Reduction in chlorine requirements by control of nitrification in an oxygen activated sludge process

The objective of the study was to determine if chlorine could be saved by controlling nitrification in an oxygen activated sludge process so that the effluent would produce an ammonia concentration in the 2–4 mg l⁻¹ range. The hypothesis was that the ammonia would react with the chlorine to produce a stable combined residual at a much lower chlorine dosage than if the effluent was completely nitrified. In the latter case, breakpoint would have to be achieved with, potentially, a substantial amount of chlorine dissipated and lost in side reactions with residual organic materials.The study utilized two portable treatment units in two truck trailers on the site of the proposed 69th Street City of Houston 100 MGD Sewage Treatment Plant. The results indicated that chlorine requirements could be cut by one half or more if nitrification was controlled. The gross savings of chlorine were estimated to be in the one quarter of a million dollar range. Other findings were that there was no apparent effect of pH on chlorine residual in the range of 6.5–7.5; and that there was no apparent effect of operating the nitrification stage with air or high purity oxygen.     

Effect of oxidants on microalgal flocculation

The effects of chlorine, ozone and chlorine dioxide on Scenedesmus sp. cultures were studied. Algal cell viability and chlorophyll concentration decreased, and the concentration of dissolved organic substances increased with increasing applied oxidant concentration. Pretreatment with chlorine dioxide (1, 3 or 5 mg l⁻¹) or ozone (2.6, 4.6 or 8.1 mg l⁻¹) on algal cultures enhanced algal flocculation with alum, while prechlorination with 10 or 20 mg l⁻¹ increased the required dosage of alum by 15%. Scanning electron micrographs of oxidized cells revealed drastically adverse effects upon the cell surface architecture: in addition to the oxidation of noncellular organic materials, the oxidants damaged both cell surface structures and intracellular components. A model explaining the effects of the different oxidants on microalgal flocculation is suggested.     

Inactivation of heterotrophic bacterial populations in finished drinking water by chlorine and chloramines

The die-off of heterotrophic bacteria from a finished drinking water reservoir, located in southern California, was evaluated using chloramines and free chlorine. Understanding the inactivation of hetertrophic populations is valuable because it reflects the response to disinfection of naturally occurring organisms in their native state and environments. Disinfection studies with the heterotrophic bacterial group were performed during summer and winter months using different chloramine application techniques at pH 6 and 8. In addition, bacteria surviving exposure to chloramines and free chlorine was influenced predominantly by the presence of highly chlorine tolerant, red-pigmented bacteria, identified as Flavobacterium spp. Inactivation by chloramines, though, was chiefly dependent upon the method of application and pH. Viable bacteria recovered from the indigenous population after 60 min of exposure to chloramines (1.0 mg l⁻¹, pH 8) included members of Pseudomonas, Acinetobacter and Flavobacterium. In general, with contact times of 1 h or more, free chlorine and chloramine solutions (1.0–1.6 mg l⁻¹, pH 8) reduced total count levels below 50 colony forming units ml⁻¹.     

The toxicity of chlorine to a common vascular aquatic plant

Myriophyllum spicatum was exposed to various chlorine concentrations on a continuous and intermittent basis in 96-h toxicity studies utilizing a proportional diluter. Continuous exposure to chlorine concentrations as low as 0.05 mg l⁻¹ total residual chlorine (TRC) depressed shoot and total plant dry weights approx. 30% relative to controls. Shoot length was depressed approx. 16% at this concentration. Chlorophyll a was depressed 25% at 0.1 mg l⁻¹ TRC. However, intermittent exposure of plants to chlorine for three 2-h periods daily for 96 h indicated an insensitivity to repeated short term chlorine exposure at all concentrations but 1.0 mg l⁻¹ TRC. These results indicate that high level chlorine discharges from waste water facilities and electric generating plants could be a contributing factor impacting nearby submerged aquatic vegetation.     

