Meso- and thermophilic posttreatment of press water coming from a thermophilic municipal solid waste digester

An efficient biogas production out of organic (waste) materials is important to contribute to a carbon-neutral future. In this study, thermophilic press water (PW) coming from an organic fraction of the municipal solid waste digester was further digested in a thermo- and mesophilic posttreatment approach using two semicontinuous 14 L digesters. The results showed that the PW can still have considerable high biogas potential-at least during the touristic high season in central Europe. The change in temperature led to an increase in volatile fatty acid concentrations and a decrease in biogas production in the mesophilic approach in the first days. However, the losses in biogas production at the beginning could be compensated thus there were no considerable differences in biogas production between thermo- and mesophilic posttreatment at the end of incubation. This can most probably be contributed to a change in the microbial community, and potentially problematic intermediates like valerate could be better degraded in the mesophilic reactor. Especially the abundance of representatives of the phylum Bacteroidota, like Fermentimonas spp., increased during mesophilic anaerobic digestion.

Prediction of hospitalisations based on wastewater-based SARS-CoV-2 epidemiology

Wastewater-based epidemiology is widely applied in Austria since April 2020 to monitor the SARS-CoV-2 pandemic. With a steadily increasing number of monitored wastewater facilities, 123 plants covering roughly 70 % of the 9 million population were monitored as of August 2022. In this study, the SARS-CoV-2 viral concentrations in raw sewage were analysed to infer short-term hospitalisation occupancy. The temporal lead of wastewater-based epidemiological time series over hospitalisation occupancy levels facilitates the construction of forecast models. Data pre-processing techniques are presented, including the approach of comparing multiple decentralised wastewater signals with aggregated and centralised clinical data. Time‑lead quantification was performed using cross-correlation analysis and coefficient of determination optimisation approaches. Multivariate regression models were successfully applied to infer hospitalisation bed occupancy. The results show a predictive potential of viral loads in sewage towards Covid-19 hospitalisation occupancy, with an average lead time towards ICU and non-ICU bed occupancy between 14.8-17.7 days and 8.6-11.6 days, respectively. The presented procedure provides access to the trend and tipping point behaviour of pandemic dynamics and allows the prediction of short-term demand for public health services. The results showed an increase in forecast accuracy with an increase in the number of monitored wastewater treatment plants. Trained models are sensitive to changing variant types and require recalibration of model parameters, likely caused by immunity by vaccination and/or infection. The utilised approach displays a practical and rapidly implementable application of wastewater-based epidemiology to infer hospitalisation occupancy.

Effects of phenyl acids on different degradation phases during thermophilic anaerobic digestion

Aromatic compounds like phenyl acids (PA) can accumulate during anaerobic digestion (AD) of organic wastes due to an increased entry of lignocellulose, secondary plant metabolites or proteins, and thermodynamic challenges in degrading the benzene ring. The effects of aromatic compounds can be various – from being highly toxic to be stimulating for methanogenesis – depending on many parameters like inoculum or molecular characteristics of the aromatic compound. To contribute to a better understanding of the consequences of PA exposure during AD, the aim was to evaluate the effects of 10 mM PA on microbial communities degrading different, degradation phase–specific substrates in thermophilic batch reactors within 28  days: Microcrystalline cellulose (MCC, promoting hydrolytic to methanogenic microorganisms), butyrate or propionate (promoting syntrophic volatile fatty acid (VFA) oxidisers to methanogens), or acetate (promoting syntrophic acetate oxidisers to methanogens). Methane production, VFA concentrations and pH were evaluated, and microbial communities and extracellular polymeric substances (EPS) were assessed. The toxicity of PA depended on the type of substrate which in turn determined the (i) microbial diversity and composition and (ii) EPS quantity and quality. Compared with the respective controls, methane production in MCC reactors was less impaired by PA than in butyrate, propionate and acetate reactors which showed reductions in methane production of up to 93%. In contrast to the controls, acetate concentrations were high in all PA reactors at the end of incubation thus acetate was a bottle-neck intermediate in those reactors. Considerable differences in EPS quantity and quality could be found among substrates but not among PA variants of each substrate. Methanosarcina spp. was the dominant methanogen in VFA reactors without PA exposure and was inhibited when PA were present. VFA oxidisers and Methanothermobacter spp. were abundant in VFA assays with PA exposure as well as in all MCC reactors. As MCC assays showed higher methane yields, a higher microbial diversity and a higher EPS quantity and quality than VFA reactors when exposed to PA, we conclude that EPS in MCC reactors might have been beneficial for absorbing/neutralising phenyl acids and keeping (more susceptible) microorganisms shielded in granules or biofilms.

