At present, the problems existing in sludge disposal methods have brought a heavy burden to sewage treatment. Sludge disposal has developed from a unit of sewage treatment in the past to an important link that must be given priority in the design and operation of sewage treatment plants. Sludge treatment will enter the stage of reduction after the stage of harmless and resource development.
Sludge produced by papermaking wastewater treatment is a big problem, because the sludge output of papermaking wastewater treatment system is greater than other wastewater.
The characteristics of papermaking sludge are as follows:
1. The water content is generally high. For example, the water content of paper mill sludge after gravity concentration in sludge concentration tank is about 97% ~ 98%. A large number of sludge with high water content produced in the process of papermaking wastewater treatment must be dehydrated as much as possible before final disposal to improve the solid content for further treatment.
2. High fiber content. Compared with sludge produced by treating other sewage, it has better dewatering performance and less flocculant consumption.
3. The amount of mud is large. According to the parameters of a paper mill, the influent SS is 2 100 ~ 4400 mg/L, and CODcr is1700 ~ 4800 mg/L; The effluent SS is15 ~ 40 mg/L, and CODcr is 70 ~100 mg/L. 。
The sludge produced by general papermaking wastewater treatment is divided into two parts: 1. Pulp discharged from the workshop; 2. Residual sludge of biochemical treatment system.
The destination of papermaking sludge can have three directions:
1. Papermaking sludge can be reused in the papermaking workshop.
Papermaking wastewater contains a lot of fiber. In the process of wastewater treatment, some fibers will remain in the sludge, so it can be reused after treatment. It should be noted at this time that biochemical sludge cannot be reused. The treatment process is as follows: the sludge is screened to remove sand, and then pumped into a paper machine to make paper. Due to the fine fibers in the sludge, the quality of paper may decline during the recycling process, and the paper machine is easy to break. It is best to use a low-speed recycling paper machine to make low-grade corrugated paper.
Secondly, paper-making sludge can be treated by pressure filtration.
In the treatment process, sludge conditioning is generally carried out first, and then filter pressing is carried out.
The pulp fiber content discharged from sludge workshop is high, and adding proper amount of polyacrylamide before entering the belt filter press can achieve good dewatering effect. Appropriate amount of polyaluminum chloride and ferric chloride are added to the sludge discharged from the biochemical treatment system. According to the situation, it is used in combination with polyacrylamide. Ordinary paper mills will mix the two kinds of sludge.
Physicochemical sludge containing fiber and excess sludge generated by biochemical treatment system during pretreatment are gravity concentrated in sludge concentration tank, dewatered by belt filter press, and then transported for disposal. The supernatant of the sludge concentration tank and the filtrate of the sludge filter press are discharged into the factory sewage collection system. After treatment, a large amount of sludge produced by papermaking wastewater will turn waste into treasure if it can be used reasonably.
First of all, papermaking sludge needs to be treated by sludge concentration tank. Sludge concentration is a process of increasing sludge concentration through gravity sedimentation. With the increase of sludge concentration, the utilization rate of flocculant will be improved accordingly, but the sludge transportation pipeline should be prevented from being blocked due to the high sludge concentration.
Before mechanical dehydration, it is necessary to chemically condition the sludge by adding flocculant to make the sludge form the best floc. Different papermaking processes produce different types of sludge, so it is necessary to add different types of flocculants. Commonly used inorganic flocculants include aluminum sulfate, polyaluminum chloride, ferric chloride and polymeric ferric sulfate. The commonly used polymer flocculant is mainly polyacrylamide. When inorganic flocculant is used alone, because the floc formed is small and the mechanical strength is low, the sludge will leak with the filtrate when it is squeezed by the filter belt, and the dewatering effect is poor and the sludge recovery rate is low. Cationic polyacrylamide alone can achieve better sludge dewatering effect, but the cost is higher. Therefore, if inorganic flocculant is combined with organic polymer flocculant, better effect can be achieved and the cost of sludge dewatering can be reduced. The type and dosage of flocculant can be determined by experimental methods.
After chemical treatment, sludge must be mechanically dehydrated. Because the operating cost and post-treatment cost of sludge dewatering account for a large proportion of the whole sewage treatment cost, it is very important to choose energy-saving and efficient dewatering equipment. Comparatively speaking, the belt filter press dehydrator has the advantages of less investment, automatic control, continuous operation, low energy consumption, high dehydration efficiency, easy management, low maintenance cost, low noise and less dosage of chemicals. Therefore, belt filter press is recommended for dewatering equipment. The filter pressing process of the belt filter press is that the sludge first passes through the gravity dewatering area, then passes through the pressure dewatering area, and finally passes through the pressure dewatering area. After three steps, a relatively dry mud cake is produced.
According to the data provided by a paper mill, the water content of paper-making sludge is reduced to 75% ~ 85% after filter pressing by belt filter press.
At this time, the mud cake was shipped abroad for final disposal.
Third, paper sludge can be burned.
In the final disposal of sludge, the appropriate sludge utilization scheme can be selected according to the local actual situation, and the sludge utilization should meet the strict environmental hygiene standards and cannot cause new environmental hazards. Incineration can be chosen, which can not only recover heat, but also reduce the area where garbage is piled up.
Because of the large amount of sludge produced by papermaking wastewater treatment, it is of great significance to choose reasonable treatment and utilization methods for enterprise and environmental development.
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