RadioLab’s program Cellmates this past week was mind-blowing. UK biogeochemist Nick Lane put forth the hypothesis
(The
Vital Question: Energy, Evolution, and the Origins of Complex Life)
that the explosion of multicellular life some 2 billion years ago was a
singular event in Earth’s history, an event of vanishingly small probability,
having never again occurred over the 2 billion years. This event was the
merging of an archaea-type organism and a bacteria-type organism, resulting in
a successful, collaborative union. This solitary union, a singular event, gave
rise to all plant and animal multicellular life on Earth, from ferns to
jelly fish to me. What is more, the chance of such a collaboration is so improbably
small that it might not be expected to occur anywhere else in the universe. At
least, that is how I understood Dr. Lane.
The improbability of multi-cellular life is, in my mind, even
more mind-blowing than the explanation of the origins of life itself, put forth
by George Mason University earth scientist Robert Hazen in his Great
Courses lecture series (The
Origin and Evolution of Earth: From the Big Bang to the Future of Human
Existence). Hazen describes a global oceanic soup replete with
nucleic acid polymers, formed by chemical reactions on reactive minerals
surfaces, existing for a hundreds of million years, in which by an exceedingly
rare chance event a self-replicating “living” DNA strand was formed, which then
exploded across the face of Earth. This emergence of “life” occurred some 3.5
billion years ago, evolving over some 1.5 billion years into a soup of prokaryotic
cells, many within the remarkable kingdom of life, Archaea. Also in that primordial
soup were Bacterium, that
other great “domain” of single-cell, non-nucleated prokaryotes. It was the merger of a single archaea
organism with a single bacterium of which Dr. Lane spoke on RadioLab.
Archaea… this is the kingdom that includes the methanogens we
have embraced with child-like enthusiasm, as evidenced at our recent WEF
specialty conference in Milwaukee. I am
probably the only one who stepped back from our profession’s precious attention
to biogas and contemplated with wonderment that human beings are a highly evolved
form of a bacteria-infected archaea cell.
Archaea are indeed pretty special. We have learned a lot about them since science
first uncovered their existence four decades ago. But I believe we have many surprises ahead for
their potential role in wastewater and biosolid treatment.
Between papers at Milwaukee, I rudely poked my head over the
shoulders of Josh Mah, PhD candidate from Virginia Tech, and Peter Loomis,
CDMSmith, both working with DC Water’s digesters, as they pored over charts of
qPCR results of sludge samples from within DC Water’s digester start up.
Communities of archaea and bacteria are still evolving inside those new DC tanks,
and with that evolution comes the possibility of directing their path into highly-effective
methane-producing communities. For Mah, this is a task still in need of
financial support (hint, hint). Nearby in that WEF conference room sat Marquette’s
professor Daniel Zitomer, a key researcher into the biology of digesters, and
the first person from whom I learned several years back that each digester
harbored unique microbial populations. We are still in the infancy of our understanding
the significance of this observation.
Just as the key to life on Earth was the unlikely joining of
cells, so too is the key to WEF’s Residuals
and Biosolids Technical conference the unlikely joining of biosolids
insights. AECOM’s Bill Barber displayed
a provocative PowerPoint slide (given in his presentation April 6, 2016,
Session 14, 9 AM, “Alternative
Configurations of Anaerobic Digestion and Thermal Hydrolysis To Enhance
Performance”) equating the use of thermal hydrolysis with digesters
to that of a Model T Ford decaled with racing flames. I had an “Ah-Hah!” moment
when Barber pointed out the wrong-headedness of our industry’s practice of continuously
overflowing slow-growing, hard-working archaea methanogens out of the anaerobic
digesters, in contrast to our careful cultivation of activated sludge bugs. So,
this put an exclamation point to the reasonableness of Alan Cooper’s proposal
to use recuperative thickening (April 6, Session 14, 10 AM, “Achieving
Advanced Digestion Using Recuperative Digestion Options”), in a
return of both bugs and organic food to the digesters. The “over-the-top” attention at the WEF conference
for co-digestion makes more sense now to me as a way of balancing the nutrient
and energy needs of archaea organisms in the digesters rather than as a way of
boosting electricity production and struggling with waste heat.
Microbial science is the future of
biosolids and, more generally, wastewater treatment. The inquiry is clearly international and has
burgeoned forth in the scientific literature over this past year. I already
mentioned Marquette’s Dan Zitomer. His
2015 paper “Relating Methanogen Community Structure and Anaerobic
Digester Function” demonstrates the immediate relevancy of this microbial
work: “nearly identical digesters can produce more methane than others because
the microbial communities are more suited to produce methane rapidly.“ In a
similar vein, Japanese researchers say it straight away in their article title:
Canonical
correlation analysis and variance partitioning analysis implied that bacterial
and archaeal community variations were significantly affected by substrate and
the operation conditions. An Italian
team explains “the applied method is suitable to describe microbiome into the
anaerobic reactor, moreover methanogen concentration may have potential for use
as a digestion optimisation tool (Traversi, et al. Application
of a real-time qPCR method to measure the methanogen concentration during
anaerobic digestion as an indicator of biogas production capacity.) A Chinese
researcher team asserts that “[t]he knowledge garnered would facilitate to
develop more efficient full-scale anaerobic digestion systems to achieve
high-rate waste sludge treatment and methane production” (Dissecting
microbial community structure and methane-producing pathways of a full-scale
anaerobic reactor digesting activated sludge from wastewater treatment by
metagenomic sequencing).
This current research on the
microbiology of anaerobic digestion soon may have direct impacts on process
design. Again, Bill Barber, who
is back in the States from a stint in Australia, explained in his review
presentation in Milwaukee that superior sludge digester performance occurred with
the sequencing of mesophilic digesters, even when compared to pre-treatment
with thermal hydrolysis. That this effect aligns with the emerging science of microbial
populations is borne out by research in Singapore. The research report Determination
of the archaeal and bacterial communities in two-phase and single-stage
anaerobic systems by 454 pyrosequencing evaluated the microbial communities of
“2-Phase anaerobic digestion (AD), where the acidogenic phase was operated at 2
day hydraulic retention time (HRT) and the methanogenic phase at 10 days HRT.”
The application of microbial
science will also help with co-digestion.
A recent journal article reported on an 18-month long monitoring period for
a co-digestion facility by a Welsh team: “Monitoring
methanogenic population dynamics in a full-scale anaerobic digester to
facilitate operational management.” The message for me was that without use
of new tools for studying microbial communities, our foray into co-digestion
will be sub-optimal and trial-and-error at best.
I have no doubt that the future design and operation of
anaerobic digestion and co-digestion at wastewater facilities will be dictated
by new scientific tools that measure and monitor the behavior of microbial
communities. The engine of these communities are microbes that are newest to our
understanding of the evolution of life on Earth, and newest to our
understanding of sludge digestion, but among the very oldest on Earth, the Archaea.
Oh my, the life in biosolids is a
miracle!
