Wastewater Water Treatment

Ozone Technology's Pressureless Ozonation Systems are often a highly efficient and cost effective aid in wastewater treatment.

Successful ozonation installations at large municipal wastewater facilities in the USA at El Paso, Denver, San Diego, and Cleveland are causing other U.S. plant operators to consider ozonation for their facilities.

For small wastewater plants that must meet the same EPA standards as larger facilities, ozonation offers an alternative to difficult-to-implement conventional methods such as aeration and activated sludge. And in addition to its disinfection capabilities, ozone is useful for controlling odor at wastewater plants.

Advantages of ozone for wastewater treatment

• More effective than chlorine in destroying viruses and bacteria.
• Needs only a short contact time, typically 10 to 30 minutes.
• Decomposes rapidly, leaving no harmful residuals.
• Following ozonation, no re-growth of microorganisms.
• Eliminates safety problems and expense associated with purchasing, shipping, handling, and storing chemicals, because the ozone is created on-site from ambient air. Chemical additives — primarily chlorine compounds — are the most common means of disinfection in U.S. plants and must be followed by dechlorination to prevent formation of carcinogenic byproducts. (UV disinfection is the most common alternative to chlorination and consumes equivalent energy.) Ozone gas offers more effective destruction of microorganisms than chlorine — without the need to transport and store large volumes of chemicals. And because ozone reverts to oxygen, effluent discharges can be chemical-free.
• Elevates dissolved oxygen concentrations in the effluent, which can eliminate the need for re-aeration and raise dissolved oxygen (DO) levels in the receiving stream.
• Able to remove detergents from municipal wastewaters.
• Enables better regulatory compliance and reduced surcharges because of lower biological oxygen demand (BOD) and chemical oxygen demand (COD) levels prior to discharge.
• When used as a pre-treatment for microbial processes, breaks down residual long-chain organics, usually toxic to microbes, for easier consumption by bacteria.
• Reduces color by oxidizing compounds such as tannins and lignins.
• Removes taste- and odor-causing compounds such as volatile fatty acids, hydrogen sulfides, and ammonia.
• Acts as a microflocculent and enables the physical removal of resulting suspended solids.
• Environmentally friendly. The EPA does not require any record-keeping or reporting of ozone use.

Emerging contaminant (pharmaceuticals, etc.) removal

Recently, micropollutant pharmaceuticals and personal care products (PPCPs), some of which are endocrine disrupting substances, have been found in bodies of water in the USA and Europe. PPCPs include painkillers, antibiotics, antiepileptic drugs, beta-blockers, blood lipid regulators, synthetic hormones, x-ray contrast media, musks, insect repellents, and caffeine. These compounds enter water primarily in sewage effluent, in runoff from confined animal feeding operations, and in leachate from landfills.

Because PPCPs affect aquatic species and possibly threaten human health by contaminating drinking water, research into detecting and removing these compounds is underway. Most experts agree that improving the treatment of wastewater is essential because if PPCPs are treated in wastewater they will have no opportunity to end up in drinking water. Researchers have found that relatively high concentrations of ozone remove antibiotics, betablockers, antiphlogistics, lipid regulator metabolites, carbamazepine, musk fragrances, and estrone in sewage treatment plant effluent.

Ozonation in industrial plants

For industrial users, ozone enables better regulatory compliance, is cost-competitive, and scales up easily. Equipment payback can be achieved within a few years of installation.

Advantages of ozone for wastewater treatment in industrial plants

• Neutralizes toxic byproducts

Industrial wastewater often contains solid and soluble pollutants that are very resistant to aeration and biodegradation. In addition, these contaminant levels are in constant fluctuation from day to day. Ozone can neutralize toxic byproducts such as ammonia, cyanide, and absorbable organic halides while removing organics from water — without the use of chemical additives.

• Disinfects industrial wastewater streams

Industrial wastewaters commonly treated by ozonation include electroplating wastes, waste streams created during electronic chip manufacture, dye-containing textile wastes, petroleum refinery wastewaters, and wastewaters containing rubber additives. Using ozone as part of an AOP can handle even oxidation-resistant biological oxygen demand (BOD) and total organic carbon (TOC).

