Industrial effluent

Industrial Wastewater

Considering that industrial wastewater causes additional costs in addition to the cost of treating municipal wastewater, the main goal should be to adopt measures that lead to a reduction in additional costs. To achieve this goal, the following measures should be considered.

• Reducing the volume of wastewater
• Reducing the concentration of pollutants
• Uniformizing wastewater
• Neutralizing

Now we will explain each of the above measures in more detail

Reducing the volume of wastewater

The volume of industrial wastewater can generally be reduced by paying attention to the following points.

First point:In many industries, there are at least three types of wastewater with completely different qualities of treatability, which unfortunately are mixed together. One type of this wastewater is cooling water, which is removed from the consumption cycle from the factory for various reasons. In this type of wastewater, the concentration of fine materials is very low, so it can be disposed of without any pre-treatment or entered into the municipal sewage network. (If it does not have a high temperature.) Another type of industrial wastewater is wastewater from process units, which can be very polluted. And the third type is sanitary wastewater, which of course depends on the number of personnel working in that factory. To have an idea of ​​the flow rate of different wastewaters, it is enough to consider the wastewater of a refinery. If about 500 million liters of wastewater are produced in a refinery every day, on average only 20 million liters of this wastewater comes from the process units that must be pre-treated before being discharged into the municipal sewage network due to high pollution. However, due to the lack of separation of different wastewaters, instead of 20 million liters, 500 million liters of wastewater must actually be discharged.

The second point:In many industries, wastewater from one department can be used in another department. Recently, in many industries, the water needed for green spaces is provided from preliminary treatment wastewaters.

The third point:In many cases, the volume of wastewater produced can be significantly reduced by applying scientific principles. For example, in the steel factory of the Mobarakeh Steel Complex; there is a need to wash steel sheets with pure water after the acid washing unit. If the steel sheets are washed in different directions or in reverse (which is currently done), it requires about 30% less water than washing in the same direction.

In general, the volume of industrial wastewater can be reduced by choosing the following methods:

Using different or better quality raw materials, keeping them cleaner and performing preventive maintenance, including:

• Checking pipes for leaks on a daily basis
• Better equipment design
• Choosing processes that produce less wastewater.
• Using water in a closed circuit
• Reducing pollutant concentration

Reducing pollutant concentration can be considered in two concepts.

First, by making changes in the process, we can make the concentration of pollutants lower and more acceptable.

Second, in some industries we have wastewater streams that are very polluted on their own, but if we mix this stream with less polluted streams, the quality of the mixed wastewater will not be a problem in terms of discharge to the municipal sewage network.

Wastewater homogenization

In many industries, the quality of production wastewater varies throughout the day, and the variability of the quality makes it difficult to treat the wastewater. Therefore, it is preferable to homogenize the quality of the wastewater before any treatment. The homogenization of the wastewater will help to stabilize the pH and BOD5 of the wastewater in particular. In some cases, especially when the main problem of the wastewater is its alkalinity or acidity, the homogenization of the wastewater can play the role of pre-treatment if it produces a neutral wastewater.

Neutralization

A necessary condition for the disposal of wastewater to the environment is its appropriate pH. The permissible pH is about 6 to 9. Various methods of achieving this goal include:

• Mixing acidic and basic wastewaters in such a way that the pH is within the permissible range.
• Passing acidic wastewaters through a bed of limestone
• Adjusting the pH of acidic wastewaters with lime water or caustic soda, although the use of caustic soda for large volumes of wastewater is completely uneconomical.
• Adjusting the pH of alkaline wastewater with sulfuric acid
• For pretreatment of industrial wastewater, which depends on the type of wastewater, reference books should be consulted.