Workers at the Santa Cruz (California) Wastewater Treatment Plant haven’t just seen the light, they’ve measured what it costs to operate.

After energy-efficient lighting was installed outdoors, Mike Sanders was confident the plant could cut electricity costs some more with a similar conversion indoors. It worked. The new lighting systems have produced measurable savings, inside and out.

The outdoor lighting project, which converted 82 high-pressure sodium and mercury vapor lights to DuroSite LED fixtures (Dialight), gave better light and saved nearly $17,000 the first year. It also reduced maintenance costs significantly.

The next budget year, Dialight replaced 120 high-pressure sodium indoor lights with more efficient fixtures — LEDs and T5HO fluorescents. The new system uses only 12 percent as much electricity as the old, saving nearly $12,000 per year. The 10-year operation and replacement costs are about 17 percent of the old system.

“It’s been working out pretty nicely so far,” says Sanders, operations manager at the 17 mgd (design) facility. “We’ve had a few bulbs go out, but Dialight replaces them right away because we have a 10-year warranty.” The plant’s security video is better, too. “We don’t have super-expensive video equipment, but there’s better clarity and brightness in the images.”

Cultural change

The new lights are technologically more efficient, but the Santa Cruz plant also made changes in procedures that helped reduce energy consumption. One of the most important was making sure that lights get turned off when they aren’t needed. More than half of the high-pressure sodium lights indoors were routinely operated 18 hours a day, and some 24 hours. With the new lighting system, the “on” time for many of those lights is two hours.

“Operators would make their rounds, and it would take maybe 10 minutes if everything’s good,” Sanders says. “Then, as they were leaving the basement area where all the equipment is, some people were turning lights off and some were leaving them on.” The team considered but rejected putting motion sensors on the lights; managers were concerned that the lights could go off too early and possibly leave an operator in the dark.

Instead, the team focused simply on efficient practices. The new rule is to make sure lights are turned off when leaving an area. “Early on when we were just developing our energy profile, people were not really thinking about that impact,” Sanders says. “It was just a lack of institutional knowledge. Now, it’s just second nature. Energy management at any kind of facility involves employee buy-in, and it’s a cultural change, for sure. These guys have done a great job as we continually evolve our energy management.”

Members of the operations, electrical, and maintenance staffs continually generate new ideas for energy efficiency, so the sustainability goals and strategies are constantly being renewed.

“What this means is the facility staff backs the efforts of sustainability and also comes up with ideas for areas to work on within the process,” Sanders says. “This type of full interaction really helps the execution. Not every facility thinks this way.”

Green power

The lighting conversion is just one example of the plant team’s dedication to sustainability.

A biogas-fueled cogeneration system with Waukesha engines (GE Power) produces nearly 70 percent of the plant’s power needs.

The staff pays close attention to electricity prices at different times of day. Power is cheapest between 9:30 p.m. and 8:30 a.m., and it’s most expensive from noon to 6 p.m. on weekdays; an intermediate rate runs from 8:30 a.m. to noon and 6 p.m. to 9:30 p.m. on weekdays.

Team members try to run the biosolids dewatering centrifuges at off-peak times only. Power management software (Ion Enterprises) helps manage the load, enabling Sanders to look at the electric bill at any given moment. It warns operators when a demand threshold is being approached so that pumps and other equipment can be turned off or turned down if possible. That helps limit demand charges.

As an example, in the first 15 days of May, the plant purchased 1,171 kWh at the peak rate, 2,136 kWh at the intermediate rate, and 87,954 kWh at the cheapest rate.

More tools, more control

That kind of power management takes the right tools and experience. The facility has invested significantly in variable-frequency drives with programmable logic controllers. “If you attach the PLC to a VFD and marry those things together, you can really do a lot to control costs,” Sanders says. The plant is also investing in submeters at motor control centers that will generate even more data about power usage and may enable more control.

“That’s what I’m getting very excited about. We were looking at energy from a 30,000-foot viewpoint, not at the equipment component level. Now, we’re going to be able to tell how much power we’re consuming at the process layer. We can monitor what’s normal, and if we make any changes, we’ll be able to quantify the energy savings if there are any.”

Sanders has become a big fan of energy audits; San Francisco State University did one a few years ago. One suggestion from the audit was to put VFDs on the four fans in the odor-reduction tower; that led to significant savings. First, the old booster fans were removed. They weren’t operating or using electricity, but they were restricting airflow in the ducts, making the operating fans less efficient.

Then, when variable speed drives and energy-efficient motors were installed, operators found they could produce the optimum airflow by operating all four fans at lower speeds rather than two or three at full speed. Energy savings hit 40 percent; with that and with an energy efficiency rebate from Pacific Gas & Electric, the equipment paid for itself in about 10 months.

“The audit really opened our eyes,” Sanders says. “If you can’t meter closely how much energy you’re using, you are really driving blind. Part of an energy plan should involve an audit.”