Linking pond and wetland treatment: performance of domestic and farm systems in New Zealand

Abstract

Wetland systems have been used extensively to supplement and upgrade waste stabilisation pond treatment systems in New Zealand. Key attributes of wetlands, such as low operational costs, minimal reliance on machinery and external energy inputs, high wildlife habitat values, and perceived “naturalness”, complement those of pond systems. Performance data for a range of New Zealand post-pond constructed wetlands treating sewage, dairy farm and piggery wastewaters show BOD and SS concentrations can be readily reduced to low levels. Bacterial indicators are commonly reduced by at least one log unit, but levels below 500 cfu (100 mls)-1 are difficult to achieve consistently. Nutrient removal efficiency is highly dependent on loading rates and wastewater characteristics. Plant establishment and maintenance, wildlife management, hydraulic design and adequacy of preceding treatment are identified as key practical issues in the implementation and management of constructed wetland systems.