My experience has only been in cleaning up septic tank effluent prior to discharge and all the plants used required permits from Maf. Class A noxious weeds in the day. Lincoln University had some people working on it many moons ago. I would think any plant that grows well and is a heavy feeder would do the job. With septic tank effluent there was also a dieoff of bacteria which was part of the attraction. That required pretty free movement around the roots. They were trying to reduce coliforms whereas you probably want to encourage the bacteria associated with the nitrogen cycle.