Hybrid electrochemical and biological systems hold promise for pro-ducing valuable products from abundant feedstocks. An electro-lyzer-bioreactor assembly using wastewater streams as catholytes could bring bioelectrochemical methanogenesis closer to practical implementation. Herein, we develop a zero-gap cell with a porous transport layer in the cathode specifically conceptualized for oper-ating in line with a wastewater-fed methanogenic reactor. In-depth analysis of the electrode composition indicates an up to 4-fold vari-ation of the current density depending on the binder and carbon black contents. This electrolyzer configuration and electrode selection, along with a robust pentlandite-type cathode catalyst, Fe3Ni3Co3S8, allow for an efficient supply of hydrogen into the catholyte that recirculates through the bioreactor, which is domi-symbolscript symbolscript Methanobacterium symbolscript Methanobrevibacter symbolscript This hybrid system produces methane over 220 days with a maximal weekly average rate of 669 LN m-2cathode d-1. The corresponding average current density sustained by the entire hybrid system is 30 mA cm -2 at a 2.2 V set potential.

A comprehensive mathematical modeling of wastewater-fed microbial fuel cells (MFC) demands an in-depth process understanding of the main electrical and bioelectrochemical interactions at both electrodes. In this study, a novel holistic simulation approach using a low-parameterized model was applied to predict pollutant transport, conversion, and electrical processes of mixed-culture single-chamber MFCs. The proposed whole-cell model couples the combined bioelectrochemical-electrical model with the well-established Activated Sludge Model No.1 (ASM1) and specific equations from ASM2. The cathodic gas-liquid mass transfer of oxygen and free ammonia nitrogen was described in terms of a diffusion film model, while the diminishing diffusivity due to salt deposits was considered via a fouling decline kinetic model. The predictive capacity of the model was validated using experimental data of three continuous-flow single-chamber MFCs operated with municipal wastewater for 150 days. Electrochemical parameters were estimated in real-time by pulse-width modulated connection of the external electrical load resistance. Following a sensitivity analysis, the most relevant model parameters were optimized through the Monte-Carlo Markov-Chain method using the adaptive Metropolis algorithm. All other parameters were adopted from benchmark simulation studies. The simulated relative contributions of aerobic carbon oxidation, denitrification, electrogenesis, and methanogenesis to the total COD removal rate were 21-22%, 44-45%, 21-25%, and 9-14%. Overall, the presented whole-cell model is able to successfully predict the evolution of electricity generation, methane production, and effluent concentrations (soluble COD and total ammonia nitrogen) under different hydraulic conditions and organic loading rates.

Experimental data that allow for a precise identification of the total ammonia nitrogen (TAN) elimination pathways in single-chamber microbial fuel cells (SC-MFCs) are still very rare. However, nitrification-denitrification and ammonia volatilization are commonly reported as the two main removal mechanisms. This work presents a mathematical model to quantify the contribution of volatilization to TAN removal in SC-MFCs. For model verification, three different experimental settings were performed with TAN concentrations of 57 to 111 mg(N) L-1: (i) biotic tests using sealed cathode chambers with variable oxygen supply, (ii) biotic tests for determination of the pH gradient within the cathodic microenvironment and (iii) pH-induced abiotic gas release tests. In biotic tests, the TAN removal rate in closed-circuit was 29-37% higher compared to open-circuit mode, which indicated additional electrochemical conservation processes. A limitation of oxygen availability on the air-facing side of the cathode (0.1%) resulted in negligible TAN removal rates. In contrast, an atmospheric oxygen content of 21% increased the biological oxidation rate of TAN to 653-730 mg(N) m(Cat)(-2) d(-1) and the electrochemical ammonia stripping rate to 210-241 mg(N) m(Cat)(-2) d(-1) at 22 C. During electricity generation, a peak pH value of 9.6 was measured by microelectrode measurements, which might lead to free ammonia nitrogen concentrations of 39-40 mg(FAN) L-1 nearby the cathode surface. Based on the proposed model and assuming an inhibition of ammonium-oxidizing bacteria, a maximum TAN removal rate via ammonia volatilization of 785 mg(N) m(Cat)(- 2) d(-1)& nbsp;(T = 22 C) at a current density of 322 mA m(Cat)(-2) is estimated.

