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Crown condition of Norway spruce in relation to sulphur and nitrogen deposition and soil properties in southeast Norway
1997
Solberg, S. | Toerseth, K. (Norwegian Forest Research Institute, Hoegskoleveien 12, N-1432 As (Norway))
Ammonia emission factors for N fertilizers applied to two contrasting grassland soils
1997
Weerden, T.J. van der | Jarvis, S.C. (Institute of Grassland and Environmental Research, North Wyke, Okehampton, Devon, EX20 2SB (United Kingdom))
Major pathways for nitrogen removal in waste water stabilization ponds
1997
Lai, Patrick C. C. | Lam, Paul K. S.
A study on the factors influencing nitrogen removal in waste water stabilization ponds was undertaken in an eight-pond series in Werribee, Australia. Nitrogen species including Kjeldahl nitrogen, total ammonia nitrogen, nitrite and nitrate were monitored monthly from March 1993 to January 1994. At the same time, pH, temperature, chlorophylla content and dissolved oxygen were also recorded. Highest nitrogen removal occurred during the period with highest levels of chlorophylla content and dissolved oxygen, but the rate of nitrogen removal was not related to temperature and pH. Enhanced photosynthetic activities resulting from an increased phytoplankton abundance due to prolonged detention time caused an increase in dissolved oxygen, and created an optimum condition for nitrification to occur. In this process, ammonia was oxidized to nitrite and nitrate which were subsequently reduced to elemental nitrogen. Apart from nitrification-denitrification which was the major nitrogen removal pathway in the study system, algal uptake of ammonium, nitrate and nitrite as nutrient sources also contributed to the nitrogen removal. The role of phytoplankton and zooplankton in the treatment process in waste stabilization ponds was discussed.
Mostrar más [+] Menos [-]Ammonia stripping as a pretreatment for landfill leachate
1997
Cheung, K. C. | CHU, L. M. | Wong, M. H.
The effectiveness of ammonia stripping at different air flow rates (0, 1 and 5 L min⁻¹) and lime dosages (0 and 10 000 mg L⁻¹ calcium hydroxide) was investigated in aeration tanks in a laboratory as a pretreatment to remove ammoniacal-nitrogen and organic load (COD) in landfill leachate. Ammoniacal-nitrogen removal at 20 °C after one day was 70% for 0 L min⁻¹, 81% for 1 L min⁻¹ and 90% for 5 L min⁻¹ regardless of the origin of leachate. Ammonia loss was mainly due to desorption through water surface. The levels of phosphorus and COD were only reduced by lime precipitation, with 85% and 93% phosphorus removal and 24% and 47% COD removed for leachate from the Junk Bay Landfill (JB) and Gin Drinkers' Bay Landfill (GDB) respectively. The highly significant difference (P<0.05) of COD removal between JB and GDB might be due to the different age of the two landfills studied. Leachate quality and configuration of the treatment reactor were important factors affecting the efficiency of ammonia removal by stripping processes.
Mostrar más [+] Menos [-]Fluxes and mass balances of nutrients in a semi-intensive shrimp farm in north-western Mexico
1997
Paez-Osuna, F. | Guerrero-Galvan, S.R. | Ruiz-Fernandez, A.C. | Espinoza-Angulo, R. (Laboratorio de Quimica Marina, Instituto de Ciencias del Mar y Limnologia, Universidad Nacional Autonoma de Mexico, Apdo. Postal 811, Mazatlan 82000, Sinaloa (Mexico))