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Wastewater systems have traditionally been designed to collect dirty water and transfer it for treatment at a remote location, and after treatment the wastewater has been discharged to a local waterway.  This has reduced or eliminated the outbreak of waterborne disease within communities, and has been a vital contributor to improving public health.  However, decreased rainfall and subsequently reduced supplies of drinking water in many parts of Australia has meant that water conservation and water reclamation are increasingly practiced.  Reduced wastewater flows arising from water conservation leads to changes in wastewater hydraulics, while the need to recycle water has seen wastewater treatment and reclamation now being practiced at various scales in new developments.

The Naiad website has a database of case studies for alternative urban water systems.  Such systems are able to offer a reduced consumption of drinking water and discharge of wastewater.  This can reduce drinking water consumption by 50% or more, and in the case of the Pimpama Coomera development in South East Queensland for which wastewater reclamation and rainwater harvesting are planned, a reduction of 84% is anticipated.

The types of wastewater systems discussed in this fact sheet are:

• Wastewater collection and remote treatment, along with the effect of water conservation on system hydraulics and the option of using pressure sewers or smart sewers
• Recycling wastewater from wastewater treatment plants
• Greywater reuse
• On-site wastewater treatment.

Wastewater collection and remote treatment

This approach represents the traditional approach taken to wastewater design for urban developments, where all wastewater is collected and transported to a wastewater treatment plant that is remote to the development.  The design principles of network design are well known and standard gradients for sewer networks are common throughout the industry. 

The gradients for sewer networks are based on historical water use patterns, but water conservation measures are leading to lower water use and therefore lower wastewater volumes.  This increases the likelihood of blockages within the sewer, as solids have less flow to carry them away.  Consequently steeper gradients may be required to assist with the carriage of solids.  Guidelines for gradients required for more concentrated sewage are not currently available, but they may be estimated using the method of Sharma and Swamee (2008).

Pressure sewers are now also available, and these have been implemented in areas with high water tables (Public Works and Engineering, 2004).  These systems use a pump at each household or building to pump the sewage to the treatment plant.  As the transport system is pressurized, the need for laying pipes at a set gradient is not required, and infiltration into the pipes does not occur.  This can reduce costs, and because a pump is required on each house, part of the cost is deferred until building construction takes place.  However, these systems do not operate unless electrical power is available, and power blackouts and the need to replace pumps does make operation of these systems more problematic than gravity systems.

Smart sewers reduce the amount of water infiltration, thereby reducing wet weather peak flows.  Such systems are usually comprised of: longer pipe lengths with fused or welded joins for pressure or vacuum transport of sewage, reduced manhole numbers or their elimination from the system, use of curved pipe sections to reduce the number of inspection points and discourage stormwater connections to the sewer by drainage relief requirements.  The advantages of these systems are that smaller pipes may be used, along with small treatment plants and lower pumping requirements.  The Gold Coast City Council is implementing a smart sewer systems in the Pimpama-Coomera development.

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Wastewater reuse from wastewater treatment plants

Where treated wastewater of the correct water quality is available, the option of taking reclaimed water as a third water source may be the most appropriate option for a development.  The wastewater treatment system is the same as a conventional development, but reclaimed water is used as a substitute for some residential uses eg. garden irrigation, toilet flushing or laundry.  The main issue of concern for such systems is the water quality and health risks associated with the use of reclaimed water.  However, the water quality would usually be guaranteed by the supplier, and provided the system is planned with the specified water quality in mind, there should be little concern for the developer in the planning phase.  There is a need to ensure that there is no cross connection between the potable water supply and the reclaimed water supply during the construction, lot development and completion phases.  Purple pipes are used for reclaimed water to differentiate reclaimed water pipes from drinking water pipes and to limit the number of cross connections.  Additional testing for cross connections may be required before the residents can occupy new buildings and on an ongoing basis after occupancy.  Approval for the reclaimed water system will also be required by either the local EPA and/or Health Regulator.

