Chlorination of Water Part 8

[A] Thomas and Sandman.[5]

Regarding the nature of this aftergrowth, there has been a considerable difference of opinion: some regard it as the result of the multiplication of a resistant minority of practically all the species of organisms present in the untreated water; others, that it is partially due to the organisms being merely "slugged" or "doped," i.e. are in a state of suspended animation, and afterwards resume their anabolic functions; whilst others believe that with the correct dosage of chlorine, only spore-forming organisms escape destruction and that the aftergrowth is the result of these cells again becoming vegetative.

The aftergrowths obtained under the usual working conditions vary according to the dosage of chlorine employed, and none of the above hypotheses alone provides an adequate explanation. When the dosage is small, a small number of active organisms, in addition to the spore bearers, will escape destruction, and others will suffer a reduction of reproductive capacity. The flora of the aftergrowth in this case will only differ from the original flora by the elimination of a majority of the organisms that are most susceptible to the action of chlorine and the weaker members of other species of greater average resistance. As the dose is increased these factors become relatively less important until a stage is reached when only the most resistant cells, the spores, remain. The resultant aftergrowth must necessarily be almost entirely composed of spore-bearing organisms. A small number of the most resistant members of non-sporulating organisms may also be present but they will, in the majority of instances, form a very small minority.

This is the condition that usually obtains in practice and it is necessary to consider whether the aftergrowth may have any sanitary significance.

Concerning the secondary development of _B. coli_, the usual index of pollution, there is but little information. H. E. Jordon[6] reported that, of 201 samples, 21 gave a positive _B. coli_ reaction immediately after treatment, 39 after standing for twenty-four hours, and 42 after forty-eight hours. These increases were confined to the warm months, the cold months actually showing a decrease. The following figures, taken from the author's routine tests for 1913 and 1914, show a similar tendency, but an a.n.a.lysis of the results by months did not show that this was confined to the warm season. The sequence of the results from left to right, in the following Table, is in the same order as the contact period. Approximately 290 samples were taken at each sampling point.

At station No. 2 the germicidal action was still proceeding but at No.

5, representing an outlying section of the city, the increase in the _B.

coli_ content is very apparent.

During 1915 and 1916 the author endeavoured to duplicate these results under laboratory conditions and entirely failed. These experiments, which were made with the same materials as were in use at the city chlorination plant, but in gla.s.s containers, were usually only carried to a forty-eight hours contact, as this was the extreme limit for the city mains; one, however, was prolonged to five days. Many experiments were made under varying conditions, with similar results. Typical examples are given in Tables VI, VIII and IX on pages 33 and 37.

TABLE XIX.--AFTERGROWTHS OF B. COLI

PERCENTAGE OF SAMPLES SHOWING B. COLI IN 10 C.CMS.

-----+---------------------------------- | SAMPLING POINT NO.

+------+------+------+------+------ | 1 | 2 | 3 | 4 | 5 +------+------+------+------+------ 1913 | 15.2 | 14.4 | 16.3 | 16.8 | 26.8 1914 | 7.0 | 5.7 | 6.0 | .... | 11.6 -----+------+------+------+------+------

In every case there was persistent diminution in the number of _B. coli_ with increase of contact period. Determination of the bacterial count on nutrient agar showed that, in several experiments, the aftergrowth had commenced, and in some instances there was evidence that the second cycle was partially complete i.e. the number had reached a maximum and then commenced to decline. The time required for the completion of the two cycles, comprising the first reduction caused by the chlorine, the increase or aftergrowth, and the final reduction due to lack of suitable food material, is dependent upon several factors of which the dosage and temperature are the most important. With a small dosage the germicidal period is short and the second phase is quickly reached; with large doses, the second phase is not reached in forty-eight hours; the higher the temperature the quicker is the action and the development of the aftergrowth. These statements refer only to the bacteria capable of development on nutrient agar. The _B. coli_ group behaved differently and persistently diminished in every case. If _B. typhosus_ acts in a similar manner to _B. coli_, the laboratory experiments show that aftergrowths are of no sanitary significance and can safely be ignored, but as the results obtained in practice are contradictory to the laboratory ones, the matter must be regarded as _sub judice_ until more definite evidence is available.

It is common knowledge that samples of water from "dead ends" of distribution mains show high counts and much larger quant.i.ties of _B.

coli_ than the water delivered to the mains. This is another phase of aftergrowth problem that often causes complaints and can only be eliminated by "blowing off" the mains frequently or by providing circulation by connecting up the "dead ends." One extreme case of this description might be cited. A small service was taken off the main at the extreme edge of the city to supply a Musketry School two miles away and was only in use for a few months in the summer season. This service pipe delivered water containing _B. coli_ in a considerable percentage of the 10 c.cm. samples and in a few instances in 1 c.cm., although the water delivered to the city mains never exceeded 2 _B. coli_ per 100 c.cms. and averaged about one-tenth that quant.i.ty. No epidemiological records of the effect of this water are available because it was put through a Forbes steriliser before consumption.

