Influence of environmental conditions on accumulated polyhydroxybutyrate in municipal activated sludge.

Poly(3-hydroxybutyrate) (PHB) was accumulated in full-scale municipal waste activated sludge at pilot scale. After accumulation, the fate of the PHB-rich biomass was evaluated over two weeks as a function of initial pH (5.5, 7.0 and 10), and incubation temperature (25, 37 and 55°C), with or without aeration. PHB became consumed under aerobic conditions as expected with first order rate constants in the range of 0.19 to 0.55 d-1. Under anaerobic conditions, up to 63 percent of the PHB became consumed within the first day (initial pH 7, 55°C). Subsequently, with continued anaerobic conditions, the polymer content remained stable in the biomass. Degradation rates were lower for acidic anaerobic incubation conditions at a lower temperature (25°C). Polymer thermal properties were measured in the dried PHB-rich biomass and for the polymer recovered by solvent extraction using dimethyl carbonate. PHB quality changes in dried biomass, indicated by differences in polymer melt enthalpy, correlated to differences in the extent of PHB extractability. Differences in the expressed PHB-in-biomass melt enthalpy that correlated to the polymer extractability suggested that yields of polymer recovery by extraction can be influenced by the state or quality of the polymer generated during downstream processing. Different post-accumulation process biomass management environments were found to influence the polymer quality and can also influence the extraction of non-polymer biomass. An acidic post-accumulation environment resulted in higher melt enthalpies in the biomass and, consequently, higher extraction efficiencies. Overall, acidic environmental conditions were found to be favourable for preserving both quantity and quality after PHB accumulation in activated sludge.

Inhibition by fatty acids during fermentation of pre-treated waste activated sludge.

Fermentation of waste activated sludge produces volatile fatty acids (VFAs), which can be used as the carbon sources for numerous biological processes. However, product inhibition can limit extent of fermentation to VFAs. In this study, product inhibition during fermentation of waste activated sludge pre-treated by a thermal hydrolysis process (THP-WAS) was investigated. Product inhibition was confirmed as spiking reactors with high levels of a mix of VFAs prevented fermentation taking place. Various inhibition models were trialled and it was found that a threshold model (based on thermodynamics) provided the best fit between model and data. This is the first time that threshold type inhibition has been shown for a mixed substrate, mixed population system. Batch fermentations carried out with THP-WAS of different dilutions were used to evaluate the impact of different organic loadings. The threshold VFA concentration for the systems studied was determined to be 17±1gCOD(VFA)L(-1). Inhibition was shown to be due to the presence of a combination of VFAs containing 2-6 carbon atoms each. When evaluated individually, by spiking individual VFAs, all VFAs except for acetate had the same impact at this threshold; acetate being approximately 50% as inhibitory as the other organic acids (COD basis). Based on this, a weighted model could be proposed to better represent the data. Strategies to improve overall yield could be increased production of acetate, or dilution to below the inhibitory level.

An evaluation of full-scale activated sludge dynamics using microbial fatty acid analysis.

Patterns of microbial fatty acids (MFAs) from activated sludge samples were analyzed over one year's operation at the Hamilton Woodward municipal wastewater treatment plant in Canada. The objective was to examine community structure dynamics and to consider the potential for interrelationships between the population dynamics and treatment performance. With the exception of a higher than normal solids discharge on one day, the treatment plant operations were otherwise stable during the year. As such, wastewater temperature appeared to be the dominant influence on the observed dynamics of the MFA community structure. MFA monitoring and analysis was demonstrated as a practical diagnostic tool in community structure trend monitoring. While the findings did suggest potential for full-scale treatment process monitoring, further development is required. Advancement in technique and greater insight for the data interpretation will be made with historical data from continued case studies. In future studies, selective sub-sampling of biomass fractions (settling and dispersed fauna), evolution in the compositional analysis methods, and, ideally, complementary genotypic and classical microscopic analyses on select samples are recommended.

Development and application of a quasi-static Langmuir isotherm for modelling selected resin acid fate in pulp mill wastewater treatment.

Resin acids are pulp mill effluent contaminants that exhibit significant solubility, diffusivity, and surfactancy changes with pH within the range typically used for biological treatment. Such physical-chemical property changes which can influence removal during biological wastewater treatment, can be characterized by dynamic surface tension measurements. Dynamic surface tension measurements were made by the maximum bubble pressure method during batch treatment of selected resin acids in pulp mill effluent. Interpretation of dynamic surface tension data was made through the framework of a quasi-static Langmuir isotherm model that was derived as part of this investigation. The results suggested that under acidic conditions, resin acids form associations with other dissolved organic matter contained in pulp mill effluent, while under alkaline conditions, they behave as relatively soluble surfactants. A resin acid residuum, or threshold concentration, has been found to increase under acidic growth conditions. This residuum increase corresponded to an inferred reduction in resin acid bioavailability that was suggested from the isotherm modelling. The development of quasi-static isotherm adsorption models has application in computer simulation for design of adsorption based unit processes, and could potentially be utilized as an informative treatment process monitor.

Quantifying Population Dynamics Based on Community Structure Fingerprints Extracted from Biosolids Samples.

This paper presents a standardized metric for quantifying the rate change in community structure of complex mixed microbial cultures such as those maintained in biological wastewater treatment systems. Quantifying the stability of microbial community structures is a first step toward more aggressive monitoring and control of biological systems for greater reliability in contaminant removal. Statistical analysis of compositions that uniquely specify the balance of populations of species in a mixed culture sample can be used to specify a biosolids community state as a unique position in an orthogonal coordinate system. Changes in biosolids state are observable as a trajectory within this coordinate space, and the rate of passage along this trajectory relates to the population dynamics. The geometric interpretation and the statistical analysis methods necessary for the proposed calculation methodology are introduced by way of simulated case studies with a simple model system. With the example of this model system, concepts of changing microbial community shape and size are contrasted. The rate change in community structure is defined geometrically in terms of a rate change in relative proportions of the characteristic community shape at constant biomass. A change in biomass is defined as the rate change in the quantity of biosolids at constant shape. The method robustness with respect to random measurement error was also demonstrated using the model system. The potential applications of the approach are presented with experimental data of microbial fatty acid compositions extracted from samples during the operation of bench-scale bioreactors degrading contaminants found in pulp mill wastewater. Scaling the level of population dynamics with a metric that is independent of chemotypic content presents a standard for direct comparisons of community responses between distinct cultures and experiments.