Biomedical subjects

M C M van Loosdrecht

Publications and source records attributed to M C M van Loosdrecht.

At least 19 recordsLinked to original sources

PubMed2026

A Mobile Glycosylation Locus Modulates Cell Wall Architecture in Lactobacillus crispatus.

Lactobacillus crispatus dominance in the vaginal microbiome is associated with beneficial health outcomes, yet strain-level variation and its implications remain poorly understood. Here, we resolve the genomic context of three glycosyltransferase gene fragments (GT1-3) previously linked with dysbiotic states. Long-read resequencing revealed that GT1-3 are part of a ~18.7 kb Wzx/Wzy-dependent cell wall polysaccharide (CWPS) locus, containing several IS256-family transposases. Serial propagation in vitro produced isolates with 4.1 kb excised via a composite transposon encompassing the GT3, UDP-galactopyranose mutase, flippase, and hypothetical protein, demonstrating structural plasticity. Transmission electron microscopy showed a ~20%-25% thinner peptidoglycan layer in the derived strains, while FT-IR and monosaccharide analysis indicated no gross changes. Molecular dynamics simulations suggest that GT3 contributes to the structural stability of the glycosyltransferase complex, without compromising catalytic function. Together, these findings establish the CWPS locus as a mobile, structurally plastic element that directly influences cell wall architecture in L. crispatus.

Lactobacillus crispatus↗

PubMed2007

Kinetic model of a granular sludge SBR: influences on nutrient removal.

A mathematical model was developed that can be used to describe an aerobic granular sludge reactor, fed with a defined influent, capable of simultaneously removing COD, nitrogen and phosphate in one sequencing batch reactor (SBR). The model described the experimental data from this complex system sufficiently. The effect of process parameters on the nutrient removal rates could therefore be reliably evaluated. The influence of oxygen concentration, temperature, granule diameter, sludge loading rate, and cycle configuration were analyzed. Oxygen penetration depth in combination with the position of the autotrophic biomass played a crucial role in the conversion rates of the different components and thus on overall nutrient removal efficiencies. The ratio between aerobic and anoxic volume in the granule strongly determines the N-removal efficiency as it was shown by model simulations with varying oxygen concentration, temperature, and granule size. The optimum granule diameter for maximum N- and P-removal in the standard case operating conditions (DO 2 mg L(-1), 20 degrees C) was found between 1.2 and 1.4 mm and the optimum COD loading rate was 1.9 kg COD m(-3) day(-1). When all ammonia is oxidized, oxygen diffuses to the core of the granule inhibiting the denitrification process. In order to optimize the process, anoxic phases can be implemented in the SBR-cycle configuration, leading to a more efficient overall N-removal. Phosphate removal efficiency mainly depends on the sludge age; if the SRT exceeds 30 days not enough biomass is removed from the system to keep effluent phosphate concentrations low.

Ammonia↗

PubMed2006

Phosphate and potassium recovery from source separated urine through struvite precipitation.

Phosphate can be recovered as struvite or apatite in fluidised bed reactors. Urine has a much higher phosphate concentration than sludge reject water, allowing simpler (and less expensive) process for precipitation of phosphates. A stirred tank reactor with a special compartment for liquid solid separation was used to precipitate struvite from urine. Magnesium ammonium phosphate as well as potassium magnesium phosphate are two forms of struvite that were successfully precipitated. Liquid/solid separation was very effective, but the compaction of struvite was rather poor in the case of potassium struvite. Crystals did not form clusters and maintained the typical orthorhombic structure. Ammonium struvite had slightly lower effluent phosphate concentrations, but an average of 95% of influent phosphate was removed regardless of ammonium or potassium struvite precipitation. Fluid mechanics is believed to be important and should inform further work.

Chemical Precipitation↗

PubMed2006

Potential phosphorus recovery in a WWTP with the BCFS process: interactions with the biological process.

The BCFS process was developed to optimize the activity of denitrifying and P-removing bacteria. In this technology in combination with optimal operating conditions for biological nitrogen removal, chemical precipitation of phosphorus is used to ensure compliance with effluent standards regarding phosphorus. This work addresses the potential of the BCFS technology for phosphorus recovery and the interactions with the biological process. The TUD model calibrated for the Hardenberg WWTP was used. Nitrification was the biological process most influenced by the P stripper operation; however, further research is needed into the effect of limiting phosphate concentrations. Phosphate removal in the anaerobic reactor causes a decrease in the sludge poly-P content. The evaluation of the process operation under dynamic conditions showed that the P stripper use for phosphate recovery does not imply complicated control strategies. The use of the BCFS for phosphate recovery implies a change in the design philosophy not only to achieve the effluent requirements but also to maximize the anaerobic phosphate release and thereby recovery.

