Trade Waste

Trade Waste

The words in bold below have specific meanings. Each word is defined to help you understand the information presented in this document.

Approval means a prior written approval given in accordance with clause 11 of the Bylaw.

Bylaw means the Hastings District Council Water Services Bylaw.

Characteristics refers to flow rate, volume per day, solids, oil and grease, metals etc.

Controlled Wastewater means a discharge containing any characteristic that exceeds the limit set in Schedule 2 of the Bylaw.

Floatable oil and grease (commonly referred to as fat) is any oil and grease that separates out of the wastewater and floats to the top when it cools.

Permitted Discharge means any discharge that has characteristics that are equal to or lower than the limits in Schedule 2.

Pre-treatment is equipment and/or chemicals used to modify the characteristics of wastewater to make it acceptable for discharge.  This includes screens, grease traps, grease removal systems, settling tanks, oil and grit interceptors and a variety of other equipment.

Schedule 2 means the schedule in the Bylaw that sets limits on any characteristic and those limits determine whether a discharge is Controlled Wastewater or Permitted discharge.

Separated Industrial Network means the sewer network used exclusively for Trade Waste that contains no Sewage.  This network is not available in all areas.

Sewage means human waste and includes septage and swimming pool and spa pool water.

Total oil and grease (commonly referred to as fat) is all oil and grease present in the wastewater whether it is floating or emulsified by a process, cleaning chemicals or additives.

Trade Waste means any wastewater generated from activities which are not primarily residential in nature (but may also include Sewage).

Trade Waste charges means the charges set annually by Council and published in the Annual Plan.  The charge for each individual business is calculated based on the characteristics of the discharge.  In most cases the charges for ‘Permitted’ discharges are already covered in the rates paid by the business.

Trade Waste Officer is the person responsible for processing applications for Approvals, issuing and monitoring Approvals and investigating problems resulting from discharges that do not comply with the Bylaw.  The Trade Waste Officer also helps businesses work through the application process or with general enquiries relating to trade waste issues.

Wastewater Network means the system of pipes, pumps, drains, treatment works and channels owned or used by Council for conveying, treating and disposal of wastewater.

Background information

Hastings District Council owns and operates the Wastewater Facility in East Clive where all the wastewater from Hastings, Havelock North, Flaxmere, Whakatu and Clive is treated before it is pumped through the long sea outfall.  The discharge from the Wastewater Facility must meet the conditions set in the Wastewater Discharge Resource Consent for the discharge into the sea environment. 

Trade Waste discharges into the Hastings District Council wastewater network are controlled by the Hastings District Council Water Services Bylaw.  The Bylaw contains a schedule (Schedule 2.) that sets limits on volume, flow rate and characteristics that a business may discharge into the wastewater network.  This enables Council to control what is in the wastewater that is discharged into the wastewater network to protect those working in or around the wastewater network and to meet the limits set in the consent for the discharge from the wastewater facility and to protect the wastewater network from potential damage and blockages. Council has a duty to protect the community-owned wastewater network and to protect people and the environment. 

How does Council control Trade Waste discharges?

Any business that wishes to discharge Trade Waste that exceeds any of the limits in Schedule 2 must apply for an Approval to discharge Controlled Wastewater.  Approval must be obtained before starting the discharge.  The Approval will state what characteristics the business is allowed to discharge.

Anyone wishing to discharge Trade Waste into the Separated Industrial Network must have Approval to Discharge Controlled Wastewater regardless of the volume or flow rate or any other characteristics.  No Sewage may be discharged into the Separated Industrial Sewer.

Any Trade Waste discharge that is within all limits of Schedule 2 is considered a Permitted discharge and does not require Approval to discharge Controlled Wastewater, however, depending on individual circumstances the discharge could be subject to Trade Waste charges.

The nature of some industries means the wastewater from them contains characteristics that are in excess of what is allowed to be discharged.  Those characteristics can be reduced by having pre-treatment in place and making the discharge acceptable for discharge.  Some will need to have an Approval to discharge even after pre-treating their wastewater but some can, by having pre-treatment in place, bring their discharge characteristics from being Controlled Wastewater to being Permitted discharge.  These include some food related businesses, mechanical workshops, service stations and truck washes.

Why do we need to control what is discharged from various industries?

To prevent excessive amounts of any characteristic being discharged that could be hazardous to those maintaining the wastewater network or cause damage to the wastewater network or a breach of the consent to discharge wastewater to the sea environment.

Why do we need to control the waste discharged from food related businesses?

Food related businesses such as takeaway shops, restaurants, butcher shops, cafes, bakeries etc. – in fact any business that processes food on the premises is likely to discharge oil and grease (fat) into the wastewater network.

If oil and grease is discharged in excessive amounts it can solidify and cause sewer blockages, resulting in overflows, hazards to public health and pollution of the environment.

Most common method of pre-treatment for these types of businesses is a grease trap.

What about mechanical workshops, service stations and truck washes?

