Learning about Anaerobic Digestion through a live tour

Sometime this September, a few of us waste geeks got invited to tour a municipal waste facility as well as a company trying to convert waste into energy. It was both fascinating and heart breaking; mainly because the company has such a great idea and business model but is still waiting for all necessary permits from the government. Hopefully they will get all necessary approvals very soon and will be in the news as a great success story. The visit still made me think this would be a great opportunity to both learn and report on the various technologies, parties, parts involved in this process of converting waste to energy; so read on.

Some related terms:

Co digestion After a bit of research, I was able to find the following general description of Co-digestion. It refers to the anaerobic digestion (AD) of multiple (hence the ‘co’ part) biodegradable substrates (feed stocks) in an AD system. The general idea is to maximize the production of biogas in an AD plant by adding substrates that produce much more biogas per unit mass than the base substrate. (src: http://www.ati-ae.com/resources/tech-talk/176-codigestion.html)

Anaerobic digestion: is a series of biological processes in which microorganisms break down biodegradable material in the absence of large supplies of oxygen. One of the end products of this process is biogas.

Aerobic digestion: In an aerobic system (such as composting), the microorganisms access free, gaseous oxygen directly from the surrounding atmosphere. The end products of an aerobic process are primarily carbon dioxide and water and of course, the reusable compost.

BOD vs. COD: The quality of the wastewater (speaking for US regulation only) is measured by a variety of factors. One of them being lab tests determining the concentration of carbon-based (i.e., organic) compounds aimed at establishing the relative “strength” of wastewater. Related measures are, Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), and Oil and Grease (O&G). (src: http://extension.uga.edu/publications/detail.cfm?number=C992)

Tipping fee: In the simplest of terms, this is the fee charged by the waste haulers (the companies that collect waste from transfer stations) for collecting the waste and then ‘tipping’ the collected waste into a landfill. The image below should help explain it.

Project Background:

This project is currently in pilot phase and aims to use municipal waste generated by the local communities to feed the digester. This waste was otherwise headed for the landfills where they would not only take space but also produce odor and harmful methane gas (a gas that contributes towards climate change). To run operations smoothly, the digester needs to receive raw material reliably, the more organic raw material (i.e. food waste), the better. Although the digester can accept all types of waste, the richer the organic component, the better. What would help is legislation encouraging and requiring food waste as a separate waste stream. Currently in the municipality where this project is based out of, only two towns collect organics/food waste as a separate waste stream. As some of you may know, there are two related food related projects gaining popularity throughout the world simultaneously. One is to produce less food waste being more aware of what we eat/produce vs. what we waste and the second initiative is trying to ensure the food waste that does get generated, doesn’t end up in the landfill. For this reason, this and similar projects are both very necessary and should be encouraged by all-government and citizens alike.

$$ and Process:

Currently the local government pays $130/ton tipping fee to waste haulers such as Waste Management to have waste put in a landfill. Using this new technology (a machine from Denmark), the project aims to charge the govt. $60/ton tipping fee for having all the waste come to the transfer facility and then be converted into 60% bioslurry and 40% clean shredded recyclable plastic that can be pelletized. The company is trying to get funds from an Energy resilience bank that specializes in sponsoring such projects that look into generating clean (renewable) energy.

The current slurry has volatile content that needs to be reduced or checked. The bioslurry once created is captured in a dewatering box. Once the majority of the water has been removed (which is then recycled and reused), the rest of the bioslurry is transported to the nearby Duck Island, NJ Anaerobic Digestion facility, is about 5 miles away. Final product from the anaerobic digester would be biogas, compost, and, liquid ammonium sulfate, (NH₄)₂SO₄, which is an inorganic salt that is used that can be used as a soil fertilizer. It is also often used as a good solution to water treatment, especially to treat wastewater. The biogas produced can power the whole facility as well as the city’s nearby water treatment facility.


This is an amazing breakthrough, which gives three immediate benefits:

  1. No transportation costs involved in moving the collected waste from the transfer stations to the landfill
  2. Significant reduction in waste going to landfills (slated for the landfill located in Grose, PA) which means no waste of land, no greenhouse gasses generated from the landfill, no NIMBY (Not In My Back Yard) claims, and no waste of recyclable material going to landfills
  3. Generation of clean gas and clean liquid fertilizer from the conversion of the waste

Additional benefits include:

  1. No compost created; currently there is too much compost with nowhere to go
  2. 130 or more jobs created to run the Anaerobic Digester and related activities
  3. No bad odors.

What could be stalling it?

Some of the reasons this project may be having a hard time getting off the ground is because of the existing monopoly of the waste haulers. Currently, for all waste haulers, tipping fee is 50% of all the revenue generated, thus a change in process would result in this revenue getting lost. Also, if legislation could be put in place to have organics collected separately, that would help since organics are exempt from tipping fee. And the fastest way to get any sort of legislation passed is to take active interest in such affairs, which is just starting to happen in public circles. For things to take a turn for the best, we just need to hope and pray the old adage stays true of ‘Better late than never.’

Interested in learning more on this project?

Garbage-container-being-tipped 13796021-standard

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