Biohydrogen production using algae : Potentiality, economics and challenges

The biohydrogen production from algal biomass could ensure hydrogen's sustainability as a fuel option at the industrial level. However, some bottlenecks still need to be overcome to achieve the process's economic feasibility. This review article highlights the potential of algal biomasses for producing hydrogen with a detailed explanation of various mechanisms and enzymes involved in the production processes. Further, it discusses the impact of various experimental parameters on biohydrogen production. This article also analyses the significant challenges confronted during the overall biohydrogen production process and comprehends the recent strategies adopted to enhance hydrogen productivity. Furthermore, it gives a perception of the economic sustenance of the process. Moreover, this review elucidates the future scope of this technology and delineates the approaches to ensure the viability of hydrogen production

Engineering principles and process designs for phosphorus recovery as struvite: A comprehensive review

The rising population relies heavily on expensive phosphate (P) fertilizers for its agricultural productivity that qualms the national food security. Globally, there is a growing concern for the profound reliance on finite phosphorite reservoirs for commercial phosphate fertilizers’ qualitative and quantitative production. On the contrary, uncontrolled discharging of nutrient-rich wastewaters into natural streams, affecting the aquatic ecosystem. These critical situations have caused a scientific threat that has forced the researchers to explore other opportunities for the conservation of nutrient resources, recovery, and recycling. This review examines the nutrient recovery paradigms for struvite production by curtailing the nutrient gap between wastewater treatment and agricultural productivity. It comprehends the fundamental chemistry, thermodynamics, and factors influencing the struvite production process with its detailed mechanisms. Further, it deliberates the possible struvite engineering strategies, including process designs to enhance P recovery at the lab, pilot, and commercial scale. Also, it emphasizes the applications of nutrient-loaded struvite as a slow-release fertilizer and the challenges associated with economic feasibility and scaling up of the process in recent decades

Biochar seeding properties affect struvite crystallization for soil application

Struvite crystallization is a viable approach for recovering phosphorus from phosphorus-rich solutions such as urine and wastewater. However, designing seed materials to promote crystal growth and enhance the efficiency of struvite crystallization remains an area of active research. In this study, we investigated the seeding characteristics of biochars on struvite crystallization and the impact of biochar feedstock type and production temperature on the process. Microwave-pyrolyzed biochars produced from different feedstocks and under different temperatures were examined as seeding materials for struvite crystallization from urine and the influence of biochar properties on the overall struvite yield, nutrient recovery and struvite crystal size. Sawdust biochar (lignocellulosic biomass) produced at 500 ​°C had the highest struvite yield (7.91 ​g ​L−1), phosphate (97.9%) and ammonium recovery (87.1%), and relative crystal size (85.2%) compared to the non-seeded treatment due to its higher surface area, pore volume, and hydrophobicity of the biochar. Manure pellet biochar (non-lignocellulosic biomass) produced at 500 ​°C also exhibited performance comparable to sawdust biochar produced at 500 ​°C. Increasing pyrolysis temperature increased biochar's hydrophobicity, zeta potential, electrophoretic mobility and bulk density, irrespective of the feedstock type, thereby improving the seeding process. The ash content of biochar was negatively correlated with its surface area, pore volume, and particle size, but positively correlated with biochar's bulk density and suspension stability. In conclusion, feedstock type and pyrolysis temperature significantly affected biochar properties, which interactively influenced struvite crystallization. Therefore, biochars should be carefully selected to improve their efficiency for phosphorus recovery from phosphorus-containing solutions such as urine and wastewater, with the recovered phosphorus being used for soil applications

Recent advances and future prospects of electrochemical processes for microalgae harvesting

Over the years, algae have found wide scope of utility in a variety of environmentally beneficial processes like biofuel production, removal of heavy metals from wastewater sources for potential bioremediation, monitoring water pollution and source of animal nutrition. However, the conventional harvesting methods pose a set-back in terms of energy, cost and operational complications due to the small size of microalgae. Of all the processes, harvesting alone corresponds to approximately 30% of the total production costs. Recent advancements in the microalgal technology have brought many efficient techniques into use for improved recovery of microalgae. This review comprehends the development, principle, influencing parameters and directions to future research of one of the state-of-the-art approaches for harvesting microalgae, electrochemical technology. Though this area was previously explored for its application in wastewater treatment, it has lately gained momentum in the field of microalgae due to its economic efficiency. This paper highlights the three prime processes used to yield microalgae namely electroflocculation, electroflotation and a combined electrocoagulation-flotation (ECF) system. Several encroachments and strategies among these techniques have also been elucidated. The review focusses on the effect of most significant process controlling parameters such as reactor and electrode design, various surface properties of microalgae, current, pH, salinity and agitation that influence harvesting. In addition, the economy and energy aspects that emphasize the welfares of this technology over others have been extensively discussed. The overall work aims to provide an insight into the electrochemical methods, their challenges and opportunities that might be beneficial for carrying out further research and scope for industrial applications