Saturday, April 23, 2016

The Miracle of Life... in Digesters!

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!

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