The complexities of the Grass Valley Wastewater Treatment Plant don’t faze supervisor Bob Bobik and his experienced operators. They relish the challenges, never stop learning and are proud of what they’ve achieved:

• Successful operation of a 2.7 mgd (design) facility in Lake Arrowhead, Calif., that includes denitrification filters and microfiltration membranes.
• A safety record that goes back several thousand days without a lost-time accident.
• The addition of 1 mgd flow train capacity for recycled water to the local golf course, helping prevent over-drafting of Arrowhead Lake, the community’s drinking-water source.

But the biggest accomplishment may be the 2012 Plant of the Year Award (category under 5.0 mgd) from the California Water Environment Association. “We targeted that award for a number of years,” says Bobik. “Perseverance and teamwork were the keys. We volunteered to be on judging panels so we could learn what made an award winner. When they evaluated us, we made sure we were ready.”

Lake Arrowhead is an unincorporated community in the San Bernardino Mountains. Reminiscent of a scenic Bavarian village, the pine-forested town surrounds Arrowhead Lake, a 1.22 square mile reservoir created by a dam on Little Bear Creek.

At 5,000 feet elevation, the town is a popular summer getaway and sits at the edge of ski country. More than 4 million visitors and second-home owners contribute several million dollars a year to the economy, providing hundreds of full- and part-time jobs. Bobik says the influx of people on weekends creates a surge in flow for which his staff must be prepared.

Advanced Treatment

Operated by the publicly owned Lake Arrowhead Community Services District, the Grass Valley facility dates to 1988, when it was built as a 1.7 mgd trickling filter plant, replacing an old activated sludge/incineration process.

In 1995, denitrification filters were added for nitrogen removal. Then in 2009, the plant added microfiltration membranes and recycle systems that pump reclaimed water to the Lake Arrowhead Country Club for seasonal irrigation. In 2011, capacity was expanded to 2.7 mgd by adding more clarifiers, a trickling filter and two denitrification filters.

Wastewater enters the plant through a Parshall flume equipped with a sonic level sensor that calculates the flow. A single Hycor Grabber climber screen (Parkson Corporation) removes rags and debris, and an aerated chamber removes grit. The climber screen has operated reliably for more than 25 years, but the plant is budgeting for a new step screen to provide 100 percent redundancy in screening.

The grit chamber performs double duty. With numerous septic systems in the area, Grass Valley also uses the grit chamber to hold septic loads, which are first aerated, then bled into the treatment plant. “It’s nasty, high-oxygen-demand stuff,”  Bobik says. “The grit chamber allows us to freshen it up a bit before treatment.”

Wastewater then moves through a trio of circular primary clarifiers and on to three high-rate plastic-media tricking filters for biological treatment. The denitrification filters, five beds in all, follow that. Supplied by Severn Trent Services, the filters use a down-flow design and consist of four feet of sand. Methanol is added to the filter influent as the carbon source. As the nitrate is metabolized to nitrogen gas, nitrogen bubbles build up in the filter media and are removed hourly through “nitrogen bumping” cycles.

The methanol is dosed automatically through Severn Trent’s TetraPace closed-loop control system, which analyzes upstream and downstream methanol levels. Each filter bed is backwashed daily. After the denitrification filters, the treated water heads either to the plant’s membrane process and UV disinfection system and then to the golf course, or directly to ponds that recharge the groundwater in the Mojave River Basin.

“Originally, we had secondary treatment and chlorination here,” Bobik says. But the state began cracking down on disinfection byproducts, particularly trihalomethanes, in the Mojave River Basin, so chlorination was eliminated in 2008. Bobik likes the move away from chlorine disinfection: “We trained and trained and focused on the hazards of chlorine gas and never had an incident. But now I think we’re a much safer operation.”

Recycling Saves

Bobik likes the recycle system as well and is proud to describe its function. “During the summer season, June through mid-November, we supply about 100 million gallons of California Title 22-compliant recycled water to the golf course for irrigation,” he says. “That has helped preserve the water levels in Arrowhead Lake, which the golf course used to use for irrigation water, and has reduced the need for the community to import expensive state water.”

