Electrocoagulation of peatland runoff: Statistical optimization and economic analysis

Abstract

Irish peatlands play a crucial role in delivering drinking water sources to large conurbations. However, peatland runoff contains a high concentration of natural organic matter (NOM), which is problematic for drinking water treatment as it decreases the effectiveness of conventional treatment and can lead to the formation of suspected carcinogenic disinfection by-products (DBPs). In this study, a low-cost and highly efficient electrocoagulation (EC) unit has been used to treat raw peatland runoff. EC processes were designed, evaluated and optimized via the response surface methodology (RSM). Total operation cost was calculated after the RSM process. Box-Behnken design (BBD) was employed in RSM to analyse the effect of the applied voltage, reaction time, and electrolyte (NaCl) addition on the removal of total organic carbon (TOC) and colour at 465 nm. Two second order polynormal equation models were fitted with a high R2 of 0.93 (TOC) and 0.96 (colour). The highest removal performance (88.44 % of TOC and 98.93 % of colour) was observed when the applied voltage and reaction time were at their middle level (i.e. 3 V and 35 min). The optimum values of operating variables obtained by the multi-objective optimization were a NaCl concentration of 130.4 mg/L, an applied voltage of 2.0 V and a reaction time of 47.0 min. Under these conditions, 85.2 % of TOC and 98.1 % of true colour (at 465 nm) was removed in the laboratory at an operating cost of 0.50 €/m3, representing a higher TOC and colour removal and lower total operating cost than previous studies. The cost of NaCl contributed the most of the three factors to the total cost of the treatment process.