Biomedical subjects

J Keller

Publications and source records attributed to J Keller.

At least 37 records · Page 2Linked to original sources

PubMed2004

Nitrogen removal of high strength wastewater via nitritation/denitritation using a sequencing batch reactor.

The sequencing batch reactor (SBR) process concept was applied to achieve efficient ammonium removal via nitrite under both laboratory and pilot-scale conditions. Both sets of experimental results show that without pH control or carbon addition the nitritation process consistently converted approximately 50% of the ammonium from biosolids dewatering liquids to nitrite with hydraulic retention times (HRT) as short as 10 h. The results from the pilot-scale study also indicate that the selective oxidation of ammonium to nitrite is a reliable process as the accumulation of nitrate was never an issue during a 330-day trial. The SBR process concept was extended to achieve complete nitrogen removal through nitritation and denitritation in the laboratory scale. The experimental results indicate that a total reduction of 96-98% of the ammonium nitrogen from biosolids dewatering liquids (influent concentration typically 1,200 g m(-3)) was achieved with a short HRT of 1.1 d and a removal rate of 1.05 kgNm(-3)d(-1). This process concept was tested at pilot scale where the nitritation process could be started up without temperature control in a short period of time. Nitrogen removal rates up to 1.2 kgNm(-3)d(-1) at an HRT of 0.88 d have been obtained. COD to nitrogen ratios required in the pilot plant were consistently in the range 1.6-1.9 kgCOD kg(-1)N removed.

Bioreactors↗

PubMed2004

Rate of nitrate production during a two-stage nitrification batch reaction.

The two steps of nitrification, namely the oxidation of ammonia to nitrite and nitrite to nitrate, often need to be considered separately in process studies. It has been assumed that these two reactions can be described by single Monod models. In this paper, the suitability of the single Monod model for describing nitrite oxidation to nitrate is discussed. The measured rate of nitrate production during a batch reaction is presented. For the system studied it was found that nitrate production actually increased after the completion of ammonia oxidation. It is suggested that the reason for the increase was a combination of: (i) likely competition for oxygen when both substrates were present, and (ii) a decrease in ammonia inhibition of nitrite oxidisers with the removal of ammonia. The result is that a single Monod expression (based on nitrite as the substrate) could not be used to describe nitrate production. In these types of systems the consequence of oxygen limitation and substrate inhibition should also be considered.

Ammonia↗

PubMed2004

Short-term effects of carbon source on the competition of polyphosphate accumulating organisms and glycogen accumulating organisms.

The effectiveness of enhanced biological phosphorus removal (EBPR) systems is directly affected by the competition of polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs). This study investigated the short-term effects of carbon source on PAO and GAO performance. The tests were designed to clearly determine the impact of volatile fatty acid (VFA) composition on the performance of two types of biomass, one enriched for PAOs and the other for GAOs. The two populations were enriched in separate reactors using identical operating conditions and very similar influent compositions with acetate as the sole carbon source. The only difference was that a very low level of phosphorus was present in the influent to the GAO reactor. The abundance of PAOs and GAOs was quantified using fluorescence in-situ hybridisation. The results clearly show that there are some very distinctive differences between PAOs and GAOs in their ability to utilise different carbon substrates. While both are able to take up acetate rapidly and completely, the GAOs are far slower at consuming propionate than the PAOs during short-term substrate changes. This provides a potentially highly valuable avenue to influence the competition between PAOs and GAOs. Other VFAs studied seem to be less usable in the short term by both PAOs and GAOs, as indicated by their much lower uptake rates.

Bacteria, Anaerobic↗

PubMed2004

A novel wastewater treatment process: simultaneous nitrification, denitrification and phosphorus removal.

Simultaneous nitrification and denitrification (SND) via the nitrite pathway and anaerobic-anoxic enhanced biological phosphorus removal (EBPR) are two processes that can significantly reduce the COD demand for nitrogen and phosphorus removal. The combination of these two processes has the potential of achieving simultaneous nitrogen and phosphorus removal with a minimal requirement for COD. A lab-scale sequencing batch reactor (SBR) was operated in alternating anaerobic-aerobic mode with a low dissolved oxygen concentration (DO, 0.5 mg/L) during the aerobic period, and was demonstrated to accomplish nitrification, denitrification and phosphorus removal. Under anaerobic conditions, COD was taken up and converted to polyhydroxyalkanoates (PHA), accompanied with phosphorus release. In the subsequent aerobic stage, PHA was oxidized and phosphorus was taken up to less than 0.5 mg/L at the end of the cycle. Ammonia was also oxidised during the aerobic period, but without accumulation of nitrite or nitrate in the system, indicating the occurrence of simultaneous nitrification and denitrification. However, off-gas analysis found that the final denitrification product was mainly nitrous oxide (N2O) not N2. Further experimental results demonstrated that nitrogen removal was via nitrite, not nitrate. These experiments also showed that denitrifying glycogen-accumulating organisms rather than denitrifying polyphosphate-accumulating organisms were responsible for the denitrification activity.