There are many such developments now operating eg. Rouse Hill, Mawson Lakes, Sandhurst and significant water reductions (50%) have been achieved.  Use of reclaimed water for garden irrigation may lead to the perception that the development will never have restrictions on garden irrigation, and it has been noted that the residents of Rouse Hill use more water for garden irrigation than similar developments without reclaimed water.  While restrictions on the use of reclaimed water have not yet been known, it may arise in the future when there is greater competition for reclaimed water.  For instance, Western Water in Victoria currently reclaims more than 80% of its wastewater and during the recent drought with restrictions on water use, there have been a number of times when there has been no inflow into there wastewater treatment plants.  Therefore, the availability of reclaimed water will become increasingly important in coming years.

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Greywater reuse

Greywater might be considered for reclamation rather than combined sewage as it contains fewer contaminants.  There are many on-site greywater treatment systems available for purchase, and a literature review of the common types is available (Innovation in on-site domestic water management systems in Australia).  There are likely to be many more greywater treatment systems now on the market since this report (eg. Nubian Water Treatment System), but it provides an overview of the generic treatment processes, their mode of operation and their performance.  The Landcom “Wastewater reuse in the urban environment: selection of technologies” also provides information on such systems, as well as small centralised treatment systems for greywater and sewage.

Greywater reclamation may also occur in a centralised mode, and Inkerman D’Lux (formerly Inkerman Oasis) and Lubeck are examples of these.  Separation of greywater from blackwater leads to different hydraulic patterns compared to conventional systems in the collections system.  This is particularly important for blackwater systems (toilet water), where the high solids and low water flows have the potential to increase the number of chokes and blockages in the collection system unless great detail is used in the design.   However, if only part of the greywater is to be reclaimed, then discharging the excess greywater with the blackwater will assist in flushing the collection system.

Storage of greywater for extended period of time generally requires treatment of the greywater.  The regulations describing the details required for greywater reuse will be determined by the local Environmental Protection Agency (EPA) and/or the Health Regulator in each state.  These organizations also require that only approved treatment units can be installed and used, and systems should be checked for local approval before purchase.  The on-going maintenance and operation of any on-site treatment system should be considered.  This may performed by a trained contractor or the householder, and the complexity of the treatment system and the health risks associated with the use of the treated greywater will determine which management systems is most appropriate. 

Greywater may be used without treatment in most states, but it can generally not be stored on site and may only be used for sub-surface irrigation.  The need for subsurface irrigation is to reduce the health risks associated with spraying untreated greywater.  If the use of untreated greywater is to be encouraged by the developer on a permanent basis, then the occupants will need to consider what household products they use in their house and how these will affect their irrigated soils.  For instance, high salt loads and boron are found in some laundry detergents (http://www.lanfaxlabs.com.au/), and these elements may impact negatively on soils over time.  Therefore, education of the occupants will be required.

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On-site wastewater treatment

Septic tanks have been the traditional on-site wastewater treatment system used in residential developments.  However, advanced systems that provide high quality water for reclamation are now available, many with remote sensing and telemetry to alert a centralized management service of operational faults (West, “Innovative on-site and decentralized sewage treatment, recycling and management systems in Northern Europe and the USA).  These systems do allow water to be reused, but as for greywater systems, the EPA or Health Regulator will require approved systems to be used and the on-going management of the treatment system needs to be considered (contractor or householder).

While treated wastewater maybe used, disposal of excess may also be required.  This is particularly important for developments where the house density is high as regulations will generally not allow treated effluent to leave the property.  Common effluent drainage systems have been employed to handle excess wastewater from on-site systems.  (See Biowater paper)

On-site systems may offer cost advantages over centralized collection systems, as the costs are incurred as the lot is being developed rather than at the beginning of the development.  It also has the potential to provide water for reclamation on-site.

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Materials selection for pipes – embodied energy

Selection of pipe materials is usually made using factors such as mechanical performance, price and availability.  However, embodied energy, that is the quantity of energy required by all of the activities associated with the production process, is also becoming a consideration in choice of pipe materials.  As companies strive to lower their carbon foot print, embodied energy contained in the products and services they use will come under increasing scrutiny.  Troy et. al. (2003) estimated that water and wastewater systems were responsible for approximately 6% of the total annualised embodied energy and greenhouse gas emissions in a residential environment. 

