Biomedical subjects

A Seco

Publications and source records attributed to A Seco.

At least 19 recordsLinked to original sources

PubMed2007

Fermentation and elutriation of primary sludge: effect of SRT on process performance.

A primary sludge fermentation-elutriation pilot plant was operated using in-line and side-stream schemes. The influence of solids retention time, recirculation sludge flow-rate and solids concentration on the fermentation-elutriation process performance has been assessed in this paper. The use of high elutriation flows (12% of influent flow) improved the volatile fatty acids (VFA) concentration in the effluent stream. Suspended solids removal efficiency decreased in the primary settler when the solids retention time (SRT) was increased from 4 to 8 days. Disintegration step during hydrolysis process was pointed out as the main reason for that decrease. Maximum VFA productions were achieved at SRT between 6 and 8 days at the highest elutriation flow tested for both configurations. Propionic, butyric and valeric volatile fatty acids percentage increased when total solids sludge concentrations above 23,000mgl(-1) were used. Hydrogen accumulation, causing acetogenic bacteria inhibition, was indicated as the reason for C(3)-C(5) fatty acids accumulation.

Bioreactors↗

PubMed2006

Effect of pH on biological phosphorus uptake.

An anaerobic aerobic laboratory scale sequencing batch reactor (SBR) was operated to study the effect of pH on enhanced biological phosphorus removal. Seven steady states were achieved under different operating conditions. In all of them, a slight variation in the pH value was observed during anaerobic phase. However, pH rose significantly during aerobic phase. The increase observed was due to phosphorus uptake and carbon dioxide stripping. When pH was higher than 8.2-8.25 the phosphorus uptake rate clearly decreased. The capability of Activated Sludge Model No. 2d (ASM2d) and Biological Nutrient Removal Model No. 1 (BNRM1) to simulate experimental results was evaluated. Both models successfully characterized the enhanced biological phosphorus removal performance of the SBR. Furthermore, BNRM1 also reproduced the pH variations observed and the decrease in the phosphorus uptake rate. This model includes a switch function in the kinetic expressions to represent the pH inhibition in biological processes. The pH inhibition constants related to polyphosphate storage process were obtained by adjusting model predictions to measured phosphorus concentrations. On the other hand, pH inhibition should be included in ASM2d to accurately simulate experimental phosphorus evolution observed in an A/O SBR.

Aerobiosis↗

PubMed2006

Calcium effect on enhanced biological phosphorus removal.

The role of calcium (Ca) in enhanced biological phosphorus removal and its possible implications on the metabolic pathway have been studied. The experience has been carried out in an SBR under anaerobic-aerobic conditions for biological phosphorus removal during 8 months. The variations of influent Ca concentration showed a clear influence on the EBPR process, detecting significant changes in Y(PO4). These Y(PO4) variations were not due to influent P/COD ratio, pH, denitrification and calcium phosphate formation. The Y(PO4) has been found to be highly dependent on the Ca concentration, increasing as Ca concentration decreases. The results suggest that high Ca concentrations produce "inert" granules of polyphosphate with Ca as a counterion that are not involved in P release and uptake. Furthermore, microbiological observations confirmed that appreciable changes in PAO and GAO populations were not observed. This behaviour could suggest a change in the bacterial metabolic pathway, with prevailing polyphosphate-accumulating metabolism (PAM) at low influent Ca concentration and glycogen-accumulating metabolism (GAM) at high concentration.

Aerobiosis↗

PubMed2006

Application of a fuzzy algorithm for pH control in a struvite crystallisation reactor.

A struvite crystallisation process is highly dependent on pH. To achieve a high phosphorus recovery as struvite it is important to have an accurate control of pH in the reactor. The high non-linear response of pH value makes manual pH control difficult. Therefore, a software based on fuzzy logic control (FLC) has been developed to maintain the pH at a set value in a stirred reactor to crystallise struvite. The FLC developed has been based on Larsen's inference. In order to confirm the improvement of the pH stability using FLC software, different experiments have been carried out with manual control of the pH value, and with the FLC software. It has been demonstrated that using FLC software allows a precise control of pH with high stability, optimises the process, and minimises the operator intervention.

Algorithms↗

PubMed2006

Calibration and simulation of ASM2d at different temperatures in a phosphorus removal pilot plant.

