Influence of Leachate and Nitrifying Bacteria on Photosynthetic Biogas Upgrading in a Two-Stage System

Photosynthetic biogas upgrading using two-stage systems allows the absorption of carbon dioxide (CO2) in an absorption unit and its subsequent assimilation by microalgae. The production of microalgae requires large amounts of nutrients, thus making scale-up difficult and reducing economic feasibility. The photosynthetic process produces oxygen (O-2) (1 mol per mol of CO2 consumed), which can be desorbed into purified biogas. Two-stage systems reduce its impact but do not eliminate it. In this study, we test the use of landfill leachate as a nutrient source and propose a viable and economical strategy for reducing the O-2 concentration. First, the liquid/gas (L/G) ratio and flow mode of the absorber were optimized for 20% and 40% CO2 with COMBO medium, then landfill leachate was used as a nutrient source. Finally, the system was inoculated with nitrifying bacteria. Leachate was found to be suitable as a nutrient source and to result in a significant improvement in CO2 absorption, with outlet concentrations of 0.01% and 0.6% for 20% and 40% CO2, respectively, being obtained. The use of nitrifying bacteria allowed a reduction in dissolved oxygen (DO) concentration, although it also resulted in a lower pH, thus making CO2 uptake slightly more difficult

Feedback and Feedforward Control of a Biotrickling Filter for H2S Desulfurization with Nitrite as Electron Acceptor

Biotrickling filters’ control for H2S removal has special challenges because of complexity of the systems. Feedback and feedforward control were implemented in an anoxic biotrickling filter, operated in co-current flow mode and using nitrite as an electron acceptor. The feedback controller was tuned by three methods—two based on Ziegler-Nichols’ rules (step-response and maintained oscillation) and the third using the Approximate M-constrained Integral Gain Optimization (AMIGO). Inlet H2S staircase step perturbations were studied using a feedforward control and the e ect of EBRT considered by feedback control. The tuning method by maintained oscillation shows the lower errors. The selected controller was a PI, because unstable behavior at the lowest H2S inlet loading was found under a PID controller. The PI control was able to maintain an outlet H2S concentration of 14.7 0.45 ppmV at three EBRT, studied at 117 s, 92 s and 67 s. Therefore, desulfurized biogas could be used to feed a fuel cell. Feedforward control enhances BTF performance compared to the system without control. The maximum outlet H2S concentration was reduced by 26.18%, although sulfur selectivity did not exceed 55%, as elemental sulfur was the main oxidation product

Integration of a nitrification bioreactor and an anoxic biotrickling filter for simultaneous ammonium-rich water treatment and biogas desulfurization

A preliminary assessment has been carried out on the integration of an anoxic biotrickling filter and a nitrification bioreactor for the simultaneous treatment of ammonium-rich water and H2S contained in a biogas stream. The nutrient consumption in the biotrickling filter was as follows (mol−1 NO3−-N): 6.3·10−4 ± 1.2·10−4 mol PO43−-P, 0.04 ± 0.05 mol NH4+-N and 0.04 ± 0.03 mol K+-K. Furthermore, it was possible to supply a mixture of biogenic NO3− and NO2− into the biotrickling filter from the nitrification bioreactor to obtain a maximum elimination capacity of 152 gH2S–S m−3 h−1. The equivalence between the two compounds was 1 mol NO3−-N equal to 1.6 mol NO2−-N. The biotrickling filter was also operated under a stepped variable inlet load (30–100 gH2S–S m−3 h−1) and outlet H2S concentrations of less than 150 ppmV were obtained. It was also possible to maintain the outlet H2S concentration close to 15 ppmV with a feedback controller by manipulating the feed flow (in the nitrification bioreactor). Two stepped variable inlet loads were tested (60–111 and 16–102 gH2S–S m−3 h−1) under this type of control. The implementation of feedback control could enable the exploitation of biogas in a fuel cell, since the H2S concentrations were 15.1 ± 4.3 and 15.0 ± 3.4 ppmV. Finally, the anoxic biotrickling filter experienced partial denitrification and this implied a loss of the desulfurization effectiveness related to SO42− production. © 2021 The AuthorsThe Spanish Government ( Ministerio de Economía y Competitividad ) and European FEDER funds provided financial support through the project CTM2012-37927-C03 ‘Monitoring, modelling and control towards the optimization of anoxic and aerobic desulfurizing biotrickling filters’

Recent advances in biological technologies for anoxic biogas desulfurization.

