Polyhydroxyalkanoate (PHA) production from sludge and municipal wastewater treatment.

Polyhydroxyalkanoates (PHAs) are biodegradable polyesters with comparable properties to some petroleum-based polyolefins. PHA production can be achieved in open, mixed microbial cultures and thereby coupled to wastewater and solid residual treatment. In this context, waste organic matter is utilised as a carbon source in activated sludge biological treatment for biopolymer synthesis. Within the EU project Routes, the feasibility of PHA production has been evaluated in processes for sludge treatment and volatile fatty acid (VFA) production and municipal wastewater treatment. This PHA production process is being investigated in four units: (i) wastewater treatment with enrichment and production of a functional biomass sustaining PHA storage capacity, (ii) acidogenic fermentation of sludge for VFA production, (iii) PHA accumulation from VFA-rich streams, and (iv) PHA recovery and characterisation. Laboratory- and pilot-scale studies demonstrated the feasibility of municipal wastewater and solid waste treatment alongside production of PHA-rich biomass. The PHA storage capacity of biomass selected under feast-famine with municipal wastewater has been increased up to 34% (g PHA g VSS(-1)) in batch accumulations with acetate during 20 h. VFAs obtained from waste activated sludge fermentation were found to be a suitable feedstock for PHA production.

Phosphorus recovery potential from a waste stream with high organic and nutrient contents via struvite precipitation.

Recovery of NH4(+)-N and PO(3-)-P via struvite precipitation (SP) was evaluated from liquor of thermally pretreated waste activated sludge, containing high levels of nutrients (1500 mg NH4(+)-N/L and 650 mg PO(3-)-P/L), organics (45.5 g COD/L) and suspended solids (3.5 g TSS/L), with reference to anaerobically digested sludge centrate. In a series of jar tests, the order of pH adjustment and chemical addition were first tested for the digested sludge centrate. The effects of MgCl2 and MgO, as Mg2+ sources, on SP were evaluated in both waste streams. Up to 80% of the dissolved PO4(3-)-P was recovered using MgO (pH = 9.2) from the pretreated sludge liquor and more than 86% of NH4(+)-N from the digested sludge centrate (pH = 8.0-8.5) regardless of the Mg2+ source used. NH4(+)-N recovery from digested sludge centrate required the addition of alkali, Mg2+ source and PO4(3-)-P, making the process less viable. The precipitates contained mostly struvite and some levels of Ca2+, Fe2+ and other Mg2+ phosphates. The levels of solids, inorganics and organics in the waste streams influenced SP, specifically struvite crystal formation and settleability in the pretreated sludge liquor, which suggests that the applicability of SP for nutrient recovery from complex waste streams requires case-by-case testing, and process optimization.

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.

Microaerophilic conditions support elevated mixed culture polyhydroxyalkanoate (PHA) yields, but result in decreased PHA production rates.

For commercial polyhydroxyalkanoate (PHA) production the objective is to maximise the fraction of feedstock that ends up as polymer, and minimise biomass growth. In this paper, oxygen limitation was applied to achieve this. Intracellular PHA content in mixed cultures in batch systems operated with low and high DO was compared. It is shown that in microaerophilic conditions a higher fraction of substrate is accumulated as PHA in comparison to high DO conditions, evidenced by elevated intracellular PHA content: in the order of 50% higher in the early stages of accumulation. However, the accumulation capacity is not affected by DO. The PHA content in biomass in both the low and high DO systems reached approximately 35%. The time taken for the PHA content in the low DO system to reach capacity was three times longer than in the high DO system.

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.

In-situ monitoring of microbial biomass in wetland mesocosms.

