Oxygen transfer and uptake, nutrient removal, and energy footprint of parallel full-scale IFAS and activated sludge processes.

Integrated fixed-film activated sludge (IFAS) processes are becoming more popular for both secondary and sidestream treatment in wastewater facilities. These processes are a combination of biofilm reactors and activated sludge processes, achieved by introducing and retaining biofilm carrier media in activated sludge reactors. A full-scale train of three IFAS reactors equipped with AnoxKaldnes media and coarse-bubble aeration was tested using off-gas analysis. This was operated independently in parallel to an existing full-scale activated sludge process. Both processes achieved the same percent removal of COD and ammonia, despite the double oxygen demand on the IFAS reactors. In order to prevent kinetic limitations associated with DO diffusional gradients through the IFAS biofilm, this systems was operated at an elevated dissolved oxygen concentration, in line with the manufacturer's recommendation. Also, to avoid media coalescence on the reactor surface and promote biofilm contact with the substrate, high mixing requirements are specified. Therefore, the air flux in the IFAS reactors was much higher than that of the parallel activated sludge reactors. However, the standardized oxygen transfer efficiency in process water was almost same for both processes. In theory, when the oxygen transfer efficiency is the same, the air used per unit load removed should be the same. However, due to the high DO and mixing requirements, the IFAS reactors were characterized by elevated air flux and air use per unit load treated. This directly reflected in the relative energy footprint for aeration, which in this case was much higher for the IFAS system than activated sludge.

Molecular characterization of effluent organic matter identified by ultrahigh resolution mass spectrometry.

Effluent dissolved organic matter (EfOM) collected from the secondary-treated wastewater of the Orange County Sanitation District (OCSD) located in Fountain Valley, California, USA was compared to natural organic matter collected from the Suwannee River (SRNOM), Florida using ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Furthermore, the two different treatment processes at OCSD, activated sludge and trickling filter, were separately investigated. The blend of these two effluents was further evaluated after it had passed through the microfiltration process of the Advanced Water Purification Facility (AWPF) at Orange County Water District (OCWD). EfOM contained 872 different m/z peaks that were unambiguously assigned to exact molecular formulae containing a single sulfur atom and carbon, hydrogen and oxygen atoms (CHOS formulae). In contrast, the SRNOM sample only contained 152 CHOS formulae. The trend in CHO molecular compositions was opposite with 2500 CHO formulae assigned for SRNOM but only about 1000 for EfOM. The CHOS-derived mass peaks with highest abundances in EfOM could be attributed to surfactants such as linear alkyl benzene sulfonates (LAS), their co-products dialkyl tetralin sulfonates (DATS) and their biodegraded metabolites such as sulfophenyl carboxylic acids (SPC). The differences between the treatments were found minor with greater differences between sampling dates than treatment methods used.