Doctor of Philosophy
Chemical and Biochemical Engineering
There has been an increased interest in alternative carbon diversion technologies in wastewater treatment to improve the efficiency and performance of primary treatment, increase treatment capacity, and minimize overall energy consumption, especially in geographies with limited space for expansion. Microsieving technologies like the rotating belt filters (RBFs) have emerged as a promising primary solids separation alternative to primary clarification. This research was conducted to study the implications of retrofitting existing wastewater treatment plants (without primary treatment) with RBF technology.
In order to fully evaluate the impact of RBF in water resource recovery facilities, it is paramount to investigate the unique characteristics of the more fibrous material removed by microsieving, cellulose, mostly in the form of toilet paper, which is a major component of the particulates in raw municipal wastewater. To date, a validated method for cellulose quantification in wastewater and sludge matrices was unavailable. This research demonstrated that the Schweitzer-reagent method is a very robust and reliable cellulose quantification method in light of its reproducibility and accuracy. Sludge from the RBF was observed to contain 37±1 % cellulose (on dry basis), whereas primary clarifier sludge contained 18±0.2 % cellulose (on dry basis) which confirmed that the RBF captures the cellulose more efficiently than the primary clarifier. The contribution from this work would have great implications on wastewater research in understanding the fate of toilet-paper-cellulose, and its impact on biosolids management given the already emerging trend to increase sustainability and resource recovery.
When looked in the context of the impact of the RBF on activated sludge processes, RBF effluent was compared with raw wastewater and primary clarifier effluent. This was accomplished using respirometric techniques to identify the most influential biokinetic parameters required for model simulations. The raw wastewater was predominantly biodegradable where 71% of the TCOD was observed to be biodegradable. Primary clarifier and RBF treatment increased the biodegradable fraction to 80% and 74%, respectively, by removing inert particulates by settling and microsieving, respectively. As expected, microsieving and settling do not impact the soluble components in the wastewaters. The fractionation of the particulate components was dictated by the primary treatment suspended solids removal efficiency and was observed to be comparable for the RBF effluent and the primary clarifier effluent. The implementation of different COD fractions and kinetic coefficients of the RBF effluent would improve the model simulations for design, control, and optimization of biological wastewater treatment processes employing RBF as a primary treatment.
In addition, the results from this study established that the RBF offers an alternative level of treatment (to primary clarification), which removes particulate solids, without impacting nitrification and denitrification processes with total nitrogen removal efficiency ranging from 68%-73% for medium-strength wastewater. Upon modeling (using GPS-X) to predict performance for high-strength wastewater, it was observed that within the TSS removal of 27%-70% by the RBF, biological nitrogen removal was not adversely affected (79% total nitrogen removal). Moreover, the overall primary and biological sludge production by a wastewater resource recovery facility employing an RBF as primary treatment was found to be 9% lower than the one with primary clarification. Chemically-enhanced-RBF treatment was observed to be ideal for plants trying to achieve BOD and ammonia limits; however, excessive removal of carbon compromised nitrogen removal efficiency (30% total nitrogen removal), especially with low-strength wastewaters.
The findings of this work would instigate further research on RBF technology for successful integration as a primary treatment alternative in wastewater resource recovery facilities.
Gupta, Medhavi, "Microsieving as a Primary Treatment for Biological Nitrogen Removal from Municipal Wastewater" (2018). Electronic Thesis and Dissertation Repository. 5288.