PROF LIU RENHUAI
Prof Liu Renhuai (刘人怀) is an academician of the Chinese Academy of Engineering (CAE). He has served as Vice President of Shanghai University of Technology and founding Dean of its School of Economics and Management, as President of Jinan University (暨南大学), and as a standing committee member of the Mechanical and Transportation Engineering Division of the CAE. He was also Deputy Director and Chief Consulting Expert of the Engineering Management Division of the CAE. As one of China’s pioneers in the theory and application of plate and shell structures, Prof Liu co-developed the Modified Iterative Method with Ye Kaiyuan (叶开沅) in 1965 to solve the relevant nonlinear differential equations. His work has been applied to six types of plate and shell models in fields such as aerospace and precision instrumentation. Liu also contributed to China’s major scientific endeavours, including the Dongfanghong (东方红) satellite, the Shenzhou (神舟) spacecraft and the J-15 carrier-based fighter jet.
Recently, the chief editor of THINK visited a food waste processing facility in Chengdu, China, and was very impressed by its bioengineering process, which converts food waste into valuable products. He subsequently arranged an interview with Prof Liu Renhuai, the mastermind behind this innovative environmental solution, which has the potential to address a significant environmental problem arising from our irresponsible consumption culture.
The interview was originally conducted in Mandarin.
Professor Liu, what was your original academic field of study? How does your expertise relate to dealing with food waste?
I am fundamentally a research scientist. In 1958, I entered Lanzhou University (兰州大学) as the top scorer in the national college entrance exam. I began scientific research at the age of 18, and it has now been 66 years. Early in my career, I participated in developing China’s first satellite, Dongfanghong. I’ve always had a strong passion for scientific research. Regardless of the field, if the country or the people needed it, I was eager to contribute. My work includes projects ranging from satellites to aircraft carriers and pressure vessels in factories.
I initially studied mathematics, then transitioned to mechanics, and later to management science, including urban management, school management, research management, teaching management and engineering management. My publications cover a wide range of disciplines. Today, I’m both a mechanic and a management scientist—an academician in both fields. In mechanics, I study pressure vessels and pipelines, while in management science, I work on urban and engineering management. Both areas are relevant to food waste processing.
However, your current work in food waste processing involves biological science, which is an entirely different field.
This happened purely by chance. In 2003, I began working as a consultant for the Guangdong Provincial Government. Guangdong is a large province with many issues to tackle, and our role was to investigate and identify problems that needed solutions. One of the issues we encountered was plastic waste, a global problem that affects almost everyone. While plastic is incredibly useful, its disposal is highly problematic.
In 2009, Guangdong established a Volunteers Association for Science and Technology Promotion to promote science education and encourage young people to participate in scientific outreach. As the association’s first president, I oversaw activities that initially focused on waste sorting. This initiative was one of the first city-level waste-sorting projects in China. The students excelled at sorting, but I soon discovered that the city’s waste collection workers were remixing the sorted waste due to a lack of processing infrastructure. It was a serious issue: tens of thousands of people had worked hard, and leaders were pleased, but the outcome was poor due to insufficient follow-up.
I DISCOVERED SERIOUS FLAWS IN WASTE TREATMENT METHODS IN GUANGZHOU. INCINERATION PLANTS, FOR EXAMPLE, EMITTED DIOXINS INTO THE ATMOSPHERE. LANDFILLING RESULTED IN LEACHATE POLLUTING RIVERS, LAKES, AND GROUNDWATER.
Combating food waste with mindful dining
The Clean Plate Campaign (光盘行动), reinvigorated in 2020 by President Xi Jinping, aims to combat the country’s food waste problem. Xi described the waste as “shocking and distressing,” urging citizens to adopt mindful dining habits. Restaurants promote smaller portions and N-1 ordering (one dish fewer than the number of diners), while public campaigns and educational efforts emphasise civic responsibility and sustainability.
Photo: 储舒婷 / 文汇报
When I investigated further, I discovered serious flaws in waste treatment methods in Guangzhou. Incineration plants, for example, emitted dioxins—a carcinogen recognised by the WHO—into the atmosphere. Landfilling resulted in leachate polluting rivers, lakes, and groundwater. Unprocessed food waste used as pig feed led to diseases similar to mad cow disease. Even the use of food waste as fertiliser caused soil salinisation. These methods appeared to address the problem but ultimately created new, more severe issues.
