Eutrophication: Causes, consequences, physical, chemical and biological techniques for mitigation strategies

Eutrophication is reckoned as an ecological challenge that exhibits adverse effects on the aquatic ecosystem as well as the sustenance of portable water required by humans for their unremitting survival on the earth. There has been a range of techniques for the prevention of eutrophication, consequent on the need for the provision of portable water and the protection of water bodies and the aquatic ecosystem. The employment of chemical coagulants such as lime, magnesium sulphate and ferric sulphate has been reported to yield more than 95% removal of nitrate and phosphate. Moreover, adsorption studies revealed that at optimum pH and a contact time of 60 min, glutaraldehyde cross-linked chitosan exhibited the highest adsorption capacity of 139.4 mg/g, compared to epichlorohydrin cross-linked chitosan and unmodified chitosan that exhibited adsorption capacity of 108.24 and 44.38 mg/g respectively for phosphate removal. The use of nano-filtration membrane coupled with bioreactor (NF-MBR) for 62 days at a flux rate of 16 l/m.h and hydraulic retention time of 2.9 h has been posited to display percentage removal of 95, 90, 89, 87 and 68% for COD, N-NH3, N-NO2, N-NO3- and P-PO43− respectively from wastewater. Lastly, biological techniques such as wetland have been posited to be effective in combating eutrophication by exhibiting percentage removal efficiencies of 86–98% (N-NH4), 99% (N-NO2), 82–99% (N-NO3−), 95–98% (total inorganic nitrogen), 71.2–31.9% (phosphate), 25–55% (COD) and 47–86% (suspended solids). Nevertheless, the success of wetland treatment techniques is slightly impeded by the hydraulic loading rate.