Acetates↗

PubMed2004

Mass transfer impacts in flocculent and granular biomass from SBR systems.

An experimental study was conducted to describe mass transfer impacts within nitrifying aggregates sourced from sequencing batch reactor (SBR) activated sludge systems. Flocculent and granular sludge with high nitrification activity was obtained in two laboratory SBR systems, supplied with a synthetic, ammonium-based feed. The flocculent biomass was fractionated using a sieving procedure, in order to obtain biomass fractions with different particle size distributions. The oxygen uptake rate (OUR) response to changes in dissolved oxygen concentration was measured under highly controlled conditions in a titrimetric and off-gas analysis (TOGA) sensor, and the results used to assess mass transfer effects. As the average particle size of the biomass increased, mass transfer limitations were found to increase significantly. Empirically fitted, apparent K(S,O2) values were demonstrated to be highly dependent on particle size, and reflect the mass transfer limitations occurring in the aggregates within a given system. Such parameters thus have little to do with the actual biokinetic parameter from which they are derived. The results obtained from the TOGA sensor study were consistent with those obtained from a microelectrode study on the same nitrifying granules. Together, these studies add considerable weight to the conclusion that consideration of external and internal mass transfer limitations is vital to the accurate description of activated sludge treatment processes, particularly those with a high oxygen uptake rate.

Biomass↗

PubMed2004

Structure and microbial composition of nitrifying microbial aggregates and their relation to internal mass transfer effects.

This paper presents an analysis of the structure and microbial composition of nitrifying aggregates, formed as either flocs or granules, in sequencing batch reactors (SBR) operated with a high ammonium load. The structure and microbial community of the aggregates was determined by fluorescence in situ hybridisation (FISH). The aggregate structure and size was related to mass transfer limitations observed by measurements of OURs measured by either a titrimetric and off-gas analysis sensor (TOGA) or by microsensors. The FISH analysis showed that the spatial arrangement of the microbial consortia correlated well with the oxygen gradients inside the aggregates. In the larger aggregates, the ammonium- and nitrite-oxidising bacteria were mainly concentrated to the outer 100-200 microm, whereas in the floc system, the bacteria were distributed throughout the entire aggregate. This indicates that the internal mass transfer resistance is considerably larger when the aggregate size increases which is directly supported by TOGA measurements.

Bacteria↗

PubMed2004

Anaerobic rumen SBR for degradation of cellulosic material.

Hydrolysis of organic particulates under anaerobic conditions is generally regarded as the rate limiting step in solid digestion processes. Rumen-based ecosystems appear to achieve very high hydrolysis rates for cellulosic organic material. This study aimed at the development and demonstration of an anaerobic sequencing batch reactor (SBR) process operating with a rumen-based microbial inoculum. Fibrous alpha cellulose was used as sole carbon substrate and the use of an SBR operating cycle allowed the utilisation of a high liquid flow rate (hydraulic retention time of 0.67 d) while maintaining a much longer solids retention time of 7 d. Complete mass balances for carbon and nitrogen, as well as COD balancing allowed the full characterisation of the process stoichiometry and kinetics. Elemental analysis of the biomass revealed a composition of C5H4.8O2.4N0.7, which is quite different from other generic biomass compositions used in the literature. The anaerobic rumen SBR was compared with another rumen-based reactor system in the literature which used a continuous filtration process for solid/liquid separation. This comparison showed that the volatile fatty acid production rate from cellulose in the anaerobic SBR was comparable with the performance achieved in the continuous system, although loading, substrate type and media composition were quite different between these two studies. Further evaluation of the anaerobic rumen SBR is required to determine its practical application for other substrates and to demonstrate the scale-up potential of this concept.

