COD concentrations anaerobically, followed by aerobic treatment of residual organic matter. Total COD removal rates can exceed 95%. (III) Advanced Treatment: Removing Residual Pollutants and Meeting Discharge or Reuse Standards

If wastewater reuse is required (e.g., for plant landscaping, equipment cleaning) or to meet strict discharge standards (e.g., discharge into sensitive water bodies), advanced treatment is required:

Coagulation/Sedimentation/Filtration

Adding coagulants (e.g., PAC) and flocculants (PAM) removes residual suspended solids, colloids, and some dissolved organic matter in the water;

Combining sand filtration with activated carbon filtration further reduces SS and color.

Membrane Separation Technologies

Such as ultrafiltration (UF) and reverse osmosis (RO) remove small organic molecules, salts, and microorganisms from water, producing high-quality recycled water suitable for reuse. However, these technologies are costly and require pretreatment to prevent membrane fouling.

Disinfection

Using ultraviolet light, chlorine dioxide, or ozone to disinfect the water and kill pathogenic microorganisms, ensuring safe discharge or reuse. III. Sludge and By-product Treatment

Sludge Treatment

The sludge produced by biochemical treatment (containing a large number of microorganisms and organic matter) must be concentrated and dehydrated (e.g., using a plate and frame filter press) before undergoing harmless treatment:

Anaerobic digestion: Further degrades organic matter to produce biogas;

Composting: Mixed and fermented with straw and other materials to produce organic fertilizer (palm oil mill sludge is rich in nitrogen and phosphorus and suitable for agricultural use);

Incineration: If the sludge volume is small and has a high calorific value, it can be incinerated (but exhaust gas pollution must be controlled).

Oil Recovery

Oil separated during the pretreatment stage can be refined and reused (e.g., as an industrial oil feedstock), achieving resource utilization and reducing processing costs.

IV. Process Optimization and Precautions

Selecting a process based on local conditions

Small plants can adopt simple processes such as "oil separation + SBR"; large plants recommend "UASB + oxidation ditch + deep filtration" to achieve a balanced efficiency and cost-effectiveness. Controlling Environmental Factors

Anaerobic treatment requires controlled temperature (mid-range temperature around 35°C or high temperature around 55°C) and pH (6.5-7.5); aerobic treatment requires maintaining dissolved oxygen (2-4 mg/L).

Wastewater Resource Utilization

Biogas produced by anaerobic treatment can be used for power generation or heating; treated wastewater that meets standards can be reused, reducing fresh water consumption.