When a predetermined quantity or loading of {HEAD ~ the pollutants}, nutrients or other undesirable species has precipitated onto the algal cell walls, a portion of {TAIL ~ the algal turf} is harvested 
When a predetermined quantity or loading of { HEAD ~ the pollutants } , nutrients or other undesirable species has precipitated onto the algal cell walls , a portion of { TAIL ~ the algal turf } is harvested
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH