In situ methane enrichment with vacuum application to produce biogas with higher methane content.

Sludge produced in sewage treatment plants is an important source of organic matter to be used in anaerobic digestion to produce energy-rich biogas. The biogas produced in anaerobic digesters has a critical impact on achieving carbon neutrality and improving energy self-sufficiency. After effective upgrading, biogas can be converted into biomethane with an increased CH4 content, resulting in a higher volumetric energy value. Upgrading biogas to biomethane thus not only improves its energy content but also broadens its potential uses. In this study, it was aimed at enrich CH4 by removing dissolved CO2 from the digestate using a vacuum, leveraging the solubility differences of gases in liquid. In this context, two digesters (R-T and R-C) were operated for 194 days, and the effect of vacuum on in-situ methane enrichment was investigated. The vacuum was only applied to the test reactor (R-T), and the CH4 percentage was increased from 63 to 87, 80, and 75% in the vacuum exposure time intervals of 30, 10, and 5 min, respectively. Extended durations were not tested, as the rate of enrichment decreased sharply after 30 min. The maximum energy requirement of a vacuum application was estimated at 0.124 kWh/m3 methane. Conversely, vacuum application did not cause any deterioration in biogas production, and the methane yields were similar in both reactors.

Enhancement of hydrazine accumulation in anammox bioreactors.

The role of hydrazine (N2H4) in anammox metabolism has been widely studied; however, studies on N2H4 biosynthesis by anammox bacteria are limited in the literature. In this context, the current research aims to investigate the enhancement of biological N2H4 production in the anammox process in a long-term manner. The experimental studies started with the optimization of the operating conditions to achieve maximum N2H4 accumulation. Under favorable conditions (pH = 8.97 ± 0.08; T = 35.5 ± 0.5 °C; initial hydroxylamine dose = 1.46 ± 0.01 mM), 17.16 ± 0.64 mg L-1 of N2H4 accumulated in the batch systems. The continuity of N2H4 bioproduction was then evaluated by long-term observations. A continuous flow bioreactor was operated in four consecutive manipulated periods under optimized conditions. In the long-term operated bioreactor, 55.10 ± 0.30 mg L-1 N2H4 was accumulated at optimal conditions, which was 2.5 times higher than reported in the literature. Although manipulation of the bioreactor operating conditions initially resulted in a significant increase in N2H4 bioaccumulation, it subsequently caused a severe deterioration in anammox activity. However, this could be mitigated by increasing the biomass concentration in the anammox systems. In addition, the relative abundance of Candidatus Kuenenia decreased by 1.88% throughout the long-term operation.

Influence of ionic liquids on the electronic environment of atomically dispersed Ir on (MgO)(100).

Recently, ionic liquids (ILs) have been used as ligands for single-site Ir(CO)2 complexes bound to metal-oxide supports because of their electron-donor/acceptor capacities. The combined effects of supports and ILs as ligands may pave the way to the tuning of the surrounding electronic properties to increase electron-donor/acceptor efficiency in metal-oxide supported Ir(CO)2 complexes. Herein, we have used Density Functional Theory to model Ir(CO)2 complexes bound to MgO supports with and without the presence of an IL to explain the role of ILs in modifying the electronic structure of the supported complex. Comparison of the ν(CO) band stretching frequencies with experimental results has led to the rationalization of the factors driving the interactions between the IL, the support, and the catalyst as well as the justification of the methodology for further studies.

Recovery profile of anaerobic ammonium oxidation (anammox) bacteria inhibited by ZnO nanoparticles.

The potential effects of nanoparticles (NPs) on biological treatment processes have become significant due to their increasing industrial applications. The purpose of this research was to investigate the self-recovery ability of anammox bacteria following acute ZnO NPs toxicity. In this context, a 2-liter lab-scale anammox reactor was operated for 550 days to enrich the biomass required to the batch exposure tests. Anammox culture was firstly exposed to four different doses of ZnO NPs (50, 75, 100 and 200 mg/L) for 24 h. Then, the ZnO NPs were removed and self-recovery performance of the anammox bacteria was assessed by evaluating the nitrogen removal capacities for 72 h. Besides the nitrogen removal performance, extracellular polymeric substances (EPS) production was also detected to deeply understand the response of the enriched anammox culture against ZnO NPs exposure. The results revealed that sudden and high load of ZnO NPs (100 and 200 mg/L) resulted in persistent impairment to the nitrogen removal performance of the enriched anammox culture. However, relatively lower doses (50 and 75 mg/L) caused deceleration of the nitrogen removal performance during the recovery period. In addition, EPS content in the reactor decreased along with escalating load of ZnO NPs.

