Biomedical subjects

M C M Van Loosdrecht

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

5 recordsLinked to original sources

PubMed2006

Waste characterization for implementation in ADM1.

Wastewater characterization as required for implementation in ADM1 is based on the identification of the numerous concentrations of the specific compounds defined in ADM1. However, identification of the individual substrate concentrations requires specific analytical techniques and in most cases only general measurements like COD, TOC, and organic nitrogen are available. This paper describes a simple method for calculation of the lumped elemental composition of the organic substrates in the wastewater from a limited number of widely available analyses. Using the elemental composition of the lumped substrate and the elemental composition of the substrates defined in the model, the influent composition as required for input in ADM1 can be calculated. Furthermore, proper waste characterization allows for an initial analysis of the biogas flow rate and composition as well as the reactor pH that can be achieved upon organic substrate degradation, as will be demonstrated. It is hoped that the methods described in this paper will stimulate and simplify future application of ADM1.

Anaerobiosis↗

PubMed2004

Production of polyhydroxyalkanoates by mixed culture: recent trends and biotechnological importance.

Polyhydroxyalkanoates (PHAs) are the polymers of hydroxyalkanoates that accumulate as carbon/energy or reducing-power storage material in various microorganisms. PHAs have been attracting considerable attention as biodegradable substitutes for conventional polymers. To reduce their production cost, a great deal of effort has been devoted to developing better bacterial strains and more efficient fermentation/recovery processes. The use of mixed cultures and cheap substrates can reduce the production cost of PHA. Accumulation of PHA by mixed cultures occurs under transient conditions mainly caused by intermittent feeding and variation in the electron donor/acceptor presence. The maximum capacity for PHA storage and the PHA production rate are dependent on the substrate and the operating conditions used. This work reviews the development of PHA research. Aspects discussed include metabolism and various mechanisms for PHA production by mixed cultures; kinetics of PHA accumulation and conversion; effects of carbon source and temperature on PHA production using mixed cultures; PHA production process design; and characteristics of PHA produced by mixed cultures.

Bacteria↗

PubMed2003

Production of polyhydroxyalkanoates by mixed microbial cultures.

Polyhydroxyalkanoates (PHAs) are biodegradable bioplastics formed from renewable resources, like sugars, with similar characteristics of polypropylene. These bioplastics are industrially produced by pure cultures using expensive pure substrates. These factors lead to a much higher selling price of PHAs compared to petroleum-based plastics, like polypropylene. The use of mixed cultures and cheap substrates (waste materials) can reduce costs of PHA production by more than 50%. Storage of PHAs by mixed populations occurs under transient conditions mainly caused by discontinuous feeding and variation in the electron donor/acceptor presence. In the last years the mechanisms of storage, metabolism and kinetics of mixed cultures have been studied. The maximum capacity of PHA storage and production rate is dependent on the substrate and on the operating conditions used. In this paper an overview and discussion of various mechanisms and processes for PHA production by mixed cultures is presented.

Journal Article↗

PubMed2003

Bio-augmentation by nitrification with return sludge.

Bio-augmentation can be used to obtain nitrification in activated sludge processes that operate at sub-optimal solid retention times. In this study, we evaluated the potential of augmenting the endogenous nitrifying bacteria, by implementing a nitrification reactor in the sludge return line. This reactor can be fed with an internal N-rich flow (e.g. effluent from the sludge treatment) or with an external ammonium source. A mathematical model based on ASM1 was developed and used to evaluate the potential of this technique. The bio-augmentation studied here aimed to enhance the nitrification process of highly loaded activated sludge systems. A calibrated simulation model of a high loaded wastewater treatment plant in The Netherlands was used for this study. A side stream process (the named BABE process) was included in the simulation. This process was fed with the ammonia-rich water generated by sludge digestion and subsequent thickening by centrifugation (the so-called rejectwater). An external source (artificial) of ammonium was also considered to evaluate the differences between the two origins of ammonium. The results showed that with the augmentation process, high loaded activated sludge systems can achieve nitrification even at low winter temperatures. The best effect is obtained for systems operating at approximately 50% of the minimal SRT without augmentation. The use of an internal ammonia source is more effective than an external source. The results of this study give a quantitative basis for the design of process internal bio-augmentation processes and the effect on the N-removal capacity of the treatment plant.

Bioreactors↗

PubMed2002

Poly-beta-hydroxybutyrate metabolism in dynamically fed mixed microbial cultures.

The kinetics of production and degradation of poly-beta-hydroxybutyrate (PHB) by a mixed activated sludge culture growing on acetate was studied in a sequencing batch reactor (SBR). Occasionally a very high amount of acetate was added to the steady state system in order to obtain high PHB concentrations in the cells (fPHB). This made it possible to follow PHB production and degradation over a wide range of fPHB-data (between 0 and 0.8 Cmol/Cmol). The results were compared with data available in literature and with equations derived by metabolic modeling. This led to some remarkable observations. For the feast period, the ratio q(feast)PHB/-q(feast)Ac (specific PHB production rate over specific acetate uptake rate) was used to indicate which fraction of the substrate is stored. Experimentally and theoretically it was shown that this ratio has a constant value for dynamically fed systems operated at a sludge retention time (SRT) > 2d. This value is 0.6 Cmol/Cmol under aerobic conditions and 0.4-0.5 Cmol/Cmol under anoxic conditions, irrespective of the specific growth rate of the biomass and the specific acetate uptake rate in the feast period. Degradation of internal stored PHB could be described with a first order degradation rate with respect to the PHB content of the cells. Degradation of PHB appeared to be independent of the type of electron acceptor present in the system and independent of the SRT of the system. The kinetic descriptions can be used to predict PHB production and consumption in general in dynamic fed wastewater treatment systems, and they provide some trends for modeling purposes.

Acetates↗