Flocculation with inorganic coagulants

There are a number of major, international manufacturers of coagulant and flocculant polymers whose primary markets are high-volume users (i.e., cities, states, and national governments). There are also many smaller regional manufacturers who tend to specialize in niche markets and produce various polymer blends (organic polymers blended with various ratios of inorganic coagulants such as ACH, PAC, and alum). These polymer blends are particularly useful in industrial facilities where process contamination and difficult clarification problems may exist. 

With lower heat-flux ratings and higher ratios of internal water volume to heating surface than is the norm today, complex external treatment was not always necessary where deemed necessary, it was often limited to basic sedimentaion or filtration techniques employing inorganic coagulants and flocculants, typically followed by the use of natural zeolites (see sections 9.2.3.1 and 9.2.5 for additional information). 

The flocculator-flotation cell can be used together in both organic and inorganic coagulation as long as the energy gradients and appropriate residence time are complied with in flocculation. 

Flocculation of petrochemical and pharmaceutical industry effluents may entail the use of up CO 500 mg l" of commercial inorganic coagulant and an intermediate settler with considerable hydroxide sludge production. In contrast, the reduction in COD achieved in this way may go up to 80 or 100, even 130 mg-l ... 

Inorganic chemicals may also be used. Beatonite may be used as a flocculant ia combination with polymer treatmeat. Alum, oace a common coagulant, is less used because its concentration can build up ia recycle water. Alum oftea biads ink to fibers and iacreases the difficulty of deinking. Removal of the very small flexographic ink particles ia process water is difficult. Ultrafiltratioa (qv) has beea proposed for removing these very small dispersed ink particles (53). 

Coagulants may be either organic such as polyelectrolytes or inorganic such as alum. Coagulants can be used alone or in conjunction with flocculants to improve the performance of the flocculant or reduce the quantity oF the flocculant required. In some systems, where a flocculant has been used in an upstream process, a coagulant may be needed to allow additional flocculant to be effective. 

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