In some instances the rate of development of the organisms after chlorination is greater than in the same water stored under similar conditions. This is especially noticeable in the presence of organic matter and has been ascribed to the action of the chlorine on the organic matter with the production of other compounds that are available as food material for the organisms.

Houston, during the treatment of prefiltered water Lincoln in 1905, found that although the removal of _B. coli_ and other organisms growing at 37 C. was satisfactory, there was almost invariably an increase in the bacteria growing on gelatine at 20 C. This was ascribed to the action mentioned above and the chemical results supported this view, more organic matter being found in the filter effluents than in the prefiltered water. Rideal's experiments with sewage at Guildford indicate that a similar action may occur in contact beds. The addition of bleach to the prefiltered water at Yonkers also resulted in an increased count and in these instances the aftergrowths are due to a disturbance of the equilibrium by the action of the chlorine on the zooglea and other organic matter invariably found in ripe filters.

Similar results can be produced by the addition of chlorinated water to small experimental sand filters. This is shown by the results in Tables XX and XXI.

TABLE XX.--AFTERGROWTHS IN SAND

--------------+---------------+---------------+---------------- | Bacteria Per | | Available | Gram of |Typical B. coli| FREE CHLORINE Chlorine in | Sand After |After 24 Hours.| AFTER 24 HRS.

Water p.p.m. +-------+-------+---+---+---+---+-------+-------- | | |100| 10| 1 |0.1|Without| After | 3 Hrs.|24 Hrs.|Gr.|Gr.|Gr.|Gr.| Acidification.

--------------+-------+-------+---+---+---+---+-------+-------- Nil | 12,000| 21,000| + | + | + | - | - | - 3.0 | 80|114,000| - | - | - | - | - | - 5.0 | 50|150,000| - | - | - | - | - | - 7.0 | 25|214,000| - | - | - | - | - | - 10.0 | 26|500,000| - | - | - | - | - | - --------------+-------+-------+---+---+---+---+-------+--------

TABLE XXI.--AFTERGROWTHS IN SAND

--------------+--------------------------------- | BACTERIA PER GRAM OF SAND AFTER Available in +----------+----------+----------- Water p.p.m. | 3 Hours. |24 Hours. |48 Hours.

--------------+----------+----------+----------- Nil | 70,000 | ..... | .....

0.1 | 7,200 | 20,400 | 12,800 0.3 | 5,240 | 6,400 | 11,200 0.5 | 5,120 | 4,700 | 10,800 1.0 | 1,100 | 8,800 | 20,400 --------------+----------+----------+-----------

It is observable that the effect of small doses was comparatively small and transient; large doses of bleach reduced the bacteria very materially but the reduction was not maintained and the subsequent increase was abnormally rapid.

BIBLIOGRAPHY

[1] Wesbrook, Whittaker and Mohler. J. Amer. Pub. Health a.s.soc., 1911, 1, 123.

[2] Thomas. Jour. Ind. and Eng. Chem., 1914, 6, 548.

[3] Smeeton. Jour. of Bact., 1917, 2, 358.

[4] Clark and De Gage. Rpt. Ma.s.s. B. of H., 1910, p. 319.

[5] Thomas and Sandman. J. Ind. and Eng. Chem., 1914, 6, 638.

[6] Jordan, H. E. Eng. Record, 1915, May 17.

CHAPTER V

COMPLAINTS

The complaints that have been made against chlorinated water since the practice was commenced have been very diversified in character and can be numbered by the legion and although some have been justifiable, the great majority has been unsubstantiated and must be ascribed to auto-suggestion.

Almost every one who has had charge of chlorination plants has noted the latter phenomenon, for in some instances complaints have been made following the publication of the information that chlorination was to be commenced but antecedent to its actual operation, and in others when for some reason or another, the chlorination plant has been temporarily stopped. Similar observations have been made in laboratory experiments when independent observers have been requested to detect the chlorinated waters from an equal number of treated and untreated waters. Such observers are wrong in the majority of the waters which they designate as treated ones if the dosage is not in excess of that required for satisfactory purification.

One amusing example of auto-suggestion was experienced by the author some years ago. During a ceremonial visit to the waterworks, the Mayor and several civic representatives happened to visit a hypochlorite plant that was built on a pier over the river and which had no ostensible connection with the city mains. One of the party expressed a desire for a drink of good river water without any hypochlorite in it and was served with water from the plant supply by an a.s.sistant engineer of the waterworks department. The water was consumed by all with great relish and as it was being finished, the writer entered the plant and was invited to join them in the enjoyment of this "dopeless" water; on asking where it had been obtained he was astonished to hear that it was from a tap which was supplied with the ordinary chlorinated water of the city.

