The cyanobacterial genus Synechocystis is of particular interest to science and industry because of its efficient phototrophic metabolism, its accumulation of the polymer poly(3-hydroxybutyrate) (PHB) and its ability to withstand or adapt to adverse growing conditions. One such condition is the increased salinity that can be caused by recycled or brackish water used in cultivation. While overall reduced growth is expected in response to salt stress, other metabolic responses relevant to the efficiency of phototrophic production of biomass or PHB (or both) have been experimentally observed in three Synechocystis strains at stepwise increasing salt concentrations. In response to recent reports on metabolic strategies to increase stress tolerance of heterotrophic and phototrophic bacteria, we focused particularly on the stress-induced response of Synechocystis strains in terms of PHB, glycogen and photoactive pigment dynamics. Of the three strains studied, the strain Synechocystis cf. salina CCALA192 proved to be the most tolerant to salt stress. In addition, this strain showed the highest PHB accumulation. All the three strains accumulated more PHB with increasing salinity, to the point where their photosystems were strongly inhibited and they could no longer produce enough energy to synthesize more PHB.

Cyanobacteria are a large group of prokaryotic microalgae that are able to grow photo-autotrophically by utilizing sunlight and by assimilating carbon dioxide to build new biomass. One of the most interesting among many cyanobacteria cell components is the storage biopolymer polyhydroxybutyrate (PHB), a member of the group of polyhydroxyalkanoates (PHA). Cyanobacteria occur in almost all habitats, ranging from freshwater to saltwater, freely drifting or adhered to solid surfaces or growing in the porewater of soil, they appear in meltwater of glaciers as well as in hot springs and can handle even high salinities and nutrient imbalances. The broad range of habitat conditions makes them interesting for biotechnological production in facilities located in such climate zones with the expectation of using the best adapted organisms in low-tech bioreactors instead of using “universal” strains, which require high technical effort to adapt the production conditions to the organism‘s need. These were the prerequisites for why and how we searched for locally adapted cyanobacteria in different habitats. Our manuscript provides insight to the sites we sampled, how we isolated and enriched, identified (morphology, 16S rDNA), tested (growth, PHB accumulation) and purified (physical and biochemical purification methods) promising PHB-producing cyanobacteria that can be used as robust production strains. Finally, we provide a guideline about how we managed to find potential production strains and prepared others for basic metabolism studies.

Acetic acid is an essential industrial building block and can be produced by acetogenic bacteria from molecular hydrogen (H2) and carbon dioxide (CO2). When gasses are supplied as substrates, bioreactor design plays an important role for their availability. Trickle-bed bioreactors (TBs) have an enhanced gas-to-liquid mass transfer and cells remain in the system by forming a biofilm on the carriers. So far, TBs have been investigated extensively for bio-methanation processes, whereas studies for their use in acetic acid production are rare. In this study, we evaluated the reproducibility of two parallel TBs for acetic acid production from H2:CO2 (= 70:30) by a mixed culture with a gas flow rate of 3.8 mL min−1 and a medium flow rate of 10 mL min−1. Additionally, the effect of glucose addition during the starting phase on the resulting products and microbial composition was investigated by setting up a third TB2. Partial medium exchanges to decrease the internal acetic acid concentration (AAC) combined with recycling of withdrawn cells had a positive impact on acetic acid production rates with maxima of around 1 g L−1 d−1 even at high AACs of 19–25 g L−1. Initial glucose addition resulted in the accumulation of unwanted butyric acid up to concentrations of 2.60 ± 0.64 g L−1. The maximum AAC of 40.84 g L−1 was obtained without initial glucose addition. The main families identified in the acetogenic TBs were Peptococcaceae, Ruminococcaceae, Planococcaceae, Enterobacteriaceae, Clostridiaceae, Lachnospiraceae, Dysgonomonadaceae and Tannerellaceae. We conclude that a TB is a viable solution for conversion of H2/CO2 to acetate using an anaerobic enrichment culture.