Animals↗

PubMed2004

Integration of titrimetric measurement, off-gas analysis and NOx- biosensors to investigate the complexity of denitrification processes.

The denitrification process, namely the reduction of nitrate (NO3-) to nitrogen gas (N2), often cannot be simply modelled as a single step process. For a more complete and comprehensive model the intermediates, particularly nitrite (NO2-) and nitrous oxide (N2O), need to be investigated. This paper demonstrates the integration of titrimetric measurements and off-gas analysis with on-line nitrite plus nitrate (NOx-) biosensors, highlighting the necessity of measuring process intermediates with high time-scale resolution to study and understand the kinetics of denitrification. Investigation of activated sludge from a full-scale treatment plant showed a significant accumulation of NO2-, which appeared to impact on the overall denitrification rate measured as NOx- reduction or N2 production. A different sludge obtained from a lab-scale bioreactor produced N2O instead of N2 as the end product of denitrification. The two examples both illustrate the complexity of denitrification and stress the need for the more versatile and detailed measurement procedures, as presented in this paper.

Bioreactors↗

PubMed2004

Comparison of methods for the determination of K(L)aO2 for respirometric measurements.

The mass transfer coefficient for oxygen in water (K(L)aO2) is an important parameter for respirometric studies. But determination of K(L)aO2 in process conditions is not straightforward, In this paper, two distinct procedures for determining K(L)aO2 in process conditions are outlined and tested. The off-gas method relies on a gas mass balance over a bioreactor while the non-steady state methods rely on analysing DO recovery after perturbation. Various means for inducing perturbation are tested and compared. K(L)aO2 values for a bioreactor are determined by the listed methods. It was found that the off-gas method resulted in the highest K(L)aO2 for the given reactor, while the non-steady state method, whereby perturbation is caused by exogenous activity on acetate, resulted in the lowest K(L)aO2. It is shown that the gas mass balancing technique is robust to unexpected exogenous activity (caused by for example, the oxidation of storage polymers formed or nitrite accumulated), while the non-steady state methods that involve inducing perturbations by exogenous activity appear susceptible to such continued exogenous activity in the DO recovery period.

Ammonia↗

PubMed2003

[Esophageal 24 hour-pH metry. Recommendations of the German Society of Neurogastroenterology and Motility and the Study Group for Gastrointestinal Functional Disorders and Function Diagnostics of the Austrian Society of Gastroenterology and Hepatology].

This article presents the recommendations for 24-hour oesophageal pH-metry of the German Society of Neurogastroenterology and Motility and the Study Group for Gastrointestinal Functional Disorders and Function Diagnostics of the Austrian Society of Gastroenterology and Hepatology. Indications for the examination, the procedures to be followed, the analysis of the obtained data and the conclusions to be drawn are delineated. The literature on which the recommendations are based is reviewed.

Adult↗

PubMed2003

Implant surface roughness affects osteoblast gene expression.

The transcription factor Cbfa1 regulates osteoblast differentiation and expression of genes necessary for the development of a mineralized phenotype. The purpose of this study was to determine if Cbfa1 and BSPII gene expression are influenced by implant surface microtopography. Osteoblasts were cultured on 600-grit (grooved) or sandblasted (roughened) cpTi implant discs. Mineralization was evaluated by Alizarin-Red-S staining. Real Time PCR was used for quantitative analysis of Cbfa1 and BSPII gene expression. Enhanced mineralization was seen in osteoblasts grown on roughened implant surfaces relative to tissue culture plastic. Real Time PCR showed significant (P < 0.05) increases in Cbfa1 gene expression in cells grown on roughened, as compared with grooved, implant surfaces. BSPII gene expression was also increased on rough surfaces in the UMR cells, but was reduced in the rat calvarial osteoblast cultures. These results suggest that osteoblast gene expression and mineralization are affected by roughened implant surface microtopographies during osseointegration of dental implants.

Analysis of Variance↗

PubMed2003

The effect of GAOs (glycogen accumulating organisms) on anaerobic carbon requirements in full-scale Australian EBPR (enhanced biological phosphorus removal) plants.