Expanding the Pathogen Panel in Wastewater Epidemiology to Influenza and Norovirus

Since the start of the 2019 pandemic, wastewater-based epidemiology (WBE) has proven to be a valuable tool for monitoring the prevalence of SARS-CoV-2. With methods and infrastructure being settled, it is time to expand the potential of this tool to a wider range of pathogens. We used over 500 archived RNA extracts from a WBE program for SARS-CoV-2 surveillance to monitor wastewater from 11 treatment plants for the presence of influenza and norovirus twice a week during the winter season of 2021/2022. Extracts were analyzed via digital PCR for influenza A, influenza B, norovirus GI, and norovirus GII. Resulting viral loads were normalized on the basis of NH4-N. Our results show a good applicability of ammonia-normalization to compare different wastewater treatment plants. Extracts originally prepared for SARS-CoV-2 surveillance contained sufficient genomic material to monitor influenza A, norovirus GI, and GII. Viral loads of influenza A and norovirus GII in wastewater correlated with numbers from infected inpatients. Further, SARS-CoV-2 related non-pharmaceutical interventions affected subsequent changes in viral loads of both pathogens. In conclusion, the expansion of existing WBE surveillance programs to include additional pathogens besides SARS-CoV-2 offers a valuable and cost-efficient possibility to gain public health information.

Viral variant-resolved wastewater surveillance of SARS-CoV-2 at national scale

SARS-CoV-2 surveillance by wastewater-based epidemiology is poised to provide a complementary approach to sequencing individual cases. However, robust quantification of variants and de novo detection of emerging variants remains challenging for existing strategies. We deep sequenced 3,413 wastewater samples representing 94 municipal catchments, covering >59% of the population of Austria, from December 2020 to February 2022. Our system of variant quantification in sewage pipeline designed for robustness (termed VaQuERo) enabled us to deduce the spatiotemporal abundance of predefined variants from complex wastewater samples. These results were validated against epidemiological records of >311,000 individual cases. Furthermore, we describe elevated viral genetic diversity during the Delta variant period, provide a framework to predict emerging variants and measure the reproductive advantage of variants of concern by calculating variant-specific reproduction numbers from wastewater. Together, this study demonstrates the power of national-scale WBE to support public health and promises particular value for countries without extensive individual monitoring.

Low-Temperature Biodegradation of Lignin-Derived Aromatic Model Monomers by the Cold-Adapted Yeast Rhodosporidiobolus colostri Isolated from Alpine Forest Soil

The contribution of cold-adapted yeasts to the emerging field of lignin biovalorization has not yet been studied. The red-pigmented basidiomycetous yeast strain Rhodosporidiobolus colostri DBVPG 10655 was examined for its potential to degrade five selected lignin-derived aromatic monomers (syringic acid, p-coumaric acid, 4-hydroxybenzoic acid, ferulic acid, and vanillic acid). The strain utilized p-coumaric acid, 4-hydroxybenzoic acid, and ferulic acid not only as the sole carbon source; full biodegradation occurred also in mixtures of multiple monomers. Vanillic acid was not utilized as the sole carbon source, but was degraded in the presence of p-coumaric acid, 4-hydroxybenzoic acid, and ferulic acid. Syringic acid was utilized neither as the sole carbon source nor in mixtures of compounds. Biodegradation of lignin-derived aromatic monomers was detected over a broad temperature range (1–25 °C), which is of ecological significance and of biotechnological relevance.

Detection and abundance of SARS-CoV-2 in wastewater in Liechtenstein, and the estimation of prevalence and impact of the B.1.1.7 variant

