Wastewater Treatment Systems in New Zealand
Introduction
Around 1.5 billion liters of domestic wastewater is discharged into the environment on a daily basis in New Zealand, which makes it the largest form of waste in terms of volume (Ministry for the Environment, 2013). Wastewater in the context of this page is defined as water that drains from toilets, sinks, showers, baths and dishwashers etc. The treatment of wastewater as to lessen its effects upon the surrounding environment such as estuaries, coasts, rivers and lakes has become increasingly important throughout the last hundred years (MFE Wastewater, 2013). This page looks at the different sewage treatment levels and how they differ in various New Zealand centers, mainly Auckland, Dunedin and Kerikeri. The current wastewater treatment levels at these centers are then compared to the wastewater treatment levels in the year 2000, in order to find out if there is an improving trend in wastewater treatment levels.
National Law
Resource Management Act 1991
The Resource Management Act 1991 (RMA) is the main law that controls discharges into the environment, including the management of wastewater (Resource Management Act, 1991). Under the RMA much of the responsibility of managing the environment is devolved down to district and regional councils. Local rules and policies are set by the district and the regional councils which have the same effect as law (Resource Management Act, 1991). Therefore wastewater treatment systems vary greatly in terms of technology and scale throughout New Zealand between districts and cities. Sections of the RMA applicable to the topic of wastewater treatment and discharge aim to create a malleable but holistic framework that can be applied to a wide range of environments ranging from urban to rural New Zealand settings.
The RMA is effects-based, and section 30 tasks regional councils to set controls in relation to (Resource Management Act, 1991):
- The quality and enhancement of the quality of water in water bodies and coastal water.
- The maintenance and enhancement of ecosystems in water bodies and coastal water.
- The prevention or mitigation of any adverse effects of the storage, use, disposal or transportation of hazardous substances.
- Discharges of contaminants into or onto land, air, or water and to the coastal marine area.
Regional councils select the “appropriate” ways of achieving these ends according to local conditions. For example regional councils set rules in their regional plans in order to manage discharges of wastewater both onto land and into water. Discharges often require a resource consent, which is a permit that makes wastewater discharges subject to site-specific conditions, such consents must take into account the quality of the wastewater discharge and the effects it might have upon the surrounding environment (Montgomery, personal communication, 2013).
Treaty of Waitangi
Recent Waitangi Tribunal meetings highlight the fact that improper treatment and disposal of wastewater that might be detrimental to the natural landscape and ecosystems is contrary to the principles of the Treaty of Waitangi. For example the Rotorua District Council’s proposal to dispose excess waste runoff into the Kaituna river was met with opposition that was later resolved through upgrading of the Rotorua Wastewater Treatment Plant so that wastewater was up to a standard that it could be discharged on land. Interpretation and application of the principles in the treaty of Waitangi is a large issue in and of itself. Maori cultural values that are applicable to the topic wastewater treatment as expressed in the treaty often represent a more environmentally conscientious approach (see section 5)(Waitangi Tribunal, 2013).
Overview of Wastewater Treatment Processes
There are a wide range of terminologies used to classify the levels of wastewater treatment, but for the purpose of this research the key terms referred to are primary, secondary, and tertiary treatment. In general, the more stages of treatment wastewater undergoes, the less of an adverse effect it will have upon re-entering the environment.
Primary Treatment (Mechanical)
Primary (mechanical) treatment removes the larger, floating solids form the raw wastewater. This is achieved through the use of grates and screens that trap and separate solid objects from the bulk wastewater. It can reduce the biological oxygen demand of the incoming sewage water by twenty to thirty percent. Some primary treatment systems utilize by-products from this treatment stage for fertilizer, this is evident in the Christchurch and Auckland wastewater treatment plants (United Nations, 2003).
Secondary Treatment (Biological)
Secondary (biological) treatment aims to remove the dissolved organic matter that is too fine to be removed through by the primary mechanical treatment processes. Biological content in wastewater sourced from human and food waste is removed via the use of microbes and aerobic biological processes. Microbes are dependent on sufficient oxygen and food (in the form of biodegradable components in the wastewater) to be effective. Settling sediment and solids from the wastewater is the follows the biological processes. Combined, these two processes can remove about eighty-five percent of the suspended solids can be removed and biological oxygen demand can be entirely removed with an efficient and effective secondary treatment system. Bi-products such as gases from this treatment stage can be utilized for energy production, making a plant self-sufficient, as is the case in Green Island Dunedin (United Nations, 2003).
