Anaerobic Digestion of Macrophytes Algae for Eutrophication Mitigation and Biogas Production

An integration of algae-mediated wastewater treatment and resource recovery through anaerobic digestion

Eutrophication is one of the major emerging challenges in aquatic environment. Industrial facilities, including food, textile, leather, and paper, generate a significant amount of wastewater during their manufacturing process. Discharge of nutrient-rich industrial effluent into aquatic systems causes eutrophication, eventually disturbs the aquatic system. On the other hand, algae provide a sustainable approach to treat wastewater, while the resultant biomass may be used to produce biofuel and other valuable products such as biofertilizers. This review aims to provide new insight into the application of algal bloom biomass for biogas and biofertilizer production. The literature review suggests that algae can treat all types of wastewater (high strength, low strength, and industrial). However, algal growth and remediation potential mainly depend on growth media composition and operation conditions such as light intensity, wavelength, light/dark cycle, temperature, pH, and mixing. Further, the open pond raceways are cost-effective compared to closed photobioreactors, thus commercially applied for biomass generation. Additionally, converting wastewater-grown algal biomass into methane-rich biogas through anaerobic digestion seems appealing. Environmental factors such as substrate, inoculum-to-substrate ratio, pH, temperature, organic loading rate, hydraulic retention time, and carbon/nitrogen ratio significantly impact the anaerobic digestion process and biogas production. Overall, further pilot-scale studies are required to warrant the real-world applicability of the closed-loop phycoremediation coupled biofuel production technology.

Methane production from peroxymonosulfate pretreated algae biomass: Insights into microbial mechanisms, microcystin detoxification and heavy metal partitioning behavior

This study investigated the methane production potential of algal biomass by anerobic digestion with the addition of peroxymonosulfate (PMS), the removal of microcystin were analyzed and discussed. The microcystin concentration in the collected algal sludge was 1.20 μg/L in the liquid phase and 1393 μg/g in the algal sludge before anaerobic fermentation. The microcystin concentration decreased to 0.20-0.35 μg/L in the liquid phase and 4.16-11.51 μg/g in the sludge phase after 60 days of digestion. The initial PMS dose and residue microcystin concentration could be simulated with a logarithmic decay model (R² > 0.87). Anaerobic digestion could recover energy from algal source in the form of methane gas, which was not affected in the presence of microcystin, and the microcystin removal rate was >99%. Digestion decreased the total contents of Cd and Zn in the liquid phase and increased the total contents of Cr and Pb in the liquid phase. The microbial community and function prediction results indicated that the PMS0.1 system had the highest methane production, which was attributed to the high abundance of Mechanosaeta (40.52%). This study provides insights into microbial mechanisms, microcystin detoxification and the heavy metal partitioning behavior of the algal biomass during methane production.

Anaerobic digestion of microalgal biomass for bioenergy production, removal of nutrients and microcystin: current status

Using renewable microalgal biomass as active feedstocks for biofuels and bioproducts is explored to substitute petroleum-based fuels and chemicals. In the last few years, the importance of microalgae biomass has been realized as a renewable feedstock due to several positive attributes associated with it. Biorefinery via anaerobic digestion (AD) of microalgal biomass is a promising and sustainable method to produce value-added chemicals, edible products and biofuels. Microalgal biomass pretreatment is a significant process to enhance methane production by AD. Findings on the AD microbial community's variety and organization can give novel in turn on digester steadiness and presentation. This review presents a vital study of the existing facts on the AD microbial community and AD production. Co-digestion of microalgal biomass with different co-substrates was used in AD to enhance biogas production, and the process was economically viable with improved biodegradability. Microcystins, which are produced by toxic cyanobacterial blooms, create a severe hazard to environmental health. Anaerobic biodegradation is an effective method to degrade the microcystins and convert into nontoxic products. However, for the cost-effective conversion of biomass to energy and other beneficial byproducts, additional highly developed research is still required for large-scale AD of microalgal biomass.

Techno-economic feasibility of anaerobic digestion of cheese whey in small Italian dairies and effect of ultrasound pre-treatment on methane yield

In Friuli-Venezia Giulia plain (North-East of Italy), a significant number of small diaries is present; this study was aimed at evaluating technical and economic feasibility of diffused anaerobic digestion implementation at dairy level. Different kinds of cheese whey were characterized, and biochemical methane potential tests were executed. Good methane yields (up to 437.3 NmL CH₄/g VS_added) were obtained, applying an inoculum-to-substrate ratio of 6. Ultrasound pre-treatment was investigated to evaluate an eventual increase in methane production and kinetics, varying applied ultrasonic energy: significant increases in methane yield (maximum +16.0%) and CH₄ production kinetics (up to +46% increase after 3 days) were obtained at low ultrasonic energy of 251.4-693.7 Wh/kg VS, while at higher ultrasonic energy of 502.8-1387.5 Wh/kg VS no significant effect was visible. Energy consumption in selected dairies was analysed, to underline the impact of anaerobic digestion implementation on electric and thermal energy need, and it was concluded that through cheese whey anaerobic digestion it is possible to cover most of the dairies energy demand. Specific electric and thermal energy consumption were evaluated to be respectively in the range of 0.009-0.133 kWh/kg milk and 0.247-0.557 MJ/kg milk, while specific energy costs were calculated as 0.0079-0.0308 €/kg milk. For each analysed plant, digester volume to install and organic loading rate were hypothesized.