Biochar amendment rapidly shifts microbial community structure with enhanced thermophilic digestion activity

Metagenomic insight into the diffusion signal factor mediated social traits of anammox consortia after starvation

Biomass starvation is common in biological wastewater treatment. As a social trait of microbial community, how quorum sensing (QS) regulated bacterial trade-off through interactions after starvation remains unclear. This study deciphered the mechanism of anaerobic ammonium oxidation (anammox) consortia in response to starvation, including reducing extracellular electron transfer (EET), adenosine 5'-triphosphate (ATP) content and amino acid metabolism. Metagenomic analysis has shown that the addition of the diffusion signal factor (DSF) resulted in a high abundance of antioxidant genes, which contributed to achieving redox balance in anammox bacteria. There was an enrichment of Geobacter and Methanosarcina, which were QS-responsive direct interspecific electron transfer participants. Furthermore, DSF stimulated the nitrogen and carbon metabolism of Ca. Kuenenia_stuttgartiensis, promoting syntrophy of metabolic intermediates within microbial community. This study highlighted the effect of DSF on the microbial interaction patterns and deciphered the QS-based social traits of anammox consortia after starvation, facilitating the stable operation of the anammox process.

Characterizing graphene oxide waste stream and assessing its impact on anaerobic co-digestion with municipal sludge

This study evaluated anaerobic co-digestion as a promising strategy for managing organic-contaminated waste streams generated from nanomaterial synthesis. The novel approach enabled precise quantification of organic content, efficient biomethane recovery, and a sustainable redirection of ethanol-contaminated graphene oxide (GO) dispersions. The proposed method achieved high accuracy (93-97%) in detecting organic content in ethanol-contaminated GO dispersions, significantly outperforming the conventional total chemical oxygen demand (tCOD) method, which only reached 75-77% accuracy. Additionally, co-digestion of trace ethanol content in GO dispersions with municipal sludge substantially enhanced methane production kinetics, resulting in a 17.6% increase in specific methane yield (per tCOD added) and a 284% increase in total methane production. Parallel anaerobic digestion (AD) experiments using conductive GO nanosheets (without ethanol) revealed the synergistic impact of GO nanosheets and trace ethanol content as a key mechanism driving these improvements. Furthermore, the study provided evidence of the biological reduction of GO and its magnetite-decorated counterpart, magnetic GO, as indicated by a shift in the ID/IG ratio from 1.06 to 0.77 and a G-band shift from 1606 cm⁻1-1565 cm⁻1. This reduction decreased the stability of nanosheets in the AD liquid phase, promoting their partitioning into the solid phase. This process facilitates the adsorption of the GO phase within the digestate and allows for the slow release of micronutrients when used as soil amendments.

Ultrafiltration fractionation of potentially inhibitory substances of hydrothermal liquefaction aqueous phase derived from municipal sludge

Hydrothermal liquefaction (HTL) is a promising thermo-chemical technology for municipal sludge treatment due to its potential for biocrude oil recovery and minimizing biosolids management costs. However, the process generates a high volume of an aqueous byproduct that needs to be treated due to its high chemical oxygen demand (COD) and various organic and inorganic compounds. Although the aqueous phase is known to contain recalcitrant and potentially inhibitory substances that may affect its biological treatment, their molecular weight distribution (MwD) and its impact on anaerobic biodegradability are poorly understood. Ultrafiltration (UF) was conducted to fractionate HTL aqueous into different molecular weight (Mw) fractions using 300, 100, 10, and 1 kDa membranes. Mesophilic biochemical methane potential (BMP) assays were conducted to assess the anaerobic biodegradability of each fraction, and the first-order model was used to calculate the degradation kinetics of potential inhibitory compounds. The highest percentage of organics (65 %) was found in the Mw<1 kDa range, whereas the 10>Mw>1 kDa had the lowest percentage (8 %). There was no significant difference in the cumulative specific methane produced from various Mw fractions (p>0.05). The Mw<1 kDa fraction had the highest first-order specific methane production rate (0.53 day-1), whereas the unfiltered HTL had the lowest (0.38 day-1). Although UF fractionation increased the rate of anaerobic degradation of HTL aqueous for the Mw<1 kDa fraction, the observed methane potential was only 55 % of the theoretical value. This implies that 45 % of COD remains undegraded even after permeation through the lowest Mw cut-off membrane. Therefore, further characterization of HTL aqueous is needed for compounds with molecular weights below 1 kDa to fully understand the nature of inhibitory organics and their impact on anaerobic digestion. Furthermore, pretreatments utilizing techniques such as adsorption and advanced oxidation may be necessary to enhance the specific methane yields from various HTL aqueous fractions, thereby bringing them closer to the theoretical yield.

