The adage that engineers design treatment plants but operators make them work is never more true than at the Henry N. Wochholz Regional Water Recycling Facility in Yucaipa, Calif.

Managers Matt Harward and Kevin King and their staff have made numerous modifications and improvements to this advanced tertiary plant, upgraded in 1992 and again in 2006 to meet tightening discharge requirements, and to prepare for total water recycling in the near future. Among the improvements:

• Managing plant influent flow with equalization tanks.
• Controlling algae growth on secondary clarifier weirs.
• Fighting Nocardia filaments and resultant foaming.
• Reducing ammonia recycle to the biological treatment system.

“Our operators do a lot of things here,” says Harward, deputy manager of the Yucaipa Valley Water District, the plant’s owner. “When we have a problem, our approach is to do something about it. We try one thing at a time and see if it works. If it doesn’t, we try another.”

Highly visible

The water recycling facility serves about 50,000 residents of the cities of Yucaipa and Calimesa in the foothills of the San Bernardino Mountains, more than 2,000 feet above the greater Los Angeles Basin.

While the community’s relatively high elevation offers several benefits — including mountain views and a high-quality groundwater table fed by snowmelt — it also presents some of the most challenging wastewater treatment requirements in the nation.

The California State Water Quality Control Board has imposed increasingly stringent wastewater treatment standards on the district to ensure that its effluent does not degrade groundwater supplies in Yucaipa itself or in surface or groundwater supplies downstream. One of the requirements calls for total inorganic nitrogen (TIN) to be less than 6 mg/l — “one of the toughest TIN standards in the country,” according to Harward.

Series of upgrades

To meet tougher standards, the district upgraded its 1982 trickling filter/activated sludge treatment facility with dual-media sand-coal filters and denitrification towers in 1992, and increased capacity from 3 to 4.5 mgd.

In 2006, when effluent requirements tightened even further, the district replaced the existing filter and denitrification facilities and eliminated the use of chlorine gas and sulfur dioxide gas by installing advanced tertiary treatment. The new system included microfiltration and UV disinfection and expanded design capacity to 8 mgd.

Wastewater begins its journey in the headworks, where quarter-inch fine screens (WesTech) and vortex grit removal by Smith & Loveless take care of debris and sand. Rectangular primary clarifiers are equipped with solids removal mechanisms from PolyChem Systems, Division of Brentwood Industries, and Muffin Monster grinders (JWC Environmental). Primary sludge is transported by seepex and Moyno pumps to the facility’s train of four anaerobic digesters.

Secondary treatment is provided by an integrated fixed-film activated sludge (IFAS) system developed by AnoxKaldnes (now owned by Veolia Water). Two anoxic basins (converted trickling filters) are followed by aerobic tanks that include floating plastic media, enabling simultaneous attached and suspended-growth biological activity. According to wastewater superintendent Kevin King, Yucaipa is one of the first treatment facilities in the western United States to use the technology.

“We contacted treatment plant operators with IFAS plants around the country to assess their opinions about IFAS and other nitrate treatment options,” he says. Harward and district general manager Joseph Zoba also traveled to Broomfield, Colo., which had recently installed an IFAS system, to ask questions and gain practical information and feedback on their experiences.

After final clarification in circular tanks, the treated water passes to a battery of microfiltration units (Pall). Pore size is 0.1 microns, and the units achieve exceptional removal. “We’re very happy with our microfiltration system,” says King. “We have the same system in our water plant, so we can share expertise as well as spare parts with our potable water staff.”

The disinfection facility includes high-intensity, low-pressure UV light units (Trojan Technologies). A portion of the high-quality effluent is held in a 4-million-gallon aboveground, recycled water tank for use by two customers for irrigation. The rest is discharged to San Timoteo Creek, a tributary of the Santa Ana River, which courses westward across Southern California through San Bernardino, Riverside and Orange counties to the Pacific Ocean.

“It’s a shame to put it into the creek,” observes Harward. And indeed, when infrastructure piping is completed over the next couple of years, all effluent will be used for irrigation in the community, and long-range plans include groundwater recharge.