Recovery of the energy contained in biogas will be essential in coming years to reduce greenhouse gas emissions and our current dependence on fossil fuels. The elimination of H2S is a priority to avoid equipment corrosion, poisoning of catalytic systems and SO2 emissions in combustion engines. This review describes the advances made in this technology using fixed biomass bioreactors (FBB) and suspended growth bioreactors (SGB) since the first studies in this field in 2008. Anoxic desulfurization has been studied mainly in biotrickling filters (BTF). Elimination capacities (EC) up to 287 gS m-3 h-1 have been achieved, with a removal efficiency (RE) of 99%. Both nitrate and nitrite have been successfully used as electron acceptor. SGBs can solve some operational problems present in FBBs, such as clogging or nutrient distribution issues. However, they present greater difficulties in gas-liquid mass transfer, although ECs of up to 194 gS m-3 h-1 have been reported in both gas-lift and stirred tank reactors. One of the major disadvantages of using anoxic biodesulfurization compared to aerobic biodesulfurization is the need to provide reagents (nitrates and/or nitrites), with the consequent increase in operating costs. A solution proposed in this respect is the use of nitrified effluents, some ammonium-rich effluents nitrified include landfill leachate and digested effluent from the anaerobic digester have been tested successfully. Among the microbial diversity found in the bioreactors, the genera Thiobacillus, Sulfurimonas and Sedimenticola play a key role in anoxic removal of H2S. Finally, a summary of future trends in technology is provided

Simultaneous removal of ammonium from landfill leachate and hydrogen sulfide from biogas using a novel two-stage oxic-anoxic system

Anoxic biodesulfurization has been achieved in several bioreactor systems that have shown robustness and high elimination capacities (ECs). However, the high operating costs of this technology, which are mainly caused by the high requirements of nitrite or nitrate, make its full-scale application difficult. In the present study, the use of biologically produced nitrate/nitrite by nitrification of two different ammonium substrates, namely synthetic medium and landfill leachate, is proposed as a novel alternative. The results demonstrate the feasibility of using both ammonium substrates as nutrient solutions. A maximum elemental sulfur production of 95 ± 1% and a maximum H2S EC of 141.18 g S-H2S m-3 h-1 (RE = 95.0%) was obtained using landfill leachate as the ammonium source. Next Generation Sequencing (NGS) analysis of the microbial community revealed that the most common genera present in the desulfurizing bioreactor were Sulfurimonas (91.8-50.9%) followed by Thauera (1.1-24.2%) and Lentimicrobium (2.0-9.7%)

Progressive change from nitrate to nitrite as the electron acceptor for the oxidation of H2S under feedback control in an anoxic biotrickling filter

Nitrate has been progressively replaced by nitrite as the electron acceptor in the oxidation of H2S from biogas mimic by an anoxic biotrickling filter. Perturbations in the inlet H2S concentration with and without the implementation of feedback controllers have been evaluated. Nitrite was successfully used without decreasing the H2S removal efficiency (94.74 ± 0.01%). Moreover, a PID controller allowed the sulfate selectivity to be maintained and reduced the maximum outlet H2S concentration when compared to the system without control (54.4–64.4%), although elemental sulfur was the main oxidation product. On using ORP control the main disadvantage was the production of peaks in the outlet H2S concentration. The stability and resilience of the biological system were assessed by analyzing the microbial community profiles by 16S rDNA-denaturing gradient gel electrophoresis (DDGE). The modification of the electron acceptor led to a reduction in the diversity and increased the dominance of the microbial populations

Operational conditions for start-up and nitrate-feeding in an anoxic biotrickling filtration process at pilot scale

A real biogas effluent was desulfurized using an anoxic biotrickling filter at pilot scale. Guidelines and recommendations have been proposed to achieve the correct inoculation and biofilm development. The hydrogen sulfide inlet concentration (4100–7900 ppmV) was not controlled. The operational variables studied were the hydrogen sulfide inlet load (37–149 gS m−3 h−1), biogas flow rate (1–3.4 Nm3 h−1) and pH (6.8–7.4). Moreover, three nitrate-feeding modes were studied: manual, continuous and automated. Without the addition of nutrients to the nitrate solution, a removal efficiency greater than 95% was obtained for loads in the range 33–55 gS m−3 h−1 along with an elemental sulfur percentage of 85 ± 5%. The nitrate solution was mainly composed of NaNO3 (500 g L−1), the macronutrients KH2PO4 (10 g L−1), NH4Cl (5 g L−1) and MgSO4·7H2O (4 g L−1), and trace elements. The critical elimination capacity was 94.7 gS m−3 h−1 (RE > 99%) on day 119 and the maximum elimination capacity was 127.3 gS m−3 h−1 (RE = 92.6%) on day 122. The recommended operational conditions for start-up are an inlet load of 100 gS m−3 h−1, a pH set-point of 6.8 to reduce sulfide accumulation and nitrate-feeding automated by oxide reduction potential

