Peracetic acid (PAA) disinfection of primary, secondary and tertiary treated municipal wastewaters

The efficiency of peracetic acid (PAA) disinfection against enteric bacteria and viruses in municipal wastewaters was studied in pilot-scale. Disinfection pilot-plant was fed with the primary or secondary effluent of Kuopio municipal wastewater treatment plant or tertiary effluent from the pilot-scale dissolved air flotation (DAF) unit. Disinfectant doses ranged from 2 to 7 mg/l PAA in the secondary and tertiary effluents, and from 5 to 15 mg/l PAA in the primary effluents. Disinfection contact times were 4-27 min. Disinfection of secondary and tertiary effluents with 2-7 mg/l PAA and 27 min contact time achieved around 3 log reductions of total coliforms (TC) and enterococci (EC). PAA disinfection also significantly improved the hygienic quality of the primary effluents: 10-15 mg/l PAA achieved 3-4 log reductions of TC and EC, 5 mg/l PAA resulting in below 2 log reductions. F-RNA coliphages were more resistant against the PAA disinfection and around 1 log reductions of these enteric viruses were typically achieved in the disinfection treatments of the primary, secondary and tertiary effluents. Most of the microbial reductions occurred during the first 4-18 min of contact time, depending on the PAA dose and microorganism. The PAA disinfection efficiency remained relatively constant in the secondary and tertiary effluents, despite of small changes of wastewater quality (COD, SS, turbidity, 253.7 nm transmittance) or temperature. The disinfection efficiency clearly decreased in the primary effluents with substantially higher microbial, organic matter and suspended solids concentrations. The results demonstrated that PAA could be a good alternative disinfection method for elimination of enteric microbes from different wastewaters.     

Inactivation of enteric microorganisms with chemical disinfectants, UV irradiation and combined chemical/UV treatments

The relative disinfection efficiencies of peracetic acid (PAA), hydrogen peroxide (H2O2) and sodium hypochlorite (NaOCl) against Escherichia coli, Enterococcus faecalis, Salmonella enteritidis and coliphage MS2 virus were studied in laboratory-scale experiments. This study also evaluated the efficiency of combined PAA/ultraviolet irradiation (UV) and H2O2/UV treatments to determine if the microbial inactivation was synergistic. Microbial cultures were added into a synthetic wastewater-like test medium and treated by chemical disinfectants with a 10 min contact time, UV irradiation or the combination of chemical and UV treatments. A peracetic acid dose of 3 mg/l resulted in approximately 2-3 log enteric bacterial reductions, whereas 7-15 mg/l PAA was needed to achieve 1-1.5 log coliphage MS2 reductions. Doses of 3-150 mg/l hydrogen peroxide achieved below 0.2 log microbial reductions. Sodium hypochlorite treatments caused 0.3-1 log microbial reductions at an 18 mg/l chlorine dose, while 2.6 log reductions of E. faecalis were achieved at a 12 mg/l chlorine dose. The results indicate that PAA could represent a good alternative to chlorine compounds in disinfection procedures, especially in wastewaters containing easily oxidizable organic matter. Hydrogen peroxide is not an efficient disinfectant against enteric microorganisms in wastewaters. The combined PAA/UV disinfection showed increased disinfection efficiency and synergistic benefits with all the enteric bacteria tested but lower synergies for the coliphage MS2. This suggests that this method could improve the efficiency and reliability of disinfection in wastewater treatment plants. The combined H2O2/UV disinfection only slightly influenced the microbial reductions compared to UV treatments and showed some antagonism and no synergies.     

