Optimization of thermal–alkaline pretreatment for dewatering of excess sludge followed by thermal/persulfate oxidation for the elimination of extracellular ARGs in TAP-treated filtrate

Abstract

This study evaluated the dewatering of excess sludge and the removal of extracellular antibiotic-resistant genes (eARGs) from the treated filtrate by thermal–alkaline pretreatment (TAP) and thermal/persulfate (PS). The optimization of TAP and thermal/PS was investigated during excess sludge dewatering and removal of eARGs via response surface methodology (RSM). The results demonstrated that TAP could effectively decrease the water content of excess sludge (41%) at optimum operating conditions (such as temperature: 88 °C, operation time: 90 min, pH: 11.2). However, the increase in eARGs abundance in TAP-treated filtrate is probably due to the dissolved effluent of the intracellular matter during dewatering. Therefore, TAP-treated filtrate was subjected to thermal/PS, and the removal of eARGs after TAP was explored. The desirability function was used to optimize two kinds of removal efficiencies of eARGs, simultaneously. The optimal pH, persulfate concentration, and reaction temperature were 10.2, 0.039 M, and 75.12 °C, respectively. 6.28 log·copies/mL of tetA and 6.57 log·copies/mL of sulI were removed under the above-mentioned conditions. The process provided efficient dewatering of excess sludge and elimination of eARGs from the filtrate. HIGHLIGHTS TAP significantly enhanced the sludge dewatering efficiency.; The abundance of eARGs increases significantly after TAP.; The desirability function was used to optimize multiple target parameters.; Thermal/PS can effectively reduce the abundance of eARGs, even below the detection limit.;

Keywords

• alkaline
• dewatering
• excess sludge
• extracellular antibiotic-resistant genes
• thermal