Influence of pH and temperature on the performance and microbial community during the production of medium-chain carboxylic acids using winery effluents as substrate.

Winery effluents containing high ethanol concentrations and diverse organic matter are ideal substrates for producing medium-chain carboxylic acids via fermentation and chain elongation. However, the process needs to be better understood. This study presents novel insights into the bioconversion mechanisms of medium-chain carboxylic acids by correlating fermentation and chain elongation kinetic profiles with the study of microbial communities at different pH (5 to 7) conditions and temperatures (30 to 40 °C). It was found that high productivities of MCCA were obtained using a native culture and winery effluents as a natural substrate. Minor pH variations significantly affected the metabolic pathway of the microorganisms for MCCA production. The maximal productivities of hexanoic (715 mg/L/d) and octanoic (350 mg/L/d) acids were found at pH 6 and 35 °C. Results evidence that the presence of Clostridium, Bacteroides, and Negativicutes promotes the high productions of MCCA. The formation of heptanoic acid was favor when Mogibacterium and Burkholderia were present.

Pretreatment of agave bagasse with ruminal fluid to improve methane recovery.

Agave bagasse, a lignocellulosic waste that results from the milling and juice extraction of Agave tequilana var azul pineapples, is a suitable substrate for the production of methane through anaerobic digestion. However, it is necessary to apply a pretreatment to convert the bagasse into energy. In this context, this paper proposes using ruminal microorganisms to hydrolyze agave bagasse. This study evaluated the effect of the initial agave bagasse to ruminal fluid (S0/X0) ratio (0.33, 0.5, 1, and 2) on the hydrolysis efficiency. Subsequently, the supernatant was used for methane production. The hydrolysis efficiency increased as the S0/X0 ratio decreased. A hydrolysis efficiency of 60 % was achieved using an S0/X0 ratio of 0.33. The S0/X0 ratio of 0.33 optimally improved the specific methane production and energy recovery (155 ± 2 mL CH4/g TS and 6.1 ± 0.1 kJ/g TS) compared to raw biomass. The most abundant hydrolytic bacteria were Prevotella, Ruminococcus and Fibrobacter, and Engyodontium was the most abundant proteolytic fungus.

Experimental evaluation of temperature, nutrients, and initial concentration on medium-chain carboxylic acids production from winery wastes.

In the wine industry, grape processing is accompanied by waste generation, such as grape stalks, winery wastewater, and grape pomace (GP). GP can be used to produce value-added compounds such as medium-chain carboxylic acids (MCCA). This work aimed to determine the operational conditions (temperature, addition of nutrients, and initial waste concentration) to improve MCCA production using waste GP from the winery industry as a substrate. The electron donor (ethanol) and electron acceptor (acetate) were directly generated from the GP and consecutively used to produce MCCA. The treatment with high concentration, temperature, and nutrient addition promotes caproic acid's maximal yield and concentration (0.11 ± 0.02 g MCCA/g TS). Nutrients' presence and temperature significantly affected electron acceptor production. The addition of nutrients and 30 °C leads to elevated acetate production. However, at 37 °C, butyrate and MCCA were mainly produced without adding nutrients, and high ethanol consumption was observed. A higher metabolic diversification was observed at 37 °C than at 30 °C. Temperature and nutrient availability significantly affected the metabolic pathway and the type of carboxylic acid produced.

Exploring resistomes and microbiomes in pilot-scale microalgae-bacteria wastewater treatment systems for use in low-resource settings.

Antibiotic resistance genes (ARGs) released into the environment are an emerging human and environmental health concern, including ARGs spread in wastewater treatment effluents. In low-to-middle income countries (LMICs), an alternate wastewater treatment option instead of conventional systems are low-energy, high-rate algal ponds (HRAP) that use microalgae-bacteria aggregates (MABA) for waste degradation. Here we studied the robustness of ARG removal in MABA-based pilot-scale outdoor systems for 140 days of continuous operation. The HRAP system successfully removed 73 to 88 % chemical oxygen demand and up to 97.4 % ammonia, with aggregate size increasing over operating time. Fourteen ARG classes were identified in the HRAP influent, MABA, and effluent using metagenomics, with the HRAP process reducing total ARG abundances by up to 5-fold from influent to effluent. Parallel qPCR analyses showed the HRAP system significantly reduced exemplar ARGs (p < 0.05), with 1.2 to 4.9, 2.7 to 6.3, 0 to 1.5, and 1.2 to 4.8 log-removals for sul1, tetQ, blaKPC, and intl1 genes, respectively. Sequencing of influent, effluent and MABAs samples showed associated microbial communities differed significantly, with influent communities by Enterobacteriales (clinically relevant ARGs carrying bacteria), which were less evident in MABA and effluent. In this sense, such bacteria might be excluded from MABA due to their good settling properties and the presence of antimicrobial peptides. Microalgae-bacteria treatment systems steadily reduced ARGs from wastewater during operation time, using sunlight as the energetic driver, making them ideal for use in LMIC wastewater treatment applications.

