What's the difference between biosolids (aka treated sewage sludge) that fertilize farms and composted biosolids that can be used at home, for parks and landscaping, and at sports fields?

As pictured, the biosolids (aka treated sewage sludge) trucked from wastewater treatment plants are typically treated in digesters. The solids are held in giant “crockpots” (digesters) for approximately 20 days at 98 degrees Fahrenheit, which allows microbes to digest the sewage solids and create biosolids. This digestion process is a way of “reverse engineering” the process of digestion in our own bodies; in this case we are removing the pathogens with the help of microbes.

As with our own bodies, the digesters also create gas. Fortunately, many plants capture and scrub the biogas in order to use it onsite in large electricity generating facilities that can fuel a significant portion of the treatment plants’ electricity needs. The biogas is renewable energy source - a big environmental win from sewage treatment.