Biogas is mainly produced from the anaerobic fermentation of biomass, containing methane with an extensive range between about 50% and 70%. Higher methane content biogas has higher energy and heat ...value, which needs biogas upgrading. There are mainly two types of biogas upgrading technologies (ex-situ and in-situ). This manuscript presents a review of technologies on in-situ biogas upgrading. These technologies comprise H2 addition technology (e.g., continuous stirring tank reactor (CSTR), hollow fiber membrane (HFM), nano-bubble (NB) technology, upflow anaerobic sludge blanket (UASB)), high-pressure anaerobic digestion (HPAD), bioelectrochemical system (BES), and additives (e.g., ash, biochar, and iron powder). The results confirm the excellence of H2-addition technology, with the highest average CH4 content obtained (HFM: 92.5%) and one of the few full-scale cases reported (Danish GasMix ejector system: 1110 m3). Meanwhile, newly pop-up technology such as HPAD delivers appropriate CH4 content (an average of 87%) and is close to the full-scale application (https://bareau.nl/en/for-professionals/). More importantly, the combo between HPAD and H2-addition technology is prominent as the former improves the low gas-to-liquid obstacle confronted by the latter. Additionally, recently emerging BES can't stand out yet because of limited efficiency on CH4 content or constraint full-scale application behaviors (disability to operate at high current density). However, its combination with H2-addition technology to form the Power to Gas (PtG) concept is promising, and its commercial application is available (http://www.electrochaea.com/). Hydrogenotrophic methanogens are imperative players in all reviewed technologies for the generation of upgraded CH4.
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•In-situ biogas upgrading technologies are reviewed.•H2-addition technology is the most prominent in-situ technology.•Hydrogenotrophic methanogens are critical microorganisms in upgrading technologies.•HFM reactor shows the highest average CH4 content (92.5%).•The combination between H2-addition technology and HPAD/BES is promising.
The knowledge on the performance enhancement of nitrogen and organic matter in the expanded constructed wetlands (CWs) with various new designs, configurations, and technology combinations are still ...not sufficiently summarized. A comprehensive review is accordingly necessary for better understanding of this state-of-the-art-technology for optimum design and new ideas. Considering that the prevailing redox conditions in CWs have a strong effect on removal mechanisms and highly depend on wetland designs and operations, this paper reviews different operation strategies (recirculation, aeration, tidal operation, flow direction reciprocation, and earthworm integration), innovative designs, and configurations (circular-flow corridor wetlands, towery hybrid CWs, baffled subsurface CWs) for the intensifications of the performance. Some new combinations of CWs with technologies in other field for wastewater treatment, such as microbial fuel cell, are also discussed. To improve biofilm development, the selection and utilization of some specific substrates are summarized. Finally, we review the advances in electron donor supply to enhance low C/N wastewater treatment and in thermal insulation against low temperature to maintain CWs running in the cold areas. This paper aims to provide and inspire some new ideas in the development of intensified CWs mainly for the removal of nitrogen and organic matter. The stability and sustainability of these technologies should be further qualified.
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Dynamics of phosphate (PO43−) adsorption, desorption and regeneration characteristics of three lab-synthesized iron oxides, ferrihydrite (F), goethite (G), and magnetite (M) were ...evaluated in this study. Batch experiments were conducted to evaluate the impact of several adsorption parameters including adsorbent dosage, reaction time, temperature, pH, and ionic strength. The results showed that PO43− adsorption increased with reaction time and temperature while it decreased with an increase in solution pH. Adsorption isotherm data exhibited good agreement with the Freundlich and Langmuir model with maximum monolayer adsorption capacities of 66.6 mg·g−1 (F), 57.8 mg·g−1 (M), and 50.5 mg·g−1 (G). A thermodynamics evaluation produced ΔG < 0, ΔH > 0, and ΔS > 0, demonstrating that PO43− adsorption onto tested minerals is endothermic, spontaneous, and disordered. The PO43− removal mostly occurred via electrostatic attraction between the sorbate and sorbent surfaces. Moreover, the PO43− sorption was reversible and could be desorbed at varying rates in both neutral and alkaline environments. The good desorption capacity has practical benefits for potential regeneration and re-use of the saturated particles in wastewater treatment systems.
Rapid economic growth in Asia and especially in China, will lead to a huge increase of food waste (FW) production that is expected to increase by 278–416 million tonnes. Among various waste ...management practices, anaerobic digestion (AD) is a useful method to transform food waste, producing renewable energy/biofuel and bio-fertilizers. This review aims to investigate some of the key factors in proposing FW for anaerobic digestion, with particular reference to China and South East Asian countries. Food waste shows variable chemical composition and a high content of biodegradable material (carbohydrates, protein and lipid). This composition led to consistent biogas production that was reported, as average for Chinese FW, of 480 ± 88 LCH4 kg−1 VS (n = 42). Since these data are higher than those reported for energy crops (246 ± 36 LCH4 kg−1 VS), this makes FW a good candidate to substitute for energy crops, avoiding food-energy conflicts. FW co-digestion with different substrates improved total bio-methane production (on average), from 268 ± 199 mL g−1 VS to 406 ± 137 mL g−1 VS. Food waste pretreatment, also, seems to be very useful in increasing total biogas production. Physical and thermal treatments were the best, increasing biogas production by 40% and 30%, respectively. Techno-economic evaluation seems to indicate the feasibility of substituting EC with FW for producing biogas and reducing total biomass costs. To achieve this, separate collection sources need to be put into place, assuring high FW quality to promote a Circular Economy approach in FW management.
