How should oily wastewater from hotel kitchens be treated? Design requirements for grease interceptors
I am Daniel Wang, a water supply and drainage specialist. Oily wastewater treatment in hotel kitchens is an easily overlooked yet critical part of plumbing design—it directly relates not only to drainage network blockages and environmental pollution, but also to fire and health safety. According to Section 4.8 of the Standard for Design of Building Water Supply and Drainage GB 50015-2019 and the Technical Specification for Environmental Protection of Catering Industry HJ 554-2010, kitchen oily wastewater must undergo grease separation treatment before being discharged into the municipal network.
**Characteristics of Oily Wastewater and Treatment Principles**
Hotel kitchen wastewater contains animal and vegetable fats, food residues, detergents, etc. Grease tends to solidify at low temperatures, clogging pipes and producing foul odors. The core of treatment is "gravity separation + auxiliary enhancement": utilizing the property that grease density is lower than water, oil-water separation is achieved through grease interceptors. For large hotels (e.g., daily treatment capacity ≥10m³), automatic grease separation and lifting equipment is recommended, integrating screening, grease separation, lifting and sludge discharge functions to avoid manual cleaning.
**Grease Interceptor Design Requirements**
According to Clause 4.8.2 of GB 50015-2019, grease interceptor design must meet the following key parameters:
- **Effective volume**: Calculated based on wastewater retention time ≥2 minutes, and not less than 1.5 times the maximum hourly drainage volume of the kitchen. For example, for a five-star hotel kitchen with an hourly drainage volume of 20m³, the grease interceptor volume should be ≥30m³.
- **Structural dimensions**: In-tank flow velocity ≤0.005m/s, surface hydraulic loading ≤1.5m³/(m²·h). Rectangular tanks are usually adopted, with a length-to-width ratio of 3:1~4:1 and effective water depth of 1.5~2.0m.
- **Grease separation and sludge discharge**: Baffles or grease-retaining plates must be provided, with the lower edge of the plate 0.3~0.5m from the tank bottom; a sludge hopper shall be provided at the tank bottom with a slope ≥0.05, equipped with a sludge discharge pipe (diameter ≥DN100).
- **Auxiliary facilities**: A screen (gap ≤10mm) shall be provided at the inlet pipe, and a vent pipe at the outlet pipe; in cold regions, thermal insulation and freeze protection are required, such as electric heat tracing or lined insulation layers.
**Practical Engineering Case**
In an international brand hotel project in Shenzhen, the kitchen drainage was originally designed with only a simple grease interceptor well, which became frequently blocked after half a year of operation. We retrofitted it according to GB 50015 with an above-ground automatic grease separation device (treatment capacity 15m³/h, with heating function), adding wastewater lifting pumps and grease collection barrels. After the retrofit, the grease removal rate exceeded 90%, the maintenance cycle was extended from once a week to once a month, and no further blockage complaints occurred.
**Summary**: Oily wastewater treatment in hotel kitchens must strictly follow the standards, give priority to automatic grease separation equipment, and reserve margin based on actual flow rates. Design must simultaneously consider grease recovery and utilization (e.g., as biodiesel feedstock) and environmental acceptance requirements.
The above are reference opinions. The actual project situation still needs further comprehensive evaluation and implementation in combination with specific operating conditions, site conditions and other factors.