Results from floating wastewater treatment plants show promise

Posted 10 February 2017

Floating wetlandsMan-made floating wetlands could be a cheap and efficient method of wastewater treatment, a US study has shown. 

Researchers from Saint Francis University and the University of Oklahoma engineered four different floating treatment wetlands (FTWs) using different materials: rainpipe, burlap, mulch, utility netting and reused plastic bottles. 

The FTWs were then planted with cattail and common rush and studied over the course of three years. According to the researchers, the results from this trial were promising.

“With respect to the control, waters underneath FTWs had lower dissolved oxygen, sulfate, nitrate, and pH, dampened diurnal temperature fluctuations and greater alkalinity,” researchers reported in the Journal of Environmental Quality

“The FTWs created habitat and were colonised by species of insects, birds, amphibians, snails and spiders.”

The study found differences in FTWs design had a negligible impact on water quality. 

“A combination of individual and aggregate water quality, habitat creation and structural performance information might present a way forward,” the paper stated.

Possible applications of FTWs include anaerobic unit processes for acid mine drainage treatment, distillery waste, dairy effluent and municipal wastewater denitrification, the authors said. 

They could also be helpful in reducing algal blooms and fish kills due to their ability to regulate temperature and solar radiation.

“Also, FTWs could help create the reducing conditions noted to encourage the biodegradation of diesel fuel, ethanol, other petroleum hydrocarbons and nitro-aromatic compounds,” the report said.

But before such applications are possible, significant design improvements are required. 

“The challenge is to create resilient, affordable, productive FTWs while minimising planting, growth medium and structural inputs, and maximising the ability of certain aquatic macrophytes to form naturally occurring stable floating mats,” the report concluded.

“Improved extensive FTWs could be expected by using more suitable planting medium/matrix, joined rhizomatous mat plantings, and stronger, more buoyant frames. One option might be seeding thin and fine mesh with Typha [cattails], growing mats under controlled greenhouse conditions and subsequent transplant for field application. 

“Future studies might investigate incorporation of high-coverage FTWs systems in applications where organic-rich, thermally insulated and less-oxygenated conditions are advantageous.”