Wioleta Kocerba-Soroka

The use of rotifers for limiting filamentous bacteria Type 021N, a bacteria causing activated sludge bulking

The excessive growth of filamentous bacteria and the resultant bulking of activated sludge constitute a serious problem in numerous wastewater treatment plants. Lecane inermis rotifers were previously shown to be capable of reducing the abundance of Microthrix parvicella and Nostocoida limicola in activated sludge. In the present study, the effectiveness of four Lecane clones in reducing the abundance of Type 021N filamentous bacteria was investigated. Three independent experiments were carried out on activated sludge from three different treatment plants. We found that Lecane rotifers are efficient consumers of Type 021N filaments.

The Toxicity of Aluminium Salts to Lecane Inermis Rotifers: Are Chemical and Biological Methods Used to Overcome Activated Sludge Bulking Mutually Exclusive?

Abstract The aim of this study was to assess the effects of two flocculants that are often used to overcome activated sludge bulking problems - aluminium chloride, AlCl3, and aluminium sulphate, Al2(SO4)3 - on Lecaneinermis (Rotifera, Monogononta) at three different temperatures: 8, 15 and 20°C. The mean EC50 value (effective concentration, mg dm-3) calculated for the 24 h mortality test was 0.012 mg Al3+dm-3. Next, the effects of low concentrations of the Al-salts on the population development from single individuals (parthenogenetic females) were tested in a 21-day experiment. At concentrations as low as EC4.8 and EC0.48, both Al-salts affected rotifer population negatively. However, temperature was the most pronounced factor that modified the toxicity of the Al-salts to the rotifers. On the 12th day of the experiment, there were significant interactions between temperature and the Al-salts, indicating that the chemicals were more toxic to the rotifers at 20°C than at lower temperatures. The weaker rotifers sensitivity to Al-salts (especially to AlCl3) in temperatures below 15°C, when the biggest problems associated with sludge bulking occurs,may means use both rotifers and chemicals reasonable and effective. Streszczenie Sole glinu są powszechnie stosowanym fl okulantem, służącym zwalczaniu puchnięcia osadu czynnego w biologicznych oczyszczalniach ścieków. Nowa idea biologicznego zwalczania tego niekorzystnego dla prawidłowej pracy oczyszczalni zjawiska polega na zastosowaniu wrotków z gatunku z Lecaneinermis. Wrotki te naturalnie występują w osadzie czynnym i są w stanie zjadać bakterie nitkowate, jak Microthrixparvicella, sprawiające najwięcej problemów w eksploatacji oczyszczalni podczas miesięcy zimowych. Celem badań było porównanie toksyczności chlorku glinu AlCl3 oraz siarczanu glinu Al2(SO4)3 dla wrotków Lecaneinermis w trzech temperaturach: 8, 15 and 20°C. Średnią wartość EC50 (stężenie powodujące 50% efekt, mg dm-3) dla śmiertelności wrotków na podstawie 24-godzinnego testu ustalono na poziomie 0.012 mg Al3+ dm-3. Następnie, badano wpływ niskich stężeń soli glinu na tempo wzrostu populacji z pojedynczego osobnika (partenogenetyczna samica) w 21-dniowym eksperymencie. Ustalono, że stężenia na poziomie odpowiadającym EC4.8, a nawet EC0.48 wpływają negatywnie na tempo wzrostu populacji. Temperatura silnie wpływała na toksyczność glinu. W 12-tym dniu eksperymentu stwierdzono, że zachodzi istotna interakcja pomiędzy toksycznością glinu i temperaturą, wskazująca, że w 20°C glin jest bardziej toksyczny dla wrotków niż w niższych badanych temperaturach. Mniejsza wrażliwość wrotków na glin w temperaturze poniżej 15°C może oznaczać, że łączenie tych dwóch metod zwalczania puchnięcia osadu czynnego w miesiącach zimowych może być racjonalnym i efektywnym rozwiązaniem.

