Industrial water treatment

There are many uses of water in industry and,in most cases, the used water also needs treatment to render it fit for re-use or disposal. Raw water entering an industrial plant often needs treatment to meet tight quality specifications to be of use in specific industrial processes. Industrial water treatment encompasses all these aspects which include industrial wastewater treatment, boiler water treatment and cooling water treatment.

Overview

Water treatment is used to optimize most water-based industrial processes, such as heating, cooling, processing, cleaning, and rinsing so that operating costs and risks are reduced. Poor water treatment lets water interact with the surfaces of pipes and vessels which contain it. Steam boilers can scale up or corrode, and these deposits will mean more fuel is needed to heat the same amount of water. Cooling towers can also scale up and corrode, but left untreated, the warm, dirty water they can contain will encourage bacteria to grow, and Legionnaires' disease can be the fatal consequence. Water treatment is also used to improve the quality of water contacting the manufactured product e.g. semiconductors, and/or can be part of the product e.g. beverages, pharmaceuticals, etc. In these instances, poor water treatment can cause defective products.

In many cases, effluent water from one process can be suitable for reuse in another process if given suitable treatment. This can reduce costs by lowering charges for water consumption, reduce the costs of effluent disposal because of reduced volume and lower energy costs due to the recovery of heat in recycled wastewater.

Objectives

Industrial water treatment seeks to manage four main problem areas: scaling, corrosion, microbiological activity and disposal of residual wastewater. Boilers do not have many problems with microbes as the high temperatures prevent their growth.

Scaling occurs when the chemistry and temperature conditions are such that the dissolved mineral salts in the water are caused to precipitate and form solid deposits. These can be mobile, like a fine silt, or can build up in layers on the metal surfaces of the systems. Scale is a problem because it insulates and heat exchange becomes less efficient as the scale thickens, which wastes energy. Scale also narrows pipe widths and therefore increases the energy used in pumping the water through the pipes.

Corrosion occurs when the parent metal oxidises (as iron rusts, for example) and gradually the integrity of the plant equipment is compromised. The corrosion products can cause similar problems to scale, but corrosion can also lead to leaks, which in a pressurised system can lead to catastrophic failures.

Microbes can thrive in untreated cooling water, which is warm and sometimes full of organic nutrients as wet cooling towers are very efficient air scrubbers. Dust, flies, grass, fungal spores, and others collect in the water and create a sort of "microbial soup" if not treated with biocides. Most outbreaks of the deadly Legionnaires' Disease have been traced to unmanaged cooling towers, and the UK has had stringent Health & Safety guidelines concerning cooling tower operations for many years as have had governmental agencies in other countries.

Disposal of residual industrial wastewaters

Disposal of residual wastewaters^[1] from an industrial plant is a difficult and costly problem. Most petroleum refineries, chemical and petrochemical plants ^[2] have onsite facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the local and/or national regulations regarding disposal of wastewaters into community treatment plants or into rivers, lakes or oceans.

Technologies

Advancements in water treatment technology have affected all areas of industrial water treatment. Although mechanical filtration, such as reverse osmosis, is widely employed to filter contaminants, other technologies including the use of ozone generators, wastewater evaporation, and bioremediation are also able to address the challenges of industrial water treatment.^[3]

Newer technologies, such as electrodeionization, have further reduced the ionic contaminants of industrial feed water to the parts per billion (ppb) levels for use in industries such as semiconductor manufacturing, power generation (high-pressure steam boilers), pharmaceutical manufacturing, medical (water for injection - WFI), laboratories, and other general industrial processes where ultrapure water is needed; for example, the boilers in power generation require very low levels of Silica (SiO2) which passes through traditional technologies such as Reverse Osmosis, however is removed to ppb levels by electrodeionization modules. This is why electrodeionization is often referred to as an industrial polishing technology.

Electrodeionization (EDI) is a process by which an electric field is used to remove ions and polar species from an aqueous stream. EDI is used with reverse osmosis to replace ion exchange resin-mixed beds, which require onsite or offsite chemical regeneration.^[4]

Ozone treatment is a process in which ozone gas is injected into waste streams as a means to reduce or eliminate the need for water treatment chemicals or sanitizers that may be hazardous, including chlorine.

Ultraviolet irradiation

Ultraviolet (UV) disinfection technology has been a common water treatment technology in the past two decades due to its ability to provide disinfected water without the use of harmful chemicals. The UV-C portion represents wavelengths from 200 nm - 280 nm which is used for disinfection. UV-C photons penetrate cells and damage the nucleic acid, rendering them incapable of reproduction, or microbiologically inactive.^[5]

Process Water Treatment Technology

Process water is water that is used in a variety of manufacturing operations, such as: coating and plating; rinsing and spraying; washing and etc. Municipal and ground water often contain dissolved minerals which make it unsuitable for these processes because it would affect product quality and/or increase manufacturing costs. A proper incoming water treatment system can remedy these issues and create the right water conditions for specific industrial processes.^[6]