Potential strategies for process control and monitoring of stabilization of dairy wastewaters in batch aerobic treatment systems

Abstract

This research was conducted to study the relationships between pH, dissolved oxygen (DO), and oxidation–reduction potential (ORP) during low-intensity aeration of dairy wastewaters and to determine potential strategies for monitoring and/or control of this treatment process. The results of this study ascertained that, close to the detection limit of commercially available DO probes (0.1 mg/l), DO is a poor indicator of the oxidation–reduction status of the dairy wastewater during this treatment processes. All the three parameters (ORP, DO, and pH) displayed features defining stabilization of the wastewater and hence all three can be used singly or in combination to monitor and/or to control this treatment process. The study also established strong linear relations between ORP and the log of DO; manifest in the high-correlation coefficients of 0.98 and 0.95 at the aeration rates of 0.067 and 0.034-l [air] l −1 [manure] min −1, respectively. The latter observation confirms the higher sensitivity of ORP over DO at very low-oxygen levels; a fact which indicates the superiority of ORP in the monitoring and control of oxidation–reduction status of the wastewater close to DO detection limit. Finally, both total volatile solids (TVS) and chemical oxygen demand (COD), which are common measures of wastewater stabilization; correlated well with pH, DO, and ORP during the entire treatment process. However, because the measurements of DO are erratic close to the DO detection limit, and because ORP and pH measurements are much more consistent than the DO in the entire range of treatment, these two parameters will be more suitable for monitoring and control especially of extended aeration treatments.