Part Three provides technical descriptions of the various wastewater servicing systems, and presents criteria that can be used to evaluate them. There is a wide range of technologies and a number of servicing systems to choose from. This part of the handbook focuses on those that are likely to be of most interest to smaller communities. Ongoing research and development mean that our knowledge about the various technologies and servicing systems is constantly improving, and the number of options will increase. (See Appendix 5 for new developments in wastewater servicing.)
Wastewater servicing scenarios
Small communities in unsewered rural–residential areas generally fall within one of the following five servicing scenarios:
- a small community currently being serviced by septic tank and soakage fields, which are performing satisfactorily, who wish to continue with on-site systems and ensure ongoing satisfactory service by initiating better individual (or communal) operation and maintenance oversight
- a small community currently being serviced by septic tank and soakage fields, some of which are not performing satisfactorily, who wish to upgrade poorly performing on-site systems, and put all systems on to an operation and maintenance programme so they do not have to convert to an off-site community sewerage scheme
- a small community currently being serviced by septic tank and soakage fields, of which a significant number are not performing satisfactorily, and where the district and/or regional council is initiating investigation of options for upgrading to a community sewerage scheme
- a developer in a rural or holiday resort area who is proposing to subdivide rural–residential lots for sale to the public, these lots to be serviced either by on-site wastewater systems or on-site/off-site cluster servicing, or an off-site community sewerage scheme
- a small community that because of unacceptable risks to public health is required under the Health Act to upgrade or install a wastewater servicing system.
In all of these cases a community finds itself having to look at how it deals with its wastewater, and how it can improve on this. It is having to look at what kind of wastewater system would be most appropriate, as well as at the appropriate wastewater technologies – for example it will need to make a choice for the components of their wastewater servicing system; a septic tank, a land disposal scheme with a wastewater treatment plant to or to send its effluent to an ocean outfall.
Any wastewater system involves four components of wastewater management:
- management at source
- collection and treatment
- ecosystem re-entry, or re-use
- operation and maintenance.
In turn there are three main types of servicing systems that deal with these management components:
The operation and maintenance aspect of wastewater management is critical to the sustainability and long life of that system. For privately owned on-site systems, this operation and maintenance responsibility has traditionally been left in the hands of the householder. However, householder neglect has been a significant contributor to the problem of poorly performing systems that eventually have to be replaced or upgraded to cluster or centralised servicing. By adopting a managed maintenance programme for on-site systems, such poor performance may be preventable, and the system life extended indefinitely. This is discussed further in Section 11.
The different servicing systems
Technically, on-site wastewater servicing refers to any system where wastewater produced on the site is treated and returned to the ecosystem within the boundaries of that site. This may be a farm (which is likely to include animal and domestic wastewater), a factory or a single home. Usually, however, 'on-site systems' refers to domestic or single-home systems only. In such cases not all residue is always dealt with on-site. It is common for sludge (septage) from the on-site treatment system to be removed off-site and returned to the ecosystem in an approved manner.
The Australia / New Zealand Standard on On-site Domestic-Wastewater Management (AS/NZS 1547:2000) defines an on-site wastewater system as a small-scale domestic wastewater system comprising the technologies and management protocols for the appropriate handling of household wastewater within the property boundaries of the place of origin of the wastewater.
The key components of such a system include some or all of:
- wastewater source technologies and management
- wastewater processing technologies and management technologies, and management for re-entry of the processed wastewater to the on-site physical environment.
Cluster wastewater servicing systems are community systems for two or more dwellings. They are generally much smaller in scale than a centralised system. The wastewater from each cluster of dwellings may be treated on-site by individual septic tanks before the septic tank effluent is transported through alternative sewer systems to a nearby off-site location for further treatment and ecosystem re-entry. In other situations the full wastewater flow from each cluster may be reticulated off-site to a local treatment and ecosystem re-entry location. As in the case of an on-site system, sludge or biosolids may be managed independently.
Here all wastewater is collected at its source and then transported (through sewer pipes) to a central site for treatment. After treatment, the resulting effluent and sludge (biosolids) is discharged at a particular point, thus re-entering the ecosystem. As in the case of cluster systems, some treatment may occur on-site prior to the wastewater being transported to the central treatment site.
Sections 6 to 9 look at the servicing options (on-site, cluster, centralised) for the different parts of the waste management process (management at source, collection and treatment, re-entry and re-use). Section 10 looks at system configuration, performance and failure issues, and Section 11 looks at the responsibilities for managing and funding wastewater systems. The final section provides summarised criteria for selecting a wastewater servicing option.
The relationship between servicing options and the elements of the wastewater management process are illustrated in the diagram in the next column.
Management at source reduces wastewater flows and loads for collection and treatment. Centralised technologies enable re-entry of treated water to land on-site. Centralised, cluster and individual technologies enable re-use and re-entry – to land (both on-site and dispersed) and to water, both at point and dispersed.