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Sat Dec 16, 2017, 11:03 PM

Substitution of Glycerol for Methanol For Denitrifying Sewage Sludge.

One of the real big environmental problems which gets less attention than maybe it used to, is involved with nitrogen chemistry.

In my view the most serious environmental impact may be the accumulation of nitrous oxide in the atmosphere, but the issue has very, very, very serious implications for both fresh and saline bodies of water.

Fixed nitrogen, along with phosphorous, was responsible for one of the most famous events related to the environmental impact of fixed nitrogen nutrients, the 2014 toxic algae bloom that shut the water supply to Toledo, Ohio because the particular species of algae produced a very potent biological toxic cyclic peptide, microcystin:

These outbreaks are now known all over the world. They are largely involved with agricultural practices.

Even where the output does not contain directly toxic compounds, these blooms can and do destroy major ecosystems. The "renewable" energy scheme to add ethanol to motor fuels, for example, has completely destroyed the ecosystem of the Mississippi Delta, because of nutrient run-off both nitrogen and phosphorous.

Although agriculture is a major cause, another is the treatment of sewage sludge.

In some, perhaps not enough, sewage plants, denitrification is accomplished using methanol as a carbon source. Although methanol can be made either by the hydrogenation of carbon dioxide or carbon monoxide, the source for the industrial quantities of all three of these starting materials is currently dangerous natural gas.

The waste product of this dangerous natural gas is directly dumped, without reserve directly into the planetary atmosphere, which it is destroying.

I'm generally an opponent of all forms of so called "renewable energy" at this point in my life, having decided in the last decade that they will never be as safe, as clean nor as reliable as nuclear energy, but a caveat is to note that one thing that living systems do better than nuclear energy will ever do is to collect carbon dioxide from the atmosphere, because biological systems, being self replicating, can cover huge amounts of surface area at almost no cost.

Algae, both deliberately grown and grown in uncontrolled conditions (such as occurred in Lake Erie) has often been studied as a source of fats, esters of fatty acids and the triol glycerol, which can be used to make biodiesel, a decent substitute for petroleum diesel, at least with some modifications.

The side product of biodiesel production is glycerol which is generally dumped as a waste product, not because it's entirely useless, but because there is much more produced by the biodiesel and soap industries than can be profitably utilized.

So I came across an old paper in my files that offered an interesting potential use for glycerol, which is to substitute for methanol as a carbon source in the denitrification of sewage sludge.

The paper is here:

Diagnosis and Quantification of Glycerol Assimilating Denitrifying Bacteria in an Integrated Fixed-Film Activated Sludge Reactor via 13C DNA Stable-Isotope Probing (Chandran and Lu, Environ. Sci. Technol., 2010, 44 (23), pp 89438949)

Some excerpts from the text, first the introduction, which I rehashed briefly above:

Methanol is one of the most widely used external organic carbon sources for enhancing denitrification at wastewater treatment plants (1-3). Of late, glycerol has emerged as an alternative to methanol due to three factors. First, the price of methanol, which is tied to the natural gas price, has been increasing (4). Second, the dramatic increase in biodiesel production as a means of moving away from petroleum as an energy source has given rise to significant quantities of glycerol as a waste product (5). Third, glycerol has been previouslyshownto foster higher denitrification kinetics than those of methanol (6, 7). Consequently, wastewater treatment plants today are intently considering glycerol as a supplement or replacement for methanol.

From the perspective of wastewater treatment process design, it is essential to determine the fraction of activated sludge bacteria assimilating any given carbon source...

Bacteria were isolated from sewage sludge treatment plants and then placed in a growth medium that was spiked with glycerol labeled with the heavy stable isotope of carbon, C-13.

They then looked for the fate of C-13 and noted the following:

The 13CDNAsequences of the biofilm samples were more diverse and dominated by Comamonasbadia(5/21),Bradyrhizobium sp. 1 (4/21), and Tessaracoccus bendigoensis (4/21) related bacteria. Bradyrhizobia and Tessaracocci belong to the family of Rhizobiales in R-proteobacteria (35) and Propionibacteriaceae in Actinobacteria (36), respectively. Very little is known about the denitrification capability of these bacteria and or their ability to use glycerol as an electron donor. It is notable that the glycerol assimilating bacteria diagnosed and quantified in this study have not been implicated in glycerol metabolism before (as reviewed by ref 5). A possible explanation for this discrepancy is that the previous studies selected their strains a priori for examining glycerol metabolism.

They find that the presence and distribution of organisms in denitrifying biofilms utilizing glycerol are considerably different than those in methanolic systems, and that the glycerol based systems seem to function better.

There's a lot of cool molecular biology in this paper, much of which is not really my bailiwick, but it's worth perusing just for general knowledge.

I personally feel that linear saturated and unsaturated fatty acids and products made by chemically modifying them might well be important tools in a putative post-petroleum age, should we ever have one before petroleum waste, along with coal and gas waste kills us. Since glycerol is a necessary byproduct of access to such materials of biological origin - ideally from microorganisms utilized in phosphorous and nitrogen contaminated waste waters - this interesting approach to denitrification seems quite interesting.

I'm not sure how much came of it - the paper is seven years old - but it's worth keeping in the back of one's mind.

I wish you a pleasant Sunday.

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