Disinfection and oxidation of sewage effluent water using ozone and UV technologies

Effect of wastewater quality parameters on coliform inactivation by tin oxide anodes

The effect of six water quality constituents on wastewater effluent disinfection by tin oxide anodes (TOAs) was investigated in single cell laboratory reactors. Several concentrations of suspended solids, chemical oxygen demand (COD), alkalinity, ammonia-nitrogen, nitrite-nitrogen, and nitrate-nitrogen were added to media containing 10⁶ total coliform bacteria mL^-1. Current was applied through the TOAs, and coliform bacteria viability was analyzed over time. Over 99.9% inactivation of coliform bacteria was found over 15 min in TOA reactors. Concentrations of the six water quality constituents typical of concentrations found in wastewaters had no effect on TOA disinfection efficacy. The results of this research demonstrate that TOAs, which could potentially be powered by solar panels, have potential as a sustainable disinfection process compared to chlorine, ozone, and ultraviolet light.

Differential removal of human pathogenic viruses from sewage by conventional and ozone treatments

Sewage contains a mixed ecosystem of diverse sets of microorganisms, including human pathogenic viruses. Little is known about how conventional as well as advanced treatments of sewage, such as ozonation, reduce the environmental spread of viruses. Analyses for viruses were therefore conducted for three weeks in influent, after conventional treatment, after additional ozonation, and after passing an open dam system at a full-scale treatment plant in Knivsta, Sweden. Viruses were concentrated by adsorption to a positively charged filter, from which they were eluted and pelleted by ultracentrifugation, with a recovery of about 10%. Ion Torrent sequencing was used to analyze influent, leading to the identification of at least 327 viral species, most of which belonged to 25 families with some having unclear classification. Real-time PCR was used to test for 21 human-related viruses in inlet, conventionally treated, and ozone-treated sewage and outlet waters. The viruses identified in influent and further analyzed were adenovirus, norovirus, sapovirus, parechovirus, hepatitis E virus, astrovirus, pecovirus, picobirnavirus, parvovirus, and gokushovirus. Conventional treatment reduced viral concentrations by one to four log10, with the exception of adenovirus and parvovirus, for which the removal was less efficient. Ozone treatment led to a further reduction by one to two log10, but less for adenovirus. This study showed that the amount of all viruses was reduced by conventional sewage treatment. Further ozonation reduced the amounts of several viruses to undetectable levels, indicating that this is a promising technique for reducing the transmission of many pathogenic human viruses.

Evaluation of synergy and bacterial regrowth in photocatalytic ozonation disinfection of municipal wastewater

The use of solar and ultraviolet titanium dioxide photocatalytic ozonation processes to inactivate waterborne pathogens (Escherichia coli, Salmonella species, Shigella species and Vibrio cholerae) in synthetic water and secondary municipal wastewater effluent is presented. The performance indicators were bacterial inactivation efficiency, post-disinfection regrowth and synergy effects (collaboration) between ozonation and photocatalysis (photocatalytic ozonation). Photocatalytic ozonation effectively inactivated the target bacteria and positive synergistic interactions were observed, leading to synergy indices (SI) of up to 1.86 indicating a performance much higher than that of ozonation and photocatalysis individually (SI≤1, no synergy; SI>1 shows synergy between the two processes). Furthermore, there was a substantial reduction in contact time required for complete bacterial inactivation by 50-75% compared to the individual unit processes of ozonation and photocatalysis. Moreover, no post-treatment bacterial regrowth after 24 and 48h in the dark was observed. Therefore, the combined processes overcame the limitations of the individual unit processes in terms of the suppression of bacterial reactivation and regrowth owing to the fact that bacterial cells were irreparably damaged. The treated wastewater satisfied the bacteriological requirements in treated wastewater for South Africa.

