• Energy Research

Energy supply is a global hot topic. The social and political pressure forces a higher percentage of energy supplied by renewable resources. The production of renewable energy in form of biomethane can be increased by co-substrates such as municipal biowaste. However, a demand-driven energy production or its storage needs optimisation, the option to store the substrate with its inherent energy is investigated in this study. The calorific content of biowaste was found unchanged after 45 d of storage (19.9±0.19 kJ g(-1) total solids), and the methane yield obtained from stored biowaste was comparable to fresh biowaste or even higher (approx. 400 m(3) Mg(-1) volatile solids). Our results show that the storage supports the hydrolysis of the co-substrate via acidification and production of volatile fatty acids. The data indicate that storage of biowaste is an efficient way to produce bioenergy on demand. This could in strengthen the role of biomethane plants for electricity supply the future.

Large waste water treatment plants (WWTP) often operate nitrification in two different process environments: the cold-dilute sewage is treated in the mainstream nitrification/denitrification system, while the high strength ammonia liquors from sludge dewatering are treated in a separate high temperature reactor (SBR). This study investigates transfer from nitrifier biomass into a two-stage WWTP, commonly referred to as bioaugmentation. Besides the quantitation of ammonia oxidising bacteria (AOB), community differences were analysed with two techniques, denaturing gradient gel electrophoresis and real-time PCR melt curve analysis. It was shown that, without bioaugmentation, two distinct AOB communities establish in the mainstream and in the SBR, respectively. A gradual shift of the two AOB communities with increasing pump rates between the systems could be demonstrated. These molecular findings support process engineering experience, that cycling of waste activated sludge improves the ability of AOB to adapt to different process environments.

Storage of woody biomass in large wood chip piles is unavoidable for biotechnological applications, but comes along with considerable biomass-, energy- and thus, economic losses due to exothermic reactions and microbial degradation. The homogeneous amendment of the storage piles with an alkaline stabilization agent, calcium hydroxide (Ca(OH)2), was found to decrease dry matter loss in Picea abies; for Populus canadensis piles the effects cannot clearly be deduced. Here we investigated the bacterial and fungal communities of industrial-scale wood chip piles (250 m3) of these two different tree species and related them to physicochemical conditions and enzymatic activities after 35 and 120 d, representing short- and long-term storage of the wood chips, respectively. Coming from different wood types (hard vs. softwood), we expected the communities to converge over time, due to similar storage conditions. Despite pH posing selective pressure, we expected a minor Ca(OH)2 effect as already known from previous studies. We found that the effectiveness of Ca(OH)2 addition depended on the wood type that determined both the native microbial seeding community and temperature pattern of all piles, thereby exerting selective forces of differing strength. Generally, a thermophilic community consisting of single fungal and variable bacterial taxa were identified. As expected, the microbial communities from P. abies and P. canadensis converged over time. Biomass loss was connected to C-cycle related enzymatic activities and to the abundance and composition of fungal communities. Chaetomium sp. was identified as potential key taxon determining biomass degradation under the given storage conditions.

Abstract Cattle excreta and two-phase olive mill wastes (TPOMW) were codigested at a 3:1 ratio in two 75 L continuous stirred tank reactors at 37 °C and 55 °C to analyse their biogas production. The contribution of each residue to the total gas production at 37 °C was evaluated in reactors digesting either 3:1 excreta:water or 3:1 water:TPOMW. The mesophilic co-fermentation of cattle excreta with TPOMW at an organic loading rate (OLR) of 5.5 g COD L −1 d −1 rendered 1096 mL biogas L −1 sludge d −1 . This was 337% higher than that of excreta alone. The methane yield resulting from the codigestion was 179 L CH 4 kg −1 VS loaded, of which 42% was attributed to the quarter of the reactor corresponding to TPOMW. Under thermophilic conditions, the codigestion yielded 17.3% more methane than mesophilically. In the reactor digesting TPOMW alone (OLR = 3.8 g COD L −1 d −1 ) the ratio VFA/alkalinity exceeded 0.8 after 21 d, leading to its acidification and inhibition of methanogenesis. Farm-scale digestion of animal excreta and TPOMW should be promoted in Mediterranean countries as an environmentally sound option for waste recycling and renewable energy production.

In biogas plants, lignocellulose-rich biomass (LCB) is particularly slowly degraded, causing high hydraulic retention times. This fact lowers the interests for such substrates. To enhance LCB-degradation, cattle rumen fluid, a highly active microbial resource accruing in the growing meat industry, might be used as a potential source for bioaugmentation. This study compares 0%, 20% and 40% rumen liquid in a batch anaerobic digestion approach. Moreover, it determines the biogas- and methane-potentials as well as degradation-speeds of corn straw, co-digested with cattle manure. It inspects microbial communities via marker-gene sequencing, qPCR and RNA-DGGE and draws attention on possible beneficial effects of rumen addition on the biogas-producing community. Bioaugmentation with 20% and 40% v/v rumen liquid accelerated methane yields by 5 and 6 days, respectively (i.e. reaching 90% of total methane production). It also enhanced LCB- as well as (hemi)cellulose- and volatile fatty acid degradation. These results are supported by increased abundances of bacteria, methanogens and anaerobic fungi in treatments with rumen liquid amendment, and point towards the persistence of specific rumen-borne microorganisms especially during the first phase of the experiment. The results suggest that rumen liquid addition is a promising strategy for enhanced and accelerated exploitation of LCB for biomethanisation.

