David Cooper, Managing Director of ARM discusses how the use of constructed wetlands has evolved to keep up with the demands of pollution control.
Where population densities are low, wastewater treatment facilities are crude at best and non–existent at worst. Where population densities are high, the facilities have to be a lot more formal and sophisticated.
The world of wastewater treatment is similar in many ways to other areas of human activity. Innovations and developments occur by fits and starts, sometimes driven by events and sometimes by man’s inherent instinct to try something different.
Since the turn of the 20th century we have seen a number of distinct periods in which domestic wastewater treatment has moved from sewage farms to sewage works. The latter consisting of separate components – primary removal of solids and some organic matter; secondary removal of biodegradable organic matter and suspended solids and finally tertiary removal of residual suspended solids.
These works were frequently configured as primary settlement tanks followed by trickling filters followed by humus tanks.
Towards the end of the 20th century a number of more compact solutions were developed where the three stages; primary, secondary and tertiary, were incorporated into one piece of equipment. At the same time, we have seen the introduction of constructed wetlands or reed beds into the mix of proven technical solutions for wastewater treatment.
Once again we have seen innovation and development by fits and starts. The initial dominance of passive horizontal flow reed beds is now being overtaken by passive and active vertical flow reed beds.
Passive vertical flow reed beds are now being used to treat the sludge generated in conventional water and wastewater treatment works. They are also being used to treat raw sewage.
Active vertical flow reed beds are now being used to treat a wide range of industrial wastewaters such as airport run-off contaminated with de-icing agents and wastewaters generated by the oil and gas industries.
Constructed wetlands provide a wide range of removal mechanisms which can be harnessed to develop natural solutions for treating wastewaters generated by ‘fracking’ and wastewaters containing ‘emergent pollutants’ which stem from household products, personal care products, medicines, hormones, drugs, pesticides and much more.
On-going research and development in all wastewater treatment technologies will result in further changes in the future as it continues to meet the challenges created by emerging pollutants and regulatory requirements.