Eutrophic water purification efficiency using a combination of hydrodynamic cavitation and ozonation on a pilot scale

Hybrid hydrodynamic cavitation (HC) technique for the treatment and disinfection of lake water

Water reclamation from lakes needs to be accomplished efficiently and affordably to ensure the availability of clean, disinfected water for society. Previous treatment techniques, such as coagulation, adsorption, photolysis, ultraviolet light, and ozonation, are not economically feasible on a large scale. This study investigated the effectiveness of standalone HC and hybrid HC + H₂O₂ treatment techniques for treating lake water. The effect of pH (3 to 9), inlet pressure (4 to 6 bar), and H₂O₂ loading (1 to 5 g/L) were examined. At pH = 3, inlet pressure of 5 bar and H₂O₂ loadings of 3 g/L, maximum COD and BOD removal were achieved·H₂O₂ was observed to significantly improve the performance of the HC when used as a chemical oxidant. In an optimal operating condition, a COD removal of 54.5 % and a BOD removal of 51.5 % using HC alone for 1 h is observed. HC combined with H₂O₂ removed 64 % of both COD and BOD. The hybrid HC + H₂O₂ treatment technique resulted in a nearly 100% removal of pathogens. The results of this study indicate that the HC-based technique is an effective method for removing contaminants and disinfection of the lake water.

Flow-mode water treatment under simultaneous hydrodynamic cavitation and plasma

Over the last two decades, the scientific community and industry have made huge efforts to develop environmental protection technologies. In particular, the scarcity of drinking water has prompted the investigation of several physico-chemical treatments, and synergistic effects have been observed in hyphenated techniques. Herein, we report the first example of water treatment under simultaneous hydrodynamic cavitation and plasma discharge with the intense generation of radicals, UV light, shock waves and charged particles. This highly reactive environment is well suited to the bulk treatment of polluted water (i.e. E. coli disinfection and organic pollutant degradation). We have developed a new prototype and have efficiently applied this hybrid technology to water disinfection and the complete degradation of methanol in water with the aim of demonstrating its scalability. We have analyzed the mechanisms of water disinfection under the abovementioned conditions and verified them by measuring cavitation noise spectra and plasma emission spectra. We have also used the degradation of textile dyes and methanol solutions as an indicator for the formation of radicals.

Water quality retrieval and algae inhibition from eutrophic freshwaters with iron-rich substrate based ecological floating beds treatment

Ecological floating rafts in restoration of eutrophic freshwaters were deemed to a frequently used method. In this study, a manipulative experiment using ecological floating rafts based on iron-rich substrate (IRS) was conducted. The approach was attempted to study the nutrient removal efficiency and algae inhibition effect of IRS. The results showed that 98.2% chlorophyll-a (chl-a) removal rate was achieved in 7-day restoration by IRS accompanied with high nutrient removal efficiency. In addition, iron-rich substrate based ecological floating beds could reached 82.1% chl-a removal rate and 98.5% total phosphorus (TP) removal rate with the increasing activity of aquatic organisms through a 50-day pilot scale experiment. The findings imply that iron-rich substrate-based ecological floating beds are an alternative method for ecological restoration of eutrophic freshwaters.

Harnessing cavitational effects for green process intensification

The impressive chemico-physical effects observed in sonochemistry are a result of cavitation, as ultrasonic and hydrodynamic cavitation does not interact with matter at the atomic and molecular levels. Bubble collapse leads to the quasi-adiabatic heating of the vapour inside bubbles, giving rise to local hot spots in the fluid. Cavitation thus transforms a mechanical energy into high kinetic energy, which is released in very short bursts that are exploited for green process intensification. This paper reviews relevant applications of hydrodynamic and acoustic cavitation with the aim of highlighting the particular advantages that these phenomena offer to the intensification of green chemical processes. Emulsification, biodiesel preparation, wastewater decontamination, organic synthesis, enzymatic catalysis and extractions are discussed among others. As a comparison, hydrodynamic cavitation technique is more advantageous in dealing with process intensification at large-scale, as well as the enhancement of mass transfer and heat transfer, while ultrasonic cavitation technique is more convenient to operate, easier to control in the studies at lab-scale, and exhibits more efficient in producing active free radicals and inducing the cleavage of volatile compounds.

Treatment of Eutrophic Water and Wastewater from Valsequillo Reservoir, Puebla, Mexico by Means of Ozonation: A Multiparameter Approach

The present work aims to elucidate the possibility of injecting ozone into surface waters combined with urban wastewaters in order to improve the water quality of the High Atoyac Sub-basin (HAS) in Central Mexico. For this purpose, twenty physicochemical parameters, eight heavy metals, seven organic compounds, and one biological indicator were assessed in water from different sites of the studied area (the Alseseca River, the Atoyac River and the Valsequillo Reservoir). Results demonstrated that O3 injection led to the decrease of the aromatic fraction of organic molecules since the Spectral Absorption Coefficient at 254 nanometers (SAC254) reduction was found to be 31.7% in the Valsequillo Reservoir water samples. Maximum Chemical Oxygen Demand (COD) removal was observed to be 60.2% from the Alseseca River with a 0.26 mg O3/mg initial COD dose. Among all the phthalates studied in the present work, Di(2-ethylhexyl) phthalate (DEHP) exhibited the highest concentration (5.8 μg/L in the Atoyac River). Treatment with O3 was not effective in eliminating fecal coliforms (FC) in waters that host high organic matter (OM) loads as opposed to waters with low OM. After the injection of 4.7 mg O3/mg COD in the VO3-AT water sample, a 90% removal of Iron (Fe) and Aluminum (Al) was registered; while Manganese (Mn), Nickel (Ni), Zinc (Zn), and Cooper (Cu) showed a 73%, 67%, 81%, and 80% removal, respectively; Chromium (Cr) registered the highest removal (~100%). The present work demonstrated that while finding a suitable O3 dose to improve the quality of water in the HAS, the 5-days Biochemical Oxygen Demand (BOD5)/COD ratio (i.e., biodegradability) is more important than the overall OM removal percentage proving that O3 injection is a feasible process for the treatment of eutrophic waters from HAS.

Study on mechanism of algal inactivation and pollution removal by Fe-ACF electro Fenton-like process

Algae inactivation and algal metabolic pollutant removal of Chlorella and Duneliella salina from seawater by the Fe-ACF electro Fenton-like process has been studied. The experiments were conducted at neutral condition of pH 8.3 (raw water) and 6.2 to break through the limit of strong acidic conditions. Experimental results indicated that the Fe-ACF electro Fenton-like process has a good effect for algae inactivation and for pollutant removal in neutral conditions, and pH has no obvious effect for the inactivation of algae. At optimum conditions, the inactivation efficiency for algae could reach up to 98%. A pH of 8.3 is more favorable for pollutant removal. Under neutral pH conditions, the coupling effect of indirect oxidation of •OH, direct oxidation of free chlorine and coagulation and adsorption of ferric and ferrous hydroxy complexes in the electro Fenton-like process was achieved, and the coupling effect promotes the inactivation of algae and the removal of metabolic pollutants.