The interest in microalgae products has been increasing, and therefore the cultivation industry is growing steadily. To reduce the environmental impact and production costs arising from nutrients, research needs to find alternatives to the currently used artificial nutrients. Microalgae cultivation in anaerobic effluents (more specifically, digestate) represents a promising strategy for increasing sustainability and obtaining valuable products. However, digestate must be processed prior to its use as nutrient source. Depending on its composition, different methods are suitable for removing solids (e.g., centrifugation) and adjusting nutrient concentrations and ratios (e.g., dilution, ammonia stripping). Moreover, the resulting cultivation medium must be light-permeable. Various studies show that growth rates comparable to those in artificial media can be achieved when proper digestate treatment is used. The necessary steps for obtaining a suitable cultivation medium also depend on the microalgae species to be cultivated. Concerning the application of the biomass, legal aspects and impurities originating from digestate must be considered. Furthermore, microalgae species and their application fields are essential criteria when selecting downstream processing methods (harvest, disintegration, dehydration, product purification). Microalgae grown on digestate can be used to produce various products (e.g., bioenergy, animal feed, bioplastics, and biofertilizers). This review gives insight into the origin and composition of digestate, processing options to meet requirements for microalgae cultivation and challenges regarding downstream processing and products.

This abstract gives a glimpse of the output revealed in a project focusing on recycling used medium from algae cultivation. In close cooperation with the University of Natural Resources and Life Sciences Vienna, the Institute of Microbiology - The Czech Academy of Sciences as well as the algae biomass production company Ecoduna GmbH, it was possible to target industrial needs with scientific research approaches.

Starch production is mainly focused on feedstocks such as corn, wheat and potato in the EU, whereas cassava, rice, and other feedstocks are utilised worldwide. In starch production, a high amount of wastewater is generated, which accumulates from different process steps such as washing, steeping, starch refining, saccharification and derivatisation. Valorisation of these wastewaters can help to improve the environmental impact as well as the economics of starch production. Anaerobic fermentation is a promising approach, and this review gives an overview of the different utilisation concepts outlined in the literature and the state of the technology. Among bioenergy recovery processes, biogas technology is widely applied at the industrial scale, whereas biohydrogen production is used at the research stage. Starch wastewater can also be used for the production of bulk chemicals such as acetone, ethanol, butanol or lactic acids by anaerobic microbes.

The food and beverage industry offers a wide range of organic feedstocks for use in biogas production by means of anaerobic digestion (AD). Microorganisms convert organic compounds—solid, pasty, or liquid ones—within four steps to biogas mainly consisting of CH₄ and CO₂. Therefore, various conversion technologies are available with several examples worldwide to show for the successful implementation of biogas technologies on site. The food and beverage industry offer a huge potential for biogas technologies due to the sheer amount of process residues and their concurrent requirement for heat and power. The following study analyzes specific industries with respect to their implementation potential based on arising waste and heat and power demand. Due to their chemical composition, several feedstocks are resistant against microbiological degradation to a great extent. A combination of physical-, chemical-, and microbiological pretreatment are used to increase the biological availability of the feedstock. The following examples will discuss how to best implement AD technology in industrial processes. The brewery industry, dairy production, slaughterhouses, and sugar industry will serve as examples.

Microalgal biomass as a feedstock for biogas production is linked to the parameters biomass productivity and biogas yield. Besides an easy-to-use strain for anaerobic digestion, the photobioreactor (PBR) design is important. A microalgae strain selection revealed Eustigmatos magnus (SAG 36.89) as the most promising strain yielding an average of 100 mg total suspended solids (TSS) L−1 day−1. The strain was tested in cost-effective sleevebag-PBR-systems of 10 cm, 20 cm and 30 cm diameter facing the light from the front or laterally. Highest mean productivity on a volumetric basis was measured in PBRs with the lowest diameter (104 and 117 mg L−1 day−1. The highest productivity per m−2 was achieved in 10 cm PBRs with front light configuration (9.35 g TSS m−2 day−1). The lateral light configuration of 10 cm PBRs had positive aspects such as the lowest mean water demand to produce 1 kg TSS (481 L−1 kg−1) and the lowest mean energy demand for medium separation of 1 kg TSS (106 Wh). The concentrated microalgal biomass was then subjected to ultrasonication and thermal pre-treatment (90 °C and 120 °C) and tested in BMP tests. Mesophilic anaerobic mono-digestion of untreated microalgae biomass led to a methane (CH4) yield of 343 L−1 kg−1 volatile solids (VS). Thermal pre-treatment at 120 °C resulted in significantly increased CH4 yields of 430 L−1 kg−1 VS. As thermal pre-treatment can be easily installed nearby a biogas plant it could be an interesting option for AD of microalgal biomass with only little investment.

Climate change affects the frequency and intensity of extreme weather, the results of which include production losses and climate-induced crop productivity fluctuations.

