Sunday, May 3, 2015
YOLO COUNTY NEWS
99 CENTS

The wastewater plant: where ‘it’ all goes

Michael Lindquist, the city of Davis’ civil engineer,  looks over the aerated grit  tank. State-mandated improvements to the wastewater treatment plant will be completed by 2017. Sue Cockrell/Enterprise photo

By
From page A1 | November 04, 2012 |

Lest we forget, the city of Davis actually is juggling two hundred-million-dollar water projects. 

For the past year, the city and the City Council have charged hard to tie down the details and feasibility of tapping the Sacramento River to provide the community with a new source of higher-quality drinking water. But the more stringent drinking water standards weren’t the only new water regulations flushed down to local jurisdictions from the Central Valley Regional Water Quality Control Board.

The state also admonished cities like Davis that the effluent discharged from wastewater treatment plants needs to be cleaner. So, by 2017, the city of Davis is obligated to redesign and rebuild its plant. There was no way around the $100 million capital improvement project.

It’s work that — aside from helping the city comply with the new regulations — will ratchet up the facility’s efficiency. The current process already is pretty cool. 

————

Michael Lindquist stands on a steel grate atop one of the wastewater treatment plant buildings northeast of Davis, while hundreds of thousands of gallons of human waste gush through a screen just inches below his feet.

The sun is warm, baking and strengthening the smell — yes, that smell — as the machines below him drive and separate what has arrived from all the toilets and showers and sinks in Davis.

All in all, it’s just kind of a gross place to be.

Yet Lindquist, the city’s civil engineer, standing there proudly wearing his maroon city of Davis Public Works shirt, has a big smile on his face.

Why?

Because he knows that in less than five years, the grate he’s standing on and the machines below him, which are essentially responsible for keeping the sewer system in Davis running, will have all been replaced by state-of-the-art equipment.

But to truly understand what needs to be changed at the wastewater treatment plant to meet the new discharge regulatory standards, one must first understand how the current treatment plant works.

So, without further “a-doo” …

Where ‘it’ all goes

The easy explanation is that sewage goes to the city’s wastewater treatment plant, the facility northeast of town off County Road 28H, just east of the Yolo County Central Landfill.

The not-so-simple explanation, however, is how it gets to the plant and what happens once it arrives.

Some may find it’s a rather interesting process.

It starts with a flush, though it should be noted that not only toilets but showers, sinks and anything else discharged from a residence or commercial or industrial building feeds into the plant.

The solid and liquid waste then flows down into the city’s sewer system, which actually more closely resembles an oil pipeline rather than the capacious tunnels you’re picturing the Ghost Busters negotiating.

The city calls this pipeline a collection system, which was built in the early ’70s into the ground at an angle, grading down deeper and deeper, aiming northeast toward the plant. Gravity does much of the work.

Think of a water park where all the curlicue slides jut out in numerous directions, but all eventually splash out into the same pool.

In some places throughout the city, the sewage is shot up to an additional high point by a pumping station, where it then falls back down through the angled pipes via the wonders of gravity.

Got it? Deep breath. Now we’re off to the plant.

Solids, liquids and other fun stuff

At the end of the line, the waste all travels down and passes through a sump, or cesspool, 40 feet below ground.

But it has no time to sit around. It’s immediately sucked up from the ground by four jumbo pumps to the plant where it finally begins its treatment process.

Those large pumps, which churn out about 4.5 million gallons of waste per day, run 24 hours a day, seven days a week.

The waste then gets pushed through a bar screen — the one where Lindquist was standing a few moments ago — to weed out any large, unusual items that may have accidentally been flushed down the toilet: rags, diapers, etc.

Next, the wastewater is deposited into its first big treatment tank: the aerated grit tank, which looks like a series of small pools, sitting side by side, out in the open air.

Back to Lindquist to explain what they do:

“The aeration process causes the heavy, mostly inorganic solids (grit and sand) to sink to the bottom of the tank where it can be removed. The ‘mostly’ organic solids continue on to the next process, the primary sedimentation tanks.”

By organic solids, he means poop. Sorry, “mostly” poop.

“The sedimentation tanks allow a place for the water to slow down and provide time for the organic solids to either settle to the bottom or float to the top.”

Taking over for Lindquist, the “sed-tank” separates the liquid waste from the solid, and diverts it to two separate processes to continue their treatments.

The liquid floods into several expansive rectangular ponds, the large brown bodies of water that you may have seen on your way to the landfill, driving down County Road 28H; the solids are transported to two nearby anaerobic digesters that look like two large silos.

The remaining liquid in the ponds is then naturally treated by the sun, allowing algae and other naturally occurring bacteria to eat up more organic substance and continue to clean the water.

The solids go into the digesters and are heated and mixed until they turn into a mulch-like material. From there, they are dried and usually hauled off to the landfill. That’s the end of its journey.

The liquid waste — which by this point is turning into a nice, clean brown color — is actually sprayed out into 100 acres of fields where the wastewater is again naturally scrubbed and treated through an overland flow process.

Anyone who has seen the solar panels near the facility has seen the 100 acres of land behind it where the city sprays that water.

The water runs off into a drainage ditch, where it is collected into one last open-air above-ground tank. This is where the water first receives any chemical treatment.

The city dumps in chlorine to disinfect the water from any “inactive pathogenic” organisms, followed by sulfur-dioxide to eliminate the chlorine.

Finally, it is fit for discharge into the Yolo County Bypass.

Hooray! Stan Gryczko, the city’s wastewater superintendent and his staff who run the place, thank you for listening.

New and improved

Now, here’s what needs to change to get the plant up to regulatory standards:

The overall reconstruction of the plant has been divided into two phases, to be completed over the next five years.

The first phase, called the “rehabilitate and replacement phase” is set to begin this fall and comprises only about $5 million of the total cost of the project ($95 million). However, out of the 10 bids submitted by contractors for the work this month, one came in as low as $3.8 million.

Phase 1 is intended to extend the useful life of the head works — essentially the pre-treatment facilities — and the preliminary and primary treatment facilities. According to the city, the work also will repair corrosion damage on one of the plant’s anaerobic digesters.

Phase 2, called secondary and tertiary improvements, is scheduled to begin in 2014 and is really the bulk of the project.

The work consists of adding new secondary biological treatment and clarification, which will replace the ponds and overland flow treatment system with conventional activated sludge process. The second phase also will include new filtration and coagulation facilities for the tertiary treatment, replace the solids handling equipment and modify the digesters.

Both phases must be complete by 2017 to meet state regulations.

— Reach Tom Sakash at [email protected] or (530) 747-8057. Follow him on Twitter @TomSakash

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Tom Sakash

Tom Sakash covers the city beat for The Davis Enterprise. Reach him at [email protected], (530) 747-8057 or @TomSakash.
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