A newly developed injection method for aluminum treatment in eutrophic lakes: Effects on water quality and phosphorus binding efficiency

Schutz J, Rydin E, Huser BJ. 2017. A newly developed injection method for aluminum treatment in eutrophic lakes: Effects on water quality and phosphorus binding efficiency. Lake Reserv Manage. 33:152-162.Application of aluminum (Al) salts has been used to reduce phosphorus (P) concentrations in lakes since the 1960s. Al is typically applied to the water column where Al-hydroxides form, settle to the sediment surface, and bind P in sediment. Al can be transported to other, non-target areas of the lake, however, potentially limiting treatment effectiveness. To alleviate this problem, a new method has been developed in which the Al salt is injected directly into the sediment as a liquid. In this study, the binding efficiency and application costs were calculated for 2 lakes in Sweden that received injection applications of polyaluminum chloride (PAC). Binding efficiency was similar to previous water column applications, implying there is little difference between the 2 application methods. Other factors, however, such as dissolved organic matter and type of Al salt used (PAC vs. Al sulfate), can also affect binding efficiency. Thus, Al injection may have improved the amount of P bound per unit Al in the study lakes given the in-lake conditions and Al salt used. Treatment cost (cost per kilogram of P bound to Al) for the injection method compared to previous water column treatments was somewhat higher due to increased costs for buffered PAC and time needed for application. Both mobile sediment P and internal loading remained reduced compared to pre-treatment conditions, showing that the Al injection treatments continued to control sediment P release. More study is needed, however, to determine the relative effectiveness of this method in different types of lakes.