Karl G. Linden

Low-Pressure UV Inactivation and DNA Repair Potential of Cryptosporidium parvum Oocysts

ABSTRACT Because Cryptosporidium parvum oocysts are very resistant to conventional water treatment processes, including chemical disinfection, we determined the kinetics and extent of their inactivation by monochromatic, low-pressure (LP), mercury vapor lamp UV radiation and their subsequent potential for DNA repair of UV damage. A UV collimated-beam apparatus was used to expose suspensions of purifiedC. parvum oocysts in phosphate-buffered saline, pH 7.3, at 25°C to various doses of monochromatic LP UV. C. parvuminfectivity reductions were rapid, approximately first order, and at a dose of 3 mJ/cm2 (=30 J/m2), the reduction reached the cell culture assay detection limit of ∼3 log10. At UV doses of 1.2 and 3 mJ/cm2, the log10 reductions of C. parvum oocyst infectivity were not significantly different for control oocysts and those exposed to dark or light repair conditions for UV-induced DNA damage. These results indicate that C. parvum oocysts are very sensitive to inactivation by low doses of monochromatic LP UV radiation and that there is no phenotypic evidence of either light or dark repair of UV-induced DNA damage.

UV disinfection of adenoviruses: molecular indications of DNA damage efficiency.

ABSTRACT Adenovirus is a focus of the water treatment community because of its resistance to standard, monochromatic low-pressure (LP) UV irradiation. Recent research has shown that polychromatic, medium-pressure (MP) UV sources are more effective than LP UV for disinfection of adenovirus when viral inactivation is measured using cell culture infectivity assays; however, UV-induced DNA damage may be repaired during cell culture infectivity assays, and this confounds interpretation of these results. Objectives of this work were to study adenoviral response to both LP and MP UV using (i) standard cell culture infectivity assays and (ii) a PCR assay to directly assess damage to the adenoviral genome without introducing the virus into cell culture. LP and MP UV dose response curves were determined for (i) log inactivation of the virus in cell culture and (ii) UV-induced lesions per kilobase of viral DNA as measured by the PCR assay. Results show that LP and MP UV are equally effective at damaging the genome; MP UV is more effective at inactivating adenovirus in cell culture. This work suggests that the higher disinfection efficacy of MP UV cannot be attributed to a difference in DNA damage induction. These results enhance our understanding of the fundamental mechanisms of UV disinfection of viruses—especially double-stranded DNA viruses that infect humans—and improve the ability of the water treatment community to protect public health.

Impact of UV Disinfection Combined with Chlorination/Chloramination on the Formation of Halonitromethanes and Haloacetonitriles in Drinking Water

The application of UV disinfection in water treatment is increasing due to both its effectiveness against protozoan pathogens, and the perception that its lack of chemical inputs would minimize disinfection byproduct formation. However, previous research has indicated that treatment of nitrate-containing drinking waters with polychromatic medium pressure (MP), but not monochromatic (254 nm) low pressure (LP), UV lamps followed by chlorination could promote chloropicrin formation. To better understand this phenomenon, conditions promoting the formation of the full suite of chlorinated halonitromethanes and haloacetonitriles were studied. MP UV/postchlorination of authentic filter effluent waters increased chloropicrin formation up to an order of magnitude above the 0.19 μg/L median level in the U.S. EPAs Information Collection Rule database, even at disinfection-level fluences (<300 mJ/cm(2)) and nitrate/nitrite concentrations (1.0 mg/L-N) relevant to drinking waters. Formation was up to 2.5 times higher for postchlorination than for postchloramination. Experiments indicated that the nitrating agent, NO(2)(•), generated during nitrate photolysis, was primarily responsible for halonitromethane promotion. LP UV treatment up to 1500 mJ/cm(2) did not enhance halonitromethane formation. Although MP UV/postchloramination enhanced dichloroacetonitrile formation with Sigma-Aldrich humic acid, formation was not significant in field waters. Prechlorination/MP UV nearly doubled chloropicrin formation compared to MP UV/postchlorination, but effects on haloacetonitrile formation were not significant.

