When is sewage typically the strongest in municipal systems?

Sewage is typically strongest in municipal systems during the morning hours, which is when most residents engage in activities that generate wastewater, such as showering, flushing toilets, and preparing meals. This peak in domestic water use results in an increased concentration of pollutants in the sewage due to the higher volume of organic waste being discharged.

During the morning, especially between around 6 AM and 10 AM, the influx of wastewater can lead to higher levels of biochemical oxygen demand (BOD) and other contaminants, as many people start their daily routines around this time. This phenomenon is known as "peak flow" and occurs because it is when a significant portion of the population is using water simultaneously.

In contrast, the other options suggest times of day that do not typically align with increased household activity. For example, late afternoon or evening hours might not experience the same concentration of pollutants, as households may have less activity related to water use, and some residents may have already shifted to recreational activities outside the home.