Wastewater plant will need upgrades as Merced grows

tmiller@mercedsunstar.comMay 22, 2014 

Merced’s Wastewater Treatment Plant cleans millions of gallons of water a day using state-of-the-art technology thanks to upgrades made over the past few years, but experts say anticipated growth will require substantial additions to the system in about eight years.

Southwest of the Merced Regional Airport, the facility sits on about 40 acres and cleans an average of 8 million gallons of water a day. It has the capacity to process 12 million gallons, which would be enough to handle a population of about 120,000.

The city’s master plan predicts that the population will reach 169,000 in 2030. Depending on the placement of additions to the plant, the price tag could exceed $93 million, according to estimates.

The $60 million upgrade of the facility completed in 2012 uses an array of highly efficient processes to clean the water before it’s flushed into Hartley Slough for use around the plant and for irrigation.

Pipes carry wastewater from drains and toilets around Merced to the plant’s intake system, called “headworks,” said Jim Osmer, the plant’s manager. The headworks uses screens, brushes and pumps to separate the wastewater from garbage and objects that don’t belong in a drain.

As one might imagine, many people flush items that don’t belong in the city’s drains – toys, hygiene products and garbage, to name a few. Toilet water should only be used for “poop and paper,” he said. The headworks also uses a vortex to separate dirt and other grit from the wastewater.

The treatment process from there consists of three parts. The primary treatment filters out the solids that are not biodegradable and sifts out as much organic material as possible.

The secondary treatment pool uses rotifers, vorticella, tardigrade and other organisms that have changed little in millions of years. The creatures eat materials in the water as it snakes through a handful of pools, and release nitrogen into the atmosphere, leaving less of the gas in the liquid. “That’s directly protecting the downstream users,” Osmer said.

The cleanest part of the water is skimmed off the top and moves on through the process, while the thicker sludge at the bottom of the tank goes back to the first pool for treatment. A third set of filters strains the water before sending it through ultraviolet lighting, which disinfects that water.

The thicker sludge is processed in the plant’s digester and then moved into a holding tank for about a month. Finally, the sludge runs through a centrifuge, which forces the waste sludge and water apart at speeds as fast as 2,700 rotations per minute. That water makes its way to the third set of filters.

Up to 366 cubic feet of methane, a byproduct, is stored on site, Osmer said. Methane is used to heat the digester, and officials would like to use it for fuel in the future. Right now, any excess methane is burned off.

The plant has about 22 employees, who work in the laboratory, run the system or do other maintenance. It’s also run by a system of computers, which use touch-screen technology and automated sensors.

The latest additions to the plant include the solar dryer, which covers about 1.7 acres. Seven greenhouse bays have robots, called “moles,” that work the waste sludge until the material has dried and can be used on crops.

The city uses the fertilizer and treated water to farm about 300 acres, growing wheat, alfalfa and other feed crops. Sales from the crops help subsidize the cost of running the plant.

UC Merced, though not actually in the city limits, is connected to the sewer system that leads to Merced’s plant. The university is also one of the factors expected to spur growth.

This week the Merced City Council was introduced to some long-term questions city staff will need to answer on their way to preparing for more sewer users. Leaders will need to decide where to put sewer trunks, a sort of satellite facility that branches off the main plant, and where to install pre-treatment sites to prepare to handle the population growth and industry that uses large amounts of water.

Some of the questions have been answered. “In the long term, it was cheaper for the city to have one treatment plant and extend trunk sewers to it,” said Dan Rich, an engineer with Stantec, the engineering firm hired to assist with the wastewater master plan.

Along with the university, the additional sewers would likely serve Campus Community, a development planned around UC Merced. The idea is to have stores, housing and services aimed at students located near campus. Mayor Stan Thurston said developers have expressed the desire to connect to the city’s system.

There will be many public meetings before the city makes any decisions on the sewer trunk alternatives and how the users will pay for the additions, Thurston said. “There’s always, ‘Who pays for it?’ ” he said. “You always get to that sooner or later.”

Sun-Star staff writer Thaddeus Miller can be reached at (209) 385-2453 or tmiller@mercedsunstar.com.

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