CONTROL OF LAKE PHOSPHORUS WITH ALUMINUM SULFATE: DOSE DETERMINATION AND APPLICATION TECHNIQUES¹

Abstract

Nutrient diversion does not always bring about prompt and sufficient reduction in lake phosphorus concentration due to recycling from nutrient rich sediments. Certain lakes and reservoirs may continue to experience nuisance algal blooms and require additional restorative steps. The phosphorus precipitation/inactivation technique is a procedure to remove phosphorus from the water column and to control its release from sediments in order to achieve P-limiting conditions to algal growth. Aluminum salts have been used in advanced waste water treatment to remove phosphorus and this technology was extended to lake rehabilitation. Guidelines for dose calculation and application are generally lacking, and are provided in this report. The dose determination suggested here allows maximum application of aluminum to bottom sediments and thus emphasizes long term control of phosphorus recycling. Dose can be calculated directly from the alkalinity of the water to be treated. Titration of lake water samples of Vatying dkalidty allows the establishment of the relationship between residual dissolved aluminum, aikalinity, and dose which can then be employed for lake scale applications of alum to lakes and reservoirs. Application equipment and procedures are described. These depend on site characteristics and treatment objectives and indude lakeside storas, a distribution pipe, and an application barge and manifold. Alum may also be used to meet other restoration objectives including the treatment of problem flow0 and the reduction of particulate concentrations.(KEY TERMS: lake restoration; phosphorus removal; aluminum sulfate; water quality; turbidity reduction.) Us, Minnesota, 250 pp.

The Bioavailability and Toxicity of Aluminum in Aquatic Environments

“…Target alum doses are supposed to keep dissolved Al concentrations below 50 µg · L -1 (Kennedy and Cooke, 1982), but from this study we cannot determine whether the fraction they consider to be "dissolved" actually represents inorganic monomeric Al as defined in Section II.A.1. This is important biologically because for algae inorganic monomeric Al measurements are one of the most meaningful predictors of pHdependent Al toxicity (Section III.E.1).…”

“…Another risk in the currently accepted alum dosing strategies is that the maximum Al dose is designed to achieve lake water pH values as low as 6.0 (Kennedy and Cooke, 1982). Given our discussion of pH-dependent toxicity to algae (Section III.D.1, Figures 5 and 6), pH 6 represents maximal toxicity to algae in several studies, particularly those using dissolved monomeric Al as the measurement of Al exposure.…”

“…Dosing strategies typically target alum additions at the highest concentrations possible without dropping water pH below 6.0 (Kennedy and Cooke, 1982). Phosphorus is removed to some extent from the water column directly, although the primary goal is to form a floc of Al hydroxides on the sediment surface to control P release from sediments .…”

Effects of alum treatment on water quality and sediment in the Minneapolis Chain of Lakes, Minnesota, USA

“…In most cases, application of Al salts has led to substantial reductions of P in the water column (e.g., Welch and Cooke 1999), but the longevity of treatment effectiveness has varied, ranging from minimal effects to reductions of water column P last-ing 20 years or more. Part of the variability in treatment effectiveness likely is explained by the use of different techniques to calculate appropriate dosing rates (Kennedy and Cooke 1982, Kennedy et al 1987, Rydin and Welch 1999. Recent calculation methods have focused either on internal release of sediment P or the mobile-P (reductant soluble and ion-exchangeable) content of the sediment (Rydin and Welch 1999).…”

Phosphate Equilibrium Between Stream Sediments and Water: Potential Effect of Chemical Amendments

“…The flux of P from bottom sediments is often much greater under anaerobic conditions in the hypolimnion of lakes and reservoirs than under aerobic conditions (James et al, 1995). Chemical amendments, e.g., aluminum sulfate [alum (Al 2 (SO 4 ) 3 )], can be used to bind readily exchangeable P in sediments and P adsorbed to minerals subject to reduction when overlying waters are anoxic (Kennedy and Cooke, 1982;Welch and Schrieve, 1994). The use of alum may be a viable option to treat and reduce elevated levels of readily exchangeable sediment P in impacted streams, such as downstream from WWTPs.…”