Grease and Oil Wastes – Problems and Solutions - Grease Trap Guide

Oct 23, 2026

Uploaded by SALUTone

Grease and oil wastes create major sewer problems when they separate from wastewater and accumulate inside pipes, reducing capacity, causing sewage overflows, offensive odour, and unhealthy conditions. The cleaning of grease deposits is difficult, costly, and can be hazardous. Restaurants and food processing factories must install and properly maintain grease traps to meet Water Pollution Control Ordinance limits in Hong Kong. The guide explains grease trap operation and key minimum design requirements, plus how to assess existing grease trap capacity from typical water use and billing data.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages11

Reading Time28 min

AccessFree to download

Grease and Oil Wastes – Problems and Solutions

Grease trap purpose and legal importance in Hong Kong

The Grease Trap

Minimum requirements for grease trap design

Assessing existing grease trap capacity

Grease and Oil Wastes – Problems and Solutions A grease trap is a device used for removing oil and grease from wastewaters. Grease traps perform this function very well, provided they are constructed and maintained properly. Grease and oil that is allowed to enter the sewer system causes problems by separating from the wastewater and accumulating on the inside of sewer pipes. Overtime, these deposits get larger as more grease and other solid material builds up. Grease deposits reduce the capacity of sewer pipes and cause sewage overflows, offensive odour and an unhealthy environment. The cleaning of grease deposits from sewers is difficult and can be dangerous and is carried out at considerable cost. All restaurants and food processing factories are required to install grease traps so that greasy materials will be separated from wastewaters before passing to communal sewers. Restaurants and the food processing industry are the main sources of greasy waste and therefore it is very important that the grease traps used at these establishments are effective in removing grease from wastewater before it passes to the sewer system. In many areas of Hong Kong, there are limits set by the Water Pollution Control Ordinance on the amount of grease and oil that can be allowed to pass to sewer. Grease traps are therefore very important as they assist you in conforming to these limits . It is YOUR RESPONSIBILITY as a discharger of greasy wastes to ensure that: • Grease traps are properly designed and constructed so as to effectively remove greasy materials from your kitchen wastewater before discharge to the sewer system. • Your grease trap is properly maintained so that it can continue to function as an effective grease removal device and so that kitchen hygiene is preserved. • Material removed from a grease trap is handled and disposed of properly in order to maintain kitchen hygiene and protect Hong Kong’s environment. The Grease Trap A grease trap is most commonly a two-chambered tank positioned along the wastewater drain pipe. Illustrations are provided on the centre pages of this booklet for reference. Wastewater slows down as it moves through the compartments of the trap, allowing time for less dense material to separate and rise to the liquid surface. Liquid and solid grease as well as light waste particles will be held in the trap while the wastewater below passes out. The minimum requirements for grease trap design are: 1) Provide sufficient capacity to slowdown the passing wastewater, giving greasy waste the opportunity to separate out. A grease trap should be able to hold all the kitchen wastewater entering it during times of maximum water use for a period of 20 minutes . A grease trap connected to a single s ink should not be smaller than 250 litre (55 gallons) capacity. A larger grease trap is used if more than one fixture is connected. Check the size of an existing grease trap or determine the approximate size of a new grease trap by following the instructions given on Page 3. 2) The length ofthe trap should be equal to between 1.3 and 2 .0 times the total depth. Note that usually the grease trap contents occupy 2/3 of the total depth; the top 1/3 of the trap is head space. Do not include wall and cover thickness in the length and depth measurements if the grease trap is built of concrete. 3) The surface area of the trap (the length times the widthin square millimeters) should be equal to between 1000 and 2000 times the total depth measuredin millimeters . Again, do not include wall and cover thickness in measuring a concrete trap. 4) Prevent wastewater entering the grease trap from mixing up the top greasy waste layer. A baffle should be present at the trap inlet (see centre pages) to slowdown the incoming wastewater and keep it separate from the top waste layer. The inlet pipe should end in a 90° downwards bend so that incoming wastewater enters the trap at least 100 mm below the water surface. T

FAQs

Why are grease traps important for restaurants and food processing factories?

Grease and oil can separate from wastewater and accumulate in sewer pipes, reducing capacity and causing overflows, odour, and unhealthy conditions. Grease traps help separate greasy materials before wastewater enters communal sewers and supports compliance with Hong Kong limits.

What is the typical structure and function of a grease trap?

A grease trap is commonly a two-chambered tank placed along the wastewater drain pipe. Wastewater slows down through compartments, allowing less dense material to rise and grease and solids to be held in the trap while wastewater passes out.

What are the minimum grease trap design requirements?

Requirements include sufficient capacity to slow wastewater (including limits based on maximum water use), appropriate length and surface area ratios to total depth, inlet baffling and a 90° downwards bend to prevent mixing, maintenance access, and safety features such as venting and prominent location/signage for larger or under-floor traps.

Oct 23, 2026

Uploaded by SALUTone