Part II of Field Research: Impact of Centrifuge Torque and Polymer Dose on Odor Production from Anaerobically Digested Biosolids

Abstract

A study was performed to optimize the operation of a full-scale high solids centrifuge in terms of dewatering performance as well as the subsequent generation of odors from the biosolids cake. The results are presented in a two paper series, one dealing with the dewatering performance, and the second covering the impact on odors. This is the second paper in the series and will present how centrifuge polymer dose, polymer addition location, and torque affect the generation of odors. The concentration of odor causing compounds produced during cake storage increased as the polymer dose increased. The increased odorant production was attributed to greater amounts of bioavailable protein in the cake at the higher polymer doses, and this protein is the substrate for production of odorous compounds. Increased torque during centrifugation resulted in a proportional increase in odors during cake storage. In addition, changes in the polymer addition location affected the polymer dose. The further upstream of the centrifuge, the greater the polymer demand and subsequent odor generation. The findings are significant and show that the centrifuge torque and polymer dosage are critical control parameters and the centrifuge is a critical control point for biosolids product quality. The results of this study have led Western Lake Superior Sanitary District to develop a centrifuge operating strategy to produce a biosolids, lower in odor, to maintain a sustainable land application program.

Impacts of feed dilution and lower solids retention time on performance of thermal hydrolysis/anaerobic digestion

“…The 18‐day cake produced the highest odors followed by the 15‐day and the 10‐day SRT. The higher odorant production could be due to the increase in biopolymer, especially protein, in solution, as that material is captured by the polymer and deposited in the cake, and it has been shown to increase the potential for odorant production (Higgins et al., ). Overall, the odorant concentrations produced by the cakes were low in comparison with many systems (Novak et al., ), which is indicative of THP biosolids (Higgins et al., ).…”

“…The 18day cake produced the highest odors followed by the 15-day and the 10-day SRT. The higher odorant production could be due to the increase in biopolymer, especially protein, in solution, as that material is captured by the polymer and deposited in the cake, and it has been shown to increase the potential for odorant production (Higgins et al, 2005).…”

Role of Protein, Amino Acids, and Enzyme Activity on Odor Production from Anaerobically Digested and Dewatered Biosolids

“…As can be seen, the methanethiol and DMS increase over a period of several days, reach a peak concentration, and then decrease to below detectable levels. The DMS concentration is typically lower than the methanethiol concentration, although it should be stressed that these profiles for methanethiol and DMS vary considerably, depending on the type of digestion, dewatering process used, and cake‐handling equipment ( Higgins et al, 2005 , 2007 ; Murthy et al, 2003 , 2004 ; Novak et al, 2006 ).…”