Integrated horizontal‐flow anaerobic and radial‐flow aerobic reactors for the removal of organic matter and nitrogen from domestic sewage

Abstract

This paper presents the conception and discusses the results obtained from the operation of an integrated biological anaerobic/aerobic/anaerobic system composed of horizontal‐flow anaerobic and radial‐flow aerobic reactors for domestic sewage treatment. The performance of a horizontal‐flow anaerobic immobilized biomass reactor, with five stages, followed by a radial‐flow aerobic immobilized biomass reactor was evaluated along 22 weeks. After the 14th week, the last stage of the HAIB reactor was used as a denitrifying unit Polyurethane foam cubic matrices with 1‐cm sides were used as support for biomass immobilization in all the units. The influent domestic sewage presented mean chemical oxygen demand of 365 ± 71 mg. l‐1 and the temperature was 23 ± 3°C. The integrated system achieved COD removal efficiency of 90% while the maximum ammonium removal efficiency was 97% in the aerobic post‐treatment unit The nitrification process was found to be better represented by first‐order reactions in series model. The apparent first‐order kinetic coefficient for nitrate formation was about 50 times higher than that estimated for the nitrite formation. The denitrification process was well represented by a Monod‐type kinetic model. The maximum specific denitrifying rate and the half‐saturation coefficient were 2.9 × 10–4 mg NO3‐N mg‐1 VSS h‐1 and 19.4 mg NO3 ‐‐N l‐1 respectively.