Explaining Sources of Biosolids Odors at Wastewater Treatment Plant (WWTP) by Utilizing Real-Time Odor Monitoring System and Statistical Models

Abstract

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.