Harvesting microalgae using vibrating, negatively charged, patterned polysulfone membranes

A review on algal biomass dewatering and recovery of microalgal-based valuable products with different membrane technologies

Efficient microalgae harvesting and dewatering are critical processes for a range of applications, including the production of raw materials, nutritional supplements, pharmaceuticals, sustainable biofuels, and wastewater treatment. The optimization of these processes poses significant challenges due to the need for high efficiency and sustainability while managing costs and energy consumption. This review comprehensively addresses these challenges by focusing on the development and application of various membrane filtration technologies specifically designed for the effective harvesting and dewatering of algal biomass. Membrane filtration has emerged as a predominant method due to its ability to handle large volumes of microalgae with relatively low energy requirements. This review systematically examines the different membrane-based technologies and their effectiveness in recovering valuable components from algal biomass, such as lipids, proteins, and carbohydrates. The discussion begins with an overview of the physical characteristics of microalgae and their cultivation conditions, which are critical for understanding how these factors influence the performance of membrane filtration processes. Key aspects such as the features of algal cells, the presence of algal organic matter, and transparent exopolymer particles are explored in detail. The review also delves into various strategies for improving membrane antifouling properties, which are essential for maintaining the efficiency and longevity of the filtration systems. In addition, the advantages and disadvantages of different membrane techniques are reviewed, highlighting their respective performance in separating microalgae and dewatering. Finally, the review offers insights into future research directions and technological advancements that could further enhance the efficiency and sustainability of microalgae processing. This comprehensive evaluation aims to provide a thorough understanding of current membrane technologies, their applications, and the ongoing developments necessary to overcome existing limitations and improve overall process performance.

Harvesting marine microalgae Tetraselmis sp. using cellulose acetate membrane

This study presents the development and application of a cellulose acetate phase-inversion membrane for the efficient harvesting of Tetraselmis sp., a promising alternative for aquaculture feedstock. Once fabricated, the cellulose acetate membrane was characterized, and its performance was evaluated through the filtration of Tetraselmis sp. broth. The results demonstrated that the developed membrane exhibited exceptional microalgae harvesting efficiency. It showed a low intrinsic resistance and a high clean water permeability of 1100 L/(m2·h·bar), enabling high-throughput filtration of Tetraselmis sp. culture with a permeability of 400 L/(m2·h·bar) and a volume reduction factor of 2.5 ×. The cellulose acetate -based membrane demonstrated robust filtration performance over a 7-day back concentration filtration with minimum irreversible fouling of only 22.5 % irreversibility even without any cleaning. These results highlighted the potential of cellulose acetate as a versatile base polymer for custom-membrane for microalgae harvesting.

Designing sustainable membrane-based water treatment via fouling control through membrane interface engineering and process developments

Membrane-based water treatment processes have been established as a powerful approach for clean water production. However, despite the significant advances made in terms of rejection and flux, provision of sustainable and energy-efficient water production is restricted by the inevitable issue of membrane fouling, known to be the major contributor to the elevated operating costs due to frequent chemical cleaning, increased transmembrane resistance, and deterioration of permeate flux. This review provides an overview of fouling control strategies in different membrane processes, such as microfiltration, ultrafiltration, membrane bioreactors, and desalination via reverse osmosis and forward osmosis. Insights into the recent advancements are discussed and efforts made in terms of membrane development, modules arrangement, process optimization, feed pretreatment, and fouling monitoring are highlighted to evaluate their overall impact in energy- and cost-effective water treatment. Major findings in four key aspects are presented, including membrane surface modification, modules design, process integration, and fouling monitoring. Among the above mentioned anti-fouling strategies, a large part of research has been focused on membrane surface modifications using a number of anti-fouling materials whereas much less research has been devoted to membrane module advancements and in-situ fouling monitoring and control. At the end, a critical analysis is provided for each anti-fouling strategy and a rationale framework is provided for design of efficient membranes and process for water treatment.

The Combined Effects of the Membrane and Flow Channel Development on the Performance and Energy Footprint of Oil/Water Emulsion Filtration