In this work, an organic and nutrient removal pilot plant was used to study the temperature influence on phosphorus accumulating organisms. Three experiments were carried out at 13, 20 and 24.5 degrees C, achieving a high phosphorus removal percentage in all cases. The ASM2d model was calibrated at 13 and 20 degrees C and the Arrhenius equation constant was obtained for phosphorus removal processes showing that the temperature influences on the biological phosphorus removal subprocesses in a different degree. The 24.5 degrees C experiment was simulated using the model parameters obtained by means of the Arrhenius equation. The simulation results for the three experiments showed good correspondence with the experimental data, demonstrating that the model and the calibrated parameters were able to predict the pilot plant behaviour.

Calibration↗

PubMed2005

Optimum design and operation of primary sludge fermentation schemes for volatile fatty acids production.

This paper presents a model-knowledge based algorithm for optimising the primary sludge fermentation process design and operation. This is a recently used method to obtain the volatile fatty acids (VFA), needed to improve biological nutrient removal processes, directly from the raw wastewater. The proposed algorithm consists in a heuristic reasoning algorithm based on the expert knowledge of the process. Only effluent VFA and the sludge blanket height (SBH) have to be set as design criteria, and the optimisation algorithm obtains the minimum return sludge and waste sludge flow rates which fulfil those design criteria. A pilot plant fed with municipal raw wastewater was operated in order to obtain experimental results supporting the developed algorithm groundwork. The experimental results indicate that when SBH was increased, higher solids retention time was obtained in the settler and VFA production increased. Higher recirculation flow-rates resulted in higher VFA production too. Finally, the developed algorithm has been tested by simulating different design conditions with very good results. It has been able to find the optimal operation conditions in all cases on which preset design conditions could be achieved. Furthermore, this is a general algorithm that can be applied to any fermentation-elutriation scheme with or without fermentation reactor.

Algorithms↗

PubMed2005

The role of potassium, magnesium and calcium in the Enhanced Biological Phosphorus Removal treatment plants.

Cations as potassium and magnesium play an important role in maintaining the stability of Enhanced Biological Phosphorus Removal (EBPR) process. In this paper potassium, magnesium and calcium behaviour in EBPR treatment plants has been studied. An ASM2d model extension which takes into account the role of potassium and magnesium in the EBPR process has been developed. Finally, a simulation of the effect on P removal of a shortage of K and Mg was studied. The experimental results showed that K and Mg play an important role in the EBPR process being cotransported with P into and out of bacterial cells. It has been observed that calcium is not involved in P release and uptake. The values of the molar ratios K/P (0.28 mol K mol P(-1)) and Mg/P (0.36 mol Mg mol P(-1)) were obtained accomplishing the charge balance, with different K/Mg mass ratios and without phosphorus precipitation. Model predictions accurately reproduced experimental data. The simulations carried out showed the important effect of the K and Mg influent concentration for P removal efficiency. The results illustrate that the proposed ASM2d model extension must be considered in order to accurately simulate the phosphorus removal process.

Aerobiosis↗

PubMed2004

An extension of ASM2d including pH calculation.

This paper presents an extension of the Activated Sludge Model No. 2d (ASM2d) including a chemical model able to calculate the pH value in biological processes. The developed chemical model incorporates the complete set of chemical species affecting the pH value to ASM2d describing non-equilibrium biochemical processes. It considers the system formed by one aqueous phase, in which biochemical processes take place, and one gaseous phase, and is based on the assumptions of instantaneous chemical equilibrium under liquid phase and kinetically governed mass transport between the liquid and gas phase. The ASM2d enlargement comprises the addition of every component affecting the pH value and an ion-balance for the calculation of the pH value and the dissociation species. The significant pH variations observed in a sequencing batch reactor operated for enhanced biological phosphorus removal were used to verify the capability of the extended model for predicting the dynamics of pH jointly with concentrations of acetic acid and phosphate. A pH inhibition function for polyphosphate accumulating bacteria has also been included in the model to simulate the behaviour observed. Experimental data obtained in four different experiments (with different sludge retention time and influent phosphorus concentrations) were accurately reproduced.

Bioreactors↗

PubMed2004

Use of biological and sedimentation models for designing Peñíscola WWTP.

