Mixed Microbial Culture Research Articles

IMPACT OF STAPHYLOCOCCUS SPP. ON OCCURRENCE OF INFECTIOUS INFLAMMATORY PROCESSES IN SURGICAL PATIENTS: A BACTERIOLOGICAL STUDY

Introduction. Staphylococci are well-known pathogens associated with purulent-inflammatory processes at various body sites. However, the specific contributions of different microorganisms within microbial communities remain poorly understood. Notably, these diverse microbes can exhibit distinct antibiotic susceptibility profiles due to their varying taxonomic classifications.
 The purpose of this study is to analyze the results of bacteriological examination of pathological material taken from patients in surgical department and to assess the contribution of S. aureus and coagulase-negative staphylococci in the form of mono- and mixed infection in the cases of infectious pathology.
 Results and discussion. 123 samples were obtained from patients in the surgical department; cultures of Staphylococcus bacteria were isolated in 37 cases, which accounted for 30.1% of all studies. Staphylococcus aureus was identified in 18 cultures (14.6%), with 11 isolates (8.9%) found as single infections (monoculture) and 7 isolates (5.7%) identified within mixed microbial communities. Additionally, 19 isolates (15.4%) were identified as coagulase-negative staphylococci. These microbial communities comprised 2 to 4 different types of microorganisms.
 Conclusion. Staphylococcus spp. were isolated from 30.1% of patients in the surgical department. Among these isolates, Staphylococcus aureus was present in 38.9% of mixed microbial cultures, while coagulase-negative staphylococci were found in 33.3% of Staphylococcus isolations. Notably, S. aureus and coagulase-negative staphylococci were never co-isolated within the same mixed culture.

Polyhydroxyalkanoates production from a waste-derived feedstock driven by the reactor operating conditions: The role of biomass microbiome and its reactivation capacity

In the last years, the production of plastics at large-scale has been an issue of great concern due to their environmental and health impacts. Biobased and biodegradable plastics, such as polyhydroxyalkanoates (PHA), have emerged as a possible more ecological and sustainable alternative to those conventional plastics. PHA can be produced by mixed microbial cultures (MMC) from waste-based feedstocks. This work aimed to maximize the PHA production from fermented brewer's spent grain by selecting an efficient PHA-accumulating MMC, applying different organic loading rates (OLR, 45 or 60 CmmolFP/(L.d)) and sludge retention times (SRT, 4 or 2 days). Additionally, the biomass reactivation capacity after storage was evaluated.The global PHA productivity depends on the operating conditions, achieving its maximum (3.55 ± 0.8 gPHA/(L.d)) at the highest OLR and SRT tested. After storage, the global PHA productivity was similar to the one achieved before the starvation period.Depending on the operating conditions, the microbiome has its own bacterial composition signature containing various PHA-producers genera (e.g., Acidovorax, Amaricoccus, Brevundimonas, Leucobacter, Leadbetterella and Thauera) that persisted over time, albeit at different relative abundancies.A comprehensive overview of PHA production with data on system performance and microbiome is presented, which thereby can further contribute to the upscale of such valorisation processes.

Environmental sustainability assessment of biodegradable bio-based poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from agro-residues: Production and end-of-life scenarios

In the context of a circular bio-based economy, more public attention has been paid to the environmental sustainability of biodegradable bio-based plastics, particularly plastics produced using emerging biotechnologies, e.g. poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or PHBV. However, this has not been thoroughly investigated in the literature. Therefore, this study aimed to address three aspects regarding the environmental impact of PHBV-based plastic: (i) the potential environmental benefits of scaling up pellet production from pilot to industrial scale and the environmental hotspots at each scale, (ii) the most favourable end-of-life (EOL) scenario for PHBV, and (iii) the environmental performance of PHBV compared to benchmark materials considering both the pellet production and EOL stages. Life cycle assessment (LCA) was implemented using Cumulative Exergy Extraction from the Natural Environment (CEENE) and Environmental Footprint (EF) methods. The results show that, firstly, when upscaling the PHBV pellet production from pilot to industrial scale, a significant environmental benefit can be achieved by reducing electricity and nutrient usage, together with the implementation of better practices such as recycling effluent for diluting feedstock. Moreover, from the circularity perspective, mechanical recycling might be the most favourable EOL scenario for short-life PHBV-based products, using the carbon neutrality approach, as the material remains recycled and hence environmental credits are achieved by substituting recyclates for virgin raw materials. Lastly, PHBV can be environmentally beneficial equal to or even to some extent greater than common bio- and fossil-based plastics produced with well-established technologies. Besides methodological choices, feedstock source and technology specifications (e.g. pure or mixed microbial cultures) were also identified as significant factors contributing to the variations in LCA of (bio)plastics; therefore, transparency in reporting these factors, along with consistency in implementing the methodologies, is crucial for conducting a meaningful comparative LCA.

