The drain may not be not at all big but its smell can be annoying. Many ways are suggested to avoid smelly drains – do not throw food in drains, pour boiling water, throw salt, put baking soda, use distilled vinegar, and many more. Saliha, guided by her professor, Suhaimi Abdul Talib, discovered that sulphur and nitrogen can help us get rid of this old age problem.
One of the ways water in drains can be smelly is due the transformation of sulphur compounds. Anaerobic decomposition of wastewater in sewer systems that generate sulphur compounds have been identified as a major cause of problems of toxicity, foul odors and corrodibility. This happens due to the transformation of sulphur compounds in wastewater that forms hydrogen sulphide (H2S), which has caused serious problem in sewer systems.
Also, the production and emission of sulphide in sewer systems also corrode the sewer structures and makes them smelly where sometimes wastewater treatment does not work. Sulphide, as well as volatile organics compounds, are very toxic and can emit obnoxious odor even at very low concentration levels (10 mg/L). Sulphide is produced when organic matters decompose in the sewer system. Worse, lack of ventilation and reaeration in the sewer system makes it smellier. Worse, hydrogen sulphide, which smells like rotten eggs, is also flammable and very poisonous to us and animals. It can cause death at a concentration of 300ppm and more.
Usually, sulphide will be produced more easily and faster in warmer climates countries. Thus Malaysia, being a hot-climate country, has a serious problem in her sewer systems in the midst of anaerobic conditions of hydrogen sulphide. Not only hot climate countries, temperate climate countries also face great problems of concrete deterioration in their sewer systems. The US Environment Protection Agency (US EPA) had investigated sewer systems in 131 cities and reported that 66 of them had corrosion problems through the emission of sulphide into the sewer atmosphere as hydrogen. Then hydrogen sulphide will diffuse into a thin liquid film present on the sewer surfaces. On the surface, chemoautotrophic bacteria will oxidize the sulphide to sulphuric acid. The biogenic sulphuric acid will react with the cementitious material of the concrete and corrode the sewer wall, eventual causing structural failure of the sewers. The US EPA reported in 1991 that the range of concrete deterioration rate in the country’s sewer pipes was 2.5-10 mm year in its investigation of 34 cities. Similar observations were made in Denmark and Portugal. Corrosion of sewer walls will then cause ex-filtration of wastewater into groundwater, polluting the receiving waters, which are both health hazardous and odor causing.
Thus Saliha and Suhaimi theorized and looked at how the microbial transformation in wastewater during transportation can improve the performance of wastewater system. As basic kinetics of anoxic sulphide oxidation in sewer systems serves as an important tool to reduce the hydrogen sulphide problem in sewer systems (by the addition of nitrate) they see that odor can be reduced. Secondly, as sulphide is reduced, the workers responsible for sewer systems will also be protected from its toxicity. Thus the corrosion of sewer wall also can be reduced.
Their test was conducted on wastewater from a manhole near the in-sewer Processes Laboratory of the Faculty of Civil Engineering, Universiti Teknologi Mara, Shah Alam. The wastewater was collected as a raw wastewater sample in the peak rate of wastewater flow between 8:30 am to 9:30 am. The wastewater was collected from three different places that were, the Faculty of Office Management, the Faculty of Applied Science and the cafeteria via the grab sampling method. Making sure the anaerobic condition occurs naturally to assimilate the condition of experiment to that of in the sewer system, the collected bulk water samples were kept in an air tight container for 14 days before being tested in a batch test.
They found that wastewater in sewer systems can oxidize sulphide biologically under anoxic conditions, thus they created a process to oxidize sulphide to sulphate in a single-step process. Also, nitrate was reduced to nitrogen gas through a two-step process. Thus less odor occurred.
The result obtained from this study can be used by our local authorities to provide guidelines to enhance municipal wastewater treatments in sewer systems, prior to treatment plant. On top of that, the results may be useful for wastewater engineering companies in Malaysia to upgrade the existing sewer systems to reduce odor, prevent corrosion problems and reduce health risk due to formation of hydrogen sulphide.
In the same vein, this study has also contributed in establishing basic kinetics and pathway of sulphide oxidation under anoxic condition in bulk water phase. However, it is recommended that one investigate the transformation rate of sulphide in biofilm to establish full anoxic sulphur oxidation. In future, the study on micro level should be conducted as knowledge on microrganisms activities at molecular level will enhance understanding on microbial transformations of sulphur compounds.
Suhaimi Abdul Talib
Faculty of Civil Engineering,
Universiti Teknologi MARA, Shah Alam,
Email: [email protected]
email: [email protected]