The use of oxidation-reduction potential (orp) as a process a process control parameter in wastewater treatment systems

David Geraint Wareham
This research explored the use of Oxidation-Reduction Potential to control two lab-scale sequencing batch reactor (SBR) wastewater treatment processes. The treatment schemes investigated were the aerobic-anoxic digestion of activated sludge (AASD) and the excess biological phosphorus (Bio-P) removal process. Evaluation of each process consisted of a consideration of the reactor performances coupled with the control stability achieved using two different operating strategies. The first strategy
more » ... The first strategy was known as "Fixed-Time Control" (FT), since it represents the "classical" management approach; control is based on conditions externally "fixed" by an operator. For the AASD set of experiments, the "fixed" variable was the ratio of air-on to air-off (3 hours each). For the Bio-P experiments, it was the time of addition of acetate to the reactor (1 hour 25 minutes into the non-aerated sequence). The second strategy was known as "Real-Time Control" (RT), since it represents an optimization technique whereby control conditions are continuously evaluated as time progresses. The Real-Time aspect of control is derived from the fact that ORP measurements evaluate the reactor conditions on-line, by invoking a bacterial vision of the process scheme. For the AASD experiments, this evaluation took the form of proportioning the ratio of air-on to air-off, based upon the bacterial "need" for sufficient time to reduce the nitrates completely to nitrogen gas (denitrification). Sufficient time is determined by the distinctive breakpoint (correlated to nitrate disappearance) occurring in the ORP-time profile. The first experiment (AASD#1) , therefore, had an air-on/airoff ratio of 3 hours air-on/nitrate-breakpoint-determined airoff. The second experiment (AASD#2) had the length of aeration time determined by a match to the previous length of time for denitrification, as determined by the breakpoint. In the Bio-P experiments, the ORP breakpoint was used to "trigger" the addition of acetate to the reactor, t [...]
doi:10.14288/1.0050500 fatcat:3vzdqonzd5cdhp3nvtgccaskxe