The experimental bacterial treatment of London sewage : being an account of the experiments carried out by the London County Council between the years 1892 and 1903 / by Frank Clowes and A.C. Houston.

  • London County Council
Date:
1904]
Catalogue details

Licence: In copyright

Credit: The experimental bacterial treatment of London sewage : being an account of the experiments carried out by the London County Council between the years 1892 and 1903 / by Frank Clowes and A.C. Houston. Source: Wellcome Collection.

    78/356 (page 58)
    I' rom .1 able XV HI. it. will be seen that the suspended solids (column 7) were removed practically to the same extent by the settling tank of Series III. at the Northern Outfall as by the primary beds of Series li. There was, therefore, a distinct gain in using settling tanks instead of primary beds, since the suspended matter which was left in the tanks was largely composed of mineral substances and of substances not readily decomposed by bacterial action, and which in previous experi- ments had been found to choke the primary beds. In a permanent installation of bacteria-beds it is proposed that in addition to the ordinary settling tanks, preliminary settling tanks or “ detritus chambersr’ should be used for the removal of road detritus. With reference to the purification effected by the coke-beds, as estimated by the relative amounts of oxygen absorbed from perman- ganate by the crude sewage and by the final effluent from any particular experiment (columns 8 and 11), that effected in the experiments of Series III. was generally lower than in any of the other experiments carried out at the Northern Outfall. It should, however, be borne in mind that in the experiments of Series III. the sewage was subjected to only one contact in coke-beds, whereas in all the experiments of Series T. and II. it was subjected to two contacts in successive beds (column 5). It should be noted that the variation in the amount of purification effected by the beds when they received two fillings per day, as compared with that effected when they received only one filling per day, was not always consistent, since sometimes the amount of puri- fication effected increased with the number of fillings of the bed per day. When the figures relating to the experiments are considered, the amount of purification effected is seen to have been influenced in a more regular manner by variations in the number of fillings per day of the coke- beds at the Southern Outfall than it was at the Northern Outfall. The only apparent exception to this regidar variation occurred during the experiments of Series II. This apparent exception is, however, most important as showing the value of a previous settlement of the sewage. It will be observed that while the 4-foot bed was being increased in depth to form the 1 o-foot single coke-bed of Series II. it was filled only once per clay. At the end of a month the bed, which was still under 18 feet in depth, was filled twice per clay, and although the efficiency of the bed was probably increasing daily yet the amount of purification effected fell during the time it received two fillings per day (column 12). The next modification of the experiments with this bed was the rough settlement of the sewage before it passed on to the coke-bed. Reference to column 12 will show that this rough settlement increased the amount of purification effected. After the bed had been dealing with two fillings per clay of roughly settled sewage for about two months, the fillings were increased to three per day and the purification effected consequently decreased in amount (columns 0 and 12). The next and last change in the experiments of Series II. was to subject the sewage to more perfect sedimentation and to fill the bed four times per day. Notwithstanding the extra work appaiently imposed upon the bed by this increase in the number of fillings, the percentage amount of puri- fication effected increased, and there is every reason to believe, that this