Monitoring of SARS-CoV-2 RNA in wastewater: A surveillance tool to foresee infection's evolution in the Mexican Caribbean.

The study aims to determine SARS-CoV-2 RNA in sewage of Cancun wastewater treatment plants, the main touristic destination of Mexico, and to estimate the infected persons during the sampling period. SARS-CoV-2 RNA traces were detected in the inlet of the five plants during almost all the sampling months. However, there is no presence of SARS-CoV-2 RNA traces in the effluent of the five WWTPs during the study period. ANOVA analysis showed differences in the concentrations of RNA traces of SARS-CoV-2 between the sample dates, but no differences were found from one WWTP to another. Estimated infected individuals by Markov chain Monte Carlo simulation are higher (between 77% and 91%) than the cases reported by the health authority. Wastewater monitoring and the estimation of infected individuals are a helpful tool, because estimation provides early warning signs on how broadly SARS-CoV-2 is circulating in the city, and led to the authorities to take measures wisely. PRACTITIONER POINTS: There is no presence of SARS-CoV-2 RNA traces in the effluent of the facilities, suggesting the effectiveness of treatment. Surveillance of viral RNA concentrations at treatment plants revealed presence in the influent of five plants Estimated infected individuals by MCMC simulation are higher than cases reported by health authority Environmental surveillance approach in wastewater influent is helpful to identify the clusters and to take informed decisions.

Polyhydroxyalkanoates and 5-aminolevulinic acid production by a mixed phototrophic culture using medium-chain carboxylic acids from winery effluents.

This work aimed to obtain polyhydroxyalkanoates (PHA) and 5-aminolevulinic acid (5-ALA) from medium-chain carboxylic acids (MCCA) using a mixed culture enriched in Rhodopseudomnas palustris. MCCA, obtained from residual wine lees, were tested in batch photofermentation experiments. First, the influence of individual MCCA (hexanoic, heptanoic, and octanoic acids) was evaluated; then, the MCCA coming directly from a fermentation reactor (LC-effluent) or after acids extraction (HC-effluent) were studied. Nutrient supplementation, bicarbonate, and acetic acid addition were also tested. Results showed that PHA production was higher in hexanoic (328 mg PHA/L) compared to heptanoic (152 mg PHA/L) and octanoic (164 mg PHA/L) acids. Bicarbonate addition and acetic acid as co-substrate improved the MCCA consumption, the PHA content and production rate. The HC-effluent, without nutrient supplementation, was allowed to increase 2.5 times the PHA content (reaching 40 % w/w and 584 mg/L) and to double 5-ALA production (7.6 µM) compared to the LC-effluent condition.

Strategy for the formation of microalgae-bacteria aggregates in high-rate algal ponds.

This work studied the formation of aggregates used for wastewater treatment in high-rate algal ponds (HRAP). For this, the establishment of microalgae-bacteria aggregates in these systems was evaluated, considering strategies for the inoculation and start-up. Two HRAP were operated in parallel, at first in batch mode and then in continuous flow. The wastewater treatment was efficient, with removal rates around 80% for COD and N-ammoniacal. Volatile suspended solids and chlorophyll for the culture grew continuously reached a concentration of 548 ± 11 mg L-1 and 7.8 mg L-1, respectively. Larger photogranules were observed when the system was placed in a continuous regime. The protein fraction of extracellular polymeric substances was identified as a determinant in photogranules formation. During the continuous regime, more than 50% of the biomass was higher than 0.2 mm, flocculation efficiency of 78 ± 6%, and the volumetric sludge index of 32 ± 5 mL g-1. The genetic sequencing showed the growth of cyanobacteria in the aggregate and the presence of microalgae from the chlorophytes and diatoms groups in the final biomass.

Study on manipulation of ruminal fermentation using a bioelectrochemical system.

