Date of Award
Master of Science (MS)
Phosphorous (P) effluent regulations from water resource recovery facilities (WRRFs) have become more stringent to reduce the damage of eutrophication caused by excess amounts of P. Enhanced biological phosphorus removal (EBPR) is a popular method to help comply with these regulations combined with other practices such as filtration. However, the sludges from facilities that employ EBPR (bio-P sludges) are difficult to dewater and require more polymer than conventional sludge, thereby increasing the cost of solids handling at these facilities. The monovalent to divalent (M/D) cation ratio, which is important in dewatering, is reportedly altered during the EBPR process. P speciation has also been suggested to affect dewaterability. Dewaterability is defined as the ease of separating water from the solids and was quantified by capillary suction time (CST). Yet, it is not well understood how the M/D cation ratio or P speciation correlate to dewaterability for different types of biosolids. Laboratory experiments were conducted in the Water Quality Center at Marquette University to meet the following objectives: i) determine the effects of the addition of different cations at various doses on dewaterability as CST of non-digested sludges, ii) determine how the M/D cation ratio is correlated to dewaterability as CST for various digested biosolids, and iii) determine if the alteration of P speciation correlates to dewaterability as CST for various biosolids. Batch studies were performed on primary and bio-P sludge to evaluate the effects of the addition of different chemicals on CST and P speciation. Using results from the batch study, a chemical pretreatment was chosen to be implemented in a lab-scale anaerobic digestion study because it improved the dewaterability of the primary and bio-P sludges. The pretreatment chosen was an addition of 200 meq/L calcium hydroxide followed by the addition of hydrochloric acid for pH adjustment. Lab-scale anaerobic digesters were fed with the chemically pretreated sludge to determine how altering the M/D cation ratio and P speciation affected dewaterability as CST. The pretreatment significantly improved the CST of the bio-P anaerobically digested biosolids relative to the control digesters but had little to negative effect on the digested primary biosolids. The chemical pretreatment decreased the M/D cation ratios for both types of biosolids, but the pretreatment had a positive correlation with CST for only the bio-P biosolids. Interestingly, these results reveal that the M/D ratio might not universally affect dewaterability as CST for all sludges and biosolids. P speciation may also play a role in dewaterability as CST. Higher amounts of particulate P improved the CST of the bio-P biosolids, but again, this was opposite for the primary biosolids. The role of specific P species on dewaterability as CST requires further investigation.