Tertiary Treatment
Tertiary treatment is defined as any treatment beyond secondary (either chemical or physical) and is often used where discharge environments are highly sensitive. Significant amounts of nitrogen and phosphorous can be removed, that are often attributed to an overgrowth of cyanobacteria, weeds and algae in discharge areas. Heavy metals, bacteria and viruses may also be removed.Disinfection, typically with chlorine, is most commonly used and can remove most of the impurities left in the wastewater (United Nations, 2003).
Trends of Wastewater Treatment in New Zealand
History
Wastewater treatment systems in New Zealand have been becoming increasingly sophisticated following colonization in the 19th century and the spread of urban centres and European culture. Prior to this a combination of Maori cultural practices (see section 5) and low density population meant that no industrialized treatment system was needed. The establishment of wastewater treatment system upgrades from no form of treatment to primary treatment systems throughout the 19th century were most often based on necessity and crisis response. This growing necessity is best exhibited in the history of Auckland wastewater treatment (see section 6).
Comparison
A comparison of the treatment level was made between various New Zealand centers and how they have improved since the year 2000 (See figures 2 and 3). The results show that in the year 2000 only a small number of the wastewater plants had a tertiary level system where as in 2013 the number of plants treating sewage at a tertiary level has more than doubled as illustrated in figure 3 (Bainbridge, personal communication, 2013; Cannel, personal communication, 2013; Dowling, personal communication, 2013; Henderson, personal communication, 2013; Kerikeri Wastewater Project, 2013; Loan, personal communication, 2013; McWilliams, personal communication, 2013; Pratt, personal communication, 2013; Thiart, personal communication, 2013; Soper, personal communication, 2013; Wastewater information sheet 1, 2013).
Public Pressure
Modern trends in wastewater treatment indicate that public pressure, both from the general public and especially local iwi, have resulted in increasingly sophisticated systems of wastewater treatment throughout New Zealand at a variety of scales. This public pressure has resulted from an increased awareness of environmental degradation that can occur where inadequate treatment infrastructure is in place. Among New Zealand citizens there appears to be a unanimous opinion that increasing treatment quality is positive however the main restricting factor is the cost, which is almost entirely paid for through rates and is therefore dependant on ratepayer numbers.
Maori Cultural Values and Perceptions of Wastewater Treatment in New Zealand
Traditional Maori culture places a great deal of value upon wai ora (water as a living entity and the source of life for all things), with many customs involving specific types of water such as birthing springs, exhumation swamps, fresh drinking water and sea water for food preparation. Water is a sacred gift from Atua to sustain life. Management and protection of water as a cherished resource is of the upmost important to Maori culture, this is manifest in the Kaitieki role where whanua, hapu and iwi exercise specific roles. Kaitieki is a complex social, cultural, economic and spiritual system that operates in specific ways at local scales (Ihka et al, 2000).
Many Maori believe that their systems of value and role of Kaitieki have been marginalized, such concerns have been expressed during a resource consent hearing for Gisborne District Council wastewater discharge in 2000. Local Maori viewed the treatment of wastewater as improper and a major contributing factor to the pollution of waterways and coasts around Gisborne. They suggested for a higher quality land based wastewater treatment system. Maori hold the view that little weight has been given to their perspective and customs with concern to conservation matters and the management of waterways. Local Maori in Gisborne view themselves as having an important role as guardians and stewards of the Girsborne Harbour and other water resources. However this role is inadequately accounted for in current policy frameworks (Ihka et al, 2000).
Disposal of waste in traditional Maori culture follows a stringent set of rules involving never mixing waste and water due to it being perceived as morally, culturally and spiritually repulsive. Water mixed with waste is termed waimate and serves no function in cultural practices. In traditional Maori cultural practices, waste produced from specific activities are disposed of separately from one another such as food and body products. Waste disposal methods are intertwined with the upholding of spiritual and cultural values (Ihka et al, 2000).
Case Study: Auckland Wastewater Treatment
Watercare Services Limited is the current water and wastewater service provider for the Auckland region and is entirely owned by the Auckland council. They provide water and wastewater services to inhabitants of the quickly growing Auckland region which now is home to around 1.3 million people. Prior to November 2010, Watercare was owned by Auckland’s territorial local authorities. As the bulk water and wastewater service provider for the region, Watercare supplied six local network operators which in turn retailed services to consumers (Wastewater information sheet 1, 2012)
Some interesting Statistics about Watercare:
- 6000 + bills issued daily
- $369 million in annual revenue
- $7.8 billion in assets
- 390 million litres of water treated daily
- 449 million litres of wastewater treated daily
- 16,000 kilometres of water/wastewater pipes
- 41 water/wastewater treatment plants
- 677 water/wastewater pump stations
- 162,500 manholes
Infancy of Auckland City
- 1878 – Auckland population 30,000. Recognized need for city-wide reticulated wastewater system.Before then ‘nightsoil’ collection of waste from individual house via horse-drawn cart. This became increasingly unacceptable due to smell and concern over the discharge of raw wastewater into streams and bays around Waitemata Harbour.