This study investigated the influence of temperature (20 and 30 °C) on the formation and stability of aerobic granules in sequential batch reactors (SBR). Therefore, two lab-scale SBRs operated at 20 and 30 °C (SBR20 and SBR30) were used. The reactors were fed with municipal wastewater (CODt:TN:TP 100:15:1.7), leading to mean organic loading rates (OLR) of 1.3 ± 0.4 kgCODt.m-3.day-1. Both reactors had the same height/diameter ratio of 4.2 and were inoculated with activated sludge from a municipal wastewater treatment plant. The operational conditions were also the same for both temperatures and lasted in stable process parameters for over 100 days. By optimizing the aeration and oxygen concentration, a high removal efficiency of NH4-N (∼99%) and COD (∼90%) was achieved in both reactors, despite the poor C:N:P ratio at the influent. Furthermore, a relatively low oxygen concentration of 2 mg.L-1 was defined as the set point for the control strategy. Nevertheless, granulation at 30 °C was significantly faster, resulting in more stable sludge volume index (SVI) values (SVI10/SVI30 < 1.1). The granules formed at 30 °C were also larger, more compact, and considerably more stable against system disturbances. However, at higher temperatures, larger granules might be required for nitrate removal because of the increased oxygen diffusion rates. Finally, microbiological 16S rRNA gene amplicon analysis for both systems indicated major differences relatively to the inoculum sludge only for nitrogen-degrading organisms.

The efficient energy recovery from wastewater through microbial fuel cells (MFC) depends on a comprehensive understanding of the electrochemical properties of the system. Different methods to infer electrochemical parameters can be applied. However, the absence of studies confirming the compatibility and inter-validity of these methods makes their comparison difficult. In this study six different electrochemical methods were compared in triplicate MFCs: i) varying circuit resistance (VCR); ii) linear sweep voltammetry (LSV); iii) current interruption (CI); iv) electrochemical impedance spectroscopy (EIS); v) pulse width modulation (R-PWM); and vi) the perturbation observation (P/O) algorithm. Comparative investigations of the ohmic resistances from CI (73.0 ? 11.4 0), EIS (70.8 ? 11.1 0) and R-PWM (73.3 ? 11.2 0) showed high agreement. Further analysis of the activation resistances using detailed model-based methods, such as EIS (26.0 ? 10.9 0) and R-PWM (25.0 ? 3.0 0) demonstrated that both methods provide identical results. The applicability of the R-PWM mode as a real-time optimization method can be supported by the calculated maximum power densities from VCR and LSV together with the adjusted resistance from the P/O algorithm. In R-PWM mode theoretical power densities up to 95% of the maximum power point can be achieved.

BACKGROUND The treatment of olive mill wastewater (OMWW) in a packed bed biofilm reactor (PBBR) and the identification of different microorganisms involved in the digestion process is an attractive field for research. RESULTS A PBBR treating OMWW under different organic loading rates (OLRs) (0.94-9.36 gCOD/(L d)), showed high stability during an extensive time (723 days) without any sign of acidification. High volumetric biogas and methane (CH4) productions, 4.1 and 2.4 L-N/(L-reactor d), respectively were registered at the highest OLR. Meanwhile, high chemical oxygen demand (COD) removal (62.5-79.7%) was obtained throughout the experiment. Phenolic compounds removal was much higher during the first steps of the experiment (75.9-84.2%), and decreased as the OLR increased to about 38%. High homogeneity of biofilm thickness and Bacteria and extracellular polymeric substance distribution were demonstrated by confocal laser scanning microscopy. Results of real-time quantitative polymerase chain reaction (PCR) and 16S rRNA amplicon analyses showed that Bacteria, mainly consisting of Firmicutes, Proteobacteria, Bacteroidetes and Chloroflexi phylum, was about eight times more abundant than Archaea in the reactor liquid phase, while Bacteria to Archaea ratio was almost one in the biofilm. This points to a major degradation of organic substances in the liquid, while methanogenesis occurred mainly within the biofilm. In the liquid, acetoclastic methanogens were more abundant than hydrogenotrophic ones, while both groups showed likely very similar contributions in the biofilm. CONCLUSION Promising results have been presented throughout this work providing information about the long-term operation of PBBR-granular activated carbon treating OMWW and analyzing, in an efficient manner, the structure and the composition of the microbial community involved in OMWW digestion. (c) 2019 Society of Chemical Industry