The new coronavirus 2 (SARS-CoV-2) is known to be also shed through feces, which makes wastewater-based surveillance possible, independent of symptomatic cases and unbiased by any testing strategies and frequencies. We investigated the entire population of the Principality of Liechtenstein with samples from the wastewater treatment plant Bendern (serving all 39,000 inhabitants). Twenty-four-hour composite samples were taken once or twice a week over a period of 6 months from September 2020 to March 2021. Viral RNA was concentrated using the PEG centrifugation method followed by reverse transcription quantitative PCR. The aim of this research was to assess the suitability of SARS-CoV-2 fragments to relate the viral wastewater signal to the incidences and assess the impact of the emerging B.1.1.7. variant. The viral load in the wastewater peaked at almost 9 × 10⁸ viral fragments per person equivalent (PE) and day on October 25, and showed a second peak on December 22 reaching a viral load of approximately 2 × 10⁸ PE^-1d^-1. Individual testing showed a lag of 4 days and a distinct underestimation of cases at the first peak when testing frequency was low. The wastewater signal showed an immediate response to the implementation of non-pharmaceutical interventions. The new virus variant B.1.1.7. was first detected in wastewater on December 23, while it was first observed with individual testing on January 13, 2021. Further, our data indicate that the emergence of new virus variant may change the wastewater signal, probably due to different shedding patterns, which should be considered in future models.

Extraction of Cofactor F420 for Analysis of Polyglutamate Tail Length from Methanogenic Pure Cultures and Environmental Samples

The cofactor F420 plays a central role as a hydride carrier in the primary and secondary metabolism of many bacterial and archaeal taxa. The cofactor is best known for its role in methanogenesis, where it facilitates thermodynamically difficult reactions. As the polyglutamate tail varies in length between different organisms, length profile analyses might be a powerful tool for distinguishing and characterizing different groups and pathways in various habitats. Here, the protocol describes the extraction and optimization of cofactor F420 detection by applying solid-phase extraction combined with high-performance liquid chromatography analysis independent of cultural or molecular biological approaches. The method was applied to gain additional information on the expression of cofactor F420 from microbial communities in soils, anaerobic sludge, and pure cultures and was evaluated by spiking experiments. Thereby, the study succeeded in generating different F420 tail-length profiles for hydrogenotrophic and acetoclastic methanogens in controlled methanogenic pure cultures as well as from environmental samples such as anaerobic digester sludge and soils.

Lignin intermediates lead to phenyl acid formation and microbial community shifts in meso- and thermophilic batch reactors

BACKGROUND

Lignin intermediates resulting from lignocellulose degradation have been suspected to hinder anaerobic mineralisation of organic materials to biogas. Phenyl acids like phenylacetate (PAA) are early detectable intermediates during anaerobic digestion (AD) of aromatic compounds. Studying the phenyl acid formation dynamics and concomitant microbial community shifts can help to understand the microbial interdependencies during AD of aromatic compounds and may be beneficial to counteract disturbances.

RESULTS

The length of the aliphatic side chain and chemical structure of the benzene side group(s) had an influence on the methanogenic system. PAA, phenylpropionate (PPA), and phenylbutyrate (PBA) accumulations showed that the respective lignin intermediate was degraded but that there were metabolic restrictions as the phenyl acids were not effectively processed. Metagenomic analyses confirmed that mesophilic genera like Fastidiosipila or Syntrophomonas and thermophilic genera like Lactobacillus, Bacillus, Geobacillus, and Tissierella are associated with phenyl acid formation. Acetoclastic methanogenesis was prevalent in mesophilic samples at low and medium overload conditions, whereas Methanoculleus spp. dominated at high overload conditions when methane production was restricted. In medium carbon load reactors under thermophilic conditions, syntrophic acetate oxidation (SAO)-induced hydrogenotrophic methanogenesis was the most important process despite the fact that acetoclastic methanogenesis would thermodynamically be more favourable. As acetoclastic methanogens were restricted at medium and high overload conditions, syntrophic acetate oxidising bacteria and their hydrogenotrophic partners could step in for acetate consumption.

CONCLUSIONS

PAA, PPA, and PBA were early indicators for upcoming process failures. Acetoclastic methanogens were one of the first microorganisms to be impaired by aromatic compounds, and shifts to syntrophic acetate oxidation coupled to hydrogenotrophic methanogenesis occurred in thermophilic reactors. Previously assumed associations of specific meso- and thermophilic genera with anaerobic phenyl acid formation could be confirmed.

Biomethanation at 45 °C offers high process efficiency and supports hygienisation

The aim of this work was to prove a process temperature of 45 °C as a practical alternative to commonly applied mesophilic (37 °C) and thermophilic (55 °C) anaerobic digestion (AD). Regarding methane production, no differences were found between the three temperature regimes. However, the maximum possible loading rate at 45 °C exceeded that at 37 °C and 55 °C. Pathogen inactivation at 45 °C was higher than at 37 °C and similarly efficient as at 55 °C. At each process temperature, a unique microbial community established. In addition, the archaeome at 55 °C was dominated by hydrogenotrophs, while at 37 °C and 45 °C it was dominated by acetotrophs. For the investigated substrate mixture, liquid cattle manure with wheat straw as co-substrate, 45 °C turned out to be preferable for AD. For other substrates, these findings still need to be confirmed.

