ABSTRACT
Laboratory columns were used to study biogeochemical processes resulting from the continuous injection of treated wastewater into an aquifer matrix. The results showed that despite levels of suspended solids (SS) between 3–4 mg/L in the influent, flow rates (hydraulic conductivities) were maintained at 20% to 50% of initial flow through three identical columns for a period of 23 days. An initial drop in the hydraulic conductivity (K) through the columns was evident early in the experiment, and initially decreased from 3 m/day to 1.4 m/day in the first 5 days of the experimental run. This was thought to be due to clogging by suspended solids as SS were filtered out on the surface of the aquifer material at the inlet end of the columns initially. The physical bioclogging was relieved midway through the experiment due to calcite dissolution and resulting formation of fissures within the columns allowing increased flow. Nitrification of nitrite and initially ammonia to nitrate and denitrification of nitrate to nitrogen gas in the columns was evident from the results obtained and provided an insight into the type of oxidation-reduction reactions could be expected during ASR using treated wastewater.