The efficiency of anaerobic biofilters (AnBF) as low-cost wastewater treatment systems was investigated. Miscanthus -biochar was used as filtration media and compared with sand as a common reference material. Raw sewage from a municipal wastewater treatment plant was stored in a sedimentation tank for two days to allow pre-settlement of wastewater particles. Subsequently, wastewater was treated by AnBFs at 22 °C room temperature at a hydraulic loading rate of 0.05 m∙h −1 with an empty bed contact time of 14.4 h and a mean organic loading rate of 509 ± 173 g COD ∙m −3 ∙d −1 . Mean removal of chemical oxygen demand (COD) of biochar filters was with 74 ± 18% significantly higher than of sand filters (61 ± 12%). In contrast to sand filters with a mean reduction of 1.18 ± 0.31 log-units, E . coli removal through biochar was with 1.35 ± 0.27 log-units significantly higher and increased with experimental time. Main removal took place within the schmutzdecke , a biologically active dirt layer that develops simultaneously on the surface of filter beds. Since the E . coli contamination of both filter materials was equal, the higher removal efficiency of biochar filters is probably a result of an improved biodegradation within deeper zones of the filter bed. Overall, performance of biochar filters was better or equal compared to sand and have thus demonstrated the suitability of Miscanthus -biochar as filter media for wastewater treatment.

In this study, the suitability of an anaerobic biofilter (AnBF) as an efficient and low-cost wastewater treatment for safer irrigation water production for Sub-Saharan Africa was investigated. To determine the influence of different ubiquitous available materials on the treatment efficiency of the AnBF, rice husks and their pyrolysed equivalent, rice husk biochar, were used as filtration media and compared with sand as a common reference material. Raw sewage from a municipal full-scale wastewater treatment plant pretreated with an anaerobic filter (AF) was used in this experiment. The filters were operated at 22 degrees C room temperature with a hydraulic loading rate of 0.05 m.h(-1) for 400 days. The mean organic loading rate (OLR) of the AF was 194 +/- 74 and 63 +/- 16 g(COD).m(-3).d(-1) for the AnBF. Fecal indicator bacteria (FIB) (up to 3.9 log(10)-units), bacteriophages (up to 2.7 log(10)-units), chemical oxygen demand (COD) (up to 94%) and turbidity (up to 97%) could be significantly reduced. Additionally, the essential plant nutrients nitrogen and phosphorous were not significantly affected by the water treatment. Overall, the performance of the biochar filters was significantly better than or equal to the sand and rice husk filters. By using the treated wastewater for irrigating lettuce plants in a pot experiment, the contamination with FIB was >2.5 log-units lower (for most of the plants below the detection limit of 5.6 MPN per gram fresh weight) than for plants irrigated with raw wastewater. Respective soil samples were minimally contaminated and nearly in the same range as that of tap water. (C) 2019 Published by Elsevier B.V.