Evaluation of polyhydroxyalkanoate recovery from food waste by sequencing batch biofilm reactor with high mixed microbial biomass

In this study, the enrichment sequencing batch biofilm reactor (SBBR) and conventional enrichment reactor (SBR) were established, and a new strategy was developed to achieve higher biomass yield and polyhydroxyalkanoate (PHA) production from food waste than those achieved through the conventional method. After the 10th day of an expanded cultivation period, the respective active biomass concentrations in SBR and SBBR were 5.16 and 13.92 g/L, indicating a significant improvement in the biomass yield of mixed microbial culture in the SBBR. The PHA accumulation test revealed that maximum PHA concentration in SBR and SBBR reached 6.60 and 12.70 g/L, respectively, after 80 days of enrichment, indicating that compared to SBR, the SBBR could more effectively improve the PHA accumulation capacity. Meganema, Thauera, and Paracoccus were the dominant PHA-accumulating bacteria in the SBR and SBBR. Additionally, the volumetric productivity of the SBBR was 3.22 g COD/L/d, twice that of the SBR. This study provides new strategies and insights for improving PHA production and reducing the costs of PHA production and reactor investment.

Sequential recovery of extracellular alginate and intracellular polyhydroxyalkanoate (PHA) from mixed microbial culture PHA production system

Polyhydroxyalkanoate (PHA) is a biodegradable plastic that exhibits properties similar to petroleum-based plastics. The mixed microbial culture (MMC) process utilized a waste carbon source to produce PHA, reducing the raw material costs associated with pure bacterial technology. However, the high cost of PHA recovery and environmental pollution are significant challenges to the sustainable development of MMC technology. In this study, a sequential recovery strategy was proposed. This strategy involved the use of Na2CO3 to break down the structural extracellular polymeric substances and rhamnolipid to digest non-PHA cell material (NPCM). The recovery rate of PHA in this strategy achieved 61.29 ± 5.92% and a purity of 97.55 ± 0.92%. Additionally, the strategy allowed the sequential recovery of the by-product alginate-like extracellular polymers. FT-IR analysis confirmed that the recovered biopolymer was PHA material, possessing mechanical and thermal properties similar to those obtained through CHCl3 extraction. However, it was important to note that this method had the potential to alter the distribution structure of the PHA polymer, although it successfully avoids the issue of reducing the molecular weight of PHA during NPCM digestion. A comprehensive evaluation demonstrates that the cost of PHA production using this method was only 14.61 CNY/kg, with a more positive environmental impact in terms of global warming potential and carbon emission reduction. Therefore, the sequential recovery strategy presents a feasible alternative for the downstream recovery process and overall economy of the MMC PHA process.

Investigating the efficiency of a two-stage anaerobic-aerobic process for the treatment of confectionery industry wastewaters with simultaneous production of biohydrogen and polyhydroxyalkanoates.

