Turning up the pressure

Sometimes the cure for one problem leaves another in its wake. For example, combating common microorganisms using disinfectants in water sometimes creates excessive levels of certain unhealthy byproducts. To control pathogens while limiting consumers’ exposure to the byproducts of disinfection, the U.S. Environmental Protection Agency (EPA) released two drinking water regulations in January that will affect virtually all water utilities, forcing many of them to make expensive changes to their treatment systems.

The Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR), which aims to reduce potentially harmful disinfection byproducts (DBPs) in drinking water, focuses on reducing DBPs uniformly throughout the distribution system. The second regulation, the Long Term 2 Enhanced Surface Water Treatment Rule (LT2) is designed to protect consumers from waterborne disease-causing microorganisms, particularly Cryptosporidium, a chlorine-resistant pathogen implicated in several outbreaks of waterborne disease. (See “Eight ways to better manage the water rules” on this page.)

Preparing for the regulations

Three water utilities — the Passaic Valley Water Commission (PVWC) in Totowa, N.J., the Umpqua Basin Water Association (UBWA) in Roseburg, Ore., and the West Valley Water District in southern California — have been preparing to meet the demands of the new rules. The Passaic Valley Water Commission faced two challenges: economically meeting increasing customer demands for finished water while readying its treatment and distribution system facilities to comply with more restrictive drinking water quality regulations.

PVWC’s aging treatment facilities were another problem. The community’s Little Falls Water Treatment Plant began operating in 1898 and, over the years, has been expanded to 90 million gallons per day (mgd) capacity to meet increased production needs. Now, as a result of increasing demands and the new regulations, PVWC has had to produce more, higher quality water while ensuring that quality remains intact as the water passes through its distribution system.

The existing pretreatment system at the Little Falls Water Treatment Plant was replaced with a high-rate, high-efficiency process using ballasted flocculation followed by ozonation to enhance disinfection. The existing granular media filters were rebuilt to increase media depth, and the anthracite media was replaced with granular activated carbon. Backwashing effectiveness was improved by converting to a combined air-water backwash system. Enhanced coagulation with ferric sulfate was used to increase the removal of disinfection byproduct precursor compounds — measured as total organic carbon (TOC) — and to capture and remove more solids during ballasted flocculation and granular media filtration. The new facilities, which began operating in early 2003, increased finished water production capacity to 120 mgd.

Before full-scale implementation, the new treatment process was pilot tested for one year, and tests verified that the higher treatment levels would allow continued use of free chlorine as the disinfectant while complying with the more restrictive disinfection byproducts requirements of the Stage 2 DBPR throughout the distribution system. The pilot study also demonstrated that the new process would remove targeted high levels of particulates, and that the combination of ozone followed by biologically active carbon filters effectively removes taste- and odor-causing compounds and enhances TOC removal. In addition, the pilot plant testing program served as an integral part of PVWC’s training program for operation of the upgraded plant.

“Our extended pilot plant testing program helped us reaffirm our dedication to providing our customers with the highest quality drinking water, service and reliability at a competitive price,” says PVWC Executive Director Joseph Bella. “Staying ahead of changing regulatory requirements is an integral part of our mission.”

Membrane protection

Like PVWC, the Umpqua Basin Water Association (UBWA) is upgrading its 4 mgd surface water treatment plant to meet projected future water demands of 8 mgd and to comply with current and future regulatory requirements. Even though the current process at the 40-year-old plant is rated for 4 mgd, the flocculation-sedimentation basins are not fully effective when operated at rates near maximum capacity. While some portions of the process, such as the chemical feed systems, are new and serviceable, others need updating.