Anoxic biogas biodesulfurization promoting elemental sulfur production in a Continuous Stirred Tank Bioreactor

Biological desulfurization of biogas has been extensively studied using biotrickling filters (BTFs). However, the accumulation of elemental sulfur (S0) on the packing material limits the use of this technology. To overcome this issue, the use of a continuous stirred tank bioreactor (CSTBR) under anoxic conditions for biogas desulfurization and S0 production is proposed in the present study. The effect of the main parameters (stirring speed, N/S molar ratio, hydraulic residence time (HRT) and gas residence time (GRT)) on the bioreactor performance was studied. Under an inlet load (IL) of 100 g S-H2S m–3 h–1 and a GRT of 119 s, the CSTBR optimal operating conditions were 60 rpm, N/S molar ratio of 1.1 and a HRT of 42 h, in which a removal efficiency (RE) and S 0 production of 98.6 ± 0.4% and 88% were obtained, respectively. Under a GRT of 41s and an IL of 232 g S-H2S m–3 h–1 the maximum elimination capacity (EC) of 166.0 ± 7.2 g S-H2S m–3 h–1 (RE = 71.7 ± 3.1%) was obtained. A proportional-integral feedback control strategy was successfully applied to the bioreactor operated under a stepped variable IL

Simultaneous methylmercaptan and hydrogen sulfide removal in the desulfurization of biogas in aerobic and anoxic biotrickling filters

Hydrogen sulfide (H2S) and methylmercaptan (CH3SH) are the most common sulfur compounds found in biogas. The simultaneous removal of H2S and CH3SH was tested at neutral pH in two biotrickling filters, one operated under aerobic conditions and the other one under anoxic conditions. Both reactors were run for several months treating a H2S concentration of around 2000 ppmv. Then, the effect of CH3SH loading rate (LR) on H2S and CH3SH removal was investigated in both reactors maintaining a constant H2S LR of 53–63 gS-H2S m−3 h−1, depending on the reactor. Initially, CH3SH concentration was stepwise increased from 0 to 75–90 ppmv. Maximum elimination capacities (ECs) of around 1.8 gS-CH3SH m−3 h−1 were found. After that, the CH3SH LR was increased by testing different empty bed residence times (EBRTs) between 180 and 30 s. Significantly lower ECs were found at short EBRTs, indicating that the systems were mostly mass transfer limited. Finally, EBRT was stepwise reduced from 180 to 30 s at variable CH3SH and H2S loads. Maximum H2S ECs found for both reactors were between 100 and 140 gS-H2S m−3 h−1. A negative influence was found in the ECs of CH3SH by the presence of high H2S LR in both biotrickling filters. However, sulfur mass balances in both reactors and batch tests under aerobic and anoxic conditions showed that CH3SH chemically reacts with elemental sulfur at neutral pH, enhancing the overall reactors performance by reducing the impact of sulfur accumulation. Also, both reactors were able to treat CH3SH without prior inoculation because of the already existing sulfide-oxidizing microorganisms grown in the reactors during H2S treatment. Co-treatment of H2S and CH3SH under aerobic and anoxic conditions was considered as a feasible operation for concentrations commonly found in biogas (2000 ppmv of H2S and below 20 ppmv of CH3SH)

Differential pathogenic response in strawberry tissues and organs by colletotrichum acutatum

The susceptibility of different tissues and organs from strawberry plants, cv “Camarosa”, to Colletotrichum acutatum was tested using a severity index based on infection response. Symptoms developed on inoculated tissues were characterized along 30 days. Flowers, except sepals, petioles and fruits were the most susceptible organs to the pathogen and they became necrotic tissues at 30 days post inoculation (dpi). Also, well-developed acervuli, which produced masses of orange-pink spores, were observed on these infected organs. An asymptomatic stage or latency phase was observed in green and white strawberry fruits. In spite of they were inoculated anthracnose symptoms were observed only when they became red fruits. On the other hand, strawberry leaves and sepals were resistant to infection by C. acutatum and only small flecks or light brown spots were observed reaching a size of 1 to 5 mm at 30 dpi. Likewise, the susceptibility of stolons and crowns to C. acutatum was evaluated as intermediate at 30 dpi. Finally, the infection process of the fungus on strawberry leaves and petioles was studied using light and electron microscopy. Pre-penetration events were similar on both, leaves and petioles: However, differences between colonization of strawberry leaves and petioles by C. acutatum were observed