Economical evaluation of sludge reduction and characterization of effluent organic matter in an alternating aeration activated sludge system combining ozone/ultrasound pretreatment

An ozone/ultrasound lysis–cryptic growth technology combining a continuous flow anaerobic–anoxic–microaerobic–aerobic (AAMA + O3/US) system was investigated. Techno-economic evaluation and sludge lyses return ratio (r) optimization of this AAMA + O3/US system were systematically and comprehensively discussed. Economic assessment demonstrated that this AAMA + O3/US system with r of 30% (AAMA + O3/US2# system) was more economically feasible that can give a 14.04% saving of costs. In addition to economic benefits, a 55.08% reduction in sludge production, and respective 21.17% and 5.45% increases in TN and TP removal efficiencies were observed in this AAMA + O3/US2# system. Considering the process performances and economic benefits, r of 30% in AAMA + O3/US2# system was recommended. Excitation–emission matrix and Fourier transform infrared spectra analyses also proved that less refractory soluble microbial products were generated from AAMA + O3/US2# system. Improvement in 2,3,5-triphenyltetrazolium chloride electron transport system (TTC-ETS) activity in AAMA + O3/US2# further indicated that a lower sludge lyses return ratio stimulated the microbial activity.