This paper presents Peñíscola wastewater treatment plant design. Peñíscola is a tourist city in Castellón (Spain), whose population changes significantly between summer and the rest of the year. The design of the biological and settling treatment units has been confirmed by computer model simulations and provided for biological organic matter, nitrogen and phosphorus removal. Two different treatment schemes have been proposed in order to optimize the plant performance during both seasonal operations. During low-load season, the plant will be operated under extended aeration conditions, so further sludge stabilization will not be needed. During high-load season, the plant will be operated under conventional process conditions and excess sludge will be aerobically digested. Since the treated water will be reused for irrigation purposes, biological nutrient removal has been considered in this design. Phosphorus released during aerobic digestion must be removed by chemical precipitation in the supernatant from dewatering process. In this way, deterioration of the enhanced biological phosphorus removal process caused by phosphate recirculation can be avoided. Mathematical models have proven to be very useful to make decisions about plant design and operation, mainly in situations with significant variations in the influent load and flow-rate. Several operation conditions have been simulated to obtain optimum operation criteria for both seasons.

Geologic Sediments↗

PubMed2004

Biological nutrient removal model No.1 (BNRM1).

This paper presents the results of the work carried out by the CALAGUA Group on Mathematical Modelling of Biological Treatment Processes: the Biological Nutrient Removal Model No.1. This model is based on a new concept for dynamic simulation of wastewater treatment plants: a unique model can be used to design, simulate and optimize the whole plant, as it includes most of the biological and physico-chemical processes taking place in all treatment operations. The physical processes included are: settling and clarification processes (flocculated settling, hindered settling and thickening), volatile fatty acids elutriation and gas-liquid transfer. The chemical interactions included comprise acid-base processes, where equilibrium conditions are assumed. The biological processes included are: organic matter, nitrogen and phosphorus removal; acidogenesis, acetogenesis and methanogenesis. Environmental conditions in each operation unit (aerobic, anoxic or anaerobic) will determine which bacterial groups can grow. Thus, only the model parameters related to bacterial groups able to grow in any of the operation units of a specific WWTP will require calibration. One of the most important advantages of this model is that no additional analysis with respect to ASM2d is required for wastewater characterization. Some applications of this model have also been briefly explained in this paper.

Acid-Base Equilibrium↗

PubMed2004

Monitoring pH and electric conductivity in an EBPR sequencing batch reactor.

This paper presents laboratory-scale experimentation carried out to study enhanced biological phosphorus removal. Two anaerobic aerobic (A/O) sequencing batch reactors (SBR) have been operated during more than one year to investigate the information provided by monitoring pH and electric conductivity under stationary and transient conditions. Continuous measurements of these parameters allow detecting the end of anaerobic phosphorus release, of aerobic phosphorus uptake and of initial denitrification, as well as incomplete acetic acid uptake. These results suggest the possibility of using pH and electric conductivity as control parameters to determine the length of both anaerobic and aerobic phases in an A/O SBR. More valuable information provided by monitoring pH and electric conductivity is the relation between the amount of phosphorus released and the conductivity increase observed during the anaerobic stages and which group of bacteria (heterotrophic or polyphosphate accumulating) is carrying out the denitrification process.

Acetic Acid↗

PubMed2003

Design of nutrient removal activated sludge systems.

A mechanistic mathematical model for nutrient and organic matter removal was used to describe the behavior of a nitrification denitrification enhanced biological phosphorus removal (NDEBPR) system. This model was implemented in a user-friendly software DESASS (design and simulation of activated sludge systems). A 484-L pilot plant was operated to verify the model results. The pilot plant was operated for three years over three different sludge ages. The validity of the model was confirmed with data from the pilot plant. Also, the utility of DESASS as a valuable tool for designing NDEBPR systems was confirmed.

Bioreactors↗

PubMed2002

Modelling of an activated primary settling tank including the fermentation process and VFA elutriation.

A complete model of a primary settler including both sedimentation and biological processes is presented. It is a one-dimensional model based on the solids flux concept and the conservation of mass that uses the Takács model for the settling velocity, which is corrected by a compression function in the lower layers. The biological model is based on the ASM2 and enlarged with the fermentation model proposed by this research group. The settler was split in ten layers and the flux terms in the mass balance for each layer is obtained by means of the settling model. A pilot plant has been operated to study the primary sludge fermentation and volatile fatty acids (VFA) elutriation in a primary settler tank. The model has been tested with pilot plant experimental data with very good results. It has been able to simulate the VFA production in the settler and their elutriation with the influent wastewater for all the studied experiments. The developed model is easily applicable to secondary settlers and thickeners, also taking into account biological activity inside them.

Biodegradation, Environmental↗

PubMed2002

Fermentation of municipal primary sludge: effect of SRT and solids concentration on volatile fatty acid production.

