Infiltration of Wastewater in a Newly Started Pilot Sand‐Filter System: II. Development and Distribution of the Bacterial Populations

Abstract

AbstractThe objective of the study was to monitor the development of the bacterial populations in a sand‐filter system consisting of a three‐chambered septic tank, a sand filter with a one‐person capacity, and eight columns. The system was loaded with 67 L m−2 day−1 of an artificial wastewater. Monitoring was conducted from start‐up until a steady state was reached. The wastewater contained over two orders of magnitude higher numbers of aerobic bacteria in the third chamber compared to the first chamber of the septic tank. Populations of aerobic and denitrifying bacteria in the sand surface layer of the columns increased markedly in number within the first 10 d, reaching peaks on Day 24. The following decline was attributed to the development of anaerobic conditions. This hypothesis was supported by an observed increase in the number of sulfate‐reducing bacteria. No increase in nitrifier populations was observed. In the sand‐filter surface layer both aerobic and denitrifying bacteria increased in numbers until Days 65 to 75, thereafter remaining in a steady state at around 108 bacteria g−1 dry sand. Populations of ammonium‐ and nitrite‐oxidizing bacteria both started out at low levels. Thereafter they increased until Days 70 to 95, by which time populations of 106 to 107 and 105 to 106 g−1 dry sand, respectively, had been established. By the time that bacterial growth had reached a steady state, an estimated 8% of the pore volume in the sand surface layer was occupied by bacterial cells. This biomass accounts for the amounts of N and P in the sewage water produced by one person during a 20‐d period.