From Trash to Treasure in Longgang: The City Turning Food Waste into Diesel

Longgang, China— By day, students in matching uniforms tour vats of bubbling sludge and high-tech filtration systems. By night, factory workers shoot hoops under LED-lit courts, while kids splash in a fountain fed by recycled wastewater.

Welcome to Longgang— a city of 400,000 in eastern China's Zhejiang province that's redefining what a waste treatment plant can be.

Nestled within its new industrial zone, the Longgang Circular Economy Industrial Park isn't just processing trash. It's hosting sports leagues, school field trips, and even summer campers— all while turning sewage, food scraps, and construction debris into clean water, energy, and raw materials."This isn't just a utility," said Chen Minxing, a city planning official."It's a community space. A classroom. A symbol of what green cities can become."

From Waste Crisis to Circular Solution

Longgang's transformation began out of necessity.Once a bustling town, it became China's first"county-level city" created by upgrading a town— a national pilot project launched in 2019. With rapid urbanization came a waste crisis: over 2,000 tons of solid waste daily, much of it from its booming printing and gift industries."Our old system couldn't keep up," Chen said."We needed a new model— one that's sustainable, efficient, and accepted by the public."The answer? Build everything together.Instead of scattering waste facilities across the city— a common but inefficient approach— Longgang created a centralized"vein industrial park," where one plant's byproduct fuels another's input. The complex houses a reclaimed water plant, food waste digester, sludge dryer, incinerator, construction waste processor, and hazardous waste transfer hub— all interconnected."It's like a metabolic system for the city," said an engineer at the site."Waste in, resources out."

Food Waste to Fuel

At the food waste plant, more than 50 tons of leftovers arrive daily from 1,052 collection points— including restaurants, schools, hotels, and homes.After sorting and shredding, the waste undergoes thermal hydrolysis and centrifugation, separating into water, solids, and oil.

The water and solids go into anaerobic digesters, producing biogas that powers the park. The oil is sold to refineries— later turned into biodiesel or even aviation fuel."The market loves it," said a plant manager."We're not just reducing pollution. We're making money from waste."

Dirty Water, Clean Future

The reclaimed water plant processes 120,000 tons of wastewater each day— from toilets, factories, and storm drains. Using advanced biological treatment, it produces water clean enough to irrigate parks, cool power plants, and flush industrial equipment. None of it goes to waste.Every day, 10,000 tons of this recycled water is piped to a nearby power station for cooling— saving millions in freshwater costs. Another 30,000 tons have already been saved through on-site reuse in landscaping, dust control, and cleaning. And soon, officials say, this water will flow into city rivers and hydrants— potentially cutting freshwater withdrawals from the Shanxi Reservoir by 4 million tons a year.

No NIMBY Here

Historically, communities resist waste plants. The"Not In My Backyard" effect has killed projects across China and beyond.Longgang flipped the script.The entire complex is landscaped like a garden. Solar-paneled walkways, wetland ponds, and open plazas invite visitors. A sports park with basketball courts, playgrounds, and picnic areas sits at its heart."It's beautiful," said Zhang Wei, a factory worker who plays basketball here three times a week."We didn't expect something like this next to a sewage plant."Children from local schools visit the Zero-Carbon Study Base, where interactive exhibits explain how"leftover food becomes fuel" and"dirty water waters the flowers."

"Old bricks can become manhole covers!" 10-year-old Lin Yuxi exclaimed during a tour."I want to tell my dad to recycle more."

A Model for China's Cities

Longgang's model is now drawing national attention.By co-locating facilities, the city saved land, cut construction costs, and streamlined regulation under its"big department" governance system. Shared pipelines, roads, and power lines reduced redundancy.Operationally, it's self-sustaining: revenue from energy, recycled materials, and water sales offsets treatment costs— a rare win for public infrastructure.

"This proves green projects can be both popular and profitable," said a Wenzhou city official.With more facilities coming online, Longgang aims to process nearly all of its waste locally— a key step toward becoming a"zero-waste city."And as China pushes its"dual carbon" goals— peaking emissions by 2030 and achieving carbon neutrality by 2060— models like Longgang's could light the way.

"Trash Is Just a Resource in the Wrong Place"

Back at the park, sunset paints the sky orange as families stroll past fountains fed by treated wastewater.For the people of Longgang, the message is clear: sustainability isn't just policy. It's part of daily life."People used to fear waste plants," Chen said."Now they come here to play, learn, and relax. That's the real victory."

In a country racing to balance growth and green goals, Longgang offers a powerful lesson:Trash isn't the end. It's a beginning.(Zhao Chenzhang, Shen Huamei)