Membrane filtration is a promising technology for oil/water emulsion filtration due to its excellent removal efficiency of microdroplets of oil in water. However, its performance is highly limited due to the fouling-prone nature of oil droplets on hydrophobic membranes. Membrane filtration typically suffers from a low flux and high pumping energy. This study reports a combined approach to tackling the membrane fouling challenge in oil/water emulsion filtration via a membrane and a flow channel development. Two polysulfone (PSF)-based lab-made membranes, namely PSF- PSF-Nonsolvent induced phase separation (NIPS) and PSF-Vapor-induced phase separation (VIPS), were selected, and the flow channel was modified into a wavy path. They were assessed for the filtration of a synthetic oil/water emulsion. The results showed that the combined membrane and flow channel developments enhanced the clean water permeability with a combined increment of 105%, of which 34% was attributed to the increased effective filtration area due to the wavy flow channel. When evaluated for the filtration of an oil/water emulsion, a 355% permeability increment was achieved from 43 for the PSF-NIPS in the straight flow channel to 198 L m^-2 h^-1 bar^-1 for the PSF-VIPS in the wavy flow channel. This remarkable performance increment was achieved thanks to the antifouling attribute of the developed membrane and enhanced local mixing by the wavy flow channel to limit the membrane fouling. The increase in the filtration performance was translated into up to 78.4% (0.00133 vs. 0.00615 kWh m^-3) lower in pumping energy. The overall findings demonstrate a significant improvement by adopting multi-pronged approaches in tackling the challenge of membrane fouling for oil/water emulsion filtration, suggesting the potential of this approach to be applied for other feeds.

Enhancing the electrocoagulation process for harvesting marine microalgae (Tetraselmis sp.) using interdigitated electrodes

Marketable value of algal biomass has been increasing in recent years due to its wide range of applications. This study investigates the performance of a novel cylindrical interdigitated electrode array in electrocoagulation for the harvesting of marine microalgae (Tetraselmis sp.). The new electrode array is expected to exert a dielectrophoretic (DEP) force which would assist in the harvesting of the microalgae in the electrocoagulation process. Through numerical investigation, the induction of dielectrophoretic force was confirmed in the new electrode array. In this study, 10 min electrolysis time was found to be sufficient to harvest 82.4% microalgae with 1 cm electrode distance and 50 mA/cm² current density. Furthermore, decreasing the electrode distance to 0.5 cm increased the algal harvesting efficiency to 96.18%. Energy analysis showed that the proposed electrode array shows 38% lower specific energy consumption than the conventional flat sheet electrode array.

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.

Runge-Kutta Numerical Method Followed by Richardson's Extrapolation for Efficient Ion Rejection Reassessment of a Novel Defect-Free Synthesized Nanofiltration Membrane

A defect-free, loose, and strong layer consisting of zirconium (Zr) nanoparticles (NPs) has been successfully established on a polyacrylonitrile (PAN) ultrafiltration substrate by an in-situ formation process. The resulting organic–inorganic nanofiltration (NF) membrane, NF-PANZr, has been accurately characterized not only with regard to its properties but also its structure by the atomic force microscopy, field emission scanning electron microscopy, and energy dispersive spectroscopy. A sophisticated computing model consisting of the Runge–Kutta method followed by Richardson extrapolation was applied in this investigation to solve the extended Nernst–Planck equations, which govern the solute particles’ transport across the active layer of NF-PANZr. A smart, adaptive step-size routine is chosen for this simple and robust method, also known as RK4 (fourth-order Runge–Kutta). The NF-PANZr membrane was less performant toward monovalent ions, and its rejection rate for multivalent ions reached 99.3%. The water flux of the NF-PANZr membrane was as high as 58 L · m⁻² · h⁻¹. Richardson’s extrapolation was then used to get a better approximation of Cl⁻ and Mg²⁺ rejection, the relative errors were, respectively, 0.09% and 0.01% for Cl⁻ and Mg²⁺. While waiting for the rise and expansion of machine learning in the prediction of rejection performance, we strongly recommend the development of better NF models and further validation of existing ones.

Harvesting microalgal biomass using negatively charged polysulfone patterned membranes: Influence of pattern shapes and mechanism of fouling mitigation

Membranes have a lot of potential for harvesting microalgae, but membrane fouling is hampering their breakthrough. In this study, the effects of charge and corrugated surface on membrane filtration performance were investigated. The clean water permeance (CWP), the microalgae harvesting efficiency and the membrane flux for a microalgal broth were determined using patterned polysulfone (PSf) membranes with different shapes of the surface patterns and containing different charge densities by blending sulfonated polysulfone (sPSf). The flow behavior near the patterned membrane surface, as well as the interaction energy between membrane and microalgae were investigated using computational fluid dynamics (CFD) simulation and the improved extended "Derjaguin, Landau, Verwey, Overbeek" (XDLVO) theory, respectively. Membrane charge and pattern shape significantly improve the membrane performance. The critical pressures of all sPSf blend patterned membranes were higher than 2.5 bar. A 4.5w% sPSf blend patterned membranes with wave patterns showed the highest CWP (2300 L/m² h bar) and membrane flux in the microalgal broth (1000 L/m² h bar) with 100% harvesting efficiency. XDLVO analysis showed that sPSf blend patterned membranes prepared obtained the lowest interaction energy and highest energy barrier for microalgal attachment. CFD simulation showed a higher velocity and wall shear on the pattern apexes.