Master of Science
Civil and Environmental Engineering
Dr. George Nakhla
Cellulose from toilet paper contributes approximately one third of the influent organic suspended solids (TSS) to wastewater treatment plants and is a key target for resources recovery. Cellulose recovery is beneficial as it reduces the required energy for treatment and biosolids treatment cost. Hence, understanding the hydrolysis of cellulose in wastewater which is mainly affected by temperature and the solids retention time (SRT), is a major key to determine the optimum location for its recovery. In order to assess the impact of temperature and SRT on cellulose degradation, this study investigated the biological aerobic degradation of cellulose in four laboratory-scale sequencing batch reactors (SBR) at four different temperatures (10-33°C) and two different sludge retention times (SRT of 15 days and 3 days). The degradation efficiency of cellulose was observed to increase with temperature and was slightly dependent on sludge retention time (80%-90% at an SRT of 15 days, and 78%-85% at an SRT of 3 days). A set of respirometry tests and modelling work was done using sludge samples from the four SBRs, tested and verified this value for fibrous cellulose, but alpha cellulose hydrolyzed significantly faster (approximately 3 times), indicating it is not an effective biochemical proxy for fibrous cellulose. In wastewater treatment plants (WWTP), the influent carbon limitations negatively affect biological nutrient removal (BNR) performance. With increasing emphasis on resource recovery, wastewater treatment plants (WWTPs) supplement internal extra readily biodegradable carbon in the form of volatile fatty acids (VFA) produced from the fermentation of primary clarification biosolids to enhance BNR processes. Despite significant work on the fermentation of primary clarification biosolids, emerging technologies like rotating belt filters (RBF) which can selectively capture cellulose leading to potentially higher VFA yields and better BNR performance, have not been investigated. In this study, the fermentability of the cellulose-rich rotating belt filter (RBF) biosolids and its impact on enhancing biological phosphorus removal (EBPR) was studied and compared to the addition of fermented primary sludge in two lab-scale SBRs operated at a solids retention time (SRT) of 10 days. PE-SBR treated primary effluent and RBF-SBR treated RBF effluent. Allylthiourea (ATU) was added at 50 mg/L concentration to both SBRs to inhibit the nitrification and focus on the biological phosphorus removal. After the addition of fermented PS to PE-SBR and fermented RBF sludge ii to RBF-SBR, the total phosphorus (TP) removal efficiencies increased from 69% and 72% to 91% and 93% for PE-SBR and RBF-SBR, respectively. Effluent soluble phosphorus (SP) concentrations averaged 0.1 mg/L and 0.3 mg/L for PE-SBR and RBF-SBR, respectively.
Keywords Cellulose degradation, temperature correction factor, cellulose hydrolysis rate, temperature, SRT, kinetics, phosphorus removal, fermentation, rotating belt filter, enhanced biological phosphorus removal with fermentation, sludge fermentation products.
Summary for Lay Audience
Achieving a lower cost for wastewater treatment by minimizing the different treatment processes energy and solids resulting from the treatment different processes is the main focus of municipal wastewater treatment plants (WWTPs). The estimated daily consumption of toilet paper in the United States is 18,000 tons. Cellulose originates mainly from toilet paper in the municipal wastewater entering the sewer systems and reaching wastewater treatment plants. The cellulose that can be recovered using physical treatment units located in most of the treatment plants, can be reused as a carbon source for treatment which reduce the treatment costs and energy. In this study, the main focus was on understanding the different factors that affect cellulose fate in wastewater treatment plants bioreactors in order to identify its recovery opportunities. Fermentation of two types of primary treatment biosolids for the recovery of volatile fatty acids, required to improve the removal of phosphorous biologically, was also assessed and compared in this study.
Elbahrawi, Moustafa Ibrahim, "Cellulose biodegradability and its impact on enhanced biological phosphorus removal" (2021). Electronic Thesis and Dissertation Repository. 8107.
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