Growing Single Cell Protein in Biosolids?


Think Different

The Apple tagline, “Think Different,” has always sounded wrong to me. I hear a “-ly” at the end of the tag. But in the Apple case, “different” is a noun, and the tag tells you to think “what,” not “how.”

“Different” came to my mind when reading this new article by corresponding author Dr.Willy Verstraete, of Ghent, Belgium (thanks to Dr. Sally Brown for bringing it to my attention) in Environmental Science & Technology, “Can Direct Conversion of Used Nitrogen to New Feed and Protein Help Feed the World?

Imagine, if you can, the WRRF of the future with a focus, not on clean water, but on microbial protein production.

In this vision of the future, the WRRF “up-cycles” reactive nitrogen (i.e., ammonia) directly to feed or food. Today’s popular nitrification-denitrification systems become outmoded, because the N is more valuable going to protein rather than back to nitrogen gas.

We are probably familiar with the indictment of today’s current agrosystem, heavily weighted as it is to animal production. Read, for example, Harry Aiking’s article Protein production: planet, profit, plus people? He closes with the assertion that a “’reversed’ diet transition back to less animal protein could make a difference.”

Verstraete would have this “reverse” accomplished at WRRFs . They would do this through “the production for single cell protein based on hydrogen (produced from renewable electricity by electrolysis of water or reforming of biogas), carbon dioxide (e.g. from biogas) and recovered ammonia, the production of the latter in high density reactor systems can surpass the normal plant protein by several orders of magnitude in terms of physical footprint.”

Several orders of magnitude?
But what is “single cell protein?”

Heading to Google Scholar, I found an article: Value-added food: Single cell protein. I learned that the forecast growth in global protein “has created a demand for the formulation of innovative and alternative proteinaceous food sources. Single cell protein (SCP) production is a major step in this direction. SCP is the protein extracted from cultivated microbial biomass. It can be used for protein supplementation of a staple diet by replacing costly conventional sources like soymeal and fishmeal to alleviate the problem of protein scarcity.”

Importantly, SCP can be grown on agricultural and some industrial wastes.

“[T]he utilization of such materials in SCP processes serves two functions as reduction in pollution and creation of  edibleprotein. …potential substrates for SCP include bagasse, citrus wastes, sulphite waste liquor, molasses, animal manure, whey, starch, sewage, etc.”

Aha! Sewage!

The attraction of SCP is in its production efficiency: “Compared to current soy production of about 3 tons/hectare-year, microbial protein production by means of renewable hydrogen is potential 1 – 3 orders of magnitude more efficient in terms of land use.”

Again, three orders of magnitude! We have got to do this!

Dr Verstraete has minced no words in criticizing our current WRRF technology. In his 2014 article “The manufacturing microbe”, he says this of conventional treatment:

“activated sludge exists as a technology for 100 years (Ardern and Lockett, 1914). Today, we must question this overall approach: we destroy organic matter at the expense of conventional energy and recover at the very best only a fraction of the energy present in the organics in the form of biogas. Moreover, in the conventional activated sludge process, basic nutrients such as nitrogen and phosphorus, as well as a primary source of life, i.e. water, are most often simply wasted. [and} the application of nitrification and denitrification… destroy(s) a valuable resource: indeed 1 kg of mineral nitrogen requires some 2 kg of fossil fuel equivalent to produce.”

The strength of Dr. Verstraete’s “manufacturing microbe” concept comes from the explosion in DNA sequencing technology and the microbiology of nitrogen transformations. The review article, Ecological Perspectives on Microbes Involved in N-Cycling, highlights several important environmental issues, such as the emission of N2O, a potent greenhouse gas, and the “bottleneck” that is conversion of dissolved organic nitrogen in wastewater into ammonia. But it shows that science is on the cusp of the capability of harnessing microbial processes, much as we have recently with Anammox and DEMON.

What would the output of used water processing for microbial protein, or SCP, look like? Certainly far different from biosolids! Single cell protein are the yeast, bacteria and fungi that grow in bioreactors with the input of nitrogen, carbon and energy. They are dried into a powder and used as a supplement or additive.

Hmmpf! Is there really a market for this?

My doubts were swept away this week with the report: Silicon Valley's Obsession With Protein Powder: Healthy or Scary? The writer says: “the start-up industry's most vigilant workers are starting to sacrifice—wait for it—food, all for the sake of getting in that extra coding time. …coders, engineers and venture capitalists are turning to liquid meals with names like Schmoylent, Soylent, Schmilk, and People Chow. The protein-packed products that come in powder form are inexpensive and quick and easy to make — just shake with water.”

Soylent? I had read about this company with amusement several months ago.

Meal Replacement Powders Gaining Popularity in Silicon Valley. According to its website, “Soylent was developed from a need for a simpler food source. …Soylent is a food product (classified as a food, not a supplement, by the FDA) designed for use as a staple meal by all adults. Each serving of Soylent provides maximum nutrition with minimum effort.

There is an intentional irony, I guess, in the naming of this product. Some 15 years ago, with guidance of a science writer, I had explored the 1973 science fiction movie Soylent Green as the representation of a basic human fear, that of cannibalism. This movie, directed by Richard Fleischer and starring Charlton HestonLeigh Taylor-Young, and, in his final film, Edward G. Robinson, delivers the bottom line horror that, in a resource-stressed world of the future, human corpses are converted into a popular, freely-distributed food, Soylent Green.

But what if, just if, today’s Soylent powder used as its protein source, not oat flour, but instead SCP grown at “used” water plants? Would that not make Soylent and Soylent Green just a little more disturbingly similar?

Recognizing just a bit of a convergence of fiction and fact over the past 40 years, Blogger Kyle Munkittrick wrote in Discover Magazine 2010, “I really want to know: Would you eat Soylent Green?”  He found, to my relief, little alignment. But would “used” water create the same kind of barrier to market acceptance in today’s Soylent as corpses do for the Soylent Green in the future world? Hard to imagine there wouldn’t be.

More importantly, can you imagine a world that will need to so carefully manage its N flows as to rely on Single Cell Protein as a key food source? and that a major source of SCP will be the local WRRF? and that today’s plant operator may be tomorrow’s microbial biotech specialist?

If you can, then, along with Steve Jobs and with Willy Verstraete, you Think Different.