On many occasions, complaints are justifiable and should be carefully investigated instead of, as is often the case, being attributed to auto-suggestion. The time and energy that are often devoted to endeavouring to persuade water consumers that their complaints are without foundation, can better be utilised in so improving the chlorination process as to eliminate tastes and odours. All complaints should be carefully investigated and a record kept for future reference, for the cause, although not manifest at the time, may be discovered later. The records then provide valuable corroborative evidence.

The nature of the complaints against chlorinated water is very diversified and includes imparting foreign tastes and odours, causing colic, killing fish and birds, the extraction of abnormal amounts of tannin from tea, the destruction of plants and flowers, the corrosion of water pipes, and that horses and other animals refuse to drink it.

_Tastes and Odours._ When an excess of hypochlorite or liquid chlorine is added to a water it imparts a sharp pungent odour and acid taste, characteristic of chlorine, that render it offensive to the nose and palate. In some instances the presence of chlorine compounds is not obtrusive when the temperature of the water is low but becomes so when the temperature is raised. It is especially observable when the faucets of hot water services are first opened and the chlorine is carried off as a vapour by the other gases liberated by the reduction in pressure.

For this reason the complaints regarding hot water are relatively more numerous and sometimes const.i.tute the whole of the complaints. In cold water containing appreciable quant.i.ties of mineral salts the hypochlorites and hypochlorous acid might not be entirely dissociated; they may become more hydrolysed with an increase in temperature and finally broken down under the influence of the carbonic acid liberated from the bicarbonates by heat.

Chlorine also forms chlorinated organic compounds by action on the organic matter present in water and some of the objectionable tastes and odours of chlorinated waters have been attributed to this agency. Some observers have stated that chloramines were amongst the chloro-organo compounds produced but the author's experience with the Ottawa supply has demonstrated that simple chloramine (NH_{2}Cl) can be successfully employed for water treatment without causing complaints. It was suggested on page 28 that some of the higher chloro-amines might be the cause of some complaints but at present there is no definite information regarding the formation of these compounds in water and all such hypotheses are little more than conjectures. Letton[1] has reported that at Trenton, in 1911, when the water of the Delaware River was first treated, the dosage was as high as 1.2 p.p.m. of available chlorine and although chemical tests showed the absence of free chlorine, the water had an extremely disagreeable taste which was especially noticeable in the hot water. The conclusion was reached that "the taste and odour were not those of chlorine, but were due to some complex chemical change brought about by the action of the chlorine on the organic matter present in the water."

The waters that require the most accurate adjustment of chlorine dosage, if complaints are to be avoided, are those containing very small amounts of organic matter. The margin between the dosage required for the attainment of a satisfactory degree of bacteriological purity and that which may cause complaints is usually very small, often less than 25 per cent, with the waters of the Great Lakes and many filter effluents.

On the other hand, coloured waters containing large amounts of organic matter can be treated with an excess of chlorine without causing tastes and odours. The author found that the addition of 1.5 p.p.m. of available chlorine to the Ottawa River water did not cause complaints although only 0.8 to 0.9 p.p.m. were usually required for satisfactory purification. Harrington of Montreal has had a similar experience with this water.

The presence of traces of foreign substances in water sometimes produces chlorinated derivatives having repugnant tastes and odours. Creosote and tar oils have caused an odour somewhat resembling that of iodoform and industrial wastes have also produced complaints.

The subst.i.tution of chlorine gas (liquid chlorine) for bleach solutions has apparently eliminated tastes and odours in some cases but this may be due to a more perfect control over the dosage rather than to any property of the bleach _per se_.

In some instances the sludge from bleach plants has caused complaints by producing an excessive concentration of chlorine during the period of its discharge. This occurred in Ottawa on several occasions before it was discovered and corrected. When the sludge in the storage tanks reached the discharge valve it was customary to wash out the tank and discharge the sludge into the river. The operators opened the wash out valves to the full extent and the sludge and liquor were discharged into the river about 70 feet away from the inlet to the sedimentation basin and on the downstream side of it. A portion of the hypochlorite was almost invariably carried into the basin and increased the dosage. This condition was remedied by carrying the sludge drain farther down stream and insisting upon the sludge being discharged at a slower rate.

Kienle[2] has reported similar occurrences at Chicago. The hypochlorite was applied at the intake cribs situated a considerable distance off sh.o.r.e. The direction of the wind often necessitated holding the sludge for a considerable length of time but occasionally it was found impossible to await favourable conditions with the result that the wind and wave action carried a portion of the sludge back into the crib and down into the shaft and tunnel.

The temperature of the water at the time of treatment is another factor bearing on the production of tastes and odours. When the temperature is low, water absorbs relatively less chlorine (_vide_ Diagram No. II, page 38) in the same period of time with the consequence that, if the dosage is kept constant, more chlorine is present in the free condition. At Milwaukee (Kienle)[2] with a dosage of 0.24 p.p.m. of available chlorine (as bleach) no complaints were received during the spring, summer, and autumn seasons but when the temperature reached 40 F., they were compelled to reduce the chlorine to 0.12 p.p.m. in order to prevent objectionable tastes and odours in the tap waters.