The basic factors that influence the embodied energy impact of water and wastewater piping systems are:

• Pipe size - the bigger the pipe the more embodied energy;
• Amount of materials used - more materials, higher embodied energy;
• Pipes produced with significant recycled material - these materials usually have a lower overall embodied energy;
• Materials with a low embodied energy coefficient - the lower the coefficient the lower the embodied energy;
• Piping systems, which are more durable and have a longer life expectancy - less repair and replacement leads to lower embodied energy over the life cycle of the system; and
• Piping systems, which can last longer with appropriate maintenance - extending life, rather than replacing reduces embodied energy for that system over its life cycle.

The table below lists the relative embodied energy coefficients for different pipe types, which demonstrates that plastic pipes have far less embodied energy per length of pipe, and would be favoured materials for pipes selected on embodied energy factors alone. 

Pipe Material Type	Nom. Size (mm)	Mass (kg/m)	Embodied Energy (MJ/kg)	Embodied Energy (MJ/m)
Ductile Iron	200	34.18	38.2	1305.7
Ductile Iron Concrete Lined	200	46.91	40.2	1885.7
PVC-U	200	11.17	74.9	836.6
PVC-M	200	8.18	76.6	626.6
PVC-O	200	7	87.9	615.3
PE80B	180	10.24	75.2	770.0
PE100	180	8.61	75.2	647.5

Source: Ambrose, M.D., Salomonsson, G.D. and Burn, S. (2002).

Read the factsheet about Efficient use of materials, inlcuding pipes.  

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Key Issues

Risks

One of the significant risks to wastewater planning is legislation. The legislation surrounding domestic water use and wastewater reuse in Australia is highly complex and varies from state to state.  It can also vary within a state. Draft National guidelines for wastewater recycling exist however these are not yet mandatory.

The principal Commonwealth environmental legislation that could affect water recycling projects is the Environment Protection and Biodiversity Conservation Act 1999 (the EPBC Act).  The Trade Practices Act 1974 can also be relevant where there is a commercial element to the recycling, or when commercial activities are impacted by wastewater.  State legislation however tends to dictate local reuse policy.

Wastewater reuse guidelines do not typically cater for stormwater however the Commonwealth Department of the Environment , Water, Heritage and the Arts (DEWHA) has produced an Introduction to Urban Stormwater Management in Australia. Another useful reference for urban stormwater management is the Urban Stormwater – Best-Practice Environmental Management Guidelines (CSIRO 1999).

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Barriers

Some of the barriers that could be faced include:

Greywater

• Requires separation of greywater and blackwater plumbing within the building
• Potential impact of high sodium and phosphorous detergents on the environment in terms of soil structural degradation, increased soil pH and poor plant growth of acid loving plants.
• Lengthy approvals process when new techniques or technologies used and additional testing or other conditions may increase cost.
• Coordination of trades people is required for more complex systems (electrical, plumbing, excavation etc)
• Drip fed irrigation encourages the use of “water inefficient” plants which can require supplementary watering.
• Odours sometimes an issue
• Embodied and operational energy of high tech treatments
• Potential maintenance issues and management of system by homeowner
• Not enough information available on garden design and water needs when greywater used for irrigation. Expert advice needed
• Costs can be high
• Safety of in ground tanks required for balancing flows
• Storage of untreated greywater in a toilet cistern
• Limited research on the effects of storage on treated greywater

Wasterwater

• Adequate treatment, safeguard of home owner and public health and vector elimination
• Potential maintenance issues and management of system by homeowner
• Odours can become an issue.
• Expert advice required for set-up.
• Costs can be high
• Disposal of sludge or biosolids. Need for increased participation and reliance on householder to ensure proper functioning of the system, including its operation. Experience with septic system management indicates that the level of diligence tends to vary.  No “flush and forget”.
• Current wastewater service provision systems are not geared for decentralized systems, no current systems are in place to ensure compliance and enforcement of proper maintenance of on-site wastewater systems.
• Approvals tend to be complex (regulators councils and water authorities).

