Yehuda Kott

Bacteriophages as viral pollution indicators

Abstract f2 Phage, attenuated Polio I (LSC) strain introduced daily to a 350 l. experimental oxidation pond showed no decrease in bacterial viruses f2 or other coliphages or Polio I strain. Ratios of coliphages to human enteric viruses ranged in flood waters from concentrations as low as 1:1 to as high as 10 3 :1; in wastewater at various seasons the ratio was 10 5 :1; in trickling filter effluents in winter it was 10 4 :1; in spring 10 5 :1, in summer and fall 10 4 :1, in oxidation pond effluents in winter 10 3 :1; in spring 10 4 :1; and in summer and fall 10 3 :1. Out of three epidemics in small communities caused by failure of water supply, coliphages were found to be positive. At the same time only two samples of human enteric viruses were positive (the third was contaminated with yeasts). Chlorination experiments using the experimental oxidation pond showed that f2 was most resistant, MS 2 was very resistant, and coliphages were more resistant than attenuated Polio I virus. Experiments with the oxidation pond effluents showed that coliphages were at least as or even more resistant to chlorine than human enteric viruses.

Effluent treatment and algae recovery by ozone-induced flotation

Separation of algae from oxidation pond effluents was tested in a bench scale flotation column using ozone-enriched oxygen. Experimental results indicated that the process could produce a clear, colorless liquid, over 98% removal of suspended solids, and up to three orders of magnitude reduction in fecal coliforms. Ozone dosage ranged from 15 to 50 mgl−1. The collapsed froth thickens to produce a pure algal mass of up to 8.5% solids. It was hypothesized and supported by experimental results that ozone reaction with algal cells results in the formation of a hydrophobic surface amenable to separation by rising bubbles. The high quality products, both liquid and solid, make the combination of stabilization ponds with ozone flotation very attractive for wastewater treatment under certain conditions.

Viruses and bacteriophages.

Many of the enteric viruses which are transmitted from person to person by the fecal-oral route are found in raw and treated wastewater, and because of their persistence under adverse conditions may also be found in slightly polluted waters. There is no routine examination procedure of water and wastewater for enteroviruses, mainly because of the cumbersome isolation techniques, high cost and the need for highly skilled laboratory personnel. Phages are specific to single species of bacteria, are known for many enteric bacteria, and are very often used for final identification of enteric pathogenic bacteria. Coliphages are prevalent in raw and treated sewage as well as in polluted water, where enteric viruses may also be found. Coliphages were often mentioned as possible viral indicators in polluted water. To be a perfect indicator, they should comply with minimum criteria as follows: (a) they should be present wherever human enteric viruses are present; (b) the coliphage numbers recovered should be equal to or larger than those of enteric viruses recovered; (c) the coliphages should be at least as resistant as enteric viruses to adverse environmental conditions; (d) isolation and quantification of the coliphage should be faster and less expensive than isolation of the enteroviruses. Comparative studies show that the coliphage to enterovirus ratio in wastewater is about 10(3):1. Levels of poliovirus 1 (attenuated) to coliphage f2 remained stable for a few months in oxidation pond effluents. f2 coliphage exhibited higher resistance to chlorination than poliovirus 1 (attenuated). When the two strains were kept in water of different quality, f2 survived longer. In addition, all coliphage counts were completed within 24 h. while those of enteroviruses required about a week. Results indicate very strongly that coliphages can be used as viral indicators and this is already the practice in a few European and other countries.

Disinfection of effluent by combinations of equal doses of chlorine dioxide and chlorine added simultaneously over varying contact times

Abstract The aim of this research was to investigate the possibility of using a combination of chlorine dioxide and chlorine, instead of using each of them as a single disinfectant for the disinfection of effluents from municipal sewage treatment plants, in order to obtain an environmentally safe source of water which can be reused for a variety of purposes. The main task was to investigate whether the combination of the two disinfectants maintains their advantages and decrease their disadvantages. Residual chlorine dioxide, chlorine, chlorite ion and Most Probable Number (MPN) per 100 ml of survived total coliforms, fecal coliforms, fecal streptococci and E-coliphages were determined as a function of these disinfectants doses and contact times. The combination produced a relatively stable high residual of both disinfectants, reduced the concentration of the undesirable chlorite ion, while increasing the concentration of chlorine dioxide. In all doses of the combined disinfectants there was an improvement in the destruction of the indicator pathogenic microorganisms.

