Case Study on Wastewater Treatment in a Cosmetic Manufacturing Plant

　　1. Project Background

　　A cosmetics manufacturing enterprise located in Luogang District, Guangzhou, primarily produces products such as toners, facial cleansers, and body washes. During its daily production operations, the facility generates a certain volume of industrial wastewater, which is discharged intermittently, with a daily wastewater volume of approximately 80 m³/day.

　　2.Problem Statement

　　Cosmetics wastewater primarily originates from raw material preparation, product manufacturing, equipment cleaning, and packaging processes. It contains a complex mixture of organic and inorganic compounds, including oils, fragrances, dyes, preservatives, surfactants, emulsifiers, and others. This type of wastewater is characterized by poor biodegradability, high surfactant content, and high color intensity. The effluent discharged by this enterprise is classified as medium-to-high-strength wastewater, with primary pollutants including CODCr, suspended solids (SS), and surfactants. Specifically, the influent average concentrations are approximately 4,000 mg/L for CODCr, 500 mg/L for SS, and 100 mg/L for surfactants.

　　3. Client Requirements

　　As the municipal sewer network outside the plant boundary has not yet been fully developed, and in compliance with national environmental regulations, the client requires that the discharged wastewater meet the Class I standards of the second time period specified in Guangdong Province’s "Discharge Limits for Water Pollutants" (DB44/26–2001).

　　4.Treatment Challenges

　　Complex Composition: The wastewater contains a wide variety of chemical constituents, which increases the complexity and difficulty of the treatment process.

　　Poor Biodegradability: Certain chemical components are resistant to biodegradation, making conventional biological treatment processes ineffective in achieving the desired treatment efficiency.

　　Impact of Surfactants: The large quantities of surfactants used in the production process adversely affect the performance of conventional wastewater treatment processes. Moreover, they generate excessive foam during the aerobic biological treatment stage, disrupting the treatment operation.

　　High Colority: The wastewater is typically deeply colored and requires specialized treatment for effective color removal.

　　5.Treatment Processes and Water Treatment Chemicals

　　A combination of pretreatment and biological treatment is adopted, as detailed below:

　　(1) Pretreatment

　　Bar screens and grit chambers: Remove large particles and suspended solids.

　　Equalization tank: Regulates water quality and flow to make it suitable for subsequent treatment processes.

　　Coagulation-flotation: Primarily consists of a chemical dosing zone, a reaction zone, and a flotation zone.

　　Chemical Dosing Zone: The water treatment chemicals used include sodium hydroxide (NaOH), polyaluminum chloride (PAC), and polyacrylamide (PAM). Sodium hydroxide adjusts the pH of the wastewater to create optimal conditions for subsequent coagulation. PAC acts as a coagulant, destabilizing suspended solids and colloidal particles in the wastewater. PAM functions as a flocculant, promoting the aggregation of destabilized particles into stable flocs.

　　Reaction Zone: The influent water is mixed with coagulants through mechanical agitation and undergoes hydraulic dispersion within the coagulation zone, causing colloidal particles in the influent to become destabilized.

　　Flotation Zone: The flocs formed during the flocculation stage attach to fine air bubbles and are carried to the water surface, achieving solid-liquid separation. Through coagulation-flotation, suspended solids, COD, and most surfactants in the wastewater can be effectively removed, reducing surfactant concentration from 80 mg/L to 10 mg/L.

　　(2)Biological Treatment

　　Anaerobic Biological Treatment: Even after pretreatment, the wastewater still contains certain macromolecular pollutants that are difficult for aerobic microorganisms to degrade. Anaerobic biological treatment can remove organic pollutants while simultaneously breaking down these macromolecular compounds into smaller molecules, thereby facilitating subsequent aerobic biological treatment.

　　Activated Sludge Process: This method utilizes the metabolic activity of microorganisms to degrade organic matter in the wastewater, further reducing its COD and BOD levels.

　　Membrane Technologies (e.g., Ultrafiltration, Nanofiltration): Used to remove fine particles and dissolved substances from wastewater, thereby improving effluent quality.

　　Decolorization Treatment: Activated carbon or other adsorbent materials are used to remove color from the wastewater.

　　Advanced Treatment: For recalcitrant organic compounds that are difficult to biodegrade, advanced oxidation processes (such as Fenton's reagent and photocatalytic oxidation) are employed for further treatment.

　　6.Treatment Performance

　　The wastewater treatment plant is now operating normally, with all effluent parameters performing well. The removal efficiencies for both COD and BOD exceed 90%, and pollutants such as surfactants and suspended solids (SS) have also been significantly reduced. The treated effluent meets the Grade A discharge standard specified in the second time period of Guangdong Province’s "Water Pollutant Discharge Limits" (DB44/26–2001), effectively minimizing environmental pollution. Additionally, this treatment process has lowered the company's wastewater treatment costs and enhanced its economic benefits.

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