Disinfecting capabilities of oxychlorine compounds

The bacterial virus f2 was inactivated by chlorine dioxide at acidic, neutral, and alkaline pH values. The rate of inactivation increased with increasing pH. Chlorine dioxide disproportionation products, chlorite and chlorate, were not active disinfectants. As chlorine dioxide solutions were degraded under alkaline conditions, they displayed reduced viricidal effectiveness, thereby confirming the chlorine dioxide free radical as the active disinfecting species.     

Inactivation of human and simian rotaviruses by chlorine dioxide

The inactivation of single-particle stocks of human (type 2, Wa) and simian (SA-11) rotaviruses by chlorine dioxide was investigated. Experiments were conducted at 4 degrees C in a standard phosphate-carbonate buffer. Both virus types were rapidly inactivated, within 20 s under alkaline conditions, when chlorine dioxide concentrations ranging from 0.05 to 0.2 mg/liter were used. Similar reductions of 10(5)-fold in infectivity required additional exposure time of 120 s at 0.2 mg/liter for Wa and at 0.5 mg/liter for SA-11, respectively, at pH 6.0. The inactivation of both virus types was moderate at neutral pH, and the sensitivities to chlorine dioxide were similar. The observed enhancement of virucidal efficiency with increasing pH was contrary to earlier findings with chlorine- and ozone-treated rotavirus particles, where efficiencies decreased with increasing alkalinity. Comparison of 99.9% virus inactivation times revealed ozone to be the most effective virucidal agent among these three disinfectants.     

Inactivation of human and simian rotaviruses by chlorine dioxide.

The inactivation of single-particle stocks of human (type 2, Wa) and simian (SA-11) rotaviruses by chlorine dioxide was investigated. Experiments were conducted at 4 degrees C in a standard phosphate-carbonate buffer. Both virus types were rapidly inactivated, within 20 s under alkaline conditions, when chlorine dioxide concentrations ranging from 0.05 to 0.2 mg/liter were used. Similar reductions of 10(5)-fold in infectivity required additional exposure time of 120 s at 0.2 mg/liter for Wa and at 0.5 mg/liter for SA-11, respectively, at pH 6.0. The inactivation of both virus types was moderate at neutral pH, and the sensitivities to chlorine dioxide were similar. The observed enhancement of virucidal efficiency with increasing pH was contrary to earlier findings with chlorine- and ozone-treated rotavirus particles, where efficiencies decreased with increasing alkalinity. Comparison of 99.9% virus inactivation times revealed ozone to be the most effective virucidal agent among these three disinfectants.     

Inactivation of simian rotavirus SA11 by chlorine, chlorine dioxide, and monochloramine.

The kinetics of inactivation of simian rotavirus SA11 by chlorine, chlorine dioxide, and monochloramine were studied at 5 degrees C with a purified preparation of single virions and a preparation of cell-associated virions. Inactivation of the virus preparations with chlorine and chlorine dioxide was studied at pH 6 and 10. The monochloramine studies were done at pH 8. With 0.5 mg of chlorine per liter at pH 6, more than 4 logs (99.99%) of the single virions were inactivated in less than 15 s. Both virus preparations were inactivated more rapidly at pH 6 than at pH 10. With chlorine dioxide, however, the opposite was true. Both virus preparations were inactivated more rapidly at pH 10 than at pH 6. With 0.5 mg of chlorine dioxide per liter at pH 10, more than 4 logs of the single-virus preparation were inactivated in less than 15 s. The cell-associated virus was more resistant to inactivation by the three disinfectants than was the preparation of single virions. Chlorine and chlorine dioxide, each at a concentration of 0.5 mg/liter and at pH 6 and 10, respectively, inactivated 99% of both virus preparations within 4 min. Monochloramine at a concentration of 10 mg/liter and at pH 8 required more than 6 h for the same amount of inactivation.     

Inactivation of simian rotavirus SA11 by chlorine, chlorine dioxide, and monochloramine

The kinetics of inactivation of simian rotavirus SA11 by chlorine, chlorine dioxide, and monochloramine were studied at 5 degrees C with a purified preparation of single virions and a preparation of cell-associated virions. Inactivation of the virus preparations with chlorine and chlorine dioxide was studied at pH 6 and 10. The monochloramine studies were done at pH 8. With 0.5 mg of chlorine per liter at pH 6, more than 4 logs (99.99%) of the single virions were inactivated in less than 15 s. Both virus preparations were inactivated more rapidly at pH 6 than at pH 10. With chlorine dioxide, however, the opposite was true. Both virus preparations were inactivated more rapidly at pH 10 than at pH 6. With 0.5 mg of chlorine dioxide per liter at pH 10, more than 4 logs of the single-virus preparation were inactivated in less than 15 s. The cell-associated virus was more resistant to inactivation by the three disinfectants than was the preparation of single virions. Chlorine and chlorine dioxide, each at a concentration of 0.5 mg/liter and at pH 6 and 10, respectively, inactivated 99% of both virus preparations within 4 min. Monochloramine at a concentration of 10 mg/liter and at pH 8 required more than 6 h for the same amount of inactivation.     

