Insights into influencing factor, degradation mechanism and potential toxicity involved in aqueous ozonation of oxcarbazepine (CHEM46939R1).

Oxcarbazepine (OXC), as a potent antiepileptic drug, is widely used in recent years, but its residue is potentially harmful to the environment. Although ozonation is a high-efficient technology for chemical oxidation during water treatment, it cannot completely mineralize organic matters, but partially transforms them into some unidentified by-products. In order to provide more insight into OXC ozonation process, the influencing factor, transformation mechanism and potential toxicity were comprehensively investigated in this study. The results showed that the optimal ozonation temperature was 20 °C with a pseudo-first-order reaction rate constant of 0.161 min-1. The increase of pH significantly enhanced OXC degradation, while the presence of bicarbonate caused a remarkable negative effect, manifesting that hydroxyl radical (OH) oxidation should play an important role in OXC ozonation. Moreover, transformation mechanism was further elucidated based on the identification of ten OXC-related by-products using UPLC-Q-TOF-MSn, which mainly consisted of electrophilic substitution, N-heterocyclic ring cleavage and re-arrangement, hydroxylation, carbonylation, demethoxylation and deamidation, etc. The toxicity evaluation, using US Environmental Protection Agency Toxicity Estimation Software Tool (US-EPA TEST), suggested that most identified by-products were probably more toxic than OXC itself. Besides, further experiments, by measuring inhibitory effect of ozonated mixture on Vibrio fischeri bioluminescence, demonstrated that by-products with higher toxicity tended to be accumulated under a short reaction time. Taken together, the present investigation provided valuable information for further understanding OXC ozonation process, and suggested that special attention should be paid to the control and elimination of toxic transformation by-products in future studies.

Effective ethanol production by reutilizing waste distillage anaerobic digestion effluent in an integrated fermentation process coupled with both ethanol and methane fermentations.

An integrated ethanol-methane fermentation coupled system characterized with full wastewater reutilization was proposed. The waste distillage originated from ethanol distillation was treated with anaerobic digestion and then recycled for medium preparation in the next ethanol fermentation run. This process could enhance wastewater reutilization, save fresh water and reduce energy consumption in the cassava-based ethanol production. The results indicated that, when using anaerobic effluents from the digestion process with only one tank, an ethanol concentration of 10.5% (v/v) compatible with that of conventional one could be achieved, but ethanol fermentation was partially inhibited and operation time gradually prolonged from 48 to 105 h. Using anaerobic effluents from the digestion process with two subsequently connected tanks, ethanol fermentation performance could be largely improved, and the fermentation lag could be completely eliminated. The performance enhancement was due to the concentrations reduction in organic acids, such as acetic and propionic acids in the digestion effluents using two digestion tanks in-series.

A novel full recycling process through two-stage anaerobic treatment of distillery wastewater for bioethanol production from cassava.

In the present study, a novel full recycling process for bioethanol production was investigated, where three mathematical models were established to simulate the accumulation of major soluble inhibitory substances, including organic compounds, total ions, volatile fatty acids (VFAs) and colorants. These inhibitory substances in the reused water reached a relative steady state after 3-7 batches of anaerobic treatment and recycling process, which coincided with the results of mathematical models. There were no negative effects of these inhibitory substances on ethanol fermentation and the final ethanol yield, fermentation time, starch utilization ratio were very close to that of the conventional process using tap water. However, approximately 7.54% (w/w) of water was lost during each circulation, which was replenished in subsequent circulations, to assure consistent fermentation broth volume. This novel process was confirmed to have a stable operation over 13 recycles. It is concluded the stable states of the inhibitory substances in the reused water can assure this recycling process will run successfully.