Anaerobic Digestion Of Algal Biomass Research Articles

Effects of different thermal and thermochemical pretreatments on the anaerobic digestion of algal biomass cultivated in urban wastewater and collected with and without chemical coagulants

Algal biomass cultivated in wastewater treatment systems is a promising feedstock for biogas production through anaerobic digestion. However, its rigid cell wall inhibits the hydrolysis of intracellular substances and limits its anaerobic digestibility. To improve anaerobic biodegradability, this study investigated the effects of different thermal and thermochemical pretreatments on the performance of anaerobic digestion of the obtained biomass. High-rate algal ponds fed with UASB effluent treating domestic sewage were used to grow algal biomass. Two methods were used for biomass harvesting: a physical method, through filtration, and a physico-chemical method, using coagulants, Tanfloc SL and Aluminum Sulfate (Al2(SO4)3). Three types of biomasses were obtained, one without coagulant (AB-P), one with Tanfloc (AB-T), and one with Al2(SO4)3 (AB-AS), which were subjected to different thermal and thermochemical pretreatments. Fourier-transform infrared spectroscopy analysis confirmed the effectiveness of the pretreatment methods, showing modifications in the structures of proteins, carbohydrates, and lipids in the microalgae cells. The alkaline thermochemical pretreatment (90 °C-3 h-pH 11) of AB-AS resulted in higher organic matter solubilization, with a 32 % increase in soluble COD. This pretreatment also resulted in the highest biogas yield, producing 460.64 mL CH4.gVS−1, with a 229 % increase, and the highest maximum production rate, with Rmax = 78.98 mL CH4.gVS−1.day−1. Acidic thermochemical pretreatments that resulted in biomass with pH ≤ 4.2 inhibited biogas production. In terms of energy, the best pretreatment was 78 °C-7 h on AB-P, with an EROI of 2.20, which demonstrates a surplus of energy. These findings underscore the potential for optimizing the anaerobic digestibility of algal biomass, thus contributing to more efficient and sustainable biogas production.

Microalgae and Cyanobacteria Biomass Pretreatment Methods: A Comparative Analysis of Chemical and Thermochemical Pretreatment Methods Aimed at Methane Production

Anaerobic digestion of microalgae and cyanobacteria was first proposed as a destination for algal biomass accumulated on stabilization ponds since it could not be disposed of directly in the environment. Now, the versatility of algal biomass makes them a suitable candidate to produce biofuels and other biomolecules in biorefineries. Anaerobic digestion of biomass is advantageous because it does not require the extraction of specific cellular constituents or drying of the biomass. Nevertheless, challenges remain regarding biomass concentration and their resistant cell walls, which are factors that could hamper methane yield. Many pretreatment methods, including chemical and thermochemical, have been proposed to break down the complex polymers present on the cell wall into smaller molecules. Unfortunately, the relationship between biomass solubilization and methane yield is not well defined. This article intends to review the anaerobic digestion of algal biomass and the role of chemical and thermochemical pretreatments in enhancing methane production. Several pretreatment conditions selected from the scientific literature were compared to verify which conditions actually improve methane yield. The severity of the selected pretreatments was also assessed using the combined severity factor. Results suggest that thermochemical pretreatment in less severe conditions is the most efficient, leading to a greater increase in methane yield. Only enzymatic pretreatments and some thermal pretreatments result in a positive energy balance. The large-scale implementation of pretreatment methods requires technological innovations to reduce energy consumption and its integration with other processes in wastewater treatment plants.

Energy recovery by anaerobic digestion of algal biomass from integrated microalgae/constructed wetland wastewater treatment.