Anaerobiosis↗

PubMed2006

Multidimensional modelling to investigate interspecies hydrogen transfer in anaerobic biofilms.

Anaerobic digestion is a multistep process, mediated by a functionally and phylogenetically diverse microbial population. One of the crucial steps is oxidation of organic acids, with electron transfer via hydrogen or formate from acetogenic bacteria to methanogens. This syntrophic microbiological process is strongly restricted by a thermodynamic limitation on the allowable hydrogen or formate concentration. In order to study this process in more detail, we developed an individual-based biofilm model which enables to describe the processes at a microbial resolution. The biochemical model is the ADM1, implemented in a multidimensional domain. With this model, we evaluated three important issues for the syntrophic relationship: (i) Is there a fundamental difference in using hydrogen or formate as electron carrier? (ii) Does a thermodynamic-based inhibition function produced substantially different results from an empirical function? and; (iii) Does the physical co-location of acetogens and methanogens follow directly from a general model. Hydrogen or formate as electron carrier had no substantial impact on model results. Standard inhibition functions or thermodynamic inhibition function gave similar results at larger substrate field grid sizes (> 10 microm), but at smaller grid sizes, the thermodynamic-based function reduced the number of cells with long interspecies distances (> 2.5 microm). Therefore, a very fine grid resolution is needed to reflect differences between the thermodynamic function, and a more generic inhibition form. The co-location of syntrophic bacteria was well predicted without a need to assume a microbiological based mechanism (e.g., through chemotaxis) of biofilm formation.

Bacteria, Anaerobic↗

PubMed2006

Determination of the decay rate of nitrifying bacteria.

The growth and decay of nitrifying organisms determines the amount of nitrifying bacteria in activated sludge systems. The growth rate of the nitrifying organisms is reasonable, well defined, and studied, while the decay rate is still rather uncertain. Experiments in previous studies were over periods up to 14 days and obtained results were not confirmed. Contradicting decay rates of nitrifiers in different bacterial communities is reported. No differentiation between ammonia and nitrite oxidizers was made. Therefore, in this studyper day the decay rate of the nitrifying organisms was studied. The starvation condition (aerobic, anoxic, or anaerobic), temperature, type of bacterial community, and the presence of higher organisms are the main aspects that were investigated. A simple and reliable method (adapted from previous studies) for determining the decay rate of nitrifying organisms under different starvation conditions and different temperatures was developed. The test procedure has been used for determining the decay rate of ammonium and nitrite oxidizing bacteria in an enriched nitrifying culture and in activated sludge. The test was successfully applied at starvation periods up to 30 days. The decay rate of the enriched culture of nitrifiers was very low compared to values for nitrifiers in activated sludge. The decay rate of the nitrifiers in activated sludge was found to be to 0.2, 0.1, and 0.06 per day for aerobic, anoxic, and anaerobic conditions, respectively. The decay rate of ammonia oxidizers and nitrite oxidizers was the same at the corresponding conditions.

Ammonia↗

PubMed2006

Long term effects of salt on activity, population structure and floc characteristics in enriched bacterial cultures of nitrifiers.

The effect of salinity on the activity, the composition of nitrifiers and floc characteristics of nitrifying sludge was studied. Non-adapted and adapted (to 10g NaCl-Cl(-)/L for one year) enriched cultures of nitrifiers were tested in three sequencing batch reactors. Salt was increased gradually with 5 up to 40 g Cl(-)/L. No difference in steady state activity was observed between the adapted and non-adapted sludge. The activities of ammonia and nitrite oxidizers dropped 36% and 11%, respectively, at salt concentrations of 10 g Cl(-)/L. At 40 g Cl(-)/L inhibition reached 95% of salt free activity for ammonia and nitrite oxidizers in both adapted and non-adapted reactors. Nitrosomonas europaea and Nitrobacter sp. (fluorescent in situ hybridization) were the only nitrifiers present at high salt levels. Increased salt concentrations resulted in better settling characteristics of the nitrifying sludge. After 118 days the sludge was brought back to the initial conditions (0 g Cl(-)/L for non-adapted and 10 g Cl(-)/L for adapted). Despite the change in population composition similar kinetics as before the salt stress were observed.