Double-cropping systems (DCSs) have been suggested as a way to increase biomass-production while simultaneously delivering environmental benefits. In a three-year field-test, two DCSs based on maize and sorghum as the main crop and rye as the preceding winter crop were compared with each other and compared with 2 single-cropping systems (SCSs) of maize or sorghum; there were comparisons of growth dynamics, optimal harvesting and growing time as well as biomass and methane yield. In addition, the impact of variety and harvest time on the winter rye optimal biomass yield was studied.

The experiments clearly showed the superiority of the DCS over the SCS. Within the DCS, the rye/sorghum combination achieved significantly higher biomass yields compared to those of the rye/maize combination. The highest dry matter biomass yield was achieved during year 1 at 27.5 ± 2.4 t∙ha−1, during which winter rye contributed 8.3 ± 0.7 t∙ha−1 and sorghum contributed 19.2 ± 1.8 t∙ha−1. At the experimental location, which is influenced by a Pannonia climate (hot and dry), the rye/sorghum DCS was able to obtain average methane yields per hectare, 9300 m3, whereas the rye/maize combination reached 7400 m3. In contrast, the rye, maize and sorghum SCSs achieved methane yields of 4800, 6100 and 6500 m3 ha−1, respectively. The study revealed that the winter rye and sorghum DCS is a promising strategy to counteract climate change and thus guarantee crop yield stability.

The microalga Acutodesmus obliquus was investigated as a feedstock in semi-continuously fed anaerobic digestion trials, where A. obliquus was co-digested with pig slurry and maize silage. Maize silage was substituted by both 10% and 20% untreated, and 20% ultrasonicated microalgae biomass on a VS (volatile solids) basis. The substitution of maize silage with 20% of either ultrasonicated and untreated microalgae led to significantly lower biogas yields, i.e., 560 dm³ kg⁻¹ VS_corr in the reference compared to 516 and 509 dm³ kg^-1VS_corr for untreated and ultrasonicated microalgae substitution. Further, the viscosities in the different reactors were measured at an OLR of 3.5 g VS dm^-3 d^-1. However, all treatments with microalgae resulted in significantly lower viscosities. While the mean viscosity reached 0.503 Pa s in the reference reactor, mean viscosities were 53% lower in reactors where maize was substituted by 20% microalgae, i.e. 0.239 Pa s, at a constant rotation speed of 30 rpm. Reactors where maize was substituted by 20% ultrasonicated microalgae had a 32% lower viscosity, for 10% microalgae substitution a decrease of 8% was measured. Decreased viscosities have beneficial effect on the bioprocess and the economy in biogas plants. Nonetheless, with regard to other parameters, no positive effect on biogas yields by partial substitution with microalgae biomass was found. The application of microalgae may be an interesting option in anaerobic digestion when fibrous or lignocellulosic substances lead to high viscosities of the digested slurries. High production costs remain the bottleneck for making microalgae an interesting feedstock.

Political, economic and ecological reasons have recently been leading to efforts to replace fossil hydrocarbons and their products in a sustainable way. In order to replace fossil-based polymers, photoautotrophically produced polyhydroxybutryrates (PHBs), which are intracellular carbon storage products of nutrient-deprived microorganisms, seem to be a promising, biobased and biodegradable alternative. Although laboratory and pilot scale experiments have already been performed, no economic evaluation has been carried out so far. Consequently, valid claims on PHB production costs and the influence of different parameters, such as intracellular PHB-content, choice of cultivation system or location, cannot be made. In this study potential demonstration plants, equipped with different photoautotrophic cultivation systems and located at two sites, were designed to identify key parameters for a successful economic realization and implementation. Material and energy balances were determined to reveal specific PHB production costs for four different scenarios. Raw material and operating supply costs, expenditures for plant construction and operation as well as product amounts were determined using literature data for specified results from laboratory and pilot scale experiments. The lowest calculated PHB production price (24 € kg−1) accomplished in a thin-layer-system plant located in Southern Europe with 60% PHB-content of the produced biomass is significantly higher than the current market price of heterotrophically produced PHB. The most important cost factors in all scenarios are cultivation and harvesting costs accounting for 62 to 72% of the total specific production costs, followed by maintenance costs with a cost share of 11 to 14%. Therefore, the choice of a suitable cultivation system is the key driving factor for an economic PHB-production due to the currently high investment costs for photosynthetic biomass production systems. Specific production costs for a Southern compared to a Central European location amount to almost half of the costs.