Inactivation of bacteria by Purogene

The bacteriocidal efficacy of Purogene, a stabilized aqueous solution of chlorine dioxide (ClO₂) was examined using bacteria of concern to public health. The organisms tested were: Escherichia coli, Pseudomonas aeruginosa, Yersinia enterocolitica, Klebsiella pneumoniae, Streptococcus pyogenes Group A, Salmonella typhimurium and Bacillus subtilis . The test organisms responded differently to inactivation by Purogene. At least a 4 log reduction in bacterial counts was noted when Purogene was applied at a concentration of 0.75 mg/l. Since Purogene is a stabilized complex, it was necessary to provide a chemical environment suitable for the release of ClO₂ in this solution. This was done by varying the pH of Purogene from 3.5 to 8.6 (pH of Purogene is 8.6) while keeping the pH of the experimental medium constant (pH 7.0). The results showed that Purogene was most efficacious at the lowest pH tested (pH 3.5). This indicates that as chlorine dioxide solutions were reduced to chlorite (which predominates at pH 8.6), their bacteriocidal efficacy was reduced, suggesting free chlorine dioxide as the active disinfecting species.     

Inactivation of bacteria by Purogene

The bacteriocidal efficacy of Purogene, a stabilized aqueous solution of chlorine dioxide (ClO2) was examined using bacteria of concern to public health. The organisms tested were: Escherichia coli, Pseudomonas aeruginosa, Yersinia enterocolitica, Klebsiella pneumoniae, Streptococcus pyogenes Group A, Salmonella typhimurium and Bacillus subtilis. The test organisms responded differently to inactivation by Purogene. At least a 4 log reduction in bacterial counts was noted when Purogene was applied at a concentration of 0.75 mg/l. Since Purogene is a stabilized complex, it was necessary to provide a chemical environment suitable for the release of ClO2 in this solution. This was done by varying the pH of Purogene from 3.5 to 8.6 (pH of Purogene is 8.6) while keeping the pH of the experimental medium constant (pH 7.0). The results showed that Purogene was most efficacious at the lowest pH tested (pH 3.5). This indicates that as chlorine dioxide solutions were reduced to chlorite (which predominates at pH 8.6), their bacteriocidal efficacy was reduced, suggesting free chlorine dioxide as the active disinfecting species.     

Mechanisms of inactivation of poliovirus by chlorine dioxide and iodine.

Chlorine dioxide and iodine inactivated poliovirus more efficiently at pH 10.0 than at pH 6.0. Sedimentation analyses of viruses inactivated by chlorine dioxide and iodine at pH 10.9 showed that viral RNA separated from the capsids, resulting in the conversion of virions from 156S structures to 80S particles. The RNAs release from both chlorine dioxide- and iodine-inactivated viruses cosedimented with intact 35S viral RNA. Both chlorine dioxide and iodine reacted with the capsid proteins of poliovirus and changed the pI from pH 7.0 to pH 5.8. However, the mechanisms of inactivation of poliovirus by chlorine dioxide and iodine were found to differ. Iodine inactivated viruses by impairing their ability to adsorb to HeLa cells, whereas chlorine dioxide-inactivated viruses showed a reduced incorporation of [14C]uridine into new viral RNA. We concluded, then, that chlorine dioxide inactivated poliovirus by reacting with the viral RNA and impairing the ability of the viral genome to act as a template for RNA synthesis.     

Use of acid-tolerant xylanase for bleaching of kraft pulps

A xylanase from Aspergillus kawachii, active at pH 2.0–2.5, was found to be suitable for improvement of bleachability. Due to the low working pH of the xylanase, the metal cations were also removed and thus the metal removal stage using chelating agents could be omitted. The use of acid-tolerant xylanase is especially beneficial prior to ozone or chlorine dioxide bleaching stages due to the minimization of pH adjustment steps during bleaching.     

Efficiency of Chlorine Dioxide as a Bactericide

We found chlorine dioxide to be a more effective disinfectant than chlorine in sewage effluent at pH 8.5. Chlorine dioxide was also found to be a more stable bactericide in relation to pH in the range studied.     

