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This study investigated the effects of the addition of micro- (Fe, Co, Ni, and Mo) and macro-(Sulfur) nutrients on mono-digestion of sorghum under mesophilic conditions. A continuous stirred-tank reactor was operated for more than 420 days under seven different experimental conditions. The experimental results showed poor performance for methane production and process stability without nutrient supplementation. Serious deficiencies in Co and S were confirmed by nutrient analysis of dry sorghum and digestate. Nutrient augmentation efficiently enhanced methane production and volatile fatty acid (VFA) removal. Methane production reached 223 mL-CH4/g-VS, almost matching the yield predicted by biochemical methane potential (BMP) test. S was demonstrated to have a critical effect on metal availability in the digester. Consequently, to maintain stable methane fermentation, suitable supplementations of S and Co are recommended for anaerobic sorghum mono-digestion.

Oily organic waste is a promising feedstock for anaerobic co-digestion. Free long-chain fatty acids (LCFAs) produced from lipids can inhibit methanogenic consortia, so optimal control of LCFA concentration is the key to successful operation of co-digestion. Most LCFAs are present in the solid phase, making them difficult to be detected and monitored. This study proposes a simple and easy method for detecting LCFAs in both the liquid and solid phases of anaerobic digestate by combining liquid-liquid extraction followed by solid-phase extraction (SPE) and spectrophotometric analysis. The extraction procedure successfully removed impurities that interfere with the absorbance spectrum and ensured high recovery rates of LCFAs. The utility of the pretreatment used for the extraction was discussed using thermodynamic analysis and calculations of phase equilibrium for the solvent extraction system. The absorbance spectrum shift of pyridinium N-phenolate betaine (PNPB) dye-stained solution showed a good correlation with LCFA concentration and enabled highly sensitive measurements. Good quantification was demonstrated in experiments using various digestate samples obtained from the laboratory, pilot, and full-scale reactors.

In this study, an integrated system of siphon-driven self-agitated anaerobic reactor (SDSAR) and anaerobic fixed bed reactor (AFBR) was conducted for the treatment of wastewater from food waste disposer (FWD), and the effect of influent total solids (TS) concentration on the process performance was evaluated. When the influent TS concentration increased from 7.04 to 15.5 g/L, the methane gas production rate increased from 0.45 to 0.92 L-CH4/L/day. However, with the influent TS concentration of food waste (FW) further increased to 23.5 g/L, a large amount of scum formed and accumulated in the SDSAR. According to the result of chemical oxygen demand (COD) recovery, the proportion of COD remained in the effluent at different TS concentrations was only around 2%. On the other hand, with an increase in TS concentration, the proportion of COD remained in the reactors increased significantly. Our results demonstrated that effluent from the integrated system can meet the water quality requirements recommended by Japan Sewage Works Association (JSWA) for wastewater from FWD. In addition, to enhance the process stability, the influent TS concentration should be maintained below 15.5 g/L.

Given the aggravated greenhouse effect caused by CO2 and the current energy shortage, CO2 capture and reuse has been gaining ever-increasing concerns. Microbial Electrolysis Cells (MECs) has been considered to be a promising alternative to recycle CO2 bioelectrochemically to low-carbon electrofuels such as CH4 by combining electroactive microorganisms with electrochemical stimulation, enabling both CO2 fixation and energy recovery. In spite of the numerous efforts dedicated in this field in recent years, there are still many problems that hinder CO2 bioelectroconversion technique from the scaling-up and potential industrialization. This review comprehensively summarized the working principles, extracellular electron transfers behaviors, and the critical factors limiting the wide-spread utilization of CO2 electromethanogenesis. Various characterization and electrochemical testing methods for helping to uncover the underlying mechanisms in CO2 electromethanogenesis have been introduced. In addition, future research needs for pushing forward the development of MECs technology in real-world CO2 fixation and recycling were elaborated.

