Reading guidance：1. Background With the sewage treatment plant of our country gradually increased with the sewage treatment technology development, sewage generated in the treatment process of sludge also gradually inc

1. Background
     With the sewage treatment plant of our country gradually increased with the sewage treatment technology development, sewage generated in the treatment process of sludge also gradually increased, at present, many waste water treatment plant will still sludge random Sinotrans, simple landfill or stacked, the waste organic matter content and water content are very high, easily rotten, to the environment caused damage.
   Sludge treatment and disposal are many ways, such as composting, incineration and so on. This paper introduces the principle and method of sludge drying, solidification and sterilization by adding calcium.
2. Basic principle 
   The sludge and fine lime are evenly mixed, and the moisture content in the lime and sludge is as follows:
 1kgcao+0.32kgh2o->1.32kgca(oh)2+1177kj
 According to this reaction, each adding 1 kg of calcium oxide 0.32 water is combined with a calcium hydroxide and the reaction heat can be evaporated to about 0.5 kilograms of water.
 Lime reacts with water to produce calcium hydroxide, continue to produce further reaction with other substances in the sludge, such as generating reaction of compound calcium hydroxide and carbon dioxide (CO2): 1.32kgca(oh)2+0.78kgco2=1.78kgcaco3+0.32kgh2o+2212kj
This reaction will further increase the total amount of solid matter, heat evaporation part of the water, and then increase the solids content of sludge treatment.
Cao, also with amorphous silicate calcium hydroxide (SiO2) or alumina (Al2O3) reaction.
These main chemical reactions produce the following results:
1. due to the role of the Ca (OH) 2, the pH value of the sludge was increased,
2. the temperature of sludge was increased due to the exothermic reaction,
3. free water is formed in the reaction product, and a part of free water is evaporated at the same time as a result of the exothermic reaction.
Final result:
1.  further dehydration, water content by dehydration of 80%-85% to 20% to 65% (according to the lime dosage dependent)
2. sterilization, temperature and pH increase can play a role in sterilization, thereby ensuring the health and safety of the use or disposal process;
3. passivation of heavy metal ions, adding a certain amount of calcium oxide to make the sludge into an alkaline, can be combined with some metal ions in the sludge to form harmless compounds to achieve the effect of passivation of heavy metal ions.
4. modification and granulation, so as to improve the storage and transportation conditions, avoid the two fly ash, leakage of leachate; Because the water is evaporated, so, although the system added to the lime, but the total amount of the final results of the system is not significant.
3. Utilization and disposal of sludge and calcium after sterilization
3.1 summary
     Figure 1 Summary of various treatment and utilization of sludge treatment and utilization. For different disposal and utilization of the way, a brief description as follows.
3.2 agriculture, afforestation, forestry and land restoration
    For low heavy metal content of the sludge, after adding calcium disinfection of sludge (also at the same time, mixed with a certain amount of structural material for, such as straw, rice straw, sawdust, etc.) for agriculture, greening, forestry and land rehabilitation. This method of Western Europe, North America more applications.
3.3 sanitary landfill
     Sewage treatment plant from the filter press sludge water rate is about 80%, usually containing a large number of microorganisms and bacteria, and the sludge volume and nature is very unstable, such as direct sanitary landfill is not in conformity with the requirements, meet the humid and rainy season sludge is very likely to occur on a large scale expansion and produce large amounts of harmful liquid leakage serious pollution to the environment.
    After treatment with calcium solidify, sludge moisture rate can be reduced to below 60%, the exothermic reaction of lime and water killed most of the microbial and bacteria, the passivation of the most of the heavy metal ions, after the treatment of sludge was granular and properties are very stable, the sludge volume rule is easy to transport, save a large number of intermediate costs.
3.4 incineration
   Sludge incineration of secondary and calcium treatment, the sludge water content could drop to below 60%, can be mixed with calcium at the same time to join part of combustible garbage increase the combustion heat value, the treated sludge had a higher ratio (conventional power plant fuel/sludge), section about a large number of incineration and transportation cost. At the same time, sludge containing alkaline calcium, beneficial in flue gas desulfurization treatment.
3.5 sludge treatment of two calcium treatment applied to building materials