The present study evaluated the potential for biogas generation from microalgae (MA) biomass and macrophytes used in vertical flow constructed wetlands (VFCW). The samples were obtained by separation and collection of MA after a hydraulic retention time of 14 days, frozen and taken to the laboratory, while the macrophytes of VFCW were obtained, by pruning, every 6 months. The obtained results presented reductions of 63.22% and 61.18% for COD and BOD5, respectively, and removal efficiencies of 53.91% for TP and 99.98% de N-NH3. Average biogas generation was 2322.51 NmL-gSV−1 with 54.61% CH4 (winter/2019), 4491.47 Nml-gSV−1 with 57.17% CH4 (spring/2019), 680.78 NmL-gSV−1 with 16.04% CH4 (summer/2020), and 681.0 NmL-gSV−1 with 19.86% CH4 (autumn/2020) for MA biomass and generation of biogas of 3826.70 NmL-gSV−1 with 44.26% CH4 for VFCW biomass in winter and spring/2019 and of 829.68 NmL-gSV−1 with 17.06% CH4 in summer and autumn/2020. Regarding electricity generation, the present work obtained 1.50 kWh/m3, therefore reaching similar values to other studies that used more traditional biomass sources.

Effect of Autoclave Pretreatment on Biogas Production through Anaerobic Digestion of Green Algae

Anaerobic Digestion (AD) is one of the most widely used methods in the field of sustainable bioenergy production from various feedstock. One such feedstock is algae waste which has become an increasingly serious environmental problem. AD of algal biomass is hindered by the presence of resistant cell walls; hence a pretreatment step is usually required to decompose the cell wall structure. This study uses green algae (Enteromorpha) and anaerobic sludge as raw materials to explore the impact of autoclave (AC) pretreatment on biogas production. AC pretreatment was performed at 120 °C and 80 °C. The cumulative biogas production of the 120 °C AC pretreatment, 80 °C AC pretreatment and control group were 600 mL, 450 mL and 400 mL, respectively. The results showed that AC pretreatment improved the biodegradability of biomass as 120 °C AC pretreatment group achieved higher degradation rate of cells (95.99 %). The energy evaluation showed that the net energy ratio of the 120 °C AC pretreatment group was 1.07, indicating high overall energy gain via AD process. The experimental data is further modeled by using Modified Gompertz Model (MGM) and Logistic Function Model (LFM). To check the applicability of better model for this AD process, an Akaike Information Criteria (AIC) test was performed. AIC showed that the MGM is basically consistent with the experimental data and more reliable for prediction modeling of Enteromorpha AD.

Biomethane production from whole and extracted algae biomass: Long-term performance evaluation and microbial community dynamics

Anaerobic digestion (AD) experiments were conducted on an industrial algae strain of Nannochloropsis salina in two identical 5-liter digesters for about 300 days. One digester was fed with whole cell algal biomass (WCB) while another with lipid-extracted algal biomass residues (LEB). WCB digester shows higher specific methane productivity ranging from 0.59 to 0.65 m3 CH4/kgVS, while that in LEB digester ranges from 0.29 to 0.42 m3 CH4/kgVS. Results show that organic loading rate (OLR) in LEB digester can reach up to 5.0 gVS/L/d, and WCB digester failed at that of 3.0 gVS/L/d since long-chain fatty acids (LCFA) were identified as the main inhibitor during AD of algal biomass. At these two maximum OLR, both WCB and LEB digester could achieve a volumetric methane production rate of 1.40 m3 CH4/m3/d. Illumina MiSeq sequencing targeting 16S rRNA genes revealed that Proteiniclasticum, Tissierella, Methanosaeta and Methanomethylovorans were dominant genus at low OLR, while Trichococcus, Levilinea Methanosaeta and Methanobacterium dominated under high OLR. Furthermore, population shifts in methanogenic archaeal communities to Methanobacterium in WCB digester were noticed as aceticlastic methanogens are more sensitive to LCFA than hydrogenotrophic methanogens.

Complementarity of Substrates in Anaerobic Digestion of Wastewater Grown Algal Biomass

