Wastewater treatment plants are usually designed keeping in mind the need to reduce organic and suspended solids loads and limit pollution of the environment. Furthermore, any metals which may have entered waste streams are unlikely to degrade naturally and are highly toxic to aquatic life, even in very low concentrations.
Most wastewater treatment processes consist of various combinations of physical, chemical, and biological operations to remove pollutants such as organic matter and nutrients from water. They may also aim to reduce heavy metals, partially to ensure compliance with applicable regulations. A final step of disinfection which is intended to remove pathogens is sometimes included as a precaution.
Industrial effluent treatment plants exist to treat the wastewater produced specifically from industrial processes. These plants may have the effect of reducing raw water costs by way ofusing various water treatment technologies to convert selected wastewaters into what is known as reclaimed water which can be used for various purposes.
Wastewater may be recycled for use in agriculture. The most appropriate treatment to be applied to the wastewater before it may be used for these purposes, is the one which will ensure that the water meets all the recommended microbiological and chemical quality guidelines while keeping input and operational costs low. Another important consideration lies in the costs of maintaining the industrial filtration system. In many contexts it may be better to design the recycling system for low-qualityinput water, rather than relying on costly treatment processes that will raise the input quality but increase costs beyond acceptable levels.
Disinfection of Water
Disinfection normally involves the use of chlorine, but in more affluent process streams, may also encompass ultra violet (UV) treatments, especially in commercial water filters. Where chlorine is used, dosage is dependent upon the type and characteristics of the wastewater. Dosages of 5-15mg per litre are most often used. In order to meet the requirements for advanced wastewater treatment, the contact time for the chlorine may reach up to 120 minutes. This is common for reclaimed wastewater that is intended for specific irrigation uses. The disinfectant effects of chlorine are largely dependent upon the pH, together with the length of contact time, the organic content, and finally the effluent temperature. Ozone irradiation is another possible method of disinfection but is not currently in common use in industrial filters.