Assessment of Anammox process against acute and long-term exposure of ZnO nanoparticles.

The impacts of nanoparticles (NPs) on wastewater treatment have become a great concern because of their widespread applications. Although the acute responses of anammox bacteria to NPs have enhanced the knowledge about the potential risks of them, deep understanding of the cumulative impacts of NPs must be assessed. The purpose of this research was therefore to further extend the current knowledge by evaluating both acute and long-term effects of Zinc oxide (ZnO) NPs on Anammox process based on nitrogen removal performance, self-recovery ability and microbial community structure. The acute exposure tests indicated that, the median inhibition concentration (IC50) of ZnO NPs on Anammox process was 84.7 mg/L (54.82 mg ZnO NPs/g VSS). Acute exposure of 200 mg/L ZnO NPs (117.54 mg Zn/g VSS) caused 80% inhibition in batch assays while the long-term inhibition dosage was 100 mg/L ZnO NPs (187.50 mg ZnO NPs/g VSS) corresponding to 1022 mg/L total Zn (1916.27 mg Zn/g VSS) in the reactor due to the accumulation of NPs. Total, soluble and biomass-associated Zn concentrations were measured throughout the long-term exposure to observe the behavior of ZnO NPs in the reactor. Total Zn in the reactor was cumulatively increased and mostly originated from biomass-associated Zn. Following the long-term inhibition tests, self-recovery of Anammox process within 120 days demonstrated that, the ZnO NPs inhibition is reversible for the applied dose. Furthermore, next generation sequencing results indicated a symbiotic relationship between the microbial groups in the anammox bioreactor while relative abundance of Candidatus (Ca.) Brocadiaceae family showed a decrease parallel to the deterioration in nitrogen removal performance of bioreactor. At the end of the long-term exposure studies, 48.76% decline on anammox quantity was detected.

Role of ionic liquids on the selectivity and the rate of organic reactions: A computational approach.

In the last years, ionic liquids have been used as substitutes to common solvents since they combine good solubility properties with small vapor pressures. Herein, the Diels-Alder reactions of cyclopentadiene (CP) with acrolein, methyl acrylate and acrylonitrile in ionic liquids ([Emim][N(Tf)2]), ([Hbim][N(Tf)2]) and ([Bmim][OTf]) have been modeled with density functional theory to explore the effect of ionic liquids on the endo selectivity in the adducts. Besides the hydogen bonding interactions between the cation and the diene in all the structures, endo transition structures are slightly better stabilized than exo transition structures because of the favorable interactions between the H's of the CP ring and the O's of the [N(Tf)2]- and [OTf]- anions of the IL's. In this study, B3LYP/6-31 + G* and M06-2X/6-31 + G* calculations have demonstrated that endo selectivity in the Diels-Alder reactions can be achieved in the presence of ionic liquids in agreement with experiments.

Assessing iron and aluminum-based coagulants for odour and pathogen reductions in sludge digesters and enhanced digestate dewaterability.

Anaerobic digestion (AD) is an effective way of recovering energy and nutrients from organic waste. However, several issues including the production of corrosive, highly odorous and toxic volatile sulfur compounds (VSCs) in digester biogas, and long digestion times to achieve sufficient pathogen reductions can limit its wider adoption. In this study, Kemira™ PIX-311 (ferric chloride), PAX XL-6 (aluminum chloride hydroxide sulfate), and PAX XL-19 (polyaluminum chlorohydrate) were added to the digester feeds to evaluate the effects on digester stability, organic removal, VSCs formation in digester headspace, pathogen removal and sludge dewaterability. After preliminary dose trials, two different doses of PIX-311, PAX XL-19, and a 1:1 mixture of PIX-311 and PAX XL-19 were selected. PAX XL-6 was removed from further study as dosing significantly increased VSC levels and the PAX XL-6 dosed digester exhibited signs of instability. During the total operation period of 100days, addition of PIX-311, PAX XL-19, a combination of PIX-311, PAX XL-19 at concentrations of 4000 and 4500mg/kg total solids (TS) to digester feed did not lead to process instability. Biogas yields of all metal added digesters were similar to that of the control (no metal addition) digester. PIX-311 achieved up to a 93% reduction in biogas VSCs, 82% better fecal coliform inactivation and exhibited improved dewaterability over the control digester. The PAX XL-19 dosed digester showed modest reductions in biogas VSC concentrations, pathogen levels and improved dewaterability versus the control. Metal addition can be an effective way to control odours from VSCs, pathogens and to improve dewaterability during AD.