Avoidance response of rainbow trout (Salmo gairdneri) to single-dose chlorination in a power plant discharge canal

Rainbow trout (Salmo gairdneri) were exposed to 20 min single-dose chlorine additions designed to achieve maximum total residual chlorine (TRC) concentrations of 0.04, 0.2, 0.6, and 1.0 mg l⁻¹. First retreats from the chlorine front occurred at 0.05 mg l⁻¹ TRC. Approximately 95% of the fish had moved downstream when TRC reached 0.5 mg l⁻¹, well before cumulative time-dose exposure approached lethal limits. Percentage of fish remaining near the discharge decreased linearly as TRC concentration rose, suggesting that a rapid rise in receiving water chlorine level might be beneficial in reducing cumulative time-dose exposure. Rainbow trout demonstrated the initial sensitivity to avoid lethal chlorine exposure, but complete assessment of the utility of the avoidance response must also consider distribution throughout chlorination and the potential for repeated exposure.     

A survey of Legionella pneumophila in water in 12 Canadian cities

A survey of 12 cities across Canada was conducted in order to determine the prevalence of Legionella species in potable water and cooling tower water within buildings. Legionellae were detected in 11.9% of the samples overall: 6.7% from potable water sources and 28.9% from cooling tower water. The maximum concentration of the organism was 45,000 l⁻¹ in one shower-water sample by culture methods. A significant difference in the isolation rate of Legionella pneumophila among cities was observed. The organism was isolated from waters at a temperature of 15–41°C and was most frequently isolated in the 20–29°C range. The concentration of free and total available chlorine in the water was not associated with legionellae recovery except that the organisms were never recovered when the free available chlorine residual exceeded 7.5 mg l⁻¹. Although L. pneumophila were in low concentrations or absent in most samples, the isolated organisms were usually serogroups 1 or 6, the same serogroups that are most often implicated in legionellosis cases in Canada.     

The effectiveness of chlorine residuals in inactivation of bacteria and viruses introduced by post-treatment contamination

The protection afforded the water consumer by the maintenance of a free or combined chlorine residual in water distribution systems was evaluated in a laboratory system provided with a simulated cross connection. Tap water, adjusted to the appropriate pH, temperature and chlorine residual, was challenged with varying levels of autoclaved sewage seeded with Shigella sonnei, Salmonella typhimurium, a coliform (IMVIC⁺⁺⁻⁻), poliovirus 1 and f2 bacterial virus. Comparative survivals of these microorganisms were evaluated over 2 h periods. As expected, microbial inactivation was increased by lower pH, higher temperature, higher initial chlorine concentration and lower sewage concentration. An initial free chlorine residual was more effective than an equivalent initial combined chlorine residual. Generally, S. sonnei, S. typhimurium and the coliform organism were inactivated at the same rate but poliovirus 1 was more resistant and f2 was the most resistant. At pH 8, with an initial free chlorine residual of 0.7 mg 1⁻¹, and added sewage levels of up to 1% by vol, 3 logs or greater bacterial inactivation was obtained within 60 min. Viral inactivation under these conditions was less than 2 logs.     

Role of aquatic plants in wastewater treatment by artificial wetlands

This report describes investigations using artificial wetlands which quantitatively assess the role of each of three higher aquatic plant types, Scirpus validus (bulrush), Phragmites communis (common reed) and Typha latifola (cattail), in the removal of nitrogen (via sequential nitrification-denitrification), BOD and TSS from primary municipal wastewaters. During the period August 1983–December 1984, the mean ammonia concentration of 24.7 mg l⁻¹ in the primary wastewater inflow (hydraulic application rate = 4.7 cm day⁻¹) was reduced to mean effluent levels of 1.4 mg l⁻¹ for the bulrush bed, 5.3 mg l⁻¹ for the reed bed and 17.7 mg l⁻¹ for the cattail bed, as compared to a mean value of 22.1 mg l⁻¹ for the unvegetated (control) bed. For all three vegetated beds, the mean effluent ammonia values were significantly below that for the unvegetated bed and for the inflow. The bulrushes and reeds (in that order) proved to be superior at removing ammonia, both with mean effluent levels significantly below that for the cattail bed. The high ammonia-N (and total N) removal efficiencies shown by the bulrush and reed beds are attributed to the ability of these plants to translocate O₂ from the shoots to the roots. The oxidized rhizosphere so formed stimulates sequential nitrification-denitrification. Similarly BOD removal efficiencies were highest in the bulrush and reed beds, both with mean effluent BOD levels (5.3 and 22.2 mg l⁻¹, respectively) significantly below that for the unvegetated bed (36.4 mg l⁻¹) and equal to or better than secondary treatment quality (30 mg l⁻¹). Our results demonstrate that higher aquatic plants can indeed play a significant role in secondary and advanced (N removal) wastewater treatment by wetland systems, a role that is completely distinct from that associated with their pollutant uptake capacity.     

