Every process industry uses water for a variety of tasks and produces effluent water as a byproduct that requires treatment. Treatment is required regardless of whether or not the effluent will be returned to a stream or lake, if it will undergo further processing at a wastewater treatment facility, or if it will be reused in another process.

Figure 1. More stringent regulations and growing awareness of water as a scarce and valuable resource are driving investments by process industries — such as this refinery — in effluent treatment monitoring and control.The reuse option is increasingly viable as water’s economic value rises. In many instances, reused water can reduce costs by lowering water consumption charges, by cutting the volume of water headed for effluent disposal and by lowering overall energy costs.

Although process water traditionally may have been viewed as an inexpensive commodity, rising environmental awareness and increasingly restrictive regulations have lifted water’s importance not only among plant managers but with C-level executives. More than ever before, water is considered a key factor of production. And as such, it needs to be monitored, controlled and in many instances conserved.

An essential part of production

Regardless of the industry, water treatment is essential for processes such as heating, cooling, cleaning and rinsing, among other industrial applications. Poor water treatment allows impurities that are inherent in source water to interact with pipes and equipment.

After its use, water typically exits the facility as effluent. Water quality issues figure prominently here too, as regulations and operating permits govern discharge standards. Effluent water typically is tested and treated for chloride, fluoride, sulphide, sulphate, nutrients, organic load and total organic compounds and electrochemical parameters. Constant, online monitoring is increasingly the operating standard for process manufacturers. Permitted discharge levels can be narrow; even brief excursions from allowed effluent ranges can trigger monetary fines and other regulatory penalties.

Focus on treatment challenges

Disposing of wastewater from an industrial plant is an increasingly complex and costly challenge. Of growing interest is zero liquid discharge (ZLD), which has the goal of removing all liquid waste from an industrial process system. As a class, ZLD technologies aim to economically reduce wastewater and produce clean water that is suitable for reuse. In practice, ZLD systems use advanced wastewater treatment technologies to purify and recycle virtually all of the wastewater produced.

To be sure, challenges around ZLD are demanding. The cost associated with treating this waste stream for reuse can be substantial, and often includes the cost of new facilities as well as instrumentation for monitoring.

Even so, the technology is spreading rapidly from developed countries in North America and Europe to emerging economies such as China and India.

Early adopters in North America were electric power plants, particularly in water-scarce parts of the United States. Roughly three-fourths of all ZLD technology deployments in the 1970s were in power plants in the desert Southwest and California.

In China, new power plants and chemical plants must include ZLD water treatment technology as a result of government directives. And in India, water reuse and ZLD requirements are being introduced for power producers and refineries.

Early ZLD systems were based on stand-alone thermal processes, where wastewater was typically evaporated in a brine concentrator followed by a brine crystallizer or an evaporation pond. The condensed distillate water was collected for reuse, and solids that were produced either were sent to a landfill or recovered as salt byproducts.

A ZLD system produces a solid residue that is made up largely of precipitate salts, which need to be transferred to a solid waste disposal facility, such as a landfill. Toxicity and other tests will determine the type of landfill that can handle the ultimate disposal of the solid residue.

Since their introduction decades ago, the breadth of ZLD systems has grown to include less complex and low-technology solutions, such as natural treatment systems, to highly complex and advanced technologies.

ZLD systems typically include:

• Combination thermal process with ZLD
• Mechanical and thermal evaporation ZLD
• Enhanced membrane and thermal ZLD
• Evaporation ponds
• Wind-aided intensified evaporation (WAIV)
• Dewvaporation
• Salt solidification and sequestration

Technologies used in conventional ZLD systems include evaporators and brine crystallizers. These separate dissolved salts from the water and tend to be relatively complex and energy intensive.

Monitoring for regulatory compliance

Wastewater treatment monitoring is critical to optimize chemical usage and to help prevent corrosion, among other benefits.

As one example, the activated sludge process for wastewater treatment requires a steady supply of oxygen to function effectively. Insufficient oxygen slows down organisms, makes facultative organisms less efficient and favors production of foul-smelling intermediate products. Since this process constitutes roughly 70% of the wastewater plant’s energy costs, precise monitoring and control of oxygen enables effective and efficient processes.

In wastewater with high organic loads, a facility may use chemical treatment and physical processing to reduce load levels either for re-use or discharge into the environment. Efficient management typically involves biological oxygen demand. However, because the test takes several days to produce results, surrogates such as chemical oxygen demand (COD), total organic carbons (TOC) and spectral absorption coefficient may be used. These offer faster test results, potentially reducing operational and maintenance costs. COD is a relatively simple lab procedure, and reduces testing time to as little as two hours. Online TOC monitoring continuously observes for real-time control.

A trusted partner

For more than 80 years, Hach has provided instrumentation and chemistries to make water analysis faster, simpler, greener and more informative than before.

Hach has been an industry leader in developing innovative solutions to help manage water efficiently and accurately. Hach solutions are in service worldwide and can be found in industries that range from municipal drinking water and wastewater to food, beverage, power, chemicals and refineries, along with every other category that touches water.

Hach is also leading the industry into a new era of data-driven decision making with their Water Intelligence System, Claros^TM. Claros connects instrumentation and software to help water professionals collect, visualize and analyze data to drive efficiencies and ensure compliance. Solutions range from data and instrument management to a variety of process management modules to support an array of parameters and process areas.

Hach also has a global service and support network to back the products they sell and maximize instrument and data dependability regardless of location. Hach is ready to provide the calibration, preventive maintenance, and repair services where and when needed.