Environmental Engineering Reference
In-Depth Information
10.6.2.4 pH Control
pH should be adjusted to maintain a range of 6.8 to 7.2 by adjusting
the feed rate, sludge withdrawal, or alkalinity additions.
Note:
The buffer capacity of an anaerobic digester is indicated by the
volatile acids-to-alkalinity relationship. Decreases in alkalinity cause a
corresponding increase in the ratio.
10.6.2.5 Temperature Control
If the digester is heated, the temperature must be controlled to a
normal temperature range of 90 to 95°F. Never adjust the temperature by
more than 1°F per day.
10.6.2.6 Mixing
If the digester is equipped with mixers, mixing should be accom-
plished to ensure that organisms are exposed to food materials.
10.6.2.7 Safety
Anaerobic digesters are inherently dangerous; several catastrophic
failures have been recorded. To prevent such failures, safety equipment
such as pressure-relief and vacuum-relief valves, flame traps, conden-
sate traps, and gas collection safety devices is necessary. It is important
that these critical safety devices be checked and maintained for proper
operation.
Note:
Because of the inherent dangers involved with working inside
anaerobic digesters, they are automatically classified as permit-required
confined spaces; therefore, all operations involving internal entry must
be made in accordance with OSHA's confined space entry standard.
10.6.2.8 Process Control Monitoring, Testing, and Troubleshooting
During operation, anaerobic digesters must be monitored and tested
to ensure proper operation. Testing should be accomplished to deter-
mine supernatant pH, volatile acids, alkalinity, BOD or COD, total sol-
ids, and temperature. Sludge (in and out) should be routinely tested for
percent solids and percent volatile matter. Normal operating parameters
are listed in Table 10.5. As with all other unit processes, the wastewater
operator is expected to recognize problematic symptoms with anaero-
bic digesters and take the appropriate corrective actions. Symptoms,
causes, and corrective actions are discussed below:
