Protozoa in wastewater treatment processes: A minireview

Abstract

Biological wastewater treatment is a process of increasing importance in a world with an ever-increasing human population. Wastewater treatment facilities are designed to maintain the high density and activity levels of those microorganisms that carry out the various purification processes. Protozoa are one of the most common components in these man-made ecosystems and play an important role in wastewater purification processes. Protozoa are responsible for improving the quality of the effluent, maintaining the density of dispersed bacterial populations by predation. Studies of the relationships between protozoa and physicochemical and operational parameters have revealed that the species structure of these communities is an indicator of plant efficiency. The Sludge Biotic Index (SBI), an index based on the structure and abundance of the microfauna inhabiting the activated sludge and mixed liquor, has been devised to monitor activated-sludge plant performance. Heavy metals and other pollutants are toxic to most microorganisms at certain concentrations. These toxicants are common pollutants of sewage, particularly where there is industrial waste input. The protozoa community is a complex assemblage of interacting organisms, often including species that are sensitive, resistant or intermediate in their tolerance to pollutants. Many studies conducted on contaminated activated sludge and mixed liquor have revealed changes in the dynamics of the protozoa community. Tests on the acute toxicity of pollutants on ciliates have revealed that these microorganisms are useful bioindicators for evaluating the toxicity of waters polluted by different concentrations of metals.

Dynamics of the microfauna community in a full-scale municipal wastewater treatment plant experiencing sludge bulking

“…S3), which may have led to the release of flocculated non-filamentous bacteria to the liquor phase, as exemplified by increased levels of suspended solids in the effluents (SS e ) (Pearson's r between SVI and SS e : r System A = 0.520, r System B = 0.693; p < 0.05; based on the 48-h average data). It is known that the four peritrich species (actually most species of bactivorous protozoa, except for crawling ciliates) can only feed on dispersed non-filamentous bacteria and particles in BWTSs (Fenchel 1987;Madoni 2011). We thus concluded that sludge de-flocculation due to the excessive growth of filamentous bacteria (e.g.…”

“…However, as shown in Fig. 3 and Table S3, E. plicatilis, V. striata, C. polypinum and V. cupifera, the four peritrich ciliates feeding on small dispersed bacteria (Fenchel 1987;Madoni 2011), were all inversely related to water temperature in the range from 14.5 • C to 26.3 • C (based on the 48-h average data) in both systems. That is to say, the abundances of the four species, especially E. plicatilis and V. striata, increased with the decrease in water temperature, suggesting that sludge bulking may have created some favorable conditions for the growth of these species, even under a temperature condition unfavorable for their growth.…”

Impact of Flowback Water on Activated Sludge Biocenosis During Municipal Wastewater Treatment

“…No group or species is ever dominant over the others, even if the ratios between various groups or species differ. In contrast, microfauna that is dominated by one group indicates a trophic imbalance caused by limiting factors that impede the development of other species [27]. In this study, flowback water was added to treated wastewater for only 9 weeks.…”

Dynamics of Microbial Indicators in Waste Water

“…Aspidisca is a colorless genus from fresh waters. It is quite widespread, being found on plants and in detritus of fresh waters and is an indicator of nitrate in the process of treating waste water (Renneberg et al, 2016 (Madoni, 2011). Sphaerotilus are aquatic periphitonic microorganisms associated with polluted water, sewage and activated sludge (Chapman, 1996).…”