By Roxanne Holland
Manager, Wastwater Department
Sedona AZ (March 13, 2019) – Amoebas, rotifers and tardigrades, oh my! The city’s wastewater treatment is a four-step process that uses a combination of separation, settling, filtration, and UV disinfection to turn wastewater into high quality effluent that can be reused in a variety of ways. The real magic of wastewater treatment happens in the secondary treatment process, which is a natural biological process where microorganisms, or bugs as the industry likes to call them, are cultivated to help break down the organic waste matter.
Secondary treatment at the Sedona Wastewater Reclamation Plant uses an activated sludge process in which waste moves through a series of four aeration basins where air is added to increase dissolved oxygen. Adding oxygen helps microorganisms such as bacteria, protozoa, and metazoa grow. The organic matter in wastewater provides a carbon source for food for these microorganisms and in the proper balance they work together to “eat” up the organic matter and clean our wastewater.
Bacteria make up 95 percent of the biomass in activated sludge and are responsible for the majority of organic degradation. Bacteria are busy little bugs that can multiply every 12-180 minutes. Bacteria are single-celled organisms and are found in many different forms, such as filamentous, spore-forming, zooglea, rod, spiral, comma, and budding bacteria. It is very difficult to look at bacteria under the microscope because of their small size, so the city laboratory uses protozoan microorganisms as indicators to determine the health of the bacterial population in the wastewater treatment process.
Protozoa microorganisms are single-celled organisms that are motile (capable of motion), respirate (breathe), and reproduce. Amoebas move by manufacturing proteins and pumping them. and eat organic material that they bump into. Flagellates absorb dissolved nutrients and have a whip-like appendage used for movement. Ciliates are larger protozoa that feed on bacteria. The presence of ciliates indicates a mature, balanced sludge and is indicative of a good effluent. The different types of ciliates seen in wastewater sludge include free-swimmers, crawlers, and stalked ciliates.
Metazoa are slower-growing multicellular microorganisms consisting primarily of rotifers, tardigrades and annelids. Too many metazoa can be indicative of an old sludge. Rotifers are the most common metazoans in wastewater sludge that feed on large organic material and small protozoa. Tardigrades, also known as water bears, are eight-legged microorganisms that feed on protozoa, nematodes, and rotifers. Tardigrades are classified as extremophiles because they are capable of surviving in extreme conditions; in 2007 water bears survived a trip into space for 10 days with no air, no water, and were exposed to intense rays from the sun. Annelids are aquatic worms that feed on just about anything.
It’s important to keep the proper ratio of microorganisms to food in order to maximize their ability to breakdown the organic material in wastewater. The city’s laboratory analyst takes daily samples of the activated sludge to determine the number of different microorganisms that are present. This helps our wastewater operators make informed decisions about how to adjust the treatment process, such as increasing or decreasing the amount of air that is added or increasing or decreasing the amount of sludge that is removed daily from the process. Several factors can influence the balance of microorganisms in the activated sludge, including temperature, pH, dissolved oxygen, and nutrients or food. When the ratio of food (organic material) to microorganisms is too high, a poor-quality effluent can result. If there are too many microorganisms, they can end up eating each other; if left unchecked, this can reduce the needed supply of microorganisms to adequately breakdown organic matter.
All of this is just the tip of the iceberg on how wastewater is treated to prevent the pollution of natural water resources such as aquifers, rivers, and lakes. We welcome visitors at the Wastewater Reclamation Plant and offer tours where residents can learn more about the amazing process of wastewater treatment in Sedona. Schedule your tour by calling (928) 204-2234.