Thérèse Mahony

Effect of pH on growth kinetics and sulphide toxicity thresholds of a range of methanogenic, syntrophic and sulphate-reducing bacteria

Abstract The effect of pH on growth rates and sulphide toxicity thresholds of a variety of key bacterial groups involved in anaerobic digestion is described. At pH 7·0–7·5, the growth rates of methane-producing bacteria (MPB) and sulphate-reducing bacteria (SRB) were similar. Above and below this pH range, MPB and SRB, respectively, have more favourable growth properties. Inhibition of all the bacterial groups studied was related to the total sulphide concentration in the pH range 7·2–8·5. Propionate-utilising SRB were the most sensitive of the bacterial groups, both in pure culture and in sludge samples, to high concentrations of total sulphide. At lower pH levels (6·8–7·2), the levels of sulphide which resulted in 50% inhibition of the growth of the bacterial groups were similar, although values obtained were higher for sludge samples than for pure cultures.

Anaerobic Granular Sludge Bioreactor Technology

Anaerobic digestion is a mature wastewater treatment technology, with worldwide application. The predominantly applied bioreactor designs, such as the upflow anaerobic sludge blanket and expanded granular sludge bed, are based on the spontaneous formation of granular sludge. Despite the exploitation of granular reactors at full-scale for more than two decades, the mechanisms of granulation are not completely understood and numerous theories have been put forward to describe the process from a biological, ecological and engineering point of view. New technological opportunities are emerging for anaerobic digestion, aided by an improved understanding of microbiological and environmental factors affecting the formation and activity of anaerobic granular sludge.

Quantitative and qualitative analyses of methanogenic community development in high-rate anaerobic bioreactors.

Methanogenic community structure and population dynamics were investigated in two anaerobic reactors treating a dairy wastewater, an Inverted Fluidized Bed (IFB) and Expanded Granular Sludge Bed (EGSB). A combination of real-time PCR, denaturing gradient gel electrophoresis and statistical techniques was employed. Distinct methanogenic communities developed in the IFB and EGSB reactors reflecting step-wise reductions in the applied hydraulic retention time from 72 to 12 h during the 200-day trial. The aceticlastic family Methanosarcinaceae was only detected in the IFB and the order Methanomicrobiales was also much more abundant in this reactor, while the aceticlastic family Methanosaetaceae was more abundant in the EGSB. The hydrogenotrophic order, Methanobacteriales, predominated in both reactors under all applied operational conditions. Non-metric multidimensional scaling (NMS) and moving-window analyses, based on absolute and relative abundance quantification data, demonstrated that the methanogenic communities developed in a different manner in the IFB, compared to the EGSB reactor. In our study, relative abundance-based quantification by NMS and moving-window analysis appeared to be a valuable molecular approach that was more applicable to reflect the changes in the anaerobic digestion process than approaches based either on qualitative analysis, or solely on absolute quantification of the various methanogenic groups. The overall results and findings provided a comparative, quantitative and qualitative insight into anaerobic digestion processes, which could be helpful for better future reactor design and process control.

Quantitative and qualitative analysis of methanogenic communities in mesophilically and psychrophilically cultivated anaerobic granular biofilims

Anaerobic granulation describes the self-immobilisation of methanogenic consortia into dense, particulate biofilms. This procedure underpins the operation of several categories of high-rate anaerobic wastewater treatment system. Full-scale anaerobic granular sludge plants have been generally operated in the mesophilic (20-45 degrees C) or thermophilic (45-65 degrees C) temperature range. On the other hand, recent studies highlighted the economic advantages of treating wastewaters at their discharge temperatures (mostly under 18 degrees C), removing a costly heating process and increasing net biogas yield. However, as yet, relatively little information is available about the microbial behaviour and interactions in anaerobic granular sludge formed under psychrophilic conditions. To this end, and in order to provide a microbial insight into low-temperature anaerobic granulation, we monitored the changes in methanogenic community structure, associated with the changes in process performance. Three, laboratory-scale, expanded granular sludge bed (EGSB) bioreactors treating a synthetic glucose wastewater were tested at two temperatures of 37+/-1 degrees C (R1) and 15+/-1 degrees C (R2 and 3). Quantitative real-time PCR and specific methanogenic activity assays highlighted a community shift towards hydrogenotrophic methanogens, particularly the order Methanomicrobiales in the low-temperature bioreactors. Corresponding to this, denaturing gradient gel electrophoresis (DGGE) analysis identified the emergence and maintenance of a Methanocorpusculum-like organism. Our results indicate that hydrogenotrophic methanogens, particularly the Methanomicrobiales-related populations, are likely to play important roles in low-temperature anaerobic granular sludge systems. This suggests that the process efficiency could be improved by facilitating the growth and retention of this group.