The scope of the current study was to investigate the efficiency of a two-stage anaerobic-aerobic process for the simultaneous treatment and valorization of selective wastewater streams from a confectionary industry. The specific wastewater (confectionary industry wastewater, CIW) was a mixture of the rinsing eluting during washing of the cauldrons in which jellies and syrups were produced, and contained mainly readily fermentable sugars, being thus of high organic load. The first stage of the process was the dark fermentation (DF) of the CIW in continuous, attached-biomass systems, in which the effect on hydrogen yields and distribution of metabolites were studied for different packing materials (ceramic or plastic), hydraulic retention times, HRTs (12 h–30 h) and feed substrate concentration (20 g COD/L- 50 g COD/L). In the second stage, the effectiveness of the aerobic treatment of the DF effluents was evaluated in terms of the reduction of the organic load and the production of polyhydroxyalkanoates (PHAs) through an enriched mixed microbial culture (MMC). The MMC was developed in a continuous draw and fill system, in which the accumulation potential of PHAs was studied. It was shown that the hydrogen production rates decreased for increasing substrate concentration and HRTs, with a maximum of 12.70 ± 0.35 m3 H2/m3 initial CIW achieved for the lowest HRT and feed concentration and using ceramic beads as packing material. Butyrate, acetate and lactate were the main metabolites generated in all cases, in different ratios. The distribution of metabolites during DF was shown to highly affect the efficiency of the second process in terms of both the reduction of organic load and the PHAs yields. The highest removal of organic load achieved after 48 h of aerobic treatment was 84.0 ± 0.9 %, whereas the maximum PHAs yield was 21.46 ± 0.13 kg PHAs/m3 initial CIW.

Extracellular polymeric substances in electroactive biofilms play a crucial role in improving the efficiency of microbial fuel and electrolysis cells.

In microbial electrochemical cells (MECs), electroactive microbial biofilms can transmit electrons from organic molecules to anodes. To further understand the production of anodic biofilms, it is essential to investigate the composition and distribution of extracellular polymeric substance (EPS) in the MECs. In this study, the structure of EPS was examined in microbial electrolysis cells from mixed cultures forming biofilm using carbon fiber fabric anode. EPS was extracted from the anode biofilm of microbial electrolysis cells inoculated with mixed microbial culture. The anode biofilm yielded 0.4mg of EPS, of which 51.2% was humic substance, 16.2% was protein, 12.6% was carbohydrates, and 20% consisted of undetermined substances. Using epifluorescence microscopy, the composition of bacterial cells and their location inside EPS were studied, and the distribution of microbial communities was compared based on current density results in the presence of various carbohydrates. On the electrode surface, bacteria and EPS gathered or overlapped in various locations can affect microbial electrochemical performance. Our findings showed that EPS formation in electroactive biofilms would be important for enhanced efficiency of electricity- or hydrogen-producing microbial electrolysis cells.

Biofilm-based Biofertilizers and Microbial Mixed Cultures: Are they Different on Plant Growth?

Intensive agriculture has increased crop yields, but at the same time has posed severe environmental problems. Organic agriculture is a good alternative to intensive agriculture in safeguarding the environment. However, handling bulky organic materials in large-scale cultivations limits the widespread use of organic agriculture. In this context, microbial biofertilizers can play a major role in replacing intensive agriculture, which is based only on chemical inputs. As a recent development in microbiology, biofilms have been formulated in vitro to be used as biofertilizers, which are then called biofilmed biofertilizers (BFBFs). Biofilms are complex, surface-attached communities of multiple microbial species that produce a wider range of ecologically important biochemicals. The present study investigated the biochemical expression and the effect on plant growth of BFBFs and just mixed cultures of the BFBF microbes, using tomato (Solanumlyco persicum) as the test plant. A plant assay and a pot experiment were carried out to evaluate this. Fourier Transform Infrared (FTIR) spectroscopy was used to analyze the biochemical expression of the BFBFs and the mixed cultures. Seeds inoculated with BFBF showed significantly higher germination percentages and seedling lengths than the mixed cultures. The BFBFs and the mixed culture increased the vigor index of tomatoes up to 177% and 120%, respectively over the non-amended control. BFBFs inoculations significantly improved the root growth and resulted in significantly higher biomass production and plant height than the mixed cultures, and this was proportional to the production of more diverse functional groups and nitrogenous compounds by the BFBFs. Thus, it can be concluded that the BFBFs secrete a wider range of biochemicals than their mixed cultures, thus leading to higher plant productivity.
 Keywords: Biofilms, Biofertilizer, Tomato, Organic agriculture

