Producing less sludge

Sludge production generates increasing direct dewatering, transportation and disposal costs. It also means indirect costs related to the disposal of the sludge when it is segregated 

Cutting down on sludge production entails acting either on the mass of DS generated, or especially on the initial concentration, which is often too low. 

Reductions in DS can be achieved by replacing Al or Fe by an organic coagulant in flocculation, if the treatment allows. Another possibility is not to discharge and dilute spent caustic in hard cooling water, where it precipitates carbonate hardness massively. Boosting the concentration is easier to plan and more feasible  

There is often an intermediate layer made up of a water-in-oU emulsion in slop tanks. It is at the root of serious problems and may have a number of causes  

Tlie slop tanlcs can be heated to 40-45 C or a little higher (60°C), except when regulated for safety reasons, and the intermediate emulsion layer can be recycled upflow through a granular coalescer if the layer is not rich in SS. An attempt should also be made to keep naphthenic 

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Membrane processes also offer other advantages over conventional treatments. They reduce the number of unit processes in treatment systems for clarification and disinfection and increase the potential for process automation and plant compactness. Designers also thought membrane plants could be much smaller than conventional plants of the same capacity and, given their modular configuration, could be easily expanded. Additionally, these plants would produce less sludge than conventional plants because they wouldn t use such chemicals as coagulants or polymers. 

The mixture flows to a clarifier—following contact of the wastewater with the sludge in a small tank for a short period of time (20-40 min)—and the sludge is returned to a stabilization tank with a retention time of 4—6 h. This system produces less sludge. 

Alum, Al2(S04)3 18H20 Easy to handle and apply most common produces less sludge than lime pFl range 6.5-7.5 Effective over a hmited pH range adds dissolved sohds to water... 

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