From Burian A, Et Al. Predation increases multiple components of microbial diversity in activated sludge communities.
Protozoa are eukaryotic residents of wastewater treatment plants that serve as primary predators of bacteria. (Some protozoa are free-living and not predatory). Since protozoa are much larger than bacteria and easily recognized by shape and motility, we use their diversity and populations as indicators of system health.
Since the protozoa “eat” bacteria and bacteria are the organisms that remove pollutants, are the protozoa detrimental to treatment efficiency?
Protozoa populations and diversity increase as you move along the growth curve where bacterial populations are higher and water quality improves. The protozoa feed on both free bacteria in solution and by grazing on the biofilm/floc. We know that by removing free bacteria in solution, the protozoa decrease turbidity and TSS. When grazing on floc, the protozoa contribute to biofilm turnover. We are concerned that protozoa predation will damage slower growing microbial populations such as Ammonia Oxidizing Bacteria (AOB) and Nitrite Oxidizing Bacteria (NOB) – Nitrifiers.
Looking at research, we find the following:
Good articles on protozoa impact on wastewater microbial populations:
Burian, A., Pinn, D., Peralta-Maraver, I. et al. Predation increases multiple components of microbial diversity in activated sludge communities. ISME J 16, 1086–1094 (2022). https://doi.org/10.1038/s41396-021-01145-z
Wu L, et al. Global diversity and biogeography of bacterial communities in wastewater treatment plants. Nat Microbiol. 2019 Jul;4(7):1183-1195. doi: 10.1038/s41564-019-0426-5. Epub 2019 May 13. Erratum in: Nat Microbiol. 2019 Dec;4(12):2579. PMID: 31086312.
Pogue AJ, Gilbride KA. Impact of protozoan grazing on nitrification and the ammonia- and nitrite-oxidizing bacterial communities in activated sludge. Can J Microbiol. 2007 May;53(5):559-71. doi: 10.1139/W07-027. PMID: 17668014.
Since the protozoa “eat” bacteria and bacteria are the organisms that remove pollutants, are the protozoa detrimental to treatment efficiency?
Protozoa populations and diversity increase as you move along the growth curve where bacterial populations are higher and water quality improves. The protozoa feed on both free bacteria in solution and by grazing on the biofilm/floc. We know that by removing free bacteria in solution, the protozoa decrease turbidity and TSS. When grazing on floc, the protozoa contribute to biofilm turnover. We are concerned that protozoa predation will damage slower growing microbial populations such as Ammonia Oxidizing Bacteria (AOB) and Nitrite Oxidizing Bacteria (NOB) – Nitrifiers.
Looking at research, we find the following:
- Bacterial populations have evolved into syntrophic communities and predatory protozoa are an important part of this ecosystem.
- Protozoa predation increases diversity in sludge biomass with a greater mix of both r-strategists (fast growing organisms) and k-strategists (slow growing specialists).
- The “ideal” spot for predation and bacterial diversity is also the decline phase growth zone where waste treatment is optimized.
- Studies on AOB, NOB, and ANAMMOX biomass found that even with predation, ammonia and nitrite removal rates remained stable.
Good articles on protozoa impact on wastewater microbial populations:
Burian, A., Pinn, D., Peralta-Maraver, I. et al. Predation increases multiple components of microbial diversity in activated sludge communities. ISME J 16, 1086–1094 (2022). https://doi.org/10.1038/s41396-021-01145-z
Wu L, et al. Global diversity and biogeography of bacterial communities in wastewater treatment plants. Nat Microbiol. 2019 Jul;4(7):1183-1195. doi: 10.1038/s41564-019-0426-5. Epub 2019 May 13. Erratum in: Nat Microbiol. 2019 Dec;4(12):2579. PMID: 31086312.
Pogue AJ, Gilbride KA. Impact of protozoan grazing on nitrification and the ammonia- and nitrite-oxidizing bacterial communities in activated sludge. Can J Microbiol. 2007 May;53(5):559-71. doi: 10.1139/W07-027. PMID: 17668014.
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