Anaerobic digestion is a common procedure of treating sewage sludge at wastewater treatment plants. However, plants differ in terms of the number of reactors and, in case of several reactors, their operation mode. To confirm the flexibility of well adapted, full-scale anaerobic digestion plants, we monitored the physicochemical process conditions of two continuously stirred tank reactors over one hydraulic retention time before and after the operation mode was switched from parallel to serial operation. To investigate changes in the involved microbiota, we applied Illumina amplicon sequencing. The rapid change between operation modes did not affect the process performance. In both parallel and serial operation mode, we detected a highly diverse microbial community, in which Bacteroidetes, Firmicutes, Proteobacteria and Claocimonetes were high in relative abundance. While a prominent core microbiome was maintained in both configurations, changes in the involved microbiota were evident at a lower taxonomical level comparing both reactors and operation modes. The most prominent methanogenic Euryarchaeota detected were Methanosaeta and cand. Methanofastidiosum. Volatile fatty acids were degraded immediately in both reactors, suggesting that the second reactor could be used to produce methane on demand, by inserting easily degradable substrates.

Anaerobic digestion has become increasingly popular as an alternative for recycling wastes from different origins. Consequently, biogas residues, most of them with unknown chemical and biological composition, accrue in large quantities and their application into soil has become a widespread agricultural practise. The aim of this study was to evaluate the effects of digestate application on the chemical and microbiological properties of an arable soil in comparison with untreated manure, compost and vermicompost. Once in the soil matrix either the addition of compost or digestate led to an increased nitrification rate, relative to unamended and manure-treated soil, after 15 and 60 days of incubation. Faecal coliform and E. coli colony forming units (CFUs) were not detected in any of the amended soils after 60 days. The highest number of Clostridium perfringens CFUs was recorded in manure-amended soil at the beginning of the experiment and after 15 days; whilst after 60 days the lowest CFU number was registered in digestate-treated soil. Denaturing gradient gel electrophoresis patterns also showed that besides the treatment the date of sampling could have contributed to modifications in the soil ammonia-oxidising bacteria community, thereby indicating that the soil itself may influence the community diversity more strongly than the treatments.

Sidestream partial nitritation and deammonification (pN/A) of high-strength ammonia wastewater is a well-established technology. Its expansion to the mainstream is, however mainly impeded by poor retention of anaerobic ammonia oxidizing bacteria (AnAOB), insufficient repression of nitrite oxidizing bacteria (NOB) and difficult control of soluble chemical oxygen demand and nitrite levels. At the municipal wastewater treatment plant in Strass (Austria) the microbial consortium was exhaustively monitored at full-scale over one and a half year with regular transfer of sidestream DEMON® biomass and further retention and enrichment of granular anammox biomass via hydrocyclone operation. Routine process parameters were surveyed and the response and evolution of the microbiota was followed by molecular tools, ex-situ activity tests and further, AnAOB quantification through particle tracking and heme measurement. After eight months of operation, the first anaerobic, simultaneous depletion of ammonia and nitrite was observed ex-situ, together with a direction to higher nitrite generation (68% of total NOx-N) as compared to nitrate under aerobic conditions. Our dissolved oxygen (DO) scheme allowed for transient anoxic conditions and had a strong influence on nitrite levels and the NOB community, where Nitrobacter eventually dominated Nitrospira. The establishment of a minor but stable AnAOB biomass was accompanied by the rise of Chloroflexi and distinct emergence of Chlorobi, a trend not seen in the sidestream system. Interestingly, the most pronounced switch in the microbial community and noticeable NOB repression occurred during unfavorable conditions, i.e. the cold winter season and high organic load. Further abatement of NOB was achieved through bioaugmentation of aerobic ammonia oxidizing bacteria (AerAOB) from the sidestream-DEMON® tank. Performance of the sidestream pN/A was not impaired by this operational scheme and the average volumetric nitrogen removal rate of the mainstream even doubled in the second half of the monitoring campaign. We conclude that a combination of both, regular sidestream-DEMON® biomass transfer and granular SRT increase via hydrocyclone operation was crucial for AnAOB establishment within the mainstream.

A globally increased demand for fuels and environmental concerns regarding fossil sources call for sustainable alternatives. Fast pyrolysis is a promising approach for converting different types of biomass to renewable Fast Pyrolysis Bio-Oil (FPBO) that can be used for heating, power generation and mobility. Side-products emerging from the process include low calorific gases and charcoal. Both are further combusted to generate energy for the process. From the charcoal, the process leaves behind fly ashes (FAs) that contain macro- and micronutrients. In this regard, FPBO-FAs might present valuable soil fertilizers, but also bear the risk of soil heavy metal (HM) contamination. In this study, the risk and potential benefit of FPBO-FAs derived from three different biomass sources (bark, forest residue and Miscanthus sp.) as soil amendments was tested. Twice, in autumn 2017 and 2018, FPBO-FAs were applied to the field (500 kg ash ha-1 y-1) in a grassland experiment. Neither physico-chemical and microbiological soil properties nor plant yield were affected following FPBO-FAs application. Seasonal differences and changes from year to year, however, were evident, both for some soil and plant properties. The lack of effects on (i) plant yield, (ii) soil microbiological and physicochemical properties, (iii) heavy metal concentrations in soil and plant suggest that the product may safely be applied. The fact that these field-trial results are in discordance with previous greenhouse trials suggest, however, that long-term trials would be needed.