Practitioner's Tool / Secondary Treatment Methods

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Secondary Treatment

Appropriate Use

Relative Cost
Operations and Maintenance
Constructed wetlands.jpg

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