No abstract

The extraction of lipids from microalgae cells of Botryococcus braunii and Chlorella vulgaris after ultrasonic and microwave pretreatment was evaluated. Cell disruption increased the lipid extraction efficiency, and microwave pretreatment was more effective compared with ultrasonic pretreatment. The maximum lipid yield from B. braunii was 56.42% using microwave radiation and 39.61% for ultrasonication, while from C. vulgaris, it was respectively 41.31% and 35.28%. The fatty acid composition in the lipid extracts was also analyzed. The methane yield from the residual extracted biomass pretreated by microwaves ranged from 148 to 185 NmL CH4/g VS for C. vulgaris and from 128 to 142 NmL CH4/g VS for B. braunii. In the case of ultrasonic pretreatment, the methane production was between 168 and 208 NmL CH4/g VS for C. vulgaris, while for B. braunii ranging from 150 to 174 NmL CH4/g VS. Anaerobic digestion showed that lipid-extracted biomass presented lower methane yield than non-lipid-extracted feedstock, and higher amount of lipid obtained in the extraction contributed less methane production. Anyway, anaerobic digestion of the residual extracted biomass can be a suitable method to increase economic viability of energy recovery from microalgae.

Hydrodynamic cavitation was recently applied as a biomass pretreatment method. Most of the studies which used hydrodynamic cavitation were applied to pretreated sugarcane bagasse or reed. High biomass yield of Sida hermaphrodita points out the necessity of studies on its effective pretreatment before methane fermentation, especially because its “wood-like” characteristics could present different disintegration properties than other lignocellulose biomass. Thus, the aim of the study was to investigate the influence of duration of hydrodynamic cavitation on lignocellulose composition in Sida hermaphrodita silage, and the assessment of disintegrated biomass as a substrate for methane fermentation. The study showed a slight decrease in lignin, cellulose, and hemicellulose content in biomass after hydrodynamic cavitation, which resulted in a higher content of carbohydrates in the liquid fraction of disintegrated substrates. Methane production was 439.1 ± 45.0 L CH4/kg total solids (TS) from the substrate disintegrated for 20 min. However, the most effective time for methane production was hydrodynamic cavitation of the substrate for 5 min. At this pretreatment duration, the highest values for chemical oxygen demand (COD), total organic carbon (TOC), and carbohydrate reduction were also noted. The study proved that hydrodynamic cavitation applied for 5 min allowed obtaining an energy profit of 0.17 Wh/g TS. The studies on a laboratory scale indicated that the technology of hydrodynamic cavitation of Sida hermaphrodita could be economically applied for methane fermentation on a large scale.

The aim of this study was to determine the effects on methane production of the addition of microalgae biomass of Arthrospira platensis and Platymonas subcordiformis to the common feedstock used in agricultural biogas plants (cattle manure, maize silage). Anaerobic biodegradability tests were carried out using respirometric reactors operated at an initial organic loading rate of 5.0 kg volatile solids (VS)/m3, temperature of 35°C, and a retention time of 20 days. A systematic increase in the biogas production efficiency was found, where the ratio of microalgae biomass in the feedstock increased from 0% to 40% (%VS). Higher microalgae biomass ratio did not have a significant impact on improving the efficiency of biogas production, and the biogas production remained at a level comparable with 40% share of microalgae biomass in the feedstock. This was probably related to the carbon to nitrogen (C/N) ratio decrease in the mixture of substrates. The use of Platymonas subcordiformis ensured higher biogas production, with the maximum value of 1058.8 ± 25.2 L/kg VS. The highest content of methane, at an average concentration of 65.6% in the biogas produced, was observed in setups with Arthrospira plantensis biomass added at a concentration of between 20%–40% to the feedstock mixture.