Oxidation of horseradish peroxidase compound II to compound I.

In the reaction between equimolar amounts of horseradish peroxidase and chlorite, the native enzyme is oxidized directly to Compound II (Hewson, W.D., and Hager, L.P. (1979) J. Biol. Chem. 254, 3175-3181). At acidic pH but not at alkaline values, this initial reaction is followed by oxidation of Compound II to Compound I. The highly pH-dependent chemistry of Compound II can be readily demonstrated by the reduction of Compound I, with ferrocyanide at acidic, neutral, and alkaline pH values. Titration at low pH yields very little Compound II, whereas at high pH, the yield is quantitative. Similarly, the reaction of horseradish peroxidase and chlorite at low pH yields Compound I while only Compound II is formed at high pH. At intermediate pH values both the ferrocyanide reduction and the chlorite reaction produce intermediate yields of Compound II. This behavior is explained in terms of acidic and basic forms of Compound II. The acidic form is reactive and unstable relative to the basic form. Compound II can be readily oxidized to Compound I by either chloride or chlorine dioxide in acidic solution. The oxidation does not occur in alkaline solution, nor will hydrogen peroxide cause the oxidation of Compound II, even at low pH.     

Mutagenic properties of spent bleaching liquors from sulphite pulps and a comparison with kraft pulp bleaching liquors

Parameters influencing the mutagenic properties of spent bleaching liquors from sulphite pulps have been studied. In addition a comparison has been made between the properties of spent liquors from sulphite and kraft pulp bleaching. In the sulphite process the cooking base had no influence on the mutagenicity of the chlorination stage. In contrast, removing the extractives before chlorination especially for dissolving pulp resulted in an increase in mutagenic activity. The mutagenicity decreased significantly after substituting 40% of the chlorine with chlorine dioxide. Sequential addition of chlorine and chlorine dioxide resulted in higher activity than simultaneous or premixed chlorination as observed for liquors from kraft pulp. Increasing the pH of the extracts or addition of sulphur dioxide decreased the mutagenicity. Expressed as 10(7) revertants per kappa number and ton pulp the mutagenicity varied between 10 and 40 for sulphite pulp while the corresponding figures for kraft pulp were 100-225.     

Optimization of hydrogen peroxide in totally chlorine free bleaching of cellulose pulp from olive tree residues

The influence of the operating conditions used in the bleaching of olive wood trimmings pulp (viz. hydrogen peroxide concentration and time) on the yield, kappa index and viscosity of the resulting pulp and on strength-related properties of paper sheets was studied to determine the optimal bleaching conditions of this pulp. Hydrogen peroxide bleached pulps at different sequences (oxygen, ozone, chlorine dioxide and alkaline extractions) were compared. Hydrogen peroxide bleaching proved to be suitable for this pulp. Considerable improvements in viscosity were obtained with respect to other bleaching sequences such as oxygen, ozone and chlorine dioxide. Hydrogen peroxide bleaching decreased the kappa index 51.3% less than ozone bleaching, 25.0% less than chlorine dioxide (D) and 6.3% less combined chlorine dioxide-alkaline extraction (DE). To obtain kappa indices 50.9% and 37.9% lower than the index achieved by hydrogen peroxide, oxygen (LaO(p)) and ozone (LaO(LaZ)R) sequences respectively were needed. Lower-medium levels of hydrogen peroxide concentrations (1-3%) and high reaction times (210 min) proved to be suitable for bleaching of pulp olive trimming residues. This approach could be used on this residue to produce adequately bleached pulp.     

Peracetic acid as an alternative wastewater disinfectant to chlorine dioxide

AIMS: The aim of this study was to compare the efficiency of peracetic acid with that of chlorine dioxide in the disinfection of wastewater from a sewage treatment plant (serving about 650 000 inhabitants) that has been using peracetic acid as a disinfectant since 1998. METHODS AND RESULTS: A total of 23 samplings were made, each consisting of three samples: from secondary effluent, effluent disinfected with 2 mg l(-1) of peracetic acid and effluent disinfected with 2.2 mg l(-1) of chlorine dioxide (contact time 20 min). For each sample, measurements were made of the heterotrophic plate count at 36 degrees C, total and faecal coliforms, Escherichia coli, enterococci, pH, suspended solids and chemical oxygen demand (COD). During the first phase of the experiment the peracetic acid was seen to be less efficient than chlorine dioxide. To improve the disinfectant action a system of mechanical agitation was added which led to a greater efficiency in the inactivation of bacteria of faecal origin. CONCLUSIONS: Both products were found to be influenced by the level of microbial contamination, the amount of suspended solids and COD but not by the pH of the effluent before disinfection. The immediate mixing of the wastewater and disinfectant caused a greater reduction in enterococci. SIGNIFICANCE AND IMPACT OF THE STUDY: Since peracetic acid was seen to produce a high abatement of micro-organisms, it can be considered as a valid alternative to chlorine dioxide in the disinfection of wastewaters.     

