Background/Reason
A seemingly age old problem with more restrictive permitted ammonia concentrations is the by-product in the form nitrates. Presence of nitrates in one of the most problematic locations, the secondary clarifier, often times leads to issues meeting permitted total suspended solids and, where applicable, total nitrogen limits. In the absence of treatment processes to either denitrify upstream of the clarifier or mitigate solids release from the clarifier via filtration, continuous release of nitrogen gas from nitrates as well as limited mixing of the various strata of sludge in the clarifier bottom provides a significant operational advantage. It should be noted that with the filtration step, there are solids loading limits that allow the filter to remain largely functional.
Description
The SSC is comprised of a plurality of chains attached to a beam supported by chains, struts or some other means of support. In this case, the beam support was attached to the scraper assembly portion above the water. All parts of the equipment should able to withstand the corrosive environment of the clarifier. The chains, in this application, are separated by about 3 inches and extend from the beam down to the floor with several inches to spare to account for the slope of the floor from the perimeter to the center. The SSC should be several feet ahead of the scraper to allow for the nitrogen gas to be released in advance of the scraper as well as limit the potential for contact between the SSC and the scraper.
Operation
This recently devised piece of clarifier equipment aiding in the disruption of settled solids as well as release of the nitrogen gas goes by the name of the Settled Sludge Conditioner (SSC). This device provides minimal disruption of settled solids with the benefits of liberating trapped gases as well as further consolidation and compaction of settled sludge. These effects are accomplished by the minimal surface area and the aforementioned spatial attributes of the SSC chains as they “plow” through the settled sludge.
Observations
Operational conditions observed with the original design and installation as part of a center feed circular clarifier system with an automated scraper system were as follows:
1. Upon start up, there was a significant solids release which continued for about a half hour with severity gradually decreasing over time
2. Slight current is created, affecting the hydraulic characteristics by making the current more circular than radial
3. The few solids that floated after start up, were very small with the majority settling before they could be discharged over the weir
4. As a test, both return sludge pumps were turned off for 4 hours under otherwise normal operating conditions allowing clarifier sludge depth to exceed 5 out of 10 feet without significant solids loss
5. During high flow, “storm”, conditions the improved resiliency of the clarifier with respect to high mixed liquor concentrations and hydraulic overload conditions was very obvious