These types of businesses will have various types of oil and fuel that will get washed off mechanical parts, various equipment or vehicles or sometimes small spills happen.  Oil and fuel is referred to as Petroleum hydrocarbons in Schedule 2 of the Bylaw.  Most common pre-treatment for the wastewater from these types of businesses is Oil and Grit interceptor.  The oil floats to the top and the grit settles to the bottom of the interceptor.  The interceptor must be of the right size for each situation and it must be emptied regularly to ensure it works properly.

How does Council know if everyone is following the rules for their discharge?

All dischargers that have Approval to Discharge Controlled Wastewater have to take regular samples of their discharge.  The samples are analysed by an approved laboratory and the results are sent to Council’s Trade Waste Officer for monitoring purposes.  The Trade Waste Officer also does random monitoring of the discharges to verify if the discharge is within approved limits.

The Trade Waste Officer also carries out random inspections of discharges from Permitted dischargers and responds to reports of blockages from Council contractors that do maintenance work on the sewers and clear blockages when they occur.  When a problem is identified it is dealt with as explained in this document.

How much oil and grease can be discharged into the wastewater system by Permitted dischargers?

A maximum of 30 mg/L of floatable oil and grease and 100mg/L of total oil and grease may be discharged into the wastewater system.  This equals only 30 grams of floatable oil and grease and 100 grams of total oil and grease per 1000L of wastewater.

The reason for the low allowable level is due in large part to how flat the city of Hastings is.

Our wastewater system does not have many hills to run down, so the wastewater flows more slowly and is therefore at more risk of build-up of grease in the pipes.

What about Petroleum hydrocarbons?

Maximum amount of Petroleum hydrocarbons that anyone is allowed to discharge is 30mg/L of wastewater.  This equals only 30 grams per 1000L of wastewater.

What happens if Permitted discharge contains more oil and grease than allowed in the Bylaw?

Discharging more oil and grease than is allowed in the Bylaw is an offence under the Bylaw.

Any Trade Waste discharge that does not comply with Schedule 2 of the Bylaw must apply for an Approval.

If Council becomes aware that a previously Permitted discharge has changed in nature and has in effect become Controlled Wastewater then it will work with the discharger to bring the discharge into compliance. One way Council may become aware of a change in the discharge is a blockage of the sewer, traced back to that specific discharge.

What happens if a business causes a restriction or blockage in the wastewater system?

Where the business causing restriction or blockage is identified it may be charged for the cost of the inspection, clearing the blockage and any clean-up costs.  Council will also look into why the business caused the restriction or blockage and take appropriate action to ensure it does not happen again.

What is a grease trap?

The most common grease trap design is simple non mechanical device that captures the oil and grease that is present in the wastewater generated by the business.  The trap is, in most cases, installed in the ground; it has an inlet, an outlet and baffle walls which separate the unit into a number of chambers. In the chambers, solids settle forming a sediment layer, with most of the oil and grease floating to the top.  Some grease traps can be installed above ground which can make it easier to install in some situations.

Grease Trap diagram

What can a business do if there is not enough room to install a typical grease trap – are there alternatives?

There are some alternative grease removal systems available.  The business can install a different system that can be installed inside the building. It is important that the system is correctly sized for the discharge volume and operated according to manufacturers or suppliers instructions.

Installing a grease trap or another type of grease removal system that is too small for the volume of wastewater is likely to result in a significant amount of the oil and grease flowing through the system and entering the wastewater system resulting in a discharge that does not comply with Schedule 2 of the Water Services Bylaw.

If using alternative grease removal system (other than typical grease trap) then any dishwashers should be plumbed in after the grease removal system because the potential heat of the water and the washing agent used is likely to adversely affect the operation of the system.  This is particularly important if using an enzyme based grease converter system.  It is best to discuss this with the service agent of the system or, for new installations, the supplier before choosing a system.

What size of grease trap is needed?

HDC recommends the following grease trap sizes

Minimum size for any premise / 1000L

Takeaway premises, bakeries etc./ 1000L

Restaurants up to 50 seats / 1000L

Restaurants 50 up to 100 seats / 1500L

Restaurants over 100 seats / 2000L


The sizes recommended by HDC vary from the sizes recommended in the Acceptable Solutions G13/AS2 because the sizes recommended in G13 (see below) are in most cases unlikely to be sufficient to meet the levels allowed in the HDC Water Services Bylaw.  This is based on results from various studies of grease traps and alternative grease removal systems here in New Zealand and Australia.


The following is copied from G13/AS2

3.4 Grease traps

3.4.1 Grease traps shall be provided for any

discharge pipe serving a sink(s) where the foul

water discharges to a soak pit.

3.4.2 In buildings other than Housing, grease

traps shall be provided where waste water is

likely to convey grease.

3.4.3 The capacity of a grease trap shall be at

least twice the capacity of all sanitary fixtures and N: This may not be enough to comply with the Bylaw.

sanitary appliances discharging to it, and in no

case less than 100 litres as shown in Figure 4.