The purpose of this work was to develop a two-chamber bioelectrochemical cell to modify the metabolic activity of rumen microorganisms by applying an electric potential to the ruminal liquid. Carbohydrate fermentation changes were evaluated along with a molecular characterization by DNA sequencing of the ruminal microbial community. We observed that an electrochemical stimulation potential of 0.75 V enhanced basal acetate, propionate, and butyrate production by 71%, 86%, and 63%, respectively, with no detectable effects on grass substrate disappearance. The applied electric potential also led to changes in the volatile fatty acids production but not on the core microbiome.

Biocatalyst developed with recovered iron-rich minerals enhances the biotransformation of SARS-CoV-2 antiviral drugs in anaerobic bioreactors.

The biotransformation of the SARS-CoV-2 antiviral drugs, ribavirin and tenofovir, was studied in methanogenic bioreactors. The role of iron-rich minerals, recovered from a metallurgic effluent, on the biotransformation process was also assessed. Enrichment of anaerobic sludge with recovered minerals promoted superior removal efficiency for both antivirals (97.4 % and 94.7 % for ribavirin and tenofovir, respectively) as compared to the control bioreactor lacking minerals, which achieved 58.5 % and 37.9 % removal for the same drugs, respectively. Further analysis conducted by liquid chromatography coupled to mass spectroscopy revealed several metabolites derived from the biotransformation of both antivirals. Interestingly, tracer analysis with 13CH4 revealed that anaerobic methane oxidation coupled to Fe(III) reduction occurred in the enriched bioreactor, which was reflected in a lower content of methane in the biogas produced from this system, as compared to the control bioreactor. This treatment proposal is suitable within the circular economy concept, in which recovered metals from an industrial wastewater are applied in bioreactors to create a biocatalyst for promoting the biotransformation of emerging pollutants. This strategy may be appropriate for the anaerobic treatment of wastewaters originated from hospitals, as well as from the pharmaceutical and chemical sectors.

Bioconversion of H2 and CO2 from dark fermentation to methane: Effect of operating conditions on methane concentration.

The main goal of this study was to assess the methane production in a biotrickling filter (BTF) using a synthetic gas mixture (H2/CO2: 60/40), evaluating the effect of the empty bed gas residence time (EBRT), pH, and temperature. The BTF was inoculated with acclimated granular anaerobic sludge. Three EBRT were tested: 11.6, 5.8, and 2.9 h. The decrease in EBRT (from 11.6 to 5.8 h) increased 1.3-fold the methane content (69 ± 3%) with H2 and CO2 removals of 100% and 24 ± 6%, respectively. The following reduction to 2.9 h showed no effect on CH4 content. The increment of the pH had no significant effect; however, the highest CH4 percentage (74%) was observed at a pH of 8.5. The system showed flexibility to adapt to changes in temperature without drastically diminishing CH4 concentration. In these stages, the principal hydrogenotrophic archaea detected was Methanobacterium flexile. Soluble microbial products such as butanol, caproate, and iso-valerate were detected in all the operating stages. This study demonstrates the potential of methane generation from a dark fermentation gaseous effluent.

Loop-mediated isothermal amplification-based electrochemical sensor for detecting SARS-CoV-2 in wastewater samples.

The current pandemic COVID-19 caused by the coronavirus SARS-CoV-2, has generated different economic, social and public health problems. Moreover, wastewater-based epidemiology could be a predictor of the virus rate of spread to alert on new outbreaks. To assist in epidemiological surveillance, this work introduces a simple, low-cost and affordable electrochemical sensor to specifically detect N and ORF1ab genes of the SARS-CoV-2 genome. The proposed sensor works based on screen-printed electrodes acting as a disposable test strip, where the reverse transcription loop-mediated isothermal amplification (RT-LAMP) reaction takes place. Electrochemical detection relies upon methylene blue as a redox intercalator probe, to provide a diffusion-controlled current encoding the presence and concentration of RT-LAMP products, namely amplicons or double-stranded DNA. We test the performance of the sensor by testing real wastewater samples using end-point and time course measurements. Results show the ability of the electrochemical test strip to specifically detect and quantify RT-LAMP amplicons below to ~ 2.5 × 10-6 ng/µL exhibiting high reproducibility. In this sense, our RT-LAMP electrochemical sensor is an attractive, efficient and powerful tool for rapid and reliable wastewater-based epidemiology studies.

Cyanide treatment of mining tailings using suspended biomass and moving bed biomass reactors.

