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Technical System Overview


View EnviroServer ES Data Sheet

The design of the EnviroServer ES and SM Model is based on well-known engineering principles in the wastewater field applied in a new way. The system can be described as a hybrid fixed film-suspended growth extended aeration wastewater treatment system with a two stage biological process to optimize denitrification.

The EnviroServer removes nitrogen using biological processes, such as ammonification followed by nitrification and denitrification. In ammonification, organic nitrogen (proteins and peptides) is decomposed to ammonia or ammonium ions. About 80% of the ammonification take place in the sewer lines before the wastewater enters the EnviroServer and the balance is ammonified in the first compartment. The ammonification is followed by nitrification. In nitrification, ammonia is removed biologically by a two-step process in which the ammonia is oxidized to nitrite, and the nitrite is oxidized to nitrate according to the following formulas3, 8, 13:

NH3 + O2 + CO2 + HCO3- + Microbes ==> New Microbes + NO2- + H+ +H2O

NO2- + O2 + CO2 + HCO3- + Microbes ==> New Microbes + NO3-


The nitrification is affected by temperature, pH, dissolved oxygen (DO), alkalinity, contact time, and mean cell residence time4, 6, 13. The temperature and pH are not specifically controlled in the EnviroServer. The temperature is normally kept between 70 to 90F by the microbial activity and some added heat from the air compressor. The pH is typically between 7 and 8.5 in the EnviroServer, since no chemicals are added to any of the compartments. Therefore, both the temperature and the pH fall well within the optimum range for nitrification.

An air compressor continuously supplies air to the two aerobic compartments in the tank to keep the dissolved oxygen above 3 mg/l. The conversion of ammonia to nitrates requires 4.57 kg of oxygen per kg of ammonia converted12, 15, 16. Furthermore, it requires about 7 mg of carbonate alkalinity per mg of ammonia nitrogen8. Typically, the alkalinity concentration in the tap water is enough to convert all the ammonia to nitrates, but in some cases an alkalinity source has to be added.

Nitrate formed during nitrification is removed by heterotrophic organisms under anaerobic conditions through conversion to gaseous nitrogen species through denitrification13, 15, 16. In this process, nitrate first is reduced to nitrite and then to nitric oxide (NO), followed by nitrous oxide (N2O) and nitrogen gas (N2). This process requires a carbon source4. In the EnviroServer, the wastewater exiting the two-stage aerobic section, which is high in nitrates and low in carbon, is recirculated back to the first anaerobic compartment where it mixes with the raw wastewater, which is high in carbon. Denitrification requires 5-6 mg of BOD per mg of Nitrate-Nitrogen removed, and it produces about 3 mg of carbonate alkalinity per mg of Nitrate-Nitrogen removed.

The biodegradable organic carbon, that causes CBOD5, is converted to carbon dioxide and settleable biomass by heterotrophic organisms13. These microorganisms require oxygen. The process is referred to as aerobic digestion and can be expressed by the following equation7, 12:

Microbes
Organic Matter + O2 + Nutrients ==> New Microbes + CO2 + H2O


The aerobic digestion takes place in the second compartment of the EnviroServer. The EnviroServer utilizes a combination of an attached and suspended growth process. The attached film is growing on a biomedia and the suspended growth is created by mixing and recirculation of sludge. This combination results in a treatment efficiency that exceeds the individual performance of an attached or suspended growth process.

The aerobic digestion of organic matter is mainly affected by dissolved oxygen, pH, temperature, mixing, and solids retention time. The design of the EnviroServer optimizes these parameters for maximum CBOD5 and nitrogen removal5, 6, 7, 10.

The fourth compartment is the clarifier where final settling of suspended solids and clarification of the effluent is taking place. The tank design is optimized with respect to the following parameters: waste water flow rate, sludge settling rate, sludge removal, surface area, tank depth, overflow rate, inlet device, and tank configuration9. It is designed for optimum performance without any chemical addition. The settled solids are recirculated back to the first compartment.

The fourth compartment is followed by a small effluent storage compartment which can be equipped with an optional gravity flow UV disinfection unit. UV-disinfection is especially recommended for shallow dispersal fields. The final chamber also serves as a reservoir for water re-use, such as irrigation.




References


3. "Design of Municipal Wastewater Treatment Plants Volume I", WEF Manual of Practice No. 8/ASCE Manual and Report on Engineering Practice No. 76 (1992).

4. "Design of Municipal Wastewater Treatment Plants Volume II", WEF Manual of Practice No. 8/ASCE Manual and Report on Engineering Practice No. 76 (1992).

5. "Operation of Municipal Wastewater Treatment Plants Volume I", Manual of Practice No. 11 Fifth Ed., WEF (1996).

6. "Operation of Municipal Wastewater Treatment Plants Volume II", Manual of Practice No. 11 Fifth Ed., WEF (1996).

7. "Operation of Municipal Wastewater Treatment Plants Volume III", Manual of Practice No. 11 Fifth Ed., WEF (1996).

8. "Nutrient Control", Manual of Practice No. FD-7, Water Pollution Control Federation, Washington, D.C. (1983).

9. "Clarifier Design", Manual of Practice FD-8, Water Pollution Control Federation, Washington, D.C. (1985).

10. "Wastewater Biology: The Microlife", A Special Publication, WEF, Alexandria, Virginia (1990).

11. "Water Reuse", Manual of Practice SM-3, Second Ed., Water Pollution Control Federation, Alexandria, Virginia (1989).

12. "Aeration", WEF Manual of Practice FD-13/ASCE Manuals and Reports on Engineering Practice No. 63 (1996).

13. "Wastewater Biology: The Life Process", A Special Publication, WEF, Alexandria, Virginia (1994).

14. "Treatment Process Digest", Water Environment Federation Digest Series, WEF, Alexandria, Virginia (1993).

15. "Wastewater Disinfection", Manual of Practice FD-10, WEF, Alexandria, Virginia (1996).

16. "Comparison of UV Irradiation to Chlorination: Guidance for Achieving Optimal UV Performance", Project 91-WWD-1, Water Environment Research Foundation, Alexandria, Virginia (1995).
17. "Wastewater Engineering: Treatment, Disposal, Reuse", Third Edition, Metcalf and Eddy, Inc. (1991).




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