Anaerobic Digesters are Good for the Environment

Don’t waste your green waste.

An anaerobic digester can magically transform your yard trimmings and food scraps into electricity and other good stuff so please do not send it to a landfill.

A reasonable question is “What the heck is an anaerobic digester?” In short, it is a giant tube that uses an anaerobic (without oxygen) fermentation process to convert the contents of your green waste bin into renewable energy (electricity or vehicle fuel), liquid fertilizer, and compost.

Kompogas Anaerobic Digestion Process Infographic
Kompogas anaerobic digester plant process infographic – source Hitachi Zosen Inova.

You cannot imagine my amazement and delight, when several weeks ago, I spotted a social media post from SLO Natural Foods Co-op offering a tour of the anaerobic digester plant in San Luis Obispo, CA. I had wanted to visit it for months, but I did not expect that my Co-op membership would be my ticket in.

My spouse and I were already scheduled for a long-awaited tour of the Cold Canyon Landfill and Materials Recovery Facility (MRF) the morning of the same day. Fortunately, the anaerobic digester tour was in the afternoon.

In the previous post entitled, All Americans Should Visit a Landfill, I covered our visit to the landfill and MRF. This post will focus on the anaerobic digester.

First, let’s talk about your green waste bin.

Green Waste Bin

The waste industry refers to the stuff you put into your green waste bin as organic waste because it comes from a plant or animal organism and contains carbon compounds. Examples include tree branches, leaves, grass clippings, fruit and vegetable peelings, meat bones, coffee grounds, eggshells, and cooked, processed, and spoiled food.

Depending on where you live, you may or may not even have a green waste bin. If you do, you may or may not be allowed to put all or only some of the items listed above in it. Check with the company that provides waste removal services for your household.

U.S. Solid Waste Generation by Material 2015 Pie Chart

According to the U.S. Environmental Protection Agency, in 2015, organic waste (wood, yard trimmings, and food) accounted for a whopping 34.6% of the total solid municipal waste generated in the United States.

The purpose of a green waste bin is to keep organic waste out of landfills where it emits CO2 in the early stages of decomposition and methane after it is buried and deprived of oxygen. Methane is a greenhouse gas twenty times more potent than CO2 and is a significant cause of global warming.

San Luis Obispo Kompogas Plant

The San Luis Obispo Kompogas Plant uses the Kompogas® patented dry anaerobic digestion technology owned by Hitachi Zosen Inova (HZI).

Aerial View of Kompogas Plant in San Luis Obispo, CA
This is an aerial view of the Kompogas Plant in San Luis Obispo, CA. The rounded rectangular building houses the anaerobic digester –source Hitachi Zosen Inova.

Bringing the anaerobic digester to San Luis Obispo County was a multi-year effort initiated by Bill Worrell, the former general manager of the San Luis Obispo Integrated Waste Management Authority. He first became aware of the Kompogas technology during a trip to Europe in 2010. At the time, the company that owned the patent was not interested in doing business in the United States.

HZI acquired Kompogas in 2014 and they did want to expand into North America. In 2015, HZI and Waste Connections collaborated on a proposal to build an anaerobic digester in San Luis Obispo.

Over the next several years, the project was approved, underwent environmental review, obtained grants and funding, and was constructed. It opened for business on November 15, 2018.

Revenue is generated from several sources.

  • 65% – tipping fees based on the weight of the green waste each truck delivers and dumps
  • 30% – electricity generated by burning the biogas produced in the anaerobic digester (enough to power about 600 homes)
  • 5% – liquid fertilizer and compost (that remain at the end of the process)

Touring the Plant

After my spouse and I finished our landfill and MRF tour, we stopped by SLO Natural Foods Co-op to grab lunch before heading over to the anaerobic digester plant.

Truck Carrying Green Waste on Weight Scale

While we were waiting for our group to assemble in the parking lot, this truck pulled onto the weigh scale. The plant receives about 100 tons of organic waste a day five days a week.

Thomas Gratz U.S. Sales Manager HZI at San Luis Obispo Kompogas Plant

Thomas Gratz, the U.S. sales manager for HZI was our tour guide.

He knows every inch of the plant and did an excellent job explaining its operations in a way non-technical people like me could understand.

Intake Area at San Luis Obispo Kompogas Plant

In the waste receiving building, Thomas talked about how various machines screen out non-organic materials.

As you can see from this pile, most of the green waste currently received at the plant is yard waste (about 90%).

Green Waste Chip Storage and Automated Crane at San Luis Obispo Kompogas Plant

After screening, everything is chopped into 2″ feedstock pieces and stored in concrete bunkers.

