H. Bach et al., POST TREATMENT OF GROUNDWATER DENITRIFICATION FLUIDIZED-BED REACTOR EFFLUENTS TO ACHIEVE DRINKING-WATER QUALITY, Journal of industrial microbiology & biotechnology, 20(6), 1998, pp. 354-359
Post treatment of effluents from heterotrophic groundwater denitrifica
tion fluidized bed reactors (FBR) designed to achieve drinking water q
uality has been investigated. The denitrification process adds to the
dissolved organic compounds, biomass and bacteria in the effluent. The
y are also lacking dissolved oxygen. Effluents from the process were t
reated in combined post treatment processes based on either a tricklin
g filter and sedimentation unit ('TF combination') or contact floccula
tion ('CF combination'). Both processes were followed by sand filtrati
on, granular activated carbon (GAC) and chlorination. Results regardin
g total suspended solids (TSS) and turbidity removal showed an advanta
ge to the 'CF combination', and the target turbidity (NTU <1) was alwa
ys achieved when the alum dose was 10 or 20 mg L-1. Backwash of the sa
nd 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 remo
val of the DOC occurred in the sand filter (28%), while the GAC contri
bution 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 chlori
nation unit before the sand filter column (pre and post chlorination)
resulted in effluent with no regrowth potential for both Pseudomonas f
luorescens P17 and indigenous bacteria.