Study on removal of ammonia from the waste water of Fenchuganj natural gas fertilizer factory (Thesis)

Abstract

The Natural Gas Fe.tilizer Factory Ltd. (NGFFL), Fenchuganj, Sylhet was cstablished in Deccmber 1961 to meet the urea demand of the country. The effluent from the plant contains high concentration of ammonia and oil and grease. Before 1986, all effluents were discharged directly into the Kushiara River. In 1986 two lagoons were constructed. The less contaminated effluent collected in lagoon 2 is subjected to equalization and dilution (with uncontaminated effluent of the plant) before discharging into the Kushiara River. Highly contaminated effluent from the plant are collected and stored into a twochambered pit near the urea plant. Lube oil is collected through siphon and oil trap. After separation of lube well, ammonia-contaminated effluent is taken in the second pit from where it is pumped to lagoon I through a 4 km pipeline. The contents of lagoon I is diluted by river water, and then slowly released in to the Kushiara River. An attempt has been made to characterize the liquid waste of NGFFL, to idcntify any changes of water quality of Kushiara River due to discharge of industrial effluent from NGFFL, to assess the efficiency of the present treatment facilities of NGFFL, and to assess effectiveness of different methods to remove ammonia from wastewater of NGFFL. The physical, chemical and biological characteristics of the wastewater of the two lagoons were determined through extensive laboratory tests and compared with effluent discharge standard. Wastewater samples were collected from the lagoons once a month from March 2005 to December 2005. Dissolved solid contents of the lagoons were within the limit, but suspended solid contents exceeded the Bangladesh Standards for industrial effluent. COD and 13005 were well below the Bangladesh Standard. Dissolved Oxygen of the wastewater was found to be between 2.0 to 3.0 mg/L, which do not satisfy the standard (4.5 -8 mglL). Oil and grease concentrations were found in the range of28 to 68 mg/L, much higher than the standard (10 mg/L) for discharge into the inland surface water. Chromium and nitrate were found to be slightly higher than the standard limit for some samples. Ammonia nitrogen concentration was very high in lagoon J, which is being directly discharged into the Kushiara River. River water quality was analyzed in the month of December. Ammonia nitrogen was found to be 0.44 mglL and 0.18 mglL at the 300 yards and J 500 yards downstream of the effluent discharge point, respectively. The efficiency of lagoon 2 was analyzed and found that the lagoon 2 is not efficiently reducing ammonia. Several techniques to remove of ammonia from wastewater were studied in the laboratory. It has been found that Lagooning after pH control could be a good option. About 60% removal of ammonia was achieved within one day by keeping the wastewater in a small container after raising the pH to J 1.0. Use of Sulfonile resin as cation exchanger was not found to be a cost effective option to remove ammonia. The airstripping method achieved very good ammonia removal. Different materials were used as 00\4, .001 and .0009 for coal, plastic ring, stone chips and wood chips, respectively. Best result was found for plastic ring for its higher surface area. Wood chips did not give good result, because the chips amalgamate with each other and hence reduces the surface area. Aeration after controlling pH was also found to be very effective in removing ammonia. On the basis of wastewater analysis of NGFFL, it is clear that new treatment plant or improvement of the existing lagoons is essential. For reducing ammonia concentration in the existing lagoons, NGFFL authority could make provision of aeration in the lagoons. Since NGFFL uses huge amount of air for producing fertilizer, NGFFL authority can transfer air through a bypass line for aeration of the lagoons. Air stripping appears to be the most effective options for treatment of plant effluent. But it requires a huge amount of calcium oxide to adjust pH. Alternatively, biological treatment of the wastewater involving nitrification and denitrification may be considered.