Strategy 3- Carbon sources and management

Biological denitrification requires the operator to correctly balance or provide enough of the essential ingredients to work correctly.  The three ingredients needed for denitrification are carbon, nitrogen, and phosphorus.  This is very similar to the Redfield ratio, discovered years ago while studying plankton in the ocean. The runoff from agricultural operations normally supplies the nitrogen (in the form of nitrate or ammonia) and phosphorus.  We have to supply an adequate amount of biologically available carbon so that the bacteria can do their job.   In general this ratio is 6 or 7 units of carbon for every unit of nitrate removed.

Call us with Questions about The Type carbon For your application

One of the most underutilized but best source of carbon is the liquid effluent containing fatty acids and alcohols that result from the anaeorobic digestion of organic wastes.  For years,  many rural communities have collected manure,  allowed bacteria to break down the manure, and captured the resulting methane gas that is generated by the process.  For our purposes though,  this process is way too slow (days to complete) and is or nearly always uneconomical.  Its not an economical solution now because of the presence of very large quantities of natural gas (methane) from the oil and gas industry. Check within 50 miles of your site- is there a source of organic waste?  We can help you upcycle the organic waste into a viable carbon source for your system

There are many carbon sources that have been tested (probably more than 20).   Established  municipal denitrification systems often use methanol as a carbon source.  But methanol is both flammable and toxic.  In addition,  most methanol is created from natural gas- a fossil fuel.  Waste glycerin is also used as a carbon source but it is not as effective as methanol.  However it is available and relatively inexpensive at about $0.1 per pound.  At a ratio of 6:1 for C:N,  the carbon cost of  reducing 1 pound of nitrate would be about $0.60.  If 1 lb of nitrate does several dollars of damage in the environment,  this is a very acceptable price to pay to eliminate this problem.

Our recommendation: Upcycled Organic Waste

Anaerobic digesters, very similar to our nitrate removal systems, can be easily built and operated to primarily produce volatile fatty acids (VFAs) such as acetic acid (vinegar) and avoid methane generation.  The advantages to this approach are multi-fold:

  1. The digester can be operated at much shorter residence times (about 8 hours compared to 72 for full methane generation).  This dramatically reduces the size and cost of the digester.

  2. Often,  by digesting the organic waste from food processors and diverting the VFAs produced to denitrification customers,  the food processors will enjoy a reduction in their cost of organic waste disposal.

  3. VFAs produced beyond the needs of denitrification customers can be purified and sold to the chemical intermediates market, given favorable economic terms.

The net result is a potential for win-win-win.   First the food processors can reduce their marginal cost of organic disposal by convertering the organic waste into VFAs.  Second,   the nitrate removal customers can get a very low cost of carbon, driving the cost per pound of nitrate removal to near 0.  Third,  regulators and stakeholders benefit as two sources of pollution are eliminated with a single econsystem of anaerobic digesters and denitrification systems.  But most of all,  we can stop the continued pollution of our surface waters and ground water.

Our Goal- NET ZERO Cost of Denitrification


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