RESUMEN
The impact of methanol (CH3OH) as a source of anthropogenic carbon dioxide (CO2) in denitrification at wastewater treatment plants (WWTPs) has never been quantified. CH3OH is the most commonly purchased carbon source for sewage denitrification. Until recently, greenhouse gas (GHG) reporting protocols consistently ignored the liberation of anthropogenic CO2 attributable to CH3OH. This oversight can likely be attributed to a simplifying notion that CO2 produced through activated-sludge-process respiration is biogenic because most raw-sewage carbon is un-sequestered prior to entering a WWTP. Instead, a biogenic categorization cannot apply to fossil-fuel-derived carbon sources like CH3OH. This paper provides a summary of how CH3OH use at DC Water's Blue Plains Advanced Wastewater Treatment Plant (AWTP; Washington, DC, USA) amounts to 60 to 85% of the AWTP's Scope-1 emissions. The United States Environmental Protection Agency and Water Environment Federation databases suggest that CH3OH CO2 likely represents one quarter of all Scope-1 GHG emissions attributable to sewage treatment in the USA. Finally, many alternatives to CH3OH use exist and are discussed.
Asunto(s)
Dióxido de Carbono/química , Metanol/química , Aguas del Alcantarillado/química , Eliminación de Residuos Líquidos/métodos , Efecto Invernadero , Nitrógeno/química , Instalaciones de Eliminación de Residuos , Aguas Residuales , Contaminantes Químicos del AguaRESUMEN
Two statistical models were used to predict the concentration of dimethyl disulfide (DMDS) released from biosolids produced by an advanced wastewater treatment plant (WWTP) located in Washington, DC, USA. The plant concentrates sludge from primary sedimentation basins in gravity thickeners (GT) and sludge from secondary sedimentation basins in dissolved air flotation (DAF) thickeners. The thickened sludge is pumped into blending tanks and then fed into centrifuges for dewatering. The dewatered sludge is then conditioned with lime before trucking out from the plant. DMDS, along with other volatile sulfur and nitrogen-containing chemicals, is known to contribute to biosolids odors. These models identified oxidation/reduction potential (ORP) values of a GT and DAF, the amount of sludge dewatered by centrifuges, and the blend ratio between GT thickened sludge and DAF thickened sludge in blending tanks as control variables. The accuracy of the developed regression models was evaluated by checking the adjusted R2 of the regression as well as the signs of coefficients associated with each variable. In general, both models explained observed DMDS levels in sludge headspace samples. The adjusted R2 value of the regression models 1 and 2 were 0.79 and 0.77, respectively. Coefficients for each regression model also had the correct sign. Using the developed models, plant operators can adjust the controllable variables to proactively decrease this odorant. Therefore, these models are a useful tool in biosolids management at WWTPs.
Asunto(s)
Contaminantes Atmosféricos/análisis , Disulfuros/análisis , Modelos Estadísticos , Odorantes/análisis , Eliminación de Residuos Líquidos , District of Columbia , Predicción , Análisis de Regresión , Aguas del AlcantarilladoRESUMEN
Complaints from the public due to odor emissions are one of the biggest problems associated with any biosolids land application program. Chemical additives to reduce or mask odors are one option for producers; however, many chemicals are too expensive or are too unstable to use safely. This project provides a preliminary evaluation of nitrate or nitrate + anthraquinone as additives in controlling odors from limed biosolids. Over a twenty-four day period, odors were measured in the headspace over several treatment levels using two different chemical analysis tools along with olfactometric evaluation of odor intensity and hedonic tone. On six days during the sample period, hydrogen sulfide was measured using a Jerome 631X, a sensor that also responds to other reduce sulfur gases. Other specific sulfides, amines, and mercaptans were also determined using solid phase microextraction with gas chromatography-mass spectrometry. A simple sniff test approach was used with six panelists on five days during the project. The chemical analysis results revealed that the addition of nitrate and especially nitrate + anthraquinone was effective in reducing concentrations of hydrogen sulfide and methylmercaptan when compared to untreated limed biosolids. However, the olfactometric results did not reveal any significant differences between treatments. The panelists also found that all treatments exhibited a fishy or ammonical character, indicative of amines, or ammonia. More advance olfactometric analysis utilizing dilution techniques might have been able to distinguish between treatments, but it is likely that amines were the dominant odorant released from all treatments. This preliminary project suggests that chemical addition of nitrate or nitrate + anthraquinone would be most effective in controlling odors from unlimed biosolids such as anaerobically digested materials.
Asunto(s)
Metilaminas/análisis , Odorantes/análisis , Aguas del Alcantarillado/química , Compuestos de Azufre/análisis , Antraquinonas/química , Compuestos de Calcio/química , District of Columbia , Nitratos/química , Óxidos , VolatilizaciónRESUMEN
Lime-stabilized biosolids produced from a wastewater treatment plant often emit odors, especially those described as "fishy" and "decaying". These odors can generate public opposition to biosolids land-application programs even though they represent an environmentally friendly recycling of organic material that is beneficial to the agricultural industry. Therefore, it is critical to examine the controlling factors involved in odor production during the lime stabilization process. Results from preliminary experiments examining added polymer and protein material to dewatered limed biosolids show increased trimethylamine (TMA) production with further increases in 1-hour and 4-hour storage times prior to liming. Further experiments with water-silica slurry reaction media reveal that enzymatically facilitated degradation of polymer and protein is the overriding factor in TMA and dimethyldisulfide (DMDS) production. It is hypothesized that macromolecules such as polymer and proteins in biosolids are first broken down enzymatically, upon which the addition of lime causes TMA and DMDS to be released.
Asunto(s)
Odorantes , Aguas del Alcantarillado , Eliminación de Residuos Líquidos , AguaRESUMEN
Because it produces an exceptional quality pellet product, heat drying of wastewater solids from municipal wastewater treatment plants is becoming more prevalent as biosolids management regulations become more restrictive. The product from heat drying is sometimes odorous as dry or wetted pellets. The odors, although not regulated, can be important for marketability and public acceptance of the product. The reasons for the odors are usually a result of upstream processing and management of wastewater solids prior to drying. The goals of this study were to determine odor characteristics and to compare the odors produced by evaluating odors from four types of heat-dried biosolids products: all undigested; primary digested-waste activated sludge (WAS) undigested; all digested; and WAS lime stabilized pellets. The results are described in this paper.