September 2007, Vol. 19, No.9
Two Problems, One Disinfection Solution
Problem: Growing town must reduce levels of disinfection byproducts in drinking water and ensure that treated wastewater is safe for discharge and reuse.
Solution: UV disinfection.
Founded less than 10 years ago, rapidly growing Anthem, Ariz., now has a population of more than 40,000. Just north of Phoenix, Anthem was named the “best place to raise a family” by Parenting magazine in 2003 and “one of the best places to live in Arizona” by Phoenix Magazine.
The town’s water and wastewater services are provided by the Arizona American Water Co. (Scottsdale), a subsidiary of American Water (Voorhees, N.J.), from its Anthem Water Campus. The campus has two treatment plants — one for drinking water and one for wastewater. Because of the town’s rapid expansion, Arizona American Water had to upgrade its water and wastewater treatment plant to meet growing demand and also to meet the requirements of the U.S. Environmental Protection Agency’s Stage 1 Disinfection and Disinfection Byproducts Rule (DBPR) for drinking water and the upcoming Arizona Pollutant Discharge Elimination System (AZPDES) permit program for wastewater.
The water treatment plant draws its water from the Wadell Canal, which is served by either the Colorado River or Lake Pleasant, depending on the time of year. Until recently, the raw water was prescreened and then pumped through an ultrafiltration membrane system for turbidity and pathogen reduction, with chlorine used for primary disinfection.
The source water was known to contain organic chemical precursors that can lead to the formation of disinfection byproducts (DBPs). Under the Stage 1 DBPR, the Anthem water treatment plant is required to set maximum contaminant levels for several disinfectants and DBPs. One of these requirements is to maintain a running annual average total trihalomethane concentration of less than 0.08 mg/L (0.08 ppm).
To ensure that the water treatment plant minimizes the formation of DBPs, Anthem installed three Aquionics (Erlanger, Ky.) medium-pressure ultraviolet (UV) disinfection systems to replace the original chlorination plant. A low chlorine dose still is required for residual disinfection in the distribution system, and this is provided by a sodium hypochlorite reactor. The UV systems treat a combined flow of 26,495 m³/d (7 mgd).
Wastewater is treated by three Aquionics InLine medium-pressure UV systems, handling a combined flow of 11,355 m³/d (3 mgd). “We chose the Aquionics UV systems as they are optimized to meet the upcoming AZPDES Permit Program for wastewater,” said Jeff Marlow, Anthem’s wastewater foreman.
The AZPDES Permit Program requires all facilities that discharge pollutants from any point source into navigable waters to obtain or seek coverage under an AZPDES permit. Pollutants can enter waters from a variety of pathways, including agricultural, domestic, and industrial sources. A stringent requirement of AZPDES is zero chlorine residual in the treated wastewater. According to Marlow, the quality of the UV-treated effluent is “A-plus.”
At present, the wastewater is supplied to two local golf courses for irrigation, and when it is not required, it is sent to a recharge field or a wash. The golf courses currently use a combination of treated effluent and fresh river water for irrigation, but, with the population increase, it is expected that the courses soon will be using treated wastewater exclusively.
The only regular maintenance required of the UV systems is the periodic replacement of UV lamps, which is carried out by onsite staff. An automatic cleaning mechanism keeps lamp sleeves free of organic deposits for consistent UV dosing. Each chamber also is fitted with UV monitors to measure actual UV doses for recordkeeping. With the addition of an on-line transmittance monitor, Anthem uses real-time transmittance values to adjust the dose pacing of the UV system automatically.
For more information about the installation, contact Patrick Bollman at Aquionics (Erlanger, Ky.) at (859) 341-0710 or firstname.lastname@example.org; or contact Jeff Marlow at the Anthem (Ariz.) Water Campus at (623) 445-2475 or email@example.com.
Nitrogen Removal for Cluster Systems
Problem: Nitrogen removal can be cost-prohibitive or infeasible in distributed wastewater systems.
Solution: Cost-effective onsite denitrification system.
Excessive nitrogen levels pose a threat to the ecological health of water resources in the United States due to excessive algal growth that causes ecological decline. Nitrogen has been identified in the nutrient-related declines of shellfish and aquatic plant life in Chesapeake Bay, Florida coastal areas, and Cape Cod. Nitrogen loads to watersheds result predominantly from stormwater runoff, agricultural or domestic fertilizers, atmospheric deposition, and wastewater discharge, with the relative contributions varying among watersheds.