Nanomaterial-amended anaerobic sludge digestion: Effect of pH as a game changer

Using nanomaterials as supplements in batch-fed anaerobic digestion (AD) has led to conflicting results in the literature, warranting the need for a standardized approach. Here, we investigate the role of pH in AD by performing batch biochemical methane potential (BMP) assays utilizing municipal sludge under two conditions: optimal initial pH (≈ 7.5) and elevated initial pH (≈ 9). We also examine the effects of synthesized nanomaterials, e.g., graphene oxide (GO), magnetite, magnetic GO, and magnetic reduced GO (MrGO), with different surface functionalities on BMP performance under these pH conditions. Our results show that the AD system is sensitive to pH, with the ultimate BMP reached much earlier at the neutral pH condition (20 days (d)) than at the elevated pH condition (45 d). Furthermore, the effects of nanomaterials on BMPs are pH-dependent, with MrGO improving the BMP rate by 56% on the onset of the plateau in the methane production graph at the neutral pH, while the BMP rate decreased by 14% at the same time scale at the elevated pH. Our findings demonstrate the need for standardized methods and highlight the importance of closely monitoring pH in future studies on nanomaterials-amended AD systems.

Advances, trends and challenges in the use of biochar as an improvement strategy in the anaerobic digestion of organic waste: a systematic analysis

A recently strategy applied to anaerobic digestion (AD) is the use of biochar (BC) obtained from the pyrolysis of different organic waste. The PRISMA protocol-based review of the most recent literature data from 2011-2022 was used in this study. The review focuses on research papers from Scopus® and Web of Knowledge®. The review protocol used permits to identify 169 articles. The review indicated a need for further research in the following challenges on the application of BC in AD: i) to increase the use of BC in developing countries, which produce large and diverse amounts of waste that are the source of production of this additive; ii) to determine the effect of BC on the AD of organic waste under psychrophilic conditions; iii) to apply tools of machine learning or robust models that allow the process optimization; iv) to perform studies that include life cycle and technical-economic analysis that allow identifying the potential of applying BC in AD in large-scale systems; v) to study the effects of BC on the agronomic characteristics of the digestate once it is applied to the soil and vi) finally, it is necessary to deepen in the effect of BC on the dynamics of nitrogen and microbial consortia that affect AD, considering the type of BC used. In the future, it is necessary to search for new solutions in terms of the transport phenomena that occurs in AD with the use of BC using robust and precise mathematical models at full-scale conditions.

Bioaugmentation of Methanosarcina thermophila grown on biochar particles during semi-continuous thermophilic food waste anaerobic digestion under two different bioaugmentation regimes

This study presents the effect of bioaugmentation of thermophilic anaerobic digestion of food waste with Methanosarcina thermophila grown on a wood-derived biochar. Two different supplementation regimes were tested, namely a single bioaugmentation (SBABC) in which 10% v/v of the microbes grown on biochar (1 g/L) is added at setup of the reactors, versus a routine bioaugmentation (RBABC) wherein the same amount of supplements were added over 10 feeding cycles. The optimally performing 'R' and 'S' reactors had increased methane yields by 37% and 32% over their respective controls while reactors SBABC 2 and 3 produced 21.89% and 56.09% higher average methane yield than RBABC 2 and 3, respectively. It appears that a single dose bioaugmentation is advantageous for improving AD as analysed in terms of average methane yield and VFA production. This study provides the basis for understanding how biochar and bioaugmentation can be used for engineering sustainable pilot-scale AD processes.

Synergistic advanced oxidation process for enhanced degradation of organic pollutants in spent sulfuric acid over recoverable apricot shell-derived biochar catalyst

The sulfuric acid-based alkylation process, which leads the industrial application market, still struggles with effectively removing a large number of organic pollutants from hazardous spent sulfuric acid. A synergistic advanced oxidation process was constructed to degrade the organic pollutants with H2O2 and sodium persulfate as the synergistic oxidants and apricot shell-derived biochar (OBC) as the catalyst. Taking the total organic carbon (TOC) and the color scale as the indices, the effects of critical experimental factors, i.e., reaction temperature, initial oxidant concentration, catalyst dosage, and aeration rate, were optimized. The results showed that the removal rates of TOC and the color of the spent sulfuric acid reached ∼91% and 96.6%, respectively, after 150 min under the optimum conditions. Besides, the efficient and low-cost OBC catalyst developed in this study could be continuously used for at least four times with about 75% TOC removal and 80% color removal, exhibiting favorable stability and good resistance to acid corrosion. Further study confirmed that the SO4-˙ and ˙OH radicals generated in the synergistic advanced oxidation process strengthened the degradation and elimination of organic pollutants. The synergistic advanced oxidation process could provide a feasible insight for spent sulfuric acid treatment.