Field trials were carried out using two types of package units designed for the treatment of domestic sewage from individual households. One of the units was a commercially available rotating biological contactor (RBC) system. The other was a newly developed sequencing batch reactor (SBR) system. Trials were carried at the site of a local sewage treatment plant where degritted raw sewage from a combined sewerage network was fed to the two units for a period of four months. Both units produced good effluent quality, well below 20/30 (BOD/SS) during steady-state performance. However, shorter start-up time was observed with the SBR unit together with better effluent quality (up to BOD<10 mg/l and SS<15 mg/l). Furthermore, the SBR unit produced effluents with ammonia nitrogen and total phosphorus levels of 3 mg/l and 2 mg/l respectively, for influent levels that varied from 20 to 60 mg N-NH3/l and from 15 to 17 mg/l of total phosphorus. On the other hand, significant nutrient removal did not seem tohave occurred in the RBC unit. During testing to meet the requirements of British Standard (BS 6297), it was observed that the SBR can tolerate shockloads and periods following zero flow better than the RBC unit.

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