ABSTRACT
Aerated lagoons are activated sludge units operated without sludge return. Historically they were developed from waste stabilization ponds in the northern US, where mechanical aeration was used to supplement the algal oxygen supply in winter. It was found, however, that soon after the aerators were put into operation the algae disappeared and the microbial community quickly came to resemble that of activated sludge. Aerated lagoons (Figure 20.1), especially those operating at short retention times in warm climates, are designed as completely mixed non-return activated sludge units. Floating aerators (Figure 20.2) are used to supply the necessary oxygen and mixing power.
