Indole and Skatole in Sewage WILLEMRUDOLFSAKD NOELS. CHAMBERLIE iYew Jersey Agricultural Experiment Station, lYew Brunswick, S.J .
I
T IS well known that most of the odors observed around
extracted with 1 cc. of reagent 3. Comparison was made with standards prepared in exactly the same way. The water test solutions consisted of 10 cc., which was equally divided into two thin-walled colorless glass test tubes, one used for the test and one held in reserve. The tubes were placed in a rack in numerical order; and a series of standard tubes containing 0, 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0, and 6.0 mmg. indole in 5 cc. of water arranged in another rack. A series of reagent burets arranged on a revolving stand contained the following reagents: water, standard indole solution, p-dimethylaminobenzaldehyde solution, hydrochloric acid, chloroform, and sometimes a modified Herter’s reagent and standard skatole solution.
sewage-disposal plants are caused by sulfur compounds, mainly hydrogen sulfide and some mercaptans. -1mong the sulfides produced in the decomposition processes in digestion tanks, allyl sulfide, which has a penetration odor and occurs especially during the first stage of digestion, or when tanks are not performing normally owing to lack of .ufficient seed material or acid conditions, is a striking example of a n odor-producing substance other than hydrogen sulfide. There are, however, still other volatile substances which, diffused in extremely small quantities into the air, h a r e a peculiar and penetrating odor. ‘rwo of these substances-namely, indole and skatole, which are nitrogenous degradation products-were selected for determination in three types of sewage-disposal plants. These substances, formed probably by a number of different bacteria in the processes of decomposition of proteins, are found in feceq and may occur in spoiled fish, meat. and other nitrogenous food products. The sewage plants selected were: Plainfield, S . J., consisting essentially of a fine screen, settling tanks, sprinkling filters, and digestors; Red Rank, S . J., with clarifier unit and digestors; and Madison-Chathani, S. J., with sediinentation and activated dudge.
RESULTS
METHODSUSED Considerable work was done to adapt met hods suitable for the purpose. It was soon found that the quantities of indole and skatole present were very small. ISDOLE. A current of live steam was passed through the mixture in the flask until 500 cc. of distillate were collected. The steam from the flask was received from the condenser into an adapter, the end of which projected below the surface of a small amount of water in the receiver (600-cc. beaker). The distillate was transferred to a liter qeparatory funnel, acidified with 10 cc. c. P. concentrated hydrochloric acid and extracted with 120 cc. ethyl ether (V. S. P.) with repeated and vigorous shaking of the funnel. After the ether had separated, the ether layer was transferred to a 250-cc. -eparatory funne! and washed free, first JT-ith 25 cc. sodium hydroxide solution (2.5 per cent), and then with 25 cc. dilute hydrochloric acid (10 cc. c. P. concentrated hydrochloric acid plus 200 cc. water). The first washing was t o remove compounds which might interfere in the color tests, and the second to neutralize any alkali left in the ethw. The ether was then placed in a small flask with 10 cc. of distilled water and evaporated on a steam bath, taking great care that, Trhile the last of the ether was being driven off, the water layer Iraq not heated appreciably above the boiling point of ether, w c e indole may be easily lost by volatilization a t tliiq stage. A 3-cc. portion of the 10 cc. of water residue Ira. then tested for indole, and 5 cc. for skatole by the modified tests listed below. SKATOLE.I n the modified Ehrlich method the reagents used were (1) 2 grams of p-dimethylaminobenzaldehyde in 100 cc. of 95 per cent alcohol; ( 2 ) 600 cc. concentrated hydrochloric acid plus 200 cc. of water; and (3) U. S. P. chloroform. T o 5 cc. of the water test solution 0.5 cc. of reagent 1 and 1 cc. of reagent 2 were added. This was placed in boiling-water bath for about 20 seconds, shaking vigorously, and then in ice water for about 30 seconds, and
The results obtained are summarized as averages of several tests in Table I. The quantities of indole and skatole in the raw sewage are small and seem to be about the same for the different places. These small quantities will produce a perceptible odor. It is of interest that the settled sewage in all cases contained less indole and skatole than the raw sewage. The rather stale Plainfield sewage contained more skatole than the sewage of the other two places. The effluents of the oxidation devices contained only traces of both indole and skatole. These volatile substances were either dispersed into the air or oxidized. The latter is more probably true than the former, since the odor arising from the aeration tanks is usually less than from a sprinkling filter, although all odors coming from sprinkling filters are by no means due to these nitrogenous compounds alone. T.4BLE
I.
INDOLE .4ND SKATOLE IN
DISPOSAL PLAXTS
(Parts per billion) PLhNT
IKDOLE
Plainfield, N . J . : Screened seaage Settling-tank effluent Sprinkling-filter effluent Red Bank, N . J.: Raw sewage Clarifier effluent Madison-Chatham, S . J.: Raw sewage Settling-tank effluent Aeration-tank effluent
SKATOLE
0.38
0.25 0.12
0.25
0.25 0.12
0.19 0.12
0 25 0.12 Trace
0.19 0.12 Trace
Trace
Trace
The putrefactive processes producing indole and skatole proceed probably by deaminization, and it is possible that such odors can be controlled by alkalies or chlorine. This phase of the work has not, however, been carried far enough to determine the quantities of chemicals required. SUM31ARY
The nitrogenous degradation products, indole and skatole, which produce penetrating odors when diffused into the air, are present in raw sewage, to a less extent in settled sewage, and only in traces in sewage treated on sprinkling filters or by the activated sludge process. RECEIVEDSeptember 10, 19;jl. Presented before the Division of Water, Sewage, and Sanitation Chemistry a t the 82nd .Meeting of the American Chemical Society, Buffalo, N. T.,August 31 t o September 4, 1931. Journal Series paper of New Jersey Agricultural Experiment Station, Department of Sewage Research.
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