Water Quality: Post-Flush

By Alex Hoeft

It’s no secret the Reno-Sparks area receives a hefty amount (85 percent) of its drinking water from the Truckee River. Water treatment facilities like Chalk Bluff and Glendale in the Truckee Meadows area are in charge of making sure the drinking water is up to snuff.

There’s another treatment facility, though, on the far edge of Sparks that treats a different type of local water: wastewater.

Truckee Meadows Water Reclamation Facility treats the wastewater of Reno and Sparks. All pipes from houses, apartment buildings, offices, etc., as well as local storm drains, feed to the plant.

Michael Drinkwater, plant manager of the Truckee Meadows Water Reclamation Facility.
Michael Drinkwater is plant manager of the Truckee Meadows Water Reclamation Facility.

Michael Drinkwater (no, really — that’s his name) is plant manager of TMWRF, and refers to the facility as his kingdom.

TMWRF was constructed in 1964, and went online in 1966. Since then, multiple expansions have taken place to meet the expectations of the customer cities. There are 45 onsite full-time staff members, including Drinkwater.

The plant treats about 27 million gallons of raw sewage per day.

“There’s the morning flush — when you get out of bed, . . . you get up, you shower, eat breakfast, use your restroom, whatever,” said Drinkwater. “So there’s a big thing in the morning, little bit at lunch, a big thing at night. We get two big peaks.”

The facility reports all measurements and findings (good and bad) to the Nevada Division of Environmental Protection.

“And then they in turn to USEPA (United States Environmental Protection Agency),” said Drinkwater. “Quarterly they come out and visit. I’ve talked to them weekly. I know our regulators well; we’re in constant communication. . . . They do depend on us being honest. If we do something stupid . . . I report it.”

The overall goal: clean up the wastewater and put it back in the Truckee river.

Listed below are the ten steps the wastewater goes through from the moment it enters TMWRF to the moment it leaves.

Preliminary treatment:
1. Headworks
2. Grit Facility
Primary treatment:
3. Primary Clarifiers
Secondary treatment:
4. Aeration Tanks
5. Secondary Clarifiers
Tertiary treatment:
6. Nitrification Towers
7. Denitrification Facility
8. Filters
9. Post Aeration Tank
10. Chlorine Contact Tank

The following is a detailed explanation of what specifically happens during those steps.


 

1. Headworks
The wastewater from the Reno-Sparks area comes into TMWRF via two pipes, one roughly north of the river, one roughly south. The pipes are 66 and 72 inches in diameter. The sewage’s first stop is at headworks — rather, 35 feet below the ground of a building called headworks.

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Step 1: Headworks. Two screens (one pictured here) weed out larger materials in the wastewater.

Two screens (one pictured above) weed out any large materials floating in the sewage — shoes, bicycle parts, rags, etc. via storm drains. Material caught in the screens is trucked off to a landfill; the remaining water continues farther into the treatment process. Each screen is a series of metal plates with a gap. Half of the plates act as a staircase and carry the captured material upwards to a dumpster.

Currently, the headworks is undergoing a renovation. The existing screens are 35 years old, and “just done,” according to Drinkwater, so they’re being replaced.

2. Grit Facility
Four pumps then chug the flow of water up to the grit facility, about 18 feet above ground.

This section tackles small inorganics like egg shells, coffee grounds, and sand. The grit chamber allows the water to flow through while the grit sinks to the bottom.

 

3. Primary Clarifiers
The water, now free of heavy grit, enters the primary clarifiers, a 100-year-old method. The clarifiers act as settling tanks — water enters the circular tank from the middle and flows laterally out. Different rings of the water force it to move up and down the sections of the clarifier. Solids (meaning content differentially settleable in water) sink to the bottom. Mechanical scum arms move very slowly around the tank, raking the floaties off the top of the water.

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Step 3: Primary clarifiers. These act as settling tanks for the wastewater. Grit settles to the bottom as mechanical arms gently move around, gathering floating scum.
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Step 3: Primary clarifiers, continued. The tanks have different rings, so water is forced to move up and down instead of skating across the top.

Primary and preliminary treatments remove 60 percent of solids.

4. Aeration Tanks
From the top of the primary clarifiers flows the water into the aeration tanks. This is where it gets technical. There’s a particular type of microorganism TMWRF is preparing to use in the aeration basin — aerobic bacteria that use phosphorus to grow. Aerobic bacteria is a special group of microorganisms that “breathe” oxygen to survive. This is opposed to anaerobic bacteria that thrive in places with no oxygen. The first section of the tank starves this bacteria of phosphorous to kick start their metabolism in the next stage.

 

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Step 4: Aeration tanks. The initial non-bubbling section starves micro bacteria of phosphorus.

Next up, the actual aeration takes place. A baffle wall marks the point where the aerobic bacteria begins destroying the organic matter (human waste) in the water. Human waste is used by this bacteria for biological growth, and the aforementioned starvation of phosphorus encourages the bugs to eat faster than they normally would.

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Step 4: Aeration tanks, continued. In the bubbling section, the micro bacteria eat the human waste in the water.

The bubbles are thanks to oxygen being pumped in from below (like a fish tank). When the air comes up and forms bubbles, TMWRF employees are able to assume the bacteria is getting everything it needs: a functioning metabolism and waste to treat.

Biochemical Oxygen Demand confirms how much waste is in the water. Here’s an explanation of what BOD is provided by Drinkwater:

“Your dog in your backyard does his thing (dog waste). If you leave it there long enough it just goes away. Nature does what nature does. It consumes oxygen out of the environment to support that operation. (But) how much oxygen?