Mexico is the top producer of silver and is on the eighth place from producing gold in the world. For instance, the hydrometallurgical extraction process produces wastewater (mining tailing) characterized by being composed with varying concentrations of cyanide and heavy metals. The purpose of this research was to study the biodegradation of cyanide contained in mining tailings by means of a bacterial consortium isolated from a tailings dam. For this purpose, three types of Eckendfelder reactors were used, one with suspended biomass (BS) and two moving bed biofilter reactors, one with biomass immobilized on Kaldnes (BK) supports, and the other on polyurethane cubes (BCP). Three experimental stages were worked; in each of them, the concentrations of total cyanide were varied. In the first one, it was 26 ± 2 mg·L-1; in the second one 40 ± 4 mg·L-1; and the third one 55 ± 4 mg·L-1. During the whole operation, the pH and temperature were maintained at 9.5 units and 25 °C. After 141 days of operation, biodegradation of the total cyanide contained in the mining tailings was 69% (17 mg·L-1) in the BS reactor, while in the BK reactor, it was 93% (3.9 mg·L-1) and in the BCP reactor 95% (2.5 mg·L-1). The predominant families in each of the reactors, as well as their respective relative abundances, were for the BS and for the BK of Cyclobacteriaceae (20.65% and 24.64%) and Rhizobiaceae (18.48% and 14.01%) and Halomonadaceae (46.97%) and Hyphomonadaceae (24.94%) in the BCP.

Growth kinetics and quantification of carbohydrate, protein, lipids, and chlorophyll of Spirulina platensis under aqueous conditions using different carbon and nitrogen sources.

This study evaluated different carbon and nitrogen sources on the growth and production of carbohydrates, protein, lipids, and chlorophyll of Spirulina platensis LEB-52 through an easy successive methodology under aqueous conditions. Spirulina platensis was cultivated at 120 rpm and light intensity of 156 µmol m-2 s-1 in a 500 mL Erlenmeyer flask with a working volume of 250 mL, using Zarrouk's medium. The biomass, carbohydrate, and protein production together with the specific growth rate did not show a significant difference between NaHCO3 and Na2CO3. The salts of urea and ammonium are not an alternative nitrogen sources of low cost for Spirulina platensis cultivation. From the experimental results obtained in this study, a successful estimate of carbohydrate, protein, lipids, and chlorophyll content inside Spirulina platensis was achieved without use advanced analytical techniques, allowing saves resources and time. This method can be extrapolated to other microorganisms and cultivation regimens.

Role of xylose from acidic hydrolysates of agave bagasse during biohydrogen production.

This study compares the H2 production from glucose, xylose, and acidic hydrolysates of Agave tequilana bagasse as substrates. The fermentation was performed in a granular sludge reactor operated in two phases: (1) model substrates (glucose and xylose) and (2) acidic hydrolysates at 35 °C, pH 4.5 and a hydraulic retention time of 5.5 h with glucose (10 g L-1) and xylose (12 g L-1). A sequencing batch reactor was used to acclimate the biomass between the glucose and xylose continuous fermentation (with a mixture of xylose-glucose) and acidic hydrolysates. During the discontinuous acclimating step, the xylose/glucose ratio increment negatively affected the H2 productivity. Although the continuous H2 production with xylose was negligible, the co-fermentation with glucose (88-12%) allowed H2 productivity of 2,889 ± 502 mL H2 L-1d-1. An acidic hydrolysate concentration of 3.3 gcarbohydrate L-1 showed a three-fold higher H2 productivity than with a concentration of 10 g L-1. The results indicated that xylose, as the only substrate, was challenging to metabolize by the inoculum, and its mixture with glucose improved the H2 productivity. Therefore, the low H2 productivity with hydrolysates could be related to the presence of xylose.

Influence of wavelength photoperiods and N/P ratio on wastewater treatment with microalgae-bacteria.

This research investigates the effect of mixing wavelength light photoperiods (12 h blue, 8 h blue: 4 h green, 4 h blue: 8 h green, and 12 h green) and N/P ratios (1.3 to 8.3) on the growth microalgae-bacteria systems, organic matter, and nutrient removals. The highest microalgae-bacteria growth performance (µ = 0.2 d-1, 481.1 ± 15.3 mg DW L-1) was observed when a 8 h blue: 4 h green mixed wavelength and a low N/P ratio were used. For both N/P ratios, biomass productivity was favored when using the blue light dominated at longer time periods. Mechanisms for nitrogen removal by assimilation depend on the N/P ratio, achieving assimilation between 49 and 65% at a low N/P ratio. High nitrogen removal (>50%) showed a strong relation with alkalinity culture conditions (pH > 8.5). The mixing of wavelength photoperiods seems to be a promising strategy to achieve high biomass productivity and nutrient removal. However, for optimal conditions, N/P ratios in the wastewater should be considered.

