Abstract
The present work aimed to study the effect of ozonation on the organic sum parameters linked to enhanced biodegradability. Laboratory experiments were conducted with the effluent of four Austrian urban wastewater treatment plants with low food to microorganism ratios and different matrix characteristics. Biochemical oxygen demand over 5 days (BOD5) was measured before ozonation and after application of different specific ozone doses (Dspec) (0.4, 0.6 and 0.8 g O3/g DOC). Other investigated organic parameters comprised chemical oxygen demand (COD), dissolved organic carbon (DOC), UV absorption at 254 nm (UV254), which are parameters that are applied in routine wastewater analysis. Carbamazepine and benzotriazole were measured as reference micropollutants. The results showed a dose-dependent increase in biological activity after ozonation; this increase was linked to the enhanced biodegradability of substances that are recalcitrant to biodegradation in conventional activated sludge treatment. The highest relative change was determined for BOD5, which already occurred between 0 and 0.4 g O3/g DOC for all samples. Increasing the Dspec to 0.6 and 0.8 g O3/g DOC resulted in a less pronounced increase. DOC was not substantially decreased after ozonation, which was consistent with a low reported degree of mineralization, while partial oxidation led to a quantifiable decrease in COD (7 to 17%). Delta UV254 and the decline in specific UV absorption after ozonation clearly correlated with Dspec. In contrast, for COD and biodegradable DOC (BDOC), a clear dose-response pattern was identified only after exposure to BOD5 measurement. Indications for improved biodegradability were further supported by the rise in the BOD5/COD ratio. The results indicated that subsequent biological processes have a higher degradation potential after ozonation. The further reduction in biodegradable organic carbon emission by the combination of ozonation and biological post treatment represents another step towards sustainable water resource management in addition to micropollutant abatement.
Highlights
Biological processes, such as the conventional activated sludge process, currently represent the majority of applied processes in wastewater treatment plants (WWTPs) worldwide
dissolved organic carbon (DOC) was not substantially decreased after ozonation, which was consistent with a low reported degree of mineralization, while partial oxidation led to a quantifiable decrease in chemical oxygen demand (COD) (7 to 17%)
The current paper dealt with the assessment of biodegradability after ozonation, focusing on the changes of Biochemical oxygen demand over 5 days (BOD5) and the impact of exposure time for biochemical oxygen demand (BOD) measurement on other relevant conventional organic sum parameters indicating enhanced bioavailability
Summary
Biological processes, such as the conventional activated sludge process, currently represent the majority of applied processes in wastewater treatment plants (WWTPs) worldwide. While conventional organic sum parameters such as COD and BOD are removed to a high degree, others comprising micropollutants are released into the environment unchanged or metabolized (Krzeminski et al, 2019; Quintana et al, 2005). To mitigate this release, particular attention has been directed towards advanced treatments, such as ozonation. The removal efficiencies of various organic micropollutants are influenced by their reactivity with ozone and spontaneously formed hydroxyl radicals (Zimmermann et al, 2011), the ozone dose (Lee et al, 2013) and the composition of the wastewater (Schindler Wildhaber et al, 2015). Ozone reacts with micropollutants (Lee and von Gunten, 2016; Rizzo et al, 2019) and targets electron-rich moieties, such as olefins, aromatic rings, and amines (von Sonntag and von Gunten, 2012)
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