It is becoming increasingly urgent to investigate the partition coefficients (expressed as log KDOC values) of polybrominated diphenyl ethers (PBDEs) in dissolved organic carbon (DOC) present in wastewater. In the current study, after 72 h of equilibration, the concentrations of four common PBDEs were measured in the presence of four DOC solutions from two laboratories and two full-scale anaerobic digestion plants. Sixteen log KDOCs were determined by calculation and unit conversion. The results for the laboratory samples, such as log KDOCs for 2,2′,4,4′,5,5′-hexabromodiphenyl ether being 6.38 and 5.46 at different reaction temperatures during the cultivate procedure, suggest that a thermophilic environment promotes the solubility of PBDEs to a greater extent than mesophilic conditions. DOC composition directly influences the solubility of PBDEs, even at the same cultivating temperature: the highest log KDOCs for 2,2′,4,4′,5,6′-hexabromodiphenyl ether were 6.71 and 6.33 in different full-scale plant digestates. A linear regression with an R2 of 0.9863 was used to construct a model describing the potential relationship between log KDOC and the composition of DOC, which includes proteins, polysaccharides and lipids, and which takes into account the positions of bromine atoms, for use in predicting the log KDOC values of PBDEs in different water systems.

Constructed wetlands (CWs) are characterized by low construction cost, convenient maintenance and management, and environmentally friendly features. They have emerged as promising technologies for decentralized sewage treatment across rural areas. Source separation of black water and gray water can facilitate sewage recycling and reuse of reclaimed water, reduce the size of treatment facilities, and lower infrastructure investment and operating cost. This is consistent with the concept of sustainable development. However, black water contains high concentrations of ammonia nitrogen, and the denitrification capacity of CWs is not excellent due to insufficient carbon source. Therefore, application of CWs for black water treatment faces challenges. This article provides a review on the progress in CWs for treatment of the sewage with high-influent nitrogen load, with emphasis on the commonly used strengthening means and the role of plants in nitrogen removal via CWs. The current issues of rural sewage treatment with high-influent nitrogen load by CWs are also assessed. Finally, the challenges and perspectives are discussed for the optimization of CWs-enhanced denitrification strategies.

Poor processing stability has been cited as the fatal shortcoming of the up-flow anaerobic sludge blanket (UASB) reactor treating starch wastewater (SW). In this study, the SW treatment performance in a one-stage UASB reactor and a pre-acidification equipped UASB process were evaluated together with the microbial dynamics. The results revealed that the pre-acidification provided improvements in terms of the substrate utilization diversity and the stability of the microbial community structure on the UASB reactor. Anaerolineaceae/Methanosaeta was the core functional microbiota in the pre-acidification equipped UASB reactor, indicated the superior abilities on the acetogenic methanogenesis of granules. The genus of Methanobacterium, a hydrogenotrophic methanogen was dominant in the archaeal community in the one-stage UASB reactor. The granules performed very strong hydrogen affinity in methane production, a small amount of propionate was detected in the effluent. These were abnormal, which suggested the high hydrogen turn-over rate in the one-stage UASB reactor.

This study employed high-throughput quantitative polymerase chain reaction to evaluate the effects of specific co-substrate and additive on the fitness of antibiotic resistome during swine manure composting. The results showed that corncob particle as a co-substrate significantly reduced the relative abundances of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) simultaneously. The diversity of ARGs was also reduced more effectively by corncob addition. Brick granule as an additive reduced the concentrations of bioavailable Cu and Zn. However, the relative abundances of ARGs and MGEs were not reduced by the addition of brick granule subsequently. Redundancy analysis indicated a negative effect of the C content and positive effects of class I integrase gene (intI) and bioavailable metals on the variation of the relative abundance of ARGs (p 0.01). The Procrustes test showed a higher goodness-of-fit between the relative abundance of ARGs and 16S rRNA genes (r = 0.8166; p 0.0001). Our results suggests that the effect of corncob particle on the relative abundance of ARGs was achieved by driving the changes in physicochemical properties and microbial communities. This study confirmed the hypothesis of fitness cost and demonstrated the contribution of extra C source to ARG attenuation during composting.

