Semicontinuous and batch ozonation combined with peroxymonosulfate for inactivation of microalgae in ballast water

The microalgal sector in Europe: Towards a sustainable bioeconomy

Microalgae are a diverse group of photosynthetic microorganisms that can be exploited to produce sustainable food and feed products, alleviate environmental pollution, or sequester CO2 to mitigate climate change, among other uses. To optimize resource use and integrate industrial waste streams, it is essential to consider factors such as the biology and cultivation parameters of the microalgal strains, as well as the cultivation system and processing technologies employed. This paper reviews the main commercial applications of microalgae (including cyanobacteria) and examines the biological and biotechnological aspects critical to the sustainable processing of microalgal biomass and its derived compounds. We also provide an up-to-date overview of the microalgal sector in Europe considering the strain, cultivation system and commercial application. We have identified 146 different microalgal-derived products from 66 European microalgae producers, and 49 additional companies that provide services and technologies, such as optimization and scalability of the microalgal production. The most widely cultivated microalga is 'spirulina' (Limnospira spp.), followed by Chlorella spp. and Nannochloropsis spp., mainly for human consumption and cosmetics. The preferred cultivation system in Europe is the photobioreactor. Finally, we discuss the logistic and regulatory challenges of producing microalgae at industrial scale, particularly in the European Union, and explore the potential of new genomic techniques and bioprocessing to foster a sustainable bioeconomy in the microalgal sector.

The Direct Air Synthesis of Hydrogen Peroxide Induced by The Giant Built-In Electric Field of Trz-CN

Graphitic carbon nitride (C3N4) has been identified as an optimal material for hydrogen peroxide (H2O2) photosynthesis, although its utility is hampered by a high photocarrier recombination rate. Herein, a novel carbon nitride material with a giant built-in electric field (BEF), Trz-CN, is synthesized through a hydrothermal-calcination tandem strategy. The giant BEF (4.8-fold) induced by the large dipole moment facilitated the efficient separation and directional migration of photogenerated carriers. Trz-CN exhibited an H2O2 production rate of 569.9 µmol·g-1·h-1 using O2 as feedstock under visible light (λ > 420 nm), marking an impressive 11.2-fold enhancement compared to bulk C3N4. Utilizing air instead of pure O2 as feedstock resulted in a trivial 1.6% decrease in the H2O2 generation by Trz-CN while maintaining a substantial production rate of 560.6 µmol·g-1·h-1. Notably, Trz-CN showcased a sterilization rate of 99.9% against Escherichia coli (E. coli) in natural seawater. Density functional theory (DFT) calculations revealed that incorporating a nitrogen-rich skeleton into the C3N4 enhanced its oxygen adsorption capacity and lowered the energy barrier for H2O2 formation. This leads to enhanced photocatalytic performance for H2O2 generation under ambient air conditions. Trz-CN provides a new exploratory idea for direct air synthesis of H2O2 and ballast water treatment.

Enhancing dark fermentative biohydrogen and VFA production via ozone pre-treatment

This study investigates the effects of ozone pre-treatment on two types of organic wastes: secondary sludge (SS) and wine vinasse (WV). Ozone pre-treatment of SS, a semi-solid waste, significantly increased the Dissolved Organic Carbon (DOC) and Total Volatile Fatty Acids (TVFAs) through hydrolysis. Conversely, ozone pre-treatment of WV, a liquid organic waste, reduced the availability of soluble biodegradable substrates and decreased the concentration of carboxylic acids with carbon chain length higher than 4. Based on these findings, the impact of ozonation on subsequent dark fermentation Biochemical Hydrogen Potential (BHP) was assessed for SS. The results, modeled for an ozone dose of 0.018 g O3/g TS, indicated a substantial enhancement in bio-hydrogen production by approximately 160% and VFA production by about 350%. In conclusion, ozone pre-treatment shows significant potential to enhance dark fermentation of particulate substrates like secondary sludge, supporting sustainable waste valorization strategies.

Modeling and optimization of synergistic ozone-ultraviolet-chlorine process for reclaimed water disinfection: From laboratory tests to software simulation

The ozone-ultraviolet (UV)-chlorine process is a highly effective method of disinfection in water reuse system, but currently still lacks precise quantification and accurate control. It is difficult to determine the dosage of each disinfectant because of the complex interactions that occur between disinfection units and the complicated mathematical calculation required. In this study, we proposed a dosage optimization model for ozone-UV-chlorine synergistic disinfection process. The model was able to identify the cost-effective doses of the disinfectants under the constraints of microbial inactivation, decolorization, and residual chlorine retention requirements. Specifically, the simulation of microbial inactivation rates during synergistic disinfection process was accomplished through quantification of the synergistic effects between disinfection units and the introduction of enhancement coefficients. In order to solve this optimization model rapidly and automatically, a MATLAB-based software program with graphical user interface was developed. This software consisted of calibration unit, prediction unit, assessment unit, and optimization unit, and was able to simulate synergistic ozone-UV-chlorine process and identify the optimal dose of ozone, UV, and chlorine. Validation experiments revealed good agreements between the experimental data and the results calculated by the developed software. The developed software is believed to help the water reclamation plants improve disinfection efficiency and reduce the operational costs of synergistic disinfection processes.