Anaerobic treatability of selected organic toxicants in petrochemical wastes

The objective of this research was to study the biodegradability of ethylene glycol, acrylic acid, acrolein and allyl alcohol using a methanogenic acetate enrichment culture. Anaerobic Toxicity Assays (ATA) and Biochemical Methane Potential (BMP) studies were performed with serum bottles. Ethylene glycol was found to be degraded to less than 5 mg/l with spikes up to 10,000 mg/l. Higher concentrations led to pH inhibition even with a design initial bicarbonate alkalinity of 6000 mg/l as CaCO₃. Acrylic acid was degraded with almost no effect on methanogens with spikes up to 100 mg/l. However, concentrations of 500, 1000 and 1500 mg/l were found to inhibit the methanogens for several days before recovery. Acrylic acid was eventually degraded to less than 1 mg/l in all cases. Acrolein was inhibitory at concentrations as low as 10 mg/l. However, recovery of the culture was observed at concentrations up to 150 mg/l. Allyl alcohol was cometabolized when acetate was supplied to the bottles in the ATA; it was not degraded well when supplied as the sole carbon source in the BMP study. Ethylene glycol and acrylic acid were found to be suitable for anaerobic treatment whereas allyl alcohol and acrolein were not suitable at the selected concentrations using a methanogenic culture.     

Solar photocatalytic thin film cascade reactor for treatment of benzoic acid containing wastewater

A solar photocatalytic cascade reactor was constructed to study the photocatalytic oxidation of benzoic acid in water under various experimental and weather conditions at HKUST. Nine stainless steel plates coated with TiO(2) catalyst were arranged in a cascade configuration in the reactor. Photolytic degradation and adsorption were confirmed to be insignificant total organic carbon (TOC) removal mechanisms. A turbulent flow pattern and, hence, improved mixing in the liquid film were achieved due to the unique cascade design of the reactor. The photoinduced consumption of oxygen during reactions was demonstrated in a sample experiment. The proposed rate equations provided good fits to 90 data points from 17 experiments. The regression results showed that the TOC removal rates averaged over 30 min intervals did not illustrate significant dependence on TOC(0) and that I(mean) was more important in affecting the photocatalytic process within the ranges of the data examined. The percentage removal of TOC in 7 l of 100 mg/l (or 100 ppm) benzoic acid solutions increased from 30% to 83% by adding 10 ml of hydrogen peroxide solution (30 wt%). Hydrogen peroxide was also shown to enhance the efficiency of the degradation process at elevated temperatures. Ortho-, meta- and para-hydroxybenzoic acids were identified by HPLC analysis as the intermediates of benzoic acid during reactions without the addition of hydrogen peroxide solutions.     

紫外消毒出水的微生物光复活及其控制技术

污水厂出水经紫外线（UV）消毒后在排放过程中会出现微生物的复活现象，为此考察了采用UV-氯和UV-过氧乙酸（PAA）控制光复活的效果。经研究发现：在UV照射剂量为5．4mJ／cm^2、投氯量为2．5mg／L、反应时间为10min和UV照射剂量为5．4mJ／cm^2、过氧乙酸投量为10mg／L、反应时间为10min的条件下，对大肠菌群的灭活率均可达4个对数级以上，并能控制光复活现象。从消毒稳定性、经济适用性、安全毒副性等方面考虑，可采用UV—PAA作为污水厂出水消毒及抑制光复活的技术。     

Inactivation of enteric adenovirus and feline calicivirus by ozone

Little information is available regarding the effectiveness of ozone on the inactivation of caliciviruses and enteric adenoviruses. Inactivation experiments were conducted with feline calicivirus (FCV), closely related to the human caliciviruses based on nucleic acid organization and capsid architecture, and adenovirus type 40 (AD40). Experiments were carried out in buffered disinfectant demand free water at pH 7 and 5 degrees C. Ct values; concentration of ozone multiplied by contact time with virus; were determined from application of the efficiency factor hom (EFH) model. Ct values for 4-log (99.99%) ozone inactivation at 5 degrees C and pH 7 ranged from 0.07 to 0.60 mg/l min for AD40 and <0.01 to 0.03 mg/l min for FCV. Ct values listed in the US environmental protection agency "Guidance Manual for Compliance with Filtration and Disinfection Requirements for Public Water Systems Using Surface Water Sources" were higher than Ct values generated by this study. Very low ozone residuals (<0.01(mg/l) substantially inactivated FCV and AD40 under the studied conditions.     

