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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5 Reasons to Buy Rooftop Solar Panels in 2019

Don’t wait for another year.

Have you been putting off installing rooftop solar panels on your home? If so, 2019 is a good year to take action and actually do it. Why this year? Read on.

The American media seems to take pleasure in portraying us as a bunch of money-grubbing consumers who are only out for ourselves, but I am not buying it. We do not have to listen to them.

I believe that we can use our purchasing power to benefit the greater good and ourselves.

Sometimes it might be a small purchase like buying socks at a locally owned store instead online and having them shipped to you via an airplane. Or opting to buy organic spinach grown by a local farmer instead of spinach that comes in a sealed plastic bag from somewhere out of state.

A rooftop solar system is a big purchase that meets the above criteria.

In this post, we will talk about how purchasing rooftop solar panels for your home is a long-term investment that will pay for itself and more, add renewable energy capacity to your community, and support local jobs.

March 8, 2019, marked the beginning of the seventh year that our rooftop solar system has been silently generating clean renewable energy from the sun. Our system is tied to the electric grid so we share electricity back and forth with PG&E the investor-owned utility currently providing service to our county.

Let’s deal with the financial stuff first.

Save Money on Electricity

The net cost of our 22-panel 5.34 kW rooftop solar system was $14,767 including tax credits that we will discuss later. Solar prices have been decreasing so now our system would cost less.

Purchasing rooftop solar panels requires a significant investment upfront. Beware of sticker shock that may cause you to waver and lose sight of the long-term benefits.

I propose a little exercise to help you think about a large amount of money in a different way and this one never pays for itself or provides free electricity.

Many people, perhaps including you, have a habit of buying a cafe latte, specialty juice drink, or another treat each day during the workweek.

Let’s say you do that 48 out of 52 weeks a year. To make it simple we will use $5.00 as the cost of the treat. Below is an example of how much money you will spend over a ten-year period on just that one item.

Rows of Green Dollar Signs

5 items a week x 48 weeks a year = 240
items per year x 10 years = 2,400 items x $5.00 each = $12,000.

You may think this is a silly example, but it does demonstrate how you, I, and everyone else can easily spend a large amount of money without really thinking about it.

Payback Period

Your tangible electricity savings will begin at the end of your payback period, which is however long it takes your electricity savings to equal the total net cost of your rooftop solar system.

Last May, I decided to attempt to calculate the payback period for our solar panel system.

I had the data. However, I soon discovered the complexity of the task. It would mean calculating electricity costs on an hourly basis 24/7/365 for 5 years. This was beyond the time I could allow to figuring it out.

Not willing to do nothing, I came up with a method to estimate our payback period, which turned out to be about 7 years. Even though it is likely that there are flaws in my approach, I think that I am well within the ballpark.

At this time next year, our rooftop solar system will have paid for itself and from then on electricity will be virtually free for the next two or three decades, except for PG&E fees. Solar panels decrease in efficiency over time, but after the 25-year warranty period ends, they will not suddenly stop working.

If you are interested in how I calculated our payback period, you can read about it in the post Rooftop Solar Panels are Worth It and this is Why.

Increase Your Home’s Value

In recent years, especially here in California, several things have occurred making it even more financially attractive to purchase rooftop solar panels for your home.

  1. In January 2017, the California Regional Multiple Listing Service recognized that a rooftop solar system is a positive selling point for many home buyers so they added standardized fields that enable realtors to enter energy production for their listings.
  2. The California legislature upped the ante on renewable energy in 2018 by enacting a law requiring solar panels on all new homes.
  3. I do not have a crystal ball, but I doubt you will disagree with me when I suggest that electricity prices will only continue to increase. Where I live the average price of a kWh of electricity has steadily increased by 22.4% in the past 6 years, which is substantially higher than the national inflation rate.

When you decide to sell your home, savvy prospective home buyers are likely to appreciate that they can instantly save on their electricity bills without doing a thing.