Chlorine dioxide inactivation of Cryptosporidium parvum oocysts and bacterial spore indicators.

Cryptosporidium parvum, which is resistant to chlorine concentrations typically used in water treatment, is recognized as a significant waterborne pathogen. Recent studies have demonstrated that chlorine dioxide is a more efficient disinfectant than free chlorine against Cryptosporidium oocysts. It is not known, however, if oocysts from different suppliers are equally sensitive to chlorine dioxide. This study used both a most-probable-number-cell culture infectivity assay and in vitro excystation to evaluate chlorine dioxide inactivation kinetics in laboratory water at pH 8 and 21 degrees C. The two viability methods produced significantly different results (P < 0.05). Products of disinfectant concentration and contact time (Ct values) of 1,000 mg. min/liter were needed to inactivate approximately 0.5 log(10) and 2.0 log(10) units (99% inactivation) of C. parvum as measured by in vitro excystation and cell infectivity, respectively, suggesting that excystation is not an adequate viability assay. Purified oocysts originating from three different suppliers were evaluated and showed marked differences with respect to their resistance to inactivation when using chlorine dioxide. Ct values of 75, 550, and 1,000 mg. min/liter were required to achieve approximately 2.0 log(10) units of inactivation with oocysts from different sources. Finally, the study compared the relationship between easily measured indicators, including Bacillus subtilis (aerobic) spores and Clostridium sporogenes (anaerobic) spores, and C. parvum oocysts. The bacterial spores were found to be more sensitive to chlorine dioxide than C. parvum oocysts and therefore could not be used as direct indicators of C. parvum inactivation for this disinfectant. In conclusion, it is suggested that future studies address issues such as oocyst purification protocols and the genetic diversity of C. parvum, since these factors might affect oocyst disinfection sensitivity.     

Alkaline protease from a new obligate alkalophilic isolate of Bacillus sphaericus

An obligate alkalophilic Bacillus sphaericus strain, isolated from alkaline soils in the Himalaya, produced an extracellular protease which was optimally active at 50–55 °C and pH 10.5. The enzyme was stable in presence of 500 mg chlorine l^–1 and as a detergent additive. Its stability in presence of laundry detergents was comparable to that of commercial proteases. The gelatin layer in 25 g of used X-ray films was efficiently hydrolyzed within 12 min at 50 °C, pH 11.0 and 25 U protease/ml.     

常用消毒剂次氯酸钠和二氧化氯对小林三代虫的杀灭效果

为了有效控制三代虫病, 实验以寄生于金鱼的小林三代虫(Gyrodactylus kobayashii)为动物模型, 研究了两种常用消毒剂次氯酸钠溶液(NaClO)和二氧化氯(ClO2)的杀虫效果。结果表明: 在离体(in vitro)条件下, 当NaClO的有效浓度0.2 mg/L或ClO2的有效浓度0.15 mg/L 时, 小林三代虫的平均存活时间均少于2h, 而对照组中小林三代虫的平均存活时间是20.8h。当ClO2的有效浓度0.15 mg/L时, 70%以上的虫体发黑, 而其他浓度处理组, 大部分虫体即使死亡, 虫体依然保持透明。在在体(in vivo)条件下, 当 NaClO的有效浓度0.2 mg/L或ClO2的有效浓度0.5 mg/L 时, 驱虫率都几乎达到100%, 并且驱虫率随着药物浓度的增加而提高,但当ClO2的有效浓度为0.6 mg/L时, 养殖水体出现了白色絮状物。在在体条件下, NaClO的驱虫效果好于ClO2。在金鱼的急性毒性实验中, NaClO和ClO2的安全浓度分别是0.18和0.48 mg/L, 仅稍低于其在在体条件下完全驱除小林三代虫的最小浓度(0.2、0.5 mg/L), 说明次氯酸钠溶液和二氧化氯在驱除三代虫时对金鱼不太安全, 因此, 在治疗金鱼的三代虫病时要慎使次氯酸钠溶液和二氧化氯。然而, 这两种消毒剂能否适用于其他鱼类三代虫病的治疗则有待进一步研究。     

Molecular and biochemical characterization of a new alkaline active multidomain xylanase from alkaline wastewater sludge