A laboratory study of landfill-leachate transport in soils

Continuous flow experiments were conducted using sand-packed columns to investigate the relative significance of bacterial growth, metal precipitation, and anaerobic gas formation on biologically induced clogging of soils. Natural leachate from a local municipal landfill, amended with acetic acid, was fed to two sand-packed columns operated in upflow mode. Degradation of the influent acetic acid resulted in the production of methane and carbon dioxide, and simultaneous reduction of manganese, iron, and sulphate. Subsequent increase in the influent acetic acid concentration from 1750 to 2900 mg/l, and then to 5100 mg/l, led to rapid increase in the dissolved inorganic carbon, solution pH, and soil-attached biomass concentration at the column inlet, which promoted the precipitation of Mn(2+) and Ca(2+) as carbonate, and Fe(2+) as sulphide. An influent acetic acid concentration of 1750 mg/l decreased the soil's hydraulic conductivity from an initial value of 8.8 x 10(-3)cm/s to approximately 7 x 10(-5)cm/s in the 2-6 cm section of the column. Increasing the influent acetic acid to 5100 mg/l only further decreased the hydraulic conductivity to 3.6 x 10(-5)cm/s; rather, the primary effect was to increase the length of the zone experiencing reduced hydraulic conductivity from 0-6 cm to the entire column. As bioaccumulation was limited to the 0-5 cm section of the column, and the effect of metal precipitation was negligible, the reduction on the deeper sections of the column is attributed to gas flow, which was up to 1440 ml/day. Mathematical modelling shows that biomass accumulation and gas formation were equally significant in reducing the hydraulic conductivity, while metal precipitation contributed only up to 4% of the observed reduction.     

Integrated biological and physiochemical treatment process for nitrate and fluoride removal

The feasibility of an integrated biological and physiochemical water treatment process for nitrate and fluoride removal has been evaluated. It consisted of two sequencing batch reactors (SBRs) in series. Performance of the process in the treatment of 24 synthetic water samples having nitrate concentrations of 40, 80, 120, 160, 200, and 250 mg/l (as N) and fluoride concentrations of 6, 10, 15, and 20 mg/l at different combinations was studied. Denitrification followed by defluoridation proved to be the best sequence of treatment. In all cases nitrate could be reduced to an acceptable level of less than 10 mg/l (as N) at 3, 5, and 7 h hydraulic retention times (HRTs) depending on its initial concentration. Fluoride concentrations up to 15 mg/l associated with nitrate concentrations up to 80 mg/l (as N) could be reduced acceptable 1.5 mg/l by alum-PAC slurry using alum doses up 850 mg/l [as Al2(SO4)3 x 16H2O] along with 100 mg/l of powdered activated carbon (PAC). Additional alkalinity produced during denitrification was used up during defluoridation for maintenance of pH avoiding the need for lime addition. On the other hand, residual organics, turbidity, and sulfide present in the denitrified water are removed by alum and PAC at the defluoridation stage along with fluoride, eliminating the need for an additional post-treatment step. At higher nitrate concentrations (> or = 120 mg/l as N), the alkalinity produced at the denitrification stage was in the range of 715-1175 mg/l as CaCO3. This excessive alkalinity inhibited reduction of fluoride to the level of 1.5 mg/l at the defluoridation stage, using alum doses up to 900 mg/l along with 100 mg/l of PAC. In all cases a fluoride concentration of 20 mg/l in water could not be reduced to the acceptable level of 1.5 mg/l.     

