District of Columbia Water and Sewer Authority (DCWASA) operates an advanced wastewater treatment plant that treats approximately 370 mgd of wastewater and generates over 400,000 wet tons of biosolids each year. The reduction of biosolids odors at the plant before distribution to the field sites is therefore, a high priority. Each unit process of a wastewater treatment plant has the potential to generate odor-causing compounds. Total Reduced Sulfur is one of the main components of the odor-generated by wastewater treatment facilities and is the dewatered solids emissions monitored by this study.Many studies have indicated that odors are generated from the upstream processes and from storage, but this research presents information about the odors arising after dewatering. It demonstrates a statistical model that forecasts which factors are significant contributions to odors and which can be used to forecast biosolids odor. The model indicates that secondary west odd blanket depth is the most significant factor for odor level after dewatering and at the depth more than 1.8 ft will be caused more odors. In addition, this research provides basic information to compare odor after lime addition which is the next phase of research, and this model can assist DCWASA to schedule routes for distribution of biosolids to field sites.
A real-time solids odor monitoring system provides an odor management feedback tool for both process control and a biosolids management program. Since higher odor levels means higher process costs, as well as greater potential for nuisance odors at land application sites, identifying the processes that contribute to these elevated levels is critical to responsible, economical, and efficient wastewater plant management and biosolids land application programs. Each year, DC Water's 370 mgd plant applies biosolids to over 20,000 acres of agricultural land. Nuisance odors from recycling biosolids on land may drift into surrounding neighborhoods and motivate neighboring communities to enact legislation to ban land application. Therefore, the reduction of odor emissions from biosolids recycled on field sites is a major concern. Odors levels generated by dewatered solids and limed biosolids are measured by headspace monitoring devices in enclosed conveyance systems. Both total reduced sulfur compounds (TRS) and nitrogen (N)containing compounds are measured with online electro-chemical sensors. The system correlates odorant levels of dewatered solids and biosolids and utilizes treatment process scenarios and various operational parameters throughout the wastewater treatment process. This study uses ordinary least squares (OLS) estimation and instrumental variable (IV) estimation to create explanatory models. Data analyses suggest that waste-activated percent solids (WAS %S) and dissolved-air flotation total solids (DAF TS) can contribute to mitigating TRS. However, all process variables at secondary sedimentation, which are gravity thickening percent solids (GT %S), gravity total solids (GT TS), and blend ratio, can contribute to increase TRS. The IV estimation indicates that % lime feeding, # centrifuges, cake percent solids (Cake %S), temperature at secondary effluent, and ambient temperature cannot directly explain TRS postlime, but they do explain TRS levels via post-lime temperature. Additionally, cationic polymer at the secondary and dewatering process coupled with post lime temperature can contribute to increase N-containing compounds at the lime addition process. The accumulated cationic polymer inside the sludge of secondary sedimentation can also contribute to high N-containing compounds downstream.
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