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ou"; '" ............,J . . . Population served by treatment plants increased 38% in four years ~e. summary includes no industrial or 1I1shtutional data. The term "muni- cipal" includes not only incorporated and. unmcorporated communities, but saIlltary districts in their many forms. All data in the inventorv are for 1957 (:~cept for :\lahama, i\r1ichi"gan and Loui- Siana communities where 1953 figures had to be used. 'Vhile Publication 609 will be a com- plete summary, the basic data that is received for each community from state pollution control administrations is scheduled to be published later on dur- ing the summer. How Municipal Inventory Was Prepared So Quickly The 1957 inventory of municipal sewage treatment was processed in a fract,ion of the time required for the prevIOus PHS inventories. Information was gathered and forwarded by state regulatory ollicials on a single PHS form for each community. Clerical per- sonnel coded the data and prepared addressagraph plates from which each community's story was printed as a one line item in tabular form. . Meanwhile, puryched cards contain- mg the same coded information were prepared and verified in standard IBM equipment. The IBM sorter then was used as a second verifier. The sorter couM check out coding of the PHS personnel, accuracy of transcription of data on addressograph and even the original supplying of data by the states (i.e., if a community showed a primary plant, there should not be a notation in the trickling filter column on the pnllched card). Of about 12,000 punched cards. the sorter kicked out 250. About half had incorrect original information, one- quarter contained' coding errors. Sur- prisingly, the last quarter of the cards contained punching errors that had gotten through the regular punched card verifiers (a second operator rc- punches the data in the original punched card, on the theory that two operators won't make the same mis- t"ke). The sorter then was used to arrange the punched cards by the desired grouping (state, basin, population group). The C"clrds were then run through an IBM 407 printer. which served as a tabulator on this job. It was found that an electronic com- puter is really necessary to do the arith- metic and percentage work. A digital computer will be used on future work of this tvpe. Data 'preparation was supervised by Arthur D. Smart, under the direction of John R. Thoman Here's the changing picture from 1940 to 1957: Treatment Assigned Percent Reduction None 0.0 Minor 0.0 Primary 31.3 Intermediate 45.5 Secondary 82.5 Total Estimated Population (Million, I .ill2.. Discharged ~ ~ 21.9 29.9 27.9 3.3 4.3 1.9 10.4 11.8 17.6 2.2 3.0 2.1 3.2 3.8 7.6 49.0 49.9 52.0 1 The only diScouraging note An increase of 4.5% in total popula- tion discharged to streams between 1945.1957, and an increase of 6.3% in the 1940-1957 period is indicated in Table I. Note that Table I is based on "population" only; comparable pop- ulation equivalent data are not available for vears earlier than 1957. However, preliminary study indicates 75 million population equivalents (PE) are being discharged to streams, and 65 million PE are being removed in treatment plants in cities around the country. The percent reductions assigned to the different treatment processes are based on data reported in 1957 for about 55% of the sowered population. Note that thev are 5 to 10% lower than convention<ll design removal rates. That may indicate overloaded plants, poor design or poor plant operation-or all three. Since Table I causes reflection as to the accomplishment of current pollu- 1957 nationwide breakdown of primary, Number Estimated Percent of Process of Pop. Served Estimated Population Plants (Millions) Served Septic tanks 7BO 1.0 3.B Imhotf tonk. 1,084 3.3 13.0 Mechanically cleaned tanks 656 IB.6 72.7 Plain, hopper bottom tanks 80 1.3 5.2 Settling tanks- No detail 53 1.0 4.0 in Inventory Others and Unknown 77 0.3 1.3 Total 2,730 25.5 100.0 4 Mechanically cleaned primary tanks lead Imhoff and septic tank primary plants show up as most numerous in Table 4. But they serve only 16.8% of the pri- lIIary population. In 1945 these two processes served 36.0% of the primary population and accounted for 83.5% of all primarv plants. On the other hand, mechanically cleaned settling tanks increased 84% in number and 95.1 % in population served between 1945 and 1957. In gcneml. septic tank and Imhoff plants prcdominClte in smaller commu- nities, while the mechanically cleaned tank is the major type in cities of over 5.000 population. Considerable variation exists among the various basins. Comparison of Tables 4 and 6 indicates that man\, of the Imhoff and spcctic tanks may be converted into exclusi\'e sludge handling facilities.