- New system, implemented by visiting hydraulics engineer William Clark. Reticulated scheme of intercepting sewers that would terminate at Stanley Street where it would be chemically treated and then discharged into the harbour near Parnell. Estimated cost 35000 pounds but was not completed due to an economic depression
- At this time in addition to the Auckland city council there were 19 separate borough councils that had ongoing conflicts due to dumping of night soils in neighboring territories (Wastewater information sheet 1, 2012)
The Orakei Scheme
In 1903, Auckland with a population of 100,000; London engineer Mr G. Midgley Taylor suggested for the development of a reticulated scheme for handling both wastewater and stormwater. Taylors plan involved a main interceptor flowing eastward from Point Chevalair to Okahu Point where storage tanks would hold the flow of untreated but screened wastewater. This would then be discharged through a 300-metre outfall pipe on the high tide. An incinerator that would burn the screenings was also part of the scheme. At a total cost of 355,000 pounds the system would serve a maximum of 300,000 people. The project led to the government forming a body made up of representatives from Auckland City Council and the suburban boroughs to pay for and administer the work. The new authority was named the Auckland and Suburban Drainage Board. The projects main outfall was the Hobson Bay sewer pipe which was built in 1914. Other sewer systems were developed in Newmarket (1880), Mt Albert (1901), One tree Hill (1913), Ellesmare (1915) and Mt Eden (1915). Systems discharging raw wastewater into the Manukau were built in Onehunga and Otahuhu (1910)(see figure 4) then later in Mt Roskill (1925) and New Lynn (1928). Even during construction it was realized that discharging of raw wastewater was polluting the surrounding sea and that the project would reach capacity sooner than anticipated (Wastewater information sheet 1, 2012).
Brown Island Scheme
In 1931, HH Watkins, the Drainage Board chief engineer recommended that the Orakei outfall be abandoned and replaced with a treatment works and outfall on Browns/Motukorea Island (located in the inner Hauraki Gulf). The proposed scheme included a pumping station, sedimentation tanks and sludge drying beds on the island, with facilities for conveying wet sludge for disposal into the sea. Following two decades of delay and controversy (both due to public opposition and the onset of WWII) and one year of construction the scheme became increasingly politicized with the help of mayoral candidate, Dove-Myer Robinson whom replaced the Brown Island Scheme with the Manukau Scheme in 1954 (Wastewater information sheet 1, 2012)
Manukau Scheme
In September of 1960 the Mangere treatment plant was built (see figure 5), (also referred to as the Manukau Sewage Purification Works (MSPW)), at a cost of $30.3 million. It was designed to serve a population of 500,000, processing all domestic and industrial wastewater of Auckland over a 40 kilometre radius. The plant featured an oxidation pond system covering over 500 hectares, which was the biggest of its kind in the world in that time. The Orakei outfall was completely abandoned with its holding tanks later being turned into the Kelly Tarlton aquarium. The MSPW aided in the restoration of mud flats in the upper Manukau as water quality improved and fish began returning. The use of oxidiation ponds was a great step forward, as they provide a natural means of treating and disinfecting wastewater through the breakdown of effluent using a combination of sunlight, fresh air and bacteria creating a positive feedback cycle. Although issues with periodic odours originating from the ponds proved to be an issue for the surrounding residents. In 1972 the Mangere plant design capacity was reached, thereafter extensions were undertaken to increase capacity to 750,000 which were completed in 1980 (Wastewater information sheet 1, 2012)
Pressure to Upgrade.
The Auckland Regional Authority (which was reconstituted to the Auckland Regional Council in 1989) initiated a wastewater study in 1987 in response to Waitangi Tribunal recommendations that resulted in the acknowledgement of widespread public aspirations for improved water quality in the Manukau harbour along with the need for the expansion of Auckland’s wastewater treatment facilities. In 1990 the Tasman Sea outfall was implemented but was soon abandoned in 1991. In 1992, as a result of local government reform, Watercare Services Limited was formed as a Local Authority Trading Enterprise, assuming ownership of the Manukau Sewage Purification Works and renaming it the ‘Mangere Wastewater Treatment Plant’. With the growth of public awareness that the facility needed to be future proofed in order to handle Auckland’s growing population for many decades to come, Watercare undertook a community consultation process. This resulted in a public consensus that supported upgrading the existing treatment plant with new, more reliable, land-based treatment systems that would replace the older oxidation ponds. This upgrade work began in July 1998 (Wastewater information sheet 1, 2012).
