Industrial Water Treatment and Clarification

Posted on Oct 12, 2024 in Geology

Industrial Water Treatment

With regard to its use, water can be classified into four main chapters, always from the industrial point of view:

  • Water for general uses
  • Process water
  • Cooling water
  • Boiler feed water

Water for General Purposes

General purpose means all those needs of an industrial plant, which are not specially connected with the production process. Here we must draw:

  • Drinking water for personal use, to be, if necessary, specially treated to eliminate microorganisms, odors, and flavors.
  • Cleaning water that does not normally undergo any treatment, assuming that it is used for the factory premises.
  • Water for irrigation and fire that does not normally have any special treatment, other than in the case of very hard water that can produce scale in sharing lines with a consequent reduction of flow at the time of use.

Process Water

The quality of water required for different processes varies very widely, so it is difficult to define what its characteristics are without knowing in advance the process in question. In any case, it should be noted, as an extreme case, for the most delicate processes, the use of distilled water or equivalent, demineralized water. The possibility of obtaining distilled water currently at relatively low costs has led to the renewal of many processes that have been greatly improved by the use of much higher quality water from a relatively low cost.

Cooling Water

This type of water also must be defined in terms of its characteristics, depending on the cooling processes in which it operates.

  • If abundant, water can be used as a first step in heat exchangers and taken directly to the drainage system.
  • If the abundance of water is less, it may be used in a first step, and then instead of sending it to drainage, it can be utilized for other purposes: process water, boiler water, or other cooler thermal steps. In this second case, it will depend on the processes that then will continue with the water, its treatment, before the cooling water is used as either one or the other.
  • If the water abundance is not as great as it is in most industries today, it is going to the recirculating cooling water, either in open systems by recovery towers, tanks, etc., or closed systems by sharing the water-air. In this case of recirculation, the water is treated so as not to produce serious inconvenience to the channels through which it passes. If cooling towers are used, there should be a decrease in the hardness of water, whichever is higher, and in the case of totally enclosed systems, it may be desirable, even the total demineralization of water use.

Boiler Feed Water

This type of water treatment will be discussed in a separate chapter.

Clarification of Water Treatment

Clarification concerns the elimination of turbidity which normally accompanies water during its journey to the point of consumption.

Natural Sediment

Decanting

Natural sedimentation means primarily the elimination of bulky particles. The settling of these particles starts at the very reservoirs where water is stored in large quantities for distribution or later use. Then, the large deposits of regulation, normally installed between the reservoir and distribution network, are then used to take place in them a natural sedimentation of suspended particles. Finally, special decanters can be used to eliminate, in a more complete way, the particles in suspension.

Sedimentation by Reagents

Coagulants

Coagulants promote flocculation, i.e., the formation of flocs that can precipitate quite readily. However, they do not act entirely on their own but, for their action to be more effective, they need the help of what are called adjuvants, products for good flocculation. Therefore, both products facilitate the deposition of colloidal particles.

The aluminum and iron salts, in principle, meet the conditions required of a good coagulant and are widely used for this purpose, especially aluminum sulfate, iron chloride, and iron sulfate.

Among the interveners, we can distinguish three broad categories:

  1. Their own sludge produced after clotting, i.e., sedimented flocs. The sludge removed from the bottom of the tank can help the formation of new flocs in the entire body of water.
  2. Second-type inorganic adjuvants, such as lime and soda ash. They also act as adjuvants: chloride, magnesium sulfate, clays, silica, activated charcoal, etc.
  3. The third type is composed of organic paste such as starch and sodium alginate.

Flocculators and Decanters

In reactive deposition, two distinct parts can be distinguished: the formation of flocs and their settling. These two operations lead to the existence of flocs and decanters that in some cases are different devices and at other times give rise to facilities while carrying out both operations.

Types of Flocculators

There are two types of flocculators: hydraulic and mechanical.

  • In hydraulic flocculators, the beating of the water is carried out in different ways. The simplest is the production of “eddies” in the raw water through the collation of different types of obstacles in the course of the stream, with a mixing tank’s walls, in which water enters the top of the tank, and its path facilitates flocculation.
  • In mechanical flocculators, the churning of the water occurs through the use of centrifugal pumps introducing the coagulant into the mainstream of water and shaking it through the use of compressed air.

Types of Decanters

The decanters can be:

  • Dynamic type: where decantation is made with the water moving.
  • Static type: where the water remains for some time without circulating.