Environmental engineering - Essay Example

Biological removal process including enhanced biological phosphorus removal process. Biological Nutrient Removal (BNR) is a process that removes nitrogen and/or phosphorous from wastewater. It uses microbial technology under different environmental conditions in the overall process (Metcalf and Eddy, 2003).BNR process has two states 1) Nitrification – The conversion (oxidation) of ammonia to nitrate caused by bacteria in the presence of oxygen and 2) Denitrification - The conversion (reduction) of nitrate to nitrogen gas caused by the absence of oxygen.

See figure 1 for BNR process block diagram.Nitrification: The nitrification phase has two main reactions given by:1) Oxidation of ammonia to nitrite by bacteria Nitrosomonas:Ammonia Nitrogen + 1.5 O2  Nitrite + H2O + Loss of alkalinity2) Oxidation of nitrite to nitrate by bacteria Nitrobacter:Nitrite Nitrogen + 0.5O2  Nitrate NitrogenDenitrification: In this process nitrates are reduced to nitrogen gas. Note that oxidation occurs in the presence of organic matter, so nitrate acts an electron acceptor in the absence of free oxygen.

The chemical reaction in this phase can be represented as:Nitrate Nitrogen + Organic Matter  Nitrogen Gas + Gain of alkalinity Figure 1: It shows BNR process block diagram.There are severals mechanisms to remove nitrogen from wastewater, such as: The precipitation of ammonia in the form of MgNH4PHO4 (MAP) through the addition of phosphoric acid and magnesium oxide is called MAP process. In this process the pH value is critical in the precipitation of MAP.

It has 90% efficiencies (Siegrist, 1996). This is a physico-chemical process.When the pH of wastewater is maintained to 10 is easy to convert NH4+ to free ammonia. Then, an air stream is used to capture NH3 and it is absorbed in a solution with sulphuric acid to form (NH4)2SO4. It has 97% efficiency, (Siegrist, 1996). This is a physico-chemical process called air stripping process.In the stem tripping process is used water steam in order to capture ammonia by condensation (Siegrist, 1996).Finally, biological phosphorus removal technique offer advantages over chemical processes, reduced energy consummation and reduce sludge production (Park, 1999).

This method is justified because phosphorus exists in several forms in wastewater: orthophosphate, polyphosphate and organic phosphates. Note that phosphorus comes from human excrement and detergents presents in domestic wastewater. Enhanced Biological Phosphorous Removal process is described by two states:1. There are some microorganisms that without oxygen and nitrates (anaerobic atmosphere), assimilate and store fermentation products produced by other facultative bacteria. The microorganisms derive energy for this assimilation from polyphosphates organisms, which are hydrolyzed to liberate energy.

The free phosphorus that results from the hydrolysis reaction is released to the mixed liquor (Sankaramanchi, 2010). 2. In the following anoxic or aerobic phase these same microorganisms, consume both phosphorus and oxygen to metabolize the previously stored substrate for energy production and cell synthesis. The organisms take up the phosphorus in excess. The phosphorus is removed from the system during the normal sludge wasting procedure (Sankaramanchi, 2010).Nowadays, there still exists controversy about real consensus for modeling the EBPRS process (Baetens 2001).

References:Baetens D., 2001 “Enhanced Biological Phosphorous Removal: Modelling and Experimenal Design” PhD Thesis. Universiteit Gent.Park J. K. and G Novotny, (1999) “Biological Phosphorous Removal Potential Test”. Research Report 179.Sankaramanchi S., 2010 “Biological Treatment and the ABJ process” http://www.sanitaire.com/pdf/TechInfo/section-Process.pdf [Accessed online 23 Nov 2010]Siegrist, H. (1996) Nitrogen removal from digester supernatant-Comparison of chemical and biological methods. Wat. Sci. Tech. Vol 34 (1-2), 399-406.