•The amount of food waste (FW) produced in the world is increasing with the population growth.•FW can be recovered by anaerobic digestion (AD) producing bio-methane and bio-fertilizers.•FW-AD has been investigated for potential bio-methane production and optimal AD conditions.•FW can replace energy crop in producing bio-methane make AD more sustainable.•Food waste pre-treatment in general benefitted anaerobic digestion giving a positive energy balance.
Three types of vertical flow constructed wetland columns (VFCWs), packed with corn cob biochar (CB-CW), wood biochar (WB-CW) and gravel (G-CW) under tidal flow operations, were comparatively ...evaluated to investigate anaerobic digested effluent treatment performance and mechanisms. It was demonstrated that CB-CW and WB-CW provide significantly higher removal efficiencies for organic matter (>59%), NH4+-N (>76%), TN (>37%) and phosphorus (>71%), compared with G-CW (22%–49%). The higher pollutants removal ability of biochar-packed VFCWs was mainly attribute to the higher adsorption ability and microbial cultivation in the porous biochar media. Moreover, increasing the flooded/drained ratio from 4/8h to 8/4h of the tidal operation further improved around 10% of the removal of both organics and NH4+-N for biochar-packed VFCWs. The phosphorus removal was dependent on the media adsorption capacities through the whole experiment. However, the NH4+-N biodegradation by microbial communities was demonstrated to become the dominant removal mechanism in the long term treatment, which compensated the decreased adsorption capacities of the media. The study supported that the use of biochar would increase the treatment performance and elongate the lifespan of CWs under tidal operation.
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•Biochar-packed VFCWs have better long-term treatment ability than gravel.•The better performance of biochar is attributed to its high sorption capacity.•Tidal operations enhance anaerobic digested effluent treatment lifespan of CWs.•Biochar supports a diverse microbial community compared to gravel in VFCWs.
Due to its high adsorption capacity, the use of biochar to capture excess nutrients from wastewater has become a central focus in environmental remediation studies. In this study, its potential use ...in adsorption and removal of ammonium in piggery manure anaerobic digestate slurry was investigated. The adsorbed amount of NH4+-N (mg·g−1) and removal percentage as a function of adsorbent mass in solution, adsorbent particle size, NH4+-N concentration in the effluent, contact time, pH and temperature were quantified in batch equilibrium and kinetics experiments. The maximum NH4+-N adsorption from slurry at 1400mgN·L−1 was 44.64±0.602mg·g−1 and 39.8±0.54mg·g−1 for wood and rice husk biochar, respectively. For both biochars, adsorption increased with increase in contact time, temperature, pH and NH4+-N concentration but it decreased with increase in biochar particle size. Furthermore, the sorption process was endothermic and followed Langmuir (R2=0.995 and 0.998) and Pseudo-second order kinetic models (R2=0.998 and 0.999). Based on the removal amounts, we concluded that rice husk and wood biochar have potential to adsorb NH4+-N from piggery manure anaerobic digestate slurry, and thus can be used as nutrient filters prior to discharge into water streams.
•Biochar adsorbed 60% NH4+-N from piggery slurry.•Absorption was sensitive to changes in particle size, pH and temperature.•NH4+-N adsorption from slurry followed the Langmuir and Pseudo second order models.•Monolayer chemisorption was the major NH4+-N adsorption mechanism from piggery slurry.
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•The AD of food waste was severely acidified due to lack of essential TEs.•TEs addition improved operation stability of AD of food waste at higher OLRs.•Deficiency of Se resulted in ...accumulation of both acetic and propionic acids.•Higher methane yield coefficient and biomass yield was achieved with TEs addition.
This study investigated the effects of trace elements (TEs) on the anaerobic digestion (AD) of food waste (FW) in laboratory-scale semi-continuously fed anaerobic digesters. The duration of digesters operation was approximately 400days. Organic loading rates (OLRs) ranged from 1.0 to 5.5gVSL−1d−1 at 37°C. Results showed that methane production of the digester was severely inhibited at a volatile fatty acid (VFA) concentration of 30,000mgL−1 at OLR of 4.0gVSL−1d−1 in the absence of TEs. Contrary to the failed digesters, a stable performance was achieved in the TEs added digesters. High methane yield (approximately 465.4mLCH4g−1VSadded) was obtained, and no significant accumulation of VFA was observed in the TEs added digesters at OLR of 1.0–5.0gVSL−1d−1 and HRT of 40days. These findings strongly indicated that the addition of TEs has an important impact on the operation stability of AD of FW.