Upgrading the Mangere Wastewater Treatment Plant.
From 1998-2005, the Mangere Wastewater Treatment Plant upgrade constituted the biggest environmental restoration programme ever undertaken in New Zealand (see figure 6). The project cost $450 million and represented the largest infrastructure investment in a generation. The treatment plant provided uninterrupted services during the upgrade. The completed plant uses primary (mechanical), secondary (biological) and tertiary (filtration and ultraviolet radiation) methods to treat wastewater and has the capacity to meet Auckland’s growing population needs for the next 30 years. New technologies that were implemented in during the upgrade have created a 10,000 fold reduction in pathogens in treated wastewater that is discharged into the harbour, allowed for the 500 hectares of oxidation ponds to be returned to the Manukau Harbour as well as initiating the restoration of 13 kilometres of shoreline (see figures 7 and 8) along with reducing the water treatment cycle from 21 days to 13 hours in length (Wastewater information sheet 1, 2012).
Case Study: Dunedin Wastewater Treatment
Treatment level
The wastewater at Tahuna Wastewater treatment plant is treated using secondary and tertiary treatment. The secondary treatment uses a High Rate Activated Sludge (HRAS) process and Biological Trickling Filters (BTF). The three HRAS tanks and the two BTF remove contaminants and nutrients from the wastewater so it is clear enough to allow tertiary treatment by ultraviolet disinfection. The ultraviolet radiation damages the bacteria so it that it cannot reproduce. This effectively reduces bacterial levels to meet discharge consents. The bacteria in the treated wastewater discharge, is less than 1% of the incoming bacteria in the raw wastewater that arrives at Tahuna (Henderson, personal communication, 2013).
The bio-solids removed during secondary treatment are de-hydrated by gravity belt press and centrifuge to approximately 30% dried solids. They are then disposed of in one of three ways:
- Incineration: About 50 - 70% of the bio solids are incinerated at about 820 degrees centigrade.
- Converted to power: About 30% of the bio solids are transported to the Green Island wastewater treatment plant bio solids digestion system. The bio solids digestion and landfill operation result in a gas stream that is fed into the new gas power generator. The generator produces enough power to run the Green Island Wastewater Treatment Plant and any excess can be exported to the Dunedin power grid.
- Removed to landfill: The remaining bio solids that cannot be digested or incinerated are transported to the Green Island Landfill (Henderson, personal communication, 2013).
Water quality
Since the Tahuna wastewater treatment has gone through its final upgrading stage the water quality in the area has also improved. This is clearly illustrated by the map on figure 9, which shows water quality tests measured through testing faecal coliform counts in mussels. The results clearly show that since the Tahuna plant has been upgraded the coliform counts in mussels have improved significantly. Therefore following the upgrade of the Tahuna wastewater treatment plant, water quality of the south Otago coast has increased (Henderson, personal communication, 2013).
History
In Dunedin the discharge wastewater was completely untreated until about the mid-1950s at which point screens were put in to filter some of the waste, with the rest of the wastewater being discharged into the Harbor (Henderson, personal communication, 2013). At Tahuna, between 2000 and 2009, the wastewater was screened, then passed through a primary sedimentation process to remove solids, prior to disinfection with Sodium hypochloride before being discharged into the ocean at Lawyers Head (Henderson, personal communication, 2013). In 2009 a long ocean outfall off St Kilda Beach was built. In 2013 the Tahuna sewage treatment was upgraded to its current state which includes primary, secondary and tertiary treatment (Henderson, personal communication, 2013). PublicPublic awareness concerning wastewater environmental issues grew in the 1990s. Over the years there have been many debates and decisions on how much to actually spend for the upgrading of the wastewater system (Porteous, 2013). In the past 20 years Dunedin’s rate payers have paid over 200 million dollars to upgrade the Tahuna Wastewater system to what it is today (Henderson, personal communication, 2013).
Case Study: Kerikeri
Current treatment
Kerikeri currently has a population of 15,000 and uses mostly septic tanks (See figure 10) for wastewater treatment. These on-site wastewater treatment systems are often associated with pollution due to spilling effluent over lawns and into streams causing adverse environmental effects in the Bay of Islands also. National surveys have shown that a lot of household septic tank systems do not work properly (Let`s talk crap, 2013).
