Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Dagnew,Martha

Abstract

The chemically enhanced primary treatment (CEPT) process is gaining momentum for carbon redirection, thereby lowering the downstream liquid train load and maximizing energy recovery from the primary sludge. CEPT technique enhances coagulation and flocculation, that enable faster settling of particulate and colloidal solids and dissolved ions such as phosphate to enhance removal efficiency. Comprehending the dynamic behaviour of CEPT clarifiers is critical to not only develop a reliable whole plant simulation but also fully understand the efficacy of the treatment plant performance. To achieve such purposes, a great amount of efforts has been contributed to the advancement of primary clarifier models. Modelling and controlling the primary clarifier have vital impacts to characterize the downstream biological and sludge treatment performance accurately, and subsequently, the full plant modelling (WWTP). This research was conducted to compares and contrasts the performance of three primary clarifier models, including volume-less point separator, three-compartments clarifier and layered flux clarifier concerning the accuracy in describing the CEPT performance. Most importantly, the characterization focused on the models' capability to accurately represent COD fractions, including colloidal COD (CCOD), soluble COD (SCOD), particulate COD(XCOD) and suspended solids (TSS) concentrations of the influent wastewater. For practical applications, our study has shown that among the three clarifier models, the three-compartments model accurately describes the effluent fractions, provides a better description of chemicals addition impacts, and comparatively a more straightforward calibration procedure. Furthermore, the impact of CEPT on the downstream solid train processes was also investigated. The experimental study was conducted on CEPT sludges with different pretreatments (ozonation and low-temperature thermal alkali pretreatments (LTTAP) in relation to the performance of anaerobic digestion for resource recovery. LTTAP process demonstrated the highest RP fraction of 53.33% in ferric based sludge (CEPT-I sludge), whereas ozonation process showed the highest RP fraction 76.38% in ferric alum- based sludge (CEPT-II sludge). Interestingly, after anaerobic digestion, not many differences were observed in the RP fraction from the pretreated samples for CEPT sludges and the control samples, implying pre-treatments may not be required due to the naturally occurred NRP conversion during digestion. Noteworthy, ferric-based sludge(control) produced 7% high methane yield than ferric alum-based sludge, indicated the inhibitory effect by the PACl coagulant on sludge digestion.

Summary for Lay Audience

Municipal wastewater is a potential resource, and future WWTP designs will primarily target the recovery of energy, nutrients, and potable water from wastewater. Design considerations must be factored in not only to produce high-quality effluent but also to minimize operating costs associated with labor, energy (electrical and heating), and byproduct stabilization and disposal/reuse. As a result, advancing/maximizing the use of unit processes or implementing additional treatment processes would be required to achieve those requirements. Primary sedimentation is one of the key processes to remove readily settleable solids and floating material in the liquid stream and to reduce the load to the downstream biological process. Advanced primary treatment such as chemically enhanced primary treatment (CEPT) is a technology that uses suitable chemicals to enhance pollutants removal in the primary stage of the wastewater treatment. To develop the whole plant simulation, and fully understand the effectiveness of the treatment plant, comprehending the dynamic behavior of CEPT clarifiers is critical. Thus, the advancement of primary clarifier models has been the main interest. Nevertheless, very limited studies sufficiently evaluated the influences of CEPT on COD and P fractions. Also, almost no studies have fully characterized CEPT effluent and compared and contrasted the effectiveness of 0-D and 1-D models.

Furthermore, the CEPT sludge contains a substantial number of all these valuable resources and has a high energy value that should be recovered. Anaerobic digestion is a widely used biological process to stabilize activated sludge. This process not only converts organic waste to produce methane (CH4) energy but also releases organically bound P making it available for recovery. Additionally, numerous amounts of research have been conducted on different pre-treatment techniques to overcome the single process limitations (hydrolysis step), However, little research has been focused on the effective enhancement of the anaerobic digestion process on methane and phosphors recovery from CEPT sludge through organic hydrolysis and conversion of nonreactive P (NRP) to reactive P (RP). In our research, we performed combined physical-chemical method and biological method to fully characterize the impacts of chemical addition process on COD on raw wastewater and CEPT effluents, simulation of CEPT process, fractionation of phosphorus in CEPT sludge, ozonation and low-temperature thermal alkali pre-treatment techniques to enhance anaerobic digestion performance, and phosphorus recovery analysis.

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