As humans, we tend to interpret the world by what we can see. If a roomful of people were asked to name what’s most important about a wastewater system, they would likely call out pipes, pumps, and treatment plants.
At King County Wastewater Treatment Division (WTD), our process specialists see the system very differently because they see a part of it that most of us don’t. “Those pipes, pumps, pump stations, – everything you see is the system that moves the wastewater around,” says one. “It’s the micro-organisms that are the wastewater treatment process – the infrastructure just helps us feed them and keep them thriving.”
Imagine the whole system as an industrial version of your digestive system. Food and water travels to your stomach and intestines, where it is broken down. Wastewater travels to the plant, where microbes process solids and organics in tanks and digesters.
If your digestive system gets so upset that you lose your appetite (or worse), you won’t go back to eating big meals right after it ends. You will ramp up your diet carefully to avoid another round of indigestion.
When a Feb. 9 equipment failure at West Point Treatment Plant resulted in flooding and damage the plant effectively became a patient in need of care before it could process our wastewater again. WTD employees have been providing that care around the clock – carefully nursing the treatment plant to health.
Operators restored limited wastewater treatment at the plant within a day of the equipment failure. Treatment includes screening, primary treatment (grit, solids and scum removal) and disinfection. Added treatment capacity has cut in half the volume of solids discharged through the plant’s deepwater outfall into Puget Sound.
As West Point is restored to normal operations, crews have repaired the equipment that feeds wastewater to the microorganisms, keeps those bugs warm, and provides oxygen for some of them to thrive. Motors, pumps, and boilers are back online. Flooded tanks
West primary tank gallery
Digesters and temporary ventilation
Meanwhile, internal and external process experts have been managing the microorganisms that clean that wastewater in the secondary treatment process. There are two phases of the secondary process- aerobic (with oxygen) and anaerobic (without oxygen). The high energy, high metabolism microbes in the aerobic process need oxygen to thrive.
In the digesters, which is the next phase of secondary treatment, everything slows down. In digestion a different group of organisms that don’t need or want oxygen do the work, metabolizing more slowly and releasing methane gas as they do. Digester conditions have to be carefully monitored and managed to avoid having certain types of microbes overtake the population and cause upsets.
King County has extensive experience getting the secondary process started, and managing this process. West Point started out as a primary treatment plant when it opened in 1966, and was upgraded to secondary treatment in 1995. Brightwater was brought online with advanced secondary treatment in 2011.
Restoring secondary treatment processes at West Point is a little different than when they first started. When secondary treatment came online over 20 years ago, the plant had an established primary system with healthy organisms. After the primary tanks flooded in the Feb. 9 incident, that part of the system hasn’t really been the same.
And when Brightwater was brought online, the digester population was grown from scratch, fed with microorganisms from South Treatment Plant in Renton. WTD managers weren’t trying to work with a population that had been sitting in cold tanks with no food for weeks – which is exactly the situation they faced at West Point.
While laboratory tests found that the digester populations were alive and would spring back with some food and heat, managers wanted to make sure that the right populations would thrive.
Process experts from within WTD and outside partners have developed and adapted strategies to restore the digester population. Digester temperature was raised slowly. Like a recovering patient, the digesters have been fed small “meals” on a scheduled basis and monitored to make sure they are processing their food.
Once again, South Plant is serving as a donor, sending a healthy complement of microorganisms to seed the digesters at West Point.
This careful, highly monitored approach is bringing the “patient back to health.” Crews have brought four anaerobic digesters online and up to their operating temperature, with a fifth digester expected to come online by mid-April.
Thanks to successful growth of the microorganisms in the secondary process, plant operators can now send about 60 million gallons per day of primary treatment effluent into the secondary treatment process. Digester chemistry is stabilized, and those slow-metabolizing anaerobic organisms are producing methane gas, indicating they are processing their food.
We can harvest resources from this secondary process. The biogas produced by these organisms is recycled onsite to fuel equipment, and about two semi-truckloads of Loop® biosolids are being produced each day.
Highly coordinated, concerted efforts by managers, operators, scientists, maintenance and cleaning crews have kept restoration tasks on schedule – and even ahead of schedule. As a result, WTD expects that West Point wastewater treatment processes will be fully restored and meeting permit discharge requirements by April 30.
Who’s Who in the Digestion Process
The common term for the complex population of organisms that digest our waste is “bugs,” and we tend to think of bugs as bacteria. It’s not that simple. Take a look under a virtual microscope and meet some of the organisms in the digestion process.