Ammonia↗

PubMed2006

Potential application of monolith packed columns as bioreactors, control of biofilm formation.

Monolith reactors combine good mass transfer characteristics with low-pressure drop, the principle factors affecting the cost effectiveness of industrial processes. Recently, these specific features of the monolith reactors have drawn the attention toward the application of the monolith reactor in multiphase reaction systems. In this study, we explore the potential application of monolith reactors as bioreactor requiring gas-liquid mass transfer for substrate supply. It is demonstrated on theoretical grounds that the monolith reactor is a competitive alternative to conventional gas-liquid bioreactors such as stirred tanks, packed beds, and airlift bioreactors because it allows for a significant reduction of the energy dissipation that is normally required for gas-liquid contacting. A potential problem of monolith reactors for biological processes is clogging due to biofilm formation. This paper presents experimental results of a study into the formation and possible removal of biofilms during operation of a monolith reactor as suspended cells bioreactor. The results indicate that biofilm formation may be minimized and postponed by a proper choice of operating conditions. Periodic biofilm removal could straightforwardly be achieved by rinsing with water at moderate pressures and allows for stable operation for prolonged periods of time.

Biofilms↗

PubMed2006

Global impact and application of the anaerobic ammonium-oxidizing (anammox) bacteria.

In the anaerobic ammonium oxidation (anammox) process, ammonia is oxidized with nitrite as primary electron acceptor under strictly anoxic conditions. The reaction is catalysed by a specialized group of planctomycete-like bacteria. These anammox bacteria use a complex reaction mechanism involving hydrazine as an intermediate. The reactions are assumed to be carried out in a unique prokaryotic organelle, the anammoxosome. This organelle is surrounded by ladderane lipids, which make the organelle nearly impermeable to hydrazine and protons. The localization of the major anammox protein, hydrazine oxidoreductase, was determined via immunogold labelling to be inside the anammoxosome. The anammox bacteria have been detected in many marine and freshwater ecosystems and were estimated to contribute up to 50% of oceanic nitrogen loss. Furthermore, the anammox process is currently implemented in water treatment for the low-cost removal of ammonia from high-strength waste streams. Recent findings suggested that the anammox bacteria may also use organic acids to convert nitrate and nitrite into dinitrogen gas when ammonia is in short supply.

Acids↗

PubMed2006

Role of nitrogen oxides in the metabolism of ammonia-oxidizing bacteria.

Ammonia-oxidizing bacteria (AOB) can use oxygen and nitrite as electron acceptors. Nitrite reduction by Nitrosomonas is observed under three conditions: (i) hydrogen-dependent denitrification, (ii) anoxic ammonia oxidation with nitrogen dioxide (NO(2)) and (iii) NO(x)-induced aerobic ammonia oxidation. NO(x) molecules play an important role in the conversion of ammonia and nitrite by AOB. Absence of nitric oxide (NO), which is generally detectable during ammonia oxidation, severely impairs ammonia oxidation by AOB. The lag phase of recovery of aerobic ammonia oxidation was significantly reduced by NO(2) addition. Acetylene inhibition tests showed that NO(2)-dependent and oxygen-dependent ammonia oxidation can be distinguished. Addition of NO(x) increased specific activity of ammonia oxidation, growth rate and denitrification capacity. Together, these findings resulted in a hypothetical model on the role of NO(x) in ammonia oxidation: the NO(x) cycle.

Ammonia↗

PubMed2006

Nitrification activities in full-scale treatment plants with varying salt loads.

The effect of salt on the nitrification activity in full-scale wastewater treatment plants (WWTP) was investigated. Not only the activity of ammonia and nitrite oxidisers was measured, but also the nitrifying population was assessed (by Fluorescent In Situ Hybridisation)--in full-scale domestic and industrial WWTPs, operated under various salt levels. The results demonstrate a decline in the activity of ammonia and nitrite oxidisers with an increase in salt content: the domestic WWTP with the lowest salt level (0.13g Cl- l(-1)) had the highest specific activity of ammonia and nitrite oxidisers (4.3 and 2.4 mg N (gVSS)(-1) h(-1), respectively), while the lowest specific activities of ammonia and nitrite oxidisers (1.1 and 0.5 mg N (gVSS)(-1) h(-1)) were measured at the highest NaCl concentration (16g Cl- l(-1)). However, comparing the nitrification activity of different types of sludge developed under different operational conditions with the reported values was not directly possible. So we have used the activated sludge model (ASM) to translate the routine operational data into parameters to enable the calculation of the actual fraction of nitrifiers and consequently the actual specific activity of ammonia and nitrite oxidisers. Expressing the activity of ammonia oxidisers in terms of actual specific activity makes the results from pure cultures, enriched cultures, pilot scale and full scale WWTPs comparable. Moreover, these results confirm the behaviour of nitrifiers under salt stress and validate the results obtained from pure and enriched cultures to be extrapolated to full scale.