Evaluation of the production and extraction of polyhydroxybutyrate from volatile fatty acids by means of mixed cultures and B. cepacia

The global consumption of plastics generates accelerated environmental pollution in landfills and marine ecosystems. Biopolymers are the materials with the greatest potential to replace synthetic polymers in the market due to their good biodegradability, however, there are still several disadvantages, mainly related to their production cost. Considering the above, the generation of biodegradable and biocompatible bioplastics stands out as an alternative solution, some of which are made from renewable raw materials, including polyhydroxyalkanoates PHAs. Although much research has been done on bacteria with the capacity for intracellular accumulation of PHAs, among others, it is also possible to produce PHAs using mixed microbial cultures instead of a single microorganism, using natural microbial consortia that have the capacity to store high amounts of PHAs. In this contribution, three methods for the extraction and purification of PHAs produced by fermentation using volatile fatty acids as a carbon source at different concentrations were evaluated, using the pure strain Burkholderia cepacia 2G-57 and the mixed cultures of the activated sludge from the El Salitre WWTP, in order to select the best method from the point of view of environmental sustainability as this will contribute to the scalability of the process. The mixed cultures were identified by sequencing of the 16S gene. A yield of 89% was obtained from the extraction and purification of PHA using acetic acid as a solvent, which according to its properties is "greener" than chloroform. The polymer obtained was identified as polyhydroxybutylated PHB.

Spatial separation of nitrifiers and denitrifiers promotes selection and enrichment of polyhydroxyalkanoates storing mixed cultures fed by crude glycerol and propionate wastewater

Polyhydroxyalkanoates (PHA) recovery from industrial wastewater has been highlighted as a promising strategy for a circular bioeconomy. However, the high and varying level of nitrogen in wastewater makes enrichment of mixed microbial culture (MMC) low efficiency. In this study, spatial separation of nitrifiers and denitrifiers was adopted by adding biocarriers in MMC and decreasing the sludge retention time (SRT) to accelerate the enrichment of PHA-storing MMC fed by mixed wastewater containing glycerol and propionate. Nitrifiers and denitrifiers were sustained on biocarriers, obtaining a high total inorganic nitrogen removal and allowing a more efficient selective pressure of a high carbon and nitrogen ratio (C/N) under low SRT conditions. The maximum PHA cell content and relative abundance of PHA-storing bacteria were increased to 60.51 % (SRT 6 d) and 49.62 % (SRT 6 d) with the decrease of SRT, respectively. This study demonstrates an efficient way to highly enrich PHA-storing MMC from crude glycerol, which provide a relevant technical support for high-efficiency enrichment of PHA-storing bacteria in low C/N wastewater.

Mixed Culture Cultivation in Microbial Bioprocesses.

Mixed culture cultivation is well renowned for industrial applications due to its technological and economic benefits in bioprocess, food processing, and pharmaceutical industries. A mixed consortium encompasses to achieve growth in unsterile conditions, robustness to environmental stresses, perform difficult functions, show better substrate utilization, and increase productivity. Hence, mixed cultures are being valorized currently and has also augmented our understanding of microbial activities in communities. This chapter covers a wide range of discussion on recent improvements in mixed culture cultivation for microbial bioprocessing and multifarious applications in different areas. The history of microbial culture, microbial metabolism in mixed culture, biosynthetic pathway studies, isolation and identification of strains, along with the types of microbial interactions involved during their production and propagation, are meticulously detailed in the current chapter. Besides, parameters for evaluating mixed culture performance, large-scale production, and challenges associated with it are also discussed vividly. Microbial community, characteristics of single and mixed culture fermentation, and microbe-microbe interactions in mixed cultures have been summarized comprehensively. Lastly, various challenges and opportunities in the area of microbial mixed culture that are obligatory to improve the current knowledge of microbial bioprocesses are projected.

