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Abstract: In the recent years, there has been an increasing interest in the development of hybrid reactors, especially in the up-grading of existing activated sludge plants that are no longer able to comply with concentration limits established by regulatory agencies. In such systems the biomass grows both as suspended flocs and as biofilm. In this way, it is possible to obtain a higher biomass concentration in the reactor, but without any significant increase of the load to the final clarifier. The paper presents the setting-up of a dynamic mathematical model aimed at quantitatively describing the biokinetic processes occurring in a hybrid moving bed biofilm reactor (HMBBR), and, more in general, in integrated fixed-film activated sludge (IFAS) processes, as well as to compare the simulation results with measured data from a HMBBR pilot plant built at the Norwegian University of Science and Technology in Trondheim (Norway). Particularly, the pilot plant consisted of three aerobic tanks in series; the first and third aerobic reactors were pure suspended biomass systems, while the second aerobic reactor was filled with the AnoxKaldnes™ K1 carriers for biofilm development. The mathematical model consists of two connected models for the simulation of both suspended biomass and biofilm. Biochemical conversions are evaluated according to the well known matrix notation used in the Activated Sludge Model No. 1 (ASM1) for both attached and suspended biomass and, in addition to biochemical conversion, the model contains the simulation of particulate detachment from the biofilm into the bulk liquid. The results showed an overall good agreement between measured and simulated data, for both biofilm and suspended biomass, with a good reproduction of dynamic processes in the hybrid moving bed pilot plant, and they are encouraging for further developments. [Copyright &y& Elsevier]

Abstract: A mathematical model for the simulation of physical-biological organic removal by means of a membrane bioreactor (MBR) has been previously developed and tested. This paper presents an analysis of the uncertainty of the MBR model. Particularly, the research explores the applicability of the Generalised Likelihood Uncertainty Estimation (GLUE) methodology that is one of the most widely used methods for investigating the uncertainties in the hydrology and that now on is spreading in other research field. For the application of the GLUE methodology, several Monte Carlo simulations have been run varying the all model influential parameters simultaneously. The model was applied to an MBR pilot plant located at the Acqua dei Corsari WWTP (Palermo, IT) where water quality data were gathered. In particular, the MBR pilot plant consists of a lab-scale hollow fibre membrane module in submerged configuration. The GLUE methodology enabled us to gain useful insight about the robustness of the model approach. Particularly, the results showed that the biological process is influenced mainly by the parameters characterising the formation and degradation of Soluble Microbial Products, whereas the fouling phenomenon is mainly influenced by the backwashing efficiency. The application of the GLUE methodology shows that the model considered for the MBR simulation is somehow too simple in order to predict plants performances. Indeed, GLUE enabled us to identify the main model components that needs to be improved and where much attention has to be paid both in terms of model algorithms and quality data to be gathered. This studies confirmed the suitability of the GLUE methodology as a powerful tool for simplified screening methodology to assess the uncertainty also in the field of wastewater treatment. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The effect of a co-substrate addition in TPH removal was studied in a MBR. • A novel hydrocarbons extraction method from complex mixture was developed. • A lower co-substrate supply enabled approximately 98% of biological TPH removal. • Bacteria able to grow on hydrocarbons as primary substrate were selected. • The membrane fouling increased under lower co-substrate supply. Abstract The paper reports the main results of an experiment carried out on a membrane bioreactor (MBR) plant designed for the treatment of shipboard slops. With a view of a co-treatment process of the slop with other wastewaters, sodium acetate, as external co-substrate, was supplied (high dosage – Period 1, low dosage – Period 2) to evaluate its effects on hydrocarbons removal. The MBR pilot plant enabled approximately 99% of total petroleum hydrocarbon (TPH) removal during the entire experiment, confirming the robustness of the MBR technology for the treatment of slops. The chromatography/mass spectrometry analysis showed that the removal efficiency for each alkane was close to the value observed for total mixture removal (>99%) and the hydrocarbons removal was mostly due to the microorganism-mediated biodegradation. The biological contribution to TPH removal increased from approximately 85% to 98% when the co-substrate was decreased. Biomass kinetics revealed that a lower co-substrate dosage enhanced the growth of bacterial groups able to use hydrocarbons as primary substrate. A clear predominance of Microthrix Parvicella under low co-substrate dosage was observed. However, the lower co-substrate addition caused a significant worsening in the physical properties of the activated sludge, which resulted enriched in soluble exopolymers (>70%), more hydrophobic (>90%) and with small and dispersed flocs (<30 μm). Consequently, the membrane permeability reduced because of the irreversible fouling increase. [ABSTRACT FROM AUTHOR]

Highlights: [•] We examined a hybrid activated/biofilm pilot plant working in cold climate region. [•] High COD and ammonium removal efficiencies in the whole period. [•] It is possible to sustain nitrification at quite low SRT values of mixed liquor. [•] Seeding effect of nitrifiers from the detached biofilm to the mixed liquor. [Copyright &y& Elsevier]

• PN process was studied in a SBR treating landfill leachate at different ALR and C/N. • Stable PN was achieved at ALR between 0.30-0.50 kg NH 4 -N m−3d-1 and C/N lower than 4. • NOB inhibition was achieved at lower ALR and higher C/N compared with the literature. • The highest PN and TN removal performances were obtained under similar ALR and C/N. • The maximum autotrophic activity was found at ALR of 0.30 kg NH 4 -N m−3d-1. Partial nitrification (PN) is a technically and economically effective solution for the treatment of wastewater featuring low C/N ratio, allowing to achieve approximately 25% energy saving and 40% carbon source for denitrification. This study investigated the effect of different carbon to nitrogen ratio (C/N) and ammonia loading rate (ALR) on PN performances in a sequencing batch reactor (SBR) treating landfill leachate with municipal wastewater. The aim was to find an optimum range for C/N and ALR to maximize PN performances. Results demonstrated that a proper balancing between ALR and C/N is crucial to achieve high PN efficiency. The results highlighted the existence of an optimum range for ALR and C/N of approximately 0.30–0.50 kg NH 4 -N m−3d−1 and 2–4, respectively. Although complete suppression of NOB was not achieved at these values, a predominance of nitrite (125 mg L−1) to nitrate (50 mg L−1) was observed. The results demonstrated the achievement of PN even at high C/N (4) but, on the other hand, C/N higher than 6 were not favorable to autotrophic growth. C/N significantly lower than 4 caused a stress condition for the biomass, leading to an excess in SMP production. Therefore, the operational parameters as well as the co-treatment ratio should be adjusted in order to operate the system under specific ALR (0.30–0.50 kg NH 4 -N m−3 d−1) and C/N (2–4). [ABSTRACT FROM AUTHOR]