Response of an EBPR population developed in an SBR with propionate to different carbon sources

The effect of different carbon sources (propionate, acetate, butyrate and glucose) on an enhanced biological phosphorus removal biomass developed with propionate as the sole carbon source was studied. Firstly, a group of different cycle studies was carried out using each substrate independently and then, another cycle study was performed with a mixture of substrates. Propionate was found to be the substrate with the highest substrate uptake rate in both sets of experiments. It was also the volatile fatty acid (VFA) which required less reducing power and less P-release to be uptaken. Four different polyhydroxyalkanoate (PHA) monomers produced during the anaerobic phase were detected, and PHB, PHV and PH2MV were quantified. Significant differences in PHA composition were obtained depending on the carbon source. The carbon recovery ratio for the anaerobic phase was also evaluated. The lowest value observed among the different cycle studies was obtained for butyrate, while the highest value was obtained for acetate.

Variation of the microbial activity during the acclimation phase of a SBR system degrading 4-chlorophenol

The variation of microbial activity during acclimation to 4-chlorophenol (4CP) in an aerobic automated sequencing batch reactor was studied. The results show a reduction in degradation time as the acclimation process occurred. During acclimation for an initial concentration of 50 mg 4CP/L, degradation time was reduced from 40 h to 50 min after 10 cycles. In the case of an initial concentration of 100 mg/L, degradation time was reduced from 52 h to 1.16 h, also after 10 cycles. Doubling the initial concentration of a previously acclimated sludge produces only a slight increase in degradation time. It was found that as acclimation took place, the affinity of the consortia to biodegrade the toxic increased, whereas the ability to biodegrade acetate decreased. The evolution of the substrate uptake rate over time during the acclimation period was highly correlated with an exponential relationship. It was also observed that acclimation decreased both the production of a toxic metabolite and the sludge volumetric index.

The effect of anoxic selectors on sludge bulking

The effect of the substrate feeding pattern on sludge settleability in denitrifying systems was investigated. The feeding pattern was simulated in two sequencing batch reactors (SBR). SBR1 simulates a system with a limiting substrate (acetate) and a non-limiting electron acceptor (nitrate), while SBR2 simulates the opposite condition. Sludge volume index (SVI) was the main observed parameter. The stoichiometry, substrate uptake rate, storage capacity as well as sludge morphology and mixed culture population dynamics were also determined. Results show that independent of the feeding pattern, the settleability of the sludge remained good (SVI ≈ 50 mL/g) and stable. Neither the concentration of the acetate nor of the nitrate offered any limitations on sludge settleability, assuring that a good bio-P activity is present in nitrate limiting systems. Filamentous bacteria belonging to the TM group were usually present, although in low numbers. Despite the diffused, irregularly shaped and open floc structure, good settleability was observed. The results obtained were in line with the hypothesis on diffusion based selection.

Modeling of mass transfer in biofilms in oscillatory flow conditions using k-ɛ turbulence model

The objective of this research is to investigate mass transfer mechanism in biofilms under oscillatory flow conditions. Numerical simulation of turbulence near a biofilm was conducted using the low Reynold’s number k-ɛ turbulence model. Substrate transfer in biofilms under oscillatory flow conditions was assumed to be carried out by turbulent diffusion caused by fluid movement and substrate concentration profile in biofilm was calculated. An experiment was carried out to measure velocity profile near a biofilm under oscillatory flow conditions and the influence of the turbulence on substrate uptake rate by the biofilm was also measured. Measured turbulence was in good agreement with the calculated one and the influence of the turbulence on the substrate uptake rate was well explained by the simulation.

The use of chemical uncouplers for reducing biomass production during biodegradation

Reducing the energy available for anabolism of cell mass was identified as a method to minimise disposal requirements of excess biomass produced in the activated sludge process. A model system consisting of Pseudomonas putida, maintained in a chemostat, was employed to investigate biomass production in the presence of the energy dissipating protonphore, p-nitrophenol (pNP). The efficiency of biomass production was reduced by up to 62% when the feed was supplemented with 100 mg pNP.l−1 with a simultaneous increase in the specific substrate uptake rate. The data obtained have been analysed to reveal maintenance energy requirements and true growth yields. Cells were found to satisfy their maintenance energy requirements prior to utilising energy in anabolism. Decreases in pH alone had no effect on biomass production, but caused additional protonphore induced reduction of biomass production. A pH 6.2 the efficiency of biomass production was reduced by up to 77% when the feed was supplemented with 100 mg pNP.l−1.