Enhancement of Biodegradability of Chicken Manure via the Addition of Zeolite in a Two-Stage Dry Anaerobic Digestion Configuration.

Leach bed reactors (LBRs) are dry anaerobic systems that can handle feedstocks with high solid content, like chicken manure, with minimal water addition. In this study, the chicken manure was mixed with zeolite, a novel addition, and packed in the LBR to improve biogas production. The resulting leachate was then processed in a continuous stirred tank reactor (CSTR), where most of the methane was produced. The supernatant of the CSTR was returned to the LBR. The batch mode operation of the LBR led to a varying methane production rate (MPR) with a peak in the beginning of each batch cycle when the leachate was rich in organic matter. Comparing the MPR in both systems, the peaks in the zeolite system were higher and more acute than in the control system, which was under stress, as indicated by the acetate accumulation at 2328 mg L-1. Moreover, the presence of zeolite in the LBR played a crucial role, increasing the overall methane yield from 0.142 (control experiment) to 0.171 NL CH4 per g of volatile solids of chicken manure entering the system at a solid retention time of 14 d. Zeolite also improved the stability of the system. The ammonia concentration increased gradually due to the little water entering the system and reached 3220 mg L-1 (control system) and 2730 mg L-1 (zeolite system) at the end of the experiment. It seems that zeolite favored the accumulation of the ammonia at a lower rate (14.0 mg L-1 d-1) compared to the control experiment (17.3 mg L-1 d-1). The microbial analysis of the CSTR fed on the leachate from the LBR amended with zeolite showed a higher relative abundance of Methanosaeta (83.6%) compared to the control experiment (69.1%). Both CSTRs established significantly different bacterial profiles from the inoculum after 120 days of operation (p < 0.05). Regarding the archaeal communities, there were no significant statistical differences between the CSTRs and the inoculum (p > 0.05).

Groundwater denitrification using a continuous flow mode hybrid system combining a hydrogenotrophic biofilter and an electrooxidation cell.

An attached-growth continuous flow hydrogenotrophic denitrification system was investigated for groundwater treatment. Two bench-scale packed-bed reactors were used in series, without external pH adjustment or carbon source addition, while inorganic carbonate salts already contained in the groundwater were the sole carbon source used by the denitrifying bacteria. The hydrogen was produced by water electrolysis using renewable energy sources thus minimizing resource-draining factors of the treatment process. The biofilter was subjected to a combination of three groundwater retention times (13.5, 27 and 54 min, corresponding to 20, 10 and 5 mL min-1 inlet water flow rates) and two hydrogen flow values (10 and 20 mL min-1) to evaluate its efficiency under different operating parameters. In all cases, significant nitrate percentage removals were achieved, ranged between 64.1% and 100%. The treatment process appears to slow down with lower retention times and H2 flow rate values, although residual nitrate concentrations were always in the range of 0-5.1 mg L-1, values below the maximum permitted limit of 11.3 mg L-1. In cases where nitrite accumulation was detected, a continuous flow electrochemical oxidation process with three different current density values (5.0, 7.5 and 10.0 mA cm-2) was examined as a post-treatment step aiming to completely remove the toxic nitrite anions. Finally, an advanced mathematical model of the attached growth hydrogenotrophic denitrification process was developed to predict concentrations of all the substrates examined in the bio-filter (nitrate, nitrite, inorganic carbon and hydrogen).

Biogas Production from Sunflower Head and Stalk Residues: Effect of Alkaline Pretreatment.

Sunflower residues are considered a prominent renewable source for biogas production during anaerobic digestion (AD). However; the recalcitrant structure of this lignocellulosic substrate requires a pretreatment step for efficient biomass transformation and increased bioenergy output. The aim of the present study was to assess the effect of alkaline pretreatment of various parts of the sunflower residues (e.g., heads and stalks) on their methane yield. Experimental data showed that pretreatment at mild conditions (55 °C; 24 h; 4 g NaOH 100 g-1 total solids) caused an increase in the biochemical methane potential (BMP) of both heads and stalks of the sunflower residues as determined in batch tests. The highest methane production (268.35 ± 0.11 mL CH4 g-1 volatile solids) was achieved from the pretreated sunflower head residues. Thereafter; the effect of alkaline pretreatment of sunflower head residues was assessed in continuous mode; using continuous stirred-tank reactors (CSTRs) under two operational phases. During the first phase; the CSTRs were fed with the liquid fraction produced from the pretreatment of sunflower heads. During the second phase; the CSTRs were fed with the whole slurry resulting from the pretreatment of sunflower heads (i.e., both liquid and solid fractions). In both operating phases; it was observed that the alkaline pretreatment of the sunflower head residues had a negligible (phase I) or even a negative effect on biogas production; which was contradictory to the results of the BMP tests. It seems that; during alkaline pretreatment; this part of the sunflower residues (heads) may release inhibitory compounds; which induce a negative effect on biogas production in the long term (e.g., during continuously run digesters such as CSTR) but not in the short-term (e.g., batch tests) where the effect of the inoculum may not permit the inhibition to be established.

Mathematical modeling of constructed wetlands for hexavalent chromium removal.

