Big solutions for small communities

From the largest metropolitan areas to the smallest rural villages, communities of all sizes face the challenge of providing effective and efficient wastewater treatment. And the challenge is only complicated by competition for financial resources.

Does a local government upgrade its treatment technology or build a new school? Does it improve the quality of a receiving stream, or does it update the facilities at the local senior center?

Ultimately, a balance must be struck between available resources and the levels of technology applied to wastewater treatment. That can be particularly difficult for small communities, where revenue sources are limited.

Fortunately, as the following communities attest, a system does not have to be large and sophisticated to be effective. Even the smallest budgets can support projects that produce operational, financial and environmental benefits.

Glendale, Ariz. Population: 220,000

In 1993, officials in Glendale, Ariz., recognized that the city’s existing wastewater collection and treatment facilities had become outdated. The plants could not meet the growing residential demand, as well as state and federal water quality standards, while retaining reasonable service rates. At the same time, Arizona was requiring cities to demonstrate assured water supplies for new development.

With all those issues to consider, the city created the WATERS (Wastewater Alternatives To Ease Rate Structures) program with the goal of implementing economically feasible treatment strategies that would be publicly and environmentally acceptable. Rather than build a conventional plant or expand the distant downstream regional treatment facility, the city wanted to implement better treatment technologies than it had at the time, and it wanted to exploit the economic value of treated effluent. The program culminated in construction of the Glendale West Area Water Reclamation Facility (WAWRF).

Completed last November, the WAWRF can treat 4.3 million gallons of wastewater per day, and capacity can be expanded to 15 million gallons per day to accommodate future growth. Situated on an 80-acre site, the facility provides three stages of treatment:

• preliminary treatment to remove screenings and grit;
• secondary treatment to remove organics and nitrogen;
  and
• advanced treatment via filtration to minimize turbidity.

• Treatment meets or exceeds USEPA and state standards for non-potable use of reclaimed water.

  The plant accepts influent from a large, regional plant, and it recharges all effluent, reducing the amount of water Glendale must obtain from the Colorado River. Additionally, by treating the wastewater at the WAWRF, the city saves the pumping and transmission costs that would be required if the wastewater were treated at the regional plant and then transmitted to Glendale.

  Eventually, the city will use the effluent for landscape irrigation, and it will recharge all excess. Both uses will be valuable as water sources become more costly and difficult to obtain.

  Glendale designed and built the WAWRF in five years, spending $39 million. It spent another $24 million to construct a sewage pump station, three miles of off-site pipeline, an aquifer recharge facility and a flood protection levee. All project costs were funded through a municipal bond issue.

  Dover, Fla. Population: 20,000

  Dover, Fla., is a small agricultural community that has steadily been assimilated into the sprawling Tampa suburbs. Situated in Hillsborough County, the city’s wastewater service is provided by the county-owned Valrico Advanced Wastewater Treatment Plant (AWTP).

  The AWTP was built in 1990 and consisted of headworks, biological treatment, gravity settling, filtration and disinfection. In 2001, the facility was treating 4 million gallons of wastewater per day, but increasing population had produced the need for additional capacity. There was plenty of land to accommodate an expansion, but — as is the case in many communities — the funds were not available.

  Officials considered adding another biological treatment train, including a second oxidation ditch with two clarifiers, to accommodate increased wastewater flow. However, a study of biological nutrient removal showed that, by maximizing volume in the existing oxidation ditch and adding one clarifier to handle increased solids loads, the county could increase capacity by 2 million gallons per day. That option would cost the county approximately $2 million dollars less than the first option, and part of the money saved then could be used to make needed plant improvements.

  The $4.2 million expansion began in May 2001 and is scheduled for completion next April. It includes the installation of a state-of-the-art control and monitoring system, a plant-wide fiber optic data highway and an improved scum removal system. The county’s water department is paying for the improvements with money from its annual budget for repairs and upgrades.

  “For smaller utilities, the direction now is not to overbuild, but to match needs with current conditions,” says Roy Neal, chief operator for Hillsborough County. “Getting the most capacity from existing equipment, without having equipment sitting idle, is critical to smaller communities. With this plant expansion and limited funds, we are [using just enough] to reach our target capacity for the next few years, before jumping into the next expansion phase.”

  Kiryas Joel, N.Y. Population: 13,100

  A unique community, Kiryas Joel was founded in upstate New York in the 1970s by Hasidic Jews, Holocaust survivors and their descendents. Served by a regional wastewater plant, the village — which boasted a 10 percent annual growth rate — soon became overcrowded when repeated permit violations at the plant effectively halted new construction and development. Furthermore, with no new connections, the village’s sewage continued to flow to the overcrowded regional plant.

  In 1994, village leaders decided to build a separate treatment plant that would provide for the current population and future growth. Initially, the new facility would treat half a million gallons of wastewater per day, and capacity could be expanded, in phases, up to approximately 1 million gallons per day.

  The facility would have to be designed so that discharge into a nearby stream would meet strict effluent permit limits (5 mg/l BOD5, 10 mg/l total suspended solids and 1.5 mg/l NH3-N). Engineers evaluated several treatment alternatives, including sequencing batch reactors, rotating biological contactors (RBCs) with secondary settling, and extended aeration tanks with secondary settling.

  All three alternatives had common elements — for example, they each incorporated influent screening, primary settling, tertiary treatment, disinfection, post-aeration and an operations building — and capital cost estimates were similar. However, the RBC facility clearly had lower operation and maintenance costs as a result of power and labor savings. (The other options involved heavy energy usage from large blowers to provide process air, and the extended aeration alternative required an additional operator to frequently monitor process variables.) Overall, the RBC alternative offered the best combination of reasonable capital cost and low operations and maintenance costs.

  Additionally, it is simple to operate and does not require constant attention or sophisticated instrumentation. Using shallow process tanks — five feet in depth compared to 15 feet to 18 feet for the other treatment methods — the RBC process would require relatively little excavation to implement and was therefore well suited to the proposed site’s steep topography.

  The final design was approved by the New York State Environmental Facilities Corp., a section of the New York State Department of Environmental Conservation. As a result, the village was able to secure money through the New York State Environmental Bond Act, as well as a low-interest loan from the state’s revolving fund. Construction on the $12.5 million project began in 1997 and was completed in spring 2000.

  Although small communities have fewer financial resources than large ones, their options for improving wastewater treatment span a broad range. Communities have to examine all their options to find the most cost-effective means of meeting their treatment goals. A complete plant overhaul or new construction is not always the answer to treatment or capacity problems, as illustrated by Dover.

  In planning improvements to a wastewater treatment system, cost-effectiveness is measured not only by the initial capital outlay, but by payback as well. For example, Glendale is preserving its water resources and saving money that would otherwise have to be spent on securing alternative resources; and Kiryas Joel will benefit from housing construction that resumes as a result of its new plant.

  Carolyn Lowe is a project manager for White Plains, N.Y.-based Malcolm Pirnie.