Biomedical subjects

T Hvitved-Jacobsen

Publications and source records attributed to T Hvitved-Jacobsen.

28 records · Page 2Linked to original sources

PubMed2002

Anoxic transformations of wastewater organic matter in sewers--process kinetics, model concept and wastewater treatment potential.

The sewer is an integral part of the urban wastewater system: the sewer, the wastewater treatment plant and the local receiving waters. The sewer is a reactor for microbial changes of the wastewater during transport, affecting the quality of the wastewater and thereby the successive treatment processes or receiving water impacts during combined sewer overflows. This paper presents the results of studies on anoxic processes, namely denitrification, in the bulk water phase of wastewater as it occurs in sewers. Experiments conducted on 12 different wastewater samples have shown that the denitrification process in the bulk wastewater can be simplified by the reduction of nitrate to nitrogen with significant accumulation of nitrite in the water phase. Utilization of nitrate was observed not to be limited by nitrate for concentrations above 5 gNO3-N/m3. The denitrification rates, under conditions of excess substrate and electron acceptor, were found to be in the range of 0.8-2.0 g NO3-N/(m3h). A discussion on the interaction of the sewer processes and the effects on a downstream located wastewater treatment plant (WWTP) is provided.

Biodegradation, Environmental↗

PubMed2002

Anaerobic transformations of wastewater organic matter and sulfide production--investigations in a pilot plant pressure sewer.

Anaerobic transformations of wastewater organic matter and sulfide production rate were studied using a pilot plant pressure sewer (inner diameter: 102 mm, length: 47 m). Furthermore, a process model description including carbon and sulfur cycle was presented. Wastewater characterization based on oxygen utilization rate (OUR) measurement and VFA analysis was employed. Under anaerobic conditions, a net production of readily biodegradable substrate was observed, which fact is important for biological removal of nitrogen and phosphorus at subsequent wastewater treatment plants. Model parameters were determined on the basis of experimental findings. The model simulation of transformations of organic matter in sewers can be used as input to the model simulation and evaluation of the processes in wastewater treatment plants. The model is also useful to evaluate the problems in both sewers themselves and treatment plants caused by hydrogen sulfide.

Bacteria, Anaerobic↗

PubMed2002

Integrated design of sewers and wastewater treatment plants.

Sewer system design must be integrated with wastewater treatment plant design when moving towards a more sustainable urban wastewater management. This integration allows an optimization of the design of both systems to achieve a better and more cost-effective wastewater management. Hitherto integrated process design has not been an option because the tools to predict in-sewer wastewater transformations have been inadequate. In this study the WATS model--being a new and validated tool for in-sewer microbial process simulations--is presented and its application for integrated sewer and treatment plant design is exemplified. A case study on a Malaysian catchment illustrates this integration. The effects of centralization of wastewater treatment and the subsequently longer transport distances are addressed. The layout of the intercepting sewer is optimized to meet the requirements of different treatment scenarios.

Facility Design and Construction↗

PubMed2002

Half saturation constants for nitrate and nitrite by in-sewer anoxic transformations of wastewater organic matter.

A significant breakthrough and progress have been made in the study of the kinetics of microbial transformation in sewers under aerobic and under changing aerobic/anaerobic conditions. Fundamental knowledge on anoxic kinetics of wastewater is still lacking, so it is not now possible to apply an integrated approach to municipal wastewater treatment incorporating sewer networks as a bio-chemical reactor. This paper presents the results of studies on determining half saturation constants for nitrate, KNO3, and nitrite, KNO2, in raw wastewater. The average values of KNO3 and KNO2, determined from experiments conducted on 7 different wastewater samples were found to be 0.76 gNO3-N/m3 and 0.33 gNO2-N/m3 respectively.

Biotransformation↗

PubMed2001

Comparison of methods for determination of microbial biomass in wastewater.

Microbial biomass in wastewater was determined by methods used in environmental microbiology and by a method used in wastewater engineering based on a conceptual model simulating fundamental microbial processes in wastewater from measured oxygen uptake rates. The methods originating from environmental microbiology are based on staining and counting of cells for the determination of total cell biomass (acridine orange and DAPI), physiological state of cells (LIVE/DEAD BacLight) and activity of cells (reduction of the redox dye CTC and microautoradiography). Depending on the staining method applied, cell biomasses yielded 15-86% of the biomass defined by the model, and good correlations between cell biomass and model biomass were found. Cell biomass, oxygen uptake and acetate uptake were measured in wastewater, where acetate was added. Substrate uptake rates were found not to be proportional to the increases in cell biomass, suggesting that only a small fraction of the cell biomass was responsible for the main part of the substrate uptake. Despite the differences found between cell biomass and model biomass, it was recommended to use the conceptual model as an engineering tool for simulation of microbial processes and wastewater quality changes. However, there should be a clear distinction between the terms 'model biomass', 'cell biomass' and different activity measurements of cells.

Bacteria↗

PubMed2001

Characterisation of organic matter from anaerobic digestion of organic waste by aerobic microbial activity.

The aim of this study was to examine whether the characterisation of organic matter on the basis of an oxygen uptake rate (OUR) could be applied to organic waste from an anaerobic waste treatment process. Three anaerobic digestion experiments were carried out in a bioreactor. Volatile fatty acids (VFA) and dissolved organic carbon (DOC) were monitored. OUR-experiments were carried out with diluted samples from the process. The graphs of the OUR-experiments showed a clear lag-phase, which was due to the slow adaptation of aerobic microorganisms. Model simulations of the OUR versus time curve showed sufficient agreement, if based on one fraction of readily biodegradable and two fractions of less easily biodegradable organic matter. The shape of the simulated graphs was affected considerably by the value of the maintenance energy requirement rate qm and could be improved by reducing the standard value qm = 1 d(-1) to qm = 0.1 d(-1). Only little agreement was achieved when comparing the results of the OUR-experiments with the VFA- and DOC-concentrations. Experiments with additional trace elements and vitamins led to an increase in the OUR and proved that the oxygen consumption was not exclusively determined by the availability of organic matter.