3.4.4 For restaurants and cafés, the capacity

of the grease trap shall be at least 5 litres for      N: This may not be enough to comply with the Bylaw.

each person for whom seating is provided,

and in no case less than that required by

Paragraph 3.4.3.

3.4.7 Other types of grease trap such as those

that separate or digest grease must be

approved by the network utility operator as

required by G14/VM1 1.2.



What size of alternative grease removal system is needed – is it different from a typical grease trap?

The size of an alternative system is very different from a typical grease trap and Council has no specific recommendation for the type of system or the size because it is different for each situation.  The best way to proceed when choosing a system is to talk to the various suppliers and get them to work out the specific requirements for the discharge.

Does the grease trap or a grease removal system need to be maintained?

Yes.  Regular emptying and cleaning is critical to correct and effective operation of the systems.

When does a grease trap need to be emptied and cleaned?

Some businesses engage a contractor to empty and clean the trap on a regular schedule.  The frequency can be established with the contractor based on observation of the condition of the trap over a period of time or by monitoring the grease trap to establish when it needs cleaning. The frequency of cleaning will vary based on the size of the trap and the amount of oil and grease generated by the business but as a general rule when approximately 25% of the working depth of the trap is taken up by the layer of solids, floating oil and grease layer, the trap should be emptied. Once the trap has been emptied and cleaned it should be filled with cold water to ensure proper operation. At the time of cleaning the trap should be checked for any faults.

For all alternative grease removal systems, the manufacturers and installers instructions must be followed to ensure proper operation of the system.  Some Council’s in New Zealand have banned the use of some systems because they have been proven to be unreliable when not used according to manufacturer’s instructions.  HDC has not placed a ban on any alternative grease removal system because if a problem does occur then it can be dealt with under the Bylaw as explained earlier. 

It is important to reduce the amount of solids (food scraps) entering the grease trap or grease removal system. This can be achieved by installing easily cleanable screens that remove most solids before the waste water enters the traps.

What happens if the grease trap or an alternative system is not emptied and cleaned regularly?

They stop working as they are designed to do and in some cases will block and cause overflow on the premises.  In other cases it will still allow the wastewater to flow through untreated. The discharge of excess oil or grease (fat) may result in a blocked sewer.  Discharging wastewater containing any characteristics in excess of what is allowed in Schedule 2 of the Water Services Bylaw makes the discharge “Controlled Wastewater” and must have Approval for discharge under the Bylaw.  To discharge “Controlled Wastewater” without Approval is an offence under the Bylaw.

Can a business use a Waste Master or waste grinder to dispose of food scraps?

It would be unwise to use one of those since it could seriously reduce the effectiveness of any grease removal system in use.  Solids would build up in the grease trap or alternative grease removal system, which reduces the effectiveness of the system and can result in anaerobic condition in the system, causing it to emit foul smells.

Who needs to install a grease trap or alternative grease removal system?

In the Acceptable Solutions G13/AS2 clause 3.4.2 (as seen earlier in this document) it is stated: “In buildings other than Housing, grease traps shall be provided where waste water is likely to convey grease”.  This means that most food related businesses building new premises or making alterations to their premises or any work that requires a building consent, must install a grease trap or alternative system to comply with the Building Act.

Why does council recommend much bigger grease traps than The Acceptable Solutions G13/AS2 stipulates?

A business can comply with the Building Code by installing a grease trap that is sized according to the code. However, the grease trap sizes in the code would not be effective enough to meet the limits allowed in the HDC Water Services Bylaw, therefore making the discharge “Controlled Wastewater” and as such it must have approval for discharge under the Bylaw.  To discharge Controlled Wastewater without Approval is an offence under the Bylaw.

Can a business install a smaller grease trap than recommended by Council?

There are some things that need to be considered when working out the size of grease trap needed for each situation.  By calculating the volume of water discharged from the operation and the retention time in the grease trap.  As a general rule, the water should have at least one hour retention time to allow it to cool down to allow the grease to separate and float to the top and any solids to settle to the bottom.  The sizes recommended by Council are pretty much fail safe sizes for the operations mentioned for each size and calculating the discharge volume is not needed.  If calculations are done and prove a smaller grease trap is enough then Council would accept a smaller trap being installed.

However, while smaller is generally cheaper at the start, the system will need to be cleaned more often, costing more per year to maintain and the amount of oil and grease in the wastewater discharge is more likely to have higher-than-allowed limits, resulting in non-compliant discharge, which is an offence under the Bylaw.

If a business has already got a small grease trap – does it need to install a bigger one?

If the nature of the discharge has changed (increased in volume or amount of oil or grease) then the short answer is yes. Consistently good housekeeping may keep the discharge within allowed limits even with a small grease trap – the question is; can the business do the right thing all the time? Is it worth taking the risk of committing an offence under the Bylaw?


Application for Controlled Wastewater Discharge Approval

 Download the Application Form for Approval to discharge Controlled Wastewater 187 KB

Need more information?

Contact the Hastings District Council Trade Waste Officer on phone (06) 871 5000 or email