Microbial community dynamics in mesophilic and thermophilic batch reactors under methanogenic, phenyl acid-forming conditions

BACKGROUND

Proteinaceous wastes exhibit high theoretical methane yields and their residues are considered valuable fertilisers. The routine anaerobic degradation of proteins often raises problems like high aromatic compound concentrations caused by the entry of aromatic amino acids into the system. A profound investigation of the consequences of aromatic compound exposure on various microorganisms, which cascade-like and interdependently degrade complex molecules to biogas, is still pending.

RESULTS

In mesophilic samples, methane was predominantly produced via acetoclastic methanogenesis. The highest positive correlation was observed between phenylacetate (PAA) and Psychrobacter spp. and between phenylpropionate (PPA) and Haloimpatiens spp. Moreover, Syntrophus spp. negatively correlated with PAA (Spearman's rank correlations coefficient (rs) = - 0.46, p < 0.05) and PPA concentrations (rs = - 0.44, p < 0.05) and was also associated with anaerobic benzene ring cleavage. In thermophilic samples, acetate was predominantly oxidised by Tepidanaerobacter spp. or Syntrophaceticus spp. in syntrophic association with a hydrogenotrophic methanogen. The genera Sedimentibacter and Syntrophaceticus correlated positively with both PAA and PPA concentrations. Moreover, Sedimentibacter spp., Tepidanaerobacter spp., Acetomicrobium spp., and Sporanaerobacter spp. were significant LEfSe (linear discriminant analysis effect size) biomarkers for high meso- as well as thermophilic phenyl acid concentrations. Direct negative effects of phenyl acids on methanogenic properties could not be proven.

CONCLUSIONS

Anaerobic phenyl acid formation is not restricted to specific microbial taxa, but rather done by various meso- and thermophilic bacteria. The cleavage of the highly inert benzene ring is possible in methanogenic batch reactors-at least in mesophilic fermentation processes. The results indicated that phenyl acids rather affect microorganisms engaged in preceding degradation steps than the ones involved in methanogenesis.

Microbial and Phenyl Acid Dynamics during the Start-up Phase of Anaerobic Straw Degradation in Meso- and Thermophilic Batch Reactors

Aromatic compounds like phenyl acids derived from lignocellulose degradation have been suspected to negatively influence biogas production processes. However, results on this topic are still inconclusive. To study phenyl acid formation in batch reactors during the start-up phase of anaerobic degradation, different amounts of straw from grain were mixed with mesophilic and thermophilic sludge, respectively. Molecular biological parameters were assessed using next-generation sequencing and qPCR analyses. Metagenomic predictions were done via the program, piphillin. Methane production, concentrations of phenylacetate, phenylpropionate, phenylbutyrate, and volatile fatty acids were monitored chromatographically. Methanosarcina spp. was the dominant methanogen when high straw loads were effectively degraded, and thus confirmed its robustness towards overload conditions. Several microorganisms correlated negatively with phenyl acids; however, a negative effect, specifically on methanogens, could not be proven. A cascade-like increase/decrease from phenylacetate to phenylpropionate, and then to phenylbutyrate could be observed when methanogenesis was highly active. Due to these results, phenylacetate was shown to be an early sign for overload conditions, whereas an increase in phenylbutyrate possibly indicated a switch from degradation of easily available to more complex substrates. These dynamics during the start-up phase might be relevant for biogas plant operators using complex organic wastes for energy exploitation.

Formation of phenylacetic acid and phenylpropionic acid under different overload conditions during mesophilic and thermophilic anaerobic digestion

BACKGROUND

Substrate spectra for anaerobic digestion have been broadened in the past decade, inter alia, due to the application of different pretreatment strategies and now include materials rich in lignocellulose, protein, and/or fat. The application of these substrates, however, also entails risks regarding the formation of undesired by-products, among which phenolic compounds are known to accumulate under unfavorable digestion conditions.

METHODS

Different states of overload were simulated in batch experiments while reviewing the generation of phenyl acids out of different lab-use substrates in order to evaluate the impact on biogas and methane production as well as some additional process performance parameters under defined laboratory conditions. Investigations were conducted under both mesophilic and thermophilic conditions.

