Agnieszka Pajdak-Stós

Inducible defence against a ciliate grazer Pseudomicrothorax dubius, in two strains of Phormidium (cyanobacteria)

Experiments were done with two strain of filamentous, mat–forming Phormidiumand their ciliate grazer Pseudomicrothorax dubius, to explain why the ciliates remain hungry in an apparent surplus of food, except for the first 24 hours after feeding. Under grazing pressure, both strains of cyanobacteria showed statistically significant increases in the number of filaments terminating in an empty sheath, compared to the control. Direct observations revealed that the mechanism behind this effect was active withdrawal of the trichomes inside the sheaths when disturbed by grazers. As P. dubius is unable to ingest trichomes with such endings, we conclude that cyanobacteria are not limited to chemical means of defence against grazers but can also defend themselves by means of movement and changes in filament morphology. This is apparently the first report on behavioural defence observed in cyanobacteria.

The role of Lecane rotifers in activated sludge bulking control.

Experiments were conducted on Lecane inermis feeding on filamentous bacteria and living in activated sludge to determine if the rotifers can control the growth of the bacteria responsible for bulking. The experiments showed that Lecane are capable of significantly reducing the density of Microthrix parvicella filaments. The rotifers not only survived the transfer from the culture to the activated sludge, but they multiplied quickly when foraging on filamentous bacteria. By reducing the number of filaments, the rotifers improved settling properties of the sludge. This is apparently the first report on the possibility of using rotifers to control bulking.

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.

Seasonal changes in the body size of two rotifer species living in activated sludge follow the Temperature-Size Rule.

Temperature-Size Rule (TSR) is a phenotypic body size response of ectotherms to changing temperature. It is known from the laboratory studies, but seasonal patterns in the field were not studied so far. We examined the body size changes in time of rotifers inhabiting activated sludge. We hypothesize that temperature is the most influencing parameter in sludge environment, leading sludge rotifers to seasonally change their body size according to TSR, and that oxygen content also induces the size response. The presence of TSR in Lecane inermis rotifer was tested in a laboratory study with two temperature and two food-type treatments. The effect of interaction between temperature and food was significant; L. inermis followed TSR in one food type only. The seasonal variability in the body sizes of the rotifers L. inermis and Cephalodella gracilis was estimated by monthly sampling and analyzed by multiple regression, in relation to the sludge parameters selected as the most influential by multivariate analysis, and predicted to alter rotifer body size (temperature and oxygen). L. inermis varied significantly in size throughout the year, and this variability is explained by temperature as predicted by the TSR, but not by oxygen availability. C. gracilis also varied in size, though this variability was explained by both temperature and oxygen. We suggest that sludge age acts as a mortality factor in activated sludge. It may have a seasonal effect on the body size of L. inermis and modify a possible effect of oxygen. Activated sludge habitat is driven by both biological processes and human regulation, yet its resident organisms follow general evolutionary rule as they do in other biological systems. The interspecific response patterns differ, revealing the importance of taking species-specific properties into account. Our findings are applicable to sludge properties enhancement through optimizing the conditions for its biological component.

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.

VULNERABILITY OF NOSTOC MUSCORUM AGARDH (CYANOPHYCEAE) MOTILE HORMOGONIA TO CILIATE GRAZING1

Experiments were carried out to investigate if the stage of life cycle of Nostoc muscorum Agardh alters vulnerability to grazing by Pseudomicrothorax dubius Maupas. When the percentage of motile hormogonia of all counted trichomes exceeded 10%, most of the grazers (80%–100%) became satiated within 2 h. In most cases (90%) grazers successfully attacked motile hormogonia. Attacks on nonmotile trichomes were much rarer (8%) and mainly unsuccessful. Direct observations revealed that hormogonia could be ingested by the ciliates as long as they remained motile. Hormogonia already adhered to the bottom were still recognized by ciliates as potential food but were not ingested. We did not observe attacks on old vegetative colonies. This is apparently the first report on the motile stage of Nostoc being susceptible to ciliate grazing. Experiments with other grazers, Nassula tumida Maskell and two different clones of Furgassonia blochmanni Faure‐Fremiet, showed that only one clone of F. blochmanni was able to feed on motile hormogonia, whereas the second clone and N. tumida showed no interest in them.

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...

Effects of grazers' species identity on cyanobacteria in bitrophic and tritrophic food webs

Using laboratory microcosms, we studied direct and indirect interactions among different components of bi- and tritrophic communities. Filamentous cyanobacteria (Phormidium sp.) and autotrophic flagellates (Chlorogonium elongatum) were primary producers. The second trophic level was represented by ciliates Furgasonia blochmanni and Pseudomicrothorax dubius grazing on the filamentous cyanobacteria and two filter feeders, Euplotes octocarinatus and Stylonychia pustulata, feeding on the autotrophic flagellates. An oligochaete, Chaetogaster sp., was used as the top predator. An experiment was carried out for all combinations of two factors: (1) the identity of the cyanobacteria consumer (Furgasonia or Pseudomicrothorax) and (2) the presence or absence of the top predator. Significant effects of the treatments on both the abundance of cyanobacteria and filter feeding ciliates and predator-induced defense in Phormidium and Euplotes were observed in a 36-day experiment. The experiment showed that the substitution of one species (Furgasonia) for another (Pseudomicrothorax) seemingly playing the same ecological role may lead to significant changes in the whole community.

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.