“What we’re trying to say is if we were to dump this (wastewater) directly into the Truckee River (which we never do, but if we were), how much oxygen would it consume, would it suck out of the environment to stabilize the organic matter, to the detriment to the fish and the frogs and everything that lives in the river? That’s how we measure the strength of waste.”

The larger the oxygen deficit in the water, the stronger the waste. The goal is to get a low BOD number via the aeration tanks.

5. Secondary Clarifiers
The secondary clarifiers are the exact same as the primary clarifiers. This time, however, the microorganisms (called activated sludge) treated in the aeration section are now settling in these clarifiers, and are separated from the wastewater.

A more apparent difference is the colors of the secondary clarifiers and the primary clarifiers. The two are compared below.

Primary clarifiers via Google Maps (there are seven, but only six shown below):
Secondary clarifiers via Google Maps (there are seven, but only five shown below):

“It’s not Crystal Springs bottled water, but we’re making progress,” said Drinkwater.

*Most wastewater treatment plants finish after the secondary clarifiers. But because TMWRF discharges to the Truckee River, the facility is held to different standards. This is because the river is a cold water fishery (thanks to the native trout), and cold water fisheries happen to be one of the hardest water quality standards to maintain.

Post-secondary treatment, the organics have been taken out and there’s a low BOD, but there’s still a lot of ammonia that needs to be removed. 

6. Nitrification Towers
The six nitrification towers are similar to a sprinkler system. In each tower, 28 feet of plastic media are sprinkled over with the water from the secondary clarifiers.

Step 6: Nitrification towers. The pictured media houses multiple sets of bacteria.

Within this honeycomb-shaped media are new sets of bacteria. Scientific details aside, the first set of bacteria converts ammonia to nitrite; the second set converts the nitrite to nitrate. This is the nitrification process.

“We don’t ever see biology. They’re just there, the bugs are there. You give them the conditions they want and they grow,” said Drinkwater. “You give them the food, the water, the warm spot, then let ‘em do their thing.”

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Step 6: Nitrification towers. The arms sprinkle wastewater over the media, and the bacteria inside turn the ammonia into nitrite, and the nitrite into nitrate.

With four of the six towers, the rotation speed of the sprinkler arms is set by the amount of water coming in. If TMWRF wants to turn the speed down, ports on the front side of the arms are opened and closed accordingly. That’s the braking system.

The other two towers’ arms are electronically moved.

7. Denitrification Facility
The nitrate will now be converted to nitrogen gas, once again biologically.

First, the oxygen is taken out of the water while carbon is added.

The water enters the denitrification tank through the bottom and bubbles upwards. In order for the bacteria to not be washed out, sand is floating in the water for the tiny bugs to latch on to.

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Step 7: Denitrification facility. The nitrate in the water is converted to nitrogen gas, and ultimately removed from the water.

The bacteria (called facultative because they can be aerobic or anaerobic depending on the conditions) are fed methanol, which provides a carbon source. While the oxygen is being taken out, the bacteria breathe aerobically with carbon as energy. Once the oxygen is gone, the bacteria breathe anaerobically using nitrate as energy — they strip the oxygen off the nitrate molecule. Nitrogen then bonds with itself and ultimately creates nitrogen gas, which bubbles out of the water.

The nitrogen meets its end here — denitrification is TMWRF’s final disposal of nitrogen.

8. Filters

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Step 8: Filters. This step removes sand that was added during the denitrifcation process.

The filters are used to remove the sand that helped out in the denitrification process. Water enters and sinks down through 12 dual media gravity filters. This means that small particulates are caught between a specially designed sand (or media) that makes up the filter.

As the filter fills up, ultrasonic sensors measure the amount of smaller particulates that have accumulated in the media, and triggers a backwash of the filter.

“When you clean a filter, you just push water through it backwards, and it takes all the crud the filters collected, and instead, obviously that can’t go to the river. . .” explained Drinkwater. “Nothing gets out of the plant without going all the way through the process. So all of this water goes back to the beginning. It’s like Chutes and Ladders, you know the game where you go back to the beginning. . . . This is just water that was used to backwash a filter. We allow it to settle, get a little bit cleaner, then put it back in.”

9. Post Aeration Tank
After the water goes through the filters, it’s sent to be re-aerated. This is meant to confirm the denitrified water is properly oxygenated, thus preventing possible anaerobic conditions.

10. Chlorine Contact Tank
“After all of that work that the biology does for us, this is where we kill it,” said Drinkwater.

Any bacteria that has made it this far is now terminated, and the water is disinfected with sodium hypochlorite, one of the common ingredients in household bleach.

Once the chlorine is mixed in, the water follows a series of baffled channels that act as a sort of racetrack for the chemicals.

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Step 10: Chlorine contact tank. All bacteria and any other chemicals are removed via this tank. This is the last step in cleaning wastewater.

A little ways into the contact tank, sodium bisulphite (a common additive to food to preserve freshness) is added to destroy the chlorine.

Nothing can be introduced to the Truckee River that isn’t a natural part of the river chemistry or biology, and the chlorine contact tank takes care of that — no more bacteria or chlorine.

The finished product goes through a pipe out to Steamboat Creek, which flows almost immediately into the Truckee River.

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The pictured pipe connects to Steamboat Creek, and eventually the Truckee River.

Glendale and Chalk Bluff water treatment plants are governed by the Safe Drinking Water Act; their water must be safe for human consumption. TMWRF doesn’t go that far, but outflow is “some pretty darn good water,” described Drinkwater.

He continued:

“I don’t mean any disrespect to the clean water folks, but they are starting with Lake Tahoe. So they’re starting with a water that’s pretty darn good. . . . We’re starting with water that’s been through a human.”