Critical parameters influencing the continuous performance of upflow microbubble airlift photocatalytic process treating pharmaceutical pollutants.

The advances in heterogeneous photocatalysts are still confined to evaluating the functional photocatalytic activity of catalysts in simple batch-mode operation. Nevertheless, the long-term stability, recovery-reusability, and cost-effectiveness of photocatalysts are critical issues in practical applications for pollution control. This study examined the critical parameters to improve the photocatalytic degradation activity of the antibiotic tetracycline and strategized successful continuous performance in a two-stage photocatalytic process adopting sequencing batch-mode microbubble upflow airlift reactor (UALR) followed by the centrifugal separation of CdS nanoparticles (NPs). The most effective strategy for NPs separation was a sequential combination of gravity separation (10 min settling) in the settling phase and subsequent high-speed centrifugation (5 min at 25,000×g) of the settled NPs sediments, providing an economic benefit by reducing the centrifugation capacity. During steady state operation under the optimal conditions, the UALR showed reliable performance, resulting in 97-91% and 85-81% degradation efficiency at 60- and 30-min reaction time per cycle, respectively. A weak basic condition (pH 8) and dissolved oxygen (DO) supplementation increased the photocatalytic activity by 12% (0.0292 min-1) and 30% (0.0363 min-1) compared to the control. Trapping studies confirmed the enhanced performance using various reactive oxygen species scavengers, revealing an increase in •OH generation (6.5%).

Antimicrobial photodynamic inactivation of wastewater microorganisms by halogenated indole derivative capped zinc oxide.

Novel 5-bromoindole (5B)-capped zinc oxide (ZnO) nanoparticles (5BZN) were synthesized to improve the antibacterial, antibiofilm, and disinfection processes for the control of microorganisms in wastewater treatment. When exposed to 5BZN, the biofilm density and cell attachment were reduced dramatically, as measured by scanning electron microscopy (SEM). The 5BZN were also investigated for photodynamic treatment of multidrug-resistant (MDR) bacteria and toxicity. The combination of 5B and ZnO exhibited strong antibacterial and antibiofilm activities against MDR bacteria even at low doses (20 µg/mL). After 12.5 mW/cm2 blue LED irradiation, the composite 5BZN showed superior photodynamic inactivation of two wastewater MDR, Enterobacter tabaci E2 and Klebsiella quasipneumoniae SC3, with cell densities reduced by 3.9 log CFU/mL and 4.7 log CFU/mL, respectively, after 120 min. The mechanism of bacterial inactivation was studied using a scavenging investigation, and H2O2 was identified mainly as the reactive species for bacterial inactivation. The 5BZN exhibited higher photodynamic inactivation towards the total coliform bacteria in wastewater effluents under a blue LED light intensity of 12.5 mW/cm2 with almost complete inactivation of the coliform bacteria cells within 40 min. Furthermore, when 5BZN (100 mg/L) was added to the reactor, the level of tetracycline antibiotic degradation was increased by 63.6% after 120 min. The toxicity test, animal model nematode studies and seed germination assays, showed that 5BZN is harmless, highlighting its tremendous potential as a self-healing agent in large-scale photodynamic disinfection processes.

Fate of antibiotic resistant genes in wastewater environments and treatment strategies - A review.

Antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs) have emerged in aquatic environments through the discharge of large amounts of antibiotics into wastewater. Well-designed wastewater treatment plants (WWTPs) with effective treatment processes are essential to prevent the release of ARGs directly into the environment. Although some systematic sequential treatment methods are used to remove ARGs, considerable gaps in removal mechanisms will be discussed. Therefore, deep analysis and discussion of various treatment methods are required to understand the ARGs removal mechanisms. In this manuscript, the role of antibiotics and the resistance mechanism of ARB are discussed in depth. In addition, the fate of ARGs in an aquatic environment and detection methods are compared comprehensively and discussed. In particular, the advantages and disadvantages of various methods are summarized and reviewed critically. Finally, combined technologies, such as advanced oxidation process (AOP) with biochemical systems, membrane separation with electrochemical AOP, ultrafiltration (UF) membrane coupled with photocatalytic treatment, and UF membrane separation coupled with sonication, are introduced. Overall, low-energy anaerobic treatment reactors with any of the above combined treatments might reduce the discharge of large quantities of ARGs into the environment. Finally, this review provides valuable insights for better ARG removal technologies by introducing combined effective treatment strategies used in real WWTPs.