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Capillary Suction Time (CST)
The results for the CST tests at optimal conditioning dose showed increasing trends with SRT for the SST and TPAD systems, and a decreasing trend with SRT for the SSM reactors. The TPAD system showed the best dewaterability as indicated by the CST, with the exception of the TPAD10/10 digester (Figure 11). It was expected that the CST times after conditioning would be below 50 seconds, but many sludges in the study were above that point. One explanation is that only the negatively charged biopolymers are coagulated by the cationic polymers, leaving positively charged particles in the sludge. Additional research has shown that positively charged chemical precipitates are not influenced by the cationic polymers, and require additional anionic polymers to increase the dewaterability, decreasing the CST. There was a noticeable trend of increasing CST for increasing SRT in both SST and TPAD reactors. There seemed to be an opposite trend by the SSM reactors, but this may be influenced by the 206 second CST for the SSM15(a) reactor. When compared against the SSM15(b) CST of 77 seconds and the lower times for SSM20 and SSM25, there appears to be a problem with the SSM15(a) reactor at the time of the tests.
Optimum Polymer Dose
The optimal polymer dose curve (Figure 12) created by plotting the amount of polymer dosed versus CST times was used to determine the optimum polymer dose (OPD) for each reactor. The OPD results (Figure 13) show the range of doses in gram of cationic polymer dosed per gram dry solids in the reactors on the day the polymer dose curves were measured. Both SSM and SST systems show an increasing trend with increasing SRT except for the largest SRT in the study. SSM systems go from a SSM15(a) value of 3.94 g polymer/ g TS to 7.78 g polymer/ g TS for the SSM20 reactor, then drops off to 4.13 g polymer/ g TS in the SSM25. Likewise, the SST systems go from a SST5 value of 3.32 g polymer/ g TS to 8.62 g polymer/ g TS for the SST10 reactor, and the SST20 reactor only requires 3.04 grams polymer for OPD. Both TPAD5/10 and TPAD 7.5/7.5 require less polymer for OPD (3.26 and 3.38 g polymer/ g TS, respectively) than the corresponding SST5 and SST7.5 reactors (3.32 and 4.22 g polymer/ g TS respectively). The largest dose required for TPAD systems was for the TPAD10/10 system with 7.61 g polymer/ g TS
Dewatered Cake Solids by Lab Centrifuge
When preparing the odor samples, total and volatile solids tests were conducted on the cake samples. It was expected that reactors with larger volatile solids reduction would have higher cake solids. Total solid (TS) results were between 13-19% for all test systems (Figure 14). The SST5 and SST20 dewatered to the highest cake solids with 18.4% and 17.1%, respectively. The lowest TS was from the SSM20 reactor with 13.2%,though all other SSM systems had cake TS over 15%. When looking at average TS for the systems, single stage thermophilic averaged 16.6%, single stage mesophilic averaged 15.0%, and the temperature phased digesters averaged 14.7%. The only trend noticeable from the results is in the SST reactors, with a downward trend seen as SRT increased, except for the SST20 reactor. Another note of interest was the relation of the SST to corresponding TPAD reactors. Both TPAD5/10 and TPAD10/10 TS went down in the second stage reactors, while TPAD7.5/7.5 increased. When comparing TS with VSD (Figure 15), a trend was observed of higher VSD giving lower TS. This was a drawback to the TPAD system. Volatile solids tests on the lab centrifuged samples showed a range of 4.8-6.8% volatile solids (VS) (Figure 16). A comparison of the performance of the digestion processes showed the highest average for single stage thermophilic digestion at 6.1%.The temperature phased digesters showed similar volatile solids with an average of 6.0%,and single stage mesophilic was lowest with 5.6%. The thermophilic reactors demonstrated the highest cake solids during the study, with an average of 16.6% TS (compared to 15.0% for SSM and 14.7% for TPAD reactors) and 6.1% VS (compared to 6.0% for TPAD and 5.6% for SSM reactors)
Literature Review
Introduction
Environmental Health Standards
Thermophilic Digestion
Temperature-Phased Digestion
Enhancing Sludge Treatment
Biosolids
Sulfur-based Odors
References
Comparing Sludges from Acid/Gas-Phased, Thermophilic, Temperature-Phased, and Conventional Mesophilic Anaerobic Digestion
Abstract
Keywords
Introduction
Objectives
Methods and Materials
Digester Performance
Sludge Properties
Conclusions
References
Vita
