Among several disruption methods tested so far, ozonation and sonication were distinguished from others by their effective cell rupturing ability. In this study, these disruption methods were combined to enhance the retrieval of biofuel feedstock (carbohydrates and lipids) from microalgae. A mixed microalgal culture was subjected to first ozonation, followed by sonication. Compared to the extraction of 22% of total lipids and 47% of total carbohydrates by sole ozonation, the retrieval of algal metabolites reached 59% and 81% of total lipids and carbohydrates, respectively. The optimum process variables were found by means of a response surface modeling and quadratic programming.

In this study, we investigated the effect of different radical scavengers on the nitrate and/or nitric acid (NO₃⁻ and/or HNO₃) formation chain in liquid while the dielectric barrier discharge plasma system (DBD) was used for ozone (O₃) generation. The effects of the excess concentration of each scavenger were studied individually. In addition, ultrapure water (UPW), tap water, and surface water samples were examined in the same condition. Due to the absence of scavengers in the UPW, we expected the highest NO₃⁻ formation in this experiment because all active species produced by the DBD system should have formed NO₃⁻. However, the obtained results were unexpected; the highest NO₃⁻ formation was obtained in the tap water at 385 ± 4.6 mg/L. The results can be explained by some compounds in tap water acting as a trap for radicals involved in chain reactions that form NO₃⁻ and/or HNO_3. The second highest result was obtained in the sodium hydroxide solution as 371 ± 4.9 mg/L, since the OH⁻ ions accelerated the decomposition of O₃ to its intermediates such as hydroperoxide (HO₂⁻), ozonide (O₃⁻), and hydroxyl radical (OH^•), and, by increasing radicals in the liquid, more chain reactions can be promoted that lead to the formation of NO₃⁻ and/or HNO₃. On the other hand, the quenching of radicals by scavengers such as carbonate ion and phosphoric acid and/or the long-term stabilization of O₃ as O₃ negatively affected the chain reactions that generate NO₃⁻ and/or HNO₃.