Evaporation treatment of cosmetic production wastewater

I. Project Background

Cosmetic production generates large amounts of wastewater containing surfactants, animal and vegetable oils, fragrances, preservatives, and some high-concentration salts. This type of wastewater is characterized by complex composition, large fluctuations in COD concentration, and poor biodegradability, making it difficult for conventional biological processes to directly achieve compliant discharge. Evaporators, as the core unit for deep wastewater reduction, can evaporate the high-salt, high-concentration mother liquor after pretreatment and membrane concentration, significantly reducing the amount of hazardous waste disposal and helping companies achieve near-zero wastewater discharge, thus meeting the emission control requirements of environmental protection departments.

II. Wastewater Quality and Treatment Objectives

2.1 Typical influent water quality

Reference for key indicators of influent water in high-concentration mother liquor production for cosmetics:

2.2 Processing Objectives

The evaporator condensate effluent indicators can reach: COD≤500 mg/L, total salt content≤500 mg/L, condensate recovery rate≥90%, concentrated mother liquor reduction factor≥8 times, which greatly reduces the subsequent hazardous waste disposal cost.

III. Overall Process Flow

The complete processing route is as follows:

Wastewater collection tank → Air flotation for oil removal pretreatment → Anaerobic + aerobic biological treatment → Ultrafiltration + reverse osmosis membrane concentration → High-concentration mother liquor storage tank → Evaporator for evaporation and crystallization → Condensate returned to the biological system for further treatment → Discharge meeting standards/reuse

The small amount of concentrated residue produced by the evaporator is entrusted to a qualified unit for hazardous waste disposal, thereby achieving overall wastewater reduction and resource recovery.

IV. Comparison of Mainstream Evaporator Selection

Based on the characteristics of cosmetic wastewater, the techno-economic comparison of three commonly used evaporators is as follows:

Comparison dimensions: MVR evaporator, triple-effect multi-effect evaporator, low-temperature heat pump evaporator;

The core energy consumption structure uses electric power to drive the compressor to recover the latent heat of secondary steam. Only a small amount of live steam is needed for startup, with live steam as the main heat source. A small amount of electric power is used to drive the pump group to drive the heat pump cycle, and low-temperature evaporation below 60°C is achieved.

Operating cost per ton of water: 20-45 yuan/ton, 90-150 yuan/ton, 30-60 yuan/ton;

Electricity consumption per ton of water: 25-50 kWh/ton of water, 8-15 kWh/ton of water, 50-70 kWh/ton of water;

Steam consumption is almost zero; 0.37-0.46 tons/ton of water; there is absolutely no steam consumption.

Suitable for evaporation capacities of 1-50 tons/hour, 5-30 tons/hour, and 0.1-5 tons/hour;

Material requirements: 316L stainless steel/titanium; 316L stainless steel is corrosion-resistant and scale-resistant; 304 stainless steel is suitable for high-salt working conditions; lower cost.

Annual maintenance costs account for 3%-5% of the original equipment value; 8%-10% of the original equipment value; 2%-4% of the original equipment value.

Start-up flexibility: Start-up can be completed within 30 minutes, suitable for intermittent production with a start-up time of more than 2 hours, suitable for continuous production with a rapid start-up and stop within 15 minutes, and suitable for small batch production;

Suitable for large-scale continuous production projects in various scenarios, with significant energy-saving advantages in long-term operation. The factory area has cheap waste heat/self-built boilers, and the steam cost is less than 100 yuan/ton. Small-volume cosmetics manufacturers with limited space and no steam support.

V. Key Design Considerations

Anti-scaling design: Oils and surfactants in cosmetic wastewater are prone to scaling on the inner wall of heat exchange tubes. The evaporator needs to be equipped with an online cleaning system with a cleaning cycle of once every 3-6 months to avoid the decline of heat exchange efficiency.

Defoaming design: In response to the foaming properties of surfactants, a high-efficiency wire mesh demister is added to the evaporation chamber, along with an automatic defoamer dosing system, to prevent foam entrainment from causing the condensate water quality to exceed the standard.

Low-temperature protection design: adopts a low-temperature evaporation condition of 60-80℃ to avoid heat-sensitive fragrances and organic matter from denaturing and coking at high temperatures, reducing the difficulty of system cleaning.

Safety features: The system is equipped with negative pressure protection, over-temperature alarm, and liquid level interlock device, and is compatible with the explosion-proof safety requirements of Class A workshops in the cosmetics industry.

VI. Reference for Operating Cost Calculation

Taking an MVR evaporator with an evaporation capacity of 1 ton/hour as an example, based on the local electricity price of 0.7 yuan/kWh in Nanjing, Jiangsu Province, and an annual operating time of 8000 hours:

Annual electricity cost: approximately 280,000 to 350,000 yuan

Annual maintenance and spare parts cost: approximately 25,000-40,000 yuan

Annual labor and management costs: approximately 60,000-80,000 yuan

The overall operating cost per ton of water can be controlled within 35 yuan. Compared with traditional multi-effect evaporators, it can save more than 600,000 yuan in operating costs per year, and the static investment payback period is about 2-3 years.

VII. Environmental Benefit Analysis

After adopting evaporator treatment, the amount of wastewater and hazardous waste generated by enterprises can be reduced by more than 80%, and carbon dioxide emissions can be reduced by about 150 tons per year. The condensate reuse rate can reach 90%, which meets the environmental protection policy requirements for water conservation and carbon reduction in the cosmetics industry. This helps enterprises pass environmental inspections smoothly and avoid the risk of exceeding emission standards.