The microfiltration membranes (Pall) remove solids from the recycle stream, and the UV system (TrojanUV) disinfects it. The membranes consist of four racks of 30 modules each with a combined capacity of 1 mgd. “We do an air scrub every 15 minutes, an enhanced cleaning daily, and a complete clean-in-place once a month using caustic soda, chlorine and citric acid,” Bobik says. “Our membrane units do a really good job on turbidity.”

About 20 to 25 percent of the plant’s treated wastewater is pumped to the golf course two miles away, and there is just enough nitrogen in the water to keep the fairways green. “We averaged 4.7 mg/L of nitrogen in 2012,” says Bobik. “It comes in handy at the course, and they’ve been able to get by with less fertilizer.”

The rest of the effluent is returned to the Mojave River Groundwater Basin aquifer through a 10-mile-long outfall to four percolation ponds with a combined surface area of 7.2 acres. “This area used to be a 350-acre alfalfa farm, but the alfalfa wasn’t taking up enough nitrogen, and area wells started to reflect an increased nitrogen level,” Bobik reports.

The situation led to the addition of the denitrification filters at the treatment plant in 1995.

The water is rotated through the ponds, and after use, the surface crust on each pond is disced up to prepare for another use cycle. “We still monitor the wells beneath our effluent management site, but we’ve had no THM hits since chlorine was eliminated, and nitrate levels remain below the required limits,” Bobik says.

Training Matters

The entire treatment process, and in fact major systems across the utility district, are monitored and controlled by SCADA-Pack (Schneider Electric) and Allen-Bradley/Rockwell Automation hardware, installed by Byrd Electronics and powered by ClearSCADA (Schneider Electric) software. Bobik’s team staffs the Grass Valley plant seven days a week, operating on a schedule of four 10-hour days, which the team members like.

“Everybody gets either Friday or Monday off,” Bobik says. “We’re a small crew, and we cooperate and work together.” The team includes Justin Luck, senior operator; Mary Pedersen, laboratory director; and Al Edwards, Trevor Cory, Matt O’Kelly and Phil Jag, operators.

Because of the complex plant processes, Grass Valley emphasizes training. “We brought in each of the vendors and made sure they stuck around until everyone was up to speed on the new processes,” Bobik says. “We were under construction for four years, so we picked our vendors’ brains and made sure our operators were part of the process during equipment startup. It was a good training opportunity.”

The plant has also implemented more formal training and records and maintains all operational and maintenance procedures in plant documents. “Only two of our current operators were here when the microfiltration units were installed,” Bobik says. “The new people have been trained by the more experienced.”

The training has paid off. “We have our challenges,” Bobik says, pointing out the nitrogen removal filters with methanol feed, the recycled effluent and the microfiltration operation. “It can be a tightrope. The methanol dosing must be very precise, for example, and you need to know what’s going on at all times."

Ditto for the automatic control system. “Automatic doesn’t literally mean automatic,” Bobik says. “We sometimes struggle to properly denitrify with our automatic controls. We used to run with manual samples and dosing; sometimes we still have to do that.”

One of his goals is to tighten up controls, get smarter and keep a tighter rein on effluent process parameters. The staff will be changing the location of one of the methanol analyzers. “We didn’t realize it was in a bad location until we kept seeing bad results,” Bobik says.

But he’s not complaining: “Neighboring agencies sometimes visit and ask how we learned all this. The complexity has actually been fun. We don’t have to twist guys’ arms to get them to learn new processes. They’ve actually gravitated toward them.”

More Information

Huber Technology, Inc. - 704/949-1010 - http://huberforum.net

Pall Corporation - 800/645-6532 - www.pall.com/water

Parkson Corporation - 888/727-5766 - www.parkson.com

Rockwell Automation - 414/382-2000 - www.rockwellautomation.com/industries/water

Schneider Electric - 888/778-2733 - www.schneider-electric.us

Severn Trent Services - 866/646-9201 - www.severntrentservices.com

TrojanUV - 888/220-6118 - www.trojanuv.com