Re-use of water containing helminth eggs during irrigation for agricultural purposes poses health risks, and likewise during research, due to the potential of spreading on contact. Therefore, polystyrene latex microspheres could be used as surrogates for chemical or biological species during colloidal transport. The aim here is to compare the settling velocities of microspheres having varied surface coatings—that is, proteins A, G and A/G; with that of real helminth eggs obtained from literature. The settling velocities of the microspheres were experimentally determined in tap- and wastewater, as well as theoretically in tap water; which was found to be within the range of mean values for those experimentally determined. There were no differences amongst the microspheres types used for settling in wastewater (i.e., A = 0.072 ± 0.02; G = 0.060 ± 0.03; A/G = 0.053 ± 0.01 mm/s). The same applied for settling in tap water (i.e., A = 0.068 ± 0.02; G = 0.047 ± 0.004; A/G = 0.095 ± 0.02 mm/s), except for microsphere G being different from microsphere A/G. All three types of microspheres settled at velocities lower than that of the wastewater particles (=0.118 ± 0.03). T-test analyses of settling velocities of microspheres in both tap- and wastewater, versus that from literature (i.e., Ascaris, Trichuris and Oesophagostomum), showed that microsphere A and A/G may surrogate for Ascaris in tap water, the same as A/G for Oesophagostomum. In wastewater however, both microspheres A and G are a good fit for Trichuris.

Re-use of water containing helminth eggs during irrigation for agricultural purposes poses health risks, and likewise during research, due to the potential of spreading on contact. Therefore, polystyrene latex microspheres could be used as surrogates for chemical or biological species during colloidal transport. The aim here is to compare the settling velocities of microspheres having varied surface coatings - that is, proteins A, G and A/G; with that of real helminth eggs obtained from literature. The settling velocities of the microspheres were experimentally determined in tap- and wastewater, as well as theoretically in tap water; which was found to be within the range of mean values for those experimentally determined. There were no differences amongst the microspheres types used for settling in wastewater (i.e., A = 0.072 \(\pm\) 0.02; G = 0.060 \(\pm\) 0.03; A/G = 0.053 \(\pm\) 0.01 mm/s). The same applied for settling in tap water (i.e., A = 0.068 \(\pm\) 0.02; G = 0.047 \(\pm\) 0.004; A/G = 0.095 \(\pm\) 0.02 mm/s), except for microsphere G being different from microsphere A/G. All three types of microspheres settled at velocities lower than that of the wastewater particles (=0.118 \(\pm\) 0.03). T-test analyses of settling velocities of microspheres in both tap- and wastewater, versus that from literature (i.e., \(\it Ascaris\), \(\it Trichuris\) and \(\it Oesophagostomum\)), showed that microsphere A and A/G may surrogate for \(\it Ascaris\) in tap water, the same as A/G for \(\it Oesophagostomum\). In wastewater however, both microspheres A and G are a good fit for \(\it Trichuris\).

Previous studies on the Miscellaneous Crenarchaeota Group, recently assigned to the novel archaeal phylum Bathyarchaeota, reported on the dominance of these Archaea within the anaerobic carbohydrate cycle performed by the deep marine biosphere. For the first time, members of this phylum were identified also in mesophilic and thermophilic biogas-forming biofilms and characterized in detail.

A 45-L pilot MFC system, consisting of four single-chamber membraneless MFCs, was integrated into a full-scale wastewater treatment plant (WWTP) and operated under practical conditions with the effluent of the primary clarifier for nine months to identify an optimal operational strategy for stable power output and maximum substrate based energy recovery (Normalized Energy Recovery, NER). Best results with the MFC were obtained at a hydraulic retention time of 22h with COD, TSS and nitrogen removal of 24%, 40% and 28%, respectively. Mean NER of 0.36kWhel/kgCOD,deg and coulombic efficiency of 24.8% were reached. Experimental results were used to set up the first described energy balance for a whole WWTP with an integrated MFC system. Energetic calculations of the model WWTP showed that energy savings due to reduced excess sludge production and energy gain of the MFC are significantly higher than the loss of energy due to reduced biogas production.