Ecological succession and community assembly of mixed microbial culture polyhydroxyalkanoate production systems: Drivers of polyhydroxyalkanoate synthesis and Bdellovibrio predation

The production of polyhydroxyalkanoate (PHA) by mixed microbial culture (MMC) can reduce the pollution of plastics. Ecophysiological study of the microbial community assembly and succession is helpful for comprehensive understanding the MMC PHA production process. The operation mode of sequential aerobic dynamic discharge - aerobic dynamic feeding (ADD-ADF) was applied and the operation can be divided into acclimation phase and maturation phase. Deterministic process caused by selective pressure dominated the community assembly throughout the operation. In the acclimation phase, the physical selective pressure recovered the settling capacity of the system, and settling ability of the MMC was closely related to function of PHA synthesis. However, in the maturation phase, stochastic process caused sludge bulking, making the settling ability and PHA synthesis function of the MMC independent on each other. Stochastic process led to the succession of the dominant PHA-producing bacteria, for example, the predation of Paracoccus and Thauera by Bdellovibrio.

Excessive Ethanol Oxidation Versus Efficient Chain Elongation Processes

PurposeChain elongation is a metabolic feature that consists of the elongation of short-chain fatty acids to longer and more valuable acids when ethanol is available. To lower the operational costs, the process can also be performed using mixed microbial cultures. However, certain microorganisms in the mixed cultures can use the ethanol provided in competing reactions, which is usually termed excessive ethanol oxidation (EEO). Although minimizing ethanol use is essential, there is a lack of studies analyzing the extent, causes, and solutions to excessive ethanol oxidation processes.MethodsTo address this knowledge gap, ethanol, and acetic acid mixtures, at a molar ratio of 5 to 2, were fermented, and the following were analyzed: the fermentation profile at different (1) pH and (2) headspace gas compositions, (3) a 16S analysis of the headspace gas composition fermentations, and (4) a thermodynamic analysis of the reactions involved.Results and Conclusions: All fermentations, except the ones at the lowest pH (5.3), exhibited a significant EEO activity that reduced the yield of chain-elongated products. It was demonstrated that neither the inhibition of methanogenic activity nor the increased H2 partial pressure is an efficient method to inhibit EEO. It was also shown that CO2 can act as an electron acceptor for EEO, promoting the growth of acetogenic bacteria. In the absence of CO2, sulfate was used as an electron acceptor by sulfate-reducing bacteria to facilitate EEO. Methods such as low pH operation with in-line extraction, and the use of alternative sulfur salts, are proposed to increase the ethanol use efficiency in chain elongation processes.Graphical

Employing Spent Frying Oil as a Feedstock to Produce Short-Chain Organic Acids Using Mixed Microbial Cultures

Food industry waste and wastewater have been explored in relation to acidogenic fermentation as sources of non-competing food carbohydrates and mixed microbial cultures (MMCs), respectively, with the aim of producing short-chain organic acids (SCOAs) with general applications in polyhydroxyalkanoates (PHAs) production. However, studies on acidogenic fermentation using lipidic substrates are scarce. In this work, it was hypothesized that spent frying oil (SFO) could be used as a substrate for SCOA production via MMCs. In this study, oleic acid was used as a model molecule. The characterization of SFO revealed that it is mainly composed of oleic acid (81%), with minor amounts of palmitic, linoleic, and stearic acids. Different MMCs and food-to-microorganism (F/M) ratios were tested. MMCs collected in the aerobic tank of a municipal wastewater treatment plant (AES), at a 1:1 F/M, allowed to obtain the highest SCOA concentration (1.50 g COD/L) and the most diverse profile of SCOAs, with the production of acetic, propionic, butyric, iso-butyric, and valeric acids at 48:17:9:13:13% on a molar basis, respectively. This variety of odd and even SCOAs is of upmost importance, with potential applications in producing PHAs. This work can be considered a starting point for future acidogenic fermentation studies using lipid-based substrates and for the future production of PHAs.

A Multifunctional Dehalobacter? Tandem Chloroform and Dichloromethane Degradation in a Mixed Microbial Culture.

