No abstract

No abstract

AbstractÐBiological nitrogen removal in activated sludge processes is conventionally obtained by a sequence of aerobic and anoxic processes. Kinetic mechanisms aecting the oxygen balance could trigger the production of total volatile organic carbon (TVOC) and nitric oxides (NO) under anoxic and anaerobic conditions. Measurements at a wastewater treatment pilot plant of capacity 1.6 m 3 wastewater show that the amount of TVOC and NO produced during the treatment process depends on carbon loading (low feed, balanced and overloaded) and aeration conditions. To con®rm the results ORP, pH and dissolved oxygen (DO) are measured on-line and chemical parameters such as nitrate (NO 3 -N), ammonium (NH 4 -N) and TOC are measured in the wastewater.The ORP observed is in the range of À60 and +198 mV includes optimal setpoints for simultaneous nitri®cation and denitri®cation. From the pattern of NO emission plot, it can be assumed that a part of the produced NO 3 -N is denitri®ed during the aeration period. NO emissions are especially high during denitri®cation conditions at low oxygen rates. The results suggest that both NO and TVOC emission concentrations in combination with ORP can be valuable parameters to control operation of a wastewater treatment plant. Continuous measurements of ORP and NO concentrations for estimation of NO emissions gauging the extent of nitri®cation or denitri®cation in the plant becomes possible.

This study examined volatile organic compounds (VOC) concentration in ambient air collected during the years 2000--2003 at several different locations of Hsinchu Science-based Industrial Park (HSIP) in Taiwan. A canister automated GC-MS system analyzed the volatile organics in ambient air grasp samples according to T0-15 method. Oxygenated volatiles were the most abundant VOC detected in HSIP followed by aromatics that are commonly used as solvents in the semiconductor industries. The major components measured in the ambient air are 2-propanol (29-135 ppbv), acetone (12-164 ppbv), benzene (0.7-1.7 ppbv), and toluene (13-20 ppbv). At some of the sampling locations, odorous compounds such as carbon disulfide and dimethyl sulfide levels exceed threshold values. The estimated toluene/benzene ratio is very high at most of the sites. However, the total amount of VOC is reduced over the years from 2000 to 2003 due to strict implementation on use and discharge of solvents in industries. There exists no definite seasonal pattern for sporadic occurrence of high levels of some of the volatile organics. Stagnant weather conditions with low wind speeds aid accumulation of toxic species at ground level. The results entail that hi-tech semiconductor industries are still a potential source for harmful organic substances to surrounding microenvironment.