Bacterioplanktonic communities, consisting of a few abundant taxa (AT) and many rare taxa (RT), are essential component of riverine ecosystems. Nonetheless, the biogeographic patterns of bacterioplankton and roles of AT and RT in community structuring and functional composition remain uncertain in large rivers. Here, we employ the Yangtze River, which is the third-longest river in the world, as model system. By using high-throughput sequencing and bioinformatics tool of Tax4Fun, the geographical patterns of bacterioplanktonic taxonomic and predicted functional communities are investigated, and the relative importance of abundant and rare subcommunities in community structuring are explored. Results showed a clear spatial variation that the bacterioplanktonic communities of upper, middle and lower reaches of the river are significantly different from each other. Besides, the Three Gorges Dam exhibited impact on the bacterioplankton of upper reach whose community is relatively closer to that of the Poyang Lake. Both the abundant and rare subcommunities showed spatial variation along the river, which is similar to the total bacterioplanktonic community. The rare subcommunity comprised a majority of community diversity with 23.6% of the total sequences and 94.2% of the total OTUs. The rare subcommunity contributes a major part (56.8%) versus abundant subcommunity (16.3%) of the spatial variation of the total community. In addition, the non-RT exhibits more interactions with RT than with themselves, and all of the 33 keystone species are belonged to RT. Hence, the RT is critical for community structuring and assembling. By contrast, no obvious spatial effect was observed for the predicted functional community. The predicted functions of abundant and rare subcommunities are consistent with that of total community, despite their contrasting community composition. In summary, the rare subcommunity show significantly impact on the community structure and assembling, and play an important role in predicted function as ‘seed bank’ in the Yangtze River.

CO2 bioelectromethanosynthesis represents a promising strategy for the capture and utilization of CO2. In such process, the continuous generation of electron (e-) and proton (H+) in anodic oxidation are of prime importance for the efficient cathodic CO2 electroreduction and process stability. Proton transfer, however, is very easy to be hindered due to the fouling of proton exchange membrane (PEM). In this study, an artificial channel in microbial electrolysis cell (MEC) was proposed to strengthen the transport of protons from anodic to cathodic compartment, and H+-rich anolyte was semi-continuously circulated to the cathodic chamber to provide protons for CO2 electroreduction. The results indicated that the daily CH4 yield in cathode with anolyte circulation (18.5 mL/d·L-reactor) was 5.4-fold higher than that without circulation (2.9 mL/d·L-reactor). Meanwhile, efficient anodic biodegradation of organic components was observed with COD, proteins and polysaccharides removal of up to 95.6 ± 1.9%, 96.3 ± 3.7% and 99.1 ± 0.2% respectively, which supplied a continuous e-/H+ donor for CO2 electroconversion. 16S rRNA gene pyrosequencing analysis identified a large number of proteins-utilizing Bacteroidetes (14.11%) and polysaccharides-consuming Thermotogae (18.49%) in anodic biofilm, conductive to the biodegradation of organic components. Moreover, a high abundance of Methanobacterium (81.07%) was detected to prevail in cathodic biofilm, demonstrating the occurrence of highly enhanced CH4 bioelectrosysthesis. The syntrophic and symbiotic relationship was established in the dual-bioelectrode system, creating a beneficial environment and an energy-efficient approach for biowaste refinery and CO2 electromethanosynthesis.

This study assessed the impact of swine manure (SM) dilution ratio on the microalgal biomass cultivation and further tested for biohydrogen production efficiency from the mixed microalgal biomass. At first, various solid/liquid (S/L) ratio of the SM ranged from 2.5 to 10 g/L was prepared as a nutrient medium for the algal biomass cultivation without addition of the external nutrient sources over a period of 18 d. The peak biomass concentration of 2.57 ± 0.03 g/L was obtained under the initial S/L loading rates of 5 g/L. Further, the cultivated biomass was subjected to two-step (ultrasonication + enzymatic) pretreatment and evaluated for biohydrogen production potential. Results showed that the variable amount of hydrogen production was observed with different S/L ratio of the SM. The peak hydrogen yield of 116 ± 6 mL/g TSadded was observed at the 5 g/L grown SM mixed algal biomass.

