Scheme for Garbage Leachate Treatment Process
一、Definition of Garbage Leachate
Garbage leachate refers to the high-concentration organic wastewater formed by the moisture contained in the garbage itself in landfills, rainwater and snowmelt entering the landfill, and other sources of water, which flows through the garbage layer and cover materials under the action of gravity in the landfill. It contains a large amount of pollutants such as organics, ammonia nitrogen, and heavy metals.
In terms of organics, the composition of organics in garbage leachate is complex, including humus substances, polysaccharides, proteins, etc. These substances make the chemical oxygen demand (COD) of leachate very high.
In terms of ammonia nitrogen, it mainly originates from the decomposition of nitrogen-containing organics in garbage, such as proteins. Its concentration can usually reach hundreds or even thousands of milligrams per liter.
In terms of heavy metals, although their content is relatively low compared to organics and ammonia nitrogen, heavy metals such as mercury, cadmium, lead, and chromium are also present. These heavy metals mainly come from waste batteries, electronic products, and other waste in garbage.
II. Challenges in Garbage Leachate Treatment
1. Large Variations in Water Quality and Quantity
Water Quality Variations: The water quality of garbage leachate changes with the age of the landfill. In the early stages of landfill, the organics in leachate are mainly volatile fatty acids that are easily biodegradable, with a high BOD₅ (five-day biochemical oxygen demand) to COD ratio, usually around 0.5 to 0.7, indicating good biodegradability. As the landfill ages, refractory humus substances gradually increase, and the BOD₅/COD ratio decreases, resulting in poorer biodegradability. For example, in the later stages of landfill, the BOD₅/COD ratio may drop below 0.1.
Water Quantity Variations: The generation of leachate is influenced by precipitation, evaporation, garbage moisture content, and other factors. During rainy seasons, with high precipitation, the generation of leachate increases sharply; whereas during dry seasons, it relies mainly on the moisture contained in the garbage and a small amount of other water sources for replenishment, resulting in reduced generation. This large fluctuation in water quantity poses challenges to the stable operation of treatment facilities. If treatment facilities are designed for the maximum water quantity during rainy seasons, they will be idle and wasted during dry seasons; if designed for the average water quantity, insufficient treatment capacity will occur during rainy seasons.
2. High Pollutant Concentration and Complex Composition
Difficulties in Treating High-Concentration Organics: The COD concentration in garbage leachate is usually several thousand milligrams per liter or even tens of thousands of milligrams per liter. These high-concentration organics are difficult to remove completely through a single treatment method. Traditional biological treatment methods have limited efficiency for high-concentration and refractory organics, while advanced oxidation and other physicochemical methods can effectively remove organics but at a higher cost.
Difficulty in Removing Ammonia Nitrogen: High ammonia nitrogen concentrations complicate the treatment process. Common biological nitrogen removal processes are affected by C/N (carbon-to-nitrogen) imbalance when treating high-ammonia nitrogen leachate. High concentrations of ammonia nitrogen in leachate require sufficient carbon sources for denitrification reactions, but as the landfill ages, the available carbon sources in leachate decrease, leading to poor nitrogen removal efficiency. Additionally, physical methods such as ammonia stripping can remove some ammonia nitrogen but generate secondary pollution, such as the need to treat stripped ammonia gas.
High Treatment Requirements for Heavy Metals: The presence of heavy metals complicates treatment. Since heavy metals cannot be biodegraded and are toxic to microorganisms, they inhibit microbial activity during biological treatment. During the treatment process, chemical precipitation, ion exchange, and other methods need to be adopted to remove or reduce the concentration of heavy metals to avoid affecting subsequent biological treatment units. Moreover, the treatment of heavy metals must also consider their recycling and the environmental safety of final disposal.
High Treatment Process and Operating Costs
Necessity and Complexity of Combined Processes: Due to the complex water quality of garbage leachate, a single treatment process is difficult to achieve the desired treatment effect. It is usually necessary to adopt a combination of multiple processes, such as biological treatment (e.g., anaerobic-aerobic processes) and physicochemical treatment (e.g., coagulation-sedimentation, activated carbon adsorption, membrane separation, etc.). However, the operation and management of such combined processes are challenging, requiring precise control and adjustment of each process unit. For example, in biological treatment units, temperature, pH, dissolved oxygen, and other parameters need to be strictly controlled to ensure microbial growth and metabolism; in membrane separation units, membrane fouling and contamination need to be prevented, with regular cleaning and maintenance.
