An assessment of sewage sludge stability with a specific oxygen utilization rate (SOUR) test method

Sewage sludge treatment systems are intended to stabilize the sludge so that its disposal or reuse can be environmentally acceptable. However, stabilized sludges may still contain residual biodegradable organic matter that can be environmentally a nuisance. This paper presents a specific oxygen utilization rate [SOUR, mgO2/(gVSS·h)] batch reactor test method to quantify the residual biodegradable organic matter content of the treated (stabilized) sewage sludges. The results of the study, in which 37 SOUR batch tests were done on 10 different sewage sludges, show that the SOUR, when determined over a prolonged period (4 to 5 days), gives an indirect measure of sludge stability defined as the % soluble and particulate residual biodegradable organics in the sludge; to determine % sludge stability, it is necessary to simulate the experimental SOUR data by means of a general activated sludge model. The % sludge stability obtained for the 10 different sludges, taking due account of their soluble and particulate constituents, was consistent with that expected from the stabilization treatment systems to which the sludges were subjected.

Floc-Load as It Relates to Enzymatic Transfer of Soluble Substrate and Sludge Bulking Control

Floc-load and enzymatic transfer of soluble substrate from a wastewater into microorganisms in an activated sludge floe are related. In the absence of other metabolic selectivity pressures, this rapid sequestering of available soluble organics is required for the avoidance of filamentous sludge bulking in various reactor configurations. The specific oxygen utilization rate response to floc-loading is a measure of the magnitude of the enzymatic transfer capacity of a biomass and can be used to determine its maximum sorptive capacity. During the transfer process the biomass Adenosine triphosphate (ATP) content undergoes a rapid depletion for 20-30 minutes before increasing again. Relevant parameters associated with soluble substrate removal and floc-forming selectivity mechanisms are summarized.