• Energy Research

Hydrogen is an environmentally friendly biofuel which, if widely used, could reduce atmospheric carbon dioxide emissions. The main barrier to the widespread use of hydrogen for power generation is the lack of technologically feasible and—more importantly—cost-effective methods of production and storage. So far, hydrogen has been produced using thermochemical methods (such as gasification, pyrolysis or water electrolysis) and biological methods (most of which involve anaerobic digestion and photofermentation), with conventional fuels, waste or dedicated crop biomass used as a feedstock. Microalgae possess very high photosynthetic efficiency, can rapidly build biomass, and possess other beneficial properties, which is why they are considered to be one of the strongest contenders among biohydrogen production technologies. This review gives an account of present knowledge on microalgal hydrogen production and compares it with the other available biofuel production technologies.

Abstract The aim of the study was to determine the influence of the light source on the taxonomic structure and chemical composition of the harvested biomass, and on the fermentative biogas/methane production. Cultivation of a mixed microalgae culture was carried out in closed vertical photobioreactors equipped with different light sources. The effectiveness of anaerobic digestion was analysed by respirometric measurements. The harvested microalgae biomass was characterized by various taxonomic structures and varied chemical composition depending on the light source used during cultivation stage. In variants where warm white LED lighting and red light were used, species from the Cyanoprokaryota division predominated, characterized by a high concentration of organic compounds and nitrogen in the biomass. TOC values amounted to almost 430 mg/g TS. In the remaining variants, Chlorophyta predominated, and TOC values were in the range of 388.0–411.3 mg/g TS. A significantly higher biogas/methane production ( p = 0.05) was found in variants in which biomass with Cyanoprokaryota predominating was tested. The biogas yield was in the range of 383.2 L/kg VS to 400.8 L/kg VS, and the methane content was close to 55%. A lower effectiveness of biogas and methane formation were observed in variants with Chlorophyta as a predominating taxonomic group.

Abstract The study was aimed to compare the methane potential from the silage of Sida hermaphrodita mixed with cattle manure pretreated by microwave (MW) thermohydrolysis with liquid hot water (LHW) pretreatment. It was illustrated that both pretreatment methods significantly improved degradation of the lignocellulosic structure and improved the methane production. The maximum methane production of MW pretreated biomass was 590 NL/kg VS at 150 °C and 15 min with an improvement of 39.1% to an untreated sample. In turn, LHW treatment provided the maximum methane production of 575 NL/kg VS with the same pretreatment conditions. The net energy output significantly higher than calculated for the control sample was achieved only for MW pretreatment at 150 °C and 15–30 min. In other variants, pretreatment step needed higher energy input than the net energy gain from methane production.

The objective of this study was to determine the possibility of using microalgae biomass from natural water bodies as a substrate for methane fermentation and to verify the effect of taxonomic structure and other physicochemical traits of the biomass on the technological effectiveness of the process. Harvested algae was characterized by a diversified taxonomic structure and on the content of nitrogen compounds and concentration of organic compounds in biomass, that was subject to seasonal dynamics of changes. The highest technological effects of the methane fermentation process were achieved with microalgae biomass harvested in July. In this period, the predominating taxonomic group were the Cyanoprokaryota, with a significant contribution of Chlorophyta. The mean yield of biogas production reached 441.15 ± 19.03 cm3/g o.d.m., at the mean production rate of r = 98.99 cm3/day and a reaction constant of k = 0.224 1/day. The mean content of methane in biogas accounted for 68.68 ± 1.67%. The lowest technological effects linked with biogas production were determined in November. These were the periods of the vegetative season with Bacillariophyceae constituting the predominating taxonomic group. The total production of biogas accounted for 333.65 ± 18.85 cm3/g o.d.m. The methane content were at mean levels of 54.19 ± 2.31%. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 858–865, 2015

