Has there been any examination of using a constructed wetland as part of the treatment process. This strategy seems particularly appropriate given that a central part of the problem is about BOD-- arising from excess fertilization of effluent. Wetlands excel at treating this problem.

http://www.acnatsci.org/erd/ea/wetland.html

http://www.nal.usda.gov/wqic/Constructed_Wetlands_all/cwall2.asc