• Reduces or removes color, taste, and odor

Water appears colored when visible radiation is absorbed by dissolved materials or when light is reflected by suspended solids. Colored wastewaters are found at dye houses, textile concerns, food and beverage processors, slaughterhouses, and other industrial plants. Many wastewater and textile processors are gradually substituting ozone — a more powerful and safer oxidant — in place of chlorine for color removal.

The best results are achieved when wastewater has been pretreated to lower BOD, COD, and suspended solid (SS) values so that the ozone reaction is primarily for color removal. Wastewater is ozonated after it exits from chemical or/and biological pretreatment at a dosage from 50 milligrams per liter to 150 milligrams per liter. At these levels, color can be reduced by 85 to 92%. The dosage simultaneously reduces chemical oxygen demand (COD) by about 40%. (Small increases of BOD, 3 to 7%, may occur.)

Color removal efficiency depends on the ozone dosage, the feed's color values, the wastewater type and temperature, and other water characteristics. Temperatures less than 30°C produce the optimum conditions for ozone solubility. Ozone installations for this application represent a significant capital cost, but offer lower operating expense than conventional treatment using chemical coagulants.

In addition to the cost of chemicals, the coagulant process generates sludge that requires disposal and further expenditures. Generally, the investment for an ozone installation can be paid back in 3 to 5 years, depending on size and other specifications.

• Elevates dissolved oxygen levels in the effluent

The quick decomposition of ozone to oxygen elevates dissolved oxygen levels in the effluent.

• Improves water quality for recycling within the treatment facility

Ozone can improve water quality for recycling within the plant, eliminating the cost of freshwater supplies and fees for noncompliance. Faced with increasingly expensive end-of-the-pipe regulations, some companies have found that ozone can help solve effluent problems within their manufacturing process.

Ozonation can make it possible to recycle water within the manufacturing plant — closing the water loop and achieving zero discharge status — treating all industrial wastewater and using it again within the plant instead of releasing it to the sewer system or to surface water. Amendments to the Clean Water Act even specify zero wastewater discharge. The 1977 regulations initially set a target goal of achieving zero discharge of pollutants to waterways by 1985. In certain industries, such as semiconductor manufacturing, zero discharge is essential. In some world regions, such as the Middle East and Asia, water shortages have made zero discharge a necessity.

• Cyanide and heavy metals removal

Cyanide compounds are used in electroplating and metal treatment. The most common method of cyanide destruction is alkaline chlorination. In this process, solution pH is raised to 10 or 11, chlorine is added, and the solution is allowed to react for 30 to 60 minutes while cyanide is oxidized to cyanate.

There are many concerns about side reactions and unwanted byproducts from the chlorination of cyanide. Known safety issues are associated with handling chlorine gas and chlorine compounds. The ever-increasing concern over chlorinated organic byproducts, which are persistent in the environment and potentially destructive to health, is also a reason to consider alternative treatment.

Ozone can oxidize wastewater that contains cyanide. Because ozonation does not employ chlorine, if the wastewater includes organic substances, trihalomethane is not generated during treatment. Ozonation also removes chemical oxygen demand (COD)-contributing substances. Ozone oxidizes cyanide in an alkaline solution using a ratio of about 3.5 ppm ozone to 1 ppm of cyanide at a pH greater than 9.5, which converts cyanide ions into nitrogen and hydrogen carbonate ions by way of cyanic acid ions. The reaction has the highest oxidation efficiency at a pH between 11 and 12. If the pH is 9.5 or higher, cyanides can be decomposed completely by increasing the amount of ozone used. Small amounts of copper ions or manganese ions can be added as catalysts to accelerate the reaction.

Ozone is also effective for assisting in the decomposition of lead, iron, zinc, cadmium, and nickel.

Other inorganics reactive to ozone include thiocyanate, sulfi te bromide, nitrite, iodide, aluminum, arsenic, cadmium, chromium, cobalt, copper, and manganese.

• Environmentally friendly

Ozone is safe for the environment. The EPA does not require any record-keeping or reporting of ozone use.