Emine Ubay-Cokgor

Acute impact of erythromycin and tetracycline on the kinetics of nitrification and organic carbon removal in mixed microbial culture

The study evaluated acute impact of erythromycin and tetracycline on nitrification and organic carbon removal kinetics in mixed microbial culture. Acclimated biomass was obtained from a fill and draw reactor fed with peptone mixture selected as synthetic substrate and operated at a sludge age of 10 days. Acute inhibition was tested in batch reactors involving a control unit started solely with substrate and the others with additional doses of each antibiotic. Modeling indicated that both steps of nitrification were totally blocked by erythromycin. Tetracycline inhibited and retarded nitrification kinetics at 50 mg/L and stopped nitrite oxidation at 200 mg/L, leading to nitrite accumulation. Both antibiotics also affected organic carbon removal by inducing partial inactivation of the heterotrophic community in the culture, increased substrate storage and accelerated endogenous respiration, with a relatively slight impact on heterotrophic growth. Major inhibitory effect was on process stoichiometry, leading to partial utilization of organic substrate.

Characteristics of mixed microbial culture at different sludge ages: Effect on variable kinetics for substrate utilization

The study focused on variable kinetics for substrate utilization, primarily addressing the following issue: Is variable process kinetics observed under different operating conditions and culture history (sludge ages), the result of changes inflicted on the metabolic machinery of the same microbial culture? Or, is this the result of a different microbial population selected under different operating conditions? For this purpose, the study mainly emphasized to assess the microbial population composition sustained at different sludge ages. It explored the relationship between observed process kinetics and microbial population structure using respirometric modeling and high-throughput sequencing of 16S rRNA gene. Experimental results indicated a significant change in the composition of the microbial community fed with the same organic substrate, when the culture history was changed, lower sludge age selecting a different and faster growing microbial community.

Effect of sludge age on population dynamics and acetate utilization kinetics under aerobic conditions.

The study addressed acetate utilization by an acclimated mixed microbial culture under different growth conditions. It explored changes in the composition of the microbial community and variable process kinetics induced by different culture history. Sequencing batch reactors were operated at steady-state at different sludge ages of two and ten days. Microbial population structure was determined using high-throughput sequencing of 16S rRNA genes. Parallel batch experiments were conducted with acclimated biomass for respirometric analyses. A lower sludge age sustained a different community, which also reflected as variable kinetics for microbial growth and biopolymer storage. The maximum growth rate was observed to change from 3.9/d to 8.5/d and the substrate storage rate from 3.5/d to 5.9/d when the sludge age was decreased from 10 d to 2.0 d. Results challenge the basic definition of heterotrophic biomass in activated sludge models, at least by means of variable kinetics under different growth conditions.

Chronic impact of sulfamethoxazole on acetate utilization kinetics and population dynamics of fast growing microbial culture.

The study evaluated the chronic impact of sulfamethoxazole on metabolic activities of fast growing microbial culture. It focused on changes induced on utilization kinetics of acetate and composition of the microbial community. The experiments involved a fill and draw reactor, fed with acetate and continuous sulfamethoxazole dosing of 50 mg/L. The evaluation relied on model evaluation of the oxygen uptake rate profiles, with parallel assessment of microbial community structure by 454-pyrosequencing. Continuous sulfamethoxazole dosing inflicted a retardation effect on acetate utilization in a way commonly interpreted as competitive inhibition, blocked substrate storage and accelerated endogenous respiration. A fraction of acetate was utilized at a much lower rate with partial biodegradation of sulfamethoxazole. Results of pyrosequencing with a replacement mechanism within a richer more diversified microbial culture, through inactivation of vulnerable fractions in favor of species resistant to antibiotic, which made them capable of surviving and competing even with a slower metabolic response.

Is the chronic impact of sulfamethoxazole different for slow growing culture? The effect of culture history.

The study evaluated impact of sulfamethoxazole on acetate utilization kinetics and microbial community structure using respirometric analysis and pyrosequencing. A fill and draw reactor fed with acetate was sustained at a sludge age of 10 days. Acute impact was assessed by modeling of respirometric data in batch reactors started with sulfamethoxazole doses in the range of 25-200 mg/L. Fill and draw operation resumed with continuous sulfamethoxazole dosing of 50 mg/L and the chronic impact was evaluated with acclimated biomass after 20 days. Acute impact revealed higher maintenance energy requirements, activity reduction and slight substrate binding. Chronic impact resulted in retardation of substrate storage. A fraction of acetate was utilized at a much lower rate with partial biodegradation of sulfamethoxazole by the acclimated biomass. Pyrosequencing indicated that Amaricoccus sp. and an unclassified Bacteroidetes sp., possibly with the ability to co-metabolize sulfamethoxazole, dominated the community.

Performance and microbial behavior of submerged membrane bioreactor at extremely low sludge ages

AbstractThe study investigated the effect of sludge age on substrate utilization kinetics, soluble microbial product generation, and composition of the microbial community sustained in a superfast submerged membrane bioreactor (SSMBR). For this purpose, a laboratory-scale membrane bioreactors (MBR) unit was operated at steady state, with three different sludge ages in extremely low range of 0.5–2.0 d, and a hydraulic retention time of 8.0 h. Substrate feeding was adjusted to 220–250 mg COD/L and involved a synthetic mixture representing the readily biodegradable COD fraction in domestic sewage. The MBR operation at sludge age of 1.0 d was duplicated with acetate feeding as the sole organic carbon source. Under different operating conditions, SSMBR was able to secure complete removal of available soluble/readily biodegradable substrate, with a residual microbial product level as low as 20–30 mg COD/L, partly retained and accumulated in reactor volume. Phylogenic analysis based on polymerase chain reactions...

Acute impact of tetracycline on the utilization of acetate by activated sludge sustained under different growth conditions.

The study evaluated acute impact of tetracycline on the biodegradation of acetate by microbial cultures acclimated to different growth conditions. Two fill/draw reactors were operated to obtain acclimated cultures at sludge ages of 2 and 10 days. Acclimated biomass seeding was used in two series of batch experiments. The first run served as control and others were started with tetracycline doses of 100mg/L and 400mg/L. Parallel batch reactors were also operated for oxygen uptake rate (OUR) measurements. Acute impact was evaluated by model calibration of OUR, chemical oxygen demand (COD) and intracellular storage profiles. Exposure to tetracycline did not impair COD removal but induced a shift in acetate utilization toward polyhydroxybutyrate (PHB) storage. This shift was more pronounced for fast growing biomass; it identified itself both in related process kinetics and the modified stoichiometry between the magnitude of acetate directly used for microbial growth and converted to PHB.