Wetland “floating islands” remove phosphorus

Sharon McLeay
Times Contributor

 

Wheatland County recently allowed a university student, Chris Banmann, to test his wetlands thesis, on the use of “floating islands” to remove phosphorus from sewage lagoons and allowing plants to utilize the nutrients for growth.
“Essentially how they work is they take the nutrients out of the effluent and grow plants like hydroponics. You don’t want to have the phosphorus go back into the river. The idea is to harvest the plants and use them, which removes the phosphorus out of the cycle,” said Dave Churchill, Wheatland County transportation and infrastructure manager.
Initially, the study began in 2015, utilizing two sea cans: flowing water ran through one sea can, simulating a treatment process; the other sea can acted as a storage tank, simulating the lagoon. Both sea cans contained floating islands. The idea was to see how much difference the sunlight would have on reductions for each process.
“As you can see it was very difficult to see any difference between the two processes and there was very little difference in the nutrient reduction,” said Churchill.
So in 2016, they changed the process to make the systems use effluent flowing through both sea cans, one with plants growing and one without. There were two different cycles, one for 25 days’ retention time and another for 50 days. The results showed the tank where plants were growing had removed 25 to 30 per cent more phosphorus than the tank without plants. It also reduced ammonia levels in the effluent.
“To this point in time, Alberta Environment has not asked us to deal with that or remove it; but that might be coming down the pipeline, as the federal government is going to be asking that we reduce as much ammonia as we can,” said Churchill.
They also found that the plants utilized the nitrates. The plants use up the nutrients and provided oxygen, as part of the ammonia breakdown. Plant growth was almost double in the primary system compared to just a storage lagoon. The root systems were extensive and micro-organisms flourished in the root tendrils. Churchill said the process would have to be a seasonal process.
Hours needed to maintain the islands were considered minimal.
“What this is saying is that the plants are helping remove phosphorus and ammonia,” said Churchill. “It was very positive.”
Churchill was not sure if the plants harvested could be used for animal consumption; however, he thought they may be used for composting. It was thought willows would be a good test plant for future applications. He said that might be the next step in the process – to research which plants could be used and how they would be utilized after harvesting.
He said there was also some good feedback from Alberta Environment about the potential for this process.