Agricultural and forestry waste, an overlooked ecological challenge

In the vast fields and forests, more than 3.8 billion tons of agricultural and forestry waste are generated each year, including crop straw (corn stalks, rice husks, wheat straw), forestry pruning branches, livestock and poultry manure, agricultural product processing by-products (such as fruit peels, bagasse), etc. These substances, once regarded as "agricultural by-products", are becoming an increasingly severe environmental burden if not properly handled: open-air burning of straw releases a large amount of PM2.5, sulfur dioxide and volatile organic compounds (VOCs), which are important causes of haze in autumn and winter; randomly piled livestock and poultry manure infiltrates into the soil, causing nitrogen and phosphorus enrichment and eutrophication of water bodies; rotten fruit and vegetable leaves produce hydrogen sulfide, ammonia and other foul-smelling gases under the action of microorganisms, which not only pollute the air, but also threaten the health of surrounding residents. The disorderly disposal of agricultural and forestry waste is forming a vicious cycle of "waste of resources - increased pollution".
Multi-treatment technology: the key to solving the waste dilemma
1. Fertilizer utilization: natural cycle dominated by microorganisms
Composting is the most traditional resource utilization path. By controlling temperature, humidity and oxygen content, organic waste is decomposed into humus using microorganisms such as Bacillus subtilis and actinomycetes. In this process, pathogens and weed seeds in livestock and poultry manure are killed by high temperature (above 55°C for 7 days), and finally organic fertilizer rich in nitrogen, phosphorus and potassium is formed. The principle is essentially the biodegradation of microorganisms, which converts macromolecular organic matter into small molecular nutrients that can be absorbed by plants, realizing the material cycle "from land to land".
2. Energy conversion: borrowing energy codes from nature
Biomass power generation and biogas engineering are the two core technologies of energy utilization. Cellulose-rich wastes such as straw and rice husks are burned in boilers and converted into electricity through steam turbines; livestock and poultry manure and kitchen waste are decomposed by methanogens in anaerobic biogas digesters to produce biogas (mainly methane), which can be directly used for heating or power generation. The more advanced pyrolysis technology heats the waste to 400-600℃ in an oxygen-free environment, and generates biochar, wood tar and combustible gas by breaking chemical bonds. Biochar can improve soil, and combustible gas can be purified to become industrial fuel. The essence of these technologies is to convert solar energy stored in plants into usable energy forms through chemical or biological means.
3. Material application: reshaping the physical properties of waste
Waste rich in lignin, such as forestry waste wood and rice husks, can be made into environmentally friendly building materials such as fiberboard and particleboard after crushing, pressing and bonding; corn straw fiber can replace some petroleum-based raw materials to produce packaging materials through chemical treatment. This treatment method uses mechanical force or chemical reaction to change the physical structure of waste, giving it new use value, and reducing dependence on natural wood and fossil resources from the source.
VOC catalyst: Accurately cracking the invisible pollution in the treatment process
In the energy and fertilizer treatment of agricultural and forestry waste, the emission of volatile organic compounds (VOCs) is a pain point that is easily overlooked. For example, when biomass is burned, harmful gases such as benzene and toluene are produced, and a small amount of aldehydes and ketones are also released during the composting process. VOC catalysts play a key role in addressing this problem: their core components (such as precious metals such as platinum and palladium or transition metal oxides such as titanium dioxide and manganese dioxide) adsorb VOC molecules through surface active sites, catalyzing their oxidation reaction with oxygen at a relatively low temperature (200-400°C), and ultimately generating harmless carbon dioxide and water (such as C₆H₆ + 7.5O₂ → 6CO₂ + 3H₂O). This catalytic oxidation technology can increase the VOCs removal rate to more than 95%, and reduce energy consumption by 60% compared to traditional high-temperature incineration methods. It is worth noting that in response to the water vapor and dust that may exist in agricultural and forestry waste treatment scenarios, researchers have improved the catalyst carrier (such as using honeycomb ceramics or activated carbon fibers) to improve its anti-poisoning ability and service life, so that it can still maintain high efficiency under complex working conditions.
Circular economy: a paradigm shift from "waste" to "new resources"
The ultimate goal of agricultural and forestry waste treatment is to build a closed-loop system of "collection - treatment - transformation - application". In Zhejiang, Jiangsu and other places, an industrial chain of "straw collection and storage center + biomass power plant + organic fertilizer plant" has been formed: the power plant burns straw to generate electricity and is connected to the grid, and the generated wood ash is transported to the organic fertilizer plant as a raw material for potash fertilizer, realizing the joint production of "power generation - fertilizer"; the flower planting base in Guangdong mixes the pruned branches with livestock and poultry manure for composting, and after the fermentation waste gas is treated with a VOC catalyst, the generated organic fertilizer is directly supplied to the nursery, forming an internal cycle of "agricultural waste - fertilizer - planting". This model not only eliminates pollution, but also creates new economic value - it is estimated that the energy utilization of each ton of straw can create an output value of about 200 yuan, and the national annual output value can exceed 70 billion yuan.