Glycogen-accumulating organisms (GAOs) were present in six full-scale plants investigated and in all but one made a significant contribution to the amount of volatile fatty acid (VFA) taken up anaerobically. While most plants surveyed contain GAOs, it was demonstrated that it is possible for a full-scale plant to operate with an insignificant GAO population. "Candidatus Accumulibacter phosphatis" were the significant polyphosphate-accumulating organisms (PAOs) in all plants surveyed. "Candidatus Competibacter phosphatis" were found in all plants along with other possible GAOs that were observed but not identified. A significant GAO population will increase the carbon requirements by removing VFA that could otherwise have been used by PAOs. Process optimization minimizing GAOs in full-scale plants would lead to a more efficient use of VFA.

Bioreactors↗

PubMed2003

Improving titrimetric techniques by modelling pH change in activated sludge systems.

Existing titrimetric techniques rely on a well defined hydrogen ion production rate. In particular, they are only suitable in circumstances in which constant background pH influencing reactions take place. This is rarely the case due to the presence of the carbonate acid/base system. In this paper, a model, which describes the influence of the nitrification process on pH and accounts for the action of the carbonate system, is presented. The validity of the model is tested by comparison of model predictions for the important state variables with that of experimental data from a batch oxidation of ammonium nitrogen. The two cases studied are the responses of an endogenously respiring nitrifying sludge to: an ammonium chloride pulse and a pulse of both bicarbonate and ammonium chloride. The results are most encouraging as the dynamic HPR response is mirrored by the model simulation. Furthermore, using the model for data interpretation, the initial nitrogen substrate levels are recovered. It is shown that this could not have been achieved in either case using existing titrimetric techniques.

Bioreactors↗

PubMed2003

Greenhouse gas production in wastewater treatment: process selection is the major factor.

Many practical design and operating decisions on wastewater treatment plants can have significant impacts on the overall environmental performance, in particular the greenhouse gas (GHG) emissions. The main factor in this regard is the use of aerobic or anaerobic treatment technology. This paper compares the GHG production of a number of case studies with aerobic or anaerobic main and sludge treatment of domestic wastewater and also looks at the energy balances and economics. This comparison demonstrates that major advantages can be gained by using primarily anaerobic processes as it is possible to largely eliminate any net energy input to the process, and therefore the production of GHG from fossil fuels. This is achieved by converting the energy of the incoming wastewater pollutants to methane which is then used to generate electricity. This is sufficient to power the aerobic processes as well as the mixing etc. of the anaerobic stages. In terms of GHG production, the total output (in CO2 equivalents) can be reduced from 2.4 kg CO2/kg COD(removed) for fully aerobic treatment to 1.0 kg CO2/kg COD(removed) for primarily anaerobic processes. All of the CO2 produced in the anaerobic processes comes from the wastewater pollutants and is therefore greenhouse gas neutral, whereas up to 1.4 kg CO2/kg COD(removed) originates from power generation for the fully aerobic process. This means that considerably more CO2 is produced in power generation than in the actual treatment process, and all of this is typically from fossil fuels, whereas the energy from the wastewater pollutants comes primarily from renewable energy sources, namely agricultural products. Even a change from anaerobic to aerobic sludge treatment processes (for the same aerobic main process) has a massive impact on the CO2 production from fossil fuels. An additional 0.8 kg CO2/kg COD(removed) is produced by changing to aerobic sludge digestion, which equates for a typical 100,000 EP plant to an additional production of over 10 t CO2 per day. Preliminary cost estimates confirm that the largely anaerobic process option is a fully competitive alternative to the mainly aerobic processes used, while achieving the same effluent quality.

Bacteria, Aerobic↗

PubMed2003

Optimisation of Noosa BNR plant to improve performance and reduce operating costs.