Constructed wetlands (CWs) have been extensively used in Cr(VI) removal and have proven their ability to achieve high removal efficiencies. Although, numerous studies have been published in the past years presenting experimental results of CWs treating wastewater with Cr(VI) concentrations, a mathematical modeling describing the processes for Cr(VI) removal in CWs is lacking. In this work a mathematical model was developed, able to accurately describe the main mechanisms and reactions (i.e. biological reduction, plant biomass uptake-sorption) which are responsible for Cr(VI) removal in a wetland system. The model was calibrated and validated using data from a previously reported experimental study of horizontal subsurface CWs. Mathematical simulation indicates that in an unplanted wetland Cr(VI) was mainly removed through the diffusion/reduction process inside biofilm, attached on the porous media, while in the planted unit Cr(VI) was mainly removed through the sorption process to the root system of the plants. The developed model's simulations showed high correlation between predicted and experimental data, indicating that the proposed model can be used to design and predict full scale constructed wetland process for Cr(VI) removal.

Assessment of Voltage Influence in Carbon Dioxide Fixation Process by a Photo-Bioelectrochemical System under Photoheterotrophy.

Bioelectrochemical systems are a promising technology capable of reducing CO2 emissions, a renewable carbon source, using electroactive microorganisms for this purpose. Purple Phototrophic Bacteria (PPB) use their versatile metabolism to uptake external electrons from an electrode to fix CO2. In this work, the effect of the voltage (from -0.2 to -0.8 V vs. Ag/AgCl) on the metabolic CO2 fixation of a mixed culture of PPB under photoheterotrophic conditions during the oxidation of a biodegradable carbon source is demonstrated. The minimum voltage to fix CO2 was between -0.2 and -0.4 V. The Calvin-Benson-Bassham (CBB) cycle is the main electron sink at these voltages. However, lower voltages caused the decrease in the current intensity, reaching a minimum at -0.8 V (-4.75 mA). There was also a significant relationship between the soluble carbon uptake in terms of chemical oxygen demand and the electron consumption for the experiments performed at -0.6 and -0.8 V. These results indicate that the CBB cycle is not the only electron sink and some photoheterotrophic metabolic pathways are also being affected under electrochemical conditions. This behavior has not been tested before in photoheterotrophic conditions and paves the way for the future development of photobioelectrochemical systems under heterotrophic conditions.

Data on cellular lipids of Yarrowia lipolytica grown on fatty substrates.

Yarrowia lipolytica, which is model oleaginous yeast with high industrial interest, was cultivated on fatty substrates. Data concerning fatty acid composition of both substrate and yeast lipids and comparisons of the experimental data with model predictions presented in "Biomodification of fats and oils and scenarios of adding value on renewable fatty materials through microbial fermentations: Modelling and trials with Yarrowia lipolytica" (Vasiliadou et al., 2018) were provided. Furthermore, the total yeast lipids were fractionated into their main fractions, that is, phospholipids, glucolipids plus sphingolipids and neutral lipids, and the fatty acid composition of each lipid fraction was reported.

Mathematical modeling of olive mill waste composting process.

The present study aimed at developing an integrated mathematical model for the composting process of olive mill waste. The multi-component model was developed to simulate the composting of three-phase olive mill solid waste with olive leaves and different materials as bulking agents. The modeling system included heat transfer, organic substrate degradation, oxygen consumption, carbon dioxide production, water content change, and biological processes. First-order kinetics were used to describe the hydrolysis of insoluble organic matter, followed by formation of biomass. Microbial biomass growth was modeled with a double-substrate limitation by hydrolyzed available organic substrate and oxygen using Monod kinetics. The inhibitory factors of temperature and moisture content were included in the system. The production and consumption of nitrogen and phosphorous were also included in the model. In order to evaluate the kinetic parameters, and to validate the model, six pilot-scale composting experiments in controlled laboratory conditions were used. Low values of hydrolysis rates were observed (0.002841/d) coinciding with the high cellulose and lignin content of the composting materials used. Model simulations were in good agreement with the experimental results. Sensitivity analysis was performed and the modeling efficiency was determined to further evaluate the model predictions. Results revealed that oxygen simulations were more sensitive on the input parameters of the model compared to those of water, temperature and insoluble organic matter. Finally, the Nash and Sutcliff index (E), showed that the experimental data of insoluble organic matter (E>0.909) and temperature (E>0.678) were better simulated than those of water.

Attachment of Pseudomonas putida onto differently structured kaolinite minerals: a combined ATR-FTIR and 1H NMR study.

The attachment of Pseudomonas (P.) putida onto well (KGa-1) and poorly (KGa-2) crystallized kaolinite was investigated in this study. Batch experiments were carried out to determine the attachment isotherms of P. putida onto both types of kaolinite particles. The attachment process of P. putida onto KGa-1 and KGa-2 was adequately described by a Langmuir isotherm. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy and Nuclear Magnetic Resonance were employed to study the attachment mechanisms of P. putida. Experimental results indicated that KGa-2 presented higher affinity and attachment capacity than KGa-1. It was shown that electrostatic interactions and clay mineral structural disorders can influence the attachment capacity of clay mineral particles.