The objective of this study was to apply the concept of substrate complementarity. Algal biomass cultivated in effluent (domestic or from the brewing industry) in combination with olive mill wastewater was anaerobically digested, without any pre-treatment or correction of the substrate, allowing stability of the process and improvement of the digestion unit performance. For biomass produced in domestic sewage, the substitution of 10% of its volume by olive mill wastewater resulted in a better performance, with a yield of 0.10 m3 CH4 kg−1 volatile solids and an increase of 61% in methane production, when compared to the yield from the digestion of only algal biomass. Concerning algal biomass produced in domestic sewage, among others, the high content of ash (40%) and the low content of carbohydrates (3.6%) were the main factors to be overcome with the addition of complementary substrate. Regarding the algal biomass produced in brewing effluent, proportions of up to 20% of olive mill wastewater could be used without inhibiting anaerobic activity, however, a period of adaptation of the inoculum should be considered. Due to its more balanced chemical composition, biomass from the brewing industry alone presented better yield in methane production; 0.16 m3 CH4 kg−1 volatile solids, 14% higher than when digested together with 10% of the volume of olive mill wastewater substrate. The best performance of anaerobic digestion of algal biomass with another substrate was not related to the carbon–nitrogen ratio used. Therefore, other characteristics have influenced the algal biomass anaerobic process, such as the chemical constitution of algal biomass, mostly associated with the type of medium where it was cultivated.

A Brief Review of Anaerobic Digestion of Algae for Bioenergy

The potential of algal biomass as a source of liquid and gaseous biofuels has been the subject of considerable research over the past few decades, with researchers strongly agreeing that algae have the potential of becoming a viable aquatic energy crop with a higher energy potential compared to that from either terrestrial biomass or municipal solid waste. However, neither microalgae nor seaweed are currently cultivated solely for energy purposes due to the high costs of harvesting, concentrating and drying. Anaerobic digestion of algal biomass could theoretically reduce costs associated with drying wet biomass before processing, but practical yields of biogas from digestion of many algae are substantially below the theoretical maximum. New processing methods are needed to reduce costs and increase the net energy balance. This review examines the biochemical and structural properties of seaweeds and of microalgal biomass that has been produced as part of the treatment of wastewater, and discusses some of the significant hurdles and recent initiatives for producing biogas from their anaerobic digestion.

Cultivation of native algal consortium in semi-continuous pilot scale raceway pond for greywater treatment coupled with potential methane production

The native algal consortium, collected from wastewater pond, was grown in greywater and the process was scaled up in open ponds raceway (800L). It showed good growth along with removal of various nutrients concentration such as ammonia, nitrate, dissolved phosphate and sCOD below safe discharge limits, in both batch (flask study) and raceway ponds. The algal biomass thus obtained was rich in lipid (45.87% TS). The estimated theoretical methane potential was 745.87mL CH4 g−1 VS while experimental cumulative yield of up to 630mL CH4 g−1 VS (calculated based on the VS conversion into methane during anaerobic digestion) was observed during 30 d anaerobic digestion of algal biomass. The digestibility of the algal biomass was low (37%) with only 44% volatile solid reduction. The tested consortium has good potential for wastewater treatment coupled with substantial biomass production. However, further attempts for pretreatment and codigestion are essential to improve the methane yield and digestibility of the tested algal biomass.

Effect of constant magnetic field on anaerobic digestion of algal biomass

ABSTRACTThe aim of the study was to determine the impact of the constant magnetic field (CMF) application on the effectiveness of anaerobic digestion of algal biomass. The highest yield of biogas in the range of 448.9 L/kg volatile solids (VS) to 456.6 L/kg VS was observed in the variants, in which the retention time in the CMF-exposed area ranged from 144 to 216 min/d. Under these conditions, the concentration of methane in the biogas was nearly 65.0%. The increase in the contact time of the fermentation medium with the CMF-exposed area had a significant impact of reducing the effectiveness of anaerobic digestion. The lowest biodegradation was observed when the retention time was 432 min/d. Under such condition, 281.1 L of biogas/kg VS with methane content of 41.8% was obtained. A correlation between the time of exposure to CMF and the values of parameters characterizing the methane production was found.

Mechanism, kinetics and microbiology of inhibition caused by long-chain fatty acids in anaerobic digestion of algal biomass.

