Zero discharge of electroplating wastewater Sludge after wastewater treatment
The dilemma of sludge treatment and disposal of urban sewage treatment plants in China is that the output is large, the composition is complex, most of the sludge treatment is unstable, harmless, and easy to cause secondary pollution. Industry insiders acknowledge that sludge treatment is a continuation of sewage treatment. If the sludge is not effectively treated, the sewage treatment is actually only 70% or even 50% completed. If the sludge is not reduced, with the current sludge production in China, if it is piled up, it needs to be piled up 5 meters high on 10000 mu of land every year.
The sludge output per 10000 cubic meters of sewage treatment (calculated by 80% of water content) is generally about 5 tons to 10 tons. The specific output depends on the influent water quality, sewage and sludge treatment process and other factors. With the increase of water volume and the upgrading of sewage treatment plants, it is estimated that China's sludge production will exceed 60 million tons (80% of water content) in 2020. In the face of the current dilemma of sludge treatment and disposal, there is an urgent need to reduce, harmless and recycle sludge, reduce sludge production from the source, and improve sludge treatment and disposal capacity. The Ten Water Rules issued four years ago clearly promoted sludge treatment and disposal, stipulating that sludge produced by sewage treatment facilities should be stable, harmless and recycled.
Calculated according to the cost of sewage treatment of domestic large-scale sewage treatment plants, 0.3-0.45 yuan/t, accounting for about 35% - 50% of the treatment cost. Different from the policy guidance focusing on investment planning in previous years, it is expected that a comprehensive charging mechanism will be gradually established in the next few years to incorporate sludge treatment into social costs. At present, sludge treatment methods are based on the dual characteristics of large output and low organic content, mainly including concentration, conditioning, dehydration, stabilization, drying, especially concentration, conditioning and dehydration. After nearly four years of efforts, China has formed four mainstream technology routes: deep dehydration+landfill technology (transition), dry incineration+landfill/reuse, aerobic fermentation+land use, anaerobic digestion+drying+land use.
According to different conditions of the sludge plant, different technologies and processes are adopted to scientifically and effectively treat and dispose the sludge. Among them, after sludge incineration, the utilization of building materials, such as gray bricks and cement, has realized the recycling of sludge treatment, which is a relatively safe and stable way out. However, due to increasingly strict agricultural access permit and unstable supply of surrounding auxiliary materials, it is unlikely that dewatered sludge will be used for agriculture. Land use mainly considers greening and other aspects, which need to pay attention to the balance of production and sales.
From the perspective of disposal, there are two ways to realize recycling - entering land or building materials, such as incineration or landfill. In general, drying+incineration is the ideal solution for sludge treatment in China at present, and its important link mainly lies in the selection of sludge dewatering and incineration facilities. In the future planning and construction, the treatment process should be selected on the basis of fully considering the disposal route to achieve the reduction, harmless, stable and recycling of sludge. Then, the new sewage treatment plant should consider building stable and reducing facilities at the same time.
