The combined effect of step-feed and recycling on RBC performance

G. M. Ayoub*, Pascal Saikaly

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

The effect of step-feed and recycling on the efficiency of treatment in rotating biological contractors (RBCs) was investigated. Experiments were conducted on a RBC system consisting of two three-stage units. The two units were operated in parallel, one unit as a control with a single feed point and the other in a step-feed mode. Seven experimental runs were conducted, using a simple synthetic wastewater, in which hydraulic loading rates were maintained constant at about 0.094m3/m2d and variable COD concentrations (800-1200mg/L), NH3-N concentrations (104-116mg/L), step-feed ratios (60/40 and 70/30), and recirculation modes. Results indicate that improvements in the treatment efficiencies of RBC systems may be attained by operating the system in a step feed mode as compared to a single point feed mode. Further improvements may also be obtained by inducing effluent recirculation to the inlet stage. In both cases, levels of improvement have shown to be more pronounced for NH3-N removals and DO residual concentrations as compared to COD removals. The combined effect of step feed and recirculation of system effluent on NH3-N removal efficiencies is appreciable. Comparing removal efficiencies between the control, step feed and the combined step-feed/recirculation modes shows an increase of about 26%. For COD removals, the effect is not that pronounced as the results for the combined modes of operation indicate a limited increase in overall removal efficiency of about 3%. Supplementing step feed by a recircutation system also markedly improved DO residuals in stages 1 and 2 and to a lower extent in stage 3 of the system. Changing the ratio in the step feed system from 60/40% to 70/30% exhibited a slight improvement in NH3-N removal efficiencies as well as improved residual DO concentrations but very limited effect on COD removals. The use of a simple synthetic wastewater in the experiments may limit extrapolation of the findings to actual operation.

Original languageEnglish (US)
Pages (from-to)3009-3016
Number of pages8
JournalWater Research
Volume38
Issue number13
DOIs
StatePublished - Jul 1 2004

Keywords

  • Ammonia nitrogen
  • Chemical oxygen demand
  • Dissolved oxygen
  • Recirculation
  • Rotating biological contactors
  • Step feed

ASJC Scopus subject areas

  • Earth-Surface Processes

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