Kinetics of bacterial sulfate reduction in an activated sludge plant (original) (raw)
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Oxygen Tolerance of Sulfate-Reducing Bacteria in Activated Sludge
Environmental Science & Technology, 2004
The oxygen tolerance of sulfate-reducing bacteria (SRB) present in activated sludge was studied in batch incubations using radiolabeled [ 35 S]sulfate and a most probable number (MPN) technique employing activated sludge medium. Sulfate reduction (SR) could not be detected in activated sludge during oxic incubation or in the presence of nitrate. However, upon anoxic incubation of both freshly sampled activated sludge and activated sludge preaerated for 40 min, SR resumed immediately at an initial rate of 2 µM h-1. During long-term aeration of activated sludge, the number of viable and culturable SRB remained constant at around 10 6 SRB mL-1 throughout a 121 h aeration period. During the first 9 h of the 121 h aeration period, the anaerobic SR activity was unaffected, as compared to that of an unaerated control sample, and recommenced instantaneously upon anoxic incubation. Even after 121 h of continuous aeration, SR took place within 1.5 h after anoxic incubation albeit at a rate less than 20% that of the unaerated control. As suggested by MPN estimates and the observed kinetics of SR, oxygen exposure resulted in temporary metabolic inactivation of SRB but did not cause cell death. Consequently, SRB have the potential for quick proliferation during anoxic storage of activated sludge.
1999
A combination of different methods was applied to investigate the occurrence of anaerobic processes in aerated activated sludge. Microsensor measurements (O 2 , NO 2 ؊ , NO 3 ؊ , and H 2 S) were performed on single sludge flocs to detect anoxic niches, nitrate reduction, or sulfate reduction on a microscale. Incubations of activated sludge with 15 NO 3 ؊ and 35 SO 4 2؊ were used to determine denitrification and sulfate reduction rates on a batch scale. In four of six investigated sludges, no anoxic zones developed during aeration, and consequently denitrification rates were very low. However, in two sludges anoxia in flocs coincided with significant denitrification rates. Sulfate reduction could not be detected in any sludge in either the microsensor or the batch investigation, not even under short-term anoxic conditions. In contrast, the presence of sulfate-reducing bacteria was shown by fluorescence in situ hybridization with 16S rRNA-targeted oligonucleotide probes and by PCR-based detection of genes coding for the dissimilatory sulfite reductase. A possible explanation for the absence of anoxia even in most of the larger flocs might be that oxygen transport is not only diffusional but enhanced by advection, i.e., facilitated by flow through pores and channels. This possibility is suggested by the irregularity of some oxygen profiles and by confocal laser scanning microscopy of the three-dimensional floc structures, which showed that flocs from the two sludges in which anoxic zones were found were apparently denser than flocs from the other sludges.
The use of primary sewage sludge (PSS) as the carbon source/ electron for biological sulfate reduction is an attractive low-cost alternative for the treatment of acid mine drainage. Sulfate-reducing bacteria cannot utilize the particulate organic matter in PSS directly, and these particulates need to be solubilised first. A series of experiments have been conducted to determine the effects of sulfate reduction, compared to methane production, on the rate of hydrolysis and solubilisation of PSS. The results show that under sulfate-reducing conditions with low aqueous sulfide concentrations, the rate of hydrolysis was increased by more than 50% over the methanogenic system, while the rates of solubilisation were near identical. The sulfate-reducing systems were able to use all available soluble organic COD, including acetate, when there was sufficient sulfate in the system. The COD: SO 4 utilization ratio was calculated at 0.8, compared to the theoretical value of 0.67.
Sulfate reducing bacteria applied to domestic wastewater
Water Practice and Technology, 2018
The application of sulfate reducing bacteria (SRB) to treat municipal wastewater is seldom considered. For instance, due to low sludge yield it can reduce the amount of excess sludge produced significantly. Several studies, mainly at laboratory-scale, revealed that SRB can proliferate in artificial wastewater systems at temperatures of 20°C and lower. So far, the application of SRB in a domestic wastewater treatment plant has been limited. Therefore, this study evaluates the proliferation of SRB at pilot-scale in a moderate climate. This study revealed that SRB were present and active in the pilot fed with domestic wastewater at 13°C, and outcompete methanogens. Stable, smooth and well-settled granule formation occurred, which is beneficial for full-scale application. In the Netherlands the sulfate concentration is usually low (<500 mg/L), therefore the application of SRB seems challenging as sulfate is limiting. Additional measurements indicated the presence of other sulfur sour...