Recycling and value-added utilization of agricultural residues through combining technologies such as anaerobic digestion and pyrolysis could double the recoverable energy, close the nutrient recycle ...loop, and ensure cleaner agricultural production. This study assessed the beneficial application of biochar to soil to recycle digestate nutrients, improve soil quality, and reduce conventional chemical fertilizer. The addition of digestate-enriched biochar improved soil quality as it provided higher soil organic matter (232%–514%) and macronutrients (110%–230%) as opposed to the unenriched biochar and control treatments. Maize grown in soil amended with digestate-enriched biochar showed a significantly higher biomass yield compared to the control and non-enriched biochar treatments but was slightly lower than yields from chemical fertilizer treatments. The slightly lower yield (20%–25%) achieved from digestate-enriched biochar was attributed to slower mineralization and release of the adsorbed nutrients in the short term. However, digestate-enriched biochar could in the long term become more beneficial in sustaining soil fertility through maintaining high soil organic matter and the gradual release of micronutrients compared to conventional chemical fertilizer. Positive effects on soil micronutrients, macronutrients, organic matter, and biomass yield indicates that enriched biochar could partly replace chemical fertilizers and promote organic farming in a circular economy concept.
Four slow pyrolyzed biochars produced from wood (WDB), corncobs (CCB), rice husks (RHB) and sawdust (SDB) were evaluated for adsorption, desorption and regeneration of phosphate (PO43−-P) from ...anaerobically digested liquid swine manure. The PO43−-P adsorption capacity increased followed by initial concentrations increasing. Maximum PO43−-P adsorptions at initial 150 mg/L of PO43−-P (highest load) were average of 7.67, 6.43, 5.73 and 5.41 mg/g for WDB, CCB, RHB and SDB, respectively. Pseudo second order kinetics model could best fit PO43−-P adsorption, which indicated the chemisorption via precipitation was the main mechanism for PO43−-P removal. The sorption process was reversible and the adsorbed PO43−-P could be desorbed in both neutral (57–78%) and acidic solution environments (75–88%) for all biochars. Meanwhile, regenerated biochar could re-adsorb up to 5.62 mg/g at the highest initial PO43−-P of 150 mg/L. The present finding implied biochar could be effectively used to recover PO43−-P from anaerobic digestate.
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•Kinetics of PO43−-P adsorption in four slow pyrolyzed biochars were investigated.•The Langmuir isotherm and pseudo-second order kinetic model provided the best fit.•Chemisorption was the major mechanism rather than intraparticle diffusion.•Biochar could be effectively used to recover PO43−-P from anaerobic digestate.•The desorption of PO43−-P could regenerate biochar for effective reuse.
Reversible PO43−-P adsorption suggested that pyrolysis of biomass coupled with biochar production could be a sustainable way for nutrient recovery from anaerobic digestate liquid.
Moringa oleifera Lam. is a common edible plant, famous for several nutritional and therapeutic benefits. This study investigates the salt -induced modulations in plant growth, physio-biochemical ...responses, and antioxidant performance of M. oleifera grown under 0, 50, and 100 mM NaCl concentrations. Results showed that the plant effectively managed moderate salinity (50 mM NaCl) by maintaining succulence, weight ratios, and biomass allocation patterns of both shoot and root with minimal reduction in dry biomass. However, high salinity (100 mM NaCl) remarkably declined all growth parameters. The plant accumulated more Na
and Cl
, while less K
under salinity as compared to the control. Consequently, osmotic potentials of both root and leaf decreased under salinity, which was corroborated by the high amount of proline and soluble sugars. Increased level of H
O
with significantly unchanged membrane fluidity indicating its role in perceiving and managing stress at moderate salinity. In addition, increased activities of superoxide dismutase, and catalase, with increased glutathione and flavonoid contents suggest an integrated participation of both enzymatic and non-enzymatic antioxidant components in regulating ROS. On the other hand, high salinity caused an outburst of ROS indicated by high H
O
, MDA, and electrolyte leakage. As a response, moringa drastically increased the activities of all antioxidant enzymes and contents of antioxidant molecules including ascorbic acid, glutathione, total phenols, and flavonoids with high radical scavenging and reducing power capacities. However, a considerable amount of energy was used in such management resulting in a significant growth reduction at 100 mM NaCl. This study suggests that moringa effectively resisted moderate salinity by modulating physio-biochemical attributes and effectively managing ion toxicity and oxidative stress. Salt stress also enhanced the medicinal potentials of moringa by increasing the contents of antioxidant compounds including ascorbic acid, glutathione, total phenols, and flavonoids and their resulting activities. It can be grown on degraded/ saline lands and biomass of this plant can be used for edible and medicinal purposes, besides providing other benefits in a global climate change scenario.
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