Environmental applications of nanobubble technology: Field testing at industrial scale

The use of water in wineries: A review

Water is essential at various stages of winemaking, from irrigation in the vineyard to cleaning equipment and facilities, controlling fermentation temperatures, and diluting grape juice if necessary. Additionally, water is used for sanitation purposes to ensure the quality and safety of the final product. This article provides an overview of the existing knowledge regarding the use of water in wineries throughout the winemaking process, water consumption values, effluent treatment, efficient use of water measures, and water reuse. Different assessment methods, including Water Footprint (WF) and Life Cycle Assessment(LCA), provide varied insights into water use impacts, emphasizing the importance of standardized methodologies for accurate assessment and sustainable practices. This research showed that the characterization of the vinification processes of each type of wine is fundamental for further analysis on the environmental impact of winemaking regarding water use. It was also observed that WF is affected by factors like climate, irrigation needs, and cleaning procedures. Thus, efficient water management in all the stages of wine production is crucial to reduce the overall WF. Water efficiency measures may involve the modification of the production processes, reusing and recycling water and the implementation of cleaner production practices and technological innovations, such as automated fermentation systems that reduce water needs. Furthermore, waste management in wineries emphasizes the importance of sustainable practices and technological innovations to mitigate environmental impacts and enhance resource efficiency.

Relationship between chlorine decay and nanobubble application in secondary treated wastewater

There has been numerous research on the uses of treated wastewater that needs chlorine disinfection, but none have looked at the impacts of injecting nanobubbles (NBs) on the decomposition of residual chlorine. Gas NB injection in treated wastewater improves its properties. The kinetics of disinfectant decay could be impacted by changes in treated wastewater properties. This paper studies the effect of various NB injections on the residual chlorine decay of secondary treated wastewater (STWW). It also outlines the empirical equations that were developed to represent these impacts. The results show that each type of NBs in treated wastewater had a distinct initial chlorine concentration. The outcomes demonstrated a clear impact on the decrease of the needed chlorine quantity and the reduction of chlorine decay rate when utilizing NB injection for the STWW. As a result, the residual chlorine will remain for a longer time and will resist any microbiological growth under the application of NBs on treated wastewater. Moreover, NBs in secondary treated effluent reduce chlorine usage, lowering wastewater disinfection costs.

Advancing nanobubble technology for carbon-neutral water treatment and enhanced environmental sustainability

Gaseous nanobubbles (NBs) with dimensions ranging from 1 to 1000 nm in the liquid phase have garnered significant interest due to their unique physicochemical characteristics, including specific surface area, low internal gas pressure, long-term stability, efficient mass transfer, interface potential, and free radical production. These remarkable properties have sparked considerable attention in the scientific community and industries alike. These hold immense promise for environmental applications, especially for carbon-neutral water remediation. Their long-lasting stability in aqueous systems and efficient mass transfer properties make them highly suitable for delivering gases in the vicinity of pollutants. This potential has prompted research into the use of NBs for targeted delivery of gases in contaminated water bodies, facilitating the degradation of harmful substances and advancing sustainable remediation practices. However, despite significant progress in understanding NBs physicochemical properties and potential applications, several challenges and knowledge gaps persist. This review thereby aims to summarize the current state of research on NBs environmental applications and potential for remediation. By discussing the generation processes, mechanisms, principles, and characterization techniques, it sheds light on the promising future of NBs in advancing environmental sustainability. It explores their role in improving oxygenation, aeration, and pollutant degradation in water systems. Finally, the review addresses future research perspectives, emphasizing the need to bridge knowledge gaps and overcome challenges to unlock the full potential of this frontier technology for enhanced environmental sustainability.

Nanobubbles in water and wastewater treatment systems: Small bubbles making big difference

Since the discovery of nanobubbles (NBs) in 1994, NBs have been attracting growing attention for their fascinating properties and have been studied for application in various environmental fields, including water and wastewater treatment. However, despite the intensive research efforts on NBs' fundamental properties, especially in the past five years, controversies and disagreements in the published literature have hindered their practical implementation. So far, reviews of NB research have mainly focused on NBs' role in specific treatment processes or general applications, highlighting proof-of-concept and success stories primarily at the laboratory scale. As such, there lacks a rigorous review that authenticates NBs' potential beyond the bench scale. This review aims to provide a comprehensive and up-to-date analysis of the recent progress in NB research in the field of water and wastewater treatment at different scales, along with identifying and discussing the challenges and prospects of the technology. Herein, we systematically analyze (1) the fundamental properties of NBs and their relevancy to water treatment processes, (2) recent advances in NB applications for various treatment processes beyond the lab scale, including over 20 pilot and full-scale case studies, (3) a preliminary economic consideration of NB-integrated treatment processes (the case of NB-flotation), and (4) existing controversies in NBs research and the outlook for future research. This review is organized with the aim to provide readers with a step-by-step understanding of the subject matter while highlighting key insights as well as knowledge gaps requiring research to advance the use of NBs in the wastewater treatment industry.

