In this study a completely stirred tank reactor was used to study the effect of sulfide to nitrate (S/N) ratio on sulfide removal while nitrate was used as electron acceptor. Several S/N ratios were studied for this purpose ranging from 0.3 to 2.4 mol/mol. The complete sulfide removal was achieved when S/N ratio 0.85 mol/mol was used with the autotrophic denitrification efficiency up to 80 %. No nitrite accumulation was observed, and the main product of sulfide oxidation was sulfate. Dissimilatory nitrogen reduction to ammonia occurred and subsequently, elemental sulfur accumulated while S/N ratio was higher than 1.3 mol/mol. The specific autotrophic denitrification rates under S/N ratios 0.8 and 1.2 were 5 and 26 mg g(-1) h(-1) (N-NO3 (-), VSS), respectively. Thiobacillus denitrificans and Thiomicrospira denitrificans were detected in the reactor by fluorescent in situ hybridization, but their overall representation was not more than 5 % of the entire microbial populations.

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Partial nitritation/anammox can provide energy-efficient nitrogen removal from the main stream of municipal wastewater. The main bottleneck is the growth of nitrite oxidizing bacteria (NOB) at low temperatures (<15 °C). To produce effluent suitable for anammox, real municipal wastewater after anaerobic pretreatment was treated by enriched ammonium oxidizing bacteria (AOB) in suspended sludge SBR at 12 °C. NOB were continually washed out using aerobic duration control strategy (ADCS). Solids retention time was set to 9-16 days. Using this approach, average ammonia conversion higher than 57% at high oxidation rate of 0.4 ± 0.1 kg-N kg-VSS d was achieved for more than 100 days. Nitrite accumulation (N-NO/N-NO) of 92% was maintained. Thus, consistently small amounts of present NOB were efficiently suppressed. Our mathematical model explained how ADCS enhanced the inhibition of NOB growth via NH and HNO. This approach will produce effluent suitable for anammox even under winter conditions in mild climates.

There is still not enough information about the influence of several important variables, which occur in natural systems, on the coagulation of humic substances. One of these rarely studied variables is type and concentration of algal exudates. Thi s paper presents the results of research of the influence of alga Scenedesmus quadricauda and its exudates on the results of coagulation experiments with model humic water. The arrangement of experiments should simulate one possible way how algae might influence natural water systems and water treatment. The results demonstrate that both the residual concentration of humic substances and residual aluminium are influenced during the time which elapses after the addition of the washed algae to the model humic water. But the influence of algae on residual colour is partly different from their influence on residual aluminium. Early after the algae addition to the model humic water, they influence the system predominantly with their surfaces, because the concentration of their exudates is low. This increases the residual concentration of aluminium. On the other hand, longer “algal residence time” in model humic water decreases the residual aluminium concentrations. Systems with algae are sensitive to overdosing with respect to both residual humic substances and residual aluminium.