Effect of the rotifer Lecane inermis, a potential sludge bulking control agent, on process parameters in a laboratory-scale SBR system

The influence of a high density of rotifers, which is known to be able to control filamentous bacteria, on the parameters of an activated sludge process was examined in four professional laboratory batch reactors. These reactors allow the imitation of the work of a wastewater treatment plant with enhanced nutrient removal. The parameters, including oxygen concentration, pH and temperature, were constantly controlled. The experiment showed that Lecane rotifers are able to proliferate in cyclically anaerobic/anoxic and aerobic conditions and at dissolved oxygen concentrations as low as 1 mg/L. In 1 week, rotifer density increased fivefold, exceeding the value of 2,200 ind./mL. The grazing activity led to an improvement in settling properties. Extremely high numbers of rotifers did not affect the main parameters, chemical oxygen demand (COD), N-NH(4), N-NO(3), P-PO(4) and pH, during sewage treatment. Therefore, the use of rotifers as a tool to limit the growth of filamentous bacteria appears to be safe for the entire wastewater treatment process.

Lecane tenuiseta (Rotifera, Monogononta) as the best biological tool candidate selected for preventing activated sludge bulking in a cold season

AbstractRotifers in activated sludge reduce the quantity of dispersed bacteria, ingest filamentous bacteria, enhance flocculation and limit biomass production. Growth rates of rotifers are inversely correlated with temperature; thus, their density declines drastically in wastewater treatment plants (WWTPs) during the winter. The only species already demonstrated to be able to control bulking is Lecane inermis. However, they cease proliferation at 8°C. The goal of our research was to select other rotifers species whose growth rates at lower temperatures are sufficiently high to maintain a favourable density during cold seasons. We conducted selection experiments in the laboratory at temperatures reflecting the temperature distribution in the majority of municipal WWTPs in the temperate zone. In the first experiment, the general selection stage, we tested the influence of the temperatures 8, 15 and 20°C on competition among different rotifer taxa in sludge samples originating from different WWTPs. The rotif...

Effect of high levels of the rotifer Lecane inermis on the ciliate community in laboratory-scale sequencing batch bioreactors (SBRs).

Due to its ability to feed on filamentous bacteria, the rotifer Lecane inermis has already been recognized as a potential control agent of activated sludge bulking, which is usually caused by the excessive growth of filamentous microorganisms. However, their effectiveness depends, in part, on their abundance. We studied the influence of high densities of L. inermis on the protozoan community in activated sludge from a wastewater treatment plant (WWTP) in 4 laboratory-scale sequencing batch bioreactors (SBRs). Two treatments and two controls were subjected to nutrient removal system in process similar to that used in a WWTP. The experiment lasted 9 days and was repeated in 24-h cycles, including phases of agitation with feeding, aeration and agitation and sedimentation with decantation at the end of the cycle. In total, 32 taxa were identified, among which 25 were ciliated protozoa, 4 were amoebae, 2 were flagellates, and one was a nematode. Rotifers were then introduced to 2 bioreactors at a final concentration of 500ind.mL(-1), and the taxonomic composition and abundance of the activated sludge microfauna were assessed 2, 5 and 8 days thereafter. The mean density of ciliates on the first day of experiment was 12,610ind.mL(-1) and diminished to 4868±432ind.mL-±432ind.mL(-1) in the control and 5496±638ind.mL(-1) in the rotifer-treated group on the last day. Thus, even extremely high densities of artificially introduced rotifers did not negatively affect the protozoan community. On the contrary, the protozoan community was more diverse in the treatment group than in the control.

Selective predation by a harpacticoid copepod on ciliates in phytotelmata: a laboratory experiment

Copepods are the most numerous metazoans in water-filled phytotelmata formed by Heliconia and Calathea floral bracts in cloud forests of Cordillera de la Costa, Northern Venezuela. We estimated the potential effect of copepods on ciliate community structure in this habitat with a laboratory experiment. Predation effects of five life stages of a harpacticoid copepod on a mixed culture of five bacterivorous ciliate species were measured during a 48-hour incubation. The predation effect depended on copepod life stage and on ciliate prey species. The abundances of Colpoda inflata, Tetrahymena pyriformis, and Colpidium kleini were significantly reduced, the actual effect strongly depending on copepod developmental stage. No detectable predation was observed on Paramecium aurelia or Tachysoma pellionellum. The results suggest that predation by harpacticoid copepods is an important factor influencing ciliate community structure in phytotelmata.