The aim of the study was to determine the use of digestate from anaerobic digestion of dairy wastewater as a culture medium for microalgae to obtain bio-oil. The experiments were conducted at a small scale in a closed raceway pond. The efficiency of the microalgae biomass production, the digestate treatment efficiency as well as the content and properties of the bio-oil obtained from the microalgal cells were analyzed. The produced biomass concentration was about 3000 ± 10.5 mg dry biomass/L, with an average growth rate of 160 ± 6.6 mgdm/L·d. The efficiency of organic compound and nutrient removal was above 90%. The bio-oil content in the biomass was about 20%. Based on the results of the study, a concept for technical-scale technology was developed.

One of the most important factors in determining the profitable production of microalgae biomass is the use of a cost effective growth medium that is rich in nutrients. The objective of the study was to determine the possibility of using digestates from anaerobic digestion of different feedstock mixtures as the media for Scenedesmus sp. cultivation. A different liquid digestate composition was obtained in terms of organic compounds, phosphorus, and nitrogen concentrations, depending on the substrates used in the anaerobic digestion. It was found that the highest biomass production was obtained when using digestate from anaerobic digestion of the feedstock mainly composed of microalgae biomass, which was characterized by low organic compounds concentration. In this case, the average biomass concentration reached 2382 mg total solids/L. A lower Scenedesmus sp. biomass yield was obtained using digestate from anaerobic digester processing feedstock based on maize silage and cattle menure. In the variants of the study, it was also found that the increase in the initial concentration of ammonia nitrogen in the growth medium up to 160 mg/L significantly reduced the growth of Scenedesmus sp. The results indicated the possibility of a high ammonia nitrogen and orthophosphates removal from anaerobic digestates by Scenedesmus sp. microalgae. Phosphorus concentration in the cultivation medium is a limiting factor for the growth of Scenedesmus sp., thus phosphorus supplementation should be considered when using liquid digestate as the culture medium. The optimization model indicated that the volume of liquid digestate that was used for preparing the cultivation medium, the initial concentration of organic compounds, and the initial concentration of ammonia nitrogen had a significant impact on the production of Scenedesmus sp. biomass.

The objective of the present study was to determine the effectiveness of biogas production during methane fermentation of wastewaters originating from the dairy, tanning and sugar industries, by means ofrespirometric measurements conducted at a temperature of 35 degrees C. Experiments were carried out with the use of model tanks of volume 0.5 dm3. A high production yield of biogas, with methane content exceeding 60%, was achieved in the case of the anaerobic treatment of wastewaters from the dairy and sugar industries. A significantly lower effect was observed in the case of tanning wastewaters. The effectiveness of the fermentation process decreased with increasing loading of the tanks with a feedstock of organic compounds. By loading a model tank with this feedstock, the effectiveness of treatment ranged from 62.8% to 71.4% residual chemical oxygen demand for dairy wastewaters and from 57.9% to 64.1% for sugar industry wastewaters. The efficiency of organic compound removal from tanning wastewaters was below 50%, regardless of the method applied.

Disintegration of lignocellulosic biomass for energy purposes has been extensively studied. The study aimed to investigate the influence of crushed and uncrushed lignocellulosic biomass on the biogas production in an innovative reactor. The substrate fed to the reactor was Sida hermaphrodita silage mixed with cow manure. The bioreactor had an innovative design of the mixing cage system. The mixing system of the bioreactor consisted of two cylindrical stirrers in the form of a cage. The cages simultaneously rotate around the axis of the bioreactor at against their own axes. The bioreactor is currently presented under the Record Biomap program (Horizon 2020). The bioreactor was operated at organic compounds loading of 2 kg/(m 3 •d) and 3 kg/(m 3 •d) and hydraulic retention time was 50 d and 33 d, respectively. The biogas production under the organic compounds loading of 2 kg VS/(m 3 •d) was 680 L/kg VS from crushed lignocellulosic biomass and 570 L/kg VS from uncrushed lignocellulosic biomass. The biogas production under the organic compounds loading 3 kg VS/(m 3 •d) was 730 L/kg VS from crushed lignocellulosic biomass and 630 L/kg VS from uncrushed lignocellulosic biomass. The crushing of substrate did not influence the methane content in the biogas. In all experiments, the biogas comprised about 54% of methane. The net energy efficiency was calculated as well.