Date of Award
Spring 2018
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Civil and Environmental Engineering
First Advisor
McNamara, Patrick J.
Second Advisor
Mayer, Brooke K.
Third Advisor
Zitomer, Daniel H.
Abstract
Phosphorus regulations are causing Water Resource Recovery Facilities (WRRFs) to implement new technologies to remove phosphorus (P) before they discharge liquid effluent. Enhanced Biological Phosphorus Removal (EBPR) is often employed to remove P from water. However, sludges from EBPR plants have shown decreases in dewaterability soon after EBPR was initiated. This decline in dewaterability is not well understood, nor is the best way to improve the dewatering EBPR sludge. Specifically, the role of different P species on sludge dewaterability is not well understood. Several laboratory experiments were conducted at the Marquette University Water Quality Center with the following objectives: i) determine the impact of P speciation on dewaterability of various sludges, ii) determine an effective method for converting non-reactive P to reactive P in sludge, and iii) determine the impact of acid treatment and decanting on anaerobic digester dewaterability. P speciation and capillary suction time (a measurement of dewaterability) of sludge were the main characteristics measured in this research. A survey of various sludges from full-scale WRRFs was conducted and revealed that particulate P correlated to poor dewaterability in undigested sludges. Lab-scale anaerobic digesters were fed acid pretreated sludge to determine the impact of pretreatment and P species on the dewaterability of anaerobic digester biosolids. Acid pretreatment did not significantly affect dewaterability relative to control digesters that received untreated sludge. Centrate reactive P, which would contain orthophosphate, was correlated to poor dewaterability in anaerobic digester biosolids. It was suspected that orthophosphate reacted with divalent cations and increased the monovalent to divalent (M/D) cation ratio. The M/D ratio was previously suggested to correlate to dewaterability. Indeed, results from these lab-scale studied revealed that an increase in M/D ratio correlated with higher CST values, i.e. worse dewaterability.