This study assessed the co-digestion of macro and microalgal biomass towards the improvement of hydrogen production. The red macroalgal biomass (Gelidium amansii) and green mixed microalgal biomass was mixed in a ratio of 8:2, with an initial substrate concentration of 10 g/L, and various amount of inoculum addition range from 3 to 15% (v/v) was evaluated to assess the feasible substrate to inoculum ratio for the effective co-digestion of the algal biomass. The results showed that the co-digestion with 6% inoculum addition provided the peak hydrogen yield of 45 mL/g dry biomass added with a high hydrogen content of 24% in the gas phase. The other tested conditions showed moderate hydrogen content in the range of 17–22%, respectively. These results suggest that anaerobic co-digestion of macro and microalgal biomass, with appropriate initial biomass loading (6%) is essential for enhanced hydrogen production.

This study investigated early stages of biofilm formation from sieved fine particles of anaerobic granules in the presence of various cationic substances using a quartz crystal sensor to improve biofilm formation in the anaerobic treatment of saline wastewater. The biomass attached on the sensor was greatly increased with Ca within the low range (8–16 mM), which was not affected by 50 mM of Na. However, the positive effect of 16 mM of Ca was strongly reduced in the co-presence of Ca and Na when Na concentrations were in the range from 25 to 150 mM because Ca may compete with Na for the limited binding sites in biofilm. The addition of cationic polymer at 150 mM of Na increased biomass adhesion by several folds at only 10–80 mg/L compared to the addition of 16 mM of Ca. Moreover, no methanogenic inhibition was presented below the polymer content of 20 mg/L.

Dewatering of waste activated sludge (WAS) is of major interest in its volume reduction, transportation and ultimate disposal. Persulfate-based oxidation process is a newly developed option for enhancing WAS dewaterability through the generation of powerful sulfate radicals (SO4−·). However, the enhancement in WAS dewaterability by persulfate differs with the species of iron catalysts used. In this study, two types of iron catalysts (i.e. Fe2+ vs. Fe0) were employed to initiate the persulfate (S2O82−), and the catalyzing behaviors and the underlying principles in enhancing WAS dewaterability were investigated and compared. The Fe2+ exhibited the high effectiveness in catalyzing the decomposition of persulfate to sulfate radicals (SO4−·), inducing the greater improvement in WAS dewatering. The WAS dewaterability (indicated by dry solids content after filtration) increased with the added S2O82−/Fe2+ dosages, with the dry solids content reaching up to 5.1 ± 0.8 wt% at S2O82−/Fe2+ dosages of 1.2/1.5 mmol/g-VS after only 30 s’ filtration, roughly 1.8-fold increase than raw WAS (1.8 ± 0.1 wt%). In contrast, the influence of the persulfate oxidation when activated with Fe0 on WAS dewaterability was statistically insignificant. The WAS dewaterability remained nearly unchanged (i.e. dry solids content of 2.0 ± 0.0 wt%), irrespective of the employed S2O82−/Fe0 dosages. Further analysis demonstrated that the WAS dewaterability negatively corresponded to loosely bound extracellular polymeric substances (LB-EPS) and tightly bound EPS (TB-EPS). The abundant SO4−· from S2O82−/Fe2+ system could effectively disrupt the gel-like EPS matrix, break apart the cells and subsequently arouse the release of the water inside EPS and cells, facilitating water-solid separation. In the case of S2O82−/Fe0, the dissolution of Fe0 particles was the rate-limiting step, due to the formation of oxide iron layer near Fe0 metallic surface, which resulted in the slow SO4−· production and thus hardly promoted WAS dewaterability. The pH adjustment could accelerate Fe0 dissolution and enhance the dewatering performance of S2O82−/Fe0 process to a certain degree, but the effect was unsatisfactory. Additionally, the observations regarding the dissolved organic matters and ammonium collectively revealed that except for enhancing WAS dewatering, S2O82−/Fe2+ oxidation could concurrently degrade COD and ammonia from WAS filtrate, lighten the burden of the subsequent sewage treatment facilities and reduce operational expense. Hence, from an environmental and economic perspective, the S2O82−/Fe2+ system possesses much greater promise for WAS dewatering.

