November, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
this difficulty the data show that practically all the organisms are caught on the intake side of the disk, and relatively few organisms are carried any appreciable depth into the capillaries. I n certain other experiments, in which two different organisms (for instance, yeast and acetobacter) were present in the juice, any. segregation of the organisms in different portions of the disk has been looked for, but no segregation due either to size or other properties has been demonstrable. It is obvious that the intake side of the disk completely plugs with organisms and colloidal material long before the filter layers deeper in the disk are incapacitated. Because of this fact, a thinner filter disk would no doubt give as satisfactory service and a t the same time reduce the cost of the filtering operation. COI~CLUSIOKS It is quite possible to sterilize fruit juices by filtration through the commercial-size Seitz germ-proofing filter and to obtain a sparkling clear product if proper operating conditions are observed. These conditions are as follows: (1) sterilization of the assembled filter and disks by steam, (2).sterilization of containers receiving the filtered juice, ( 3 )
1223
sterilization of caps or seals, (4) proper attention to pump pressure, and (5) general sanitary room conditions. The rate of filtration through the Seitz filter disk is somewhat slower than is desirable for American commercial practice, and improvement along this line is to be sought. ACKNOWLEDGMENT The writers acknowledge their indebtedness to Philipp Wirth, Inc., of New York, for placing a t their disposal an allmetal Seitz germ-proofing filter, size 30/8, for these experiments. LITERATURE CITED Bartell and Carpenter, J . Phgi. Chem., 27, 252 (1923). Bechhold, Z. Hug. Infektionskrankh., 112, 413 (1931). Bigelow and Bartell, J . Am. Chem. Soc., 31, 1194 (1909). Carpenter and Walsh, N. Y . State Expt. Sta., Tech. Bull. 202 (1932). (5) Kohman, Eddy, and co-workers, IND.ENG. CHEM.,15, 273 (1923); 16, 52, 1261 (1924); 22, 1015 (1930); Natl. Canners hssoc., Bull. 19L (1924). RECEIVED July 15, 1932.
Stream :Pollution by Irrigation Residues C.
S. SCOFIELD, United
States Department of Agriculture, Washington, D. C.
T
HE water supplies for many of our irrigated areas are obtained by diverting from stream channels all or a portion of the stream flow. The irrigation water is spread over the land where part of it is absorbed by crop plants or lost by evaporation, the remainder being returned to the stream channel as drainage. This return drainage contains the major portion of the dissolved salts carried by the irrigation water, with the result that successive (diversions from a stream cause a progressive increase in the salinity of its water in the downstream direction. COSDITIOXSI I ~THE RIO GRANDEREGION Observations on the Rio Grande in the vicinity of El Paso, Texas, during 1931 show that a t four points below Elephant Butte Reservoir the average salt content of the stream expressed as parts per million was as follows: At Leasburg 610, a t El Paso 956, a t Fabens 1500, a t Fort Quitman 2206. The annual discharge of the Rio Grande a t Leasburg is, approsimately 750,000 acre-feet of water containing approximately 650,000 tons of dissolved salts. At Fort Quitman the annual discharge is approximately 200,000 acre-feet of water containing approximately 650,000 tons of salt. These figures show that, while the irrigated lands in the vicinity of El Paso consume annually about 550,000 acre-feet of water, the total salt burden of the stream through that section is not diminished. This is manifestly as it should be if we have in view the sustained productivity of these irrigated lands. Were the salt balance conditions of this area such that the annual salt outflow was substantially less than the salt inflow, it would be evident that there was occurring an accumulation of salt in the irrigated land to its ultimate detriment for crop production. The investigation here reported has shown that, while the annual tonnage of salts leaving the project a t Fort Quitman is substantially the same as that entering the project a t Leasburg, the relative proportions of the salt constituents are very different a t the two points. The analyses included three
