A Disaster Waiting to Happen
by Kristin Taormina
Chemicals are routinely used in food and beverage production plants as product ingredients or for the cleaning and sanitizing of equipment and work areas. The chemicals work their way into downstream biological treatment plants through normal use, accidental spillage, or overdosing. Upsets to biological treatment systems occur whenever abnormally high concentrations of chemicals reach the biomass (aerobic or anaerobic).
The chemicals of major concern, used in many of the most effective sanitizers, are quaternary ammonium and halogen-based compounds and acids and bases. Some of the first signs of possible problems from production plant chemicals in wastewater are:
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A noticeable and unusual chemical odor from the wastewater
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A reduction in biogas production (anaerobic system) or increase in dissolved oxygen level (aerobic system)
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Increased foaming with a thicker, more viscous consistency (aerobic system)
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A reduction in COD/BOD removal (anaerobic and aerobic systems)
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A reduction in biomass activity and diversity, and an increase in cellular debris as viewed through a microscope (aerobic system)
Returning a biological system to normal following a chemical-induced upset takes time. Although the damage can be done within hours, recovery times are often multiples of the system’s sludge age (days) as the biomass struggles to regenerate.
If possible, the first step should be to determine if the influent wastewater still has abnormal concentrations of chemicals. Only immediate notification from the production plant or quick sampling and testing will provide such information. Concurrently, the influent wastewater feed to the biological process should be reduced or stopped. This is only possible if excess equalization or emergency storage capacity is available or if the production plant can curtail or stop generating wastewater.
Once the inhibitory or toxic influent wastewater condition is removed, run an inventory of the biomass available in the biological treatment process (TSS and VSS). Run accelerated biomass activity tests (BMP for anaerobic, O2 uptake for aerobic) and determine their viability. If the results are positive and time is available, slowly bring the biological process back online with an acceptable wastewater feed. Increase the organic loading in small steps (10-20%) and continue to monitor performance until full-load conditions are again achieved.
If the test results are negative, reseeding of the biological system with “fresh” biomass may be required. Aerobic biomass is readily available from neighboring industrial or municipal treatment plants. Suitable anaerobic biomass will be more difficult to find.
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