Earlier this year, a woman living in the Washington Heights area of New York City filed a lawsuit against the Sugar Hill Project, the impressive $84 million subsidized housing building located in nearby Harlem. Completed in 2014, the mixed-use facility was designed to be an affordable living space for one of New York's poorest communities, yet the development had one major issue that belied its high-minded, revitalization goals: it was getting people sick.
Last summer, more than 50 people in the surrounding area were hospitalized resulting in 2 fatalities, all related to Legionnaire's Disease. The outbreak was connected to the housing project's cooling tower, which has since been shut down. If not properly filtered, cooling towers can instigate microbiological growth that can lead to health problems, such as those caused by Legionella.
As an integral component of many cooling systems, cooling towers are typically used in industrial applications and in large commercial buildings to extract heat from a process or building system through evaporative cooling. Cooling tower systems operate most efficiently when their heat transfer surfaces are clean, but by design, require a large air-water interface to obtain this cooling and thus the system is subject to four major water treatment concerns: corrosion, scaling, fouling and microbiological activity.
As waterborne deposits collect, they reduce heat transfer efficiency which can be very costly. Traditionally, the deposits are controlled by system blowdown, which increases wastewater discharge as well as concerns about water usage due to drought and environmental threat. As a result, cooling towers are being operated at higher contaminant concentrations, which only compound the problem.
Addressing it involves full flow and side stream filtration. Filtration reduces blowdown, energy consumption and the kinds of fouling that leads to harmful microbial growth. Full flow filtration uses a filter installed after the cooling tower on the discharge side of the pump and is designed to continuously filter all of the recirculating system water. Side stream filtration continuously filters a percentage of the flow which significantly reduces system footprint, capital investment and operational cost -- all very important considerations for affordable housing budgets. Additionally, these systems can be cleaned offline without shutting things down, eliminating the need for planned downtime.
There is an array of filtration technologies available in the market, but few achieve adequate efficiencies. Screens require frequent backwash which increases water discharge. Hydroclones suspend solids through centrifugal force which can leave smaller particles behind. Sand filters can offload sand into the system. Bag filters have limited surface area, requiring large vessels to address flow requirements. All address some of the costs associated with inefficient cooling tower filtration, but in many cases introduce new ones.
Cartridge filters, on the other hand, address all costs: environmental, operating and health. They're a disposable medium that exists in both non-pleated (lower cost, generally lower efficiencies) and pleated designs (high surface area) and offer high retention down to sub-micron levels, thus effectively addressing bio-burden issues. Some newer designs in the market such as large diameter offer further improvements in flow rates while reducing operating costs.
In March, the New York City Council voted to reform the city's cooling tower inspection protocol requiring the city's Department of Buildings and Department of Health to present an annual report of cooling tower inspection results to the city council and post the results online. Cartridge filtration could play a critical role in those results, as well as the well-being of the surrounding Harlem and Washington Heights communities. The entire story is yet to be told, but it deserves a happy ending. Especially when one considers that the Sugar Hill Project has been designed with a Children’s Museum of Art and Storytelling at its base.