Anoxic treatment

There is — in addition to the use of nitrate for control of anaerobic conditions in sewers — a potential for anoxic treatment in terms of removal of organic matter. The anoxic treatment is an alternative to aerobic treatment. An advantage is that the addition of nitrate is simple compared with the injection of oxygen. However, a NUR value that is of the same order of magnitude as the actual OUR value—compared in units of electrons transferred—is crucial to obtain a relatively high removal rate of organic matter. For this and other reasons it is important to compare aerobic and anoxic transformations (cf. Example 5.5). 

The decay of proteins and amino acids in phytoplankton cultures, under oxic and anoxic conditions, indicated very little selectivity (Nguyen and Harvey, 1997). However, 15 to 95% of the total particulate amino acid pool consisted of polypeptides/proteins in anoxic treatments versus 8 to 65% in oxic conditions. The similarity of particulate amino acid composition during phytoplankton decay agrees with other work in the Delaware Bay estuary (USA), which showed similar composition in the dissolved combined amino acid (DCAA) pool (Keil and Kirchman, 1993). 

The concept of anoxic treatment is simple, and is the same for any anoxic gas used. It consists, essentially, of the following three steps ... 

Figure 3. Colonies formed on Yeast Mannitol Agar plates by Sinorhizobium meliloti 41 (B) and aniA-mutant strain (A). Cells were plated after 70 h anoxic treatment.

Meade et al. [24] reported the responses of heat and oxygen flux to varying levels of environmental oxygen for the Australian crayfish Che rax quadricarinatus. When crayfish were exposed to p y2 values less than approximately 5 kPa, both heat dissipation and oxygen uptake were depressed. However, the depression of heat dissipation was only transient, and it recovered to normoxic values within 4 h, which suggested some form of metabolic compensation. CR ratios at or below the critical Pq2 were not determined, so the quantitative contribution of anaerobic pathways to any compensation could not be estimated. These juvenile crayfish were incapable of surviving a 1-2 h anoxic treatment at 28"C. 

The constructed wetland with the aerobic tank and anaerobic/anoxic tank connected in series was employed for the treatment of raw municipal wastewater. More than 94% of the initial BOD and 80% of the initial T-N could be removed. Successful biological nitrification was... 

Confirmation of the diagnosis with an ECG is necessary in order to determine appropriate treatment. ECG reveals no organized, recognizable QRS complexes. If treatment is not initiated within a few minutes, death will occur, or at best, resuscitation of the patient with permanent anoxic brain injury. 

Canto and colleagues52 operated an integrated anoxic-aerobic treatment of wastewaters from a synthetic resin producing factory (Figure 19.9). These authors managed to treat up to 2.01 kg/m3 d COD and up to 0.93 kg/m3 d TKN with removal efficiencies of 80 to 95% and 58 to 93% for COD and TKN, respectively. 

Canto, M., Gomez, J., Kennes, C., and Veiga, M.C., Integrated anoxic-aerobic treatment of wastewaters from a synthetic resin producing factory, European Conference on New Advances in Biological Nitrogen and Phosphorus Removal for Municipal or Industrial Wastewaters, Narbonne, France, October 12-14,1998. 

Idil AA, Betul HG, Jens-Ejbye S (2008) Advanced oxidation of acid and reactive dyes effect of Fenton treatment on aerobic, anoxic and anaerobic processes. Dyes Pigm 78 117-130... 

Panswad T, Iamsamer K, Anotai J (2001) Comparison of dye wastewater treatment by normal and anoxic+anaerobic-aerobic SBR activated sludge process. Water Sci Technol 43 355-362... 

Anox An integrated water treatment process for removing organic contaminants. The energy is obtained by burning the biogas generated in the process, which contains approximately 70 percent methane. Developed by W. D. Evers a demonstration plant was built in France in 1979. 

Abdul-Talib, S., T. H vitved-Jacobsen, J. Vollertsen, and Z. Ujang (2001), Anoxic transformations of wastewater organic matter in sewers — process kinetics, model concept and wastewater treatment potential, Proceedings from the 2nd International Conference on Interactions between Sewers, Treatment Plants and Receiving Waters in Urban Areas (INTERURBAII), Lisbon, Portugal, February 19-22, 2001, pp. 53-60. 

The microbial activity of wastewater under anoxic conditions is lower compared with aerobic conditions (Abdul-Talib et al., 2001). This is important to consider, because a low nitrate uptake rate (NUR) compared with the oxygen uptake rate (OUR) in units of electron equivalents means a reduced transformation rate of the most biodegradable fractions of the organic matter. As mentioned under the point on injection of air, this may have implications in terms of treatment. Furthermore, a relatively low NUR value also has operational advantages because of a reduced demand for nitrate to suppress sulfide formation. 

A biosensor for nitrite [24] was recently proposed for monitoring nitrite concentration in activated sludge exposed to oxic/anoxic cycles. The biosensor contains bacteria reducing only N02 into N20, which is subsequently monitored by a built-in electrochemical sensor. Up to 90% of the response is obtained in about 1 min, and the detection limit is around 5 mg L1, a concentration sufficient for treatment process monitoring. Unfortunately, the maximum operational lifetime of the N02 biosensor is 6 weeks and some problems may occur with time. 

Richards DJ, Shieh WK. 1989. Anoxic-oxic activated-sludge treatment of cyanides and phenols. Biotechnol Bioeng 33 32-38. 

Methods developed for treatment of landfill leachates can be classified as physical, chemical and biological, which are usually used in combinations in order to improve the treatment efficiency. Biological treatment methods used for the leachate treatment can be classified as aerobic, anaerobic and anoxic processes which are... 

When considering the type of treatment strategy to adopt, it is generally advisable for a multi-barrier system to be installed this will enable different kinds of conventional and persistent compounds (PhCs) to be removed or eliminated by different steps. In fact, different chemicals require different operational conditions (aerobic, anoxic, anaerobic ones) to be efficiently removed from the water phase. 

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