For wastewater, because the impurities are very fine and suspend, thus if finally need sludge dewatering to reuse water, it must add chemicals. Here mainly refers to coagulant. It is very important to choose a right coagulant for a wastewater filter press. Because it not only directly affects the filtering performance, also decide the dewatering efficiency. In Chinese market, generally there are two types: inorganic and polymer.
Inorganic coagulants popularly has two types: iron salts and aluminum salts. The flocs formed by iron salts are more dense, so needs less dosage. Especially for the regulation of activated sludge, its coagulation effect is basically equivalent to polymeric coagulant, but it is highly corrosive and difficult to store and transport. Normally when the usage of iron salt is large, lime will needed to adjust pH value. The flocs formed by aluminum salt coagulant are features of low density, high dosage, weak corrosion and convenient storage and transportation. In general, inorganic coagulants are cheap and easy to get, but there might cause big amount of slag, and it’s greatly affected by the pH value. After treatment by inorganic coagulant, the sludge quantity and the proportion of inorganic components will increases, but the combustion value will decreases.
The main characteristics of polymer coagulant is lower consumption than inorganic coagulants, and is much safer to handle and easier to operate. After dissolved in the water, it appears very weak acid / alkaline, and has less corrosive. Using it, the quantity of filter cake increased little. If the filter cake finally want to be used as fuel, it help generates high heat and burns less ashes. So different coagulants have different characteristics and functions, and it is important to choose appropriate coagulants.