RESUMEN
The effects of shock loads of 1-chloro-2,4-dinitrobenzene (CDNB); cadmium; 1-octanol; 2,4-dinitrophenol (DNP); weakly complexed cyanide; pH 5, 9, and 11; and high ammonia levels on activated sludge biomass growth, respiration rate, flocculation, chemical oxygen demand removal, dewaterability, and settleability were studied. For all chemical shocks, except ammonia and pH, concentrations that caused 15, 25, and 50% respiration inhibition were used to provide a single pulse shock to sequencing batch reactor systems containing a nitrifying or non-nitrifying biomass. Cadmium and pH 11 shocks were most detrimental to all processes, followed by CDNB. The DNP and cyanide primarily affected respiration, while pH 5, pH 9, octanol, and ammonia did not affect the treatment process to a significant extent. A chemical source-process effect matrix is provided, which we believe will aid in the development of methods that prevent and/or attenuate the effects of toxic shock loads on activated sludge systems.
Asunto(s)
Eliminación de Residuos Líquidos/métodos , Administración de Residuos/métodos , Contaminantes Químicos del Agua , Purificación del Agua/métodos , 1-Octanol/metabolismo , 1-Octanol/toxicidad , 2,4-Dinitrofenol/metabolismo , 2,4-Dinitrofenol/toxicidad , Biomasa , Cadmio/metabolismo , Cadmio/toxicidad , Cianuros/metabolismo , Cianuros/toxicidad , Dinitroclorobenceno/metabolismo , Dinitroclorobenceno/toxicidad , Floculación , Concentración de Iones de Hidrógeno , Nitritos/química , Nitritos/metabolismo , Oxígeno/química , Oxígeno/metabolismo , Contaminantes Químicos del Agua/metabolismo , Contaminantes Químicos del Agua/toxicidadRESUMEN
Simple methods that rapidly detect nitrification inhibition are needed to enforce pretreatment programs and prevent upsets. The objective of this study was to demonstrate a rapid method for measuring nitrification inhibition by using nitrate generation rates (NGRs) coupled with direct UV detection of nitrate. The NGRs were measured with UV spectrophotometry at wavelengths between 225 and 240 nm, without chemical manipulation, and verified against ion chromatography. The method was shown to quickly and accurately measure nitrate concentrations after correcting for nitrite interference. Cadmium, hypochlorite and 1-chloro-2,4-dintrobenzene (CDNB) were tested for their ability to cause nitrification inhibition using this method. The CDNB was found to cause a correctable interference with the test, while hypochlorite provided an uncorrectable interference. Used as a batch method coupled with biotic and abiotic controls, this approach can be deployed at full-scale treatment plants as a relatively rapid (1.5 hours) means of identifying nitrification-inhibiting wastewaters.
Asunto(s)
Nitratos/análisis , Contaminantes Químicos del Agua/análisis , Bacterias/efectos de los fármacos , Bacterias/metabolismo , Reactores Biológicos , Cadmio/farmacología , Dinitroclorobenceno/farmacología , Ácido Hipocloroso/farmacología , Nitratos/metabolismo , Nitritos/análisis , Espectrofotometría Ultravioleta , Eliminación de Residuos Líquidos , Contaminantes Químicos del Agua/metabolismoRESUMEN
Activated sludge facilities are susceptible to upset by shock loads of toxic compounds. We hypothesized that floc size plays an important role in determining the sensitivity of mixed liquor to shock by cadmium and 2,4-dinitrophenol (DNP). To test this hypothesis, heterotrophic respiration inhibition experiments were conducted using mixed liquor from a pilot-scale membrane bioreactor (MBR) and full-scale activated sludge (FSAS) facility with gravity settling secondary clarifiers that were operated under similar process conditions. MBR mixed liquor flocs were both 41% smaller and 2 and 1.25 times more sensitive to equivalent soluble cadmium and DNP concentrations, respectively, compared to FSAS mixed liquor flocs. Similarly, FSAS mixed liquor that had been sheared (resulting in a smaller average floc diameter) was 1.5 times more sensitive to soluble cadmium than non-sheared FSAS mixed liquor. These results suggest that activated sludge process conditions that create smaller floc particles, such as the use of membranes for liquid-solid separation, are more susceptible to upset events caused by shock loads of cadmium and DNP. The particle size distribution (PSD) and average floc diameter of a mixed liquor suspension should be measured and reported when stating the inhibition concentration of a specific toxicant.