Disinfection of wastewater by a complete equipment based on a novel ultraviolet light source of microwave discharge electrodeless lamp: Characteristics of bacteria inactivation, reactivation and full-scale studies

Ultraviolet (UV) light is widely used for wastewater disinfection. Traditional electrode-excited UV lamps, such as low-pressure mercy lamps (LPUV), encounter drawbacks like electrode aging and rapid light attenuation. A novel UV source of microwave discharge electrodeless lamp (MDEL) has aroused attention, yet its disinfection performance is unclear and still far from practical application. Here, we successfully developed a complete piece of equipment based on MDELs and achieved the application for disinfection in wastewater treatment plants (WWTPs). The light emitted by an MDEL (MWUV) shared a spectrum similar to that of LPUV, with the main emission wavelength at 254 nm. The inactivation rate of Gram-negative E. coli by MWUV reached 4.5 log at an intensity of 1.6 mW/cm2 and a dose of 20 mJ/cm2. For Gram-positive B. subtilis, an MWUV dose of 50 mJ/cm2 and a light intensity of 1.2 mW/cm2 reached an inactivation rate of 3.4 log. A higher MWUV intensity led to a better disinfection effect and a lower photoreactivation rate of E. coli. When inactivated by MWUV with an intensity of 1.2 mW/cm2 and a dose of 16 mJ/cm2, the maximum photoreactivation rate and reactivation rate constant Kmax of E. coli were 0.63 % and 0.11 % h-1 respectively. Compared with the photoreactivation, the dark repair of E. coli was insignificant. The full-scale application of the MDEL equipment was conducted in two WWTPs (10,000 m3/d and 15,000 m3/d). Generally 2-3 log inactivation rates of fecal coliforms in secondary effluent were achieved within 5-6 s contact time, and the disinfected effluent met the emission standard (1000 CFU/L). This study successfully applied MDEL for disinfection in WWTPs for the first time and demonstrated that MDEL has broad application prospects.

Efficient wastewater disinfection using a novel microwave discharge electrodeless ultraviolet system with ozone at an ultra-low dose

Microwave discharge electrodeless lamp (MDEL) is a novel ultraviolet (UV) light source. Synergistic disinfection using UV light emitted by MDEL (MWUV) coupled with ozone (O3) at an ultra-low dose was investigated. Escherichia coli and Bacillus subtilis were deactivated more effectively by MWUV/O3 than by either MWUV or O3 alone. MWUV/O3 treatment using an O3 concentration of 0.4 mg/L gave an E. coli inactivation rate of 5.52 log. The photoreactivation degree and rate of E. coli were lower after inactivation by MWUV/O3 treatment than after MWUV treatment alone. The maximum photoreactivation rates after the MWUV/O3 and MWUV treatments were 2.90% and 16.08%, respectively. MWUV/O3 disinfection also inhibited dark resurrection of E. coli and gave a maximum dark resurrection rate of 0.0036%. Electron paramagnetic resonance spectroscopy indicated that more hydroxyl radicals were generated during MWUV/O3 treatment. Scanning electron microscopy and laser confocal scanning microscopy observations indicated that O3 played a key role in breaking down the cell structure. MWUV/O3 treatment gave a good disinfection effect on fecal coliform bacteria in actual domestic wastewater. The results indicated that inactivation of bacteria can be more effectively achieved by MWUV treatment with O3.

