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The paper presents a set of comparative tests to evaluate the inhibitory effect of crystal violet on the respiration rate of microorganisms in conventional activated sludge and aerobic granular sludge. The tests were performed in similar conditions with the only variable of the type of sludge tested. The results emphasized that the aerobic granular sludge is less susceptible to the toxicity induced by crystal violet. The concentration of crystal violet that inhibits by 50% (CE50) the respiration rate of sludge microorganisms was determined to be, for the specific test conditions, 22.39 mg/L for the conventional activated sludge and 33.88 mg/L for the aerobic granular sludge. The paper also assesses the biodegradability potential of crystal violet from aqueous solution, in the presence of sodium acetate as co-substrate in a lab-scale sequential biological reactor with aerobic granular sludge. The experiments showed that most of the crystal violet is being initially absorbed in the matrix of the granules during the first minutes and subsequently is being removed with efficiencies above 95% within a treatment cycle of 8 hours.

Organic fractions assessment in influent wastewater is essential for designing the biological wastewater treatment plant. The characteristics of the influent organic load (readily biodegradable, biodegradable or inert) and form of distribution (soluble/suspended) may induce the design and operational parameters of primary settlers and biological treatment step. The current work presents the comparative assessment of organic fractions in three wastewater samples evaluated experimentally through three different fractionation methodologies, respectively modified ATV-A131 guidelines, IWA methodology and the Łomotowski-Szpindor methodology. The wastewater samples were collected from the influent of two municipal wastewater treatment plants. In all wastewater samples tested the biodegradable fractions, both soluble and suspended had the highest share in the total organic load. This is consistent with the biodegradable character of municipal influents and the suitability for organic and advanced nutrient removal through biological processes. The amount of non-biodegradable fractions SI and XI, varied from 18 to 54% of total organic load, on momentary grab samples of studied influents.