Up-flow anaerobic sludge blanket (UASB) reactor belongs to high-rate systems, able to perform anaerobic reaction at reduced hydraulic retention time, if compared to traditional digesters. In this review, the most recent advances in UASB reactor applications are critically summarized and discussed, with outline on the most critical aspects for further possible future developments. Beside traditional anaerobic treatment of soluble and biodegradable substrates, research is actually focusing on the treatment of refractory and slowly degradable matrices, thanks to an improved understanding of microbial community composition and reactor hydrodynamics, together with utilization of powerful modeling tools. Innovative approaches include the use of UASB reactor for nitrogen removal, as well as for hydrogen and volatile fatty acid production. Co-digestion of complementary substrates available in the same territory is being extensively studied to increase biogas yield and provide smooth continuous operations in a circular economy perspective. Particular importance is being given to decentralized treatment, able to provide electricity and heat to local users with possible integration with other renewable energies. Proper pre-treatment application increases biogas yield, while a successive post-treatment is needed to meet required effluent standards, also from a toxicological perspective. An increased full-scale application of UASB technology is desirable to achieve circular economy and sustainability scopes, with efficient biogas exploitation, fulfilling renewable energy targets and green-house gases emission reduction, in particular in tropical countries, where limited reactor heating is required.

Up-Flow Anaerobic Sludge Blanket (UASB) Technology for Energy Recovery: A Review on State-of-the-Art and Recent Technological Advances.

Microalgae are promising sustainable energy sources for biodiesel production due to their rapid photosynthesis growth rate and capacity to be cultivated in wastewater, seawater, or freshwater. Moreover, microalgae could complete the entire growth cycle via photosynthesis reactions that convert light energy into renewable energy. The closed photobioreactor, PBR is resistant to infection from uninhabited algae species and allows frequent monitoring of various factors such as temperature, light intensity, and pH during the cultivation phase. Thus, this study focuses on continuous cultivation technology which produces higher biomass productivity with sustainable energy-saving operation as compared to batch culture. High productivity of microalgae biomass tends to accumulate higher concentrations of lipid and carbohydrates composition which is essential for the production of biofuels. The energy balance of numerous microalgae-based biofuels was discussed, and it was discovered that the net-energy ratio was greater than 1, indicating that the process is both commercially feasible and environmentally friendly. This study also summarizes the most recent discoveries on continuous cultivation constraints through photobioreactors, PBRs as well as potential challenges to tackle in scaling up the continuous sustainable culture mechanism. The research gaps, market opportunities, and future development directions of continuous photobioreactor systems are discussed to explore future development opportunities. A continuous photobioreactor, architecture is recommended for a pilot-scale trial, as a cost-benefit comparison would be beneficial in commercializing the framework. • Microalgae production decreases greenhouse gas emissions by absorbing CO 2 . • Impact of culture medium to optimize the microalgae cultivation. • Continuous cultivation could increase the microalgae biomass productivity. • Net Energy Ratio, NER for microalgae-based biofuel production. • Overview of latest novel photo-bioreactors system operations. 

Continuous cultivation of microalgae in photobioreactors as a source of renewable energy: Current status and future challenges

Microalgae are promising sustainable energy sources for biodiesel production due to their rapid photosynthesis growth rate and capacity to be cultivated in wastewater, seawater, or freshwater. Moreover, microalgae could complete the entire growth cycle via photosynthesis reactions that convert light energy into renewable energy. The closed photobioreactor, PBR is resistant to infection from uninhabited algae species and allows frequent monitoring of various factors such as temperature, light intensity, and pH during the cultivation phase. Thus, this study focuses on continuous cultivation technology which produces higher biomass productivity with sustainable energy-saving operation as compared to batch culture. High productivity of microalgae biomass tends to accumulate higher concentrations of lipid and carbohydrates composition which is essential for the production of biofuels. The energy balance of numerous microalgae-based biofuels was discussed, and it was discovered that the net-energy ratio was greater than 1, indicating that the process is both commercially feasible and environmentally friendly. This study also summarizes the most recent discoveries on continuous cultivation constraints through photobioreactors, PBRs as well as potential challenges to tackle in scaling up the continuous sustainable culture mechanism. The research gaps, market opportunities, and future development directions of continuous photobioreactor systems are discussed to explore future development opportunities. A continuous photobioreactor, architecture is recommended for a pilot-scale trial, as a cost-benefit comparison would be beneficial in commercializing the framework.

Microalgae in a global world: New solutions for old problems?

Food waste leachate treatment using an Upflow Anaerobic Sludge Bed (UASB): Effect of conductive material dosage under low and high organic loads

Upflow anaerobic sludge blanket in microalgae-based sewage treatment: Co-digestion for improving biogas production.

Sewage treatment plants have been investigated in order to identify sustainable options for managing the by-products. Due to the widespread use of upflow anaerobic sludge blanket reactors (UASB) for the treatment of sewage in Brazil, one of these solutions would be the use of a high rate algal pond as a post-treatment for this effluent. In addition to being efficient in removing pollutants, the microalgal biomass produced can be introduced in the UASB reactor, being co-digested with raw sewage. This practice would increase methane production at UASB. However, little is known about the co-digestion of microalgae and raw sewage in these reactors. This technical note (TN) aims to report the most important aspects of this practice, as well as to clarify the weaknesses and potentialities for future full-scale implementation. This TN also proposes a sustainable way, based on solar radiation, for the thermal treatment of microalgae. Promising results show a 35% to 40% increase in methane production in UASB with microalgae co-digestion with and without pre-treatment, respectively, compared to a control reactor without co-digestion.

Part B: Sludge sewage pre-treatment and codigestion
Technical Note 5 – Anaerobic co-digestion of domestic sewage and microalgal biomass with and without solar thermal pre-treatment

Alcino Trindade Rosa Machado

Papers

Upflow anaerobic sludge blanket in microalgae-based sewage treatment: Co-digestion for improving biogas production.

Part B: Sludge sewage pre-treatment and codigestion Technical Note 5 – Anaerobic co-digestion of domestic sewage and microalgal biomass with and without solar thermal pre-treatment