Biomedical subjects

L S Serafim

Publications and source records attributed to L S Serafim.

6 recordsLinked to original sources

PubMed2006

Microbial community analysis with a high PHA storage capacity.

Activated sludge was submitted to aerobic dynamic substrate feeding for the production of biodegradable plastics. Two sequencing batch reactors were operated with acetate or propionate as sole carbon substrates. With acetate a homopolymer of polyhydroxybutyrate (PHB) was obtained and with propionate a copolymer of hydroxybutyrate and hydroxyvalerate P(HB/HV) was produced. Three main morphotypes were identified in both sludges: two belong to the Alphaproteobacteria class and the third to the Betaproteobacteria class. Bacilli belonging to Betaproteobacteria were shown by FISH analysis, applied in combination with Nile Blue post-staining, to be the main responsible for PHAs storage. The latter were affiliated to Azoarcus genus within Betaproteobacteria.

Alkanes↗

PubMed2004

Polyhydroxyalkanoates production by activated sludge in a SBR using acetate and propionate as carbon sources.

In this work, sludge was submitted to aerobic dynamic substrate feeding. Two sequencing batch reactors were operated, with acetate or propionate as carbon substrates. When acetate was used the system only produced a homopolymer of polyhydroxybutyrate (PHB). In order to maximize the PHB production, tests with different concentrations of acetate and ammonia were preformed. The best results (67.2% of PHB by cell dry weight) were obtained for 0.7 Nmmol/l of ammonia and 180 Cmmol/l of acetate. The PHB cell content was further improved by pulse addition of substrate, three times 60 Cmmol/l of acetate, reaching a value of 78.5%. Propionate can be used as a precursor for hydroxyvalerate. In conjunction with other substrates, it allows for the formation of copolymers, which present better processing properties on commercial applications. Tests with different concentrations of propionate and ammonia were performed. Under the operating conditions used, the maximum PHA accumulated inside cells was 34.8%, with 30 Cmmol/l of propionate and no ammonia.

Acetates↗

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

Production of polyhydroxyalkanoates by a mixed culture in a sequencing batch reactor: the use of propionate as carbon source.

In this work, sludge adapted to anaerobic/aerobic conditions, AN/AE, showing a high capacity of P accumulation, was submitted to aerobic dynamic substrate feeding (ADF). The fermenter was operated as a Sequencing Batch Reactor, with propionate as carbon substrate. Propionate is an important waste product from several industrial processes that can be valued, using it as a precursor for hydroxyvalerate in PHA production. Under the operational conditions used, apart from 3-hydroxyvalerate as its major component, 3-hydroxy-2-methylvalerate, 2-hydroxyisovalerate and 4-oxovalerate were also produced. A second reactor operated under the same conditions was adapted for the use of acetate as carbon substrate. The global metabolism of the organisms involved on PHA production, utilizing acetate or propionate, was studied using in vivo 13C Nuclear Magnetic Resonance (NMR).

Alkanes↗

PubMed2002

Change in metabolism of PHA accumulation by activated sludge modifying operating conditions.

In the present work, sludge from a stable and efficient phosphorus removal process was used to evaluate the change in the metabolism when the reactor operation was modified from anaerobic/aerobic to aerobic dynamic substrate feeding. The change in operational conditions allowed the population to modify the metabolism of phosphorus and polyhydroxyalkanoates (PHA) accumulation. Under aerobic dynamic feeding, phosphorus accumulation was almost hindered while the amount of PHA accumulation increased significantly. After ten days of operation under dynamic substrate feeding, the reactor operation turned back to anaerobic/aerobic cycles and the metabolism of phosphorus was progressively recovered.

Bacteria, Aerobic↗

PubMed2002

Effect of pH control on EBPR stability and efficiency.

Biological phosphorus removal from water surfaces is an important process for the control of eutrophication. Even though much attention has been devoted to understanding the metabolism of bacteria and the effect of operational parameters on the efficiency of the phosphorus removal process, certain aspects are still unclear. The aim of this work was to evaluate the influence of pH control on the stability and efficiency of two sequenced batch reactors (SBR): one operated with pH control (pH 7.0) and the other without pH control (pH raised from around 7.8 to 8.5). The reactor operated without pH control showed higher efficiency on phosphorus removal and stability than the reactor with pH control. Based on the kinetics of both reactors it could be inferred that a different population developed in both systems.

Bacteria↗