Noosa WWTP is publicly owned and privately operated by Australian Water Services. The process includes primary sedimentation, raw sludge fermentation, biological nutrient removal (BNR), sand filtration and ultraviolet (UV) disinfection. An innovative feature of the plant is the supplementary carbon dosing facility to avoid the use of metal salts (alum or ferric) for phosphorus removal. The average flow treated during 2000 was 9.0 ML/d. The annual 50 percentile effluent quality requirements for nutrients are total N < 5 mg/L and total P < 1 mg/L. The objectives of this project were to: determine the cause of variability in phosphorus removal; develop a strategy to control the variability in phosphorus removal; and minimise the operating cost of supplementary carbon dosing while achieving the effluent quality requirements. An investigation of chemical and microbiological parameters was implemented and it was concluded that there were several factors causing variability in phosphorus removal, rather than a single cause. The following four major causes were identified, and the control strategies that were adopted resulted in the plant achieving annual 50 percentile effluent total P = 0.37 mg/L and total N = 3.0 mg/L during 2001. First, phosphorus removal was limited by the available VFA supply due to consumption of VFA by other organisms competing with phosphate accumulating organisms (PAO), and due to diurnal variations in the sewage VFA and phosphate concentrations. Therefore, supplementary carbon dosing was essential to make allowance for competing reactions. Second, increasing the fermenter VFA yield via supplementary carbon dosing with molasses was found to be an effective and economic way of ensuring reliable phosphorus removal. Third, nitrate in the RAS resulted in consumption of VFA by denitrifying bacteria, particularly with process configurations where the RAS was recycled directly into the anaerobic zone. Incorporating a RAS denitrification zone into the process rectified this problem. Finally, glycogen accumulating organisms (GAO) were observed in BNR sludge samples, and consumption of VFA by GAO appeared to cause decreased phosphorus removal. Better phosphorus removal was obtained using VFA derived from the fermenter than dosing an equivalent amount of acetic acid. It was hypothesized that GAO have a competitive advantage to use acetate and PAO have a competitive advantage to use propionate, butyrate or some other soluble COD compound in the fermenter effluent. Contrary to popular belief, acetate may not be the optimum VFA for biological phosphorus removal. The competition between PAO and GAO for different VFA species under anaerobic conditions requires further investigation in order to control the growth of GAO and thereby improve reliability of biological phosphorus removal processes.

Bioreactors↗

PubMed2003

Investigation of membrane processes for the removal of volatile fatty acids.

The accumulation of volatile fatty acids such as acetic acid can cause reactor pH problems and the inhibition of microorganisms utilised in anaerobic digestion processes. A cross-flow membrane process using Teflon and ion-exchange membranes was investigated as a means of separating acetic acid from pure acetic acid solution and rumen fluid. Acetic acid transfer across the Teflon membrane was dependent on the free acid concentration (CH3COOH) in the acid solution. Concurrent transfer of water was minimal due to the hydrophobic nature of the membrane. The strong base anionic exchange membrane facilitated the separation of acetic acid from both pure solutions and rumen fluid with flux again being dependent on the free acid gradient across the membrane. Flux rates were lower than other studies of diffusion dialysis, however, this may be partly attributed to improper preparation of the membrane. The currently achieved rates of transfer using these membranes are very low and are therefore not yet suitable for full-scale use in anaerobic digestion. Additional research is needed to achieve higher trans-membrane transport rates at reasonable costs.

Acetic Acid↗

PubMed2003

Industrial applications of the IWA anaerobic digestion model No. 1 (ADM1).

In this paper, the IWA anaerobic digestion model No. 1 (ADM1) is applied to two case studies from contract work on industrial treatment plants. The first was the assessment of acid addition for pH decrease and avoidance of calcium carbonate (CaCO3) precipitation in a paper mill fed UASB. The simulation work found, with a high degree of confidence, that acid dosing was neither economical for pH control, nor had any real effect on the CaCO3 levels present in the reactor. A specific calcium carbonate precipitation equation was added to the ADM1 to undertake this study. The second case study was an assessment of the benefits of thermophilic (as opposed to mesophilic operation) for reduced ammonia inhibition, improved stability and gas production in a solids digester at a gelatine production facility. Here, it was predicted that thermophilic operation could not attain either goal to a satisfactory extent. In addition to demonstrating the application of the ADM1 to the two systems, we have also assessed the predictions generated in the case studies in terms of quality and utility.

Bacteria, Anaerobic↗

PubMed2003

Microbial quantification in activated sludge: the hits and misses.

Since the implementation of the activated sludge process for treating wastewater, there has been a reliance on chemical and physical parameters to monitor the system. However, in biological nutrient removal (BNR) processes, the microorganisms responsible for some of the transformations should be used to monitor the processes with the overall goal to achieve better treatment performance. The development of in situ identification and rapid quantification techniques for key microorganisms involved in BNR are required to achieve this goal. This study explored the quantification of Nitrospira, a key organism in the oxidation of nitrite to nitrate in BNR. Two molecular genetic microbial quantification techniques were evaluated: real-time polymerase chain reaction (PCR) and fluorescence in situ hybridisation (FISH) followed by digital image analysis. A correlation between the Nitrospira quantitative data and the nitrate production rate, determined in batch tests, was attempted. The disadvantages and advantages of both methods will be discussed.

Bioreactors↗