A.M. Breure

Microbial degradation of polycyclic aromatic hydrocarbons : effect of substrate availability on bacterial growth kinetics

SummaryIt is demonstrated that bacterial growth on crystalline or adsorbed polycyclic aromatic hydrocarbons can result in a linear increase in biomass concentration. A simple mathematical approach is presented, showing that under these circumstances mass transfer from the solid phase to the liquid phase is rate-limiting for growth.

Influence of phase separation on the anaerobic digestion of glucose—I maximum COD-turnover rate during continuous operation

Abstract A mineral medium containing 1% of glucose as the main carbon source was subjected to one-phase and to two-phase anaerobic digestion processes under comparable conditions. The one-phase system consisted of an anaerobic up-flow reactor containing both acidogenic as well as methanogenic populations allowing a complete conversion of the carbon source into gaseous end products and biomass. The two-phase system consisted of an acid reactor and a methane reactor connected in series allowing sequential acidogenesis and methanogenesis of the glucose. Performance of the one-phase system and of the methane reactor of the two-phase system is presented by carbon mass balances. By gradually increasing the feed supply to both systems, maximum turnover of COD was determined. Maximum specific sludge loadings of the methanogenic phase of the two-phase system was over 3 times higher than that of the one-phase system. In a second experiment both systems were subjected to overloading, resulting in the accumulation of volatile fatty acids (VFA). In the one-phase system propionate and acetate were formed in considerable amounts. Although acetate disappeared rapidly after cessation of the feed supply, no turnover of propionate was observed within one week. On overloading the methane reactor of the two-phase system accumulation of several fatty acids within the reactor was observed. Rapid conversion of all fatty acids took place immediately after interruption of feed supply. The eco-physiological significance of phase separation is discussed briefly.

Chapter 1 Definitions, strategies and principles for bioindication/biomonitoring of the environment

Abstract In the context of environmental monitoring studies bioindicators reflect organisms (or parts of organisms or communities of organisms) that contain information on quality of the environment (or a part of the environment). Biomonitors, on the other hand, are organisms (or parts of organisms or communities of organisms) that contain informations on the quantitative aspects of quality of the environment. When data and information obtained by bioindication are moved up to the level of knowledge the subjectivity of interpretation increases with the complexity and dynamics of a system (“staircase of knowing”). In this article clearcut definitions are attempted for most terms used in environmental monitoring studies. From there a comparison of instrumental measurements with the use of bioindicators/biomonitors with respect to harmonisation and quality control will be drawn. Precision, accuracy, calibration and harmonisation in between national standards and international routines seem to be the leading goals in quality studies of international working groups dealing with biomonitoring throughout the world. Common strategies and concepts will fill the gap in between single source results and integrated approaches related either for human health aspects or environmental protection purposes, f.e. via biodiversity monitoring. Here we report on well established monitoring programmes like Environmental Specimen Banking (ESB) or newly developed strategies as the Multi-Markered Bioindication Concept (MMBC) with its functional and integrated windows of prophylactic health care.

INFLUENCE OF PHASE SEPARATION ON THE ANAEROBIC DIGESTION OF GLUCOSE-~-II

A mineral medium, containing 1% (w/v) glucose as the main carbon source, was subjected to one-phase and to two-phase anaerobic digestion processes under comparable conditions. The one-phase system consisted of an anaerobic up-flow reactor containing both acidogenic as well as methanogenic populations. The two-phase system consisted of an acid reactor and a methane reactor connected in series allowing sequential acidogenesis and methanogenesis of the glucose. After maximum turnover rates of glucose had been attained in both systems, by gradually increasing feed supply rate, both systems were switched to the batch mode and subjected to shock loadings with glucose or fatty acids. Maximum specific turnover rates of fatty acids in the one-phase process averaged 0.39 g COD · g biomass−1 d−1 and 2.23 g g−1 d−1 for the methane reactor of the two-phase system. Charging the one-phase system with doses of glucose resulted mainly in an accumulation of propionate which was degraded relatively slowly. It was concluded that interspecies hydrogen transfer may become rate limiting at high loading rates, stimulating formation of propionate. Therefore a two-phase system, as compared with a one-phase digestion process for easily hydrolyzable carbohydrates, was characterized as being essentially the more stable.

Glucose fermentation byClostridium butyricum grown under a self generated gas atmosphere in chemostat culture

SummaryClostridium butyricum was grown anae-robically under glucose-limited conditions in che-mostat cultures under self generated gas atmo-sphere. It is shown that the quantitative composi-tion of the fermentation products is dependent on the pH value, the growth rate, the concentration of glucose in the growth medium and the compo-sition of the gas atmosphere developed in the reactor. The ratio qacetate/qbutyrate increases from 0.06 to 0.66 in parallel with an increase in growth rate from 0.02 h−1 to 0.29 h−1 (at pH = 6.0). De-creasing the partial pressure of H2 results in an in-crease of the qacetate/qbutyrate ratio. The partial pressure of CO2 in the reactor does not influence the fermentation products whatsoever. Increasing pH values (>6.8) and concentrations of glucose in the growth medium also result in increasing qacetate/qbutyrate ratios. The maximal YATP is con-stant from pH 4.8–6.0. The functioning of NADH2-ferredoxin oxi-doreductase is discussed.

