Development of a two-stage biofilter system to enhance the effluent quality of a UASB pre-treated domestic sewage

Abstract

This paper proposes a new development in post-treatment technology entailing a pilot-scale anaerobic upflow anaerobic sludge blanket (UASB) followed by a two-stage biofilter system. As filter media, local crushed recycled plastic and anthracite were used in the anaerobic filter (AF) and passive aerated rapid filter (RF) respectively. Domestic sewage from Birzeit town was treated at an average flow rate of 0.50m3/d under variable organic loading rates (OLRs) and hydraulic retention times (HRTs). The applied HRTs for the treatment chain (UASB-AFRF) along three run phases were (32.5, 2.2 and 1 h), (19.5, 1.3 and 0.7 h) and (14, 1, and 0.4 h). The applied OLR (kgCOD/m3.d) were (0.16, 1.90 and 6.97), (1.53, 10.68 and 10.54) and (0.57, 6.17 and 20.40) respectively. The overall removal efficiency of the treatment chain for CODt was (42, 83 and 50%) respectively, however the achieved CODt removal efficiency by the UASB alone was (18.5, 53 and 29%). The suspended solids removal efficiency for the complete treatment chain was (70, 65 and 55%) at variable OLR and HRT, the UASB suspended solids removal efficacy was around (35, 27 and 21%) for the three run phases respectively. During the first run phase (Highest HRT), an average removal efficiency of 8 and 14% for ammonia and phosphorus in the RF was achieved, high OLR applied during the second and third run phases might be behind low nutrients removal efficiency. Removal of Kjeldahl nitrogen (TKN) in the AF and RF was associated with similar reduction tendency in BOD. The proper design and adequate operation of the UASB reactor appeared to be the main efficacy-limiting factors of the developed post treatment system.