Primary and waste activated sludge are mixed in the anaerobic digesters, then thickened and dewatered into Class B biosolids on Ashbrook belt presses. A local landscaper takes all the material — about 450 wet tons per month — and composts it for sale.

Making it work

While the Yucaipa system is an elegant design, it’s the ingenuity and perseverance of the operators that have enabled the plant to achieve its discharge goals. The ability to control flows using equalization tanks is a key to success, senior operator Kevin Lee believes.

“Our original design included a secondary EQ tank, but we were certain that wasn’t enough,” he recalls. “We insisted on having a second EQ tank at the primary stage.” Both tanks are compacted soil ponds lined with polyethylene, with capacities of 1.3 and 0.8 million gallons.

Lee says the biggest advantage is the ability to smooth out diurnal flows by banking water and then releasing it for treatment at night. This is especially helpful in the operation of the microfiltration system. The EQ tanks also help with larger repairs and maintenance.

For special maintenance or repairs to parts of the treatment system, the plant can essentially turn off flow for up to 12 hours by using the EQ basins. “It’s almost unheard of,” King says. “We really like this feature.”

One thing the staff didn’t like was the rapid buildup of algae on the weirs of the secondary clarifiers. “In this hot climate, our water is quite warm,” says Harward. “Plus, we get a lot of sun, so the conditions are right for algae growth.”

The plant staff tried a number of remedies and finally settled on NEFCO covers over the launders and weirs to keep the sunlight off the surfaces. “We’ve tried scrubbing the algae off the surfaces, but we ended up having to scrub almost every day,” says Harward. “It’s a matter of removing the algae or preventing it from forming in the first place. We’ve elected to go with the latter.”

The plant is also “blessed” with a persistent crop of Nocardia. “Because of the way the secondary system is designed, with isolated compartments to keep the plastic media from escaping, the Nocardia doesn’t move out,” says Harward. “It can build up foam and run down the sidewalk and into the street. It’s a big problem for us.”

King’s staff is working on a solution that involves creating passages between the unit processes so that the Nocardia can move through the plant and not build up. But it’s necessary to install screens in these passages so the plastic media stays in place.

The staff tried several other measures, including spraying chlorine on the water surfaces, but nothing else has really worked. “Once we understood the issue, we were able to come up with a workable solution,” King says. The technique promises to help reduce a $30,000 per month expenditure for de-foaming chemicals. The ultimate goal is a chemical-free solution.

In another improvement, staff has reduced the ammonia returning to the secondary treatment process by blending the microfiltration backwash water with the filtrate from the dewatering process. The filtrate is high in ammonia, and the backwash water, mixed at a ratio of about 50/50, dampens its effect. “We pump the flow back at night to minimize the load on the aeration basin,” explains Thaxton Van Belle, senior operator.

Smooth operation

As a result of the operational improvements, the Yucaipa facility works very well. King says the coliform count is essentially non-detectable, even coming out of microfiltration. “We’re looking at re-rating our UV system, and perhaps going with a single channel because of the negligible coliforms,” he says. “We’re really using our UV for virus removal only.”

More challenges lie ahead. The district is considering adding reverse osmosis to the facility to recycle all of its effluent in the future. At first, the water would be used for community irrigation, but ultimately recycled water would be injected into the aquifer.

“For that to happen,” King says, “the district must complete a brine discharge line some 12 miles through several communities to the main brine discharge line in San Bernardino. The cost is around $12 million.” Eventually, the line goes to the Pacific Ocean.

“The RO units will enable us to get our total dissolved solids (TDS) down under 370 parts per million, which is the state requirement,” says Harward. “We obviously want to do everything we can to be in compliance. The challenge for us has been that state regulations have been evolving faster than we could bring new facilities online or ensure that the water treatment technologies recommended to us by outside consultants would work as advertised.”

Whatever the new requirements call for, and whatever system is designed to meet them, you can bet the Yucaipa staff will figure out how to make it work.