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In Zacatecas, Mexico, four plants are operating to extract Ag, Au, and Hg using CaS sub(2)O sub(3) solution from surface soil containing tailings from the amalgamation method used during 1550-1900. The metal ions extracted are cemented by scrap Cu wires. Hg is separated by evaporation from the cemented amalgam and Ag and Au are obtained from the residue. A part of the soil to be leached was separated and leached as in the industrial process. Only 121 ppm of Hg was freed from 168 ppm of extractable Hg. About a half of the remaining Hg in the soil evaporated during 18 months. This confirms that the Hg in the soil is metallic. Pb and As are also freed in the same process. It is estimated that 13 000-34 000 t of Hg had been discarded in the extraction of Ag.

In recent years, pelagic Sargassum has invaded the Caribbean coasts, and anaerobic digestion has been proposed as a sustainable management option. However, the complex composition of these macroalgae acts as a barrier to microbial degradation, thereby limiting methane production. Microbial adaptation is a promising strategy to improve substrate utilization and stress tolerance. This study aimed to investigate the adaptation of a microbial consortium to enhance methane production from the pelagic Sargassum . Microbial adaptation was performed in a fed-batch mode for 100 days by progressive feeding of Sargassum . The evolution of the microbial community was analyzed by high-throughput sequencing of 16S rRNA amplicons. Additionally, 16S rRNA data were used to predict functional profiles using the iVikodak platform. The results showed that, after adaptation, the consortium was dominated by the bacterial phyla Bacteroidota, Firmicutes, and Atribacterota, as well as methanogens of the families Methanotrichaceae and Methanoregulaceae. The abundance of predicted genes related to different metabolic functions was affected during the adaptation stage when Sargassum concentration was increased. At the end of the adaptation stage, the abundance of the predicted genes increased again. The adapted microbial consortium demonstrated a 60% increase in both biomethane potential and biodegradability index. This work offers valuable insights into the development of treatment technologies and the effective management of pelagic Sargassum in coastal regions, emphasizing the importance of microbial adaptation in this context.

In the last decade, Sargassum spp. seaweed species have caused massive flooding on the Caribbean Sea coasts. These seaweed species have a high content of recalcitrant compounds, such as insoluble fibers and polyphenols, which generate low methane yields in anaerobic digestion (AD). This study investigated the effect of solid–liquid separation of Sargassum biomass on biodegradability and methane yield. A biochemical methane potential (BMP) test was conducted with both fractions and raw biomass (RB). A mass balance was developed to assess the distribution of the components. The obtained liquid fraction (LF) showed high biodegradability and a high methane production rate, and it generated a methane yield of 159.7 ± 7.1 N L kg VS−1, a value that corresponds to approximately twice that achieved with RB and the solid fraction (SF). The component distribution analysis showed that about 90% of total solids (TS), volatile solids (VS), ash, carbon, and cellulose were retained in the SF. In conclusion, the LF had high biodegradability and methane yield. This suggests the potential for LFs of Sargassum biomass to be treated in large-scale high-load reactors; however, studies applied to SFs are needed because they retain a large amount of organic matter with low biodegradability.

The relationship of microbial community and cometabolic consumption of 2-chlorophenol (2-CP) in a nitrifying sequencing batch reactor (SBR) was studied. The assessment of the population dynamics of the nitrifying sludge during the cometabolic 2-CP consumption with increasing ammonium (NH 4 + ) concentrations in the SBR showed the presence of 39 different species of which 10 were always present in all cycles. Fifty-five percent of the species found were grouped as Proteobacteria (45% as β-proteobacteria and 10% as γ-proteobacteria class), 30% as Acidobacteria, and 15% as Deinococcus-Thermus phyla. NH 4 + and cometabolic 2-CP consumption could be related to the presence and permanence of ammonium-oxidizing bacteria (AOB) species and heterotrophic bacteria, while the complete nitrification to the presence of nitrite-oxidizing bacteria (NOB) species. A correlation analysis showed that the complete and stable nitrifying performance (NH 4 + consumption efficiencies (ENH 4 + -N) > 99% and nitrate production yields (YNO 3 − -N) between 0.93 and 0.99), as well as the increase in specific rates (ammonium (qNH 4 + -N) and 2-CP (q2-CP-C) consumption and nitrate production (qNO 3 − -N)), was associated with the homogeneity of the bacterial community ( J index = 0.99). The increase in the proportion of individuals of AOB species such as Nitrosomonas oligotropha and Nitrosomonas marina was associated with the increase in qNH 4 + -N ( r  ≥ 0.69) and q2-CP-C ( r  ≥ 0.64) and, therefore, with the 2-CP cometabolic consumption in the SBR. Finally, the increase in the proportion of individuals of heterotrophic species such as Dokdonella ginsengisoli , Deinococcus peraridilitoris , Truepera radiovictrix , and Stenotrophobacter terrae was associated with the increase in q2-CP-C ( r  ≥ 0.59). Key points • Thirty-nine bacterial species were identified in the nitrifying sludge population of the SBR. • β-Proteobacteria and Acidobacteria were the prevalent (85%) bacterial groups. • AOB and heterotrophic bacteria participate in NH 4 + and cometabolic 2-CP consumption. Graphical abstract

