Small communities often have many challenges related to wastewater treatment including:
- Stringent discharge quality requirements (same limits as for larger communities but with economic constraints)
- High per capita costs (do not benefit from economies of scale)
- Limited finances
- Limited operation and maintenance budgets
- Limited expertise to manage wastewater treatment systems
On-site wastewater treatment systems often used for individual residences and other community facilities in unsewered areas include:
Septic Tanks - Pre-fabricated tanks that serve as a combined settling and skimming tank and acts as an unheated-unmixed anaerobic digester.
Grease/Oil Interceptor Tanks - Can be placed before septic tanks to trap grease and oil.
Imhoff Tanks - Similar to septic tanks with sedimentation occuring in the upper compartment and digestion of settled solids accomplished in the lower compartment.
Disposal Fields - Series of narrow, shallow trenches filled with porous medium (gravel) into which effluent is disposed.
Filters - Are sometimes used when disposal fields cannot be used.
The principle considerations required when selecting and designing on-site wastewater treatment systems are:
- Hydraulic assimilation capacity (soil and hydrogeological characteristics, percolation testing, etc)
- Disposal field design (wastewater quality and quantity, hydraulic gradient, etc)
- Treatment requirements (wastewater quality)
Package Wastewater Treatment Plants can successfully treat wastewaters if they are properly sized, operated and maintained. Typical package plants utilise the following components:
- Rotating Biological Contactors (RBCs)
- Sequence Batch Reactors (SBRs)
- Extended aeration
- Contact stabilisation