From green waste to renewable energy: A look inside SLO County’s anaerobic digester facility

San Luis Obispo County’s Green Waste Transformed into Renewable Energy

After San Luis Obispo County residents toss yard waste and food scraps into their green bin, the waste is transformed into renewable energy.

San Luis Obispo County green waste travels from its green bin on the curb to Kompogas San Luis Obispo, an anaerobic digester facility that converts about 36,000 tons of waste per year into electricity that powers 600 homes.

“We’re taking organic waste and we’re using it as a resource to produce renewable energy,” said Thomas Gratz, the United States Sales Manager for Hitachi Zosen Inova, the parent company of Kompogas.

The digester is a sealed, oxygen-free environment that “acts like a large, metal stomach,” Gratz said.

Bacteria in the digester converts proteins and sugars in the waste into energy that’s plugged into PG&E’s power grid, similar to how a stomach extracts energy from food to energize the body.

The facility also produces liquid and solid compost sold to commercial farms “to help build healthy soil,” Gratz said.

The facility, located at 4300 Old Santa Fe Road in San Luis Obispo, opened in 2018, and is the first of its kind in North America, according to Gratz.

The facility processes green waste from communities south of the Cuesta Grade and North of Santa Barbara County, along with Cal Poly, Cuesta College, Costco, the California Men’s Colony and even a load a week from Paso Robles.

Kompogas is a zero waste facility, according to Gratz. Plants use compost as they grow into food. When that food is discarded, it runs through the anaerobic digester facility to make more compost, he said.

From Food Scraps to Electricity: How the Facility Operates

First, a garbage truck dumps a pile of green waste onto the receiving floor of the plant. The plant receives about 100 tons of green waste per day, Gratz said, including heaps of tree limbs and discarded jack-o’-lanterns.

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Machines remove contaminants like plastic bags, rubber balls and treated lumber from the waste before it is shredded into smaller pieces. A magnet then pulls metals like forks and barbed wire out of the waste pile.

“There might be the occasional tea kettle that somebody tries to hide in the green bin or tractor weights or things like that,” Gratz said. “We need to get that out.”

Then, a machine collects and stores any grease in the pile. The grease is later fed into the digester in small amounts to avoid harming the bacteria.

“If you eat a bowl of whipped cream, you’re going to get an upset stomach,” Gratz said. “Same here. If you dump all these fats or grease, which is very powerful, you basically kill the bacteria and then you shut it down.”

Then, a crane loads the garbage onto a conveyor belt that feeds the belly of the beast: the digester.

The waste stews in the digester for 14 days at 131 degrees Fahrenheit, Gratz said. The temperature is hot enough to kill “bad actors” like salmonella and E. coli, while destroying seeds that would contaminate the compost, he said.

“The digester is heated, very similar to our stomachs,” Gratz said. “That’s when the bacteria is happy and does the job.”

According to Gratz, 600,000 gallons of porridge-like waste churn in the digester at all times.

No one ever opens the digester because oxygen disrupts the bacteria, he said. The oldest anaerobic digester facility has remained sealed for 28 years, according to Gratz.

Like humans, the digester also needs a “balanced diet,” Gratz said.

Typically, the garbage is 80% yard waste, 12% food waste and 8% fats or grease, according to Gratz. The ideal recipe, however, would be 25% yard waste and 70% food waste because food produces more energy, he said.

And the primary goal of the plant is to produce renewable energy, according to Gratz.

Gratz said 20% of the waste is converted into biogas for renewable energy, while the rest becomes liquid and solid compost.

The biogas produces enough electricity to power the facility and about 600 homes per day, according to Gratz.

About 20% of the electricity powers the anaerobic digester facility, while the rest is sold to PG&E for the grid, he said.

Meanwhile, the compost is sent to another corner of the facility to “blow dry” for 21 days, removing excess odors and moisture, he said.

That compost is sold to commercial farmers, continuing a sustainable cycle, according to Gratz.

SDGs, Targets, and Indicators Analysis

1. Which SDGs are addressed or connected to the issues highlighted in the article?

• SDG 7: Affordable and Clean Energy
• SDG 12: Responsible Consumption and Production
• SDG 13: Climate Action
• SDG 15: Life on Land

The article discusses the conversion of organic waste into renewable energy, which aligns with SDG 7 (Affordable and Clean Energy). It also emphasizes the responsible management of waste and the production of compost, which relates to SDG 12 (Responsible Consumption and Production). Additionally, the article mentions the reduction of greenhouse gas emissions and the generation of renewable energy, connecting to SDG 13 (Climate Action). Finally, the focus on utilizing green waste and promoting healthy soil aligns with SDG 15 (Life on Land).

2. What specific targets under those SDGs can be identified based on the article’s content?

• Target 7.2: Increase substantially the share of renewable energy in the global energy mix.
• Target 12.5: By 2030, substantially reduce waste generation through prevention, reduction, recycling, and reuse.
• Target 13.2: Integrate climate change measures into national policies, strategies, and planning.
• Target 15.3: By 2030, combat desertification, restore degraded land, and strive to achieve a land degradation-neutral world.

Based on the article’s content, the specific targets identified are related to increasing the share of renewable energy (Target 7.2), reducing waste generation (Target 12.5), integrating climate change measures (Target 13.2), and combating land degradation (Target 15.3).

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

• Indicator 7.2.1: Renewable energy share in the total final energy consumption.
• Indicator 12.5.1: National recycling rate, tons of material recycled.
• Indicator 13.2.1: Number of countries that have integrated mitigation, adaptation, impact reduction, and early warning measures into national policies, strategies, and planning.
• Indicator 15.3.1: Proportion of land that is degraded over total land area.

The article does not explicitly mention indicators; however, the identified targets can be measured using indicators such as the renewable energy share in total energy consumption (Indicator 7.2.1), national recycling rate (Indicator 12.5.1), integration of climate change measures into national policies (Indicator 13.2.1), and the proportion of degraded land (Indicator 15.3.1).

Table: SDGs, Targets, and Indicators

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Source: ca.style.yahoo.com

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