Moreover, China faced a significant “gutter oil” issue. This substandard cooking oil, extracted from food waste, was widely consumed. My calculations showed that each Chinese person ingested an average of 2.8 kilograms of gutter oil annually. As a researcher, I felt compelled to address these problems through science.
Chowing down for views
Mukbang, a trend originated in South Korea where social media influencers consume excessive amounts of food while interacting with viewers, has been criticised for promoting food waste and unhealthy habits. In 2021, China implemented regulations banning binge-eating videos and imposing fines on platforms that air them. However, mukbang content has resurfaced on platforms like Douyin (抖音) and Kuaishou (快手), prompting further government crackdowns.
Photo: Global Times
How much of urban waste is made up of food waste?
Food waste accounts for half of all household waste. This ratio is consistent across Chinese cities. The other half includes materials like steel, glass and plastics, which are easier to sort and process.
I’VE ESTIMATED THAT THE AVERAGE CHINESE PERSON GENERATES 0.5 KILOGRAMS OF FOOD WASTE DAILY. WITH A POPULATION OF 1.4 BILLION, THAT RESULTS IN 700 MILLION KILOGRAMS EVERY DAY.
Does food waste include packaging and utensils, or just the food itself?
It’s primarily the food itself. This includes discarded parts from slaughterhouses, such as bones and offal, as well as spoiled fruits and vegetables from markets. Substantial amounts of food waste also originate from households and the catering industry. I’ve estimated that the average Chinese person generates 0.5 kilograms of food waste daily. With a population of 1.4 billion, that results in 700 million kilograms every day. This has led to “trash-encircled cities” in metropolises like Guangzhou and Shenzhen. The ramifications of this are immense. China has a high number of cancer patients, with many cases attributed to this.
Initially, I didn’t think waste was a problem. There wasn’t a specialised field for it in school, and no one seemed to take it seriously—everyone just thought it was no big deal. Later, I realised the problem was enormous. I spent an entire day discussing the issue of waste with the then-Mayor of Guangzhou, Chen Jianhua (陈建华). Both the Party Secretary and the Governor of Guangdong Province were highly concerned about it, as Guangzhou was generating seven to eight thousand tonnes of waste daily at the time, which was a complicated problem to solve.
The hidden danger lurking in landfills
Leachate is a hazardous liquid formed when rainwater filters through landfills, pulling harmful chemicals from decomposing waste. This toxic brew can leak into the soil and groundwater, contaminating drinking water and harming ecosystems. With food waste making up a significant portion of landfill waste, the production of leachate intensifies, causing long-term environmental pollution and health risks.
Photo: Imaginechina Limited / Alamy Stock Photo
That’s an enormous volume of waste. Were you confident you could solve such a daunting problem?
I realised early on that this was a multidisciplinary issue requiring solutions from multiple fields. Fortunately, I had a unique resource: my youngest son, Liu Zehuan (刘泽寰), who holds a PhD in biology from Sun Yat-Sen University (中山大学) and specialises in using yeast to convert agricultural waste into ethanol. I asked him to take on this challenge, and he agreed. In 2010, he began developing a “waste-consuming yeast” to ferment food waste into valuable resources. It took him three years to achieve success in the lab.
In 2013, we launched a small-scale, three-year pilot project with strong support from the mayor of Guangzhou. We established a facility capable of processing five tonnes of food waste daily. This initiative was groundbreaking in China due to its multidisciplinary nature. Although I am not an environmental engineer, the project involved complex mechanics and management aspects with which I was familiar, while my son handled the core biological technology. By 2016, the plant was operational and running smoothly.
Could you please describe how the facility processes food waste and what products it generates?
The process takes approximately 36 to 48 hours. First, the waste is deodorised, crushed, pulped, sterilised, and then fermented using our patented yeast. The output includes crude industrial oil, ethanol (with 95 to 99% purity, suitable for sustainable aviation fuel, SAF), high-protein feed additives, and refuse-derived fuel (RDF) briquettes. Wastewater is treated to meet environmental standards before discharge.
From one tonne of food waste, we can produce approximately 25 kilograms of ethanol, 70 kilograms of crude oil, 25 kilograms of feed additives, 90 kilograms of RDF, and over 780 kilograms of treated water. This method converts waste into zero-pollution, economically valuable resources, making us the first in China to achieve this. We effectively turn urban waste into a gold mine. This also contributes significantly to achieving the dual carbon goals of carbon peaking and carbon neutrality.
