The removal of nitrogen and ...

The removal of nitrogen and phosphorus from wastewater has become an emerging worldwide concern because these compounds cause eutrophication in natural water.

ammonia removal,  phosphorus  removal, activated sludge plant, extended aeration, municipal  wastewater . Nitrogen appears in  wastewater  as ammonia , ni- trite, nitrate and organic nitrogen. In a second step, nitrate is converted to gaseous nitrogen and is removed from the  wastewater .

Nitrifying organisms are present in almost all aerobic biological treatment processes, but usually their numbers are limited, depending on the mean cell residence time (because of the threshold effect) and on the BOD5/N ratio. In most conventional activated-sludge processes, with a BOD5/N ratio of 3, the fraction of nitrifying organisms is estimated to be considerably less than 0.083, while for BOD5/N ratios of 5 to 9, the estimated percentage is between 0.054 and 0.029.

An activated sludge process is commonly used in wastewater treatment, but it is often the case that the effluent from wastewater treatment plants has remaining phosphorus and nitrogen in the form of ammonium and/or nitrate. A post-treatment process is therefore required to remove nitrogen and phosphorus from the effluent. However, because such effluents contain only small amounts of organic compounds, a carbon source must be added to remove the nitrogen.

The conventional methods for post-treatment denitrification often employ methanol for the removal of nitrate . Although methanol does achieve a high rate of denitrification, there are concerns about the risks posed by treatment-plant outflow containing excessive amounts of organic carbon and its flammability. In practice, wastewater treatment managers hope to minimize post-treatment operation and maintenance costs. Therefore, post-treatment technologies that will enable the use of waste materials such as municipal refuse, agro-industrial residues, and wood waste are desired. In a previous study, nitrate was successfully removal from synthetic wastewater in a bioreactor packed with wood as an organic carbon source under anoxic conditions. Interestingly, the denitrification efficiency was assumed to enhance sulfur denitrification via wood degradation by sulfate reduction

Sulfate-reducing bacteria can use wood chips or animal manure as electron donors and carbon sources and then use various types of organic substances .The sulfate-reducing bacteria Desulfovibrio sp. CMX have been used to remove nitrogen oxide (NO) in iron/ethylenediaminetetraacetic acid (FeEDTA) solutions. Yücel et al.  reported that sulfate reduction (i.e., sulfide production) occurs in degrading wood in marine environments. Sulfate-reducing bacteria seem to play an important role in nitrogen removal with wood. On the other hand, ferrous ions generated by iron polarization are known to combine with phosphate to produce vivianite and other ferrous phosphates, and thereby remove phosphorus [8]. Till et al. demonstrated that steel wool was effective at removing nitrogen in autotrophic denitrifying bacteria. However, iron corrosion is enhanced under oxic conditions and under high nitrate conditions. For this reason, the addition of another electron donor is useful to support the corrosion resistance. We therefore hypothesized that a bioreactor packed with iron and wood could remove nitrogen and phosphorus simultaneously over a long-term operation. And indeed, our earlier study showed that both denitrification and phosphate removal occurred in a bioreactor filled with synthetic wastewater and packed with iron and wood and allowed to react over a long-term.