ANALYSIS OF THE REMOVAL CAPABILITIES OF INTERMITTENTLY AND CONTINUOUSLY RUN SLOW SAND FILTERS

Open Access
Author:
Byrne, Timothy Michael
Area of Honors:
Engineering Science
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Brian Dempsey, Thesis Supervisor
  • Clifford Jesse Lissenden Iii, Honors Advisor
  • Judith A Todd, Faculty Reader
Keywords:
  • slow sand filtration
  • biosand filter
  • intermittent
  • organic fractionation
  • removal
Abstract:
Over 80,000 household scale intermittent slow sand filters (SSF) have been installed in 20 different countries. However, case studies reveal that the operating removal performance does not comply with design expectations and can be variable. Therefore, additional study, better characterization, and design improvements are needed. In this study, both continuous and intermittent SSFs were operated for a duration of 110 days. Performance was monitored in terms of conventional parameters (turbidity, BOD, COD, coliform organisms, etc.) and by changes in the composition of organic matter (TOC and content of organic acids and other organic fractions) in the influent and the effluents. The continuous-flow SSF was operated with 91 cm of head, and, after providing at least 24 hours for maturing, flow ranged from 350 to 20 ml/min (1150 to 65 Lm-2hr-1loading rate). The intermittent flow SSF was charged with 20 L per day, and, after maturing, the flow typically ranged between 55 and 29 ml/min (181 to 72 Lm-2hr-1 loading rate) during a single run, due to changing hydraulic head. Removals for the conventional parameters showed that effective biological and physical treatment was achieved within the SSFs. As expected, the continuous-flow SSF performed marginally better than the intermittent-feed SSF. Both hydraulic modes provided good removal of organic acids, but hydrophilic base/neutrals were consistently produced in the columns. Unexpectedly, removal of total organic carbon (TOC) increased with increasing flow in the continuously run SSF, but the reverse occurred with the intermittently run filter. This could have been due to better penetration of O2 and nutrients and thus a deeper bio-filter layer in the continuous-flow SSF, and due to shearing of organic matter with increased flow in the intermittent-feed SSF. The results are consistent with several other studies completed on both municipal and pilot scale SSFs, while they are in conflict with a small number of investigations. These results indicate that intermittent SSF could be improved with better flow control, including reeducated fluctuation in flow rate.