Father-son duo wins carbon neutral award
Prof Liu Renhuai and his son, Dr Liu Zehuan, were honoured with the 2023 China Top 10 Carbon Neutral Technology Innovation Award in August 2024 for their project on sustainably processing kitchen waste. Their work transforms food waste into zero-pollution, economically valuable resources, supporting the circular economy and advancing China’s carbon neutrality goals.
Besides Guangzhou, have you promoted this method of food waste processing elsewhere?
Our method can be applied not only across China but also worldwide. I have visited over 50 countries, many of which struggle with waste management, particularly food waste. Many still rely on incineration or landfilling, which harms both the environment and human health. Furthermore, recyclable resources are wasted. Therefore, we are keen to introduce this method to other cities and countries.
After our pilot project succeeded in Guangzhou, we sought to scale up. In 2019, we built a facility in Chengdu with a daily processing capacity of 200 tonnes. This facility, which you’ve visited, is beautifully designed—it doesn’t look like a waste treatment plant from the outside. In addition to processing Chengdu’s food waste, it also serves as our research base to optimise and innovate our production techniques and management systems continuously.
Our project recently received the “2023 China Top 10 Carbon Neutral Technology Innovation Award,” reflecting national recognition of our work. We are constructing an even larger facility near our current plant, which will have a daily capacity of 500 tonnes. Once it begins operations in the first quarter of 2025, our total daily capacity will reach 700 tonnes.
THIS METHOD CONVERTS WASTE INTO ZERO-POLLUTION, ECONOMICALLY VALUABLE RESOURCES, MAKING US THE FIRST IN CHINA TO ACHIEVE THIS. WE EFFECTIVELY TURN URBAN WASTE INTO A GOLD MINE.
Developing and implementing this technology took several years. What were the biggest challenges you faced, either technical or otherwise?
The technical challenges were relatively minor. The biggest hurdle was securing research funding. While I had a good relationship with Guangzhou’s mayor and high standing in Guangdong Province as an academician and university president, the financial support didn’t come easily. Building a facility required leasing thousands of square meters of land, purchasing expensive equipment, and covering operational costs—all of which were beyond my personal finances.
Ultimately, my students helped solve the funding issue. Many of my students were successful entrepreneurs or business leaders who had studied for MBAs or EMBAs with me. When they heard their professor needed funding, they pooled together 10 million yuan, allowing us to proceed.
Regulatory approvals presented another challenge. Despite strong backing from provincial and municipal leaders, the project required expert assessment. The initial evaluation panel, comprising environmental experts, unanimously rejected it. They argued that I wasn’t an environmental scientist, although I had a strong reputation. My project, however, was multidisciplinary, involving mechanics, urban planning and management sciences, in addition to environmental science. While I am a mechanician, I have contributed to the planning of Shanghai’s Pudong district and the Huangshan tourist area. I have also conducted in-depth research on waste management, striving to come up with the best solutions to address issues others have failed to solve. Many environmental experts overlook the significance of interdisciplinary collaboration. After further discussions with government leaders and multiple rounds of deliberation, we finally received approval.
Chengdu’s food waste treatment facility
The food waste treatment facility in Chengdu, built in 2019, processes 200 tonnes of food waste daily. Designed to blend seamlessly with its surroundings, it functions both as a waste treatment plant and a research base, continually optimising production techniques and management systems to drive innovation and sustainability.
Photo: Sichuan Lixinlong Environmental Technology
China’s low-carbon lending programme
In August 2024, China’s central bank announced the extension of its low-carbon lending programme until 2027. The initiative provides low-cost loans to banks financing green projects, including renewable energy and energy-efficient technologies. This effort aligns with China’s broader strategy to reduce carbon emissions and transition toward a sustainable, low-carbon economy.
Photo: zhongguo / iStock
Processing food waste seems to involve more than just scientific and technical hurdles; it also involves financial challenges, regulatory issues, management difficulties, resource allocation problems, and even challenges regarding public trust; am I correct?
Absolutely. Initially, I thought it would be simple—complete the pilot tests and quickly scale up. But scaling up proved to be much more challenging than I had anticipated. I visited over 20 provinces across China, but many places were reluctant to adopt the project. It involves the reallocation of many resources, including land for the processing plant. People didn’t trust us and were protective of their vested interests, despite knowing me as Academician Liu. They questioned whether someone without an environmental background could solve these problems.
They were sceptical even when we explained our technology and sought partnerships with existing waste management entities. They feared we would disrupt their operations or compete with their interests. I tried to assure them that I was not there to take away their business; my goal was to improve waste management for the environment and public health. However, convincing them wasn’t easy.
