Calcium compounds, calcium oxide (quick lime), calcium hydroxide (hydrated or slaked lime) and calcium carbonate (lime) have been used for hundreds of years as cost effective water treatment chemicals. They have been successfully applied in lakes, reservoirs and drinking water supplies.
Calcium hydroxide technology removes soluble reactive phosphorus from the water column thereby denying blue-green algae and some species of weeds the nutrient they need to sustain their growth. It also enriches the water column with calcium ions that under the influence of photosynthesis cause settlement of algae.
In an effort to reduce soluble reactive phosphorous within the lake basin from point sources and the main water column, data was developed to support future lake-wide use. A number of site specific experiments were completed and evaluated which resulted in large scale lake field test initiated during 2007. Experimentation consisted of the following projects:
Ponce de Leone Calcium Hydroxide Injection
Project goals and system configuration: Reduce soluble reactive phosphorous levels from the inflowing waters of Ponce de Leon Creek utilizing a calcium hydroxide injection system. An injection system consisting of perforated pvc piping was installed across the streambed. Liquid calcium hydroxide formulations were dispensed through the injection manifold via a metering pump system. Pre and post injection analysis took place approximately 150 feet from the injection manifold.
Results: Over a three day period of time numerous concentrations of calcium hydroxide were injected across the creek bed. Data was collected and evaluated. Those concentrations that produced positive results were replicated and then evaluated for feasibility as a long term control alternative. Results clearly indicated that calcium hydroxide was an effective means in reducing soluble reactive phosphorous from the inflowing creek waters. Material storage, site security and financial concerns associated with full scale implementation curtailed further consideration of utilizing a calcium hydroxide injection system as a viable means of reducing soluble reactive phosphorous from the creek waters.
Ponce de Leone Calcium Hydroxide Granular Experimentation
Project goals and system configuration: Determine the effectiveness of calcium hydroxide granules to reduce the concentration of soluble reactive phosphorus (SRP) contained in the inflowing waters of Ponce de Leon Creek and deep water southern basin spring areas of Lake Steilacoom. The experiment involved setting up a one-gallon cylindrical test chamber containing glass beads in its bottom. The glass beads simulated the gravel bed of Lake Steilacoom. Into the chamber was placed different formulations of calcium hydroxide consisting of binder and active ingredient. Water from Ponce de Leon Creek was pumped (using a metering pump) into the bottom of the test chamber beneath the glass beads to simulate inflowing groundwater. Discharge waters from the outflow tube located at the top of the cylinder were monitored at 30 minute intervals utilizing a Hydrolab. In conjunction with the electronic monitoring water samples were collected and analyzed for ortho phosphorous. Data was used to assess the following:
- To determine the rate at which a known quantity of calcium hydroxide granules dissolve when exposed to a known volume (quantity) of water flow, under the temperature conditions that exist in Ponce de Leon Creek.
- To determine the effect that the dissolved calcium hydroxide and sodium silicate (binder) has on the physical and chemical attributes of treated Ponce de Leon Creek water.
- To gather sufficient jar test data to be able to determine proper dosing and the likely chemical and biological response of Lake Steilacoom to a full scale field application (seeding) of calcium hydroxide granules to selected bottom areas (groundwater inflow sites) of the lake.
Results: Granular formulations of calcium hydroxide were successful in reducing the soluble reactive phosphorous from the test chamber waters.
Calcium Hydroxide Deep Water Injection
Project goals and system configuration: Determine if deep water injection of a calcium hydroxide slurry below the lakes thermocline is capable of reducing the soluble reactive phosphorous levels of the cold water layer of Lake Steilacoom. Powdered calcium hydroxide was mixed into a slurry and injected below the thermocline covering approximately one surface acre of the lake. Ortho phosphorous levels were monitored pre and post application,
Results: This project, again, resulted in positive results indicating that deep water injection of a calcium hydroxide slurry can effectively reduce the soluble reactive phosphorous concentrations of the treated waters. Post sampling results clearly supported the project goals showing that soluble reactive phosphorous levels were reduced below the detectable levels of the analytical equipment
Calcium Hydroxide Granular Deep Water Application
Project goals and system configuration: Determine if a granular formulation of calcium hydroxide can produce a sustained reduction in the soluble reactive phosphorous concentrations within the deep water spring and cold water discharge layer of Ponce de Leon Creek. Calcium Hydroxide in the form of cat litter was distributed over the targeted treatment sites at designated concentrations until a reduction in soluble phosphorous levels were confirmed through laboratory analysis.
Results: Granular calcium hydroxide was applied on three different occasions. The first application produced no positive results while the second attempt reduced soluble reactive phosphorous by 50%. The third application was an attempt at reproducing the results obtained during the second application. Results obtained from the Ponce de Leon site indicated that soluble reactive phosphorous levels were reduced by 50% and sustained throughout the five day monitoring timeframe. The deep water spring site produced an initial decline in soluble reactive phosphorous levels. However, concentrations returned to background levels within 48 hours.