Ammonia↗

PubMed2006

Model-based evaluation of struvite recovery from an in-line stripper in a BNR process (BCFS).

Phosphate removal and recovery can be combined in BNR processes. This may be realised by struvite precipitation from the supernatant of the sludge in anaerobic compartments. This can be beneficial for either improving bio-P removal effluent quality or lowering the influent COD/P ratio required for bio-P removal. For this reason, a patented BNR process, BCFS, was developed and applied in The Netherlands. Several questions relating to P-recovery and behaviour of the system remain unclear and need to be ascertained. For this purpose, a modelling technique was employed in this study. With the help of a previous developed model describing carbon oxidation and nutrient removal, three cases were fully simulated. The simulations demonstrated that there was an optimal stripping flow rate and P-recovery would increase in costs and bio-P activity might be negatively affected due to decreased bio-P efficiency if this value was exceeded. The simulations indicated that the minimal COD(biod)/P ratio required for the effluent standard (1 g P/m3) could be lowered from 20 to 10 with 36% of P-recovery. A simulation with dynamic inflow revealed that the dynamic influent loads affected slightly the anaerobic supernatant phosphate concentration but the effluent phosphate concentration would not be affected with regular P-recovery.

Chemical Precipitation↗

PubMed2006

Integration of sulphate reduction, autotrophic denitrification and nitrification to achieve low-cost excess sludge minimisation for Hong Kong sewage.

An integrated anaerobic-aerobic treatment system of sulphate-laden wastewater was proposed here to achieve low sludge production, low energy consumption and effective sulphide control. Before integrating the whole system, the feasibility of autotrophic denitrification utilising dissolved sulphide produced during anaerobic treatment of sulphate rich wastewater was studied here. An upflow anaerobic sludge blanket reactor was operated to treat sulphate-rich synthetic wastewater (TOC=100 mg/L and sulphate=500 mg/L) and its effluent with dissolved sulphide and external nitrate solution were fed into an anoxic biofilter. The anaerobic reactor was able to remove 77-85% of TOC at HRT of 3 h and produce 70-90 mg S/L sulphide in dissolved form for the subsequent denitrification. The performance of anoxic reactor was stable, and the anoxic reactor could remove 30 mg N/L nitrate at HRT of 2 h through autotrophic denitrification. Furthermore, sulphur balance for the anoxic filter showed that more than 90% of the removed sulphide was actually oxidised into sulphate, thereby there was no accumulation of sulphur particles in the filter bed. The net sludge productions were approximately 0.15 to 0.18 g VSS/g COD in the anaerobic reactor and 0.22 to 0.31 g VSS/g NO3- -N in the anoxic reactor. The findings in this study will be helpful in developing the integrated treatment system to achieve low-cost excess sludge minimisation.

Filtration↗

PubMed2006

Controlling the nitrite:ammonium ratio in a SHARON reactor in view of its coupling with an Anammox process.

The combined SHARON-Anammox process for treating wastewater streams with high ammonia load is the focus of this paper. In particular, partial nitritation in the SHARON reactor should be performed to such an extent that a nitrite:ammonium ratio is generated which is optimal for full conversion in an Anammox process. In the simulation studies performed in this contribution, the nitrite:ammonium ratio produced in a SHARON process with fixed volume, as well as its effect on the subsequent Anammox process, is examined for realistic influent conditions and considering both direct and indirect pH effects on the SHARON process. Several possible operating modes for the SHARON reactor, differing in control strategies for O2, pH and the produced nitrite:ammonium ratio and based on regulating the air flow rate and/or acid/base addition, are systematically evaluated. The results are quantified through an operating cost index. Best results are obtained by means of cascade feedback control of the SHARON effluent nitrite:ammonium ratio through setting an O2 set-point that is tracked by adjusting the air flow rate, combined with single loop pH control through acid/base addition.

Air Movements↗

PubMed2006

Optimization of nitrogen and phosphorus limitation for better biodegradable plastic production and organic removal using single fed-batch mixed cultures and renewable resources.