Ultimately, we succeeded in Chengdu thanks to a local leader, a student I met while advising doctoral students at Nanjing Aeronautical University. He trusted me and supported the project. After more than a decade of effort, we have achieved our current scale. Winning the “Top 10 Carbon Neutral Technology Innovation Award” recently brought me immense satisfaction—it recognised our perseverance and the value of our research.
THEY WERE SCEPTICAL EVEN WHEN WE EXPLAINED OUR TECHNOLOGY AND SOUGHT PARTNERSHIPS WITH EXISTING WASTE MANAGEMENT ENTITIES. THEY FEARED WE WOULD DISRUPT THEIR OPERATIONS OR COMPETE WITH THEIR INTERESTS.
Given the success of your technology in addressing environmental issues, should it be implemented nationwide or even globally? If applied abroad, where would you start? Would the type of food waste in different regions affect its effectiveness?
We’ve already started constructing our second and third facilities in China. Our technology is protected by patents in the US, EU and Japan, and we’ve published academic papers in leading international journals to introduce our method. Those of us engaged in scientific research all understand that we must first achieve theoretical results and then work on their transformation for real-world application. However, since our project involves a wide range of societal aspects, the transformation process tends to be more complex and challenging.
If we were to expand internationally, I would prioritise regions like Hong Kong, Macau and Southeast Asia, where the local food is similar to Chinese food, and we have some familiarity with the local language and culture. Regarding effectiveness, I am confident in our technology. Our yeast is highly resilient—it has been cultivated to process Sichuan cuisine, which is renowned for being very spicy, very salty and very greasy. This suggests it can manage other types of food waste effectively as well.
When operating abroad, we may not need to build and run facilities ourselves. Instead, we could license our technology, transfer it to local companies, or act as consultants, sharing the economic benefits to sustain growth. This approach would allow us to scale up quickly and benefit more people.
Prof Liu Renhuai in his office in Hangzhou.
Prof Liu Renhuai attended the 2020 Guangdong-Hong Kong-Macau Academician Summit, which focused on promoting scientific innovation and collaboration to accelerate the Greater Bay Area's development as a global tech hub.
OUR YEAST IS HIGHLY RESILIENT—IT HAS BEEN CULTIVATED TO PROCESS SICHUAN CUISINE, WHICH IS RENOWNED FOR BEING VERY SPICY, VERY SALTY AND VERY GREASY. THIS SUGGESTS IT CAN MANAGE OTHER TYPES OF FOOD WASTE EFFECTIVELY AS WELL.
While your method provides significant environmental and public health benefits, it requires a substantial upfront investment. Do you think government subsidies are necessary to ensure the sustainability of such enterprises?
If managed well, our method is profitable without subsidies. Waste collection generates revenue, and the products derived from waste—crude oil, ethanol, and protein feed—can be sold. I’ve calculated that processing one tonne of food waste can yield 600–1,000 yuan. The initial investment can be recouped within three to five years.
That said, government support is crucial for obvious reasons. Waste collection and sanitation are managed at the municipal level, so government approval is required to collect food waste. During our pilot tests in Guangzhou, we collected hundreds of batches of food waste, and each batch required government authorisation. We often mention “industry, academia and research” (产、学、研), meaning that industries, academic institutions, and research organisations must collaborate. However, I believe what we really need is “policy, industry, academia, research and finance” (政、产、学、研、金)— we require policy and financial backing as well. Since I am not an entrepreneur and cannot afford the initial investment, I rely on the support of entrepreneurs. Similarly, projects like this cannot succeed without government backing.
I BELIEVE WHAT WE REALLY NEED IS “POLICY, INDUSTRY, ACADEMIA, RESEARCH, AND FINANCE” (政、产、学、研、金)—WE REQUIRE POLICY AND FINANCIAL BACKING AS WELL.
As an industry addressing both environmental and public health issues, what do you envision for the future of food waste processing?
I believe this industry has timeless value—our society will always need it. As long as humans exist, whether in Eastern or Western societies, food waste will be generated, and it must be properly processed to avoid environmental damage and public health risks. This need transcends economic cycles, technological advancements, and even crises like wars or natural disasters.
By maintaining innovation and optimisation in this field, we can continue contributing to society and humanity. Properly managed, turning waste into resources is a profitable and sustainable business. My ultimate wish is to establish a foundation using the profits from our technology to further promote waste-to-resource initiatives and share its benefits with more people. ∞
FEBRUARY 2025 | ISSUE 13
MIND THE GAPS; BRIDGING THE GAPS