Chloroform (CF) and dichloromethane (DCM) contaminate groundwater sites around the world but can be cleaned up through bioremediation. Although several strains of Dehalobacter restrictus can reduce CF to DCM and multiple Peptococcaceae can ferment DCM, these processes cannot typically happen simultaneously due to CF sensitivity in the known DCM-degraders or electron donor competition. Here, we present a mixed microbial culture that can simultaneously metabolize CF and DCM and create an additional enrichment culture fed only DCM. Through genus-specific quantitative polymerase chain reaction, we find that Dehalobacter grows while either CF alone or DCM alone is converted, indicating its involvement in both metabolic steps. Additionally, the culture was maintained for over 1400 days without the addition of an exogenous electron donor, and through electron balance calculations, we show that DCM metabolism would produce sufficient reducing equivalents (likely hydrogen) for CF respiration. Together, these results suggest intraspecies electron transfer could occur to continually reduce CF in the culture. Minimizing the addition of electron donor reduces the cost of bioremediation, and "self-feeding" could prolong bioremediation activity long after donor addition ends. Overall, understanding this mechanism informs strategies for culture maintenance and scale-up and benefits contaminated sites where the culture is employed for remediation worldwide.

How temperature shapes the biosynthesis of polyhydroxyalkanoates in mixed microbial cultures.

Three sequential batch reactors were operated for the enrichment in microbial communities able to store polyhydroxyalkanoates (PHAs) using activated sludge as inoculum. They ran simultaneously under the same operational conditions (organic loading rate, hydraulic and solids retention time, cycle length, C/N ratio) just with the solely difference of the working temperature: psychrophilic (15°C), mesophilic (30°C), and thermophilic (48°C). The microbial communities enriched showed different behaviors in terms of consumption and production rates. In terms of PHA accumulation, the psychrophilic community was able to accumulate an average amount of 17.7 ± 5.7wt% poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), the mesophilic 40.3 ± 7.0wt% PHBV, and the thermophilic 14.8 ± 0.3wt% PHBV in dry weight over total solids. The average PHBV production yields for each selected community were 0.41 ± 0.12 CmmolPHBV /CmmolVFA at 15°C, 0.64 ± 0.05 CmmolPHBV /CmmolVFA at 30°C, and 0.39 ± 0.14 CmmolPHBV /CmmolVFA at 48°C. The overall performance of the mesophilic reactor was better than the other two, and the copolymers obtained at this temperature contained a higher PHV fraction. The physico-chemical properties of the obtained biopolymers at each temperature were also measured, and major differences were found in the molecular weight, following an increasing trend with temperature. PRACTITIONER POINTS: PHBV molecular weight is influenced by the operational temperature increasing with it. Increasing temperatures promote the production of HB over HV. The best accumulation performance was found at 30°C for the tested operational conditions.

From Shallow to Deep Bioprocess Hybrid Modeling: Advances and Future Perspectives

Deep learning is emerging in many industrial sectors in hand with big data analytics to streamline production. In the biomanufacturing sector, big data infrastructure is lagging compared to other industries. A promising approach is to combine deep neural networks (DNN) with prior knowledge in hybrid neural network (HNN) workflows that are less dependent on the quality and quantity of data. This paper reviews published articles over the past 30 years on the topic of HNN applications to bioprocesses. It reveals that HNNs have been applied to various bioprocesses, including microbial cultures, animal cells cultures, mixed microbial cultures, and enzyme biocatalysis. HNNs have been applied for process analysis, process monitoring, development of software sensors, open- and closed-loop control, batch-to-batch control, model predictive control, intensified design of experiments, quality-by-design, and recently for the development of digital twins. Most previous HNN studies have combined shallow feedforward neural networks (FFNNs) with physical laws, such as macroscopic material balance equations, following the semiparametric design principle. Only recently, deep HNNs based on deep FFNNs, convolution neural networks (CNN), long short-term memory (LSTM) networks and physics-informed neural networks (PINNs) have been reported. The biopharma sector is currently a major driver but applications to biologics quality attributes, new modalities, and downstream processing are significant research gaps.

