Abstract
Fine macadams (granite origin) was filled into a filtering bed with a bed volume of 1m3 and a bed depth of 1m, while artificial filtering media (plastic origin) were filled into two filtering beds with a bed volume of 1m3 and a bed depth of respectively 1m and 3m. The surface. area of the plastic media was 81.344m2/m3 and the vacant space ratio was 65.9%. These filtering beds were used for continuous treatment tests of filthy water from swine-pens during a period from May 1973 to March 1974.
The filter bed was designed so as to be supplied trickled water through a fixed water trough with natural aeration through the aeration vents located at the lower half of the bed. The test groups were classified by the loads of BOD volumes into 0-0.9kg BOD/m3/day, 3.0-4.9kg BOD/m3/day, and 5.0kg BOD/m3/day. The returning water during the continuous run amounted to 37.98 liters/min (54-55m3/day with a recycle ratio of 16.4-88.7%). Since the volume of the applied filthy water was adjusted in accordance with the pre-estimated BQD concentrations, the loading conditions could not always be maintained at the previously designed level.
The results were as described below.
1) About 2 weeks and more than 50 days were respectively required for summertime (May-August) and wintertime after the start of trickling water for the biological membrane to grow into grossly uniform conditions.
2) Following operation of the trickling filter system with a returning ratio of 16.4-88.7%, it was realized that a loading condition of 4-6kg BOD/m3/day would be efficient except during winter time if the aimed BOD removal rate is set at more than 70%. In summertime, even a high loading volume of 9-10kg BOD/m3/day could result in a BOD removal rate as high as 73.7-86.3%.
3) The BOD removal rates during wintertime were 38.3-62.0% (4.3-6.1kg BOD/m3/day load) and 52.5-58.3% (2.8-3.5kg BOD/m3/day load), which were drastically lower than those during spring and summer seasons. The removal rate of nitrogen was as low as 30-35% (Alb-N) and 4-10% (NH4-N) and the removal rate during wintertime was extremely low.
4) The amount of sludge per removed BOD (kg) with 33 test specimens collected during the season from May to August resulted in 0.358kg SS/kg BOD. Even if the self-oxidation coefficient was 0.05-0.1. the sludge formation coefficient of this method was deemed to be equal to or slightly lower than those of various types of active sludge methods.
5) The artificial filtering material was found to attain better BOD removal rate than the macadamized filtering material by 0.1-0.7%. The comparison of depths of filter-beds in terms of BOD removal rates turned out that the 1m depth of the filtering bed showed higher rate in summertime by 1.9-2.3%. while the 3m depth of the filter bed did higher one in wintertime by 5.8-19.0%.
