An alternative A-stage process - Investigating the novel alternating activated adsorption (AAA) system for carbon management under different wastewater strengths.

The interest in the A-stage of the adsorption/bio-oxidation (A/B) process has considerably increased due to its capacity of carbon redirection to the solids stream. Induced by its flexible and compact design, the Alternating Activated Adsorption (AAA) was recently implemented in full-scale as an alternative A-stage system. However, the literature on such a system is scarce. In this article for the first time, the performance of the novel AAA system is evaluated. Two lab-scale AAA systems were operated as a primary settler replacement (AAA-1) or to complement the primary settler (AAA-2). Systems were assessed in terms of process control, effluent quality and carbon diversion. As settling and aeration are performed in the same reactor, AAA maintained high MLSS (2121 ± 293 mg/L for AAA-1 and 806 ± 116 mg/L for AAA-2) compared to the literature at such a very low aerobic SRT (<6 h). Regardless wastewater strength, AAA attains low oxidation (16-17%) owing to the oxygen supply pattern and short aerobic SRT. Moreover, AAA-1 showed high COD removal efficiency for soluble (67 ± 8%) and particulates (62 ± 14%) as well as COD redirection (47 ± 7%). In addition, it is demonstrated that the simultaneous bottom feeding and top discharging regime adds unique capacity for particulates capture in AAA. On the other hand, low particulates removal and total carbon redirection were observed in the AAA-2. Yet, the overall removal efficiencies are comparable with the literature. It can be concluded that, with further optimizations, AAA system has the potential to outcompete other A-stage systems. As such, sludge settleability is found to be challenging when treating low strength wastewater.