840
T H E JOURNAL OF INDUSTRIAL AAVD ENGINEERING CHEMISTRY
Vol. 14,No. 9
Chemistry of Sanitation By A. M. Buswell CHIEP,ILLINOIS STATEWATERSURVEY,URBANA, ILLINOIS
man, with the aid of a number of filter plant operators, compiled this year a considerable amount of data which will be ITH THE development of quantitative bacteriolog- published in the journal of that society. Clark and Theriical technic, chemical tests for determining the ault4report that hydrogen electrode experiments have shown sanitary quality of water lost much of their former that equilibria in aluminium solutions with the solid phase importance. Because of increasing necesrity for the use of (aluminium hydroxide?) present are complex. The peculiarsurlace supplies, all of which are more or ities nullify the value of methods Dreless subject to pollution, the main quesviously used to estimate the isoele6tric tion has become one of purificfition rather point. By taking advantage of these pecuthan of a test for freedom from infection, liarities the isoelectric point has been and it should be remembered that purififound to lie between pH 5.5 and 6.0. Excation involves a great deal more than disperiments on time of flocculation have infection. Disease germs can be killed or shown minimum time a t or near pH 5.5. got rid of with comparative ease, but An empirical equation has been found tastes, odors, and turbidity must also be relating time for first appearance of floc removed in order to produce a potable and pH under uniform sets of laboratory water. conditions. Time of flocculation is also Water purification is, therefore, an esa function of circulation, and rough relations have been found whereby small sential chemical process and it is along the vessel experiments may be extrapolated line of the investigations of the reactions to large volume conditions. involved and methods for their control Buswell and Edwards5 have shown that that the water chemist is again coming the unprecipitated aluminium in treated into his own. Though it is possible a t the water is less than is ordinarily found in present time to produce a potable water untreated natural waters even when the from almost any source, no matter how pH is far from the optimum. This should polluted, yet there is room for improvequiet the fears, expressed occasionally in ment of the product as well as of the medical circles, of the physiological effect process. Furthermore, the art is at presof the “alum” used in water purification. A. M. BUSWYBLL ent ahead of the theory. We can purify While the DHdetermination has not moved water with reasonable success, bnt we do not understand the mechanism of the reactions involved. the panacea some would *have led us to expect, *it has “Who but the chemist is to fix the proper value for the already proved its usefulness in the operation of certain dore of chemicals?” said Professor Mason’**seven years ago, filter plants, notably the one a t Baltimore.6 The colloidal and we might add, “Who but the chemist can investigate phase of the problem is generally recognized; yet, with the exception of the work of Catlett7 and of 0. M. Smiths and the complicated reactions of these chemicals?” , ~ progress has The following steps represent what may fairly be considered some theoretical proposals by P i r ~ ~ i elittle been made along that line. as present standard practice in purification of munioipal T.TThilethe role of oxygen in causing corrosion has long surface supplies for general domestic use : coagulation with been recognized, several articleslO have recently appeared aluminium sulfete or ferrous sulfate; sedimentation; rapid filtration through sand; and, finally, disinfection with chlorine. describing various devices for preventing corrosion by means Some of the earlier “slow sand” filters are still in use, espe- of “deoxidation.” These are in general of two types: (1) cially in Europe. I n some cases chlorination without filtra- Filtering the water over iron or other metal turnings to tion is used as a more or less temporary measure and in a “deoxidize” it, or (2) boiling out the dissolved gases. In few instances filtration without chlorination is regarded as some cases a combination of the two is used. Tillmans and sufficient. Softening or iron removal is Rometimes attempted, Heublein” and later KolthoffJ2have shown that, as would but in general such treatment is left to the private or indus- be predicted from the mass law, the presence of Ca(HCOa)z lessens the solvent action of H2COaon CaCOa. The amount trial consumers. The relstion of pH to precipitation of Al(OH), has probably of CaCOa which a water will dissolve is a measure of the been the most extensively investigated problem in the last “aggressive” C 0 2 which is a different numerical value from few years. Practice had been to add lime t o waters which “free” COz. Don’s13 recent investigation of the adsorption of ammoafter alum treatment showed a residuum of less than 20 p. p. m. of CaC03 (alkalinity). But Wolman and Hannan2 showed nium salts in sand filters recalls the much earlier work of not only that the addition of lime was unnecessary in moPt Chick1*on the same subject but from the standpoint of sewcases but, that in pome instances the addition of small amounts age treatment. The cause of surface shrinkage in filters has of acid favored precipitation. At the same time Buswell been attributed to adsorption.16 A symposium on tastes and odors was held a t the last and Greenfield3 investigated the various reactions of water purification and water softening, following the course of the convention4 of the American Water Works Association. reactions with the hydrogen electrode. A committee of the Chlorine may be noticeable if present in excess or it mayproAmerican Water Works Association, R. S. Weston, chair- duce organic compounds which cause a “chemical” or “iodoform” taste. British operators recommend “antichlors” for the former and KMn04 for the latter. * Numbers in text refer to Bibliography at end of this article.