The yellow automated crane (it reminded me of the claw in Toy Story) grabs chips and deposits them on a staging platform for a conveyor.

Chip Conveyor Intake Area to Anaerobic Digester at San Luis Obispo Kompogas Plant

This is part of the conveyor that transports the feedstock chips from the intake building on the right to the anaerobic digester building on the left.

Pipe Feeding Chips into Anaerobic Digester at San Luis Obispo Kompogas Plant

The black tube structure delivers the chips from the conveyor into the anaerobic digester.

The digester has a plug-flow design meaning that the chips being fed into the tube push the material down the digester.

Motor that Turns Agitator Blades in Anaerobic Digester at San Luis Obispo Kompogas Plant

This motor, which is lower on the building than the tube above, turns agitator blades that run the length of the anaerobic digester to keep the contents mixed up.

I am sure Thomas told us the dimensions of the anaerobic digester but I did not record them. I estimate it is about 140 feet long with a diameter of 30 feet or so. This construction photo depicts its scale – source Hitachi Zosen Inova.

Inside the anaerobic digester bacteria and heat ferment the feedstock chips turning them into biogas and digestates (more on this later).

Anaeraboic Digester at San Luis Obispo Kompogas Plant
This shot is from the door of the building that houses the anaerobic digester. The digester is the black structure running the length of the building.
Earthquake Footings and Heating Pipes for Anaerobic Digester at San Luis Obispo Kompogas Plant

Thomas explained the seismic features of the digester like the footing show here.

You can also see some of the pipes and tubes that connect the heating system to the bottom of the digester to keep the bacteria happy during fermentation.

After walking up several flights of metal stairs, we reached the top platform from which we could survey the grounds of the plant and the hills surrounding San Luis Obispo.

The plant has several safety measures to ensure that no pressure builds up inside the anaerobic digester.

  • The first line of defense is a domed storage tank that can hold several days of produced biogas if for some reason it cannot be burned in the combined heat and power plant on site.
  • If the tank is full, then the excess biogas would be burned inside a concrete flare tube.
  • As a last resort, a gas overpressure valve would burst to release the methane-containing biogas into the air.

An environmentally friendly feature of the plant is that everything is surrounded by curbs and drains. Stormwater runoff is collected in stormwater ponds. Cleaning and wash down water are contained on site and reused in the anaerobic digester.

Combined Heat and Power Equipment and Pipes at San Luis Obispo Kompogas Plant

The combined heat and power plant burns the biogas (methane) produced by the anaerobic digester.

The heat is used to keep the inside of the digester at the proper temperature. Electricity not used to run the plant is sent to the electric grid.

Various impurities are removed prior to and after burning the biogas. For instance, hydrogen sulfide, a highly corrosive chemical compound is converted into sulfur that can be used to make fertilizer.

Tour Group and Conveyor to Compost Building at San Luis Obispo Kompogas Plant

The pipe on the right returns about 30% of the liquid digestate to the digester. The remaining liquid is stored in a tank for later sale.

The conveyor on the left moves solid digestate to the composting building.

Tanker Truck Pumping Out Liquid Digestate at San Luis Obispo Kompogas Plant

This tanker truck pulled up while we were admiring the back end of the anaerobic digester building.

The liquid digestate being pumped from the storage tank was destined for a local vineyard to be used as fertilizer.

Compost Bunkers at San Luis Obispo Kompogas Plant

The solid digestate is stored in these bunkers while it is aerated to create compost for sale.

Inside the composting building, it was extremely humid and the air felt heavy to breathe. Negative air pressure keeps any odors inside the building.

Tree Root Air Filter for Compost Building at San Luis Obispo Kompogas Plant

Microorganisms growing on this mass of tree roots absorb the volatile organic compounds (smelly stuff) in the exhaust air from the composting building.

Dan Kallal in our group took this photo.

Lastly, Thomas showed us how the plant is monitored 24/7/365 via an online system linked with the home office overseas.

My impression of the Kompogas Plant is that it has been carefully designed and constructed to safely take in green waste and food waste and convert it to biogas, fertilizer, and compost. The process is both straightforward and complex.

I know I barely scratched the surface of the anaerobic digestion process in this post, but hopefully, you got the gist. There is more information in the resources section.

A Few Words about Food Waste

I cringe whenever I read or hear the words “food waste.”

Growing, transporting, processing, distributing, and preparing food requires a tremendous amount of land, resources, water, energy, and people power.

Our first option should always be to eat the food we buy and to make sure everyone else has enough food to eat. Sending food to an anaerobic digester or a composting facility should be the last option.

