Comparison of seven sludge treatment and disposal process technologies
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The main current processes for sludge treatment and disposal include: 1. Anaerobic fermentation of sludge; 2. Aerobic composting of sludge; 3. Incineration of sludge for power generation; 4. Sanitary landfilling of sludge; 5. Drying in rotary kilns; 6. Secondary pressure filtration using plate and frame filters; 7. Stabilization using curing agents. Below, the author will explain in detail the core technical characteristics of each of these processes for your reference. I. Anaerobic fermentation of sludge: three anaerobic stages – hydrolysis, fermentation, and methanogenesis. The first stage of hydrolysis involves converting particulate matter into soluble compounds; the second stage is fermentation, whose final product is a precursor to methane formation; the third stage is methane production, where acetotrophic bacteria split acetate and methanotrophic bacteria produce methane. Disadvantages: 1. High investment, high operating costs, and security issues. 2. Preheating the sludge requires a large amount of thermal energy, which cannot meet its own needs. 3. A large amount of biogas residue is generated, which requires further treatment. 4. Methane gas is difficult to integrate into municipal pipeline networks for use. 5. It cannot operate in the northern regions during winter. 6. Safety hazards, and it occupies a large area. There are currently over 50 such companies in the country, of which 29 have ceased operations. II. Aerobic composting of sludge: Straw and other supplementary materials are used to reduce the moisture content of the sludge to 60%, increasing the void space to achieve the specified CN ratio; oxygen is continuously supplied, and after 25–30 days of fermentation, humus is formed. Once stabilized, it can be used for landscaping and land improvement purposes. The main types include: natural composting, closed-system composting, drum composting, and vertical multi-layer composting. Disadvantages: 1. The quality of the sludge is unstable, and heavy metals within it are difficult to stabilize; it can only be used as fertilizer for landscaping. 2. The composting process generates large amounts of foul odors, contaminating the surrounding environment. 3. A large amount of additives such as straw are added, along with continuous oxygen supply; the operating cost is over 200 yuan per ton. III. The core equipment for sludge incineration for power generation is the incinerator; its main structure is tower-shaped, with a perforated plate at the bottom on which heat-carrying sand is placed to form a combustion bed. The interior of the tower is lined with refractory materials. Gas is introduced from the bottom, and once the sludge enters, it burns in a state of bubbling fluidization. Disadvantages: 1. High investment, severe corrosion of the boiler, and high maintenance costs. 2. Sludge with an moisture content of 80% has a low calorific value, which requires a large amount of energy for incineration; burning 1 ton of such sludge consumes 70 Kg of standard coal, resulting in operating costs that are 300–400 yuan per ton higher. 3. It has a significant impact on exhaust emissions, and is prone to producing harmful gases such as dioxins. IV. Sanitary landfilling of sludge is mainly carried out in China by mixing it with waste; the construction of landfill sites costs 50–60 yuan per ton. This method can contaminate water sources and the atmosphere, requires large amounts of land, poses safety risks. Moreover, land resources available for landfilling in China are currently limited, so there will soon be no viable options for sludge disposal. V. Rotary kiln drying: Utilizes energy sources such as coal or natural gas to dry and dehydrate sludge. Disadvantages: 1. High energy consumption, with operating costs of over 300 yuan per ton. 2. High-temperature drying can easily produce odors. 3. Strict dust control requirements are needed during the drying process, posing safety hazards. VI. Secondary plate and frame filtration dilutes the sludge by about 90%; after adding chemicals, secondary filtration is carried out. Disadvantages: 1. The moisture content can only be adjusted between 75% and 65%. 2. A large amount of chemicals are added to increase the dry basis weight of the sludge, resulting in higher operating costs of 180 yuan per ton. 3. The limitations of sludge reuse increase. VII. Curing agents: Lime and other curing agents are added to the original sludge, where they undergo a chemical reaction with the sludge to release large amounts of heat, thereby reducing its moisture content. Disadvantages: 1. The addition of large amounts of lime and aluminum-based materials increases the sludge volume. 2. The sludge cannot be reused and can only be landfilled. 3. Operating costs are relatively high, at 130–150 yuan per ton. At present, it is difficult to meet the requirements for sludge treatment and disposal relying on a single process. For different regions and different types of sludge, it is a relatively ideal approach to consider factors such as climate, regional characteristics, and site conditions, and to combine various treatment processes skillfully in order to achieve the best results. When choosing sludge treatment process technologies, there is no best option – only the most suitable one
The HIROS technology enables the rapid resource utilization of sludge. The HIROS (High-rate Recovery of Organic Solid-wastes) technology enables the rapid resource recovery of organic solid wastes such as sludge. This technology employs a process that combines preliminary oxidation with subsequent reduction. First, the readily biodegradable organic substances in the sludge—such as sugars, fats, and proteins—are hydrolyzed and oxidized, thereby reducing their volume and rendering them harmless; at the same time, energy is released for reuse in the process. Next, the more difficult-to-degrade substances like lignin and cellulose are reduced to highly adsorbent materials, which, together with the substances obtained through the hydrolysis and oxidation of the readily biodegradable organic substances, are used to create high-quality organic fertilizers or fertilizer bases, thus enabling resource recycling. The entire processing process takes place continuously within a closed reactor system. Electric heating is used as the heat source to start up the system, and the heat generated by the reaction itself is utilized fully during the processing to reduce the energy consumption of the entire system. Impurities or harmful substances present in the feed are also removed during the process (such as various types of microorganisms, heavy metals, etc.), and no other secondary pollutants are generated during the manufacturing process. It takes only one hour for organic waste to be transformed into valuable products once it enters the system. The processing capacity of the equipment can be customized as needed; typically, the processing capacity of a single unit ranges from 50 tons per day to 500 tons per day. The recycled products obtained through this treatment possess high water absorption and retention capabilities; when applied to soil, they help to improve the slow-release of nitrogen, phosphorus, and potassium (NPK) in the soil, as well as enhance its aeration, heat insulation properties, and particle stability. The product can be used directly as high-quality organic fertilizer, and it can also be employed for various purposes such as preventing pollution from agricultural non-point sources, addressing soil compaction and infertility, restoring vegetation, combating desertification, conserving water and soil, and other ecological protection efforts.