Ultraviolet-based synergistic processes for wastewater disinfection: A review

Ultraviolet (UV) irradiation is widely used for wastewater disinfection but suffers from low inactivation rates and can cause photoreactivation of microorganisms. Synergistic disinfection with UV and oxidants is promising for enhancing the inactivation performance. This review summarizes the inactivation effects on representative microorganisms by UV/hydrogen peroxide (H₂O₂), UV/ozone (O₃), UV/persulfate (PS), UV/chlorine, and UV/chlorine dioxide (ClO₂). UV synergistic processes perform better than UV or an oxidant alone. UV mainly attacks the DNA or RNA in microorganisms; the oxidants H₂O₂ and O₃ mainly attack the cell walls, cell membranes, and other external structures; and HOCl and ClO₂ enter cells and oxidize proteins and enzymes. Free radicals can have strong oxidation effects on cell walls, cell membranes, proteins, enzymes, and even DNA. At similar UV doses, the inactivation rates of Escherichia coli with UV alone, UV/H₂O₂, UV/O₃, UV/PS (peroxydisulfate or peroxymonosulfate), and UV/chlorinated oxidant (chlorine, ClO₂, and NH₂Cl) range from 2.03 to 3.84 log, 2.62-4.30 log, 4.02-6.08 log, 2.93-5.07 log, and 3.78-6.55 log, respectively. The E. coli inactivation rates are in the order of UV/O₃ ≈ UV/Cl₂ > UV/PS > UV/H₂O₂. This order is closely related to the redox potentials of the oxidants and quantum yields of the radicals. UV synergistic disinfection processes inhibit photoreactivation of E. coli in the order of UV/O₃ > UV/PS > UV/H₂O₂. The activation mechanisms and formation pathways of free radicals with different UV-based synergistic processes are presented. In addition to generating HO·, O₃ can reduce the turbidity and chroma of wastewater to increase UV penetration, which improves the disinfection performance of UV/O₃. This knowledge will be useful for further development of the UV-based synergistic disinfection processes.

Somatostatin receptors SSTR2 and SSTR5 are expressed in the human thoracic duct

Somatostatin and its analog octreotide have been used successfully to treat postoperative chylothorax, and it has been shown that octreotide binds with high affinity to somatostatin receptor (SSTR) subtypes 2 and 5. Therefore, we investigated expression of SSTR2 and SSTR5 in the human thoracic duct by immunohistochemistry. Normal rat pancreas was used as a positive control for antibodies against SSTR2 and SSTR5, and Factor VIII-related antigen, SMA, actin, elastin, or collagen type II, III, IV or V antibodies were used to identify cell types and structures within the human thoracic duct. The antibodies against SSTR2 and SSTR5 worked well and yielded positive staining in control rat islets. In the human thoracic duct, SSTR2 was present in smooth muscle cells and some scattered structures which were stained by antibodies against Factor VIII-related antigen, SMA, actin, elastin or collagen type II, III, IV or V. SSTR5 was also present in smooth muscle cells. The presence of SSTR2 and SSTR5 in the human thoracic duct sheds light on the mechanism of somatostatin and octreotide use in the successful treatment of chylothorax and offers new molecular pathways to explore for potential future therapies.

Regulated expression of a cell division control-related protein kinase during development

Protein kinases are important signaling molecules that are known constituents of cellular pathways critical for normal cellular growth and development. We have recently identified a new protein kinase, p58, which contains a large domain that is highly homologous to the cell division control p34cdc2 protein kinase. This new cell division control-related protein kinase was originally identified as a component of semipurified galactosyltransferase; thus, it has been denoted galactosyltransferase-associated protein kinase. In vitro, this protein kinase has been shown to phosphorylate a number of substrates, including histone H1, casein, and galactosyltransferase. In vivo, we have found that this protein kinase affects galactosyltransferase enzyme activity and that it is apparently involved in some aspect of normal cell cycle regulation. In this report, we find that the p58 gene is evolutionarily well conserved and expressed ubiquitously, but to varying extents, in adult tissues. In developmentally staged embryos, p58 expression was elevated early in embryogenesis and then decreased dramatically. In the murine submandibular gland, p58 expression was elevated between day 14 and day 16 post coitus. Expression in the submandibular gland appeared to parallel the proliferation and differentiation of specific cell types as judged by in situ hybridization. These studies indicate that the p58 protein kinase may have a critical function during normal embryonic development and that this protein kinase continues to be expressed in differentiated adult tissues.