Thermophilic biogas production from microalgae-bacteria aggregates: biogas yield, community variation and energy balance.

Biogas production through anaerobic mesophilic digestion is the most straightforward biofuel production route integrated into microalgae-bacteria wastewater treatment plants. Improvement of this biofuel route without adding pretreatment units is possible through the temperature increase. This paper presents a comprehensive evaluation of the transitory effect of different temperatures (35 °C and 55 °C) and hydraulic retention times (HRT) of 15 and 30 d on the long-term methane production using non-pretreated microalgae-bacteria aggregates as a feedstock. The thermophilic transition from mesophilic inoculum adapted to microalgae-bacteria aggregate increased 1.7-fold the methane production (0.41 m3CH4 kgVS-1) at HRT of 30 d. A substantial decrease in the microbial community's diversity present in the anaerobic reactor was observed when thermophilic conditions were applied, explaining the long adaptation period needed. The increase of the operative temperature condition promotes changes in the dominance pathway of methanogenesis from hydrogenotrophic to acetolactic. The energy balance assessment showed a positive net energy ratio when the digester was operated at an HRT of 30 d. A maximum net energy ratio of 1.5 was achieved at mesophilic temperature. This study demonstrated, based on experimental data, that microalgal digestion with an HRT of 30 d favors energy self-sustainability in microalgal wastewater treatment plants.

Thermophilic anaerobic digestion of winery effluents in a two-stage process and the effect of the feeding frequency on methane production.

This investigation evaluates a two-stage process to treat highly concentrated winery effluents, including a thermophilic methanogenic stage. The inoculum adaptation, the effect of the organic loading rates on both stages, and the methanogenic reactor's feeding frequency on the process performance were studied. An active thermophilic inoculum was obtained by a one-step temperature increase from 35 to 55 °C. The application of organic loads above 120 kg COD m-3 d-1 in the acidogenic stage ensured the highest acetic acid concentration, while methane production rates as high as 7.1 Nm3 CH4 m-3 d-1 and a yield of 348 L CH4 kg-1 COD were obtained in the thermophilic methanogenic stage using an organic loading rate of 29.9 kg COD m-3 d-1. However, a lower removal of organic matter was observed under that condition. Lower feeding frequencies improved methane productivity and yield, suggesting that this parameter is a useful process optimization tool.

A review on the factors influencing biohydrogen production from lactate: The key to unlocking enhanced dark fermentative processes.

Dark fermentation (DF) is one of the most promising biological methods to produce bio-hydrogen and other value added bio-products from carbohydrate-rich wastes and wastewater. However, process instability and low hydrogen production yields and rates have been highlighted as the major bottlenecks preventing further development. Numerous studies have associated such concerns with the inhibitory activity of lactate-producing bacteria (LAB) against hydrogen producers. However, an increasing number of studies have also shown lactate-based metabolic pathways as the prevailing platform for hydrogen production. This opens a vast potential to develop new strategies to deal with the "Achilles heel" of DF - LAB overgrowth - while untapping high-performance DF. This review discusses the key factors influencing the lactate-driven hydrogen production, paying particular attention to substrate composition, the operating conditions, as well as the microbiota involved in the process and its potential functionality and related biochemical routes. The current limitations and future perspectives in the field are also presented.

Polyhydroxyalkanoates from organic waste streams using purple non-sulfur bacteria.

Many microorganisms can produce intracellular and extracellular biopolymers, such as polyhydroxyalkanoates (PHA). Despite PHA's benefits, their widespread at the industrial level has not occurred due mainly to high production costs. PHA production under a biorefinery scheme is proposed to improve its economic viability. In this context, purple non-sulfur bacteria (PNSB) are ideal candidates to produce PHA and other substances of economic interest. This review describes the PHA production by PNSB under different metabolic pathways, by using a wide range of wastes and under diverse operational conditions such as aerobic and anaerobic metabolism, irradiance level, light or dark conditions. Some strategies, such as controlling the feed regime, biofilm reactors, and open photobioreactors in outdoor conditions, were identified from the literature review as the approach needed to improve the process's economic viability when using mixed cultures of PNSB and wastes as substrates.