Urban water reuse: microbial pathogens control by direct filtration and ultraviolet disinfection.

Physicochemical treatment efficiency for unrestricted urban water reuse was evaluated at a conventional activated-sludge wastewater treatment plant (WWTP). Pilot plant set-up consisted of an alum coagulation step, granular media upflow flocculation and direct downflow dual-media filtration followed by ultraviolet disinfection (dose of 95 mJ cm⁻²). Optimum aluminum sulfate dosage of 10 mg L⁻¹ and coagulation pH 7.0 were preset based on bench scale tests. Under WWTP stable operation, water quality met United States Environmental Protection Agency (USEPA) suggested guidelines for unrestricted urban reuse regarding turbidity (mean value 1.3 NTU) and suspended solids (mean value 2.1 mg L⁻¹). When WWTP overall plant performance dropped from 90 to 80% (although BOD value stayed below 6 mg O2 L⁻¹, suggesting unrestricted reuse), solids breakthrough in filtrate was observed. Microorganism removal rates were: total coliforms 60.0%, Escherichia coli 63.0%, Giardia spp. 81.0%, and helminth eggs 62.5%; thus organisms still remained in filtrate. Ultraviolet (UV) disinfection efficiency was 4.1- and 3.8-log for total coliforms and E. coli, respectively. Considering low UV efficiency obtained for helminths and the survival of protozoa and helminths in the environment, effluent quality presents risk to public health if destined for unrestricted urban reuse.

Inactivation of bacteria and helminth in wastewater treatment plant effluent using oxidation processes.

The contamination of bodies of water by raw and even treated sewage is worrying because pathogens that affect public health and the environment are not fully eliminated in wastewater treatment systems. The disinfection step is an important barrier to adopt to reduce this contamination. However, widely used disinfectants such as chlorine do not guarantee the inactivation of resistant organisms such as spore-forming bacteria and helminth eggs. This study evaluated the effectiveness of processes of peroxidation (H2O2), ultraviolet radiation (UV) and peroxidation assisted by ultraviolet radiation (H2O2/UV) in terms of reduction and inactivation of total coliform bacteria, Escherichia coli, helminth eggs and larvae present in a treated sewage. Doses of UV radiation of 70 mJ cm(-2) and hydrogen peroxide concentration of 30 mg L(-1) were used. The number of bacteria reduced after UV and H2O2/UV processes was 3 and 4 log, respectively. An average reduction of 59% in the number of eggs was verified when using H2O2, UV, and H2O2/UV processes. Helminth larvae were reduced by 24% after H2O2 and UV; the process H2O2/UV did not reduce the number of larvae. Statistically significant differences between the processes for both organisms were not observed.

Cryptosporidium spp. and Giardia spp. in surface water supply of Campinas, southeast Brazil.

Surface water contaminated by domestic sewage discharges is a potential source of pathogens, including protozoa. During 2005-2006, the source water (Atibaia River) of the Surface Water Treatment Plant (WTP) of Campinas city, São Paulo, Brazil was sampled to obtain an assessment of Cryptosporidium oocyst and Giardia cyst concentrations. Calcium carbonate flocculation (CCF) and membrane filtration (MF) concentration techniques, with and without purification by immunomagnetic separation (IMS) were evaluated. The cysts and oocysts were detected by immunofluorescence assay (IFA) and confirmed by differential interference contrast (DIC). Membrane filtration method generally produced higher recovery efficiency. Giardia spp. was detected in 87.5% of the water samples analyzed with densities ranging from 2.5 to 120 cysts per L. Cryptosporidium spp were detected in 62.5% and the concentrations ranged from 15 to 60 oocysts per L. Cryptosporidium oocyst and Giardia cyst concentrations detected in this study were elevated and are associated with discharge of untreated sewage in Atibaia River. Measures should be taken to protect surface water from sources of contamination.

Giardia duodenalis: Number and Fluorescence Reduction Caused by the Advanced Oxidation Process (H2O2/UV).

This study evaluated the effect of peroxidation assisted by ultraviolet radiation (H2O2/UV), which is an advanced oxidation process (AOP), on Giardia duodenalis cysts. The cysts were inoculated in synthetic and surface water using a concentration of 12 g H2O2 L(-1) and a UV dose (λ = 254 nm) of 5,480 mJcm(-2). The aqueous solutions were concentrated using membrane filtration, and the organisms were observed using a direct immunofluorescence assay (IFA). The AOP was effective in reducing the number of G. duodenalis cysts in synthetic and surface water and was most effective in reducing the fluorescence of the cyst walls that were present in the surface water. The AOP showed a higher deleterious potential for G. duodenalis cysts than either peroxidation (H2O2) or photolysis (UV) processes alone.

Infectivity of Giardia duodenalis Cysts from UV Light-Disinfected Wastewater Effluent Using a Nude BALB/c Mouse Model.

Giardia duodenalis is a protozoan of public health interest that causes gastroenteritis in humans and other animals. In the city of Campinas in southeast Brazil, giardiasis is endemic, and this pathogen is detected at high concentrations in wastewater effluents, which are potential reservoirs for transmission. The Samambaia wastewater treatment plant (WWTP) in the city of Campinas employs an activated sludge system for sewage treatment and ultraviolet (UV) light for disinfection of effluents. To evaluate this disinfection process with respect to inactivating G. duodenalis cysts, two sample types were investigated: (i) effluent without UV disinfection (EFL) and (ii) effluent with UV disinfection (EFL+UV). Nude immunodeficient BALB/c mice were intragastrically inoculated with a mean dose of 14 cysts of G. duodenalis recovered from effluent from this WWTP, EFL, or EFL+UV. All animals inoculated with G. duodenalis cysts developed the infection, but animals inoculated with UV-exposed cysts released a lower average concentration of cysts in their faeces than animals inoculated with cysts that were not UV disinfected. Trophozoites were also observed in both groups of animals. These findings suggest that G. duodenalis cysts exposed to UV light were damaged but were still able to cause infection.