Effect of chemical species and temperature on the stability of air nanobubbles

The colloidal stability of air nanobubbles (NBs) was studied at different temperatures (0-30 °C) and in the presence of sulfates, typically found in mining effluents, in a wide range of Na2SO4 concentrations (0.001 to 1 M), along with the effect of surfactants (sodium dodecyl sulfate), chloride salts (NaCl), and acid/base reagents at a pH range from 4 to 9. Using a nanobubble generator based on hydrodynamic cavitation, 1.2 × 108 bubbles/mL with a typical radius of 84.66 ± 7.88 nm were generated in deionized water. Multiple evidence is provided to prove their presence in suspension, including the Tyndall effect, dynamic light scattering, and nanoparticle size analysis. Zeta potential measurements revealed that NBs are negatively charged even after two months (from - 19.48 ± 1.89 to - 10.13 ± 1.71 mV), suggesting that their stability is due to the negative charge on their surface. NBs were found to be more stable in alkaline solutions compared to acidic ones. Further, low amounts of both chloride and sulfate dissolved salts led to a reduction of the size of NBs. However, when high amounts of dissolved salts are present, NBs are more likely to coalesce, and their size to be increased. Finally, the investigation of the stability of air NBs at low temperatures revealed a non-monotonic relationship between temperature and NBs upon considering water self-ionization and ion mobility. This research aims to open a new frontier towards the application of the highly innovative NBs technology on the treatment of mining, mineral, and metal processing effluents, which are challenging aqueous solutions containing chloride and sulfate species.

Characteristics and practical treatment technologies of winery wastewater: A review for wastewater management at small wineries

The wine-making industry drives tourism and rural revitalization in several countries. Meanwhile, winemaking generates wastewater at all production stages, mainly from cleaning of equipment, floors, vessels, and bottles. This review presents a comprehensive analysis with statistical characteristics on the overall quality and generation rate of winery wastewater since 2007, identifies the technologies used by wineries in pilot- and full-scale wastewater treatment systems, and offers insights on practical wastewater treatment at small wineries. The median wastewater generation rate has been reduced to 1.58 L/L-wine, with a weekly peaking factor of 1.6-3.4 and monthly peaking factor of 2.1-2.7. Winery wastewater is acidic and of high organic strength. The organic substances are largely biodegradable and constituent concentrations do not exceed 50% inhibitory levels for biological treatment. However, the small ratios of nitrogen and phosphorus to biochemical oxygen demand indicate substantial needs to supplement nutrients for aerobic biological treatment. The frequency of processes used to pretreat winery wastewater was in the order of sedimentation > coarse screening > equalization > neutralization. The most frequently reported treatment methods were constructed wetland, activated sludge process, membrane bioreactor, and anaerobic digestion. Advanced oxidation processes have been pilot tested for polishing. The best wastewater management practice at small wineries is physical pretreatment, followed by land-based treatment systems. Covered anaerobic lagoons and underground digesters are practicable anaerobic digestion designs to reduce organic loading to land-based treatment systems. Research is needed to develop sufficient design criteria for the best practicable treatment processes and compare land-based treatment systems at pilot and full scales.

Effects of Gas Type, Oil, Salts and Detergent on Formation and Stability of Air and Carbon Dioxide Bubbles Produced by Using a Nanobubble Generator

Recent developments in ultrafine bubble generation have opened up new possibilities for applications in various fields. Herein, we investigated how substances in water affect the size distribution and stability of microbubbles generated by a common nanobubble generator. By combining light scattering techniques with optical microscopy and high-speed imaging, we were able to track the evolution of microbubbles over time during and after bubble generation. Our results showed that air injection generated a higher number of microbubbles (<10 μm) than CO₂ injection. Increasing detergent concentration led to a rapid increase in the number of microbubbles generated by both air and CO₂ injection and the intensity signal detected by dynamic light scattering (DLS) slightly increased. This suggested that surface-active molecules may inhibit the growth and coalescence of bubbles. In contrast, we found that salts (NaCl and Na₂CO₃) in water did not significantly affect the number or size distribution of bubbles. Interestingly, the presence of oil in water increased the intensity signal and we observed that the bubbles were coated with an oil layer. This may contribute to the stability of bubbles. Overall, our study sheds light on the effects of common impurities on bubble generation and provides insights for analyzing dispersed bubbles in bulk.

Formation of Bulk Nanobubbles Induced by Accelerated Electrons Irradiation: Dependences on Dose Rates and Doses of Irradiation

Radiation on aqueous solutions can induce water radiolysis with products of radicals, H₂, H₂O₂, and so on, and their consequent biological effects have long been interested in radiation chemistry. Unlike the decomposition of water by electric current that produces a significant number of bubbles, the gas products from the radiolysis of water are normally invisible by bare eyes, little is known on whether nanosized bubbles can be produced and what their dynamics are upon irradiation. Here, we first presented the formation of nanoscale bulk bubbles by irradiating pure water with accelerated electrons and their concentration and size distribution changes with the dose and rate of irradiation. The nanoparticle tracking analysis showed that irradiation can actually produce a certain amount of bulk nanobubbles in pure water. They exhibited a dependence on the irradiation dose rates and irradiation doses. The results indicated that the concentration of formed bulk nanobubbles increased as the irradiation dose rates increased, but it will increase and then decrease with the increased irradiation doses. The formed bulk nanobubbles could maintain stability for several hours. Our findings will provide a new angle of view for the radiation chemistry of water, and the formed nanobubbles may help elucidate the biological effects of irradiated solutions.