Keith Boger, founder of WasteWater Technology Trainers (WWTT), offered a class on anaerobic digestion. We finally got around to updating Keith’s material and, last week, we had our first class on anaerobic digestion, sponsored by the City of Oceanside. In preparing for the class, I developed a new found appreciation for anaerobic digestion, not the least of which is the important role it plays in what we teach is the overarching goal of all wastewater treatment plant operators:

“To remove pollutants from the incoming water, while complying with all permit requirements−water, land, and air−and convert them to safe disposable biosolids as sustainably and cost effectively as possible.”

Many of our former students will recognize the simplified schematic of wastewater treatment that I use to establish the notion that a wastewater treatment plant is like a manufacturing plant, where each process unit is affected by upstream process units and, in turn, affects downstream process units. In preparing for the class last week, it occurred to me that some key elements were missing from my original schematic. The three outputs I now show on the figure—effluent, heat & power, and nutrients & biosolids—represent “products” that will become more and more valuable as time goes on. As I say in just about every class, “It is a very good time to be a wastewater treatment plant operator.”

It also occurred to me that while most of the wastewater treatment profession’s focus for all the years I have been in the business has been on effluent permit compliance, the solids treatment train is absolutely central to wastewater treatment: it produces heat & power, it produces nutrients & biosolids, and, from it, the recycle streams are returned to the liquid treatment train where, depending on their quantity and quality, they can have a profound impact on capacity and performance.

I was delighted when one of the students in the class, the superintendent of a 5-MGD activated sludge plant with anaerobic digesters in California, expressed his appreciation for the graphic given its simplicity but, at the same time, the profound complexity of wastewater treatment.

The updated graphic is shown here: