Facultative lagoons utilize which two types of processes?

Facultative lagoons are designed to treat wastewater by providing a combination of aerobic and anaerobic processes. In these systems, the upper layer of the lagoon generally has aerobic conditions due to the presence of sunlight and mixing caused by wind and buoyancy, which supports the growth of aerobic bacteria. This process effectively breaks down organic pollutants in the wastewater by utilizing oxygen.

In contrast, the deeper layers of the lagoon tend to be anaerobic, where insufficient oxygen diffuses, creating an environment suitable for anaerobic bacteria. These microorganisms thrive under these conditions and further break down organic matter, albeit more slowly than aerobic processes. The interaction between these two types of processes allows facultative lagoons to be efficient at treating various organic contaminants within the wastewater while also facilitating the natural biological processes that contribute to self-purification.

This combination of aerobic and anaerobic processes is a defining characteristic of facultative lagoons, making option A the most accurate choice. Other processes listed in the incorrect options do not accurately reflect the functioning of facultative lagoons. For example, photosynthetic and chemosynthetic processes are specific to organisms that either produce energy using light or are involved in chemical reactions, which are not the primary functions of facultative lagoons. Similarly, thermal and mechanical