| Secondary Treatment |
Appropriate Use |
Relative Cost |
Operations and Maintenance |
Effectiveness |
 Constructed Wetlands |
For septic tank or primary treated effluent. Sites with no power, where land is plentiful. Useful where soils are shallow, unlike lagoons that require greater depth |
Moderate - The media, typically crushed stone and liner material are significant cost items |
Low - Periodic plant weeding and plant maintenance required | High - Can be highly effective and will produce discharge quality effluent when sized properly |
 Cocopeat Filters |
Cocopeat, sand and gravel can be used as filtration media for secondary treatment. Used as intermittent flow or recirculating filters. Use these systems where local materials are available |
Low - When locally available materials can be used for the filter media | Low - For cocopeat systems, will require raking of the surface every few months and replacement of the media every 2 to 3 years | High - Can be highly effective and reduces biochemical oxygen demands and total suspended solids |
 Aerobic Systems |
For sites where power is available and land area for wastewater is limited and expensive | Variable – Cost per cubic meter of treatment drops as size of the systems increase. For very large systems, the cost per cubic meter treated can be very low | High – Requires specific knowledge of process control, instrumentation and electronics | Variable to High - Can be custom designed for a wide variety of wastewater strengths and variability |
 Rotating Biological Contactors |
Requires electricity. Generally used for small to medium-sized residential or commercial sources. Useful when land area for wastewater treatment is limited | High - Manufactured and electrical components generally not locally available except in largest municipal centers | Moderate - Lubrication of shaft and removal of biosolids required periodically. Electrical components must be checked frequently for corrosion | High - When sized properly, can remove high percentage of pollution in wastewater. Requires generator to keep system operational during power outages |