anions-bicarbonate, chloride, and sulfate--and two cationscalcium and magnesium-with the alkali bases determined by difference. With respect to these constituents the annual summaries shorn that for bicarbonates the inflow was 100,000 tons, with the outflow 37,000 tons; for chlorides the inflow was 70,000, the outflow was 234,000 tons; and for sulfates the inflow was 240,000 and the outflow 138,000 tons. Thus for the anions, the bicarbonates and sulfates were retained in the project lands, whereas there was a very large net r e lease of chlorides. With respect to the cations, the inflow of calcium was 80,000 tons, the outflow 50,000 tons; for magnesium the inflow was 16,000, the outflow 12,000 tons; and for the alkali bases (chiefly sodium), the inflow was 111,000 and the outflow 165,000 tons. Thus it appears that the salts of low solubility (chiefly calcium carbonate and calcium sulfate) were precipitated in the irrigated soil, whereas a substantial quantity of sodium chloride was removed from the soil and carried away in the drainage water. This represents a favorable salt balance for the irrigated land, but is also a striking example of stream pollution by irrigation residues. The salt concentration of the Rio Grancle as it passes Fort Quitnian is too high to be safe for irrigation use. Fortunately the streams joining the river below that point, chiefly from the hIexican side, contribute large volumes of water of low salinity, so that the mater as diverted a t Roma and below for use in the area above Brownsville is not too saline for safe use where adequate drainage is provided. CONDITIONS
I N THE
COLORADO BASIN
The Colorado is a larger stream than the Rio Grande with a much larger salt burden. It has no important tributaries below the Grand Canyon. Observations reported by Howard for the Grand Canyon gaging station show that for the five years ending in 1930 the mean annual discharge of the river a t that point has been 15,700,000 acre-feet of water, carrying 12,000,000 tons of dissolved solids. It is believed that a substantial part of this salt burden is contributed by the drainage
froiii irrigdt,cd lands in the upper IiiLsiii. Altlioogli future diversions Sor irrigatiw in the upper basin may diniinisli t.lie flo\v of water tlrrouglr thc Grand Caiiyun, it seems p r ~ ~ l i a bthat le the annual discliarRe of salt passing t.lris point will riot be ap-
~~rccial.ily di~iiinisl~e~l, Ol!servations as tu salt Imltince caiditirms lin on for tlic past three years frrr two irrigated areas i n tilt. lowrr Colorado basin. These are t,lie Y i m a Vallry iii Arizw:i and the Iiiiporial Valley in Califonii:i. 13iitIi tlieso i)rrater to Parins 1m licen 10%,0l10 acre-fcik, wvliereas 45,000 acre-feet hare I m i i ilischiirgril tis cir:iiii:iRr. The inean anrind salt iriflow litis l i r w ll2,OOIl toris arid tho salt outHow !B,OlOO to:is. On t,liix project, as OLI ( h n d e , the present drainage Ewilities appear to he t,o prevent tile serious nccniriiiltitioii OS salts i n the lands. 'Die water siipldy fir tlic Iinpcrial Vtilky in C'aliiwria is diverted from the (.'oIor:i&~1Uvw jast b r h w Yuma, carried by canal t.liroiigli I\lesican territory, and delivered to t l i e Imperial Irrigition District at tile i~rterrratii~nallioiindnry. Tliere is some divtmion from this canal for the irrigation of Mexican lands, but these lands are not provided rvith drainage. The irrigated lands of tlie Iniperial Valley are served hy a drainage system that diseliarges into Saltori Sea, wliicli lies iielow sea level. The figures liere reported Sur irrigation inflow are based i i 1 1 ~ 1rceords of tlie watcr crossing t,lie international boundary. Those for the drainage indnde the two main drains, Alarm and Sew Rivers, hut tliere are in addition a few small drains that discliargo directly int,o Salton Sea or into tlie main drains below the gaging stations. Tlins tlie tot,als reported for drainage discliarge are prohalrly aomcwliat helow the trutli. For the past two years the mean annual inflow of irrigation water to the Imperial Irrigation District lias been 2,430,000 acre-feet, carrying slightly more than 3,000,QOOtons of salts. The annual oritflow OS drainage water has been 963,000 acrefeet, carrying 1,997,000 tons of salts. The irrigated area consumed annually as evaporation and transpiration losses nearly 1,500,000 acre-feet of water, and the adverse salt balance was slightly more than 1,000,000 toils a year. That is to say, the salt outflow was annually about 1,000,000 tons less than the inflow. This situation iniplies the need of more effective drainage of the irrigated land iS injiiry from salt accurnulat.ion is to he avoided. The three instances here described show clcarly that the norrrid operation of an irrigation project results in diniinishing the voluine of discharge of water without a corresponding decrease in the quantity of dissolved salts. In other words, the divcrsion of water from n stream for irrigation use operates normally t o increase the concentration of salts in the streani I_
rvator. From this it becumea apparent that in formulating a program for the most complete and effective utilisation of the streams of our desert region?, consideration sliould be position of tlie salt burden. in let ns eonaider the Colorado River. The plans for this stream, so far as t h y have heen developed, allocate nearly half its water to t i l e ripper basin aiid slightly inore tlinri half to tlie lower Lasin. Wlien this prograin tins hceii achieved it is t o be expected that bile 8 or $3 million acreScet OS water aunually passing through tire Grand Canyon will mrry approximately the iage of salts as is now carr i d hy the l6,000,000 a 111 other mords, tiic \rater
