Reducing emissions from byproducts: [1] An overlooked resource

Bringing byproducts back into the production chain

Following administrative merger, Ho Chi Minh City now generates roughly 14,000 tons of daily domestic solid waste requiring treatment. In addition, given the city's large demand for agricultural produce and food, as well as its extensive agricultural production areas, farming, livestock raising, slaughtering, processing, and agricultural trading activities also generate a significant volume of organic byproducts.

According to Dr. Le Thuy Binh Phuong, head of the research project "Developing Production Processes for Circular, Low-Carbon Agriculture to Reduce Greenhouse Gas Emissions in Ho Chi Minh City," the volume of byproducts and residues across the city is considerable.

Surveys at wholesale markets show waste generation reaching hundreds of tons per day. For example, according to Nguyen Hong Nguyen, Deputy Director of the Ho Chi Minh City Department of Agriculture and Environment, the Hoc Mon Wholesale Agricultural and Food Market (in Xuan Thoi Son commune) alone generates about 62 tons of waste per day. Most of this is collected, transported, and treated by the Ho Chi Minh City Urban Environment Company. According to the research team's survey, byproduct and residue volumes reach roughly 242 tons per day, while livestock waste ranges from 114 to 801 tons per day.

However, collecting byproducts faces obstacles because production is scattered, and many processing facilities focus mainly on their core products without prioritizing byproduct recovery and recycling. This is why the same material, if properly channeled, can serve as a raw input, but when mixed with other waste, becomes a treatment cost instead.

Dr. Binh Phuong noted that the same holds true for straw collection, recovery, and recycling. A large volume of straw left in the fields does not mean it can be immediately added to cattle feed rations. Raw straw has limited nutritional value and low digestibility. To use it effectively, it must be processed, preserved, and blended with other ingredients.

"The first bottleneck in circular agriculture isn't a lack of technology, it's organizing the flow of materials," Dr. Binh Phuong added.

From a greenhouse gas reduction standpoint, this is not simply a waste management issue. Organic matter, when landfilled or decomposed under unsuitable conditions, can generate methane (CH₄), while burning byproducts also increases emissions. If properly sorted and returned to production, a portion of organic byproducts can become inputs for livestock feed, fertilizer production, and new production cycles, reducing the volume of waste requiring treatment, limiting emissions from final-stage disposal, and partially replacing newly produced raw materials, feed, or fertilizer.

From waste reduction to carbon reduction

Based on the finding that recovering and reusing agricultural byproducts can ease the waste treatment burden, reduce greenhouse gas emissions, and generate economic benefits, Dr. Le Thuy Binh Phuong's research team tested two models: using organic byproducts to raise black soldier fly larvae, and using straw as feed for beef cattle. Both models proved effective across three dimensions: byproduct utilization, economic performance, and environmental impact.

In the black soldier fly model, byproducts made up 60–70% of the feed ration, with an average gross profit margin of 57.92%, a 60.8% improvement in economic efficiency, and an 89.91% reduction in CO₂-equivalent emissions compared with composting. The larvae produced after rearing also yielded a protein-rich biomass source, while the growing substrate was further utilized.

In the beef cattle model, byproducts accounted for as much as 95.8% of the feed ration, helping cattle gain approximately 0.7 kg per day compared with 0.56 kg per day under the conventional model. Economic efficiency rose by 14.31%, while CO₂-equivalent emissions fell by roughly 54%.

"When properly processed and blended, byproducts can become inputs for a new production cycle, easing waste pressure while creating additional economic value," Dr. Binh Phuong affirmed.

However, the research also shows that reuse does not mean utilization at any cost. Each type of byproduct must be classified, controlled, and matched with an appropriate process to ensure both effectiveness and the safety of the resulting product.

For livestock waste reuse, households and farms must have technology suited to their scale. For organic waste from wholesale markets, sorting must take place right at the source. If byproducts continue to be burned, landfilled, or treated using methods that generate large amounts of greenhouse gases, the goal of emissions reduction will be difficult to achieve.

Notably, agricultural byproducts are seasonal in nature. A farm may have an abundance of straw after harvest but face a shortage of raw materials at other times of the year. The supply of discarded vegetables and produce likewise fluctuates with the season and market activity.

For this reason, if Ho Chi Minh City wants to turn byproducts into a viable source of alternative raw materials and maintain a stable flow of this material, it needs to establish a network for collection, preliminary processing, storage, and market linkage. When raw materials are put to immediate use in other production cycles, the city not only reduces the volume of waste requiring treatment but also lowers demand for newly produced raw materials, helping cut emissions across the entire supply chain.