PRODUCTION OF POTABLE WATER
W
Sept., 1922
THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY
841
The most serious recent trouble due to tastes was that sources of most of the troubles have been found and a satisproduced by Synuria in New York Cityle supply. This taste factory technic worked out, which will appear in the new was removed by treating with an excess of (312. Another edition of Standard Methods. The results of the extensive investigation of the Ohio case is recorded in which an attendant attempted to dislodge by force a specimen of Mephitis mephitis (vulgarly River by the U. 5.Public Health Service are to be published known at3 skunk) which had perched on the water intake. in the near future. The report will contain much informaThe obvious disadvantage of waiting 24 to 48 hrs. for bac- tion on methods of stream study and the course of the autoteriological results to tell whether or not chlorine treatment purification reactions. The same organization has been has been sufficient, has led to the immediate popularity of making a study of the Illinois River, in which opportunity has the chemical “excess chlorine” test of Enslow and W ~ l m a n , ~ ‘ been afforded for checking and improving their investigawhich can be read within half an hour. The study of filter tional methods. We may expect considerable improvement plant loading by Streeter18 has thrown considerable light on in the “tools” of sanitary chemistry as well as voluminous data on the particular problems studied as the result of these what may be expected from various purification plants. No radical changes have taken place in the field of matter investigations. A symposium2*on “Stream Pollution and Sewage Disposal” softening since the introduction of zeolites 10 or 15yrs. ago. Comparatively little has been published on the zeolite base held a t a meeting of the American Society of Civil Engineers exchangcP reactions outside the patent literature, but it is in New York in November 1921, together wibh the discussion now apparent that the power to exchange bases is possessed which followed, contains considerable information of a chemical nature. DonaldsonZ9has reported on the relation by a large number of “alumino silicate” compounds. Indican20 as an indicator of pollution has been suggested. of coal and oil, tannery, paper, and various other industrial Various modifications of the hardness testsz1 have recently wastes to water supplies. The limit of 200 to 400 p. p. m. been proposed. Several attempts to develop a delicate test of chlorides which has been setZ9Joon the allowable pollution for phenols22 in water have met with questionable success, from oil-well wastes and sea water seems to the writer to be appareni ly because of the interference of natural coloring unjustifiably low. Several cases of ground-water supplies matter. ScheringaZ3has recently investigated the Nz cycle containing 1000 p. p. m. or more of chlorides could be cited, in water, and Nicholsz4has made a new study of the signifi- and there is evidence that vegetation3I and cattle will tolerate 2000 to 3000 parts. G o ~ l dhas ~~ discussed the oxygen recance of nitrates. quirement of New York harbor and the various sources from The A . P. H. A. standard methods of water and sewage analysis have been revised with the cooperation of a com- which this demand may be met. He concludes that surface mittee from this ~ O C I E T Yand are to be published in the near aeration is the principal source of 0, while Purdy in the disfuture. Public Health Engineering Abstracts, issued weekly cussion calls attention to the importance of microorganisms by the Treasury Department Public Health Service, covers and aquatic plants. Streeter in discussing the same paper American and foreign literature. The American Water calls attention to the fact that turbulence must be depended Works Association has recently included an abstract depart- upon for rapid aeration. ment in its journal. Additional articlesz6 of importance SEWAGE PURIFICATION are mentioned in the Bibliography, page 842. Activity in conserving nitrogen has been largely devoted STREAM POLLUTION to the development of the activated sludge process which is discussed in a separate article. Richards and Weekes33 Probably the most important advance in this field has have proposed straw filters for sewage disposal and find that been along the line of analytical methods. The older tests, the bacterial growths which occur, fix ammoniacal and oxygen consumed from NMn04 and solids lost on ignition, nitrate nitrogen. After a time the straw is replaced and, were admittedly empirical and since there was little uni- because of the nitrogen accumulated in the bacterial growths, formity of technic among different workers there was the used straw is good for fertilizer. small basis for comparing their results. No less than five A r d e r ~has ~ ~discussed ~ sewage disposal with reference to different methods for the oxygen consumed from. KMnO, colloid chemistry, and he gives an excellent summary of the are givvn by various authoritative textbooks. The esti- various theories of sewage purification together with valuable mation of the degree of pollution from the forms of com- lists of references. He favors a middle gr0ur.d between the bined njtrogen has not been found feasible. The present biochemical and co~loidaltheories. method, originally described by the Royal Commission on considers that the microbial growths on trickling Sewage DisposallZ6measures the amount of dissolved oxygen filters are of greater importance than they are usually deemed required to satisfy or “stabilize” the organic matter in the to be. He gives lists of organisms found and concludes that sample. This is accomplished by diluting the sample with the flora and fauna of the filter determine the biochemical an amount of aerated distilled or tap water sufficient to con- reactions produced. Thompson36 has made a similar study tain an excess of dissolved oxygen and then titrating the of trickling filter biology, more especially with reference to residual oxygen after a period of incubation (1, 2, or 5 days) activity of enzymes which he proved were produced. a t constant temperature (usually 20’ C.). From the titraWagenhals3’ concludes from an extensive engineering and tion and the length of incubation the “biochemical oxy- chemical survey of sewage treatment plants that the Gooch gen demand” is calculated, or the results may be expressed crucible determination of suspended matter and the five-day as “1-dtLy demand,” ‘%day demand,” or “5-day demand.” biochemical oxygen demand a t 20’ are the best tests for When Frst proposed this method met with some oppo- determining the efficiency of sewage treatment plants. The sition i n this country owing to the frequency of erratic paper contains considerable chemical data. Buswell and results, and the method was not included in the 1917 Weinhold3* call attention to advantages of the ultra filter edition of Standard Methods of A. P. H. A. The method over the Gooch crucible, vix., portability, speed, and the had much to recommend it, however, on account of its fact that it may be calibrated to give a notion of the size of similarity to natural conditions and was adopted for colloidal particles. Mohlman and P e a r ~ ehave ~ ~ reviewed stream pollution investigations by the U. S. Public Health the various methods for estimating colloids and have sugService. Largely through the efforts of this Service2’ the gested the use of the nephelometer.