Long-term (1243 days), low-temperature (4–15 °C), anaerobic biotreatment of acidified wastewaters: Bioprocess performance and physiological characteristics

The feasibility of long-term (>3 years), low-temperature (4-15 degrees C) and anaerobic bioreactor operation, for the treatment of acidified wastewater, was investigated. A hybrid, expanded granular sludge bed-anaerobic filter bioreactor was seeded with a mesophilic inoculum and employed for the mineralization of moderate-strength (3.75-10 kg chemical oxygen demand (COD)m(-3)) volatile fatty acid-based wastewaters at 4-15 degrees C. Bioprocess performance was assessed in terms of COD removal efficiency (CODRE), methane biogas concentration, and yield, and biomass retention. Batch specific methanogenic activity assays were performed to physiologically characterise reactor biomass. Despite transient disimprovements, CODRE and methane biogas concentrations exceeded 80% and 65%, respectively, at an applied organic loading rate (OLR) of 10 kgCODm(-3)d(-1) between 9.5 and 15 degrees C (sludge loading rate (SLR), 0.6 kgCOD kg[VSS](-1)d(-1)). Over 50% of the granular sludge bed was lost to disintegration during operation at 9.5 degrees C, warranting a reduction in the applied OLR to 3.75-5 kgCODm(-3)d(-1) (SLR, c. 0.4-0.5kgCOD kg[VSS](-1)d(-1)). From that point forward, remarkably stable and efficient performance was observed during operation at 4-10 degrees C, with respect to CODRE (>or=82%), methane biogas concentration (>70%) and methane yields (>4l(Methane)d(-1)), suggesting the adaptation of our mesophilic inoculum to psychrophilic operating conditions. Physiological activity assays indicated the development of psychroactive syntrophic and methanogenic populations, including the emergence of putatively psychrophilic propionate-oxidising and hydrogenotrophic methanogenic activity. The data suggest that mesophilic inocula can physiologically adapt to sub-optimal operational temperatures: treatment efficiencies and sludge loading rates at 4 degrees C (day, 1243) were comparable to those achieved at 15 degrees C (day 0). Furthermore, long-term, low-temperature bioreactor operation may act as a selective enrichment for psychrophilic methanogenic activity from mesophilic inocula. The observed efficient and stable bioprocess performance highlights the potential for long-term, low-temperature bioreactor operation.

Distribution, Localization, and Phylogeny of Abundant Populations of Crenarchaeota in Anaerobic Granular Sludge

ABSTRACT Eight anaerobic granular sludges were surveyed for Crenarchaeota using rRNA gene cloning. Microbial arrangement and substrate uptake patterns were elucidated by fluorescent in situ hybridization and beta imaging. Group 1.3 Crenarchaeota represented up to 50% of Archaea and 25% of the total microbiota in five sludges. Crenarchaeota were localized in close association with methanogenic Archaea.

Low-temperature anaerobic digestion for wastewater treatment

Methanogenesis is an important biogeochemical process for the degradation of organic matter within cold environments, and is associated with the release of the potent greenhouse gas, methane. Cold methanogenesis has been harnessed, in engineered systems, as low-temperature anaerobic digestion (LTAD) for wastewater treatment and bioenergy generation. LTAD represents a nascent wastewater treatment biotechnology, which offers an attractive alternative to conventional aerobic and anaerobic processes. Successful, high-rate, LTAD of sewage and industrial wastewaters (e.g. from the brewery, food-processing and pharmaceutical sectors), with concomitant biogas generation, has been demonstrated at laboratory-scale and pilot-scale. A holistic, polyphasic approach, which integrates bioprocess, physiological and molecular biological datasets has been critical to the development of the LTAD concept.

