You might recall our earlier food waste guide this year. We received over 500 questions from you regarding California's recent law to keep food waste out of landfills. One frequently asked question was why some cities, like Pasadena, require us to bag our food waste before placing it in the green bin. I embarked on a food waste journey to find the answers.

Discover the Hidden Path of Food Waste - From Trash to Treasure

Separating Food Waste

At the top of the landfill, diligent workers meticulously pick through the spread green waste, deftly removing plastic and other contaminants. As Michael Chee, a spokesperson for L.A. County Sanitation Districts, pointed out, "There's no automated magic here; actual people are digging, separating, and pulling out plastic." A worker casually tosses a whole bag of raw chicken into a dumpster that's already half-filled with bagged food waste. Nearby, a coyote sneaks in for a few nibbles from the food waste yet to be collected. Workers identify bags of food waste to be placed in a separate dumpster from yard waste. It's advisable to use bags you already have, such as bread bags, carrot bags, or potato sacks, as buying more expensive "compostable" bags is often unnecessary. These bags will be torn off and end up in the landfill anyway, further reducing waste. Properly bagged food waste at Scholl Canyon Landfill is a sight to behold.

Turning Food Waste into Slurry

Once the food waste dumpster at Scholl Canyon is full (which happens once or twice a week), it's transported half an hour away to the Puente Hills Materials Recycling Facility. In a massive warehouse, a frontloader lifts bags of food waste. Will Chen, the supervising engineer, explained how an attachment on the frontloader shreds the bags, allowing the food waste to be dropped into a hopper. The hopper then further shreds the food waste, filters out contaminants, and eventually turns it into a kind of slurry, or as the folks here like to joke, a smoothie. A frontloader scoops bagged food waste at the Puente Hills Materials Recovery Facility. The attachment on the frontloader that removes bags holding food waste is a crucial part of the process. The slurry is then piped into storage tanks. "We have meters monitoring how thick it is as that's critical for us," Chen said. Thickness matters as the slurry needs to easily move through the pipes and into a tanker truck, ensuring the food waste reaches its final destination - the A. K. Warren Water Resource Facility, a wastewater treatment plant in Carson.

Turning Food Waste into Fuel

At the Warren facility in Carson, the food waste slurry enters huge tan circular structures called anaerobic digesters. "They store about 4-and-a-half million gallons of sludge, where all the bugs are feasting on the material and converting it into gas," Chen explained. Microscopic bugs eat the food waste and wastewater slurry and convert it into methane gas. The gas from the food waste is piped across the street to a new compressed natural gas (CNG) station. There are three main categories of biofuels: ethanol, which is mostly made from corn; renewable diesel, made from crop-based vegetable oils like soy and used cooking oils or animal fat (about 70% of the diesel used in California is this type); and biogas, made from methane gas captured from livestock manure, landfills, and now, food waste. These fuels are less carbon-intensive than traditional oil and gas, emitting less carbon into the atmosphere. At the CNG station on a recent day, L.A. city garbage trucks and other heavy-duty trucks are already fueling up. The gas generated from food waste will also be sold to SoCalGas for use in their pipelines. Currently, about 5% of the gas SoCalGas delivers is from biofuels, and they expect this to grow to 20% by 2030. "We definitely see the demand for CNG fueling, which is why we're doing this," Chen said. "However, it's not going to be forever. I think CNG will have a place in the transportation sector until electrification technology and/or hydrogen become more prevalent and available."Infrastructure remains a challenge for increasing these efforts. L.A. County Sanitation Districts are in a good position to implement more biogas production due to their existing infrastructure. As they transition their fleets to electric, the carbon footprint of transporting food waste to these facilities is expected to decrease significantly. Already, their trucks largely run on biofuels. CalRecycle estimates that California needs as many as 100 new or expanded organic waste recycling facilities to recycle an additional 20 to 25 million tons of organic waste annually. The agency, which oversees the state's waste management, estimates there are now 20 operating standalone anaerobic digestion facilities, with six more planned, and 10 co-digestion facilities like the Warren facility in Carson, with 10 more planned. The state is providing more than $120 million in grants to boost this infrastructure. "In L.A. County alone, we're estimating that 4,000 tons of food waste is generated every day that needs to be diverted," Chen said. "It will take a collective effort across the entire state, and it will be a long and costly journey. But we'll eventually get there with heavy investment in the necessary infrastructure."Scientists say reducing methane is crucial in addressing human-caused climate change. In California, our main methane sources are dairies, landfills, and oil and gas operations. Methane at landfills mainly comes from food waste decomposing. Usually, methane at landfills is captured and "flared" (burned), which is better for the climate but bad for local air quality. Some landfills also use the captured methane to generate electricity, like Glendale is planning at Scholl Canyon Landfill. "I think [using food waste for fuel] is definitely in the right direction," Chen said. "Now, instead of it going to the landfill to rot, it can fuel trucks, produce power, and heat homes. It really moves us in the right direction and helps us be more sustainable."Compressed natural gas does have fewer dangerous emissions than diesel, and using food waste helps reduce methane emissions from landfills. However, Katherine Blauvelt, a researcher with Industrious Labs, a nonprofit think tank, believes it doesn't solve the problem of existing methane emissions from landfills. "The big problem with putting too many eggs in the biomethane basket is that it creates misaligned incentives that perpetuate our current harmful system," Blauvelt said. "We can create more jobs and stimulate economic development when a community does more than use something and trash it." The state is considering updating its landfill regulations to address this issue.The cost of turning food waste into fuel is also a consideration. Aaron Smith, an agricultural and resource economics professor at UC Berkeley, questions whether it's worth it. "To deal with these problems, you have to choose something, and currently, biogas production from food waste seems feasible. But a downside is that you might end up locking in a more expensive mitigation method." The efforts to keep food waste out of landfills have likely contributed to the increase in trash bills. But with landfills filling up and methane pollution worsening climate change, it's a difficult problem to solve when we have so much food waste in the first place. "You can imagine a more efficient system with less waste, but given the waste we have, this seems like one of the only options," Smith said. Ultimately, the more effective solution is to generate a lot less waste in the first place.