Regulations in force urge for thermal pre-treatment of post-slaughter waste prior to its anaerobic digestion. Increased interest in biomethane as a fuel in gas networks or vehicles of road transport forces the need to look for heating methods that are alternative to heat recovery from cogeneration. The goal of this study was to determine the synergistic effect of simultaneous ultrasound heating and disintegration on the technological efficiency and energetic balance of the anaerobic digestion of high-load slaughter poultry wastewater. The highest efficiency of anaerobic digestion was obtained for the ultrasound thermal pre-treatment (60 min, 90 °C, OLR = 2.0 gCOD/dm3). In this experimental variant, the biogas production rate reached 9.0 ± 0.2 cm3/gCOD·h, biogas yield was 492 ± 10 cm3/gCOD, and the biogas produced contained 69.8 ± 1.4% CH4. Given the incurred energy outputs, the highest net energetic efficiencies, i.e., 5.92 ± 0.43 Wh and 5.80 ± 0.42 Wh, were obtained in the variants with the conventional thermal pre-treatment (60 min, 70 °C, OLR = 6.0 gCOD/dm3) and ultrasound thermal pre-treatment (60 min, 70 °C, OLR = 6.0 gCOD/dm3), respectively.

In this study, a new reactor concept was designed for combining the advantages of anaerobic baffled reactors and biofilm reactors for treating dairy wastewater. The magneto-active microporous packing media manufactured by extrusion technology and modified by the addition of relevant amounts of metal catalysts and magnetic activation was used. The effects of active packing media placing in the different functional areas (hydrolysis or methanogenic) on the reactor performance (organic matter and nutrients removal, biogas production) were studied. The highest biogas production of 337 L/d and biogas yield of 415 mL/g CODremoved were achieved when the packing media with magnetic properties were placed in the methanogenic tanks. A stimulatory effect of placing the active packing media in methanogenic tanks on organic matter removal (86% as COD) and suspended solids elimination from wastewater were noted, however magnetic properties did not contribute higher organic matter and nutrients removal. Incorporation of metals into the plastic packing media enhanced phosphorus removal (85 - 87%).

AbstractThe 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.

The aim of presented research was to determine the influence of magnetoactive filling (MAF) on the process of anaerobic purification of model diary sewage. The research in the pilot plant scale allowed to obtain high efficiency of removing organic compounds (72–76%) and phosphorus (84–88%). Restraint of concentration of nitrogen compounds and suspensions in the outflow was observed. It was stated that effectiveness of sewage purification was directly connected to amount of MAF in the hydrolysis zone. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 427–431, 2015

Studies on harnessing solidified carbon dioxide (SCO2) for municipal sewage sludge (MSS) pre-treatment have been conducted exclusively in batch reactors. This makes it difficult to accurately assess how long-term SCO2 treatment affects anaerobic digestion (AD) conditions and performance. The aim of our study was to evaluate the effect of long-term MSS pre-treatment with SCO2 on AD conditions, anaerobic bacterial community, and biogas composition and yields. The presented experiments are the first studies on the effect of pre-treatment with SCO2 on the efficiency of AD of MSS in continuous reactors. So far, the impact of the organic load rate (OLR) on the efficiency of MSS methane fermentation has not been assessed, which is also a novelty of the conducted research. The AD process was conducted in continuous-stirred, continuous-flow anaerobic with an active volume of 20 dm3. The digestion process was run at 38 ± 1 °C. The experiment was divided into two stages. Raw (non-pretreated) MSS was used in stage 1, whereas the MSS used in stage 2 was pre-treated with SCO2. The SCO2/MSS ratio was 1:3. Each stage was sub-divided into four variants, with different levels of the OLR ranging from 2.0 to 5.0 gCOD/dm3·day. Pre-treatment with SCO2 was found to improve AD performance at an OLR of 3.0–4.0 gVS/dm3·day. The 3.0 gVS/dm3·day variant offered the best biogas production performance—both daily (29 ± 1.3 dm3/day) and per VS added (0.49 ± 0.02 dm3/gVS)—as well as the highest CH4 content in the biogas (70.1 ± 1.0%). In this variant, the highest energy output effect of 187.07 ± 1.5 Wh/day was obtained. The SCO2 pre-treatment was not found to change the pH, FOS/TAC, or the anaerobic bacterial community composition. Instead, these variables were mainly affected by the OLR. Our study shows that MSS pre-treatment with SCO2 at a SCO2/MSS ratio of 0.3 (by volume) significantly improves AD performance in terms of methane production and feedstock mineralization. The pre-treatment was found to have no negative effect on the long-term continuous operation of the reactor.