BackgroundOleaginous microalgae contain a high level of lipids, which can be extracted and converted to biofuel. The lipid-extracted residue can then be further utilized through anaerobic digestion to produce biogas. However, long-chain fatty acids (LCFAs) have been identified as the main inhibitory factor on microbial activity of anaerobic consortium. In this study, the mechanism of LCFA inhibition on anaerobic digestion of whole and lipid-extracted algal biomass was investigated with a range of calcium concentrations against various inoculum to substrate ratios as a means to alleviate the LCFA inhibition.ResultsWhole algal biomass of Nannochloropsissalina represents high lipid content algal biomass while lipid-extracted residue represents its low lipid counterpart. The anaerobic digestion experiments were conducted in a series of serum bottles at 35 °C for 20 days. A kinetic model, considering LCFA inhibition on hydrolysis, acidogenesis as well as methanogenesis steps, was developed from the observed phenomenon of inhibition factors as a function of the LCFA concentration and specific biomass content or calcium concentration. The results showed that inoculum to substrate ratio had a stronger effect on biogas production than calcium, and calcium had no effect on biogas production when inoculum concentration was extremely low. The microbial community analysis by high-throughput Illumina Miseq sequencing indicated that diversity of both bacterial and methanogenic communities decreased with elevation of lipid concentration. Hydrolytic bacteria and aceticlastic methanogens dominated bacterial and archaea communities, respectively, in both high and low LCFA concentration digesters.ConclusionsThis study demonstrated that inoculum concentration has a more significant effect on alleviating LCFA inhibition than calcium concentration, while calcium only played a role when inoculum concentration met a threshold level. The model revealed that each functional microbial group was subject to different levels of LCFA inhibition. Although methanogens were the most susceptible microbes to LCFA inhibition, the inhibition factor for hydrolytic bacteria was more highly affected by inoculum concentration. The microbial community analysis indicated that the bacterial community was affected more than the methanogenic community by high LCFAs concentration. Syntrophic acetogens were sensitive to high LCFA concentrations and thus showed a decreased abundance in such an environment. Graphical abstractProposed mechanism of calcium mitigated LCFA inhibition

Goethite promoted anaerobic digestion of algal biomass in continuous stirring-tank reactors

With the depletion of fossil energy, third-generation biofuel feedstocks represented by micro- and macro-algae have significant advantages. It has been shown that anaerobic digestion of algae is a simple and cost-effective strategy. In this study, goethite was added to continuous stirred-tank reactors (CSTRs) to promote the methanogenesis of algal biomass. The results indicated that biogas and methane production increased by 16.1% and 24.1%, respectively. Goethite increased the conversion efficiency of the acidogenic and methanogenic phases. Goethite supplementation influenced the bacterial and methanogenic community significantly, which further enhanced the syntrophic effects between acidogenic and methanogenic microorganisms. The results confirmed that goethite could promote the anaerobic digestion of algal biomass in a CSTR, demonstrating its potential application to accelerate methane production process.

Ultrasound pretreatment of filamentous algal biomass for enhanced biogas production

The filamentous alga Hydrodictyon reticulatum harvested from a bench-scale wastewater treatment pond was used to evaluate biogas production after ultrasound pretreatment. The effects of ultrasound pretreatment at a range of 10–5000J/mL were tested with harvested H. reticulatum. Cell disruption by ultrasound was successful and showed a higher degree of disintegration at a higher applied energy. The range of 10–5000J/mL ultrasound was able to disintegrated H. reticulatum and the soluble COD was increased from 250mg/L to 1000mg/L at 2500J/mL. The disintegrated algal biomass was digested for biogas production in batch experiments. Both cumulative gas generation and volatile solids reduction data were obtained during the digestion. Cell disintegration due to ultrasound pretreatment increased the specific biogas production and degradation rates. Using the ultrasound approach, the specific methane production at a dose of 40J/mL increased up to 384mL/g-VS fed that was 2.3times higher than the untreated sample. For disintegrated samples, the volatile solids reduction was greater with increased energy input, and the degradation increased slightly to 67% at a dose of 50J/mL. The results also indicate that disintegration of the algal cells is the essential step for efficient anaerobic digestion of algal biomass.