The decomposition of municipal organic waste (MOW) results in the generation of gasses and liquid fractions called leachates that may contain high concentrations of organic matter and ammonium (NH4+). Leachates can be treated through biological processes to reduce the environmental problems they cause. Thus, in the present study, the physiology and microbial community of a sequential nitrification-denitrification process (SNDP) were analyzed during MOW leachate treatment. First, the acclimation of nitrifying (SBR with up to 600 mg NH4+-N/L) and denitrifying (UASB reactor with up to 166 mg NO3--N/L d) sludge was carried out. The SBR was then fed with leachate (28.92 ± 13.32–76.26 ± 13.94 mg NH4+-N/L and 5661.69 ± 1002.36–6070.28 ± 554.04 mg COD/L), and the effluent was fed to the UASB reactor. Both processes were completed during acclimation, and efficiencies and yields higher than 92% and 0.89 were obtained, respectively. During the leachate treatment, the SBR reached an ammonium consumption efficiency (ENH4+-N) of 99.01 ± 1.79% and a COD consumption efficiency (ECOD) of 81.62 ± 13.15%. However, the yields and specific production rates of nitrate decreased by 41.0% and 99.8%, respectively. The UASB reactor fed with the SBR effluent (17.68 ± 0.77 mg/L nitrate, 55.20 ± 0.84 mg/L nitrite, and 55.20 ± 0.84–324.86 ± 9.94 mg COD/L) reached nitrate, nitrite, and ECOD efficiencies of 81.53 ± 1.53%, 64.49 ± 1.03%, and 97.42 ± 2.03%, respectively. During acclimation in the nitrifying SBR, the groups that predominated in the microbial community were Nitrospira, Bacteroidetes, Nitrosomonas, and Thauera (25%, 21%, 4%, and 3%, respectively). However, in the presence of leachate, nitrite accumulation and low O2 availability decreased the values of Nitrospira and Nitrosomonas to 0.2% and 0.08%, respectively. In the UASB reactor, members of the family Pseudomonadaceae and the genera Cecembia and Thauera were predominant, regardless of the stage evaluated. The use of an SNDP allowed the removal of up to 99% of NH4+ and 98% of COD, and thus, it may be an alternative method for MOW leachate treatment.

Climate and land management affect nutrient cycling in grassland ecosystems. We aimed to understand whether temperate and tropical grasslands differ in terms of soil organic carbon (SOC), nitrogen (N), and phosphorus (P) concentrations, and their C:N:P stoichiometric ratios in grazed and ungrazed natural grasslands and pastures. For this, we used a meta-analysis approach (1296 records, 241 papers), and regression models to explain the observed patterns in terms of mean annual precipitation (MAP), mean annual temperature (MAT), altitude, and latitude. SOC, N, and P concentrations were higher in temperate regions than in tropical ones, and they negatively correlated with MAT and MAP. The grassland type effect was more significant for tropical regions. In tropical regions, soil C:N ratios were higher in ungrazed than in grazed pastures, and soil N:P ratios in ungrazed sites were higher in pastures than in natural grasslands. Grazing increases soil N and SOC for natural grasslands in temperate regions. Our findings suggest that soil stoichiometric C:N:P stoichiometric signatures in grasslands differed between tropical and temperate regions on a global scale. P is a key element in regulation and restriction on soil C and N cycling in tropical regions but less in the temperate ones. Our findings suggest the direction of effects of grazing or grassland type on C:N:P stoichiometric signature. Since imbalances in soil stoichiometric ratios may have implications for ecosystem functioning, the assessment of these patterns could serve as a valuable tool for management and conservation of grasslands and pastures in both tropical and temperate regions.