Estimates of benthic fluxes of nutrients across the sediment-water interface (Guarapiranga reservoir, São Paulo, Brazil)

Concentration profiles of nutrients (dissolved organic carbon, nitrate, nitrite, ammonium and soluble reactive phosphorus) were determined in pore waters from sediment from the Guarapiranga reservoir (S?o Paulo, Brazil). Redox potential and acid volatile sulfide measurements on bulk sediment samples were determined in the field and laboratory, respectively. The sediment redox potential ranged from -170 to -220 mV at 0-1 cm and increased to somewhat higher values at 20 cm. The acid volatile sulfide (AVS) profile had a bimodal pattern with concentration peaks at 3 cm (27-55 mg kg(-1)) and 14 cm (70-110 mg kg(-1)). Dissolved organic carbon (DOC) concentrations increased from the surface (4.7-5.6 mg l(-1)) to 20 cm (values up to 12 mg l(-1)). The concentration of ammonium increased significantly with depth, with maximum concentrations occurring at 15 cm; nitrate-nitrite concentrations only increased appreciably at 10 cm. The SRP profiles increased in concentration from the surface to approximately 10-cm depth, with a maximum value of 1200 microg H2PO4- l(-1). Benthic fluxes from the sediment into the pore water ranged from 278 to 339 mg cm(-2) year(-1) for ammonium ions and from 8 to 18 mg cm(-2) year(-1) for SRP. These upward diffusive fluxes correspond to 47-70% and to 10-24% of the total deposition of N and P measured in the reservoir, respectively. The burial rates for N and P in these sediments are 30-54% and 76-89%, respectively.     

Disinfection efficiency of peracetic acid, UV and ozone after enhanced primary treatment of municipal wastewater

The City of Montreal Wastewater Treatment Plant uses enhanced physicochemical processes (ferric and/or alum coagulation) for suspended solids and phosphorus removal. The objective of this study was to assess the ability of peracetic acid (PAA), UV, or ozone to inactivate the indicator organisms fecal coliforms, Enterococci, MS-2 coliphage, or Clostridium perfringens in the effluent from this plant. PAA doses to reach the target fecal coliform level of 9000 CFU/100mL exceeded 6 mg/L; similar results were obtained for enterococci, and no inactivation of Clostridium perfringens was observed. However a 1-log reduction of MS-2 occurred at PAA doses of 1.5 mg/L and higher. It was expected that this effluent would have a high ozone demand, and would require relatively high UV fluences, because of relatively high effluent COD, iron and suspended solids concentrations, and low UV transmittance. This was confirmed herein. For UV, the inactivation curve for fecal coliforms showed the typical two-stage shape, with the target of 1000 CFU/100 mL (to account for photoreactivation) occurring in the asymptote zone at fluences >20 mJ/cm(2). In contrast, inactivation curves for MS-2 and Clostridium perfringens were linear. Clostridium perfringens was the most resistant organism. For ozone, inactivation was already observed before any residuals could be measured. The transferred ozone doses to reach target fecal coliform levels ( approximately 2-log reduction) were 30-50 mg/L. MS-2 was less resistant, but Clostridium perfringens was more resistant than fecal coliforms. The different behaviour of the four indicator organisms studied, depending on the disinfectant, suggests that a single indicator organism might not be appropriate. The required dose of any of the disinfectants is unlikely to be economically viable, and upstream changes to the plant will be needed.     

Municipal-treated wastewater reuse for plant nurseries irrigation

Results of an experiment aimed at assessing the possibility of reusing reclaimed wastewater for nursery ornamental plants are presented. Tests were carried out in Pistoia (Italy). A pilot plant for tertiary treatment (filtration and peracetic acid + UV disinfection) of the local wastewater treatment plant (WWTP) effluent was set up. An experimental plot with six containerized ornamental species was irrigated with the tertiary effluent and growth and physiological parameters were monitored. A control plot irrigated with fertigated water (nutrient-enriched groundwater) was also set up in order to compare the plants response to different kinds of irrigation water. The refinery treatment by filtration and disinfection with Peracetic Acid (PAA) and UV together was very effective in bacteria removal. The value of 2 MPN of Total Coliforms in 100 ml set by Italian law (until June 2003) for unrestricted irrigation was constantly satisfied. Agronomic results indicate no major limitations to the use of a tertiary effluent as an irrigation source in an ornamental plant nursery. The nutrient content of the tertiary effluent was able to maintain good plant growth as well as fertigated water for most of the tested species.     