Plan to Upgrade
The population in Keri Keri, though small, has increased quickly over the last 25 years which has extenuated adverse environmental effects of the antiquated wastewater treatment system. In July 2013, the Far North District Council led a survey in the “Let’s Talk About Crap Campaign”. Initially there were three options proposed, as described by figure 11. Public response was in favor of reticulated wastewater system, projected to cost $30 million with the potential for a conditional $7 million Government subsidy. If the project is to go ahead it will be planned for in the 2014-15 draft annual plan. The reticulated system was chosen over the maintenance of existing septic tanks as it is projected as costing less overall (Let`s talk crap, 2013). The proposed extent of a reticulated wastewater treatment scheme map is clearly illustrated in figure 12.
Summary:
Overall it is evident that wastewater treatment is improving throughout New Zealand centers. Better wastewater treatment levels also appear to have a positive impact on the quality of the water bodies affected by wastewater discharge. The main factor that inhibits the development of better wastewater treatment plants throughout New Zealand is money, which is usually in the form of rates. This then might be expected to be dependent on rate paying populations, considering the case study in Auckland, a city which now has a considerably advanced treatment system and the largest population of a center in New Zealand. However other smaller centers such as Whangerei and Dunedin have managed to develop tertiary wastewater treatment processes. This highlights the fact that the main drivers and pressures for the development of wastewater treatment systems are in fact the general public and Maori groups such as iwi who are aware of environmental issues surrounding poor wastewater treatment and highly value maintaining or improving the state of the environment. Through consultation and consent processes provided within RMA frameworks, water quality and wastewater treatment can become a highly politicized issue for local councils that subsequently drives change. Following such trends, it should be expected that New Zealand will continue to improve wastewater treatment quality in order to meet both a growing population and heightened public expectations.
References
- Bainbridge, A. (2013) Manager of the Wastewater Treatment Plant, Rotoroua District Council, personal communication 27th September.
- Cannel, P. (2013) Supervisor, 3 Waters, Westland District Council, personal communication 1st October.
- Dowling, S. (2013) 3 Waters Asset Manager, Gore District Council, personal communication 27th September.
- Henderson, C. (2013) Waste Treatment, Dunedin City Council, personal communication 26th July.
- Ihaka M., Awatere, S. and Harrison, D. (2000) Tangata Whenua Perspectives of wastewater, A report prepared for the Gisborne Distric Council.
- Kerikeri Wastewater Project (2013) Far North District Council, Interim consultation report.
- Let`s talk crap (2013) Let`s Talk Crap Campaign, For North District Council. Online: http://www.letstalkcrap.co.nz/index.html (Accessed: 28th September 2013).
- Loan, M. (2013) Drainage Manager, Invercargill City Council, personal communication 30th September.
- McWilliams, B. (2013) Wastewater Treatment Manager, Hastings District Council, personal communication 30th September.
- Ministry for the Environment (2013) Waste; Wastewater. Online: http://www.mfe.govt.nz/issues/waste/wastewater/. (Accessed: 20th August 2013).
- Montgomery, F. (2013) Executive Relations Team, Ministry for the Environment, personal communication 25th July.
- Porteous, D. (2013) “Cost of doing business money well spent”, Otago Daily Times 1st October.
- Pratt, F. (2013) Waste and Drainage Project Engineer, Whangarei District Council, personal communication 30th September.
- Radio New Zealand News (July 2013) Kerikeri told to bite bullet re sewerage costs. Online: http://www.radionz.co.nz/news/regional/214185/kerikeri-told-to-bite-bullet-re-sewerage-costs (Accessed 20th August 2013).
- Radio New Zealand News (August 2013) Kerikeri votes for town-wide sewerage system. Online: http://www.radionz.co.nz/news/regional/218097/kerikeri-votes-for-town-wide-sewerage-system (Accessed: 3rd September 2013).
- Resource Management Act (1991) – Parliament of New Zealand.
- Thiart, J. (2013) Engineering Adviser, Nelson City Council, personal communication 27th September.
- Soper, G. (2013) Waste Water Treatment Plant Superintendant, New Plymouth District Council, personal communication 1st October.
- United Nations, Economic and Social Commission for Western Asia (2003) Waster-water Treatment Technologies: A General Review. New York, USA.
- Waitangi Tribunal (1984) Report of the Waitangi Tribunal on the Kaituna River Claim. Waitangi Tribunal, Department of Justice, Wellington.
- Wastewater information sheet 1 (2012) The history of wastewater treatment in Auckland, Water care services limited.