You can do your part by eating the food you buy and putting your yard trimmings and food scraps in your green waste bin.

Featured Image at Top: this infographic shows the Kompogas process ecological cycle – source Hitachi Zosen Inova.

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Organic Food – Healthy Soil is Good for the Environment

Buying organic food is good for the soil and good for the soul.

Why should you shell out extra money to buy organic food? One reason is that healthy soil is important to your wellbeing, possibly in more ways than you think.

The soil is like different neighborhoods connected to each other by invisible underground roadways. Neighborhoods have their own vibe that depends on their location, climate, and building materials. Community residents vary widely, are mostly microscopic, and live in high-density housing. All inhabitants have jobs they perform on a regular basis for no financial gain or personal glory.

These communities form the surface of the Earth and support the plants that provide our food. The soil is essential for life. Yet, humans have paved over, poisoned, and even disappeared countless soil communities, endangering ourselves in the process.

Imagine watching your way of making a living, your way of life, literally blowing away in a cloud of dust. That is what happened during the Dust Bowl of the 1930s when severe drought, poor soil conditions, and high winds blew away the topsoil of over 100,000,000 acres of farmland. Tens of thousands of farmers lost their homes and their farms and millions of poverty-stricken people migrated away from the Great Plains in search of work. United States agriculture was decimated and the Great Depression worsened.

1930s Dust Bowl - Baca County, CO - Photo Credit D.L. Kernodle, U.S. Library of Congress
1930s Dust Bowl – Baca County, CO – Photo Credit D.L. Kernodle, U.S. Library of Congress

Belatedly, the federal government took action by forming the Soil Conservation Service to help farmers and land managers learn about the soil and how to keep it healthy and in place. They also oversaw projects across the country aimed at reforesting the land and preventing erosion.

“The nation that destroys its soil destroys itself.” – Franklin D. Roosevelt

It seemed as if soil communities were finally earning some attention and respect.

But then in the aftermath of World War II, chemical manufacturers needing new lines of business began producing synthetic fertilizers and pesticides and leaning on the government to convince farmers to apply these products to their farmland. Crop yields increased and so did air and water pollution. Pesticides killed crop pests and everything else from soil organisms to birds. This was the beginning of industrialized agriculture and a new assault on the soil.

Fortunately, there were other people and farmers taking a different path. Over several decades, they learned about the soil and experimented with holistic practices for keeping soil healthy without heavy doses of synthetic fertilizers and pesticides. This led to the modern organic food movement that gained support during the 1970s when Americans were fed up with air, water, and land pollution and were taking to the streets demanding action.

It took a couple of decades, but eventually, Congress passed the Organic Foods Production Act leading to the USDA’s National Organic Program that standardized what substances can and cannot be used to grow organic crops, raise organic livestock, and make processed organic foods. It defines farming practices for keeping the soil healthy, reducing pests and weeds, and raising livestock animals without preemptive antibiotics.

Now that you have some background let’s talk about the soil. Then you can decide whether buying organic food (at least sometimes) is worth it to you.

What Constitutes Healthy Soil?

“Soil is a mixture of organic matter [remains of plants and animals and their wastes], minerals, gases, liquids, and organisms that together support life. The Earth’s body of soil is the pedosphere, which has four important functions: it is a medium for plant growth; it is a means of water storage, supply, and purification; it is a modifier of Earth’s atmosphere; it is a habitat for organisms; all of which, in turn, modify the soil.” —Wikipedia

Healthy soil is alive with activity. Bacteria produce antibiotics, fix nitrogen (convert it for plants to use to form chlorophyll), and decompose materials to be recycled as plant nutrients. Fungi spread miles of filaments that transport nutrients and information among plants and trees. Larger organisms like ants and earthworms aerate the soil and mix things up as they move about.

These soil communities feed plants, absorb, hold and release water, maintain low levels of pests, pathogens, and salinity, and resist degradation and erosion.

If you grab a handful of healthy soil, it will hold together unlike dirt that will fall through your fingers.

Why is Healthy Soil Important for Growing Food?

At its most basic level, healthy soil provides a physical support system for plants. It holds together but is not tightly compacted allowing roots to grow and spread anchoring the plants above.

Healthy soil contains a wondrous network of microscopic organisms that deliver minerals and nutrients to plants so they can grow and thrive. Rainwater and irrigation water percolates through the spaces in the soil created by the aerators and then gets absorbed and released to the roots of the plants. Plants also receive assistance in fighting off pests and diseases.

How Do Organic Farmers Help Keep Soil Healthy?

