C3 Waste water
Relates to Healthy Living Practices:
- removing waste water safely
- reducing the negative effects of animals, insects and vermin
- reducing the impacts of over-crowding
Waste water or sewage contains germs, also known as pathogens that can be very harmful to people’s health. Systems that remove waste water from the house, treat it and dispose of it safely are critical items of environmental health infrastructure in any community.
Increasingly, waste water in rural and remote communities is being treated and disposed of in off-site sewerage schemes that collect both the grey and black water from houses and treat and dispose of the waste water in a centralised facility. The advantage of an off-site system is that all waste water is removed from yards and living areas and handled at one place away from people, and the operation and maintenance happens in one place rather than in every yard in the community. A disadvantage is that the system can be more expensive to operate than onsite systems such as septic tanks.
There are three stages in the process of managing waste water. All three stages need to be considered when designing a sewerage system for the community and all three have some impact on decisions made during a housing project. These stages are described below.
Stage 1―Collection
Waste water is collected from the immediate living area and removed to a treatment facility in drain pipes. Initially this is done via the house drains, see B3.2 House drains. If the waste water is being treated off-site, the house drains will discharge to a communal sewer pipe, which is usually near one of the property boundaries.
Step 2―Drainage
The most common sewer drains in communities are deep sewers. Fifty four percent of surveyed houses had deep sewer drains. These are large diameter pipes with a slight fall. The household waste water flows through the pipes by gravity to the treatment ponds. In most communities, pumps are required at some points to pump the waste water back up to a higher point so that it will start flowing by gravity again. The pumps require power and maintenance. ‘Vacuum sewers’ have been developed to reduce the need for pumps; however, they require specialised maintenance and it is usually more cost effective to use pumps in remote communities, because they are easier to maintain or replace.
Another form of sewer drain is the ‘small bore’ sewer, which forms part of a common effluent disposal (CED) system. This consists of smaller, shallower pipes with a steeper fall. A small bore sewer may also require pumps to assist the gravity flow and can be subject to blockages if the on-site treatment tanks have failed. If connecting to a small bore sewer, it will be necessary to provide a primary treatment tank, that is, a septic tank, at the house.
Stage 3―Treatment
Waste water needs to be treated before it can be safely disposed of into the environment or recycled for use in the community. The level of treatment depends on how and where the effluent is disposed.
The first level of treatment (‘primary’ treatment) removes solids and some bacteriological pollutants. Septic tanks provide primary treatment to waste water. Effluent that has only received primary treatment poses a significant threat to people’s health, and is of such a poor quality that it must not be disposed of into the environment, except in underground trenches.
The next level of treatment of waste water is called ‘secondary’ treatment. During secondary treatment more of the pollutants that are harmful to health are removed, as well as some of the pollutants that are harmful to the environment. The treatment ponds in most sewerage systems treat waste water to a secondary level so that it can be discharged to the sea, a river, an evaporation pond, or some other licensed disposal point. A licence is required for any effluent discharge, and the license conditions will require a minimum quality of treatment to be achieved. Secondary treated effluent may be re-used for irrigation in sub-surface systems, but should not be sprayed or used for food crops or on playing fields. It may be suitable for use on a woodlot or community wind break or for growing pasture for stock.
The effectiveness of the treatment pond in treating effluent will depend on how long the water stays in the ponds. If there are multiple water leaks from faulty taps or toilet cisterns in the houses, there will be more water flowing through the treatment ponds, which lessens the treatment time and reduces the quality of the treated effluent. Some communities have made substantial improvements to the performance of their sewage ponds by fixing all leaking taps in the community. If stormwater pipes are connected to sewerage systems, the ponds will not work effectively whenever it rains due to the additional water load.
‘Tertiary’ treatment is a higher level of waste water treatment after which the effluent can be recycled in the community. However, tertiary treated effluent is not safe to drink unless the treatment system is specifically designed to produce potable water. Package treatment systems usually provide tertiary level treatment, and mechanical and chemical treatment systems can be added to treatment ponds to achieve tertiary level treatment. Although it is expensive to treat waste water to a tertiary level it may, in some situations, it can be more cost effective than developing additional water sources. In environmentally sensitive areas, government agencies may require tertiary treatment before effluent can be discharged to the environment.
Design and specification
For new housing projects:
- confirm the type of sewerage system currently available in the community and any future planned upgrades, design the house drains to suit the circumstances
- check the location and height of the nearest sewer pipe, and confirm there is enough fall to get the waste water from the house to the main sewer connection point and avoid using pumps wherever possible
- ensure the overflow points in the main sewer line and overflow relief gullies in the yard are lower than the floor of the house, and that all house drains are located so that any emergency sewer overflow will not flood the house or outside living areas, will not pond in the yard and will not overflow near paths and door ways
- if permitted by the local council, consider first treating grey water from the laundry and/or bathroom and then connecting these drains directly to a sub-surface irrigation system, as this will assist in saving water and in reducing the load on the treatment ponds
- find out the level of waste water treatment available/planned for the community and, if appropriate, provide a second system of supply pipes in the yard and house that could be used for recycled water.
Quality control
During construction and before making the final payment, check that:
- all house drains have been inspected before backfilling and are legally connected to the disposal system
- the local council or essential services operator has inspected, tested and approved the connection to the sewer
- ‘as built’ drawings are completed, showing the location of house drains and the connection to the sewer
- stormwater pipes are not connected or discharged to the house drains or mains sewer.
Maintenance
As part of cyclical maintenance:
- repair leaking taps to reduce the load on the waste water disposal system
- check and maintain house drains
- ensure that downpipes and stormwater drains are not connected to the sewer, and disconnect or re-direct any drains that are connected
- pump out septic tanks that form part of a CED system
- service and maintain pumps and valves in the sewer to avoid failure
- maintain the treatment ponds
- fix broken or blocked stormwater pipes that are flowing into local land application areas.
| Waste water systems and detail | Percentage of houses | Total houses surveyed | Change since 2003* |
|---|---|---|---|
| Type of waste water system | |||
| No waste water system | 3% | 3,658 | |
| Deep sewer system | 54% | 3,658 | << |
| Houses using septic systems of any type Septic tank and common effluent system 28% Septic tank and soakage trenches 14% + |
42% | 3,658 | ++ |
| Aerobic waste water package treatment system | 1% | 3,658 | |
| All drainage around the house OK (this question records if drainage failures are obvious in the yard area around the house) | 73% | 3,660 | |
| Dry system toilets | |||
| Dry toilet | 5% | 1,961 | |
| In-ground pit toilet | 2% | 1,961 | |
| Contained composting toilet | 3% | 1,961 | |
| Details of the waste systems | |||
| Grease trap | 8% | 3,632 | |
| Septic tank not able to be located | 5% | 1,089 | |
| Pump out truck had access to septic tank | 91% | 1,089 | |
| Septic tank lid protected from damage | 60% | 1,089 | |
| Septic tank lid not protected from damage | 33% | 974 | |
| No soakage trench (CED (common effluent disposal) system) | 58% | 1,303 | |
| Functional soakage trench | 31% | 1,303 | |
| Non-functional soakage trench | 12% | 1,188 |
* See ‘Changes in the conditions of houses’ for an explanation of the symbols used in this column.