You can learn more about this topic by reading the post You Can Increase Your Home’s Value with Owned Solar Panels.

Receive a Solar Investment Tax Credit

Mostly free electricity in the future and adding to your home’s value are two sound financial reasons to purchase a rooftop solar system. A compelling reason to do it in 2019 it that this is last year can receive the full 30% federal tax credit.

Solar-Electric Property
  • 30% for systems placed in service by 12/31/2019
  • 26% for systems placed in service after 12/31/2019 and before 01/01/2021
  • 22% for systems placed in service after 12/31/2020 and before 01/01/2022
  • There is no maximum credit for systems placed in service after 2008.
  • Systems must be placed in service on or after January 1, 2006, and on or before December 31, 2021.
  • The home served by the system does not have to be the taxpayer’s principal residence.
The 30% tax credit we received for our initial rooftop solar installation resulted in a refund from the federal government. This photo shows 3 of the 6 additional solar panels we bought with the money.

Visit the DSIRE website to learn more about federal tax credits and state incentive programs.

I hope you can see that owning a rooftop solar system makes financial sense. Now, let’s look at how going solar contributes to the greater good.

Build Renewable Energy Capacity in Your Community

Extracting, transporting, refining, storing, and burning fossil fuels (coal, oil, and natural gas) is a dirty and dangerous business that is jeopardizing the health and well-being of people everywhere, especially the people who live near fossil fuel extraction sites, rail lines, refineries, pipelines, and power plants.

Major Sources of U.S. Electricity Generation 1949-2018 Line Graph
Electricity generation from renewable energy is increasing and coal is decreasing. Unfortunately, natural gas is on the rise. Image credit – U.S. Energy Information Administration.

Each one of us can choose to help our country get off fossil fuels by taking a variety of actions from running our dishwashers after peak electricity demand time to installing solar panels on our roofs.

Using the existing real estate available on top of our homes and other buildings to generate clean renewable energy just makes sense to me. The roof is already there so why not use it. If I were an investor-owned utility executive, I would be renting every rooftop I could get my hands on and installing solar panels.

Keep Your Money in Your Community

I am a fan of locally owned businesses, including solar companies, for a number of reasons. First and most importantly, I know that my money is supporting jobs in my own community versus lining the pockets of far distant shareholders who have never heard of my town or me.

Local companies are embedded in the communities they serve providing jobs, spending money, and contributing to causes important to their employees and the community.

We selected A.M. Sun Solar for our home rooftop solar project. I think they embody what is wonderful about locally owned companies. Here are a few examples.

A.M. Sun Solar Team in 2017
This is the A.M. Sun Solar team shown outside of their office in Paso Robles, CA in 2017. Photo courtesy of A.M. Sun Solar.

The people at A.M. Sun Solar treat me like a person, not a number.

Years after our installation, Glen, Cory, and now Brian, are always willing to answer questions or provide information for a post I am writing.

The company gives back to the community by donating time and money to local organizations like Jack’s Helping Hand and the Paso Robles Children’s Museum.

Of course, just like any other company that you give your business to a locally owned company needs to provide quality products and services at a reasonable price. I chronicled this aspect of our relationship with A.M. Sun Solar in the posts Go Solar with Home Rooftop Photovoltaics – We Did and Rooftop Solar Costs Less than You Think.

Be Part of the Solution

Okay, so now I have shown you the money and presented you with an opportunity to help build the renewable energy capacity of your community while supporting local jobs. What could be better?

If you call a local solar company tomorrow, you could have solar panels on your roof before the arrival of the hot summer weather. This time next year you could be claiming the 30% tax credit on your federal income tax return.

Better yet, you will be taking a significant step to live more lightly on Earth.

Our Rooftop Solar Environmental Benefits March 2013-March 2019
This image shows the energy production and carbon offset for our rooftop solar panel system from March 2013 to March 2019.

Featured Image at Top: 12 of the 16 solar panels that were installed on our roof during our initial installation in 2013.

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