Aerobiosis↗

PubMed2001

Sulfide production and wastewater quality--investigations in a pilot plant pressure sewer.

The relationship linking sulfide production rate and wastewater quality in terms of its biodegradability was studied using a pilot plant pressure sewer (inner diameter: 102 mm, length: 47 m). Furthermore, anaerobic transformations of wastewater organic matter were investigated. Wastewater characterization based on oxygen utilization rate (OUR) measurements and VFA analyses was employed. As wastewater quality parameters essential for the sulfide production, COD components and dissolved carbohydrate were focused on. Readily biodegradable substrate and fermentable, readily biodegradable substrate were better parameters than traditional dissolved COD for the prediction of sulfide production rates in a pressure sewer. From the results obtained, it was possible to integrate the sulfide production process with the transformation processes of wastewater organic matter in pressure sewers.

Biodegradation, Environmental↗

PubMed1999

Highway runoff and potential for removal of heavy metals in an infiltration pond in Portugal

Highway runoff from IP 4, a mountain road in the north-east of Portugal, has been monitored using a system integrating a raingauge, a flowmeter and an automatic water sampler. Average daily traffic (ADT) is 6000 and the study catchment has 5970 m2 of total area and 2500 m2 of road pavement. A single stormwater outlet discharges into an infiltration pond with overflow to a creek. Sampling was carried out before the runoff water entered the pond. Among the parameters analysed in the runoff water, the heavy metals cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and zinc (Zn) were emphasised because of their toxicity. Concentrations of Cd and Cr were usually lower than the detection limit (1 microgram/l). Copper levels found were between 1 and 54 micrograms/l; lead from 1 to 200 micrograms/l and zinc from 50 to 1460 micrograms/l. A first flush effect was observed, meaning that the first 50% of the runoff volume for each event typically transported between 61 and 69% of the total suspended solids, Zn, Cu and Pb loads. Runoff water is totally infiltrated into the pond and heavy metals are being sorbed to the soil. Soils used in infiltration ponds should have specific characteristics in order to perform effectively and ensure groundwater protection. Not only well-known soil texture and composition characteristics are relevant: the soil sorption capacity--the extension and reversibility of the processes--is of main importance in this kind of highway runoff treatment. Experiments concerning the sorption of Zn, Cu and Pb to soils, followed by desorption at pH values of 2, 4 and 6 were conducted in the laboratory. These experiments were performed with the soil existing at the highway IP 4 infiltration pond and with two other common types of Portuguese soils. The three types of soil showed different behaviours, which must be related to their characteristics; the soil pH seemed to play a significant role in controlling the Zn, Cu and Pb sorption processes. As expected, as lowering of the pH value increased the desorption rate. The infiltration pond soil is the one with the lowest sorption capacity, however, it showed a relatively high sorption strength which means that it is considered reliable, concerning highway runoff treatment and groundwater protection.

Journal Article↗

PubMed1997

Acetate removal in sewer biofilms under aerobic conditions.

Removal of acetate has been investigated in sewer biofilms by continuous-flow biofilm reactor studies simulating the conditions in a gravity sewer. Non-steady-state conditions are prevailing in sewers, due to periodic variations in substrate concentrations. In order to simulate two extreme situations in a gravity sewer, biofilms defined as high-loaded and low-loaded, respectively, were grown by continuously feeding wastewater to the reactors with and without supplementary addition of acetate. During short-term experiments with high acetate concentrations (1-2 h), surface removal rates of acetate and dissolved oxygen (DO) and observed yield coefficients were determined, as well as the influence of DO concentration on acetate removal rates. The low-loaded biofilms showed very high acetate removal rates in short-term experiments at high acetate concentrations. The DO uptake rates were low, resulting in an average observed yield coefficient of 0.79 g biomass produced per gram acetate (as chemical oxygen demand, COD) consumed. This indicated a luxury uptake by the cells probably for storage inside the cells or for production of extracellular polymeric substances. The high-loaded biofilms showed lower acetate removal rates during the short-term experiments, with an average yield coefficient of 0.49 g biomass produced per gram acetate (as COD) consumed. The level of the acetate removal rates seemed to be related to the structure of the biofilm. The highest acetate removal rates were found for the low-loaded biofilm, where the biofilm was very hairy with 'streamers" with a length of 8-9 mm. At low acetate removal rates (high-loaded biofilm), the "streamer" lengths were only 3-5 mm. The surface removal rates for acetate and DO seemed to follow 1/2 order approximations to biofilm kinetics. For a DO of 0.8 and 6.0 g/m3, the limiting acetate concentrations were about 34 and 20 g-COD/m3, respectively. Under real gravity sewer conditions, the typical concentration ranges for acetate and DO are at levels where any of them may be rate-limiting for microbial acetate removal.

Acetates↗

PubMed1990

Heavy metal accumulation and transport through detention ponds receiving highway runoff.

Sediment accumulations and associated heavy metal concentrations into retention/detention ponds receiving highway runoff from several ponds and metal concentrations in various sediment layers were analyzed to determine the extent of vertical migration. Extraction of heavy metals had been evaluated using various solutions including the United States Environmental Protection Agency Toxicity Characteristics Leaching Procedures (TCLP). Also, sediments were incubated under various conditions of redox potential and pH to investigate the effects of changes in sediment conditions on the stability of metal-sediment associations.

Florida↗