Laboratory bench-scale experiments were conducted to investigate the performance of primary sludge fermentation for volatile fatty acids production. Primary sludges from two major wastewater treatment plants located in Valencia (Pinedo and Carraixet) were used. Experiments were performed at solids retention times between 4 and 10 days, and total volatile solids concentrations between 0.6% and 2.8%. Operation at two temperatures (20 degrees C and 30 degrees C) was also checked. Results indicated the importance of feed sludge characteristics on volatile fatty acids yields, being approximately double for the Carraixet wastewater treatment plant sludge than for the Pinedo plant. In both cases, higher volatile fatty acids yields were observed at higher total volatile solids concentrations. Solids retention times above 6 days scarcely improve volatile fatty acids yields, while experiments conducted at 4 days of solids retention times show an important decrease in volatile fatty acids yields. On raising temperature an increase in volatile fatty acids yields was observed, mainly due to an improvement in the hydrolysis of particulate organic matter.

Bioreactors↗

PubMed2002

Calibration and validation of activated sludge model No.2d for Spanish municipal wastewater.

Activated Sludge Model No. 2d (ASM2d) was validated with data obtained from pilot scale plant treating municipal wastewater from the city of Valencia (Spain). First of all, ASM2d was calibrated using experimental data from anaerobic, anoxic and aerobic batches. A set of kinetic and stoichiometric parameters resulted from these assays. Differences between the values obtained and default values proposed in ASM2d can be explained by the presence of glycogen accumulating organisms (GAOs). The calibrated model was then used to simulate results from a pilot plant. Simulation using the set of parameters obtained accurately reproduces experimental results. This paper also presents a detailed procedure to estimate kinetic and stoichiometric parameters for heterotrophic, autotrophic and polyphosphate accumulating bacteria.

Bacteria, Aerobic↗

PubMed2002

A supervisory control system for optimising nitrogen removal and aeration energy consumption in wastewater treatment plants.

A fuzzy logic supervisory control system for optimising nitrogen removal and aeration energy consumption has been developed. This control system allows optimising and controlling the dissolved oxygen (DO) concentration in the aerobic reactors, the blowers discharge pressure and the effluent ammonia and nitrate concentrations. DO is controlled by adjusting control valve opening and blower discharge pressure is controlled by modifying rotational speed of the blowers. Optimum nitrification/denitrification is achieved by modifying the DO set point in the last aerobic reactor and the internal recirculation. This system has been tested by simulation in a Bardenpho process using the Activated Sludge Model No2. A significant improvement in stability on the activated sludge process is achieved. Moreover, significant energy saving has been achieved with this control strategy.

Aerobiosis↗

PubMed2001

Evaluation of Activated Sludge Model No. 2 at high phosphorus concentrations.

This paper presents laboratory scale experimentation carried out to study enhanced biological phosphorus removal at high phosphorus concentrations in a sequencing batch reactor. Four series of data obtained in a sequencing batch reactor are examined in light of the Activated Sludge Model No. 2. This model was calibrated using data from the first and second series working at low phosphorus concentrations. The Activated Sludge Model No. 2 successfully characterised the enhanced biological phosphorus removal performance of the sequencing batch reactor at low phosphorus concentrations. The calibrated model was then used to adjust experimental results of the other series working at high phosphorus concentration. Differences between model predictions and experimental data could be explained by redissolution in the anaerobic phase and precipitation in the aerobic phase of calcium phosphates not taken into account by the model. This hypothesis can be justified by the conditions of pH and phosphorus concentration prevailing in the experiments and it was confirmed by the results of another experiment in which precipitated phosphorus profile was measured during the cycle.

Bioreactors↗

PubMed2001

A modification to the Activated Sludge Model No. 2 based on the competition between phosphorus-accumulating organisms and glycogen-accumulating organisms.

A modification to the ASM2 is proposed which permits representation of the competition between phosphorus accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs) in a nutrient removal activated sludge system. Some important aspects, which are not considered in ASM2, are discussed. The proposed modification includes denitrification by PAOs, PAO glycogen storage capability and GAO metabolism model. It is shown that the proposed modification is capable of describing pilot plant data using a single set of stoichiometric and kinetic parameters over three different sludge ages (16, 14 and 12 days). The modified ASM2 may be applicable to a wide range of situations where PAOs and GAOs can compete. This modification may well provide a better understanding about GAO behaviour.

Aerobiosis↗