Introduction of Conditioner(Dehydrating Agent )
In order to discharge or reuse the wastewater after treatment, a variety of chemicals are required in the wastewater sewage water treatment process.
According to different uses, these agents can be divided into the following categories:
Conditioner(Dehydrating Agent )
Conditioner is also known as dehydrating agent, it is used to regulate the residual sludge before sludge dewatering, and its varieties include some of the above flocculants and coagulant aids.
Types of Sludge Conditioner
Conditioners, also known as dehydrating agents, can be divided into two categories: Inorganic Conditioners and Organic Conditioners.
Inorganic Conditioner is generally applicable to vacuum filtration and plate frame filtration of sludge.
Organic Conditioner is applicable to centrifugal dewatering and belt filter pressing dewatering of sludge.
1. Inorganic Conditioner
The most effective, cheapest and most commonly used inorganic conditioners mainly include Iron Salt and Aluminum Salt.
Iron Salt conditioners mainly include ferric chloride (FeCl3 ·· 6H2O), ferric sulfate (Fe2 (SO4) 3 ·· 4H2O), ferrous sulfate (FeSO4 ·· 7H2O) and polymeric ferric sulfate (PFS) ([Fe2 (OH) n (SO4) 3-n/2] m).
Aluminum Salt conditioners mainly include aluminum sulfate (Al2 (SO4) 3 ·· 18H2O), aluminum chloride (AlCl3), basic aluminum chloride (Al (OH) 2Cl), and polymeric aluminum chloride (PAC) ([Al2 (OH) n ··· Cl6-n] m).
After adding inorganic conditioner, the sludge thickening process can be greatly accelerated, and the filtration dehydration effect can be improved. Moreover, the combination of iron salt and lime can further improve the conditioning effect.
The first disadvantage of adding inorganic conditioner is that the dosage is large. Generally speaking, the dosage should reach 5%~20% of the dry solid weight of sludge, which leads to the increase of filter cake volume; Secondly, the inorganic conditioner itself is corrosive (especially iron salt), and the dosing system should have anti-corrosion performance.
It should be noted that when ferric chloride is used as the conditioner, it will increase the corrosivity to the metal components of the dewatered sludge treatment equipment. Therefore, the anti-corrosion level of the dewatered sludge treatment equipment should be appropriately improved.
2. Organic conditioner
There are many kinds of organic synthetic polymer conditioners, which can be divided into Low Polymerization Degree (molecular weight is about 1000~tens of thousands) and High Polymerization Degree (molecular weight is about hundreds of thousands~millions) according to polymerization degree; According to ionic type, it can be divided into Cationic Type, Anionic Type, Non-ionic Type, Anionic and Cationic Type, etc.
Compared with inorganic conditioner, the dosage of organic conditioner is less, generally 0.1%~0.5% of the weight of dry solid sludge, and it is not corrosive.
The organic conditioner used for sludge conditioning is mainly the flocculant product of high polymerization degree polyacrylamide series, mainly including cationic polyacrylamide, anionic polyacrylamide and non-ionic polyacrylamide.
Among them, cationic polyacrylamide can neutralize the negative charge on the surface of sludge particles and produce bridging effect between particles, which shows strong cohesion. The conditioning effect is significant, but the cost is high. In order to reduce the cost, the cheaper anionic polyacrylamide lime combination method can be used to adsorb the negatively charged flocculant and sludge particles together with the positively charged Ca (OH) 2 floc to form a composite coagulation system.
Relationship between Dehydrating Agent, Conditioning Agent, Flocculant and Coagulant Aid
Dehydrating Agent is the agent added before sludge dewatering, which is also the sludge conditioner. Therefore, the meaning of dehydrating agent and conditioner is the same. The dosage of dehydrating agent or conditioner is generally calculated as the percentage of dry solid weight of sludge.
Flocculants are used to remove suspended solids in sewage and are important agents in the field of water treatment. The dosage of flocculant is generally expressed by the dosage in unit volume of water to be treated.
The dosage of dehydrating agent (conditioner), flocculant and coagulant aid can be called as dosage. The same agent can be used not only as flocculant in sewage treatment, but also as conditioner or dehydrating agent in excess sludge treatment.
Coagulant Aids are called coagulant aids when they are used as flocculant aids in the field of water treatment. The same coagulant aid is generally not called coagulant aids in the treatment of excess sludge, but collectively called conditioner or dehydrating agent.
When using flocculants, because the amount of suspended solids in water is limited after all, in order to achieve full contact between flocculants and suspended particles, mixing and reaction facilities need to be equipped with sufficient time, such as tens of seconds to several minutes for mixing and 15-30 minutes for reaction.
However, the time from adding conditioner to sludge entering the dehydrator during sludge dewatering is usually only tens of seconds, that is, only equivalent to the mixing process of flocculant and no reaction time. Experience also shows that the conditioning effect will decrease with the extension of the stay time.
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