Comparison of chlorine and chlorine dioxide toxicity to fathead minnows and bluegill

The comparative toxicity of total residual chlorine (TRC) and chlorine dioxide (ClO₂) was evaluated by conducting 96 h flow-through bioassays with three types of fish. The fish were subjected to an intermittent exposure regime in which biocide residuals were present for approx. 2-h periods beginning at 0, 24, 48 and 72 h into the tests. These conditions simulated the antifouling procedure (1 h day⁻¹ biocide addition) used to control biofouling of nuclear reactor heat exchangers at the Savannah River Plant near Aiken, South Carolina. LC₅₀ values showed that ClO₂ was approx. 2–4 times more toxic than TRC to: (1) juvenile and 1-year-old fathead minnows (Pimphales promelas); and (2) young-of-the-year bluegill (Lepomis macrochirus).The TRC mean 96-h LC₅₀ values were: 0.08 mg l⁻¹ for juvenile fathead minnows, 0.35 mg l⁻¹ for adult fathead minnows and 0.44 mg l⁻¹ for young-of-the-year bluegills. The ClO₂ mean LC₅₀ values were: 0.02 mg l⁻¹ for juvenile fathead minnows, 0.17 mg l⁻¹ for adult fathead minnows and 0.15 mg l⁻¹ for young-of-the-year bluegills.     

The effect of intermittent chlorination on freshwater phytoplankton

Lake Michigan phytoplankton showed a significant loss of chlorophyll a and permanent reduction of carbon uptake rates after exposure for 30 min to concentrations of total residual chlorine at or above 1 mg l⁻¹. At this level the photosynthetic system of the algae was irreversibly destroyed. Below 0.1 mgl⁻¹ total residual chlorine only slight changes in chlorophyll a were noted, and, following an initial decrease, carbon uptake rates exhibited nearly complete recovery after 24 h.     

Effects of inhibitors on nitrification in a packed-bed biological flow reactor

The individual effect of trivalent arsenic, hexavalent chromium and fluoride on nitrification is studied under continuous load in a packed bed biological flow reactor. The results show that Michaelis-Menten rate expression gives the best representation of nitrification data in the absence of inhibitors. However, in the presence of inhibitors, the system follows a non-competitive mode of inhibition with the following rate expression: The values of V_max and K_s are estimated as 1.466 mg l⁻¹ min⁻¹ and 2.349 mg l⁻¹ respectively. The inhibitor constant K_i is evaluated as 273 mg l⁻¹ for trivalent arsenic, 56 mg l⁻¹ for hexavalent chromium and 1185 mg l⁻¹ for fluoride.     

Chlorine demand in deep sea-water

Samples of deep sea-water were obtained at 25, 250 and 2000 m from the Sargasso Sea. The chlorine demands in these samples at any given contact time decrease with the depth at which the sample was obtained. The dissipation of chlorine occurs in two phases. The consumption rate of chlorine is similar in all three samples during the second phase at about 1 × 10⁻⁴ mg l⁻¹ min⁻¹. The difference in chlorine demand is caused primarily by the decrease in the organic chlorine demand, which occurs during the first phase of reactions, with depth reflecting the decreasing amount and increasing inertness of dissolved organic matter. The organic chlorine demands at 25, 250 and 2000 m are 0.9, 0.5 and 0.4 mg l⁻¹ respectively. These organic chlorine demands are significantly lower than those observed in coastal sea-waters with similar dose of added chlorine of about 5 mg l⁻¹. If sea-waters from various depths are available, deeper sea-water would be preferred as a coolant because of its smaller chlorine demand and lower initial temperature.     