Significant quantities of antibiotics are used in modern livestock husbandry and are found in livestock waste. Such waste has been reported to exert inhibitory effects if used as a substrate in biogas facilities. The goal of this study is to analyze the inhibitory effect of the antibiotics chlortetracycline (CTC) and enrofloxacin (EFX) on biogas production with pig slurry. Antibiotic concentrations up to 8,000 mg kg−1 dry matter (DM) pig slurry were added in continuous fermentation tests. Impacts on methane production and on the microbial community structure were analyzed. The results clearly show that chlortetracycline and enrofloxacin negatively affect biogas production. Higher concentrations of antibiotics led to lower methane production. The addition of 200 mg kg−1 DM of CTC or EFX reduced the specific methane yields up to 49 and 44 %, respectively. The microbial community did not show any changes at this concentration. When chlortetracycline was added at a concentration of 8,000 mg kg−1 DM, the biodiversity changed slightly compared to the control without antibiotics.

Wastewater reuse could help to reduce the pressure from global water scarcity, especially in arid and semi-arid regions. Efficient and cheap water treatment technologies need to be developed, particularly in low-income countries where wastewater treatment is often lacking. Slow sand filtration (SSF) is a proper, efficient and well known technology to reduce the amount of pathogens and turbidity. However, an efficient use of SSF requires low water turbidity to prevent rapid filter clogging, which could be achieved by an upstream roughing filter (RF). The focus of this study was on the evaluation of biochar and woodchips as alternative and locally available filter materials in RF as pre-treatment for SSF and low cost production of safer irrigation water for urban agriculture in developing countries. The experimental setup consisted of nine glass columns, which were filled in triplicates with biochar, woodchips and gravel (grain sizes: 5–16 mm). Filters were fed with raw wastewater from the municipal treatment plant Ölbachtal (Bochum, Germany). Samples of influent and effluent were taken once per week and analysed for the fecal indicator bacteria (FIB) E. coli and intestinal enterococci, using the Most Probable Number (MPN) method and physico-chemical parameters (e.g. turbidity, chemical oxygen demand, electrical conductivity, pH). FIB concentration of raw wastewater was in the range of 106 to 5×107 MPN 100 mL−1. Removal rates for enterococci and E. coli were in the range of 0.5 to 1.5 log10 units MPN 100 mL-1, which is similar to other published results with respect to RF. Influent turbidity was in the range of 60 to 360 NTU. Beside FIB, turbidity (effluent turbidity below 35 NTU) and COD (reduction up to 89%) could be significantly reduced and effluent of all filter types were expected to be suitable for further treatment with slow sand filtration. Over the entire observation, biochar filter showed slightly higher removal rates than other materials. Overall, roughing filter seems to be a proper pre-treatment step for wastewater treatment with SSF.

Microbial communities involved in biogas production from wheat straw as the sole substrate were investigated. Anaerobic digestion was carried out within an up-flow anaerobic solid-state (UASS) reactor connected to an anaerobic filter (AF) by liquor recirculation. Two lab-scale reactor systems were operated simultaneously at 37°C and 55°C. The UASS reactors were fed at a fixed organic loading rate of 2.5gL−1d−1, based on volatile solids. Molecular genetic analyses of the bacterial and archaeal communities within the UASS reactors (digestate and effluent liquor) and the AFs (biofilm carrier and effluent liquor) were conducted under steady-state conditions. The thermophilic UASS reactor had a considerably higher biogas and methane yield in comparison to the mesophilic UASS, while the mesophilic AF was slightly more productive than the thermophilic AF. When the thermophilic and mesophilic community structures were compared, the thermophilic system was characterized by a higher Firmicutes to Bacteroidetes ratio, as revealed by 16S rRNA gene (rrs) sequence analysis. The composition of the archaeal communities was phase-separated under thermophilic conditions, but rather stage-specific under mesophilic conditions. Family- and order-specific real-time PCR of methanogenic Archaea supported the taxonomic distribution obtained by rrs sequence analysis. The higher anaerobic digestion efficiency of the thermophilic compared to the mesophilic UASS reactor was accompanied by a high abundance of Firmicutes and Methanosarcina sp. in the thermophilic UASS biofilm.

