Abstract:
The objective of this work was to evaluate the use of pond bacteria paired with acetate and sawdust as viable
inoculums for facilitating heterotrophic denitrification in household slow sand filters. This was achieved through
culturing pond sediment bacteria and pairing it with both carbon sources in nitrate contaminated batch and filter
column experiments. The inoculum culture tested positive for denitrifying bacteria including those of the Bacillus,
Paraclostridium and Clostridium genera. Batch experiments conducted over 17 h with the acetate carbon source
achieved complete denitrification for the C/N ratios of 2 and 5 at concentrations of 200 and 400 mg/L of nitrate.
Incomplete denitrification was attained at C/N ratio of 0.5. Sawdust batches loaded with 1 g sawdust under
similar concentration, volume, and time loading achieved incomplete denitrification with nitrite accumulation of
up to 100 mg/L. In inoculated filter column experiments fed with 2 L of contaminated feed daily, the acetate
carbon source fed filters achieved complete denitrification at feed concentrations of 200 and 400 mg/L nitrate,
while sand/sawdust mixed columns only achieved complete denitrification for the 200 mg/L nitrate feed. 400
mg/L nitrate feed was reduced to 237 mg/L. No significant nitrite accumulation was observed in the filters. TOC
readings in the control, sawdust and acetate filters were 7.072, 13.702 and 11.764 mg/L carbon at the 200 mg/L
nitrate feed and 5.984, 6.630, and 7.142 mg/L carbon at the 400 mg/L nitrate feed.