The effect of dissolved oxygen concentration on nitrification

The effect of dissolved oxygen concentration on the rate of nitrification has been investigated by a number of researchers using both pure and mixed cultures, and cultures found in wastewater treatment systems. The maximum growth rate of both nitrification reactions are reported to be affected by dissolved oxygen concentration over the range of 0.3 mg l⁻¹ to as much as 4.0 mg l⁻¹. In some instances, it has been reported that a dissolved oxygen concentration in excess of 4.0 mg l⁻¹ is required to achieve maximum nitrification rates, while other investigators have found that only 0.5 to 1.0 mg l⁻¹ is required.It has been proposed that several factors are responsible for the wide range of reported nitrification rates with varying dissolved oxygen concentrations. Among these factors are the effects of oxygen diffusion in flocs, variation between measured results due to steady-state and dynamic measuring techniques, and double-substrate limited kinetics. This paper reviews the nitrification literature with respect to the effects of dissolved oxygen concentration, and shows that double-substrate limiting kinetics could account for the variation in the reported results.     

Mass transfer and reaction kinetics in the ozone/tap water system

The mass transfer and the reaction kinetics of ozone in tap water were examined. The contacting system was a well-mixed reactor with perpendicular jets. The ozone residual range was the lowest detectable range. A simple mathematical model was proposed to describe the mechanism of the ozone in the reactor and was checked over the range of water flow rates from 2.170 to 3.080 l min⁻¹, gas flow rates from 0.667 to 1.333 l min⁻¹ and different temperature conditions. The proposed model describes quite accurately the mass-transfer behavior in the reactor and determines the operational parameters which control the reactor operation. There is a linear relationship between the ozone feed rate and ozone residual. Zero order kinetics best describe the autodecomposition of ozone in plain tap water. The mass transfer coefficient is about 1.14 min⁻¹. Without use of agitation, there is a large decrease in the value of the mass transfer coefficient, to about 0.250 min⁻¹. The magnitude of the reactor rate constant is between 0.05 and 0.13 mg min⁻¹ l.     

Ozonation of water containing chlorine or chloramines. Reaction products and kinetics

Ozone reacts with free aqueous chlorine when present as hypochlorite ion (OCl⁻) with a second order rate constant of 120 ± 15 M⁻¹ s⁻¹ at 20°C. About 77% of the chlorine reacts to produce Cl⁻ and 23% is oxidized to ClO⁻₃. No ClO⁻₄ is formed. Conversion of chlorine to monochloramine reduces the ozone reaction rate to 26 ± 4 M⁻¹ s⁻¹, independent of pH, NH₂Cl is transformed quantitatively to NO⁻₃ and Cl⁻ by O₃. Rate data for other chloramines are also presented. The direct reaction of ozone with chlorine accounts for a significant amount of the chlorine and ozone demand found when the two oxidants are used in combination under water works conditions.     

Mechanism of disinfection: Effect of chlorine on cell membrane functions

To elucidate the mechanism of disinfection by chlorine, its effects on some vital properties associated with cell membrane of Escherchia coli were studied. There was no significant change in Zeta potential at bactericidal doses of chlorine. Treatment with chlorine induced the leakage of macromolecules from the cells indicating the permeability changes of the membrane. Proteins and RNA were detected in the supernatant when the cells were treated with chlorine dose of 1.5 mg 1⁻¹ (100 μg Cl mg⁻¹ N). The presence of DNA was observed only at high chlorine doses. The studies on oxidative phosphorylation of cell free extract indicated the complete cessation of phosphate uptake at a dose of 0.4 mg 1⁻¹ (30 μg Cl mg⁻¹ N). There was about 70% decrease in the oxygen uptake corresponding to chlorine dose of 0.8 mg 1⁻¹.     

