On-site effluent treatment systems

Since 2005 many advanced (aerobic) wastewater treatment systems (also known as On-site effluent treatment or OSET) have gone through the trial facility established by Bay of Plenty Regional Council in conjunction with Waikato Regional Council and Rotorua District Council and now operated by Rotorua District Council, to determine which system could meet the approved standard.

The table below highlights the systems approved for installation in the Rotorua lakes' catchments. All systems shown may be installed elsewhere in the Bay of Plenty, however conventional septic tanks are still permitted in most areas outside Rotorua lake catchments. Unless there is a council sewerage scheme planned for your area, any new septic systems installed into the Rotorua catchment must be of an approved model or a resource consent needs to be obtained.

The On-Site Effluent Treatment (OSET) National Testing Programme (NTP) has now been taken over by WaterNZ. 

Trial 1 Note

In early 2009 Bay of Plenty Regional Council decided to no longer recognise the results of Trial 1 in approving waste water treatment systems for installation in our region. Trial 1 had a number of limitations in terms of flow variability which may have influenced systems' performance. The current trial facility has undergone a complete rebuild since the early days and now has very robust systems in place to ensure a high degree of flow uniformity and consistency.

Note 'A'

This system is almost identical to the trialled SuperTreat SB440(N12), however it is marketed by Waipapa Tanks and includes a modified venturi (pat pend) for improved energy efficiency.

Notes on Power Use

1. The irrigation pump trialled in the Reflection treatment system is too small for most irrigation applications. The electricity use in a Biolytix treatment system in a typical household setup totals about 0.6 kWh per day. Electricity use by irrigation pumps associated with household wastewater treatment systems is around 0.5 kWh per 1000 litres (i.e. approximate average household daily flow). This will vary depending on pump efficiency, difference in elevation, distance to irrigated area, pipe size etc.
2. The electricity usage figures presented need to be treated with caution. Various factors could influence them including blockages and pump efficiency. Note that only some systems included irrigation pumps in the trial.
3. The annual power cost was calculated using a nominal cost per kWh of 20 cents plus GST. The exact cost will vary depending on the region, pricing plan and discounts available.

Trial 4 Note

Trial 4 testing was the first full trial under OSET NTP supervision. SWANS-MAG Trial 4 and subsequent audit reports are available on request through the individual companies. Company contact details are available from the WaterNZ website.  

These comparative results reports are not publicly available as they are restricted to Funding Partners only. However, the performance certificates are available to the public at the WaterNZ website.

Other factors to consider:

Visit our page about choosing a system.

If you want to install an advanced system, Rule 13 of the On-site Effluent Treatment Regional Plan applies.

Existing conventional septic tank systems in Rotorua Lakes' catchments

Refer to Rule 2 of the On-Site Effluent Treatment Regional Plan for more information.

Standard septic tanks

Outside the Rotorua Lakes' catchments new conventional septic tank systems can be permitted, provided that the conditions of Rule 3 and schedule 1 of the On-site Effluent Treatment Regional Plan are met. Refer to the Onsite Effluent Treatment Regional Plan to view these.

When dealing with district and city councils it is helpful to have a printout of tables 6 and 7 of schedule 1.

Advanced wastewater system

If you want to install an advanced system rule 12 of the On-site Effluent Treatment Regional Plan applies.

Choosing a system

Things to consider when choosing an advanced wastewater treatment system (not a septic tank system):

Fixed Costs - When getting a quote, check if it includes delivery, and installation. Does it also include the irrigation system and pump?

Running Costs - Do these include electricity, maintenance, servicing, etc? Use the table above in the 'Yes I am in a Rotorua Lake catchment' section to get an indication of electricity usage of the models we have tested.

Servicing/Maintenance - How often is this required? What is involved? How much servicing is included in the purchase price? Who is available to repair the system if it breaks down?

Operation - Is it noisy? Does it smell? How does it handle peak loads - for instance for the extended family at Christmas time. Some chemicals and cleaners can cause the useful 'bugs' to die off, which can result in the entire system malfunctioning.

Size - How much space does it require?

Warranty - What guarantees are offered?

References - Check at least one or two references from people who own them.

Compliance with Regional Plan

Will the manufacturer take responsibility for ensuring that the system meets the regional plan requirements, including providing the necessary certification to Bay of Plenty Regional Council? Refer to rule 12 or 13 of the On-Site Effluent Treatment Regional Plan.