Background: The production of bio-methane from renewable raw material is of high interest because of the increasing scarcity of fossil fuels. The process of biomethanation is based on the inter- and intraspecific metabolic activity of a highly diverse and dynamic microbial community. The community structure of the microbial biocenosis varies between different biogas reactors and the knowledge about these microbial communities is still fragmentary. However, up to now no approaches are available allowing a fast and reliable access to the microbial community structure. Hence, the aim of this study was to originate a Flow-FISH protocol, namely a combination of flow cytometry and fluorescence in situ hybridization, for the analysis of the metabolically active microorganisms in biogas reactor samples. With respect to the heterogenic texture of biogas reactor samples and to collect all cells including those of cell aggregates and biofilms the development of a preceding purification procedure was indispensable.Results: Six different purification procedures with in total 29 modifications were tested. The optimized purification procedure combines the use of the detergent sodium hexametaphosphate with ultrasonic treatment and a final filtration step. By this treatment, the detachment of microbial cells from particles as well as the disbandment of cell aggregates was obtained at minimized cell loss. A Flow-FISH protocol was developed avoiding dehydration and minimizing centrifugation steps. In the exemplary application of this protocol on pure cultures as well as biogas reactor samples high hybridization rates were achieved for commonly established domain specific oligonucleotide probes enabling the specific detection of metabolically active bacteria and archaea. Cross hybridization and autofluorescence effects could be excluded by the use of a nonsense probe and negative controls, respectively.Conclusions: The approach described in this study enables for the first time the analysis of the metabolically active fraction of the microbial communities within biogas reactors by Flow-FISH.

The bacterial and archaeal communities and their dynamics from start-up to stable biogas formation were investigated using a novel anaerobic digester system designed for efficient digestion of lignocellulosic biomass. The lab-scale reactor systems each consisted of an up-flow anaerobic solid-state reactor (UASS) connected to an anaerobic filter (AF) with recirculation of the liquid phase. Mesophilic and thermophilic digestion was carried out in parallel systems. Both reactor systems were fed with wheat straw as sole substrate at an organic loading rate of 2.5 gVS L -1 d over a time period of 218 days. Samples were taken from the effluent of UASS and AF and of digestates. Additionally, at the last sampling day, biofilm carriers from the AF were analyzed. Terminal restriction fragment length polymorphism (T-RFLP) of PCR-amplified 16S rRNA genes was applied to analyze changes in the biocoenosis structure over time. Furthermore, for the samples of the last sampling, 16S rRNA gene libraries were constructed to obtain detailed insights into the taxonomical composition of the microbial communities responsible for biogas formation at stable process conditions. The results offer a considerable higher taxonomic variety of Bacteria compared to Archaea, whereas the mesophilic communities were much more diverse than the thermophilic. Furthermore the mesophilic and thermophilic communities were entirely different – only five common OTUs were found at both temperature regimes. The fingerprinting pattern showed a clear alteration during and even after establishment of a steady-state biogas formation process.

In this experimental work, the feasibility of wheat straw as a feedstock for biogas production is investigated using the newly developed upflow anaerobic solid-state (UASS) process. With the analytical emphasis placed on methane and metabolite production, both mesophilic and thermophilic 39 L UASS reactors were operated for 218 days at an organic loading rate of 2.5 g(VS)L(-1)d(-1) using wheat straw as sole substrate. For improved methanization of soluble metabolites, each UASS reactor was connected to an individual 30 L anaerobic filter (AF). During steady state thermophilic straw digestion was found to have a 36% higher methane yield (0.165 L g(VS)(-1)) whereas the hydrolysis rate constant increased by 106% (0.066 d(-1)).