A brief introduction of the long history of biofilm-based wastewater treatment is given together with basics of biofilm behavior and mechanisms in removal and transformation of pollutants. Moving bed biofilm reactor (MBBR) principles and applications of such are presented. Advantages and limitations of such solutions are given together with evaluations of emerging MBBR applications. The basis of biofilm processes and biofilm layer classification based on dissolved oxygen gradient is discussed. Organisms grow at the protected surface of the biocarrier where oxygen gradients create aerobic, anoxic, and anaerobic layers allowing simultaneous nitrification and denitrification in one MBBR (nitrification, nitritation, autotrophic, and heterotrophic denitrification). Combination of MBBR with activated sludge, continuous flow intermittent cleaning (CFIC®), and integration with anaerobic digestion increases the potential usage of MBBR for enhanced efficiency and energy recovery and is partly discussed as case studies (COD, ammonium, and solid removal). Biofilm thickness and scaling control can be crucial for MBBR performance. The type of carriers, filling degree, and operational conditions play a major role for process performance; hence, the effect of those parameters is presented.

In the process industry arena, analytical endeavors are today well served by the Process Analytical Technology (PAT) framework, offering a plentitude of on-line analytics, mostly spectroscopic: UV-VIS, NIR, RAMAN, NMR, “acoustic chemometrics” a.o. This context is generally considered satisfactory, but there is a major catch. The present paper focuses on a fundamental feature in process sampling, the link between an on-line analytical technique and a moving stream of matter, which is to be characterised, monitored, and analysed. A process sampling operation can serve many objectives; process regulation, product or interim product characterisation, optimisation of raw material consumption, maximizing energy efficiency, pollution, and environmental impact management ‒ or process, plant, company, corporation decision making at supervisor and management levels concerning economics and risk management. All these objectives can only be meaningfully undertaken if based onrelevant information, that is, if based on reliable analytical data, which in turn is 100% dependent upon representative samples, or representative sensor signals. The singular common element in all of this is the process sampling interface. This paper develops a critique of most current interfaces, with a scathing verdict: the dual role of the process sampling interface as both delineating an appropriate aliquot volume while facilitating the specific analytical technique, has largely been overlooked, with a significant negative effect that is spelled out in full detail across implemented solutions across widely different application sectors. Most current process sampling interfaces do not comply with TOS’ demands, putting representativity severely at risk for heterogenous materials.

This study presents a series of experiments to test the integration of syngas fermentation into a single-cell microbial electrosynthesis (MES) process. Minimal gas–liquid mass transfer is the primary bottleneck in such gas-fermentation processes. Therefore, we hypothesized that MES integration could trigger the thermodynamic barrier, resulting in higher gas–liquid mass transfer and product-formation rates. The study was performed in three different phases as batch experiments. The first phase dealt with mixed-culture fermentation at 1 bar H2 headspace pressure. During the second phase, surface electrodes were integrated into the fermentation medium, and investigations were performed in open-circuit mode. In the third phase, the electrodes were poised with a voltage, and the second phase was extended in closed-circuit mode. Phase 2 demonstrated three times the gas consumption (1021 mmol) and 63% more production of acetic acid (60 mmol/L) than Phase 1. However, Phase 3 failed; at –0.8 V, acetic acid was oxidized to yield hydrogen gas in the headspace.

Moving bed biofilm reactor (MBBR) is a robust, flexible and compact technology for treatment of medium to high strength wastewater. However, while treating wastewater with high concentration of ammonium, phosphorus and metal ions, scaling on the biofilm carriers can occur, causing biofilm carriers to sink the bottom of reactors. That leads to less carrier motion, higher energy consumption and deteriorated mass transfer, causing lower process efficiency and increased operational cost. This can be a major MBBR operational challenge for certain types of wastewater. In this study, scaling on biofilm carriers in an MBBR reactor treating reject water from anaerobically digested wastewater sludge was investigated. The 67 L reactor was operated at 16 h hydraulic retention time (HRT) for over 250 days. The metal ion concentrations in the reject wastewater in and out of the MBBR were analyzed using microwave plasma-atomic emission spectroscopy (MP-AES). The chemical equilibrium simulation tool-Visual MINTEQ 3.1 was applied to determine the possible mineral precipitates. The measured concentrations of Mg 2+ , Ca 2+ , Fe 3+ , NH4-N, PO4 3-, SO4 2and alkalinity from the inlet and outlet of the reactor were used as inputs to the model. Dry biomass and precipitates from biofilm carriers were digested by a DigiPREP digestion system and element analysis performed using MP-AES for simulated data validation. The results show that Fe 3+ and Ca 2+ had the highest potential to form mineral precipitates and scaling on the biofilm carriers. Hematite, Maghemite, Hydroxyapatite, Geothite and Magnesioferrite were the first five predominant forms of mineral precipitates, in the pH range from 6.0 to 9.0. The saturation indices (SI) of these five minerals increased with pH, implying that measures to lower pH may reduce the problem. Digested biomass composition and inorganic solid analysis confirmed that calcium is the major cause for scale formation on the biofilm carriers. Crystal formations in the biofilms were confirmed by optical microscopy images.

Biogas upgrading to biomethane with microbial electrosynthesis (MES) is receiving much attention due to increasing biomethane demands and surplus renewable energy. Research has demonstrated the feasibility of MES to increase methane yield by reducing CO2 in anaerobic digestion (AD). Such CO2 reduction occurs at the cathode and requires the supply of both protons and electrons. The most studied sources of protons and electrons are oxidation of organic substances and water, generated at the anode. These anodic reactions, however, also imply the production of CO2 and O2, respectively, both with negative implications for the AD process. A source of protons and electrons without CO2 and O2 as by-products would be beneficial for MES-enhanced biomethane production. This opinion article discusses the possibility of ammonium to serve as a sustainable proton and electron source.

Water from anaerobic sludge dewatering (reject water that is recycled to the inlet main process treatment) from the Knarrdalstrand municipal wastewater treatment plant in Porsgrunn, Norway, contains 2.4 g/L of total chemical oxygen demand (TCOD) and 550 mg/L NH4-N (annual average). The high concentration of ammonium causes disturbances in the mainstream physical and chemical processes, while only a small fraction of the organics is biodegradable. A pilot-scale hybrid vertical anaerobic biofilm (HyVAB) reactor combining anaerobic and aerobic treatment was tested for reject water treatment to reduce process disturbances. The pilot HyVAB was prepared for the study with continuous aeration of the aerobic part of the reactor for 200 days, while two intermittent aeration schemes were applied during the three-month test period. Ammonium removal efficiency increased from 8% during the continuous aeration period to 50% at the end of the test when a short (7 min) aeration cycle was applied. COD removal was close to 20%, which was mainly obtained in the anaerobic stage and not significantly influenced by the aerations schemes. Simultaneous partial nitrification and denitrification were established in the biofilm that alternated between aerobic and anoxic conditions. The observed high ammonium removal is explained by two alternative shortcut processes via nitrite. The lack of biodegradable organics in the aerated stage suggests that most of the nitrogen removal was via the anammox pathway (autotrophic denitrification). The HyVAB, combining an anaerobic sludge bed and an intermittently aerated biofilm, appears to be an efficient process to treat high ammonium containing reject water.

No abstract

No abstract