Sargassum spp. flood the Caribbean coastline, causing damage to the local economy and environment. Anaerobic digestion (AD) has been proposed as an attractive option for turning macroalgae into valuable resources. Sargassum spp. has a complex composition that affects the microbial composition involved in AD which generates a low methane yield. This study aimed to improve the methane yield of pelagic Sargassum , using different energy-saving pretreatments and identifying the microbial community associated with methane production. We applied different energy-saving pretreatments to algal biomass and assessed the methane yield using a biomethane potential (BMP) test. The microbial communities involved in the AD of the best- and worst-performing methanogenic systems were analyzed by high-throughput sequencing. The results showed that pretreatment modified the content of inorganic compounds, fibers, and the C:N ratio, which had a strong positive correlation with BMP. The water washing pretreatment resulted in the best methane yield, with an increase of 38%. DNA metabarcoding analysis revealed that the bacterial genera Marinilabiliaceae_uncultured , DMER64 , Treponema , and Hydrogenispora , as well as the archaea genera Methanosarcina , RumEn_M2 , Bathyarchaeia , and Methanomassiliicocus , dominated the microbial community with a high methane yield. This study is the first to demonstrate the microbial community structure involved in the AD of Sargassum spp. The pretreatments presented in this study can help overcome the limitations associated with methane yield.

Leachates from municipal organic waste contain high concentrations of ammonium and organic matter, making their treatment a top priority. The present study addressed leachate treatment under nitrification and focused on the diversity and abundance of comammox bacteria and their interaction with other canonical microorganisms. Batch reactors (1L) were fed with synthetic (100 mg HN4+-N/L) or leachate ammonium and operated at 150 rpm, 3 mg DO/L, pH 7, and 30 °C. Reactor performance was evaluated using metabolic response variables and the microbial community by shotgun metagenomic sequencing. The results showed ammonium and organic matter (5200 mg COD/L) consumption efficiencies above 95%. The abundance and richness of the microbial community decreased in the presence of leachates. Sequences of the genus Nitrosomonas predominated with the synthetic medium, while the genus Nitrospira was the most abundant when fed with leachates. Archaea and anammox sequences were also detected. Comammox sequences of Candidatus Nitrospira inopinata, C. N. nitrificants, C. N. kreftii, C. N. neomarina, C. N. nitrosa, and C. N. allomarina were also detected, with the first species being predominant in the presence of leachates. These findings demonstrate that comammox and canonical microorganisms coexist during ammonium removal from leachates.

The tropical endogeic earthworm Pontoscolex corethrurus, a non-standard species used in ecotoxicity, has been found in crude oil-contaminated habitats. We estimated the removal of total hydrocarbons from heavy crude “Maya” oil on an artificially contaminated soil with a median lethal concentration of P. corethrurus and an addition of oil palm bagasse. P. corethrurus had a high survival rate, and the addition of oil palm bagasse led to a greater growth and an increase in abundance of bacteria and fungi. The activity of P. corethrurus and the nutritional quality of oil palm bagasse had a significant impact on the removal of a larger amount of petroleum hydrocarbons from contaminated soil. We concluded that the endogeic earthworm P. corethrurus and oil palm bagasse acted synergistically to achieve a more effective removal of total petroleum hydrocarbons from soil. These results show the potential for using P. corethrurus to remove, either directly or indirectly, crude oil from soil.

The aim of this paper is to describe a study of the anaerobic digestion of industrial citrus solid waste (ISCW) in both batch and semi-continuous modes for the production of bioenergy without the elimination of D-limonene. The study was conducted at the pilot plant level in an anaerobic reactor with a working volume of 220 L under mesophilic conditions of 35 ± 2 °C. Cattle manure (CM) was used as the inoculum. Three batches were studied. The first batch had a CM/ISCW ratio of 90/10, and Batches 2 and 3 had CM/ISCW ratios of 80/20 and 70/30, respectively. In the semi-continuous mode an OLR of approximately 8 g total chemical oxygen demand (COD)/Ld (4.43 gVS/Ld) was used. The results showed that 49%, 44%, and 60% of volatile solids were removed in the batch mode, and 35% was removed in the semi-continuous mode. In the batch mode, 0.322, 0.382, and 0.316 LCH4 were obtained at STP/gVSremoved. A total of 24.4 L/d (34% methane) was measured in the semi-continuous mode. Bioenergy potentials of 3.97, 5.66, and 8.79 kWh were obtained for the respective batches, and 0.09 kWh was calculated in the semi-continuous mode. The citrus industry could produce 37 GWh per season. A ton of processed oranges has a bioenergy potential of 162 kWh, which is equivalent to 49 kWh of available electricity ($3.90).