The effects of phenol and some alkyl phenolics on batch anaerobic methanogenesis

Phenol and seven alkylphenols (o-, m- and p-cresol, 2.5-, 2.6-, 3.4- and 3,5-dimethylphenol) were added at various concentrations to aliquots of domestic anaerobic sludge in Hungate serum bottles and these were incubated at 37°C. The concentration of methane in the headspace gas was monitored to determine if the phenolics were fermented to methane or if they inhibited the anaerobic process. Only phenol and p-cresol were fermented to methane. At 500 mg l⁻¹ (but not at 300 mg l⁻¹) 2,5-, 3,4- and 3,5-dimethylphenol reduced the rate and the amount of methane produced. The cresols were inhibitory at 1000 mg l⁻¹ but not at 400 mg l⁻¹.In cultures supplemented with acetate and propionate (VOA), and in unsupplemented cultures, phenol at concentrations up to 500 mg l⁻¹ was fermented to methane. Between 800 and 1200 mg l⁻¹ phenol, methane production was neither enhanced nor inhibited relative to control cultures containing no phenol. Inhibition of methane production was evident when phenol was present at 2000 mg l⁻¹. Thus the methanogens are less susceptible to phenol inhibition than are the phenol-degrading acid formers. In similar experiments with p-cresol: enhanced methane production was observed at concentrations of 400 mg l⁻¹; no enhancement or inhibition was observed at 600 mg l⁻¹; and inhibition was noted when p-cresol was present at 1000 mg l⁻¹.     

Hazards associated with the use of chlorinated oxidation pond effluents for irrigation

Eight milligrams per litre chlorine applied to oxidation pond effluents caused no algal kill within the first 2 h of contact. The available chlorine attacks bacteria causing coliform count to drop from 10⁵ 100 ml⁻¹ to a few tens. Enterovirus counts dropped from about 80 100 ml⁻¹ before chlorination to 37 100 ml⁻¹ (after chlorination). Vibrio cholerae (El-Tor) were killed under these adverse conditions, and MPN dropped from 10³ 100 ml⁻¹ in the influent wastes to 2 100 ml⁻¹ in the effluents. A 5 mg l⁻¹ dose of chlorine at 1 h contact time killed these sensitive bacteria decreasing MPN to less than 2 100 ml⁻¹.Differences between the efficiency of chlorination experiments under laboratory and field conditions would necessitate the application of 15 mg l⁻¹ chlorine for 2 h of contact.     

Chlorinated organics from chlorine used in water treatment

The contribution from impurities in chlorine to levels of chlorinated organics found in potable water after chlorination was investigated. Techniques for sampling of chlorine and gas chromatography (GC) determination of chlorinated organics in chlorine are described. The detection limits were better than 1 ppm for each of chloromethane, dichloromethane, chloroform, carbon tetrachloride, trichloroethylene, tetrachloroethylene, hexachloroethane, hexachloropropane and hexachlorobenzene in chlorine. With the exception of chloroform which occasionally accounted for nearly 1 μg l⁻¹ in water, the levels of the nine compounds in chlorine accounted for less than 0.1 μg l⁻¹ of each compound in chlorinated water from 10 Canadian treatment plants. The occurrence of these nine and 28 additional chlorinated organics previously detected in water supplies was determined by aid of liquid-liquid extraction of water samples. Seven compounds, including chloroform, carbon tetrachloride, trichloroethylene and tetrachloroethylene were detected, usually at levels ranging from 0.1 to 1 μg l⁻¹ in chlorinated water from the treatment plant.     

Determination of ozone in water by the indigo method

The concentration of aqueous ozone can best be determined by the decolorization of indigo trisulfonate (600 nm, pH below 4) whenever the ozone cannot be measured directly by its u.v. absorption. The method is stoichiometric and extremely fast. The change of absorbance vs ozone added is −2.0 ± 0.1 × 10⁴ M⁻¹ cm⁻¹ and is independent of the concentration of aqueous ozone in the range 0.005–30 mg 1⁻¹. The precision of the analysis is 2% or 3 μg 1⁻¹ for low concentrations if a spectrophotometer or a good filter instrument is used. Visual methods can be used to measure 0.01 mgl⁻¹ ozone. Secondary oxidants produced by ozone in natural water, including hydrogen peroxide or chlorite, do not interfere; chlorine can be masked. The reagent solution is stable for 3 months. The method is recommended for kinetic measurements, for studies of ozonation processes and for visual field methods.