The mining of clay resources, has seriously affected agricultural production, soil environmental protection. Therefore, if the use of sludge containing the ash as a substitute for clay production building materials, not only turning waste into treasure to solve problem of sludge pollution, and sludge resource reasonable use, also can alleviate the contradiction of building materials industry and agriculture contend for the soil. The calcium and dry processing sludge, moisture removal and stabilization after granulation, are manufactured into a sludge bricks by sintering, floor tile, made of concrete filler, instead of partial cement; or as a raw material for cement production instead.
4. Key technology and process
    Sludge and calcium treatment process is the key to the sludge and lime effective mixing and how to realize the low running costs (i.e., low power consumption, low consumption of Cao) and sludge with good physical form is mixed technology key. Traditional mechanical stirring mixing technology can not satisfy the requirement.
   The original treatment device is to add calcium powder in the worm conveyor, the material is mainly through the push process, so it is difficult to achieve the improvement of sludge characteristics.
   Sludge is generally thick, dense material, modern sludge mixing equipment with mechanical drive fluid bed process, through a plow shovel turning throwing function sludge scattered and loose state and calcium oxide in the fully mixed.
   Sludge is generally thick, dense material, modern sludge mixing equipment with mechanical drive fluid bed process, through a plow shovel turning throwing function sludge scattered and loose state and calcium oxide in the fully mixed.
Figure 2 is used for sludge mixed loedige Ronaldo fluidized bed reactor digger mechanical drive schematic.
1. Calcium oxide dosing system
2. Mixing reaction system
3. Sludge conveying system
  In many cases, it can also be mixed with a variety of materials, such as when dealing with sludge landfill, can add fly ash and a small amount of cement, to save costs and increase the hardness, granulation effect.
5. Application
   Sludge dehydration and calcium in Western Europe and North America have a long history, has in sludge treatment and disposal still adopt a method, such as Washington sewage treatment plant every day more than 1000 tons (2005 data) of sludge after calcium plus disinfection for agriculture, forestry and land restoration. Following the introduction of Germany a sludge and calcium process oriented application.
5.1 disposal aims
  System design and implementation in order to adapt to the flexibility of sludge treatment and disposal, considering the future of different application models, respectively.
1. Sludge adding calcium disposal technology can be used for sterilization and agricultural field.
2. Used for incineration
3. Landfill
5.2 processes
Main processes:
1. adding lime to the mechanical action of a fluid bed reactor
2. mechanical type: loedige high efficiency mixer
3. lime: fine lime, >90% content of Cao
4. the solid content of the inlet sludge of the mixer: about 23%
5. the solids content of the mixer outlet sludge: can be freely selected between 23 and x%
6. sludge structure: can be adjusted according to the use
5.3 disposal device
  Stored in the silo lime by conveying screw conveyor to the middle of the storage tank, the storage tank and lime dosing device supporting. Metering and feeding device is arranged in the middle of the tank has two functions: formed stable lime material column ensure lime continue to transport into the feeding device, once the system starts immediately can provide lime.
5.4 intermediate storage of sludge
In view of the sludge and calcium has a further reaction process, so after calcium treatment sludge should be a certain amount of time.
Table 1: the temperature, pH value and solid content of sludge treated with calcium

 6. Summary
     Along with our country to increase the intensity of urban sewage treatment, sludge has become an urgent problems to be solved. On sludge dehydration of and calcium treatment can achieve semi drying, curing and sterilization role. In application in agriculture, forestry, sanitary landfill, incineration, building materials, such as the final disposal way before, a stable treatment effect, reduce the pollution of the environment, reduce the cost of processing etc. effect, sludge treatment in a effective treatment method.
    Sludge and calcium treatment of the key lies in the mixed reaction of high efficiency, low energy consumption. Through the reasonable processing parameters and optimization can be in very small amounts of calcium oxide consumption to achieve sludge sterilization and sludge modification, convenient storage and transportation, by appropriate to increase the calcium content, can be flexible to achieve a variety of disposal and utilization ways of pretreatment, reached the semi dry and curing effect.
 
 
 
 
 
 
 
 
 
 
 

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