In many watersheds, nitrogen from wastewater contributes 40% to 80% of total nitrogen loads, much of which must be removed to achieve total maximum daily load (TMDL) requirements. Due to concerns about eutrophication and public health limits for nitrate in drinking water, many states require wastewater nitrogen removal in water supply recharge and ecologically sensitive areas. Centralized wastewater treatment plants can achieve total nitrogen concentrations of 3 mg/L, which is considered the current limit of technology.
But what about areas where centralized wastewater systems are not feasible or are cost-prohibitive or undesirable? Septic systems produce effluent with total nitrogen levels of 50 to 70 mg/L. Septic system effluent will be increasingly subject to stringent nitrogen limits as TMDL studies are completed and corrective actions required. When faced with the need to remove nitrogen from wastewater, communities with septic systems and developers in nitrogen-sensitive areas have two options: Construct sewers and centralized treatment facilities, or implement reliable decentralized technologies for removing wastewater nitrogen on an individual or cluster-system basis.
The Main Street Village in Mashpee, Mass., is a residential and commercial community with the atmosphere of a small New England village. The development broke ground in early fall 2004 and was fully occupied and operational in 2006. Southside Realty Trust (Mashpee) owns the development, and Lombardo Associates Inc. (Newton, Mass.) served as the wastewater treatment engineer, with McShane Construction Inc. (Osterville, Mass.) serving as contractor. The development consists of 24 units of mixed housing styles, single-family and multifamily residences with 43 bedrooms, 910 m² (9800 ft²) of retail space, with a design flow of 19.8 m³/d (5226 gal/d). The facility is served with town water.
The community wastewater system is located in an area defined by the Massachusetts Department of Environmental Protection as nitrogen-sensitive, a Zone II of a public water supply well, in addition to being in a coastal pond watershed that already has excessive nitrogen contributions causing ecological decline. Zone II areas contribute to a water supply well and require a wastewater effluent total nitrogen concentration of less than or equal to 10 mg/L. McShane chose the NitrexTM system developed by Lombardo Associates.
The wastewater system includes a conventional wastewater collection system, septic tank, and a Waterloo (Rockwood, Ontario) biofilter, followed by a Nitrex filter to reduce effluent total nitrogen prior to discharge to a drainfield.
Many communal wastewater treatment technologies are able to reduce septic system effluent nitrogen concentrations by 50% to 75%, depending on nitrogen loadings and the type of technology used. This filter was able to provide virtually complete single-pass passive nitrate removal to produce an effluent quality averaging 3 mg/L total nitrogen, which is comparable to the most sophisticated centralized wastewater treatment plants.
The filter also was chosen because of its affordability and due to its easy installation — requiring no pumping or chemical addition equipment. The filter is maintenance-free for years after installation. Numerous installations have been completed in various applications, such as for single-family residential, commercial, campground, public school, and large wastewater treatment systems. Overall average nitrate removal rates of more than 97% have been attained.
To achieve total nitrogen less than 5 mg/L for a typical residential septic application (three- to four-bedroom home), the installed filter cost is $4000 to $5000, in addition to a pretreatment system. For larger wastewater flows, the filter application will approximately cost less than $2 to $3/L∙d ($8 to $12/gal∙d) of design capacity. Sites requiring concrete tanks will cost $4 to $6/L∙d ($15 to $22/gal∙d) of design capacity. Significant cost reductions can occur when the filter is used as a nitrogen polishing filter at wastewater treatment plants.
Operations and maintenance requirements consist of monthly visits for routine maintenance and treatment system performance sampling. Daily electrical consumption is approximately 5 kW•h (6.7 hp•h), or $0.75/day with electric unit costs of $0.15/ kW•h. Telephone connection allows remote monitoring of flow and notification of alarm conditions. No chemicals and no other utilities are required.
The Mashpee results are similar to those developed and presented by the Barnstable County (Mass.) Health and Environment Department that show the system achieved a total nitrogen of less than 5 mg/L based upon 3 years of testing at the Massachusetts Alternative Septic System Test Center (Sandwich). The filter produced an effluent with average total nitrogen of 4.0 mg/L at the test center.
For more information, contact Pio Lombardo, president, or Gary Rubenstein, project engineer, at Lombardo Associates (Newton, Mass.), (617) 964–2924, or at firstname.lastname@example.org or email@example.com.