Harvesting microalgal biomass using crossflow membrane filtration: critical flux, filtration performance, and fouling characterization

Nano-clay modified membranes: A promising green strategy for microalgal antifouling filtration

Membrane fouling is a major challenge which limits the sustainable application of membrane filtration-based microalgal harvesting at industrial level. Membrane fouling leads to increased operational and maintenance costs and represents a major obstacle to microalgal downstream processing. Nano-clays are promising naturally occurring nanoparticles in membrane fabrication due to their low-cost, facile preparation, and their superior properties in terms of surface hydrophilicity, mechanical stability, and resistance against chemicals. The membrane surface modification using nano-clays is a sustainable promising approach to improve membranes mechanical properties and their fouling resistance. However, the positive effects of nano-clay particles on membrane fouling are often limited by aggregation and poor adhesion to the base polymeric matrix. This review surveys the recent efforts to achieve anti-fouling behavior using membrane surface modification with nano-clay fillers. Further, strategies to achieve a better incorporation of nano-clay in the polymer matrix of the membrane are summarised, and the factors that govern the membrane fouling, stability, adhesion, agglomeration and leaching are discussed in depth.

Textile dye removal in wastewater by peroxymonosulfate (PMS) activation on a zero-valent iron nanoparticle-modified ultrafiltration catalytic membrane (nZVI@PES)

The use of the nano zero-valent iron (nZVI) nanoparticle-based advanced oxidation systems in conjunction with an activator such as peroxymonosulfate (PMS) to generate hydroxyl and sulfate radicals for the degradation of organic pollutants has been extensively used in recent studies. In this study, a nZVI-modified polyethersulfone (PES) membrane (nZVI@PES) was produced successfully by attaching the nZVI catalytic nanoparticles on the surface of a commercial microporous polymeric membrane material using a simple and easy filter press coating method. The presence of nZVI nanoparticles on the nZVI@PES membrane was confirmed by XRD, SEM, and EDS analyses. The nZVI@PES membrane was applied in the dead-end filtration system in the presence of the PMS activator to treat the reactive black 5 (RB5) dye solution. The effect of catalyst loading, RB5 dye concentration, PMS dosage, and pH level on the nZVI@PES membrane/PMS system was investigated. Quenching experiments were carried out to identify the reactive species responsible, and reusability tests were conducted on the membrane. The highest decolorization efficiency (96.8%) was obtained at 20 mg/L RB5 dye solution, initial pH of 3, the nZVI loading of 5 mg/cm2, and the PMS dosage of 300 mg/L at the end of a reaction time of 30 min. The formation of HO•, [Formula: see text], [Formula: see text] and, 1O2 was confirmed by quenching experiments. The results indicate that the nZVI@PES membrane/PMS system could successfully treat wastewater contaminated with an organic dye.

Lutein production from microalgae: A review

Lutein production from microalgae is a sustainable and economical strategy to offer the increasing global demands, but is still challenged with low lutein content at the high-cell density for commercial production. This review summarizes the suitable conditions for cell growth and lutein accumulation, and presents recent cultivation strategies to further improve lutein productivity. Light and nitrogen play critical roles in lutein biosynthesis that lead to the efficient multi-stage cultivation by increasing lutein content at the later stage. In addition, metabolic and genetic designs for carbon regulation and lutein biosynthesis are discussed at the molecule level. The in-situ lutein accumulation in fermenters by regulating carbon metabolism is considered as a cost-effective direction. Then, downstream processes are summarized for the efficient lutein recovery. Finally, challenges of current lutein production from microalgae are discussed. Meanwhile, potential solutions are proposed to improve lutein content and drive down costs of microalgal biomass.

Membrane Fouling in Algal Separation Processes: A Review of Influencing Factors and Mechanisms

The use of algal biotechnologies in the production of biofuels, food, and valuable products has gained momentum in recent years, owing to its distinctive rapid growth and compatibility to be coupled to wastewater treatment in membrane photobioreactors. However, membrane fouling is considered a main drawback that offsets the benefits of algal applications by heavily impacting the operation cost. Several fouling control strategies have been proposed, addressing aspects related to characteristics in the feed water and membranes, operational conditions, and biomass properties. However, the lack of understanding of the mechanisms behind algal biofouling and control challenges the development of cost-effective strategies needed for the long-term operation of membrane photobioreactors. This paper reviews the progress on algal membrane fouling and control strategies. Herein, we summarize information in the composition and characteristics of algal foulants, namely algal organic matter, cells, and transparent exopolymer particles; and review their dynamic responses to modifications in the feedwater, membrane surface, hydrodynamics, and cleaning methods. This review comparatively analyzes (i) efficiency in fouling control or mitigation, (ii) advantages and drawbacks, (iii) technological performance, and (iv) challenges and knowledge gaps. Ultimately, the article provides a primary reference of algal biofouling in membrane-based applications.

Evaluating the effect of hydraulic retention time on fouling development and biomass characteristics in an algal membrane photobioreactor treating a secondary wastewater effluent

Coupling algal biomass growth to wastewater treatment is a promising alternative for the simultaneous removal and recovery of nutrients. This study aims to evaluate the effects of the Hydraulic Retention Time (HRT) on the fouling behavior and biomass characteristics of C. Vulgaris in a Membrane Photobioreactor (MPBR), fed with a secondary synthetic wastewater effluent. The changes in the algal cell characteristics and in their metabolic products were assessed at three different HRTs (12 h, 24 h and 36 h). Experimental results showed that higher loading rates led to a broader Particle Size Distribution (PSD) resulting from looser and less stable algal flocs. In contrast, bigger and homogeneously distributed particles observed at lower loading rates, led to a porous layer with lower fouling rates and organic removal. The presence of smaller particles and dissolved organics resulted in a more compact and less porous layer that increased the removal of small-MW organics.

A review of membrane fouling and its control in algal-related membrane processes

Membrane technologies have received much attention in microalgae biorefinery for nutrients removal from wastewater, carbon dioxide abatement from the air as well as the production of value-added products and biofuel in recent years. This paper provides a state-of-the-art review on membrane fouling issues and its control in membrane photobioreactors (MPBRs) and other algal-related membrane processes (harvesting, dewatering, and biofuel production). The mechanisms of membrane fouling and factors affecting membrane fouling in algal-related membrane processes are systematically reviewed. Also, strategies to control membrane fouling in algal-related membrane processes are summarized and discussed. Finally, the gaps, challenges, and opportunities in membrane fouling control in algal-related membrane technologies are identified and discussed.