Post treatment of groundwater denitrification fluidized bed reactor effluents to achieve drinking water quality |
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Authors: | H Bach S Tarre M Green |
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Institution: | (1) Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv, Israel, IL;(2) Faculty of Agriculture Engineering, Technion, 32000 Haifa, Israel, IL |
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Abstract: | Post treatment of effluents from heterotrophic groundwater denitrification fluidized bed reactors (FBR) designed to achieve
drinking water quality has been investigated. The denitrification process adds to the dissolved organic compounds, biomass
and bacteria in the effluent. They are also lacking dissolved oxygen. Effluents from the process were treated in combined
post treatment processes based on either a trickling filter and sedimentation unit (‘TF combination’) or contact flocculation
(‘CF combination’). Both processes were followed by sand filtration, granular activated carbon (GAC) and chlorination. Results
regarding total suspended solids (TSS) and turbidity removal showed an advantage to the ‘CF combination’, and the target turbidity
(NTU <1) was always achieved when the alum dose was 10 or 20 mg l−1. Backwash of the sand filter and GAC column was required after 27 h of operation (average value). An average total reduction
in dissolved organic carbon (DOC) of 40% was observed with a final DOC of 3.5–4 mg L−1. Most of the removal of the DOC occurred in the sand filter (28%), while the GAC contribution was smaller (18%). No regrowth
potential was observed using the Werner method when a pure culture of Pseudomonas fluorescens P17 was used as inoculum in samples of chlorinated effluent (post chlorination). When a mixed culture of indigenous bacteria
was used as inoculum, a high regrowth potential was observed. Installing an additional chlorination unit before the sand filter
column (pre and post chlorination) resulted in effluent with no regrowth potential for both Pseudomonas fluorescens P17 and indigenous bacteria.
Received 17 October 1997/ Accepted in revised form 29 May 1998 |
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Keywords: | : fluidized bed drinking water post treatment dentrification bacterial regrowth |
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