Oxidation–Reduction Potential Changes in Aeration Tanks and Microprofiles of Activated Sludge Floc in Medium‐ and Low‐Strength Wastewaters

Abstract

Real-time control of aeration tank operation is key to highefficiency pollutant removal and energy savings. One of the aims of this study was to examine the potential for using redox potential (oxidation-reduction potential [ORP]) to indicate wastewater quality online in aeration tanks treating medium (chemical oxygen demand [COD] of 70 to 150 mg/L) and low (COD of 15 to 30 mg/L) pollutant-concentration wastewaters. The fieldscale data provide a good relationship between ORP values and nutrient removal along the length of the aeration tanks. The ORP values increased dramatically as organic matter was removed along the aeration tanks, indicating the improvement of the bulk liquor redox status. Dissolved oxygen higher than 1.0 mg/L was necessary for good biodegradation and improvement of the liquid redox status. Nitrification occurred at higher ORP values (380 to 420 mV) than was the case for organic substrate oxidation (250 to 300 mV). The microprofiles obtained from microelectrode measurements substantiate the heterogeneity of the microbial processes inside activated sludge flocs. Because of microbial oxygen utilization, the aerobic region in the activated sludge floc was limited to the top layer (0.1 to 0.2 mm) of the activated sludge aggregate present in medium-strength wastewater, with an anoxic zone dominating inside the flocs. When dissolved oxygen in the bulk water was higher than 4.0 mg/L, the anoxic zone inside the floc disappeared. At low wastewater pollutant concentrations, the ORP and dissolved oxygen inside the activated sludge aggregates were higher than those from medium-strength wastewater. The prospect of using ORP as an online control approach for aeration tank operation and the potential reasons for activated sludge floc size varying with pollutant strengths are also discussed. Water Environ. Res., 76, 394 (2004).

Characteristics of a cobalt-based phosphate microelectrode for in situ monitoring of phosphate and its biological application

“…While DO concentration shifted the Y-intercept, the response (slope) still showed good sensitivity toward phosphate ions. From the results, it is recommended that DO profiles should be measured simultaneously with phosphate in environmental applications, especially microbial flocs in which DO is known to gradually be depleted along depth into the floc [18]. …”

“…The micro-profile measurements were carried out using an up-flow chamber with laminar flow conditions so that the floc was kept suspended but stationary while the microelectrode was inserted into the floc [17, 18]. Positioning and movement of the tip of the microelectrode was accomplished using a three-dimension micromanipulator (Model 11N, Narisige, Japan) located outside the Faraday cage (TMC, MA).…”

Power production in MFCs inoculated with Shewanella oneidensis MR‐1 or mixed cultures

“…In studies using ORP for real time control of aeration tanks in wastewater treatment systems, ORP values were strongly related to COD removal, and were different during organic substrate oxidation than when nitrification occurred. The researchers concluded that ORP measurements of the effluent could be used for online aerator control when combined with other parameters such as temperature, pH, and dissolved oxygen concentration (Li and Bishop, 2004). So far, no studies have examined MFC performance in relation to ORP.…”

Real-time control of oxic phase using pH (mV)-time profile in swine wastewater treatment

“…The ORP and DO levels can successfully indicate the oxidative and biological state of the wastewater, and pH is a good indicator of ongoing biological reactions. Additionally, OUR signals can efficiently indicate the end point of nitrification and denitrification reactions [1,[11][12][13][14][15][16][17]. Several researchers [1,3,10,16,18,19] studied nutrient removal from animal wastewater using a sequencing batch reactor (SBR) and a real-time control strategy that included considerations of the ORP and pH.…”