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Extra Ways to Clean Up Your Facility’s Wastewater

Aug. 29, 2022
Using the right kind of “polishing” technique can help increase the effectiveness of a pretreatment program and keep wastewater in spec for its ultimate purpose, whether reuse or disposal.

Pretreating wastewater is usually an expensive proposition, requiring installation of an elaborate system. Some not-so-expensive steps can help make pretreatment more effective.

Cleaning up wastewater before you throw it away may sound paradoxical, but it’s the purpose of industrial water treatment plants. Bioreactors, settling ponds and other methods remove sludge from wastewater and reduce its chemical/biochemical oxygen demand (COD/BOD) loads and other components. The purpose is to get the wastewater into a condition where it can be partially reused within the plant and/or meets local environmental regulations for disposal.

Certain kinds of supplemental treatment can enhance wastewater cleanup. These “polishing steps” can make a pretreatment system more effective at a relatively low additional cost, or even make more wastewater available for reuse.

Suez’s line of analyzers can determine total organic compounds in wastewater in the lab, in the field or on the line.

“By adding polishing steps such as UV or ozone, which avoid additional chemicals, wastewater can meet more stringent discharge permits or be reused on site to offset water usage,” says Amanda Tyndall, a product manager for Suez.

These kinds of treatments can meet different goals, says Thomas Peacock Sr., an industry technical consultant for the Nalco Water unit of Ecolab.

“In some cases, treatment is used to oxidize or destroy odor-causing molecules,” Peacock says. “In other circumstances, treatment can disinfect water intended for reuse. As an example, water reused for agriculture irrigation needs to meet specific pathogen and bacteria conditions, and these methods would help treat the water to meet those requirements.”

In most food and beverage applications, the primary target will be organic (i.e., carbon-based) substances of various kinds. These have the most potential to pollute, both directly and indirectly, by feeding algae and other forms of life that can use up oxygen and destroy the ecological balance of a body of water. That’s why organic substances are an important metric in wastewater quality.

“Considering most food and beverage ingredients (flavors, dyes, sugars, proteins, etc.) are organic compounds, and incoming source water contains both natural organic matter and synthetic organic contaminants, measuring organic levels of the water used across sites is a simple and comprehensive way to assess quality, cleanliness and deviations,” Tyndall says.

Ultraviolet (UV) treatment is one of the most common supplemental disinfection methods, used to treat incoming process or wash water as well as wastewater. UV is effective at killing microorganisms because it penetrates their cell walls, destroying their ability to reproduce.

UV treatment systems come in contact and non-contact versions. The contact type, which is more common, comprises mercury lamps in quartz sleeves (to minimize heat transfer) immersed in the wastewater. In the non-contact version, the lamps are positioned over a transparent conduit that carries the wastewater flow. Non-contact versions use less energy but are suitable only for applications where the water is relatively clear, with total suspended solids (TSS) below 30 mg/liter.

Ancillary treatment systems like this polymer activation system can give a final “polishing step” to wastewater. Photo: Nalco/Ecolab

A big advantage of UV treatment is that it’s a non-chemical method, which removes the need to store and handle toxic substances like chlorine. UV systems have a relatively small footprint, and they can keep wastewater flowing relatively quickly, requiring only 20 to 30 seconds of exposure for disinfection. On the downside, they’re not as effective as some chemical methods, due to the tendency of some microorganisms to repair themselves in a process known as “photo reactivation.” The lamps also have to be cleaned regularly to prevent fouling.

Ozone treatment

Ozone is another ancillary treatment method that serves as an alternative to chemicals. It’s most often used in the food industry to treat incoming process water, but also is an option for wastewater treatment.

Ozone is a gas formed when oxygen is exposed to electric current, with a molecule that consists of three oxygen atoms instead of the two of regular oxygen gas. It quickly oxidizes anything exposed to it, which gives it antimicrobial potential as well as the ability to neutralize other potential pollutants.

“Specific to wastewater, ozone treatment is often combined with hydrogen peroxide to destroy volatile organics through a process called advanced oxidation, which is used to break down toxic containments, such as benzene, toluene or other substances, into non-toxic material,” Peacock says.

Because ozone gas is unstable, it has to be generated at the time and place where it is used. Some manufacturers have portable units that can manufacture ozone wherever needed. Evoqua Water Technologies, for instance, offers a trolley-mounted unit that can provide ozonated water from ambient air and electricity.

Such a unit helped a fish processing plant in Norway deal with an outbreak of listeria. Not only did the Evoqua ozone generator alleviate the problem, it reduced the plant’s “fishy” odors by attacking the extracellular polysaccharides that formed sticky, smelly biofilms on floors and other surfaces.

Chlorination and wastewater

Chlorination is a more common disinfection method, and is the most common of all chemical methods. It’s more often used to treat incoming water, but has a place in wastewater treatment also.

“In specific instances, food processors may use break-point chlorination to convert ammonia nitrogen directly into nitrogen gas to remove it from the wastewater,” Peacock says.

Chlorination is arguably the easiest, cheapest way to treat wastewater. The potential problem is that in excessive amounts, it can lead to contamination and rejection of the wastewater by the local municipal treatment facility. This problem is especially difficult because determining the right amount of chlorine to treat wastewater is not a straightforward matter of the chemical-to-water ratio; it depends on what’s in the water.

While chlorine can convert ammonia nitrogen into nitrogen gas, it also reacts with nitrogen to form chloramine, a solution that persists in the water (as opposed to straight chlorine, which dissipates quickly when exposed to air). Some municipal wastewater operations deal with this situation by dechlorinating the water before discharge, but this may not be practical for a smaller private system. An alternative is to use chlorine dioxide, a gas that does not form chloramines.

The Trasar system from the Nalco Water unit of Ecolab can continuously monitor wastewater and adjust chemical treatment in real time.

In situations like that, it can be helpful to continually monitor the wastewater stream to determine the right ratio of chlorine, ozone or other treatment chemicals, at any given moment. Monitoring can also be helpful for UV treatment, which depends on an unencumbered path between the light source and the microorganisms it is targeting. Keeping track of the wastewater’s total suspended solids (TSS) in real time can help the system determine how intense the UV exposure needs to be.

“Many ozone and UV installations monitor influent organic levels to properly dose to achieve the target quality goals, so maintaining an O3 [ozone]/TOC ratio or UV/TOC ratio are critical to success of the treatment,” Tyndall says.

As part of its 3D Trasar wastewater treatment system, Nalco offers continual remote monitoring with “smart dose technology” to adjust treatment chemical doses in response to changing wastewater conditions.Pretreating wastewater is a tricky challenge that often requires adjustment on the fly. Using the right kind of “polishing” technique can help increase the effectiveness of a pretreatment program and keep wastewater in spec for its ultimate purpose, whether reuse or disposal.

About the Author

Pan Demetrakakes | Senior Editor

Pan has written about the food and beverage industry for more than 25 years. His areas of coverage have included formulations, processing, packaging, marketing and retailing. Pan worked for Food Processing Magazine for six years in the 1990s, where he was operations editor (his current role), touring dozens of food plants of every description. He has also worked for Packaging and Food & Beverage Packaging magazines, the latter as chief editor, during which he won three ASBPE awards. He is a graduate of Stanford University with a BA in communications.

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