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This review compiles information on sidestream characteristics that result from anaerobic digestion dewatering (conventional and preceded by a thermal hydrolysis process), biological and primary sludge thickening. The objective is to define a range of concentrations for the different characteristics found in literature and to confront them with the optimal operating conditions of sidestream processes for nutrient treatment or recovery. Each characteristic of sidestream (TSS, VSS, COD, N, P, Al 3+ , Ca 2+ , Cl - , Fe 2+/3+ , Mg 2+ , K + , Na + , SO 4 2- , heavy metals, micro-pollutants and pathogens) is discussed according to the water resource recovery facility configuration, wastewater characteristics and implications for the recovery of nitrogen and phosphorus based on current published knowledge on the processes implemented at full-scale. The thorough analysis of sidestream characteristics shows that anaerobic digestion sidestreams have the highest ammonium content compared to biological and primary sludge sidestreams. Phosphate content in anaerobic digestion sidestreams depends on the type of applied phosphorus treatment but is also highly dependent on precipitation reactions within the digester. Thermal Hydrolysis Process (THP) mainly impacts COD, N and alkalinity content in anaerobic digestion sidestreams. Surprisingly, the concentration of phosphate is not higher compared to conventional anaerobic digestion, thus offering more attractive recovery possibilities upstream of the digester rather than in sidestreams. All sidestream processes investigated in the present study (struvite, partial nitrification/anammox, ammonia stripping, membranes, bioelectrochemical system, electrodialysis, ion exchange system and algae production) suffer from residual TSS in sidestreams. Above a certain threshold, residual COD and ions can also deteriorate the performance of the process or the purity of the final nutrient-based product. This article also provides a list of characteristics to measure to help in the choice of a specific process., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

In response to the growing global resource scarcity, wastewater is increasingly seen as a valuable resource to recover and valorise for the benefit of the society rather than another waste that needs treatment before disposal. Conventional wastewater treatment plants (WWTPs) oxidise most of the organic matter present in wastewater, instead of recovering it as a feedstock for biomaterials or to produce energy in the form of biogas. In contrast, an A-Stage is capable of producing a concentrated stream of organic matter ready for valorisation, ideally suited to retrofit existing large plants. This technology is based on the principle of high-rate activated sludge process that favours biosorption and storage over oxidation. In this paper, we summarize peer-reviewed research of both pilot-scale and full-scale studies of A-Stage process under real conditions, highlighting key operational parameters. In the majority of published studies, the sludge retention time (SRT) was identified as a key operational parameter. An optimal SRT of 0.3 days seems to maximize the redirection of influent COD - up to 50% to the sludge flux, while simultaneously keeping mineralization under 25% of total influent COD. Other key optimal parameters are a hydraulic residence time of 30 min and dissolved oxygen levels of 0.5 mg⋅L - 1 . In addition, nutrient removal efficiencies of 15-27% for total nitrogen and 13-38% for total phosphorus are observed. Influence of mixing on settling efficiencies remain largely underexplored, as well as impact of wet weather flow and temperature on overall recovery efficiencies, which hinders to provide recommendations on these aspects. Evolution of modelling efforts of A-Stage process are also critically reviewed. The role of extracellular polymeric substances remain unclear and measures differ greatly according to the different studies and protocols. Better understanding the settling processes by adding Limit of Stokesian and Threshold of Flocculation measures to Sludge Volume Index could help to reach a better understanding of the A-Stage process. Reliable modelling can help new unit processes find their place in the whole treatment chain and help the transition from WWTPs towards Wastewater Resource Recovery Facilities., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier Ltd.)

Nitrifying biologically active filters (BAFs) have been found to be high emitters of nitrous oxide (N 2 O), a powerful greenhouse gas contributing to ozone layer depletion. While recent models have greatly improved our understanding of the triggers of N 2 O emissions from suspended-growth processes, less is known about N 2 O emissions from full-scale biofilm processes. Tertiary nitrifying BAFs have been modeled at some occasions but considering strong simplifications on the description of gas-liquid exchanges which are not appropriate for N 2 O prediction. In this work, a tertiary nitrifying BAF model including the main N 2 O biological pathways was developed and confronted to full-scale data from Seine Aval, the largest wastewater resource recovery facility in Europe. A mass balance on the gaseous compounds was included in order to correctly describe the N 2 O gas-liquid partition, thus N 2 O emissions. Preliminary modifications of the model structure were made to include the gas phase as a compartment of the model, which significantly affected the prediction of nitrification. In particular, considering gas hold-up influenced the prediction of the hydraulic retention time, thus nitrification performances: a 3.5% gas fraction reduced ammonium removal by 13%, as the liquid volume, small in such systems, is highly sensitive to the gas presence. Finally, the value of the volumetric oxygen transfer coefficient was adjusted to successfully predict both nitrification and N 2 O emissions., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

A full-scale nitrifying biofilter was continuously monitored during two measurement periods (September 2014; February 2015) during which both gaseous and liquid N2O fluxes were monitored on-line. The results showed diurnal and seasonal variations of N2O emissions. A statistical model was run to determine the main operational parameters governing N2O emissions. Modification of the distribution between the gas phase and the liquid phase was observed related to the effects of temperature and aeration flow on the volumetric mass transfer coefficient (kLa). With similar nitrification performance values, the N2O emission factor was twice as high during the winter campaign. The increase in N2O emissions in winter was correlated to higher effluent nitrite concentrations and suspected increased biofilm thickness., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The standard oxygenation performances of fine bubble diffused aeration systems in clean water, measured in 12 cylindrical tanks (water depth from 2.4 to 6.1m), were analysed using dimensional analysis. A relationship was established to estimate the scale-up factor for oxygen transfer, the transfer number (N(T)) The transfer number, which is written as a function of the oxygen transfer coefficient (k(L)a(20)), the gas superficial velocity (U(G)), the kinematic viscosity of water (nu) and the acceleration due to gravity (g), has the same physical meaning as the specific oxygen transfer efficiency. N(T) only depends on the geometry of the tank/aeration system [the total surface of the perforated membrane (S(p)), the surface of the tank (S) or its diameter (D), the total surface of the zones covered by the diffusers ("aerated area", S(a)) and the submergence of the diffusers (h)]. This analysis allowed to better describe the mass transfer in cylindrical tanks. Within the range of the parameters considered, the oxygen transfer coefficient (k(L)a(20)) is an increasing linear function of the air flow rate. For a given air flow rate and a given tank surface area, k(L)a(20) decreases with the water depth (submergence of the diffusers). For a given water depth, k(L)a(20) increases with the number of diffusers, and, for an equal number of diffusers, with the total area of the zones covered by the diffusers. The latter result evidences the superiority of the total floor coverage over an arrangement whereby the diffusers are placed on separate grids. The specific standard oxygen transfer efficiency is independent of the air flow rate and the water depth, the drop in the k(L)a(20) being offset by the increase of the saturation concentration. For a given tank area, the impact of the total surface of the perforated membrane (S(p)) and of the aerated area (S(a)) is the same as on the oxygen transfer coefficient.

This note presents and compares two models to predict the equilibrium temperature in aerated basins. They differ by their degree of complexity and therefore by the input data they require. Both models were able to estimate the temperature of an industrial aerated lagoon, the more complex model giving, in addition, a complete breakdown of the heat exchanges.