Accessing the Black Box of Microbial Diversity and Ecophysiology: Recent Advances Through Polyphasic Experiments

The microbial ecology of a range of anaerobic biological assemblages (granular sludge) from full- and laboratory-scale wastewater treatment bioreactors, and of crop-growing and peat soils, was determined using a variety of 16S rRNA gene-based techniques, including clone library, terminal restriction fragment length polymorphism (TRFLP) and denaturing gradient gel electrophoresis (DGGE) analyses. Fluorescent in situ hybridization (FISH) using 16S rRNA gene-targeted probes was employed to complete a “full-cycle rRNA approach” with selected biomass. Genetic fingerprinting (TRFLP and DGGE) was effectively used to elucidate community structure-crop relationships, and to detect and monitor trends in bioreactor sludge and specific enrichment cultures of peat soil. Greater diversity was resolved within bacterial than within archaeal communities, and unexpected reservoirs of uncultured Crenarchaeota were detected in sludge granules. Advanced radiotracer incubations and micro-beta imaging were employed in conjunction with FISH to elucidate the eco-functionalism of these organisms. Crenarchaeota clusters were identified in close associated with methanogenic Archaea and both were localised with acetate uptake in biofilm structure.

Microbial community dynamics associated with biomass granulation in low-temperature (15°C) anaerobic wastewater treatment bioreactors

Granular biofilms underpin the operation of several categories of anaerobic wastewater treatment bioreactors. Recent studies have demonstrated the feasibility of treating both industrial and domestic wastewaters at their discharge temperatures (usually <18 degrees C), thereby avoiding the heating expenses of mesophilic (20-45 degrees C) or thermophilic (45-65 degrees C) treatments. Previous low-temperature trials used mesophilic inocula and little information is available on the viability of low-temperature anaerobic granulation. Six laboratory-scale, expanded granular sludge bed bioreactors (R1-6) were operated at 15 degrees C (R1-2 and R4-5) and 37 degrees C (R3 and R6). R1-3 were fed glucose-based wastewater and R4-6 were fed volatile fatty acid-based wastewater. Quantitative real-time PCR and qualitative denaturing gradient gel electrophoresis of 16S rRNA genes identified the dominance of Methanomicrobiales (mainly Methanocorpusculum-like organisms) during low-temperature granulation. Granulation only occurred in glucose-fed bioreactors. The results suggest that (i) granulation is feasible in low-temperature bioreactors; (ii) carbohydrate decomposition likely favoured granulation, (iii) Methanocorpusculum-like organisms play a critical role in low-temperature granulation.

Microbial community structure and dynamics in anaerobic fluidized‐bed and granular sludge‐bed reactors: influence of operational temperature and reactor configuration

Methanogenic community structure and dynamics were investigated in two different, replicated anaerobic wastewater treatment reactor configurations [inverted fluidized bed (IFB) and expanded granular sludge bed (EGSB)] treating synthetic dairy wastewater, during operating temperature transitions from 37°C to 25°C, and from 25°C to 15°C, over a 430‐day trial. Non‐metric multidimensional scaling (NMS) and moving‐window analyses, based on quantitative real‐time PCR data, along with denaturing gradient gel electrophoresis (DGGE) profiling, demonstrated that the methanogenic communities developed in a different manner in these reactor configurations. A comparable level of performance was recorded for both systems at 37°C and 25°C, but a more dynamic and diverse microbial community in the IFB reactors supported better stability and adaptative capacity towards low temperature operation. The emergence and maintenance of particular bacterial genotypes (phylum Firmicutes and Bacteroidetes) was associated with efficient protein hydrolysis in the IFB, while protein hydrolysis was inefficient in the EGSB. A significant community shift from a Methanobacteriales and Methanosaetaceae towards a Methanomicrobiales‐predominated community was demonstrated during operation at 15°C in both reactor configurations.