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The coagulant is a type of chemicals mainly including the inorganic coagulant and the high polymer flocculant. Among the inorganic coagulant, the aluminum salt and the ferric salt has been most widely used. Besides, the other regular inorganic coagulant such as the aluminum sulfate, the aluminum chloride, the ferric sulfate and the ferric chloride, and the inorganic high polymer flocculant such as the poly aluminum chloride (PAC), the poly ferric sulfate (PAS) and other inorganic high polymer flocculants also have been used in the urban sewage treatment applications.
According to the research report and the current existing practical applications, these kinds of inorganic coagulants above mentioned can all achieve roughly the same purification effect under the appropriate dosage and the suitable coagulation reaction conditions. It can also achieve the satisfied application effect by using the aluminum salt and the ferric salt together. The lime itself has the coagulating function, if using the lime with the ferric salt along with the suitable PH value, it can achieve the better removal effect.
From the operation situation of the sewage treatment plants in the recent 10 years, the advanced countries mostly choose the ferric chloride plus the lime to be used as the enhanced primary coagulant in the treatment, that is likely because of the lower cost of the dosage, the compact flocculants and the good settlement performance. The use of the lime can help to achieve the better comprehensive application effect than the use of the aluminum salt in the alkaline condition, furthermore, the dewatering performance to the sludge by using the lime is also better than the the use of the aluminum salt. Besides, the physical sludge generated from the treatment by the ferric salt can generally be subjected to the anaerobic digestion treatment after being merged with the biochemical sludge. The treatment effect of the municipal waste water by using the Poly Aluminum (PAC), the Polymeric ferric sulfate (PFS) and the Poly Ferric Chloride Aluminate (PFCA) is also satisfied, therefore it is popular and widely used in our country, however, with the comprehensive consideration of the treatment cost, it may not be the best choice in practical.
The characteristics of the coagulant
1. The compact flocs with the less dosage
2. The high water purification after the treatment
3. The wide PH value application
4. The enhanced dewatering effect to the sewage by the outstanding filtration and dehydration performance
The function of the coagulant product
1. The clarification and the purification effect
2. The sedimentation promotion effect
3. The filtration promotion effect
The dosage of the coagulant
The larger and dense flocs reflect the better coagulating and flocculating effect. The dosage of the coagulatant normally has a best value, it is not the more the better, the excess adding of the coagulant will increase the turbidity of the water. This best value can be achieved by the trial test, and then in the practical application it is increased slightly. The proposed optimum dosage of the coagulant treatment PAM is 0.05 ~ 0.4 gram per ton.
The organic high polymer anionic flocculant
The anionic flocculant is a type of the Polyacrylamide, it is of organic high polymer which can help precipitate the impurities in the waste water, it is also called as a coagulant, or the similar name as the organic high polymer coagulant.
What is the flocculant? The flocculant is used to improve the speed and the efficiency of the the settlement, the clarification,the filtration, the floatation and the centrigugal separation process etc. The flocculation process is the formation of the aggregates (the flocs or the alum) of the huge amount of the separate particles suspending in the liquid.
The flocculating process is also the process of the coagulating, it will generate a large amount of the alum or the flocs in the water, the alom or the flocs will float in the upper part of the water or settle to the bottom due to theirs different density.
The ordinary sewage / waste water, especially the electroplating waste water, the drinking water, the swimming pool water, the paper making plant sewage and the sanding washing waste water etc, could all be treated by the anionic flocculant as the precipitation agent.
Strictly speaking, as the organic high polymer most of the flocculants figures high molecular weight, and have the specific electrical features (or as the inionc features) and the charge density (or as the ion degree).
According to the statistics from a lot of experiments, the anionic flocculant is suitable for the flocculating of the inorganic suspending matter, and the treatment of the relatively simple and normal sewage.
The anionic flocculant is often used as the purifying agent, and at the same time it also has the thickening, the water retention and the other functions, which could be used in various industries. The aninoic flocculant and the cationic flocculant are both widely used as the water purifying agent. The organic high polymer flocculant has the anionic type, the cationic type and the nonionic type, not only just one type the anionic type.
How to configure and make up the anionic floculant solution
1. Make the water treatment flocculant into the solution, the appropriate concentration is from 0.05% to 0.1%.
2. Configure the flocculant solution
The most important and critical key point in compounding the flocculant solution is to prevent the degradation of the macro molecular, it is required to focus on the points as below:
1) Do not use high speed stirring, do not do long time stirring
2) Avoid the contact with the iron
3) Lowder the solubility temperature, such as 50 degree to 60 degree or blow
4) Use the clean soft water, do not use the cloudy water or the water with the rust or the high hardness water
5) The dissolution process should be completed in one time, that is to be dissolved directly to the desired concentration, do not make the high concentration solution first and then make the dilution.
6) The dissolving device should be round shaped without the dead angle. The dissolving process of the high molecular weight high polymer flocculant is fairly slow. The powder absorb the moisture first, swell and then gradually spread out. In the beginning of the process, the solution is not uniform, it needs to be stirred for a while till the concentration consistency get achieved. It is required the qualified equipment and the operation, otherwise it will take longer time to complete this process.
In the practical application, the dissolving process could be operated in the afternoon, and then the solution could be used in the next morning. One point needs to be remarked, that is the concentration of the flocculant solution should be lower, such as 0.1%, the concentration should not exeeed 0.3%.