RESULTS

It could be shown that the tested input materials led to the formation of phenyl acids in a substrate-dependent manner with the formation itself being less temperature driven. Once formed, the formation of phenyl acids turned out to be a reversible process.

CONCLUSIONS

Although a mandatory negative impact of phenyl acids per se on the anaerobic digestion process in general and the methanogenesis process in particular could not be proven, phenyl acids, however, seem to play an important role in the microbial response to overloaded biogas systems.

Temperature shapes the microbiota in anaerobic digestion and drives efficiency to a maximum at 45 °C

Throwing longstanding habits over the pile may be necessary to improve biogas production, in particular when it comes to the process temperature. Its effect on biogas production was investigated with lab-scale reactors operated in fed-batch mode (cattle slurry and maize straw) at 10-55 °C over six months. Biochemical and microbial changes were comprehensively investigated. Production was highest and most efficient at 45 °C with an average methane yield of 166 NL kg^-1 VS, and thus 12.8% and 9.6% higher than at 37 and 55 °C. Temperature significantly affected the microbiota and higher temperature provoked a shift from Bacteroidetes/Proteobacteria to Firmicutes. A transition from hydrogenotrophic to acetoclastic methanogenesis was observed from 10 to 45 °C, while the trend was reversed at 55 °C. The results contest the textbook notion of preferred and most efficient temperatures for AD and suggest reconsideration of the temperature range around 45 °C for efficient manure-based co-fermentation.

Hydrogenotrophic Methanogenesis and Autotrophic Growth of Methanosarcina thermophila

Although Methanosarcinales are versatile concerning their methanogenic substrates, the ability of Methanosarcina thermophila to use carbon dioxide (CO2) for catabolic and anabolic metabolism was not proven until now. Here, we show that M. thermophila used CO2 to perform hydrogenotrophic methanogenesis in the presence as well as in the absence of methanol. During incubation with hydrogen, the methanogen utilized the substrates methanol and CO2 consecutively, resulting in a biphasic methane production. Growth exclusively from CO2 occurred slowly but reproducibly with concomitant production of biomass, verified by DNA quantification. Besides verification through multiple transfers into fresh medium, the identity of the culture was confirmed by 16s RNA sequencing, and the incorporation of carbon atoms from 13CO2 into 13CH4 molecules was measured to validate the obtained data. New insights into the physiology of M. thermophila can serve as reference for genomic analyses to link genes with metabolic features in uncultured organisms.

Biological pre-treatment: Enhancing biogas production using the highly cellulolytic fungus Trichoderma viride

With regard to renewable sources of energy, bioconversion of lignocellulosic biomass has long been recognized as a desirable endeavor. However, the highly heterogeneous structure of lignocellulose restricts the exploitation of its promising potential in biogas plants. Hence, effective pre-treatment methods are decisive prerequisites to overcome these challenges in order to improve the utilization ratio of (ligno) cellulosic substrates during fermentation. In the present study, the application of Trichoderma viride in an aerobic upstream process prior to anaerobic digestion led up to a threefold increase in the yield of methane and total gas in a lab-scale investigation. Due to its highly efficient cellulolytic activities, T. viride seemed to be responsible for an improved nutrient availability that positively influenced the anaerobic microbiocenosis. Aerobic pre-treatment of organic matter with T. viride is therefore a promising solution to achieve higher methane yields and degradation performances without any additional energy demand, nor undesired by-product inhibition.

A closed loop for municipal organic solid waste by lactic acid fermentation

In order to investigate the feasibility of producing lactic acid from municipal organic solid waste different pH values (4-7) and temperatures (37°C and 55°C) were tested. For the evaluation of fermentation conditions the chemical, physical, and microbial characters were monitored over a period of 7days. Quantitative real time PCR, PCR-DGGE, and next generation sequencing of a 16S rRNA gene library were applied to identify the key players of the lactic acid production and their association. Lactobacillus acidophilus and its closest relatives were found to be efficient lactic acid producers (>300mM) under most suitable fermentation conditions tested in this study: 37°C with either uncontrolled pH or at a pH of 5. These data provide the first step in the realization of the idea "reuse, reduce, and recycle" of municipal organic solid waste.