Hydrolysis and acidogenic fermentation of a protein, gelatin, in an anaerobic continuous culture

SummaryModel studies of anaerobic protein digestion were performed using gelatin dissolved in a mineral medium, which was fed to a mixed population of bacteria in a carbon-substrate limited chemostat culture. The dilution rate and culture pH value were varied progressively in order to determine the optimal conditions for hydrolysis and acidification (i.e., fatty acids formation). The optimum pH value appeared to be in the neutral region (pH>6.3), and the maximal dilution rate allowing steady state growth was 0.23 h-1. At this dilution rate and at pH 7 hydrolysis of gelatin was 78% complete, and 79% of the protein hydrolysed was fermented to identifiable products. At submaximal dilution rates both these values were higher. The main fermentation products were acetate, propionate, and valerate, and minor amounts of other volatile fatty acids. The product composition was relatively independent of the dilution rate, but varied substantially with the pH value.

Bioregeneration of powdered activated carbon (PAC) loaded with aromatic compounds

Abstract Bioregeneration of powdered activated carbon (PAC) loaded with aromatic compounds was quantitatively determined using carbon dioxide production as a measure of substrate consumption. Two types of powdered activated carbon (one chemically activated, wood-based carbon, CA1, and one thermally activated, peat-based carbon, SA4) and two aromatic compounds (o-cresol and 3-chlorobenzoic acid) in single solute batch systems were used. Interaction of EDTA, present as chelating agent in all experiments with o-cresol as substrate, and SA4 resulted in abiotic CO2 production (in absence of microorganisms). The extent of bioregeneration varied considerably, from 15 to 85% of total PAC loading, depending on type of PAC used and compound involved and, in one case, on the time of contact between PAC and the compound. The results revealed that the data corresponded with a mechanism of bioregeneration where desorption precedes biodegradation. Microorganisms reduced the dissolved compound concentration, forcing desorption and subsequent biodegradation, but were unable to influence the desorbability of the PAC-sorbed compounds. The practical applicability of the results is discussed.

REVERSIBILITY OF ADSORPTION OF AROMATIC COMPOUNDS ONTO POWDERED ACTIVATED CARBON (PAC)

Desorption of sorbed compounds is an important process in the powdered activated carbon-activated sludge (PAC-AS) wastewater treatment system, where sorption and biodegradation interact. To assess the extent of desorption to be expected in the PAC-AS system, reversibility of adsorption was investigated using isotherm studies and a leaching technique under the conditions prevalent in the PAC-AS system. Two aromatic compounds, o-cresol and 3-chlorobenzoic acid (3-CB), and two types of powdered activated carbon (PAC) were used to study desorption. High degrees of irreversible adsorption were observed with both desorption techniques, depending on the type of PAC and the compound. The thermally activated, peat-based PAC (SA4) showed a high degree of irreversible adsorption compared to the chemically activated, wood-derived PAC (CA1). The phenolic compound, o-cresol, could be desorbed to a lesser extent than 3-CB from both types of PAC. Contact time between the PAC and the compound was found to affect the desorption of o-cresol adversely. Oxygen availability enhanced the adsorptive capacity of SA4 for o-cresol. Sorption of 3-CB proved unaffected by either contact time or oxygen. Oxidative polymerization as a probable mechanism for the irreversible adsorption observed is also discussed. Desorption kinetics from SA4 showed a first phase of rapid desorption followed by a second phase of slow desorption. CA1 displayed the first rapid desorption phase only.

Effect of micro-organisms on the bioavailability and biodegradation of crystalline naphthalene

Bacterial growth on crystalline naphthalene was measured and found to be related to the dissolution rate of the substrate. No evidence for enhancement of substrate availability due to bacterial influence could be detected. Using a model based on dissolution kinetics for substrate availability and Monod kinetics for bacterial growth it was possible to simulate bacterial growth on naphthalene. This model is widely applicable for growth of micro-organisms on poorly water-soluble substrates and can easily be adapted to a more complex system such as microbial growth on substrates adsorbed to matrices.

Determination of Field Effects of Contaminants—Significance of Pollution-Induced Community Tolerance

The concept of pollution-induced community tolerance (PICT) consists of the phenomenon that communities in an ecosystem exhibit increased tolerance as a result of exposure to contaminants. Although a range of ‘classic’ ecological principles explains the processes that increase tolerance of a community, the value of PICT for ecological risk assessment was recognized only recently (Blanck et al. 1988). The following issues are recognized: First, regarding the question on the role of suspect compounds causing ecological effects, the PICT approach covers the issue of causality better than ‘classical’ ecological community response parameters like species densities or species diversity indices. This relates to the fact that the level of PICT is assumed to be relatively constant (compared to density and diversity), whereas the suspect compound causing the observed effect can be deduced with relative clear inference from artificial exposure experiments. Second, PICT directly addresses a level of biological organization (the community), the level of concern for many ecological risk assessment methods. Other methods for risk assessment, like toxicity testing or bioassays, focus on individual or population-level effects, and need extrapolation of the results to the field. Such extrapolation step may pose problems regarding validity of the outcome of risk assessment. The occurrence of PICT is, however, not (yet) a community endpoint that is sufficiently underpinned to trigger risk mitigation activities. This paper especially focuses on the possibility to improve risk assessment approaches by incorporation of PICT assessments, especially focusing on the issue of causality and on the ecological meaning of PICT. Despite the advantages over ‘classical’ parameters, literature analysis suggests that the PICT approach may be strengthened by determining to which degree the PICT approach relates to ecological changes, like shifts in community structure, functioning, and stability. The aim of this paper is to summarize some literature, putting the emphasis on terrestrial studies, to get insights whether PICT is a sensitive and powerful tool to quantify ecological effects in field conditions, to link them to toxicant stress, and thus to determine whether PICT may be taken into consideration in risk assessment.