Efficiency of rotating biological contactor in removing pathogenic bacteria from domestic sewage

Abstract Fecal coliform bacteria and Salmonella typhimurium (S. tym) die-off were examined in an experimental RBC which received settled domestic sewage from the city main sewer. During the four seasons of the year, pH of effluents was always 8.0. Dissolved oxygen was always present in the bath compartment and although influent BOD5 fluctuated between 70–250 mg l−1, the effluent BOD5 was about 10 mg l−1. Varying hydraulic loads did not influence the number of coliform or fecal coliform bacterial numbers. There was a significant difference in survival of fecal coliform placed in dialysis bags attached to the rotating disks (drum) and to those submerged in the bath; the latter died much more slowly. When the dialysis bags containing S. tym were placed in the bath, the bags that did not contain algae (diatoms and Oscillatoria), showed slower die-offs which was one order of magnitude within 1 day, compared to over two orders of magnitude in bags that contained the algae. It is assumed that RBC is very efficient in removing pathogenic bacteria found in domestic sewage.

Preferential feeding behaviour of Daphnia magna

Preferential feeding behaviour by Daphnia magna was shown when Daphnia were fed on a mixture of 14C-labelled algae (Chlorella vulgaris or Scenedesmus quadricauda) and 3H-labelled bacteria (Escherichia coli). Daphnia consumption of bacteria was equal or higher in the presence of algae. On the other hand, in the presence of bacteria, algal consumption decreased by 40–70% compared to algal consumption in the absence of bacteria. 14C radioactive uptake was in good agreement with the chlorophyll content and demonstrates the preferential feeding behaviour of Daphnia.

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

Abstract 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.

Effect of halogens on algae—II. Cladophora SP.

Abstract Halogenation of natural tufts gave no fruitful results. Using isolated filaments of Cladophora sp. showed that halogens cause changes in cell colour from green to yellow or even to colourless, very often damage to cell wall. Leaching of cell content also occurred, or contraction of cytoplasm was observed. Using dark field technique it was observed that the normal red fluorescence seen in healthy cells disappeared. Very high concentrations (50 mg/l and over) caused severe deformation of cells. In the absence of a recommended procedure for measuring viability of filamentous algae, one hundred cells were counted in each filament and a bioassay was performed at the end of each experiment. Addition of 5 mg/1 of halogens has caused some effect on the algae, while addition of copper sulphate at this concentration showed no effect at all. With higher concentrations of halogens or copper sulphate, cell damage was caused. Ten mg/1 chlorine for 2 hr, 10 mg/1 bromine for 10 hr or 10 mg/1 copper sulphate for 4 days of contact caused complete algal kill.

Effect of industrial wastes on oxidation pond performance

Abstract Cadmium, copper, nickel, zinc and hexavalent chromium ions were tested in a benchbioassay experiment for toxicity limits and possible application to experimental oxidation ponds. It was found that the metal ions mentioned above are toxic, inhibiting chlorella growth. However, when added at concentrations of 0·5–1·5 mg 1−1 to influent of oxidation ponds, the ponds continued to operate normally. Higher concentrations of 3 and 6 mg 1−1 did not affect adversely pond performance—not even a concentration of 6 mg 1−1 of each ion (a total metal ion concentration of 30 mg 1−1). A mixture of 60 mg 1−1 metal ions brought about a decrease in algal numbers and caused a sharp drop in dissolved oxygen concentration. It is believed that since high pH causes metal ions to precipitate, oxidation ponds operating normally above pH 8-0 will tolerate metal ions in sewage containing industrial wastes for a long time, before sludge accumulation will effect pond performance.

Lagooned, secondary effluents as water source for extended agricultural purposes

Abstract Chlorination of trickling filter effluents at 40 mg l −1 chlorine for 4 h and 20 mg l −1 for 4 and 6 h showed very limited coliform survival. The number of viruses decreased from a few hundred in 100 ml before chlorination to 0 after chlorination. A 70,000 m 3 pond (4 m deep) was used for holding non-chlorinated secondary effluents for 73 days. Bacterial and viral counts were performed every few days. In addition BOD, TC, pH and solar radiation were monitored. After this, the water was pumped out and chlorinated in a pipeline with 8 or 20 mg l −1 chlorine. After chlorination the coliform count was reduced by from 3 to 5 orders of magnitude. After storage for 43 days the non-chlorinated secondary effluents viral count was nil. After chlorination these effluents were also virus-free. In the second experiment, secondary effluents chlorinated with 20 mg l −1 chlorine with a contact period of 2 h. They were then introduced to the pond. No viruses were found in the incoming water, neither during holding nor after the second chlorination, Coliform regrowth was very slow because of the temperature of the water was only 18–20°C. Identification of the M. Endo membrane filter grown isolated colonies proved that E. coli I disappeared, and all the coliforms were of non-fecal origin or that other growths were non-coliform organisms growing on the MF. The third experiment was a repetition of the first, in spring, after the temperatures rose. The results confirmed the findings in the first experiment. Therefore, it is thought that 70 days holding of wastewater would permit its extensive agricultural use. For safety, the addition of 20 mg l −1 chlorine to effluents and a short storage could be adequate from a public health point of view.