The heterotrophic biomass has the capacity of utilizing substrate predominantly for growth or storage processes under steady-state conditions. In this study, the short-term variations in growth and storage kinetics of activated sludge under disturbed feeding conditions were analyzed using a multi-component biodegradation model. The variations in growth and storage kinetics were investigated with the aid of multi-response modeling and identifiability analysis. It was found that the heterotrophic biomass is able to increase its direct growth activity together with reducing the substrate storage capability under the availability of external substrate. Reducing the sludge age (SRT) from 10 to 2 days increased the maximum specific growth rate, μ (OHO,Max) from 3.9 to 7.0 day(-1), but did not considerably affected the maximum storage rate, k (Stor,OHO). The alteration of sludge age also elevated the half-saturation constant for growth (K (S,OHO)) from 5 to 25 mg COD/L. The increase in primary growth metabolism together with reduced storage rate was validated by model for two different sludge ages in the availability of external substrate. Aside from having a lower storage capability, the biomass had fast adaptation ability to direct growth process at low SRTs. The alteration of feed conditions was found to have different impacts on storage and growth kinetics. These results are significant and advance the field of activated sludge modeling under dynamic conditions by incorporation of short-term effects. Appropriate modifications including short-term effects in model structure may also reduce dynamic model recalibration efforts in the future.
"mg COD/mg COD within consecutive cycles; with five-higher acetate dosage the PHB/acetate ratio was increased to 0.76 mg COD/mg COD, a level which indicated full acetate storage. Similarly, Beun et al., (2002) indicated that a four-time higher dose of acetate did not appreciably affect the PHB acetate ratio of 0.70 mg COD/mg COD associated with the regular acetate level of 420 mg/L, while an eight-time higher acetate level increased this ratio to 0.76 mg COD/mg COD Recently, Insel et al., (2012) suggested that the heterotrophic biomass was able to increase its direct growth activity, while reducing its storage potential, when the cyclic availability of acetate, which was used as the organic carbon source in the experiments was reduced. These results, while useful, still require additional information for a clear understanding of the stoichiometry and kinetics of substrate storage sustained at different F/M ratios. "
[Show abstract][Hide abstract] ABSTRACT: The study investigated the effect of variations in the acetate to biomass ratio on substrate storage potential, and the kinetics of substrate utilization. A series of batch experiments were conducted with biomass taken from the fill and draw reactor operated at a sludge age of 2d. One of the batch reactors duplicated the substrate loading in the main reactor. The others were started with different initial acetate to biomass ratios both in lower and higher ranges. Increasing available acetate did not totally divert excess substrate to storage; the microbial culture adjusted the kinetics of the metabolic reactions to a higher growth rate so that more substrate could be utilized for direct growth at high acetate levels. Conversely, storage rate was increased, utilizing a higher substrate fraction for polyhydroxybutyrate generation when acetate concentration was lowered. The physiological and molecular bases of storage at low substrate levels were discussed.
"It was implemented by means of an iterative calibration procedure based on manual calibration of model components (Hocaoglu et al., 2011). The model outputs were found to be sensitive to all selected model coefficients (Insel et al., 2012). "
[Show abstract][Hide abstract] ABSTRACT: 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 50mg/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.
[Show abstract][Hide abstract] ABSTRACT: The study involved model evaluation of the fate and utilization of starch by microbial culture acclimated to different growth conditions and feeding regimes. For this purpose, parallel sequencing batch reactors were operated with pulse and continuous feeding of soluble starch at sludge ages of 8 and 2days. High-rate adsorption was identified as the initial process for starch utilization under all operating conditions. Hydrolysis mechanism acted as the rate limiting mechanism for different substrate removal/storage modes sustained under pulse and continuous feeding at different sludge ages. Together with variable growth kinetics, faster growth conditions also triggered high-rate hydrolysis and relatively slower storage kinetics to ensure the level of substrate supply for faster microbial growth. Model evaluation indicated the presence of particulate sugar adsorbed, especially under continuous feeding. It enabled accurate interpretation of observed particulate sugar values and this way, differentiating glycogen from the adsorbed starch remaining on the biomass.
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