Source: Diaper, C., Tjandraatmadja, G. and Kenway, S. (2006)

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Development phase actions

Feasibility

The initial feasibility of wastewater systems should focus on understanding the requirements of the wastewater system and identify the design requirements.  These will vary with the level of water conservation envisaged and the amount of infiltration that is being planned for.

The feasibility study should consider the following:

• Peak flows: Identify the level of water conservation being planned for and estimate the impact of this on sewage flows.  Low flows of concentrated sewage will require steeper gradients and smaller pipes.
• Wet weather flows:  Identify if reductions in wet weather flows is required and if it will have a significant impact on the cost, operation and impact of the sewage system.  If low levels of infiltration are required, then a Smart Sewer design is required.
• Life cycle costing: Undertake a life cycle costing on all options to enable a comparison of costs over the life time of the scheme. 
• Environment/social: The potential impact of the scheme on the environmental and the community should be considered.

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Planning

The preferred option from the feasibility stage is now assessed in greater details in order to develop the design.  The following need to be considered:

• Legislative and regulatory requirements: Implementation of on-site or small scale wastewater schemes will require local EPA or Health Regulator approval, and these will need to be obtained. 
• Health risks:  Undertake a health risk assessment of the preferred scheme and consider how to minimise these risks.  This may affect the ownership and management considerations of on-site treatment systems.  These issues are discussed in the US EPA Voluntary National Guidelines for management of onsite and clustered (decentralised) wastewater treatment systems and the Handbook for managing onsite and clustered (decentralised) wastewater treatment systems.
• Environmental impact: Undertake an environmental risk assessment of the preferred wastewater system and develop a plan for management of any environmental risks identified.

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Design

The formal design process needs to consider the following:

• Approvals: The design should conform to all requirements of the approvals process, and all technologies (particularly onsite systems) should be approved by the local EPA and/or Health Regulator.
• Standards: System should be designed in adherence to AS/NZS 3500 (Plumbing and Drainage Code, AS/NZS 2003).  Allowance should also be made to ensure that anticipated low flows arising from water conservation can be effectively handled by the sewer system and along with the need to reduce infiltration.
• Materials selection:  Select pipe material based on performance, price, availability and embodied energy.

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Construction

• Contractors:  Ensure the contractors are familiar with the non-standard design features of the wastewater system and are capable of delivering on the design.  Variations in the design can compromise the performance of the system.

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Lot Creation

• Location:  Ensure that the location of onsite treatment systems or pressure pumps is in accordance with any conditions of the approvals process.
• Validation of system:  Prior to residents moving into the estate and using the on-site wastewater systems there is a need to commission such system.  This may include verification of treated water quality.
• Householder education: Incoming residents need to be aware of any on-site wastewater equipment (eg. on-site treatment systems, on-site pressure pump), their responsibilities and obligations in managing these items and the responsibilities of other parties (ie. if company to manage maintenance and compliance monitoring)
• Plumber education: All plumbing work should be carried out by a licensed plumber.  The risk of incorrect installation needs to be managed through education of plumbers.

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Completion

• Audits: Random auditing of plumbing works may be carried out to identify any defective pipework.
• Monitoring: There is a need for ongoing monitoring of the on-site wastewater systems to ensure that it is performing as intended. 

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Ambrose, M, Salomonsson, G & Burn,S 2002 'Piping systems embodied energy analysis', CMIT Doc. 02/302, CSIRO.

Diaper, C, Tjandraatmadja, G and Kenway, S 2007, 'Sustainable subdivisions - review of technologies for integrated water services', Icon.Net Pty Ltd, Brisbane.

Sharma, A and Swamee, P 2008 'Design methods for circular and non-circular sewer sections', Journal of Hydraulic Research – IAHR, 46(1), 133-142.

Troy, P, Holloway, D, Pullen, S and Bunker, R 2003 'Embodied and Operational Energy Consumption in the City', Urban Policy and Research, 21:1, 9 – 44