Data-driven analysis on immobilized microalgae system: New upgrading trends for microalgal wastewater treatment

Immobilized microalgae: principles, processes and its applications in wastewater treatment

Microalgae have emerged as potential candidates for biomass production and pollutant removal. However, expensive biomass harvesting, insufficient biomass productivity, and low energy intensity limit the large-scale production of microalgae. To break through these bottlenecks, a novel technology of immobilized microalgae culture coupled with wastewater treatment has received increasing attention in recent years. In this review, the characteristics of two immobilized microalgae culture technologies are first presented and then their mechanisms are discussed in terms of biofilm formation theories, including thermodynamic theory, Derjaguin-Landau-Verwei-Overbeek theory (DLVO) and its extended theory (xDLVO), as well as ionic cross-linking mechanisms in the process of microalgae encapsulated in alginate. The main factors (algal strains, carriers, and culture conditions) affecting the growth of microalgae are also discussed. It is also summarized that immobilized microalgae show considerable potential for nitrogen and phosphorus removal, heavy metal removal, pesticide and antibiotic removal in wastewater treatment. The role of bacteria in the cultivation of microalgae by immobilization techniques and their application in wastewater treatment are clarified. This is economically feasible and technically superior. The problems and challenges faced by immobilized microalgae are finally presented.

Cytoprotective alginate microcapsule serves as a shield for microalgal encapsulation defensing sulfamethoxazole threats and safeguarding nutrient recovery

Microalgal encapsulation technology is expected to broaden more possibilities for employing microalgae for upgrading conventional biological wastewater treatment. However, only limited and fragmented information is currently available on microalgal encapsulation and pollutant removal. It is ambiguous whether it hold potential for wastewater treatment. Particularly, it remains to be determined whether this technology can provide more possibilities in harsh sewage environments. Here, potential of encapsulated technology to recover nutrients from wastewater was examined, simultaneously compared with commonly adopted suspended system. Results indicate the encapsulated microalgal system showed outstanding advantages in nutrient recovery and defense against antibiotic threats. Moreover, by examining the cellular oxidative stress response and changes of the photosynthetic system, the encapsulated system exhibited potential cytoprotective advantages to microalgal cells for defensing antibiotic threats. Molecular dynamics simulation revealed that the differences among superficial aggregation between the nutrients' ions and molecular sulfamethoxazole on the cross-linked alginate microcapsule surface dominated the nutrient recovery and cytoprotective functions. Ultimately, the molecular nature of pollutants was found to be the most critical aspect for predicting application of this microalgal microcapsule. Cytoprotective systems created with alginate microcapsules can potentially handle more diverse threats with a single type of surface charge in their outermost layer.

A review of microalgae biofilm as an eco-friendly approach to bioplastics, promoting environmental sustainability

In this comprehensive review, we delve into the challenges hindering the large-scale production of microalgae-based bioplastics, primarily focusing on economic feasibility and bioplastic quality. To address these issues, we explore the potential of microalgae biofilm cultivation as a sustainable and highly viable approach for bioplastic production. We present a proposed method for producing bioplastics using microalgae biofilm and evaluate its environmental impact using various tools such as life cycle analysis (LCA), ecological footprint analysis, resource flow analysis, and resource accounting. While pilot-scale and large-scale LCA data are limited, we utilize alternative indicators such as energy efficiency, carbon footprint, materials management, and community acceptance to predict the environmental implications of commercializing microalgae biofilm-based bioplastics. The findings of this study indicate that utilizing microalgae biofilm for bioplastic production offers significant environmental sustainability benefits. The system exhibits low energy requirements and a minimal carbon footprint. Moreover, it has the potential to address the issue of wastewater by utilizing it as a carbon source, thereby mitigating associated problems. However, it is important to acknowledge certain limitations associated with the method proposed in this review. Further research is needed to explore and engineer precise techniques for manipulating microalgae biofilm structure to optimize the accumulation of desired metabolites. This could involve employing chemical triggers, metabolic engineering, and genetic engineering to achieve the intended goals. In conclusion, this review highlights the potential of microalgae biofilm as a viable and sustainable solution for bioplastic production. While acknowledging the advantages, it also emphasizes the need for continued synthetic studies to enhance the efficiency and reliability of this approach. By addressing the identified drawbacks and maximizing the utilization of advanced techniques, we can further harness the potential of microalgae biofilm in contributing to a more environmentally friendly and economically feasible bioplastic industry.