A kinetic study on bacterial sulfate reduction
Bioprocess and Biosystems Engineering, 2013
The activity of anaerobic sulfate reduction was studied using sulfate-reducing bacteria isolated from the water produced from a Brazilian oil reservoir. The effects of the initial sulfate concentration on the anaerobic sulfate reduction and sulfide generation kinetics were investigated. The redox potential, the biomass solution content, and the sulfate and the sulfide solution content were measured. The results indicate that the sulfate conversion and the sulfide generation are both first-order processes for the initial sulfate concentration of 823, 1,282, and 1,790 mg/L. The results for the kinetic constants for the sulfate conversion indicate an inhibition with the enhancement of the initial sulfate solution content. The kinetic constants for the sulfide generation indicate that this reaction is almost independent of the initial sulfate solution content due to the presence of at least two in-series processes that are faster than the microbial conversion of the sulfate. The kinetic test using the water from an onshore oil field, with an initial sulfide content of 228 mg/L and sulfate content of 947 mg/ L, shows a sulfate conversion of 50 % in 528 h. The kinetic modeling for the net content of sulfate and sulfide indicates that the sulfate conversion is slower for this water than for the deionized water tests; however, the sulfide formation has almost the same conversion velocity. The reactions are first order in both cases.
Effects of electron acceptors on sulphate reduction activity in activated sludge processes
Applied Microbiology and Biotechnology, 2017
The concentration of sulphate present in wastewater can vary from 10 to 500 mg SO 4 2− /L. During anaerobic conditions, sulphate is reduced to sulphide by sulphatereducing bacteria (SRB). Sulphide generation is undesired in wastewater treatment plants (WWTPs). Previous research indicated that SRB are inhibited by the presence of electron acceptors (such as O 2 , NO 3 and NO 2). However, the contact times and concentrations used in those studies are by far higher than occur in WWTPs. Since sulphide can influence the biological nitrogen and phosphorus removal processes, this research aimed to understand how the different electron acceptors commonly present in biological nutrient removal (BNR) systems can affect the proliferation of SRB. For this purpose, a culture of SRB was enriched in a sequencing batch reactor (approx. 88% of the total bacteria population). Once enriched, the SRB were exposed for 2 h to typical concentrations of electron acceptors like those observed in BNR systems. Their activity was assessed using three different types of electron donors (acetate, propionate and lactate). Oxygen was the most inhibiting electron acceptor regardless the carbon source used. After exposure to oxygen and when feeding acetate, an inactivation time in the sulphate reduction activity was observed for 1.75 h. Once the sulphate reduction activity resumed, only 60% of the original activity was recovered. It is suggested that the proliferation of SRB is most likely to occur in BNR plants with an anaerobic fraction higher than 15% and operating at sludge retention times higher than 20 days (at a temperature of 20°C). These results can be used to implement strategies to control the growth of sulphate reducers that might compete for organic carbon with phosphate-accumulating organisms.
Extracellular polymeric substances (EPS) are the construction materials for microbial aggregates such as biofilms, flocs and sludge, and greatly contribute to the structural integrity of sludge flocs in wastewater treatment processes. The loss of integrity of the sewage sludge floc is believed to be due to enhanced hydrolysis of important structural components such as lignin, protein and cellulose in the sludge floc matrix. The mechanism of enhanced sludge floc fracture, due to the action of enzymes hydrolysing these structural components, remains a key element in our understanding of how the floc integrity in systems utilising a sulphate reducing system is compromised. A range of relatively non-specific exogenous enzymes (ß-glucosidase, cellulase, proteases: trypsin, pronase E and chymotrypsin) were added to a sulphidogenic bioreactor- (containing both sulphate reducing bacteria (SRB) and a methanogenic bacterial system) and a (control) methanogenic bioreactor sample, and the effec...
A Kinetic Analysis of Microbial Sulfate Reduction in an Upflow Packed-Bed Anaerobic Bioreactor
The activity of anaerobic sulfate reduction was studied using sulfate-reducing bacteria isolated from the water produced from a Brazilian oil reservoir. The effects of the initial sulfate concentration on the anaerobic sulfate reduction and sulfide generation kinetics were investigated. The redox potential, the biomass solution content, and the sulfate and the sulfide solution content were measured. The results indicate that the sulfate conversion and the sulfide generation are both first-order processes for the initial sulfate concentration of 823, 1,282, and 1,790 mg/L. The results for the kinetic constants for the sulfate conversion indicate an inhibition with the enhancement of the initial sulfate solution content. The kinetic constants for the sulfide generation indicate that this reaction is almost independent of the initial sulfate solution content due to the presence of at least two in-series processes that are faster than the microbial conversion of the sulfate. The kinetic test using the water from an onshore oil field, with an initial sulfide content of 228 mg/L and sulfate content of 947 mg/ L, shows a sulfate conversion of 50 % in 528 h. The kinetic modeling for the net content of sulfate and sulfide indicates that the sulfate conversion is slower for this water than for the deionized water tests; however, the sulfide formation has almost the same conversion velocity. The reactions are first order in both cases.