Comparative disinfection efficiency of pulsed and continuous-wave UV irradiation technologies

Pulsed UV (PUV) is a novel UV irradiation system that is a non-mercury lamp-based alternative to currently used continuous-wave systems for water disinfection. PUV polychromatic irradiation disinfection efficiency was compared to that from continuous-wave monochromatic low-pressure (LP) and polychromatic medium-pressure (MP) UV systems, using two types of actinometry (ferrioxalate and iodide-iodate) and an absolute spectral emission method for fluence measurement. All three methods were in good agreement. Once accurate and reliable methods for fluence measurement were established, the inactivation of Escherichia coli and pathogen surrogates phage T4 and T7 were investigated under each technology. Inactivation was significantly faster using PUV irradiation compared to LP or MP UV lamps at equivalent fluence levels. A significant fraction of the enhanced PUV inactivation efficiency was due to wavelengths greater than 295 nm.

Phototransformation of selected organophosphorus pesticides: Roles of hydroxyl and carbonate radicals

The phototransformation of two organophosphorus pesticides, parathion and chlorpyrifos, by hydroxyl radicals and carbonate radicals in aqueous solution were studied. Addition of hydrogen peroxide increased the UV degradation rates of both pesticides and data were simulated through kinetic modeling. The second-order rate constants of parathion and chlorpyrifos with hydroxyl radical were determined to be 9.7 +/- 0.5 x 10(9) and 4.9 +/- 0.1 x 10(9) M(-1) s(-1), respectively. The presence of bi/carbonate ions reduced the pesticide degradation rates via scavenging of hydroxyl radical but the formation of carbonate radical also contributed to the degradation of the pesticides with second-order reaction rate constants of 2.8 +/- 0.2 x 10(6) and 8.8 +/- 0.4 x 10(6) M(-1) s(-1) for parathion and chlorpyrifos, respectively. The dual roles of bicarbonate ion in UV/H2O2 treatment systems, i.e., scavenging of hydroxyl radicals and formation of carbonate radicals, were examined and discussed using a simulative kinetic model. The transformation of pesticides by carbonate radicals at environmentally relevant bi/carbonate concentrations was shown to be a significant contributor to the environmental fate of the pesticides and it reshaped the general phototransformation kinetics of both pesticides in UV/H2O2 systems.

Enhanced biodegradation of carbamazepine after UV/H2O2 advanced oxidation.

Carbamazepine is one of the most persistent pharmaceutical compounds in wastewater effluents due to its resistance to biodegradation-based conventional treatment. Advanced oxidation can efficiently degrade carbamazepine, but the toxicity and persistence of the oxidation products may be more relevant than the parent. This study sets out to determine whether the products of advanced oxidation of carbamazepine can be biotransformed and ultimately mineralized by developing a novel methodology to assess these sequential treatment processes. The methodology traces the transformation products of the (14)C-labeled carbamazepine during UV/hydrogen peroxide advanced oxidation and subsequent biotransformation by mixed, undefined cultures using liquid scintillation counting and liquid chromatography with radioactivity, mass spectrometry, and UV detectors. The results show that the oxidation byproducts of carbamazepine containing a hydroxyl or carbonyl group can be fully mineralized by a mixed bacterial inoculum. A tertiary treatment approach that includes oxidation and biotransformation has the potential to synergistically mineralize persistent pharmaceutical compounds in wastewater treatment plant effluents. The methodology developed for this study can be applied to assess the mineralization potential of other persistent organic contaminants.

UV/H2O2 treatment of drinking water increases post-chlorination DBP formation

Ultraviolet (UV) irradiation has become popular as a primary disinfectant because it is very effective against Cryptosporidium and does not directly form regulated disinfection by-products. Higher UV doses and UV advanced oxidation (UV/H2O2) processes are under consideration for the treatment of trace organic pollutants (e.g. pharmaceuticals, personal care products). Despite the disinfection effectiveness of UV light, a secondary disinfectant capable of maintaining a distribution system residual is required to meet current U.S. regulation. This study investigated changes in disinfection by-product (DBP) formation attributed to UV or UV/H2O2 followed by application of free chlorine to quench hydrogen peroxide and provide residual disinfectant. At a UV dose of 1000 mJ/cm(2), trihalomethane (THM) yield increased by up to 4 microg/mg-C and 13 microg/mg-C when treated with low and medium pressure UV, respectively. With the addition of hydrogen peroxide, THM yield increased by up to 25 microg/mg-C (5mg-H2O2/L) and 37 microg/mg-C (10 mg-H2O2/L). Although no changes in DBPs are expected during UV disinfection, application of UV advanced oxidation followed by chlorine addition was assessed with regard to impacts on DBP formation.