Assessment of microbial viability in municipal sludge following ultrasound and microwave pretreatments and resulting impacts on the efficiency of anaerobic sludge digestion.

A range of ultrasonication (US) and microwave irradiation (MW) sludge pretreatments were compared to determine the extent of cellular destruction in micro-organisms within secondary sludge and how this cellular destruction translated to anaerobic digestion (AD). Cellular lysis/inactivation was measured using two microbial viability assays, (1) Syto 16® Green and Sytox® Orange counter-assay to discern the integrity of cellular membranes and (2) a fluorescein diacetate assay to understand relative enzymatic activity. A range of MW intensities (2.17-6.48 kJ/g total solids or TS, coinciding temperatures of 60-160 °C) were selected for comparison via viability assays; a range of corresponding US intensities (2.37-27.71 kJ/g TS, coinciding sonication times of 10-60 min at different amplitudes) were also compared to this MW range. The MW pretreatment of thickened waste activated sludge (tWAS) caused fourfold to fivefold greater cell death than non-pretreated and US-pretreated tWAS. The greatest microbial destruction occurred at MW intensities greater than 2.62 kJ/g TS of sludge, after which increased energy input via MW did not appear to cause greater microbial death. In addition, the optimal MW pretreatment (80 °C, 2.62 kJ/g TS) and corresponding US pretreatment (10 min, 60 % amplitude, 2.37 kJ/g TS) were administered to the tWAS of a mixed sludge and fed to anaerobic digesters over sludge retention times (SRTs) of 20, 14, and 7 days to compare effects of feed pretreatment on AD efficiency. The digester utilizing MW-pretreated tWAS (80 °C, 2.62 kJ/g TS) had the greatest fecal coliform removal (73.4 and 69.8 % reduction, respectively), greatest solids removal (44.2 % TS reduction), and highest overall methane production (248.2 L CH4/kg volatile solids) at 14- and 7-day SRTs. However, despite the fourfold to fivefold increases in cell death upon pretreatment, improvements from the digester fed MW-pretreated sludge were marginal (i.e., increases in efficiency of less than 3-10 %) and likely due to a smaller proportion of cells (10-20 %) in the polymeric network and mixed sludge fed to digesters.

Treatment of landfill leachate using UASB-MBR-SHARON-Anammox configuration.

Leachate treatment is a challenging issue due to its high pollutant loads. There are several studies on feasible treatment methods of leachate. In the scope of this study, high organic content of young leachate was eliminated using an upflow anaerobic sludge blanket (UASB) and a membrane bioreactor (MBR) in sequence and effluent of the system was given to single reactor for high activity ammonia removal over nitrite (SHARON) and anaerobic ammonia oxidation (Anammox) reactors to remove nitrogen content. All reactors were set up at lab scale in order to evaluate the usage of these processes in sequencing order for leachate treatment. COD and TKN removal efficiencies were over 90 % in the combined processes which were operated during the study. The biodegradable portion of organic matter was removed with an efficiency of 99 %. BOD5 concentration decreased to 50 mg/L by UASB and MBR in sequence even the influent BOD5 concentration was over 8,000 mg/L. Although high nitrogen concentrations were observed in raw leachate, successful removal of nitrogen was accomplished by consecutive operations of SHARON and Anammox reactors. The results of this study demonstrated that with an efficient pretreatment of leachate, the combination of SHARON-Anammox processes is an effective method for the treatment of high nitrogen content in leachate.

Solidification/stabilization of landfill leachate concentrate using different aggregate materials.

The application of reverse osmosis for the treatment of landfill leachate is becoming widespread in Turkey as well as in Europe. A major drawback of this process is the production of concentrate, which could be as much as 30% of the feed stream, and high concentrations of salts and contaminants. The reverse osmosis concentrate is disposed of by using several methods including re-infiltration, drying, incineration and solidification/stabilization. In this study, solidification/stabilization (S/S) technology was studied for the treatment of reverse osmosis concentrate produced from landfill leachate. In order to benefit from its capability to absorb heavy metals, ammonia and some other pollutants, zeolite and different aggregate materials were used in solidification experiments. Main pollutants in the leachate concentrate, TOC, DOC, TDS and ammonia were successfully solidified and approximately 1% of TOC, DOC, TDS and ammonia remained in the eluate water. The results indicated that the landfill disposal limits could be attained by solidification/stabilization process.