A xylanase gene, xyn-b39, coding for a multidomain glycoside hydrolase (GH) family 10 protein was cloned from the genomic DNA of the alkaline wastewater sludge of a paper mill. Its deduced amino acid sequence of 1,481 residues included two carbohydrate-binding modules (CBM) of family CBM_4_9, one catalytic domain of GH 10, one family 9 CBM and three S-layer homology (SLH) domains. xyn-b39 was expressed heterologously in Escherichia coli, and the recombinant enzyme was purified and characterized. Xyn-b39 exhibited maximum activity at pH 7.0 and 60 °C, and remained highly active under alkaline conditions (more than 80 % activity at pH 9.0 and 40 % activity at pH 10.0). The enzyme was thermostable at 55 °C, retaining more than 90 % of the initial activity after 2 h pre-incubation. Xyn-b39 had wide substrate specificity and hydrolyzed soluble substrates (birchwood xylan, beechwood xylan, oat spelt xylan, wheat arabinoxylan) and insoluble substrates (oat spelt xylan and wheat arabinoxylan). Hydrolysis product analysis indicated that Xyn-b39 was an endo-type xylanase. The K _m and V _max values of Xyn-b39 for birchwood xylan were 1.01 mg/mL and 73.53 U/min/mg, respectively. At the charge of 10 U/g reed pulp for 1 h, Xyn-b39 significantly reduced the Kappa number (P < 0.05) with low consumption of chlorine dioxide alone.     

Behavior of hydrogen peroxide in electrolyzed anode water

Oxygen electrodes and spectrophotometric analysis have been used to evaluate the contribution of H2O2, in addition to available chlorine, to the high redox potential of electrolyzed anode water (EAW) with potassium chloride as an electrolyte. H2O2 was added externally to EAW, and the reaction between H2O2 and the available chlorine in the water was examined. EAW has a low pH (2.5), a high concentration of dissolved oxygen, and extremely high redox potentials (19 mg/l and 1,319 mV) when the available chlorine is at the concentration of about 580 microM. The addition of H2O2 to EAW led to H2O2 decomposition, and the amount of oxygen produced was equivalent to the amount of available chlorine. Oxygen production was reduced by ascorbic acid, and completely inhibited by 600 microM ascorbate. The rate of oxygen production was much affected by pH, and was slowest at or near pH 5.0. Rates were particularly high in alkaline solution. Absorbance at 235 nm (pH 3.0 and 5.0) and 292 nm (pH 10.0) decreased when H2O2 was added to the EAW at these pHs, and the extent of decrease was similar pH dependency to that of the oxygen production rate. Oxygen was not produced after H2O2 was added to EAW at pH 2.6 when available chlorine was absent, but oxygen was produced after potassium hypochlorite was added to such EAW. The oxygen production rates in EAW without available chlorine at pH 5.0 and 2.0, pH adjustment with KOH and HCl, respectively, were faster than the rate at pH 2.6, and fastest at pH 2.0. These results suggest that H2O2 or hydroxyl radicals derived from Fenton's reaction did not contribute to the high redox potential of EAW prepared with chlorine compounds as an electrolyte, so that the decomposition of H2O2 occurred rapidly with the reactions of chlorine and hypochlorite ions in EAW.     

Susceptibility of the brine shrimp Artemia and its pathogen Vibrio parahaemolyticus to chlorine dioxide in contaminated sea-water.

Adults and nauplii of the brine shrimp, Artemia, together with Vibrio parahaemolyticus, were placed in sewage-contaminated sea-water which had been treated with chlorine dioxide (Hallox E-100TM) to test its potential as a disinfectant for salt water aquaculture. The nauplii were very susceptible to low concentrations of chlorine dioxide (47 micrograms/l Cl-), but the adults were slightly more resistant. Sterile sea-water treated with lower concentrations of chlorine dioxide (less than 47 micrograms/l Cl-) had no effect on the shrimp, but inhibited the growth of V. parahaemolyticus. In sewage-contaminated sea-water, chlorine dioxide levels of 285-2850 micrograms/l, necessary for the inactivation of V. parahaemolyticus and any native bacteria, destroyed the Artemia culture. Hallox E-100TM persisted in sea-water for 18 h, but later decayed. We conclude that: (i) Artemia nauplii are a sensitive and convenient test-organism to determine low concentrations of chlorine dioxide in sea-water; (ii) chlorine dioxide is efficient for controlling V. parahaemolyticus in sea-water; and (iii) chlorine dioxide should be further evaluated as a potential disinfectant for aquaculture, but, for higher organisms than Artemia.