Application of a probabilistic modelling approach for evaluation of nitrogen, phosphorus and organic carbon removal efficiency during four successive cycles of aquifer storage and recovery (ASR) in an anoxic carbonate aquifer

摘要

Aquifer storage is increasingly being recognised in its role as a treatment process barrier within a multiple barrier approach to water reuse. Aquifers are postulated to have the ability to provide sustainable treatment for removal of nitrogen, phosphorus and organic carbon, the dominant nutrient hazards in water recycling, but, to date this treatment performance has remained difficult to validate in field studies. This study applied a statistical method, proposed for validation of the performance of advanced water treatment processes, to evaluate nutrient removal during aquifer storage and recovery (ASR) with recycled water. Analysis of observed water quality changes during four successive ASR cycles with highly variable source water quality was used to describe the removal efficiencies for selected nutrients by an anoxic carbonate aquifer. The use of this method was found to be suitable to calculate removal efficiencies for total organic carbon (TOC) and total nitrogen (TN) over four ASR cycles with temporally variable concentrations of nutrients in the tertiary treated wastewater injectant. TOC and TN removal was dominated by redox processes, aerobic respiration and denitrification. Median removal of TOC ranged from 25 to 40% and TN from 46 to 87% over the four cycles. There was no observable reduction in this removal with time, suggesting that removal of TOC and TN by redox processes can be sustained in an ASR system. Contrastingly, total phosphorous (TP) was subject to reversible removal via adsorption and desorption processes and as a result, removal efficiency could not be calculated with this method. Thus in general, results indicated that this statistical method could be used to characterise the capacity of the anoxic carbonate aquifer treatment barrier for removal of carbon and nitrogen, but not for removal of phosphorus.