Analyzing the design criteria of primary settlers for small sewage treatment systems: A national survey in Taiwan

Model of Suspended Solids Removal in the Primary Sedimentation Tanks for the Treatment of Urban Wastewater

“…This could be due to the fact that at higher sewage temperatures, particle-settling velocities increase, and consequently the effect of flocculation and SSi on SS removal becoming less significant [1]. The next variable with the greatest influence on the variability of the system was the surface hydraulic load, which, as many authors have studied [1][2][3]6,24,31,33,34] had a strong negative correlation, i.e., the lower the HRT in the tank (higher hydraulic loads), the more the process performance is greatly reduced. The organic matter concentration, on the other hand, hardly showed any correlation in the variability of the system (angle of the vector near 90 • ).…”

“…Comparative full-scale evaluations seldom result in meaningful and/or distinguishable results [29], and there is a considerable difference between the expected removal efficiency rates (50-70%) for SS and (25-40%) for BDO 5 when using the currently used values for the design, such as q and HRT, more frequently the removal rate of different PSTs shows an increasingly strong fluctuating pattern even for the same range of the HRTs [2]. Some research [30] shows the difference between real plant removal rates with the recommendations of the ATV guideline and analyzing the design criteria applied to small systems of wastewater treatment, the official HRT design criteria may be too conservative Q < 0.21 m 3 /h, as well as inadequate for Q > 0.83 m 3 /h [31].…”

“…Previous works have related removal efficiencies to surface overflow rates [1][2][3]6,24,31,33,34]; some of them [2,3,24,33] focused their research in a high value of surface overflow rate, in the range of 4 m 3 /m 2 •h to 13 m 3 /m 2 •h, which are considerably higher than those recommended in the design guidelines. Other works [1,32] [27], in cold climates, the viscosity increases of water, slow the sedimentation rate, establishing a relation between the temperature and the increase of the hydraulic retention time.…”