Poly(vinyl alcohol)/modified porous starch gel beads for microbial preservation and reactivation: preparation, characterization and its wastewater treatment performance

Poly(vinyl alcohol) (PVA)/modified porous starch (MPS) gel beads were prepared through in situ chemical cross-linking by incorporating with MPS, which was obtained by modifying porous starch (PS) with polyethyleneimine (PEI) and glutaraldehyde (GA). Addition of MPS could improve the storage modulus and the effective crosslinking density (ve) of the gel beads, and the mechanical properties were enhanced. The PVA-MPS gel beads were preserved as immobilized microbial carriers for 40 d and reactivated in wastewater. Scanning electron microscope (SEM) observations showed that the beads were highly porous and conducive for microorganism adhesion. The PVA-MPS gel beads were able to remove 97% of ammonia nitrogen and 80% of chemical oxygen demand (COD) after reactivation under all four preservation conditions. The abundance of Hydrogenophaga as denitrifying bacteria on PVA-MPS gel beads increased, with abundance of 8.44%, 5.55%, 8.90% and 9.48%, respectively. It proved that the carrier provided a partial hypoxic environment for microorganisms.

Quantified trend of photosynthetic rate along the depth of microalgae biofilm

Compared with suspended microalgae cultivation, attached microalgae cultivation for wastewater treatment has advantages of low biomass recovery costs and high robustness. As a heterogeneous system, the variation of photosynthetic capacity along biofilm depth lacks quantitative conclusions. The distribution curve of oxygen concentration along the depth of attached microalgae biofilm (f(x)) was detected by dissolved oxygen (DO) microelectrode, and a quantified model was built based on mass conservation and Fick's law. It revealed that the net photosynthetic rate at a certain depth (x) in the biofilm showed a linear relationship with the second derivatives of the distribution curve of oxygen concentration (f″(x)). In addition, the declining trend of photosynthetic rate along attached microalgae biofilm was relatively slow compared with the suspended system. The photosynthetic rate at 150-200 μm depth of algae biofilm was only 3.60 %-17.86 % of that at the surface layer. Moreover, the light saturation points of the attached microalgae got lower along the depth of biofilm. Compared to 400 lx light intensity, the net photosynthetic rate of microalgae biofilm at the depths of 100-150 μm and 150-200 μm increased by 389 % and 956 % under 5000 lx, respectively, showing the high photosynthesis potential with increasing light.

Quorum Sensing as a Trigger That Improves Characteristics of Microbial Biocatalysts

Quorum sensing (QS) of various microorganisms (bacteria, fungi, microalgae) today attracts the attention of researchers mainly from the point of view of clarifying the biochemical basics of this general biological phenomenon, establishing chemical compounds that regulate it, and studying the mechanisms of its realization. Such information is primarily aimed at its use in solving environmental problems and the development of effective antimicrobial agents. This review is oriented on other aspects of the application of such knowledge; in particular, it discusses the role of QS in the elaboration of various prospective biocatalytic systems for different biotechnological processes carried out under aerobic and anaerobic conditions (synthesis of enzymes, polysaccharides, organic acids, etc.). Particular attention is paid to the biotechnological aspects of QS application and the use of biocatalysts, which have a heterogeneous microbial composition. The priorities of how to trigger a quorum response in immobilized cells to maintain their long-term productive and stable metabolic functioning are also discussed. There are several approaches that can be realized: increase in cell concentration, introduction of inductors for synthesis of QS-molecules, addition of QS-molecules, and provoking competition between the participants of heterogeneous biocatalysts, etc.).