Microbial succession during thermophilic digestion: the potential of Methanosarcina sp

A distinct succession from a hydrolytic to a hydrogeno- and acetotrophic community was well documented by DGGE (denaturing gradient gel electrophoresis) and dHPLC (denaturing high performance liquid chromatography), and confirmed by qPCR (quantitative PCR) measurements and DNA sequence analyses. We could prove that Methanosarcina thermophila has been the most important key player during the investigated anaerobic digestion process. This organism was able to terminate a stagnation phase, most probable caused by a decreased pH and accumulated acetic acid following an initial hydrolytic stage. The lack in Methanosarcina sp. could not be compensated by high numbers of Methanothermobacter sp. or Methanoculleus sp., which were predominant during the initial or during the stagnation phase of the fermentation, respectively.

Improvement of methane generation capacity by aerobic pre-treatment of organic waste with a cellulolytic Trichoderma viride culture

Trichoderma viride is known as a potent cellulose decomposer and was successfully used to improve and accelerate the decomposition process of aerobic composting. In contrast, the role of fungi as pre-treatment organisms for anaerobic digestion is not clear, since the fast aerobic decomposition is thought to be responsible for a rapid depletion of easily available nutrients, leading to a lack of these for the anaerobic community. In the present study carried out in lab-scale, the application of T. viride for the aerobic pre-incubation of organic matter derived from the inlet port of a 750,000 L anaerobic digester led to an increase in total gas and methane production in a subsequent anaerobic digestion step. A high cellulase activity caused by the addition of T. viride seemed to be responsible for a better nutrient availability for anaerobic microorganisms. Therefore, aerobic pre-incubation of organic residues with T. viride for subsequent anaerobic digestion is a promising approach in order to increase methane yields.

Cultivation of moonmilk-born non-extremophilic Thaum and Euryarchaeota in mixed culture

PCR-DGGE, qPCR and sequencing highlighted a quite homogenous archaeal community prevailing in secondary calcite deposits, so-called moonmilk, within the cold alpine Hundalm cave in Tyrol (Austria). Furthermore, the depth profile of this moonmilk could prove that the Archaea are located in oxygen-rich near- and oxygen-depleted sub-surface layers. To gather these communities we therefore applied an aerobic and anaerobic cultivation approach in oligotrophic and methanotrophic media. The mixed moonmilk community was analyzed with a combination of molecular methods using qPCR, PCR-DGGE and sequencing. Anaerobic and aerobic cultures were additionally investigated with GC and HPLC analyses. It was possible to initially cultivate and enrich the supposed aerobic/microaerophilic and anaerobic archaeal fraction, representing the natural archaeal community. While the naturally less abundant near-surface Archaea are closely related to members of the Thaumarchaeota (Nitrosopumilus maritimus), the highly abundant anaerobic Archaea are more distantly related to members within the Euryarchaeota. It is possible that these cultivable moonmilk-born Archaea represent new ecotypes or are so far undescribed. Based on the sequencing results and the production of very low amounts of methane, a corresponding methanogenic community is thought to represent only a minor abundant archaeal fraction. On a physiological level the cultivated moonmilk community is cold-adapted and basically of oligotrophic and organotrophic character.

Impact of protein-, lipid- and cellulose-containing complex substrates on biogas production and microbial communities in batch experiments

In the present study, nine complex organic substrates from three classes (protein-, lipid-, and cellulose-rich) were investigated in batch experiments and compared with a control in order to evaluate their potential for utilisation as substrates for biogas production. High methane production was observed from protein-rich substrates; problems arose from lipid-containing, lactose and cellulose fermentation. Using DGGE analysis it could be shown that different classes of substrate resulted in different microbial communities, whereupon similar substrates tended to show a similar microbial structure. By means of qPCR Methanoculleus sp., a hydrogenotrophic methanogen was found to be the most abundant organism in the batch experiments. Additionally, it could be demonstrated that methanogenic organisms withstood adverse environmental conditions for at least an incubation period of 55 days, pointing to a high stability of the archaeal community even in times of decreasing or even failing fermenter performance.

Effects of different nitrogen sources on the biogas production - a lab-scale investigation

For anaerobic digestion processes nitrogen sources are poorly investigated although they are known as possible process limiting factors (in the hydrolysis phase) but also as a source for fermentations for subsequent methane production by methanogenic archaea. In the present study different complex and defined nitrogen sources were investigated in a lab-scale experiment in order to study their potential to build up methane. The outcome of the study can be summarised as follows: from complex nitrogen sources yeast extract and casamino acids showed the highest methane production with approximately 600 ml methane per mole of nitrogen, whereas by the use of skim milk no methane production could be observed. From defined nitrogen sources L-arginine showed the highest methane production with almost 1400 ml methane per mole of nitrogen. Moreover it could be demonstrated that the carbon content and therefore C/N-ratio has only minor influence for the methane production from the used substrates.