Evaluation of a coagulation/flocculation-lamellar clarifier and filtration-UV-chlorination reactor for removing emerging contaminants at full-scale wastewater treatment plants in Spain

The presence and elimination of 25 emerging contaminants in two full-scale Spanish wastewater treatment plants was studied. The tertiary treatment systems consisted of coagulation, flocculation lamellar settlement and filtration (pulsed-bed sand filters) units, and disinfection was carried out by medium pressure UV light lamps and chlorination. Diclofenac and carbamazepine were found to be the emerging contaminants with the highest concentrations in secondary effluents. Photodegradable emerging contaminants (e.g. ketoprofen, triclosan and diclofenac) were removed by filtration-UV light radiation-chlorination whereas most hydrophobic compounds (e.g. galaxolide and tonalide) were eliminated by coagulation-flocculation followed by lamellar clarification, a unit in which a seasonal trend was observed. Overall mass removal efficiency was about 60%. 1-(8-Chlorocarbazolyl) acetic acid, an intermediate product of the photodegradation of diclofenac, was detected after filtration-UV-chlorination, but not after coagulation-flocculation and lamellar clarification. This study demonstrated potential for general applicability of two established tertiary treatment systems to eliminate emerging contaminants.

Disinfection of a wastewater flow treated by advanced primary treatment using O₃, UV and O₃/UV combinations

This study was conducted to evaluate the ozone, UV and O₃/UV processes for the reuse of sewage treatment plant effluent (Universidad Autonoma Metropolitana Azcapotzalco wastewater treatment plant). The ozone/UV process was compared to individual ozone and the UV processes and control parameters were total and fecal coliforms. Different ozone concentrations (6-12 mg O₃/min) and different UV fluencies (6.7-20.12 mJ/cm²) were tested. It is possible to conclude than none of the processes achieved the disinfection levels required to comply with the Mexican standard NOM-003-SEMARNAT-1997. The continuous ozone process offered the lower total and fecal coliforms reductions, while UV light resulted a disinfection agent with higher germicide power than ozone. The maximum logarithmic reduction achieved due to the combined ozone/UV process was of 2.04 for fecal coliforms and of 2.17 for total coliforms. The next 8 combinations showed lower removal efficiencies, but always higher than those obtained with the single ozone or UV processes. The ozone/UV process was highly effective for the disinfection and a synergistic effect was observed.

Field investigation of advanced oxidation of secondary effluent from municipal wastewater treatment plant

Successful treatment of the secondary effluent ensures its safe disposal and water reclamation for water reuse. To understand the effect of ultraviolet (UV) irradiation in combination with hydrogen peroxide (H(2)O(2)) on secondary effluent under field conditions, an advanced oxidation system, UV+H(2)O(2), was installed and fed with the effluent at 1.0, 1.5 and 2.0 m(3) h(- 1) over a period of 6 months. The electrical energy density for the UV reactor was varied between 0.5 and 5.2 kWh m(-3) and H(2)O(2) added at concentrations of 0, 13 or 26 mg L(-1). The feed and product water samples were taken periodically and analyzed for biological (heterotrophic plate count-HPC, total and fecal coliform-TC and FC) and chemical (NH(4)(+)-N, NO(3)(-)-N, NO(2)(-)-N and total organic carbon-TOC) parameters. For the treatment of UV+26 mg L(- 1) H(2)O(2), flow rates of 1.0, 1.5 and 2.0 m(3) h(- 1) resulted in > 4-log removal of HPC with a maximum survivor of 20 CFU mL(-1) and > 4 log reduction of FC with a survivor of 8 CFU (100 mL)(- 1). The electrical energy density of 1.5 kWh m(-3) was optimum for the inactivation. The NO(2)(-)-N concentrations of the product water were 0.09-0.42 mg L(- 1) compared with 0.04-0.09 mg L(- 1)in the feed. With or without H(2)O(2) addition, NO(2)(-)-N concentration increased with increases in UV electrical energy density. The highest increase in NO(2)(-)-N was associated with the maximum energy density of 5.2 kWh m(-3). Increase in H(2)O(2) dose reduced NO(3)(-)-N concentration by 2.0 to 5.7%. The overall results showed that the advanced oxidation technology prepared the effluent for safe disposal and/or for water reclamation for reuse.