By Carol Chamberland,
Central NM Group Zero Waste chair
Like most city dwellers, I pay my monthly water bill with scarcely a thought for what happens downstream after each flush of the toilet. When Central Group staffer Cecilia Chávez Beltrán suggested we take a tour of the local wastewater treatment facility, I told her it was beyond the scope of our zero-waste focus. But if she wanted to organize a tour, I’d go along. So, she did, and I did. Many thanks to Cecilia.
We lucked out with a sunny day in an otherwise rainy week. The odor hit me before I exited my car at the South Valley Wastewater Treatment plant. We assembled in a classroom for an overview of the operation and to don regulation hard hats and safety vests. The ABCWUA (Albuquerque Bernalillo County Water Utility Authority) is a political subdivision of the state, with board members representing Albuquerque’s City Council, Bernalillo County Commissioners, the Albuquerque Mayor’s office, and the village of Los Ranchos. They have stringent EPA guidelines to observe as they treat 55 million gallons of wastewater per day.
As our guide, chief engineer Jeffrey Romanowski, shuttled us around the base, we observed the process of filtering out solids and cleaning the water. I’d imagined lots of chemicals involved, but I was wrong. Gravity is a big factor and mechanical means predominate.
Wastewater flows through bar screens, grit chambers, clarifiers, aeration tanks, and final clarifiers, then passes through an ultraviolet disinfection chamber before being released into the Rio Grande. Sludge removed from the wastewater is concentrated and collected in anaerobic digesters, where it produces methane gas. The on-site cogeneration plant uses the methane to produce 70% of the facility’s electrical needs.
The aeration tanks are large pools of water that filter the brown stuff out while slow-moving arms scrape off the foamy, oily bits from the surface. To capture the foul odors, most of these pools have been covered with metallic domes, giving the plant the semblance of a UFO parking lot. Water moves between successively cleaner pools, is shunted along a fast-flowing maze and subjected to UV light for disinfection. As we headed further west, the odors diminished, and by the time we reached the Rio Grande, the smell was gone. It was a refreshing sight to behold; gallons of cleaned city water flowing into the high, muddy waters of the Rio Grande.
Meanwhile, the brown stuff is processed into a substance described as “the color and texture of chocolate cake” — an unfortunate analogy for cake-lovers. These biosolids are eventually loaded onto trucks and delivered to their sister facility on the West Mesa for composting. Some of the re-use water is sold to corporate and governmental customers for landscape irrigation. This product is not available for private citizens.
Now that they had my attention, I booked us a tour of the Compost del Rio Grande. Supervisor Joe Bailey gave us an intro and handed out hardhats and safety vests. I expected this site to smell like the wastewater facility, but I was wrong again. There’s an odor, but it’s the earthy smell of mulch, not human waste.
The compost facility accepts truckloads of untreated wood, food scraps, yard waste, horse stable bedding, and biosolids from the South Valley plant. There is no charge to drop off materials, but the standards are high. If the load is unacceptable, the truck is reloaded and sent down the road to the city landfill that requires payment for dumping. 35% to 40% of the trucked-in biosolids are mixed with other amendments to make compost, and the remainder is spread out to amend on the open land.
Dumped matter is exposed to the elements and aged for months in the open air. When preparing a new batch of compost, these ingredients are mixed in proper proportions and piled into great windrows in the shelter of a huge warehouse. They cook for months more, reaching temperatures that are precisely calculated to kill microbes but not so hot as to create a microbial feeding frenzy. A large machine appropriately called the Scarab routinely turns the compost piles until they are cooked to perfection.
The end product is offered for sale by the truckload. The resulting certified biosolids compost typically consists of 50% animal stable bedding, 30% biosolids and 20% green waste. It sells for $25 per ton and may be used in the production of crops for human consumption. DOT uses a special form of the compost to line highway shoulders. This product is heavy and does not blow away, so they seed it with grasses and flowers.
Local wildlife loves this place. On chilly nights, coyotes burrow into the composting heaps to sleep in their warmth, then retreat into the surrounding desert when employees arrive in the morning. A nesting pair of Great Horned Owls lives a comfortable life in the rafters of the giant warehouse, raising chicks and sending them on their way once they’ve fledged. There’s a plentiful supply of rodents, lizards and snakes to keep the owls and coyotes happy and the employees on their toes.