In advance of the new regulations’ release, and anticipating the requirements of LT2, UBWA evaluated various treatment systems to determine which would be most effective in removing or inactivating Cryptosporidium. The evaluation focused on conventional treatment with ultraviolet (UV) light and chlorine disinfection (coagulation, sedimentation, and rapid sand filtration followed by UV and chlorine disinfection) and membrane filtration (microfiltration or ultrafiltration-MF/UF) followed by chlorine disinfection. “Our project team evaluated the current and expected regulatory climate as well as options to meet all foreseeable regulations, then recommended membrane filtration as the best way for us to proactively meet anticipated requirements,” says UBWA General Manager Noel Groshong.

The UBWA is now designing and constructing a 6 mgd (expandable to 8 mgd) UF membrane treatment plant, which is expected to begin operation in September 2006. The membrane treatment system is being designed to meet current and anticipated water quality requirements using direct filtration with little or no pretreatment.

A submerged membrane filtration system was competitively bid based upon life cycle costs. Because the membrane system was selected first and the facility will be designed around it, UBWA can maximize the use of existing infrastructure in the upgrade.

UV shines bright

The southern California-based West Valley Water District faced an interesting challenge to compliance with the new regulations during expansion of its Oliver P. Roemer Water Filtration Facility (WFF) in Rialto, Calif., to treat additional water from the State Water Project (SWP). Historically, the Roemer WFF treated raw water from Lytle Creek, the SWP, or blends of the two to produce up to 9.6 mgd of drinking water. Expansion of the treatment facilities to 14.4 mgd to meet increasing system demands will result in increased use of the SWP supply.

The difficulty in meeting the new water quality requirements lies in the characteristics of the two supplies, which differ widely, and, as a result, require different treatments. Lytle Creek is used for recreation and in the summer has high heterotrophic plate counts (HPCs) which means increased levels of disinfection are required. SWP water, on the other hand, contains high concentrations of TOC and bromide, which present a substantial challenge to compliance with the disinfection byproduct reduction requirements of the Stage 2 DBPR.

Historically, the district has used only free chlorine as a disinfectant, and increasing the amount of SWP water entering the WFF would raise finished water DBP concentrations to levels nearing or even exceeding the pending limits if chlorine would continue to be used as the primary disinfectant. To reduce the formation of DBPs and to meet the LT2 Giardia and Cryptosporidium inactivation requirements, the district installed UV as the primary disinfectant. Chlorine use was reduced to levels required both to maintain an effective residual within the distribution system and to achieve 2-log virus inactivation.

Using UV disinfection, the expanded plant, which began operating in January 2006, can treat 14.4 mgd of blended raw water from the two surface sources while meeting all current and foreseeable future drinking water standards. “The district was interested in UV as a strategy to help us remain on free chlorine and let us avoid the costs and technical complexities of a system-wide conversion to chloramines,” says District Superintendent and Chief Operator Ken Sikorski. “Our distribution system includes 22 floating reservoirs, which would have required inlet and outlet changes and could have experienced nitrification problems.”

During the system’s design, the district worked closely with the California Department of Health Services to ensure approval of using UV to comply with the pending rules. Because little UV transmittance (UVT) data was available for the treated SWP supply, a conservative approach using the lowest recorded UVT data from a nearby plant treating SWP was used when designing the UV system to ensure compliance with anticipated LT2 requirements.

Meeting the demands

All water utilities are facing a new set of rules that will govern their future treatment and distribution practices. Many utilities will have to increase the removal and/or inactivation of pathogenic organisms, and/or lower the levels of disinfection byproducts throughout their distribution systems.

Utility managers and local government leaders should consider and evaluate alternative methods to ensure implementing the most effective, reliable, economical combination of measures to comply with the new rules. PVWC, UBWA and the West Valley Water District each evaluated what could be achieved by optimizing the existing facility’s operation, enhancing current treatment processes or adding new treatment processes before arriving at a course of action. Considering the changing regulatory climate, other utilities should consider following the same path.

Doug Elder, Bob Hulsey and Bruce Long are senior water treatment process engineer, director of water treatment technology and vice president, respectively, in the Kansas City, Mo., office of Black & Veatch Corp. in Overland Park, Kan.