Ecology Report Example: The Removal of Nitrogen from Wastewater

1.0 Introduction

The removal of nitrogen from wastewater has increasingly become important because phosphorous and nitrogen are the main elements that promote the growth of organic which is known to cause eutrophication. The discovery of methods to reduce and prevent accumulation of nitrogen in wastewater treatment plans has resulted in increase of quality of water in water bodies globally.

1.1 Significance of Nitrogen Removal from Wastewater

Nitrogen in wastewater mainly exists in the form of ammonia which is difficult to precipitate. Accumulation of ammonia in water bodies promotes the growth of alga blooms which exhaust oxygen hence risking the life of aquatic organisms. Also, alga blooms block sunlight from reaching aquatic plants which is significant to their growth. importantly, they produce toxic elements that promote bacterial growth which poses health risk to people who consume the water.

Drinking water with nitrogen is risky to health especially to pregnant women and children. High amounts of nitrogen compounds cause methemoglobinemia syndrome which reduces the ability of blood to transport oxygen in the body. The presence of nitrates in drinking water is a major concern particularly in agricultural areas where drinking water is obtained from groundwater sources. Although nitrogen exists in many forms, ammonia, nitrate (NO2), and nitrate (NO3) are most threatening in the environment (Henze p 25). Nitrate and nitrite are available naturally after ammonia from decomposing organic materials undergoes oxidation to form nitrite and nitrate. However, there are other sources of nitrite and nitrate including atmospheric deposition, sewage and septic systems, fertilizers, and animal wastes.

2.0 Background Information Nitrogen compounds from land sources are deposited in groundwater sources faster than other elements such as phosphorous. This is due to the fact that nitrogen compounds are more soluble than phosphates which bond well with soil particles. Due to this reason, nitrates are used as an indicator of the likelihood of a sewage source pollution during dry weather. Water polluted with nitrogen compounds has low nitrate levels when tested. This is attributed to the fact that decomposition of the compounds reduces the level of dissolved oxygen which consequently lowers the rate of oxidation of ammonia to nitrite (NO2) and nitrate (NO3) (Schmidt p 485). In such conditions, it is advisable to monitor the levels of nitrites which are considered more harmful to aquatic organisms than nitrates.

2.1 Modified Ludzack-Ettinger Process

In this experiment, Modified Ludzack-Ettinger Process will be used to remove nitrogen from wastewater. The technique entails the modification of commonly activated sludge process whereby an anoxic region is added upstream of the aerobic zone. Typically, the process utilizes an internal recycler that transports nitrates generated in the nitrification process to the aerobic zone together with the fluid to be added into the anoxic zone. Studies have shown that the quantity of nitrogen removed in the anoxic zone is dependent on the availability of influent of BOD and the recycle flow. Nitrogen is removed as the influent is recycled from the membrane tank to the anoxic tank. In order to determine the amount of nitrogen removed, a HACH spectrophotometer kit is used using volunteering programs.

Volunteer monitoring programs typically comprise of two methods including the nitrate electrode and the cadmium reduction method. In this experiment, the cadmium reduction method was used. The method produces a color reaction which was then measured by a spectrophotometer. The cadmium reduction method is a colorimetric method which entails contact between nitrate in the sample tested and cadmium particles. The contact results in the conversion if nitrates to nitrites. Then, spectrophotometer was used to measure the red color by comparing with a scale in mg per liter which increases with the increase in color hue. A spectrophotometer determines the quantity of light absorbed by the sample under treatment at a 543-nanometer wavelength. Through the use of a standard curve, the absorbance value will be equated to concentration of nitrate.

The use of this method requires that the samples used are clear. For turbid samples, they should be filtered through a 0.45micron filter which should be nitrate-free. The presence of metals (copper, iron, or others) increases the reaction time by slowing down the rate of reaction. The reagents used are prepared for different ranges based on the concentration of nitrate in the effluent.

2.2 Procedure

Before the start of the sampling process, all safety considerations were met, supplies checked and weather conditions noted. The apparatus used in the experiment included:

Field spectrophotometer with sample tubes

Reagent powder to turn the color of water to red

Distilled water to rinse the sample tubes

Waste bottle with a well-secured lid

Mixing container

Clean, lint-free wipes to wipe and dry the sample tubes.

After collection of the samples using screw-cap bottles, they were analyzed using the following procedure.

The first field sample was poured into the sample cell test tube and inserted into the sample cell of the spectrophotometer.

The bottle number was noted and recorded on the sheet

The cover of the sample cell was then placed. The concentration (absorbance) of the sample was noted and recorded.

The sample was then poured back into the waste bottle for disposal.

3.0 Results and Discussion

After the experiment, the following data was collected.

Table 1 experiment results

DateInfluentPrimary Eff.EffluentGBT FiltrateCent. Centrate9/22/20174422.70.71.737610/6/201746.823.70.21.223610/13/201746.225.20.170.51525310/20/201724.644.10.1851.3410510/27/201712.25.890.2190.84319411/3/201717.916.00.0971.12117

Figure 1 Graph of absorbance against concentration

The table and graph above show the results obtained from the experiment. The absorbance values were obtained by comparing the concentrations against the spectrophotometer. Then, a graph of absorbance values against concentrations was plotted as shown above.

4.0 Summary and Recommendations

In the process of nitrate removal, samples are passed through a cadmium solution to break down the compound. The nitrites then react with the reagents resulting in a red colored solution which is then measured against a spectrophotometer. The absorbance values obtained have a relationship with the concentration of the sample.

The removal of nitrogen and measurement of the amount of nitrogen is significant due to the potential adverse effects of nitrogen compounds in the water. Drinking water should have minimal levels of nitrogen. Obtaining a graph of absorbance values against concentrations helps to determine the safety of usage of water for consumption. Ideally, a graph of absorbance against concentration should yield a straight line. The graph helps to predict the absorbance value or the nitrogen content in the water at any instant of concentration of nitrogen. The table results show that it is difficult to obtain the absorbance values for turbid water hence the need to carry out filtration before carrying out the test.

Work Cited

Henze, M. Biological Wastewater Treatment: Principles, Modelling and Design. London: IWA Pub, 2008. Print.

Schmidt, Ingo, et al. "New concepts of microbial treatment processes for the nitrogen removal in wastewater." FEMS microbiology reviews 27.4 (2003): 481-492.