• Aerobic systems: require aeration, are energy- and capital-intensive, do not result in any by-product, produce excessive sludge and are difficult to handle

• Lagooning: requires extensive land

• Well-designed ponds: treatment is partially aerobic and partially anaerobic; land and time requirements are high

• Anaerobic systems: not as energy- or capital-intensive as their aerobic counterparts and do result in value-added products