The harvesting step collects both the algal turf and {TAIL ~ the pollutants}, nutrients or other undesirable species precipitated thereon, thus removing {HEAD ~ the species} from the water 
The harvesting step collects both the algal turf and { TAIL ~ the pollutants } , nutrients or other undesirable species precipitated thereon , thus removing { HEAD ~ the species } from the water
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH