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Nano-biochar application was investigated for anaerobic digestion of orange peel waste. The application for methane production focused on the optimization of biochar feedstock, rescue of failed digesters, and microbial succession analysis. It showed that sewage sludge (SS) derived biochar had the highest performance enhancement among the different feedstocks, which could be ascribed to the improvement of electron transfer, interspecies hydrogen transfer, and supply of trace elements. Subsequently, nano SS biochar-amended digestate was evaluated for rescuing failed digesters, and the experimental results indicated its positive roles through gradual bioaugmentation operation. The dynamic analysis of microbial succession indicated the successful application was through the mechanism of restoring partially the functional microbial communities. The major reconstruction of functional microorganisms included bacteria phyla Hydrogenispora (24.5%) and Defluviitoga (18.8%) as well as methanogenic genera of Methanosarcina (41.5%) and Methanobacterium (27.3%). These findings would contribute to rescuing failed anaerobic digesters by bioaugmentation with biochar-amended digestate., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

To find the optimal operation parameters and provide an explanation of methanogenic pathway for methane production in mesophilic (35 °C) and thermophilic (55 °C) anaerobic digestion (MAD, TAD) of soybean curd residue (SCR), MAD and MAD were contrastively investigated for 95 days. The maximum available OLR was identified as 3.3 gVS/L for both MAD and TAD. Compared to MAD, TAD exhibited a 20% higher average methane yield (0.591 L/gVS) and a 7.5% higher volatile solids removal efficiency (74.1 ± 10.4%). Bacterial phyla Bacteroidetes, Firmicutes and Proteobacteria dominated in MAD digesters while genus Defluviitoga was selectively enriched in TAD digesters due to higher temperature and organic loading pressure. Principal coordinates analysis of methanogen community showed that both temperature and OLR were crucial environmental variables shifting the taxonomic patterns of the methanogens. The enriched methanogen genus Methanothermobacter (93%) with a hydrogenotrophic methanogenic pathway had a close correlation with the TAD performance., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

A common challenge for the anaerobic digestion (AD) of food waste (FW) is the contamination by disposable plastic materials and utensils. The objective of this batch study was to investigate the effects of disposable plastic materials - polystyrene (PS), polypropylene (PP), high density polyethylene (HDPE) and wooden chopsticks (WC) on the AD of FW. Results showed that methane production from the AD of FW was inhibited to different extents when different materials were present in FW. PS and PP were found to reduce methane production from food waste more than HDPE and WC. The reduction in methane production was hypothesized to be due to the production of toxic plastic by-products or due to reduced contact between microbes and FW. Pyrosequencing and Field Emission Scanning Electron Microscope (FESEM) results indicated that the reduction in methane production was more likely due to the interference of good contact necessary between microbes and FW for biodegradation, and that the biological processes of AD were not affected by the contamination of plastics. Greater reductions in methane yields were also observed when the surface areas of the disposable materials were increased. Studying the effects of disposable materials on the AD of FW would provide plant operators with more information that could optimise the process of resource recovery from food waste., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A novel compact three-stage anaerobic digester (HM3) was developed to combine the advantages of high solids anaerobic digestion (AD) and wet AD for co-digestion of food waste and horse manure. By having three separate chambers in the three-stage anaerobic digester, three different functional zones were created for high-solids hydrolysis, acidogenesis and wet methanogenesis. The results showed that the functionalized partitioning in HM3 significantly accelerated the solubilization of solid organic matters and the formation of volatile fatty acids, resulting in an increase of 11~23% in methane yield. VS reduction in the HM3 presents the highest rate of 71% compared to the controls. Pyrosequencing analysis indicated that different microbial communities in terms of hydrolyzing bacteria, acidogenic bacteria and methanogenic archaea were selectively enriched in the three separate chambers of the HM3. Moreover, the abundance of the methanogenic archaea was increased by 0.8~1.28 times compared to controls.

Biotransformation is a green and useful tool for sustainable and selective chemical synthesis. However, it often suffers from the toxicity and inhibition from organic substrates or products. Here, we established a hollow fiber membrane bioreactor (HFMB)-based aqueous/organic biphasic system, for the first time, to enhance the productivity of a cascade biotransformation with strong substrate toxicity and inhibition. The enantioselective trans-dihydroxylation of styrene to (S)-1-phenyl-1,2-ethanediol, catalyzed by Escherichia coli (SSP1) coexpressing styrene monooxygenase and an epoxide hydrolase, was performed in HFMB with organic solvent in the shell side and aqueous cell suspension in the lumen side. Various organic solvents were investigated, and n-hexadecane was found as the best for the HFMB-based biphasic system. Comparing to other reported biphasic systems assisted by HFMB, our system not only shield much of the substrate toxicity but also deflate the product recovery burden in downstream processing as the majority of styrene stayed in organic phase while the diol product mostly remained in the aqueous phase. The established HFMB-based biphasic system enhanced the production titer to 143 mM, being 16-fold higher than the aqueous system and 1.6-fold higher than the traditional dispersive partitioning biphase system. Furthermore, the combination of biphasic system with HFMB prevents the foaming and emulsification, thus reducing the burden in downstream purification. HFMB-based biphasic system could serve as a suitable platform for enhancing the productivity of single-step or cascade biotransformation with toxic substrates to produce useful and valuable chemicals.

Continuous phenol biodegradation was accomplished in a two-phase partitioning osmotic membrane bioreactor (TPPOMBR) system, using extractant impregnated membranes (EIM) as the partitioning phase. The EIMs alleviated substrate inhibition during prolonged operation at influent phenol concentrations of 600-2000mg/L, and also at spiked concentrations of 2500mg/L phenol restricted to 2 days. Filtration of the effluent through forward osmosis maintained high biomass concentration in the bioreactor and improved effluent quality. Steady state was reached in 5-6 days at removal rates varying between 2000 and 5500mg/L-day under various conditions. Due to biofouling and salt accumulation, the permeate flux varied from 1.2-7.2 LMH during 54 days of operation, while maintaining an average hydraulic retention time of 7.4h. A washing cycle, comprising 1h osmotic backwashing using 0.5M NaCl and 2h washing with water, facilitated biofilm removal from the membranes. Characterization of the extracellular polymeric substances (EPS) through FTIR showed peaks between 1700 and 1500cm(-1), 1450-1450cm(-1) and 1200-1000cm(-1), indicating the presence of proteins, phenols and polysaccharides, respectively. The carbohydrate to protein ratio in the EPS was estimated to be 0.3. These results indicate that TPPOMBR can be promising in continuous treatment of phenolic wastewater., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A two-phase partitioning membrane bioreactor (TPPMB) was designed and operated for treatment of high strength phenolic wastewater through extraction/stripping and concomitant biodegradation. Tributyl phosphate dissolved in kerosene was used as the organic phase, sodium hydroxide as the stripping phase and Pseudomonas putida for biodegradation. In a semi-dispersive approach, organic phase dispersed in the stripping solution was contacted with wastewater through semi-permeable membranes for removal of phenol from wastewater, while the microorganisms were inoculated directly into the wastewater for biodegradation. The TPPMB exhibited high phenol removal rates, and phenol concentrations of 1000-3000mg/L were reduced to undetected amounts within 2-4h. Up to 80% phenol was recovered through extraction, while the remaining was metabolized by the microorganisms. Phenol recovery in the TPPMB was enhanced by increasing the mass transfer rate of phenol through the membranes, and it was also estimated that phenol diffusion through the aqueous boundary layer on the tube side was the rate limiting step. The flexibility in adjusting inoculation time in the TPPMB prevented microorganisms from adverse effects of substrate inhibition, which facilitated complete removal of phenol from the wastewater. TPPMB retained the advantages of both solvent extraction and biodegradation, and it can be highly promising for the treatment of toxic industrial wastewater., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

A hollow fiber membrane photobioreactor (HFMP) for microalgal growth and bacterial wastewater treatment was developed. C. vulgaris culture was circulated through one side of the HFMP and P. putida culture was circulated through the other. A symbiotic relationship was demonstrated as reflected by the photo-autotrophic growth of C. vulgaris using CO 2 provided by P. putida and biodegradation of 500 mg/L glucose by P. putida utilizing photosynthetic O 2 produced by C. vulgaris . Performance of the HFMP was significantly enhanced when the microalgal culture was circulated through the lumen side of the HFMP: the average percentage of glucose degraded per 8-h cycle was as high as 98% and microalgal biomass productivity was increased by 69% compared to the reversed orientation. Enhanced glucose biodegradation was achieved in an HFMP packed with more fibers indicating the easy scalability of the HFMP for increased wastewater treatment efficiency. [ABSTRACT FROM AUTHOR]

Chlorella vulgaris encapsulated in alginate beads were added into a bioreactor treating synthetic wastewater using Pseudomonas putida. A symbiotic CO/O gas exchange was established between the two microorganisms for photosynthetic aeration of wastewater. During batch operation, glucose removal efficiency in the bioreactor improved from 50 % in 12 h without aeration to 100 % in 6 h, when the bioreactor was aerated photosynthetically. During continuous operation, the bioreactor was operated at a low hydraulic retention time of 3.3 h at feed concentrations of 250 and 500 mg/L glucose. The removal efficiency at 500 mg/L increased from 73 % without aeration to 100 % in the presence of immobilized microalgae. The initial microalgae concentration was critical to achieve adequate aeration, and the removal rate increased with increasing microalgae concentration. The highest removal rate of 142 mg/L-h glucose was achieved at an initial microalgae concentration of 190 mg/L. Quantification of microalgae growth in the alginate beads indicated an exponential growth during symbiosis, indicating that the bioreactor performance was limited by oxygen production rates. Under symbiotic conditions, the chlorophyll content of the immobilized microalgae increased by more than 30 %. These results indicate that immobilized microalgae in symbiosis with heterotrophic bacteria are promising in wastewater aeration. [ABSTRACT FROM AUTHOR]

Highlights: [•] No substrate inhibition in HFMB, high cell growth and biodegradation rates obtained. [•] Absence of foaming and emulsification in HFMB, organic phase completely recycled. [•] Biodegradation first limited by cell growth and later by phenol mass transfer. [•] Phenol diffusion through the shell side boundary layer was slowest. [•] Biofilms on the membranes did not affect the biodegradation kinetics significantly. [ABSTRACT FROM AUTHOR]

Highlights: [•] Trioctylphosphine oxide (TOPO) was impregnated in polypropylene membranes. [•] TOPO-containing membranes acted as partitioning phase in two-phase biodegradation. [•] 800–3000mg/L phenol was biodegraded at high cell growth and biodegradation rates. [•] Two-phase biodegradation was not limited by interphasic mass transfer of phenol. [•] The bioreactor exhibited stability over 400h of operation. [ABSTRACT FROM AUTHOR]

A hollow fiber membrane bioreactor (HFMB) was employed for aqueous-organic two-phase biodegradation of phenol using Pseudomonas putida ATCC 11172, and the results were compared with that in a two-phase partitioning bioreactor (TPPB). Phenol containing 2-undecanone was nondispersively contacted with mineral medium that was inoculated with the bacteria. P. putida in suspension was able to biodegrade inhibitory phenol concentrations at without experiencing severe substrate inhibition. For example, phenol was completely biodegraded in 46 h at a maximum specific growth rate of , whereas the biomass yield and average biodegradation rate were and , respectively. Biomass yield and maximum specific growth rate decreased concomitantly with increasing phenol concentration. Phenol removal started at an exponential rate, and subsequently attained a linear profile in nutrient-limited conditions. Unlike conventional two-phase biodegradation systems, HFMB offered a better growth environment for the cells, as evident from the absence of the lag phase. The HFMB was more environmentally friendly and offered ease of operation and analysis that could mitigate the problems of foaming and emulsification that are associated with conventional TPPBs. In evaluating the effects of membrane area on biodegradation rate, the writers found that by doubling the interfacial area, phenol could be mineralized within 43 h with improved growth and removal rates. For comparable mass transfer flux across the aqueous-organic interface, biodegradation was faster in the HFMB relative to that in TPPB. [ABSTRACT FROM AUTHOR]

Abstract: A hollow fiber supported liquid membrane bioreactor (HFSLMB) was developed for two phase biodegradation of phenol. 2-undecanone dispersed into phenolic wastewater was indirectly contacted with the cell culture through the supported liquid membranes. The semi-dispersive approach stabilized the liquid membrane and facilitated non-dispersive transport of substrate from the solvent to the cells. Pseudomonas putida could biodegrade phenol at 1000–4000mgL−1 without experiencing severe substrate inhibition. For example, 4000mgL−1 phenol was biodegraded within 76h while the specific growth rate and biomass yield were 0.31h−1and 0.26g/g, respectively. Substrate removal occurred in two sequential steps: removal during log growth phase and removal under diffusion limitation. The biodegradation rates could be enhanced by changing the phase ratio, hydrodynamic conditions and the interfacial area. Repeated batch runs were conducted for more than 400h to evaluate long term stability of the HFSLMB. Bioreactor performance deteriorated after 5 runs (approximately 100h) due to the presence of biofilms on the membrane but a proposed 5h washing cycle after every 100h of operation could restore the performance. These results suggest that the HFSLMB can be a promising alternative to conventional two-phase partitioning bioreactors. [Copyright &y& Elsevier]

Abstract: The advantages from a 4-l external-loop inversed fluidized bed airlift bioreactor (EIFBAB) reported by Loh and Liu [2001. Chemical Engineering Science 56, 6171–6176] was synergized with preferential adsorption by granular activated carbon (GAC) for the enhanced cometabolic biotransformation of 4-chlorophenol (4-cp) in the presence of phenol as a growth substrate. This was achieved by incorporating a GAC fluidized bed in the lower part of the riser with the gas sparger relocated above this fluidized bed to avoid the presence of a 3-phase flow in the fluidized bed consequently providing larger gas holdup. Expanded polystyrene beads (EPS) were used as the supporting matrix for immobilizing Pseudomonas putida ATCC 49451, in the downcomer of the bioreactor. The hydrodynamics of the bioreactor system was characterized by studying the effect of the extent of valve opening, under cell-free condition, on gas holdup and liquid circulation velocity at different gas velocities and solids loading (EPS and GAC). The experimental data for gas holdup were modeled using power law correlations, while a Langmuir–Hinshelwood kinetics model was used for the liquid circulation velocity. The bioreactor was tested for batch cometabolic biotransformation of 4-cp in the presence of phenol at various concentration ratios of phenol and 4-cp (ranging from phenol: 4-cp to phenol: 4-cp) at 9% EPS loading and 2.8% (10g) GAC loading. The 4-cp and phenol biotransformations were achieved successfully in the bioreactor system, which ascertained the feasibility of the bioreactor. Biotransformation of high 4-cp and phenol concentrations, which was oxygen limited, was also effectively achieved by increasing the gas holdup in the riser. This was possible in the current EFBAB system because of the synergistic effect of the GAC fluidized bed, the globe valve and cell immobilization by EPS. [Copyright &y& Elsevier]

A chemostat was coupled with a forward osmotic hollow fiber membrane bioreactor (FOHFMB) for treatment of high strength saline phenolic wastewater using Pseudomonas putida ATCC 11,172. The microorganisms were protected from the inhibitory effects of phenol and sodium chloride through dilution of the feed wastewater. This resulted in high cell growth and biodegradation rates during transient operation and steady state was achieved within 20 h. Effluent from the chemostat was desalinated in the FOHFMB through forward osmosis (FO) using magnesium chloride as the draw solute (DS). Permeate flux during FO remained stable for over 70 h in the orientation with DS facing the porous side of the membranes (PRO mode of operation). Water used for dilution could be recovered using 0.8 M DS when the wastewater did not contain any sodium chloride, whereas, 1.5 M DS was required to recover water from the wastewater containing 0.6 M sodium chloride. Biomass attachment on the membranes during FO operation was visualized using SEM, which showed that FO membranes was susceptible to fouling propensity and biomass deposition on the membranes was directly associated with permeate flux. Nevertheless, biofouling of membranes was reversible and membrane performance was recovered by osmotic backwashing. [ABSTRACT FROM AUTHOR]

Highlights: [•] We developed an immersed membrane bioreactor for pharmaceuticals biotransformation. [•] System showed enhanced cis-indandiol conversion from indene. [•] Optimized operation increased product concentration by 4.5 times compared to suspension cultures. [•] Membranes served to immobilize cells and sequester inhibitory indene. [•] Reusability of membranes demonstrated over 5 repeated cycles. [ABSTRACT FROM AUTHOR]

• Food waste & horticultural waste co-digested in three-stage thermophilic bioreactor. • Average methane yields and VS removal increased by 31–45% and 32–61%, respectively. • Functional segregation aided selective enrichment of functional microbial species. • Methanosarcina and Methanothermobacter balanced diversified methanogenesis pathways. • Three-stage thermophilic bioreactor recycled 64–77% of total energy to serve itself. The thermophilic anaerobic co-digestion of food waste and horticultural waste with a three-stage bioreactor was investigated to produce renewable energy, focusing on performance evaluation, microbial community analysis, and energy balance assessment. The results of this study indicated that the average methane yield (0.42 ± 0.06 L/gVS) in the bench-scale three-stage thermophilic bioreactor was approximately 45% and 31% higher than that of the one and two-stage bioreactors, respectively. The average volatile solid (VS) reduction achieved in the bench-scale three-stage thermophilic bioreactor was 63.0 ± 8.2%, which was 61% and 32% higher than that of the one and two-stage bioreactors, respectively. Pyrosequencing analysis of microbial communities in simulated thermophilic three-stage co-digestion experiments showed that bacterial phyla Firmicutes , Thermotogae and Bacteroidetes dominated in all three types of bioreactors. However, significant differences were observed at the genus level of bacterial communities between the one, two and three-stage bioreactors. Indeed, due to selective enrichment, the dominant methanogenic pathways in the three-stage bioreactor shifted from hydrogenotrophic methanogenesis at a low organic loading rate (OLR) to a balance of hydrogenotrophic and acetoclastic pathways at high OLR. Furthermore, assessments of the energy balance and the economic viability of the bench-scale system demonstrated that the three-stage thermophilic co-digestion could be a promising process for the treatment of food waste and horticultural waste as well as for bioenergy recovery at an industrial scale. [ABSTRACT FROM AUTHOR]