Farmers who market their food with the USDA organic seal are required to adhere to the USDA organic program standards and be certified by a third party organization. Good stewardship of the land is at the core of organic farming.

Like people, healthy soil needs year-round care.

Organic Farm Cover Crop Plots at University of Minnesota
Organic Farm Cover Crop Plots at University of Minnesota – Photo Credit Jim Riddle, University of Minnesota

For instance, if the soil is left bare and exposed after crops are harvested it is subject to being relocated without its consent. Rain can cause the soil to run off fields and wind can pick up the unprotected soil and fly away with it. Organic farmers protect their soil by planting cover crops, an apt name for crops grown to cover the land between rotations of income-producing crops.

Cover crops can also provide food for the soil. Leguminous plants like peas, beans, lentils, clover, and vetch are especially good at returning nitrogen to the soil. This so-called green manure acts as a natural fertilizer for plants. Other plants and animal wastes are composted and used on fields to feed the soil.

Maintaining biodiversity is important for soil and plant health. Organic farmers rotate crops and plant a variety of crops together making life more difficult for pests who can devastate a monocrop field. They also incorporate buffer areas of native plants that attract and provide habitat for pollinators, birds, animals, and predator insects that eat crop pests.

These are just a few of the ways that organic farmers contribute to keeping the soil healthy.

Why is Healthy Soil Important to You and Your Family?

Well, of course, there is the food. However, there are other benefits that might not readily come to mind when you think about healthy soil and organic farming.

In addition to providing water for plants and preventing erosion, healthy soil acts as a sort of time-release water purification and refilling system. As water seeps through the soil, it filters out impurities and pollutants. Depleted soil cannot perform this function. The water continues its downward journey through rock layers and refills groundwater basins in its path. You could be one of the many people whose drinking water comes from a groundwater basin.

Organic Farm Buffer Zone with Pheasants Forever Sign
Organic Farm Buffer Zone with Pheasants Forever Sign – Photo Credit Oregon Tilth

Healthy soil eliminates the need for synthetic fertilizers, which are applied heavily on industrial agriculture fields. Besides nourishing the dead soil so that it can grow plants, these fertilizers run off into streams, lakes, and oceans creating dead zones where nothing can live. People rely on riverbanks and wetlands to prevent flooding. If these areas are dead, there is no protection.

When the soil is healthy, it eliminates the need for industrial strength pesticides. Spraying these poisons causes air pollution and runoff from fields causes water pollution. Widespread and heavy use of pesticides has had other unintended consequences. Pests have evolved quickly resulting in “super pests” requiring evermore powerful poisons. I am unconvinced that there is any safe level of exposure to pesticides for anyone and I do not believe farm workers should be required to wear masks and hazmat suits to work.

You may not realize that along with retaining moisture healthy soil grabs and holds onto carbon helping to keep it sequestered in the ground and out of the atmosphere.

Certainly, certified organic farmers are not the only farmers living in harmony with the land and contributing to maintaining healthy soil communities, but they have gone the extra mile to certify (prove) that they do.

Buying Organic Food Supports Healthy Soil

While reading this post, I hope you learned something about how important healthy soil is and how organic farming helps soil communities stay healthy.

You can promote healthy soil by choosing to buy organic food, at least some of the time.

Organic Tomatoes in a Paper Bag with Fresh Produce in the Background
Organic Tomatoes in a Paper Bag with Fresh Produce in the Background – Photo Credit iStock/mrPliskin

The purchase price of organic food is often higher than its taxpayer-subsidized industrial counterparts and prices may vary widely depending on the type of food and where you buy it. Be a savvy shopper and check prices at farmers markets, co-ops, farm stands, grocery markets, and even big box stores.

I realize that paying more for organic food may not fit easily into everyone’s budget so here are a few ideas on how you can support organic food in various ways.

  • Select one fruit or vegetable and start buying the organic version all the time or at least once a month.
  • Buy all organic fresh produce once a month or as often as you can.
  • Switch to organic milk, butter, cheese or the dairy product of your choice.
  • Try buying organically raised chicken, pork, or beef. It is expensive so you may find yourself eating less meat and more plants, which is good for you and the environment.
  • Support healthy land and people in your own community or region by purchasing organic food grown or raised locally.

I look forward to the day when all food is grown organically and everyone can afford it. I hope you will join me in buying at least one organic food item if you can, so we can inform the agricultural community at large that we want to eat food that is healthy for us and the planet.

Featured Image at Top: Close-up of Onions Growing in Soil – Photo Credit iStock/YuriyS

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