The objective of the present investigation has been to combine tracer principles and a hydrolytic microbial activity assay using fluorescein diacetate to monitor changes in microbial biomass within subsurface flow wetland mesocosms. The mesocosm hydrolytic activity was referenced to activated sludge concentrations treating a typical domestic wastewater at full scale. Microbial biomass activity levels within four laboratory wetland mesocosms treating a synthetic domestic wastewater were routinely monitored over a 21-week period of plant growth and rhizosphere development. Although above ground plant mass and tracer dispersion numbers suggested progressive root zone development, plant growth did not result in any measurable enhancement in microbial activity when compared to a mesocosm operating without plants. Dispersion numbers also suggested a reduction in the mass transport kinetics in these planted mesocosms. In-situ biomass monitoring enabled the assessment of a characteristic response in terms of the steady-state food to microorganism (F/M) ratio that was observed in mesocosms receiving both low and high organic loading. Wetland treatment performance is sensitive to the degree to which bed volume is exploited in terms of wastewater flow to regions of bioactivity. The in-situ reactive tracer technique for mesocosm biomass monitoring provided an assessment of the collective substratum and rhizosphere microbial biomass in direct contact with wastewater contaminants. Thus, in-situ biomass monitoring has application in further understanding of plant function and strategies for plant implementation in wetland research and development.

Integrated production of polyhydroxyalkanoates (PHAs) with municipal wastewater and sludge treatment at pilot scale.

A pilot-scale process was operated over 22 months at the Brussels North Wastewater Treatment Plant (WWTP) in order to evaluate polyhydroxyalkanoate (PHA) production integration with services of municipal wastewater and sludge management. Activated sludge was produced with PHA accumulation potential (PAP) by applying feast-famine selection while treating the readily biodegradable COD from influent wastewater (average removals of 70% COD, 60% CODsol, 24% nitrogen, and 46% phosphorus). The biomass PAP was evaluated to be in excess of 0.4gPHA/gVSS. Batch fermentation of full-scale WWTP sludge at selected temperatures (35, 42 and 55 °C) produced centrate (6-9.4 gCODVFA/L) of consistent VFA composition, with optimal fermentation performance at 42 °C. Centrate was used to accumulate PHA up to 0.39 gPHA/gVSS. The centrate nutrients are a challenge to the accumulation process but producing a biomass with 0.5 gPHA/gVSS is considered to be realistically achievable within the typically available carbon flows at municipal waste management facilities.

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.

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.

A comparison of conventional activated sludge and low sludge production strategies for advanced treatment of kraft pulp mill effluent.

Parallel laboratory investigations were conducted to examine aspects of two distinct but related bioprocess strategies for low sludge production in the treatment of the same TCF kraft pulp mill effluent. The purpose of this article has been to compare the performance results from these two bench-scale trials with respect to nutrient demands, nutrient discharge, COD removal, and waste sludge characteristics. The LSP (Low Sludge Production) process can be used to significantly reduce sludge yield with excellent sludge characteristics. These sludge characteristics seemed to be related to elevated protozoan grazing pressures. The BAS (Biofilm-Activated Sludge) process achieves similar reduced sludge yields and sludge characteristics while at the same time significantly reducing the nutrient demands and discharge levels. For both LSP and BAS process optimization, the selector nutrient loading is critical to the overall process performance. Selector nutrient requirements are distinct from the overall process nutrient requirements.

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.

Production of volatile fatty acids by fermentation of waste activated sludge pre-treated in full-scale thermal hydrolysis plants.

This work focuses on fermentation of pre-treated waste activated sludge (WAS) to generate volatile fatty acids (VFAs). Pre-treatment by high-pressure thermal hydrolysis (HPTH) was shown to aid WAS fermentation. Compared to fermentation of raw WAS, pre-treatment enabled a 2-5x increase in VFA yield (gVFA(COD)gTCOD(-1)) and 4-6x increase in VFA production rate (gVFA(COD) L(-1) d(-1)). Three sludges, pre-treated in full-scale HPTH plants, were fermented. One was from a plant processing a mix of primary sludge and WAS and the other two from plants processing solely WAS. The HPTH plants solubilised suspended matter, evidenced by a 20-30% decrease in suspended solids and an increase of soluble COD : total COD from 0.04 to 0.4. Fermentation of the three sludges yielded similar VFA concentrations (15-20gVFA(COD) L(-1)). The yields were largely independent of retention time (1 d-6 d) and temperature (42°C, 55°C). Also, the product spectrum depended mostly on the composition of the sludge rather than on operating conditions.