Operating Cost Factors: The operating costs of garbage leachate treatment include energy consumption, reagent costs, equipment maintenance costs, etc. Membrane treatment technology is effective in removing pollutants but has a limited membrane lifespan and high replacement costs. Moreover, to prevent membrane fouling, frequent chemical cleaning is required, which also increases reagent costs. Additionally, some advanced oxidation processes (e.g., Fenton oxidation) consume a large amount of chemical reagents, resulting in high treatment costs. At the same time, the energy consumption during the treatment process is also significant, such as the aeration equipment in biological treatment units and water pumps in physicochemical treatment units, which require substantial electricity consumption.
III. New Treatment Processes for Garbage Leachate
Addressing the pain points of garbage leachate treatment, Keli'er Technology has introduced a new treatment process for garbage leachate centered on CDOF ozone advanced oxidation technology. Compared to traditional processes, it has many advantages, as introduced below:
CDOF Technology Principle
The CDOF device consists of an oxygen production system, an ozone generation system, an efficient ozone dosing system, a multiple catalytic reaction system, and a swirling dissolved air flotation system. It integrates ozone multiple catalytic oxidation technology, hydraulic cavitation technology, and swirling air flotation technology. Under the action of a catalyst, ozone produces reactive species such as hydroxyl radicals with strong oxidizing properties. These reactive species can undergo redox reactions with pollutants such as organics and ammonia nitrogen in garbage leachate, decomposing large-molecule organics into small-molecule organics or even directly oxidizing them into carbon dioxide and water, and oxidizing ammonia nitrogen into nitrogen and other harmless substances, thereby achieving the purpose of removing pollutants. Meanwhile, hydraulic cavitation technology can create a local high-temperature and high-pressure environment, further promoting the oxidation reaction, while swirling air flotation technology can timely separate insoluble substances generated during the oxidation process, achieving efficient oxidation and air flotation integration.
Advantages of the New Process
Avoiding Drawbacks of Traditional Processes: It completely avoids traditional treatment processes such as nanofiltration, reverse osmosis, and concentrated liquid treatment, eliminating issues such as membrane fouling and scaling, short lifespan, high energy consumption, and concentrated liquid generation in membrane treatment.
Cost Reduction: It significantly reduces investment, and due to the stable operation of the equipment, the number of maintenance and repair costs is reduced, resulting in substantial reductions in operating and maintenance costs.
Excellent Environmental Performance: With low reagent usage and sludge (hazardous waste) generation, it reduces sludge treatment costs and environmental risks. The equipment is integrated, and CDFU and CDOF operate under pressure and in a sealed manner throughout, which is environmentally friendly and free from secondary pollution.
High Efficiency and Stability: The core treatment equipment has low energy consumption, fast reaction speed, and an oxidation efficiency 2-5 times higher than traditional ozone catalytic oxidation. Using self-developed heterogeneous catalysts, through catalyst loading and segmented precise temperature-controlled sintering technology, it ensures activity and high strength while reducing loss rates, resulting in stable equipment performance and high treatment efficiency.
Convenient Operation: It operates fully automatically and informatively, allowing remote monitoring, reducing manual intervention, and facilitating low-cost operation and maintenance.
Treatment Effect
After treatment, the COD of CDOF effluent is ≤400mg/L, color ≤30, with no odor. The COD of biochemical effluent is ≤20mg/L, ammonia nitrogen ≤1mg/L, and total phosphorus ≤0.2mg/L, meeting Surface Water Quality Standards Class III. When combined with BAF for treating garbage leachate concentrated liquid, it can make the treated water quality meet the standards in Table 2 of the "Standards for Pollution Control on the Landfill Site of Household Refuse" (GB16889-2008), i.e., COD < 100mg/L, ammonia nitrogen < 25mg/L, and total nitrogen < 40mg/L.
Application Prospects
With increasing requirements for garbage leachate treatment and increasingly stringent environmental policies, Keli'er Technology's new garbage leachate treatment process centered on CDOF technology has good application prospects in the fields of garbage landfills, garbage incineration plants, and other garbage leachate treatment due to its advantages of high efficiency, stability, low cost, and no secondary pollution. It can effectively solve the problems of traditional treatment processes and provide new ideas and methods for garbage leachate treatment.