High pressure thermal hydrolysis as pre-treatment to increase the methane yield during anaerobic digestion of microalgae

Anaerobic digestion of algal biomass will be an essential component of algal biofuel production systems, yet the methane yield from digestion of algae is typically much lower than the theoretical potential. In this work, high pressure thermal hydrolysis (HPTH) is shown to enhance methane yield during algae digestion. HPTH pre-treatment was applied to both raw algae and algal residue resulting from lipid extraction. HPTH and even the lipid extraction process itself increased methane yield, by 81% and 33% respectively; in combination they increased yield by 110% over that of the raw algae (18L CH4 gVS−1 substrate). HPTH had little effect on the rate of anaerobic digestion, however lipid extraction enhanced it by 33% over that for raw algae (0.21day−1). Digestion resulted in solubilisation of nitrogen (and phosphorous to a lesser degree) in all cases, showing that there is potential for nutrient recycling for algal growth.

Production of Biodiesel and Biogas from Algae: A Review of Process Train Options

Algae are an attractive biofuel feedstock because of their fast growth rates and improved land use efficiency when compared with terrestrial crops. Process train components needed to produce algal biofuels include (1) cultivation, (2) harvesting, and (3) conversion into usable fuel. This paper compares various process train options and identifies knowledge gaps presently restricting the production of algal biodiesel and algae-derived biogas. This analysis identified energy-intensive processing and the inability to cultivate large quantities of lipid-rich algal biomass as major obstacles inhibiting algal biodiesel production. Anaerobic digestion of algal biomass requires fewer process train components and occurs regardless of lipid content. In either scenario, the use of wastewater effluent as a cultivation medium seems necessary to reduce greenhouse gas emissions and maximize water use efficiency. Furthermore, anaerobically digesting algal biomass generated from low-technology wastewater treatment processes represents an appropriate technology approach to algal biofuels that is poorly investigated. Coupling these processes can improve global health by improving sanitation, while providing a cleaner burning biogas alternative to indoor biomass cooking systems typical of less-developed areas.

Nutrient Removal & Greenhouse Gas Abatement with CO2 Supplemented Algal High Rate Ponds

High rate algae ponds fed clarified domestic wastewater and CO2-rich flue gas are expected to remove nutrients to concentrations similar to those achieved in mechanical treatment technologies, such as activated sludge. However, the energy intensity of wastewater treatment with CO2-supplemented high rate ponds (HRPs) would be less than that of mechanical treatments. In conjunction with anaerobic digestion of algal biomass and co-substrates, the algae-based system would produce a substantial excess of electricity. Greenhouse gas abatement from such CO2-HRP/digestion systems would stem mainly from energy conservation and the offset of fossil fuel electricity with biogas-derived electricity. Laboratory experiments showed nutrient removals of >98% for ammonium and >96% for phosphorus with mixed culture microalgae grown on CO2-supplemented primary wastewater effluent. An engineering numerical model for CO2-HRP/digestion facilities (based in part on large-scale algae production under southern California conditions) indicates a potential energy surplus of 330 kWh/ML (1,200 kWh/MG) from biogas-derived electricity, compared to the net energy consumption of about 760 kWh/ML (2,900 kWh/MG) at typical activated sludge facilities with nitrification/denitrification. Considering the net electricity production and energy savings of the CO2-HRP/digestion systems, a greenhouse gas abatement potential of 660 kg CO2eq/ML (2,500 kg CO2eq/MG) treated is expected for a 100-ha facility treating 20 MGD.

Biogas production from anaerobic digestion of Spirulina maxima algal biomass

Biotechnology and BioengineeringVolume 24, Issue 8 p. 1919-1924 Communication to the Editor Biogas production from anaerobic digestion of Spirulina maxima algal biomass Réjean Samson, Réjean Samson Department of Chemical Engineering, Laval University, Sainte-Foy, Qué, Canada G1K 7P4Search for more papers by this authorAnh Leduy, Anh Leduy Department of Chemical Engineering, Laval University, Sainte-Foy, Qué, Canada G1K 7P4Search for more papers by this author Réjean Samson, Réjean Samson Department of Chemical Engineering, Laval University, Sainte-Foy, Qué, Canada G1K 7P4Search for more papers by this authorAnh Leduy, Anh Leduy Department of Chemical Engineering, Laval University, Sainte-Foy, Qué, Canada G1K 7P4Search for more papers by this author First published: August 1982 https://doi.org/10.1002/bit.260240822Citations: 89AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume24, Issue8August 1982Pages 1919-1924 RelatedInformation