Date of Award

Fall 2006

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Civil, Construction, and Environmental Engineering

First Advisor

Zitomer, Daniel H.

Second Advisor

Switzenbaum, Michael S.

Third Advisor

Crandall, Clifford J.

Abstract

Thermophilic digestion is often coupled with mesophilic digestion in a temperature-phased anaerobic digestion (TPAD) system. Previous studies have reported that TPAD systems may produce more biogas, increase volatile solids destruction, and inactivate pathogenic microorganisms more completely than comparable conventional mesophilic digestion systems. For these reasons, some wastewater treatment facilities have moved to TPAD systems. In this study, a comprehensive survey and diagnostic tests were completed on municipal thermophilic and mesophilic phases of anaerobic sludge digesters, specifically four TPAD systems and a four-stage thermophilic system. From normalized plant operating data, the thermophilic systems studied on average had more total digester volume per flow than average conventional mesophilic digesters but the averages were not statistically different. In addition, thermophilic systems and conventional mesophilic digestion systems produced the same biogas per total plant flow and about the same gas per digester volume. Finally, thermophilic systems produced a higher gas volume per volume of raw sludge, but the difference was not statistically higher. Diagnostic tests included determining the maximum potential acetate utilization rate (MPAUR), the maximum potential propionate utilization rate (MPPUR), a nickel, cobalt and iron nutrient assay, biochemical methane potential (BMP) test, and an anaerobic toxicity assay (ATA) testing using nickel, cobalt, and iron. Results showed all but one biomass tested were stimulated by nutrient supplementation and reported a statistical increase in maximum methane production rate. There were a total of four mesophilic biomasses tested and five thermophilic biomasses tested. Of these, four out of four mesophilic biomasses were stimulated with percent stimulations ranging from 7.2 to 35.5%. Three out of five thennophilic biomasses were stimulated with percent stimulations ranging from 4 to 50.5%. With regards to MPAUR and MPPUR testing, results indicate a potential 159% increase in maximum specific acetate utilization rate and a potential 84% increase in maximum specific propionate utilization rate from mesophilic to thermophilic temperatures. BMP testing results showed increased stabilization for mesophilic biomass from the TPAD systems, with an average BMP5 of 0.29 ± 0.09 vol CH4/vol biomass, compared with conventional mesophilic systems reported in literature as having an average BMP5 of 0.7 ± 0.5 v/v. The ATA results show that the average mesophilic IC50 values compared to the average thermophilic IC50 were statistically the same. This result indicates toxicities of nickel, cobalt, and iron are approximately equal when operating al mesopllilic conditions compared to operating at thermophilic conditions.

Download

Share

COinS

Restricted Access Item

Having trouble?