Use of Aluminum to Treat Lakes

Aluminum compounds are coagulants used in water and wastewater treatment to settle solids and pull dissolved solids out of solution. In water treatment these compounds convert impurities into particles that can be settled or filtered. In wastewater treatment aluminum does the same thing, but is also noted for its ability to find phosphorus and lower the fertility of effluents. Over 40 years ago it was hypothesized that aluminum could do in lakes what it did in treatment facilities and might be especially useful for inactivating phosphorus in sediment that was being recycled to create what we now call an “internal load”. While a lot has been learned in the intervening years that makes such treatments more effective, even the earliest treatments provided enough benefits to make continued use worthwhile. Although aluminum treatments will clear the water of most algae, it is not an algaecide, defined simply by the root words as something that kills algae.

Aluminum application to a lake.

While the majority of regulatory agencies in New England appear to understand why and how aluminum is used in lake management, there seems to be some confusion in a few places about aluminum use. The State of New York created a regulatory definition of algaecide that expands coverage to any additive that prevents algae from growing. This would include aluminum, which limits phosphorus availability, and is not on the federal list of registered algaecides, since the EPA does not consider it to be one. Consequently, aluminum treatment cannot be permitted in New York. Of course, by this logic algaecides would also include oxygen if added to keep phosphorus bound to iron and unavailable to algae, and to air used to circulate water, thereby disrupting the growth of many buoyant cyanobacteria. It would also include water used to dilute phosphorus concentrations or even flush a small lake. Arguments about other additives being “natural” simply do not hold water. New England states have generally not bought into this faulty logic, but apparently the Connecticut Department of Health has applied the New York definition of an algaecide in some cases and has not approved aluminum treatments in drinking water supplies, despite approval by CT DEEP for such treatments in recreational lakes.

There is no doubt that control of phosphorus before it enters a lake is preferable where feasible, but there are very real limits on our ability to do that, and where phosphorus has accumulated in a lake, it has to be inactivated to rehabilitate the lake. It is much like fixing a boat that has sprung a leak; the leak needs to be patched, but that won’t get rid of the water that has leaked in. Aluminum treatments offer control of internal loading, and can also be used to treat inflows where watershed management is not yet up to the task or to reduce phosphorus availability in the water column after significant loading events. We have learned over the years how to prevent toxicity, making it a relatively safe technique. Creating regulatory restrictions based on faulty logic or incomplete understanding of the technique hinders lake management in a time when we need every viable technique we can get.