Wastewater sludge as a potential raw material for antagonistic fungus (Trichoderma sp.): role of pre-treatment and solids concentration

Feasibility of production of antagonistic Trichoderma sp. conidial spores using wastewater sludge as a raw material employing different suspended solids concentration (10-50 g/l) was investigated in shake flasks. Maximum conidial spore count obtained for raw sludge was 1.98 x 10(4) CFU/ml, which was enhanced by sludge pre-treatments (alkaline and thermal alkaline). Conidial spore count ranging from 1.3 x 10(6) to 2.8 x 10(7) CFU/ml was observed for alkaline and thermal alkaline treated sludges. Optimal suspended solids concentration was 30 g/l (10(7) CFU/ml) whereas, lower (<20 g/l) and higher (>30 g/l) solids concentration were less efficient. Thermal alkaline pre-treated sludge showed diauxic growth due to multiplicity of sludge biodegradability. A simple, modified CFU filtration technique was also developed for fungal spore assessment in sludge. Bioassay of fermented sludge against spruce budworm larvae showed entomotoxicity (15036 SBU/microl), on par with Bacillus thuringiensis biopesticides. This study successfully demonstrated potential of wastewater sludge as a raw material for production of value added product, aiding in sludge management and proliferation of eco-friendly and economical biocontrol agents.     

Effects of low-level chlorination on zebra mussel,Dreissena polymorpha

Mortality pattern of different size groups (5-20 mm shell lengths) of the zebra mussel Dreissena polymorpha (Pallas), was studied in the laboratory under different chlorine concentrations (0.25-3.0 mgl(-1)). Results showed that exposure time for 100% mortality of mussels significantly decreased with increasing chlorine concentration. For example, mussels in the 10mm size group exposed to 0.25mg l(-1) chlorine residual took 1080h to reach 100% mortality whereas those exposed to 3 mg l(-1) chlorine took 252 h. All size groups (between 5 and 20 mm shell length) took identical exposure time to reach 100% mortality at given chlorine concentration (between 1 and 3mg l(-1)). The effect of acclimation temperature on D. polymorpha mortality in the presence of chlorine was significant. For example, 1026 h is required to reach 95% mortality using 0.5mg l(-1) residual chlorine at 10 degrees C, compared to 456h at 0.50 mg l(-1) chlorine and 25 degrees C. Resistance of D. polymorpha to chlorine appeared to be lower than that for other mussel species in The Netherlands viz., Mytilus edulis L. and Mytilopsis leucophaeata (Conrad). The present study also suggests that 100% mortality data for European populations of D. polymorpha at different chlorine concentrations are similar to those for the North American populations.     

Study of the impact of land use and hydrogeological settings on the shallow groundwater quality in a peri-urban area of Kampala, Uganda