The process for the production of biodegradable plastic material (polyhydroxyalkanoates, PHAs) from microbial cells by mixed-bacterial cultivation using readily available waste (renewable resources) is the main consideration nowadays. These observations have shown impressive results typically under high carbon fraction, COD/N and COD/P (usually described as nutrient-limiting conditions) and warmest temperature (moderate condition). Therefore, the aim of this work is predominantly to select mixed cultures under high storage responded by cultivation on a substrate - non limited in a single batch reactor with shortest period for feeding and to characterize their storage response by using specific and kinetics determination. In that case, the selected-fixed temperature is 30 degrees C to establish tropical conditions. During the accumulated steady-state period, the cell growth was inhibited by high PHA content within the cells because of the carbon reserve consumption. From the experiments, there is no doubt about the PHA accumulation even at high carbon fraction ratio. Apparently, the best accumulation occurred at carbon fraction, 160 +/- 7.97 g COD/g N (PHAmean, = 44.54% of dried cells). Unfortunately, the highest PHA productivity was achieved at the high carbon fraction, 560 +/- 1.62 g COD/g N (0.152 +/- 0.17 g/l. min). Overall results showed that with high carbon fraction induced to the cultivation, the PO4 and NO3 can remove up to 20% in single cultivation.

Biodegradation, Environmental↗

PubMed2006

Biological treatment of sludge digester liquids.

Nitrogen removal in side stream processes offers a good potential for upgrading wastewater treatment plants (WWTPs) that need to meet stricter effluent standards. Removing nutrients from these internal process flows significantly reduces the N-load to the main treatment plant. These internal flows mainly result from the sludge processing and have a high temperature and a high concentration of ammonia. Therefore, the required reactor volumes as well as the required aerobic SRT are small. Generally, biological treatment processes are more economical and preferred over physical-chemical processes. Recently, several biological treatment processes have been introduced for sludge water treatment. These processes are available now on the activated sludge market (e.g. SHARON, ANAMMOX and BABE processes). The technologies differ in concept and in the limitations guiding the application of these processes for upgrading WWTPs. This paper reviews and compares different biological alternatives for nitrogen removal in side streams. The limitations for selecting a technology from the available ones in the activated sludge market are noted and analysed. It is stressed that the choice for a certain process is based on more aspects than pure process engineering arguments.

Aerobiosis↗

PubMed2006

Critical analysis of some concepts proposed in ADM1.

The Anaerobic Digestion Model No. 1 (ADM1) has been developed by the expert task group of the IWA to establish a common platform for simulation of a wide variety of anaerobic degradation processes. It enables comparison of different methods and parameter values for description of specific sub-processes, with the methods and default values proposed by the task group. This will hopefully stimulate a more structured discussion on anaerobic digestion modelling compared to the recent past, when many different researchers developed a slightly different model and it remained largely unclear what could, and what could not be compared. In this paper we take the liberty to criticize some aspects of ADM1 and its implementation, as we think they represent concepts that are too easily extrapolated from activated sludge models. The specific subjects discussed here are the COD-based description of the reaction stoichiometry (i), the widely adopted use of a constant value for the solid retention time high-rate anaerobic bioreactors (ii), and the kinetic description of the acetogenic reactions as proposed in ADM1 (iii).

Anaerobiosis↗

PubMed2006

Variable stoichiometry with thermodynamic control in ADM1.

The effect of a variable stoichiometry of the carbohydrate fermentation process in the IWA Anaerobic Digestion Model No.1 (ADM1) is investigated. Most existing anaerobic digestion models including ADM1 consider a fixed-stoichiometry for their conversion processes. The ADM1 model was first transformed into an only mol based model to remove some errors derived from the mixed COD-mol based standard model and to allow for implementation of the variable stoichiometry. Consequently, the values of the butyrate and acetate catabolic yields of carbohydrate fermentation are made dependent on the hydrogen concentration and the reactor pH according to the predictions of a recently developed mixed culture fermentation model based on thermodynamic considerations. The simulation results obtained showed no significantly different responses in terms of effluent quality and system robustness between the standard and the variable stoichiometry ADM1 under overload conditions, and for both single- and two-step anaerobic digestion configurations. This behaviour is explained by the non-limiting acetogenic activity that compensated for the changes in the acidogenic products, typical behaviour for serial processes close to equilibrium. Based on the results obtained, thermodynamic rather than kinetic control for these conversions is suggested. Depending on the objectives to be met, lumping of carbohydrate fermenters and oxidative acetogens into a single biomass group with a variable stoichiometry is proposed for further consideration.

Anaerobiosis↗