Utilisation of single added fatty acids by consortia of digester sludge in batch culture

Inocula derived from an anaerobic digester were used to study (i) their potential for methane production and (ii) the utilisation rates of different short chain fatty acids (SCFAs) by the microbial community in defined media with mono-carbon sources (formic-, acetetic-, propionic-, butyric acid) in batch culture. It could be demonstrated that the microbial reactor population could be transferred successfully to the lab, and its ability to build up methane was present even with deteriorating biogas plant performance. Therefore, this reduction in performance of the biogas plant was not due to a decrease in abundance, but due to an inactivity of the microbial community. Generally, the physico-chemical properties of the biogas plant seemed to favour hydrogenotrophic methanogens, as seen by the high metabolisation rates of formate compared with all other carbon sources. In contrast, acetoclastic methanogenesis could be shown to play a minor role in the methane production of the investigated biogas plant, although the origin of up to 66% of methane is generally suggested to be generated through acetoclastic pathway.

Reduction of accumulated volatile fatty acids by an acetate-degrading enrichment culture

The effects of the addition of an acetate-degrading enrichment culture to an anaerobic digester with a stagnating biogas production were investigated. Initially, a thermophilic batch-operated lab-scale digester was inoculated with the diluted fermenter sludge of a biogas plant, and process parameters including the concentration of volatile fatty acids (VFAs) and gases in the headspace were measured. After a phase of high gas production, a stagnation of biogas production followed for a further 30 days. An acetate enrichment culture was added 34 days after the commencement of the experiment and this resulted in a sharp decrease in the concentrations of accumulated VFAs and an increase in total biogas and CH(4) production. An archaeon with a sequence similarity of 98% to Methanosarcina sp. and the ability to degrade acetic acid was introduced with the enrichment culture and is proposed to have been the driving factor for the changes that occurred within a few days to the process.

Process parameters within a 750,000 litre anaerobic digester during a year of disturbed fermenter performance

A 750,000litre fermenter was studied throughout one entire year by investigating the concentrations of volatile fatty acids (acetic, butyric, i-butyric, propionic, valeric and i-valeric acids), pH, concentrations of total C, N, S and NH(4)(+)-N, amounts of chemical and biological oxygen demand, and abundance of acetogenic microorganisms. Additionally several process parameters such as temperature, retention time, dry weight and input of substrate and liquids, and the concentrations and amounts of CH(4), H(2), CO(2) and H(2)S within the biogas were monitored continuously. Various volatile fatty acids and the ratio of acetic to propionic acid were shown to allow a rough indication on the fermentation but were not sufficiently precise to describe the fermenter performance. Nutrient compounds and special fractions, such as easily extractable carbohydrates or the concentration of total fats were more strongly correlated to the gas production of the fermenter. Results of an MPN-method for the determination of acetogenic microorganisms point to an important role of these microorganisms during the phase of restoration of the fermenter performance.

Survival of selected pathogens in diluted sludge of a thermophilic waste treatment plant and in NaCl-solution under aerobic and anaerobic conditions

Decimal reduction times (DRT or D-value) of Campylobacter jejuni, Salmonella enterica (formerly Salmonella choleraesuis) serovar Senftenberg, Escherichia coli, and Listeria monocytogenes were determined in two different matrices, diluted fermenter sludge (DFS) and 0.95% NaCl-solution (NaCl) at 50 degrees C, both under aerobic and anaerobic conditions. Depending on aeration, matrix composition, and the respective organism, the D-values varied between 10min and more than 15h. Generally the viability of bacteria decreased faster in DFS compared to NaCl-solution and under aerobic compared to anaerobic conditions. After 24h no viable cells could be detected in DFS, both under aerobic as well as under anaerobic conditions, whereas viable cells were still found in NaCl solutions. In both matrices the detection limits determined by means of PCR-based and classical microbiological methods were compared and pointed to lower detection limits of the latter methods. Results of the present investigation show that test organisms were far from surviving several days in DFS whereas hydraulic retention times normally used for thermophilic anaerobic digestion are in the range of 2 weeks. However, an underestimation of survival rates of the test organisms seems probable when applying aerobic standard methods.