Lake DeForest (LDF) Water Treatment Plant

Cutting-Edge Pilot Demo Takes On Challenging Source Waters

Utilities must often take action to combat source water challenges, including seasonal algae spikes. High amounts of algae can lead to taste and odor events, cyanotoxin production and high total organic carbon (TOC) concentrations, which often result in high disinfection byproduct (DBP) formation. Seasonal lake stratification can enhance internal phosphorus cycling that exacerbates these algae spikes and elevate dissolved manganese levels resulting in additional treatment challenges.

Lake DeForest (LDF) Water Treatment Plant, owned and operated by SUEZ Water New York Inc. (Suez), is a 20 million gallon per day treatment facility located in Rockland County, NY.

To address challenging source water concerns at the LDF plant, Suez undertook the design, construction and operation of a complete pilot-scale system. HDR’s Water Institute applied research staff helped operate and evaluate the pilot on a full-time basis and will assist in the preparation of a final pilot report. Ultimately, the results of the pilot testing will guide future upgrade requirements at the LDF plant.

The pilot system is fairly large, with an operating capacity ranging from 50 to 100 gallons per minute (gpm). The pilot draws water directly from the full-scale plant raw water source. This location allows the pilot to duplicate the existing LDF plant raw water at the pilot, and for the efficient collection and disposal of residuals generated from treatment processes.

The pilot plant treatment scheme includes advanced treatment technologies including pre-ozonation, powdered activated carbon, chlorine dioxide, dissolved air flotation (DAF), intermediate ozonation and six filter columns with different media configurations including granular activated carbon and various chemical addition capabilities. Each of these treatment processes was assessed on its ability to handle challenging source water conditions.

Baseline performance tests were conducted by replicating the existing full-scale operation at LDF on an as-needed basis whenever a significant change in source water conditions was observed. Once this baseline was established, a sequential experimental plan was initiated to identify optimal process configuration, process loading rates and chemical dosages for improved water quality. Of particular importance was the removal of taste and odor compounds, TOC/DBPs, removal of other compounds likely to be regulated in the future, and improving the existing LDF plant performance. An important consideration was the evaluation of potential negative impacts of various treatment processes on water quality. For example, bromate formation by ozonation was a key consideration when selecting ozone dosages to evaluate.

As the pilot study comes to completion this month, after eight months of continuous operation, the benefits of evaluating various operational conditions can be fully realized and translated to full-scale benefits.