ODOR AND PERFORMANCE CHANGES OF THERMOPHILIC ANAEROBIC DIGESTERS DURING PERIODS OF TEMPERATURE INCREASES IN PILOT AND FULL-SCALE OPERATIONS
This contribution discusses the production of volatile sulfur compounds (VSCs) and performance of full-scale digesters during short periods of increasing temperature in the range of about 53 to 65 °C and long periods with gradual increases in temperature from 53.9 to 57.2 °C. The City of Los Angeles, Bureau of Sanitation, has converted the digesters of the Hyperion and Terminal Island Treatment Plants (HTP and TITP) to thermophilic operation to comply with the Class A pathogen reduction requirements of U.S. EPA 40 CFR Part 503. HTP uses a two-stage continuous-batch process. The temperature was quickly increased from 54 to 58 °C to comply with Alternative 1 of 40 CFR 503.32, which required a relatively high temperature because of the limited batch digester capacity at HTP (T≥56.3 °C at 16 hours holding). TITP's single-stage sequencing batch process (T ≥ °C at 24 hours holding) already complied with the Alternative 1 time-temperature relationship. The temperature at this plant was rapidly increased to 65 °C to investigate the effect on fecal coliform recurrence that was observed in post-digestion biosolids when the digester temperature was about 55 – 57 °C. The digesters at both plants showed increased production of volatile fatty acids, methyl mercaptan and hydrogen sulfide. At TITP decreases in volatile solids destruction and methane production were also observed. It is likely that these effects were transient responses to rapid changes in temperature. Additional tests were conducted to investigate the steady-state digester performance at a gradually increasing temperature. The Hyperion Advanced Digestion Pilot Program indicated stable, steady-state operation at temperatures as high as 56 – 58 °C with minimum impact on digestion performance. Likewise, an increase of 0.55 °C per month from 53 to 57.2 °C in a dedicated digester at HTP indicated no significant impact on digestion performance, but VSC production increased at temperatures 56.6 °C and higher.
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Document Type: Research Article
Publication date: 2004-01-01
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