Understanding the AAA: A Promising Alternative A-stage Process for Organics Recovery from Wastewater

Recently, the achievement of energy neutrality and resources recovery in wastewater treatment plants has become inventible. Accordingly, the interest in the A-stage of the adsorption/bio-oxidation (A/B) for carbon management has considerably increased. To this end, high-rate activated sludge and high-rate contact stabilization systems are employed. Induced by its flexible and compact design, the Alternating Activated Adsorption (AAA) system was recently proposed and patented as an alternative A-stage system. Yet, literature on such a system is scarce. Hence, in this article for the first time, the performance of the novel AAA system is evaluated. Two systems were operated to assess AAA as a primary settler replacement (AAA-1) or to complement the primary settler (AAA-2). The goal of this study is to assess and position the AAA system among other A-stage systems. 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 hours). Moreover, AAA-1 has 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 bottom feeding/top discharging regime adds unique capacity for pCOD capture in AAA. Whereas further enhancements are needed to improve the AAA-2’s pCOD removal and TCOD redirection. Owing to the oxygen supply pattern and short SRT, AAA attains low mineralization regardless wastewater strength (16-17%). Compared with other systems, it can be concluded that, with further optimizations, AAA system has the potential to outcompete other A-stage systems. As such, improving sludge settleability is found to be the bottleneck, especially when treating low strength wastewater.