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Wastewater Treatment with Ozone

written by: Jayant R Row • edited by: Rebecca Scudder • updated: 3/17/2011

Ozone is a form of oxygen that readily gives up its additional atom to react with bacteria, molds, and other pollutants to oxidize them and render them less harmful. Wastewater ozone treatment is thus one of the advanced wastewater treatments that is considered worldwide for its effectiveness.

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    What is Ozone?

    wastewater treatment 

    Ozone or O3 is a gas that is highly reactive and is composed of three oxygen atoms. It is naturally formed in the stratospheric region six miles above the earth’s surface, and the layer of ozone can be as much as 20 to 25 miles thick. This ozone is formed by ultraviolet radiation from the sun reacting with atmospheric oxygen. The ozone layer is instrumental in reducing the amount of harmful ultraviolet radiation that reaches the earth. Ultraviolet radiation is dangerous to all forms of life.

    Ozone is also formed on earth by the combination of volatile organic compounds and nitrogen oxides. Both of these are pollutants and the presence of sunlight promotes the formation of ozone.

    Ozone reacts with bacteria, molds, and other pollutants in wastewater and oxidizes them to render them less harmful. It also kills bacteria effectively and oxidizes iron and sulfur, thus allowing these substances to be filtered out of the water. It then reconverts to oxygen and leaves no trace of its usage. There are no residues or odors left after wastewater ozone treatment, which is a much desired result.

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    Ozone generators have a very high demand on power due to the high voltage that is needed to be applied across a dielectric. The energy enables the oxygen molecules to split into atoms and these atoms to combine again to form the three atom ozone. The cost of ozone is also increased if oxygen is used as a starting point. Ozone generators using air cost less, but produce much lower concentrations of oxygen.

    Despite the high cost, many advocates point to the benefits of ozone treatment, as it contains no pollutants and breaks down into oxygen.

    When producing ozone for waste water treatment it is important to use the appropriate ozone equipment, including tools for ozone measurement.

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    Primary Treatment of Wastewater

    Wastewater is normally pretreated by allowing it to pass through a grit chamber. In this chamber the rate of flow is adjusted so that gravitational forces are predominant and allow the sand or grit in the wastewater to settle.

    The wastewater then goes through a primary sedimentation stage in large tanks. Here the sludge settles to the bottom of this tank and is collected in hoppers, where it is pumped out to facilities that can treat the sludge.

    Sludge can be treated by putting it in chambers and allowing anaerobic digestion to take place. This leads to production of biogas, which can be further used as a source of energy. Sludge can also undergo an aerobic process of digestion by allowing aeration of the organic matter in the sludge. Sludge can be converted into compost with the addition of extraneous matter like wood or wood chips, which help to produce heat during the digestion process. This compost can be used to add to improve soil.

    Grease and oil in the wastewater is removed from the floating material. These tanks remove 60 percent of the suspended solids and reduce the BOD or oxygen demand by 35 percent.

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    Wastewater Ozone Treatment is a Form of Advanced Wastewater Treatment

    Using ozone coupled with biological treatment has been known to be a very efficient form of wastewater treatment that is cost effective as well. In such wastewater treatment plants there are four distinct stages of holding; pre-treatment with ozone, biological digestion through aeration, and the final polishing stage using oxidation by ozone.

    In the holding stage the wastewater is macerated with a grinder pump. In this maceration larger solids are broken down so that larger areas are available for reactions with the ozone. Large pieces of organic material are removed as sludge and separately treated as listed above. The tanks in this stage are also used to balance the quantities of wastewater for further stages so that the process proceeds with continuous batches.

    The pre-treatment with ozone is then carried out in the primary ozone treatment tank. Ozone is generated by an ozone generator using oxygen enriched air. The fluid in this tank is continuously circulated through an ozone diffusion system. Tools for measurement of ozone levels are used to monitor activity.

    The wastewater is then transferred to the aeration tank where the water is treated with air to encourage aerobic biological treatment. Biomass is accumulated with microbes that utilize the organic matter in the wastewater to produce additional biomass and carbon dioxide and water. Only a certain portion of the tank’s content is transferred to the subsequent proceeds, thus allowing the biomass helping aerobic digestion to accumulate to proper proportions.

    The polishing, or final process, of wastewater ozone treatment is meant to reduce the biochemical oxygen demand to its lowest level. Ozone is added at predetermined hydraulic rates depending on the condition of the water flowing into this tank. Through continuous circulation dissolved ozone levels are maintained at predesignated levels. After the designed detention time the treated water is released through surface drains into the environment or to any other usage desired. Each tank is connected to the other, and the filling and discharge from the tanks is determined by the high level float in the initial tank.

    Discharged treated wastewater can be used directly for firefighting and other water needs, apart from use as drinking water.

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