A study to assess the impacts of land use and hydrogeological characteristics on the shallow groundwater in one of Kampala's peri-urban areas (Bwaise III Parish) was undertaken for a period of 19 months. Water quality monitoring was carried out for 16 installed wells and one operational protected spring to ascertain the seasonal variation. The aspects of hydrogeological setting investigated in the study were the subsurface unconsolidated material characteristics (stratigraphy, lithology, hydraulic conductivity, porosity and chemical content), seasonal groundwater depths and spring discharge, topography and rainfall of the area. Both laboratory and field measurements were carried out to determine the soil and water characteristics. Field surveys were also undertaken to identify and locate the various land use activities that may potentially pollute. The results demonstrate that the water table in the area responds rapidly to short rains (48 h) due to the pervious (10(-5)-10(-3) ms(-1)) and shallow (<1 mbgl) vadose zone, which consists of foreign material (due to reclamation). This anthropogenically influenced vadose zone has a limited contaminant attenuation capacity resulting in water quality deterioration following the rains. There is widespread contamination of the groundwater with high organic (up to 370 mgTKN/l and 779 mgNO-3/l), thermotolerant coliforms (TTCs) and faecal streptococci (FS) (median values as high as 126E3 cfu/100 ml and 154E3 cfu/100 ml respectively) and total phosphorus (up to 13 mg/l) levels originating from multiple sources of contamination. These include animal rearing, solid waste dumping, pit latrine construction and greywater/stormwater disposal in unlined channels leading to increased localised microbial (faecal) and organic (TKN/NO-3) contamination during the rains. The spring discharge (range 1.22-1.48 m3/h) with high nitrate levels (median values of 117 and 129 mg/l in the wet and dry seasons) did not vary significantly with season (p=0.087) suggesting that this source is fed by regional base flow. However, the microbial quality deterioration observed in the spring discharge after a rain event (median values of 815TTCs cfu /100 ml and 433 FS cfu/100 ml) was attributed to the poor maintenance of the protection structure. Identification and selection of appropriate management solutions for the protection of shallow groundwater in informal settlements should not only be based on water quality problems and the causal physical characteristics as demonstrated by this study, but also institutional and socio-economic factors.     

The influence of the abandoned Kalecik Hg mine on water and stream sediments (Karaburun,Izmir, Turkey)

This study covers the geochemical investigations on water and stream sediments to evaluate the influence from the abandoned Kalecik Hg mine. The groundwater samples (S5, S8, S9, WW10) are neutral, slightly alkaline waters which have pH values varying between 7.3 and 7.5. Electrical conductivity (EC) values of groundwaters for spring samples are low (250-300 microS/cm). However, groundwater obtained from a deep well has a higher EC value of 950 microS/cm. Hg concentrations of groundwater samples vary between 0.01 and 0.13 microg/l. Hg concentrations of other water samples taken from mining area from surface waters and adits are between 0.10 and 0.99 microg/l. Adit water (A4) collected at the mine has the highest Hg content of 0.99 microg/l and a pH of 4.4. Trace element concentrations of mine water samples show variable values. As is observed only in MW1 (310 microg/l). A4 was enriched in Cd, Co and Cr and exceed the Turkish drinking water standards (Türk Standartlari Enstitüsü, 1997). Cu concentrations vary between 6.0 and 150 microg/l and are below the Turkish water standards. Mn concentrations in mine waters are between 0.02 and 4.9 mg/l. Only for sample A4 Mn value (4.9 mg/l) exceeds the standard level. Ni was enriched for all of the mine water samples and exceeds the safe standard level (20 microg/l) for drinking water. Of the major ions SO(4) shows a notable increase in this group reaching 650 mg/l that exceeds the drinking water standards. Stream sediment samples have abnormally high values for especially Hg and As, Sb, Ni, Cr metals. With the exception of sample Ss6 of which Hg concentration is 92 mg/kg, all the other samples have Hg contents of higher than 100 mg/kg. Pollution index values are significantly high and vary between 69 and 82 for stream sediment samples.     

Removal of organic matter from water by PAC/UF system

The laboratory-scale ultrafiltration (UF) experiments were conducted to determine the effect of the presence of powdered activated carbon (PAC) on the UF process performance, in terms of flux decline and the possibilities of membranes cleaning during backwashing. Poly(vinylidene fluoride) membranes formed by the phase inversion technique were used in the UF experiments. A model solution was prepared as a mixture of humic acids (HA) and phenol in concentration of 10 and 1 mg l(-1), respectively. Commercial powdered activated carbons CWZ 11 and CWZ 30 (Gryfskand Sp. z o. o., Hajnówka, Poland) were used as the adsorbents. PAC dosage was in the range of 10-100 mg PAC l(-1). The process was carried out in the cross-flow system. It was found that PAC addition to the distilled water leads to a small drop in the permeate flux, regardless of PAC dose and its type. Although PAC particles are too large to block the membrane pores inside, they deposit on the membrane surface and partially can plug the surface pores. The experimental results demonstrate that the backwashing process applied in combined PAC/UF system was especially effective when PAC dosages were <20mg PAC l(-1). However, a similar permeate flux was maintained for all carbon dosages used and reached the value of about 1 m3 m(-2) d(-1). Moreover, no further drop in the permeate flux for PAC addition to the solution containing foulants (HA) was observed. Effectiveness of the removal of HA and phenol from the model solutions was also investigated. In the PAC/UF system HA were removed in about 90%, whereas the complete removal of phenol was achieved for PAC dosage equal to 100 mg l(-1).     

