Interrelationships between biological, chemical, and physical processes as an analog to clogging in aquifer storage and recovery (ASR) wells

Laboratory columns were used to understand and predict bore clogging issues at a South Australian recycled water aquifer storage and recovery site, before field trials proceeded. The columns were used to study biogeochemical processes resulting from the continuous injection of recycled water 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 20–50% of initial flow through three identical columns for a period of 22 days. An initial decline in the hydraulic conductivity (K) through the columns was evident early in the experiment, and decreased from 0.78 m/day to 0.062 m/day in the first 7 days of the experiment. This was thought to be due to physical clogging by suspended solids and then biological clogging by biomass accumulation and polysaccharide production at the inflow end of the columns. The physical bioclogging was relieved midway through the experiment due to calcite dissolution mainly at the inlet end of the columns. Calcite reprecipitation at the outflow end of the columns was evident from SEM micrographs.