Enhanced UV Inactivation of Adenoviruses under Polychromatic UV Lamps

ABSTRACT Adenovirus is recognized as the most UV-resistant waterborne pathogen of concern to public health microbiologists. The U.S. EPA has stipulated that a UV fluence (dose) of 186 mJ cm−2 is required for 4-log inactivation credit in water treatment. However, all adenovirus inactivation data to date published in the peer-reviewed literature have been based on UV disinfection experiments using UV irradiation at 253.7 nm produced from a conventional low-pressure UV source. The work reported here presents inactivation data for adenovirus based on polychromatic UV sources and details the significant enhancement in inactivation achieved using these polychromatic sources. When full-spectrum, medium-pressure UV lamps were used, 4-log inactivation of adenovirus type 40 is achieved at a UV fluence of less than 60 mJ cm−2 and a surface discharge pulsed UV source required a UV fluence of less than 40 mJ cm−2. The action spectrum for adenovirus type 2 was also developed and partially explains the improved inactivation based on enhancements at wavelengths below 230 nm. Implications for water treatment, public health, and the future of UV regulations for virus disinfection are discussed.

Degradation of Antibiotic Activity during UV/H2O2 Advanced Oxidation and Photolysis in Wastewater Effluent

Trace levels of antibiotics in treated wastewater effluents may present a human health risk due to the rise of antibacterial activity in the downstream environments. Advanced oxidation has a potential to become an effective treatment technology for transforming trace antibiotics in wastewater effluents, but residual or newly generated antibacterial properties of transformation products are a concern. This study demonstrates the effect of UV photolysis and UV/H2O2 advanced oxidation on transformation of 6 antibiotics, each a representative of a different structural class, in pure water and in two different effluents and reports new or confirmatory photolysis quantum yields and hydroxyl radical rate constants. The decay of the parent compound was monitored with HPLC/ITMS, and the corresponding changes in antibacterial activity were measured using bacterial inhibition assays. No antibacterially active products were observed following treatment for four of the six antibiotics (clindamycin, ciprofloxacin, penicillin-G, and trimethoprim). The remaining two antibiotics (erythromycin and doxycycline) showed some intermediates with antibacterial activity at low treatment doses. The antibacterially active products lost activity as the UV dose increased past 500 mJ/cm(2). Active products were observed only in wastewater effluents and not in pure water, suggesting that complex secondary reactions controlled by the composition of the matrix were responsible for their formation. This outcome emphasizes the importance of bench-scale experiments in realistic water matrices. Most importantly, the results indicate that photosensitized processes during high dose wastewater disinfection may be creating antibacterially active transformation products from some common antibiotics.

Degradation and byproduct formation of parathion in aqueous solutions by UV and UV/H2O2 treatment

The photodegradation of parathion in aqueous solutions by UV and UV/H(2)O(2) processes was evaluated. Direct photolysis of parathion both by LP (low pressure) and MP (medium pressure) lamps at pH 7 was very slow with quantum yields of 6.67+/-0.33x10(-4) and 6.00+/-1.06x10(-4)molE(-1), respectively. Hydrogen peroxide enhanced the photodegradation of parathion through the reaction between UV generated hydroxyl radical and parathion with a second-order reaction rate constant of 9.70+/-0.45x10(9)M(-1)s(-1). An optimum molar ratio between hydrogen peroxide and parathion was determined to be between 300 and 400. Photodegradation of parathion yielded several organic byproducts, of which the paraoxon, 4-nitrophenol, O,O,O-triethyl thiophosphate and O,O-diethyl-methyl thiophosphate were quantified and their occurrence during UV/H(2)O(2) processes were discussed. NO(2)(-), PO(4)(3-), NO(3)(-) and SO(4)(2-) were the major anionic byproducts of parathion photodegradation and their recover ratios were also discussed. A photodegradation scheme suggesting three simultaneous pathways was proposed in the study.