Comparative life cycle analysis of PHA-based consumer items for daily use

USABLE Packaging project has developed an innovative value chain based on mixed microbial cultures using organic wastes as feedstock to produce prototypes of PHA-based items that were compared to their commercial counterparts, so the expected better environmental performance can be checked. To do so, a cradle-to-grave life cycle assessment was carried out. The system was modeled integrating all available knowledge, from pilot-scale data to process simulators, and following upscaling frameworks. PHA-based items outperform their commercial counterparts since they show environmental benefits thanks to the avoided electricity obtained in the cogeneration heat and power unit within the PHA production; however, these environmental benefits are very sensitive to the substituted electricity environmental burdens. The different levels of development and market implementation are seen as critical and therefore attention should be paid on how upscaling affects the results and interpretation of the LCA while serving as a guide for process and product development.

Removal of heavy metals from mine tailings by in-situ bioleaching coupled to electrokinetics

This work utilizes a combined biological-electrochemical technique for the in-situ removal of metals from polluted mine tailings. As the main novelty point it is proposed to use electrokinetics (EK) for the in-situ activation of a bioleaching mechanism into the tailings, in order to promote biological dissolution of metal sulphides (Step 1), and for the subsequent removal of leached metals by EK transport out of the tailings (Step 2). Mine tailings were collected from an abandoned Pb/Zn mine located in central-southern Spain. EK-bioleaching experiments were performed under batch mode using a lab scale EK cell. A mixed microbial culture of autochthonous acidophilic bacteria grown from the tailings was used. Direct current with polarity reversal vs alternate current was evaluated in Step 1. In turn, different biological strategies were used: biostimulation, bioaugmentation and the abiotic reference test (EK alone). It was observed that bioleaching activation was very low during Step 1, because it was difficult to maintain acidic pH in the whole soil, but then it worked correctly during Step 2. It was confirmed that microorganisms successfully contributed to the in-situ solubilization of the metal sulphides as final metal removal rates were improved compared to the conventional abiotic EK (best increases of around 40% for Cu, 162% for Pb, 18% for Zn, 13% for Mn, 40% for Ni and 15% for Cr). Alternate current seemed to be the best option. The tailings concentrations of Fe, Al, Cu, Mn, Ni and Pb after treatment comply with regulations, but Pb, Cd and Zn concentrations exceed the maximum values. From the data obtained in this work it has been observed that EK-bioleaching could be feasible, but some upgrades and future work must be done in order to optimize experimental conditions, especially the control of soil pH in acidic values.

Comparison of different aerobic sludge on enriching polyhydroxyalkanoate mixed microbial culture using lactic acid fermentation broth of agricultural wastes

Lactic acid fermentation broth derived from pig manure and apple waste is a potential high-quality feedstock for production of the biodegradable plastic polyhydroxyalkanoate (PHA). Enrichment of active PHA-synthesizing bacterial consortia, namely mixed microbial culture (MMC), is an important factor in high-efficiency synthesis of PHA. In this study, two types of aerobic sludge (pig farm sludge and municipal sludge) were selected to acquire active MMCs in the enrichment process with sludge retention times of 2 and 8 days using the lactic acid fermentation broth. Batch reactors and PHA accumulation reactors were used to evaluate the MMC activity. Results showed that pig farm sludge was acclimated to the superior MMC with the maximum PHA content of 25% during the enrichment process with sludge retention time of 8 days. The structure of microbial communities in all treatments tended to be similar after 45 days’ enrichment, and the dominant bacteria were genus Paracoccus with abundance of 15.41–41.45%. The maximum dry cell weight, PHA content, and PHA yield of batch reactors using the superior MMC were 0.69 g/L, 36%, and 0.86 g PHA-COD/g COD, respectively. Dry cell weight concentrations reached 3.16 g/L in the PHA accumulation reactor with PHA content of 40–50% and PHA yield of 0.57 g PHA-COD/ g COD. The findings of this study provide an effective enrichment strategy for MMCs, which could improve the high efficiency synthesis of PHA from the fermentation broth of agricultural wastes and enhance the economy of PHA production at a marketable scale.