Phenol biodegradation and its effect on the nitrification process

Phenol biodegradation under aerobic conditions and its effect on the nitrification process were studied, first in batch assays and then in an activated sludge reactor. In batch assays, phenol was completely biodegraded at concentrations ranging from 100 to 2500 mg l(-1). Phenol was inhibitory to the nitrification process, showing more inhibition at higher initial phenol concentrations. At initial phenol concentrations above 1000 mg l(-1), the level of nitrification decreased. In the activated sludge reactor, the applied ammonium loading rate was maintained at 140 mg N-NH(4)(+)l(-1)d(-1) (350 mg N-NH(4)(+)l(-1)) during the operation time. However, the applied organic loading rate was increased stepwise from 30 to 2700 mg COD l(-1)d(-1) by increasing the phenol concentration from 35 up to 2800 mg l(-1). High phenol removal efficiencies, above 99.9%, were maintained at all the applied organic loading rates. Ammonium removal was also very high during the operation period, around 99.8%, indicating that there was no inhibition of nitrification by phenol.     

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.     

The effects of bubble size on microflotation

Microflotation has been shown to be an efficient process for the removal of various colloidal sized impurities from water and waste water. Laboratory studies have shown that for this purpose very small bubbles are required. This study is to determine the effects of concentration of frother (ethanol) and collector (lauric acid) upon bubble size and upon efficiency of humic acid removal.Bubble sizes were measured photographically and humic acid removals determined spectrophotometrically. Ethanol was varied from 0.25 to 7.50 ml l^?1 and lauric acid from 0 to 100 mg l^?1 concentration. Initial humic acid concentration was 50 mg l^?1 and 0.0005 m aluminum sulfate was employed as a coagulant. All experiments were conducted at an adjusted pH of 7.5 in a 400 ml batch flotation cell. Ethanol produced a greater effect on bubble size than lauric acid; small additions of ethanol (ml l^?1) reduce bubble size drastically.The investigation showed a rapid decrease in microflotation removal efficiencies when bubble diameters exceed 55–60 μm. Efficient separations are extremely rapid, being essentially complete in 30 60 s.     

Preservation du contenu en o-phosphate d''echantillons d''eau du fleuve saint-laurent

On a étudié l'efficacité d'un certain nombre de produits comme préservatifs du contenu en o-phosphate d'échaotillons d'eau du fleuve St-Laurent à des températures d'entreposage de −10°, 4° et 20°C. Parmi les produits testés soit le thymol (0.01%), le fluorure de potassium (0.01%), ;lácide sulfurique (0.0 N), le chlorure de tributylétain (0.001%) et le chloroforme (5 ml/l), seuls les deux derniers se sont revélés potentiellement intéressants. Une série d'expériences a confirmé que le contenu en o-phosphate pouvait ètre préseré de façon süre pendant au moins deux sernaines par un entreposage à 4°C en présence de chloroforme (5 ml/l).

Abstract

The effectiveness of some materials in preserving the o-phosphate content of water samples from the St-Lawrence River at storage temperatures of −10°, 4° and 20°C was studied.

Tests were done with thymol (0.01%), potassium fluoride (0.01%), sulfuric acid (0.1 N), tributylin chloride (0.001%) and chloroform (5 ml/l), the last two products showing some activity. From further testing it can be concluded that the o-phosphate content is stable for at least two weeks of storage at 4°C with chloroform added as preservative.