Lub npuas loj plays lub luag haujlwm tseem ceeb hauv kev ua haujlwm ntawm cov npuas diffuser. Cov neeg ua haujlwm cov khib nyiab tshem tawm hauv cov dej phwj tuaj thiab cov dej khib nyiab yuav tsum tau decomposed thiab nyob rau hauv lub thib ob clarifier los yog membrane lim. Qhov no tuaj yeem tshem tawm cov khib nyiab thiab qhov zoo tshaj plaws cov dej ntws tawm los yog cov dej tawm. Ib txoj hauv kev zoo tshaj plaws yog tso cai rau cov kab mob enzymes kom decompose cov khoom ib txwm muaj.
Kev noj qab nyob zoo ntawm cov enzymes no nyob ntawm cov khoom noj thiab qhov chaw txaus ntawm oxygen. Cov khib nyiab pov tseg muab cov khoom noj thaum cov dej aerated kom muaj cov pa oxygen txaus. Cov dej khib nyiab aeration suav rau feem ntau ntawm kev siv hluav taws xob hauv txhua qhov chaw kho mob.