In order to boost the economics of biogas utilization in those small facilities for food waste (FW) digestion, proximate grease trap waste (GTW) was employed to co-digest with FW. A bench-scale continuous stirred tank reactor was set up and operated at mesophilic temperature to investigate the co-digestion limit and lipid/long chain fatty acid (LCFA) conversion by increasing lipid loading stepwise. Mixing FW and GTW at lipid/total solids (TS) 55%, where the lipid loading was 1.61 g/(L·d), was proved to be appropriate, and the maximum methane yield reached 68% higher than the mono-digestion of FW, with a similar lipid reduction at approximately 90%. In addition, since acetic acid accumulation above 100 mg HAc/L had been observed under the optimal loading, the threshold value for anaerobic co-digestion of FW and GTW was confined to the lipid loading around 1.61 g/(L·d). The rapid recovery strategy of mixing the inhibited sludge with fresh inoculum at 1:4 (V/V) took effect after process failure resulted from further increasing lipid/TS to 70%. Lipid/LCFA concentrations in the effluent rose with the increased lipid loading, while palmitic acid accounted for the most percentage among the residual LCFAs, as high as 73.7% at lipid/TS 55%. Acetoclastic methanogens played an important role in accelerating process conversion, due to the fact that raising GTW addition led to the increased methanogenic activity, with a value of 26.9 mL-CH4/(g-VS·d) at the optimal loading.

The effects of organic loading rate (OLR) and operating temperature on the performance of siphon-driven self-agitated anaerobic reactor (SDSAR) in an on-site food waste (FW) treatment system were investigated. Two reactors were operated in parallel for comparison between mesophilic condition (35 ± 1 °C) and thermophilic condition (55 ± 1 °C). With HRT above 15 d and OLR below 4.8 kg-COD/m3/d, relatively high COD removal in the range of 84.5–92.3% was obtained in both reactors. The limits of the loading capacity of the mesophilic SDSAR were observed when OLR was further increased to 7.3 kg-COD/m3/d by shortening HRT. Blocking and gas production reduction occurred and COD removal decreased sharply to 75.9% in the mesophilic reactor. In contrast, the thermophilic reactor can be operated at this OLR with satisfactory COD removal and biogas production. Furthermore, at OLR of 14.4 kg-COD/m3/d, the COD removal was maintained as high as 87.5% in the thermophilic reactor. The conversion of influent COD to methane was maintained above 80% at all the OLR applied in both reactors. The results of this study indicated that thermophilic SDSAR is preferred for the on-site FW treatment.

In this pilot-scale study, an innovative mainstream treatment process that couples the anaerobic membrane reactor (AnMBR) with a one-stage PN/A system was proposed for advancing the concept of carbon neutrality in the municipal wastewater treatment plant. This work demonstrates the start-up procedure of a pilot-scale one-stage PN/A system for mainstream treatment. The 255-day start-up of the one-stage PN/A system involved the cultivation of ammonium-oxidizing bacteria (AOB) from the activated sludge, suppression of nitrite-oxidizing bacteria (NOB), investigation of in-situ growth kinetics of anammox bacteria (AnAOB), and the 50-day operation of the pilot-scale AnMBR-PN/A process for natural mainstream treatment. It is verified in the pilot-scale system for the first time that the in-situ free ammonia (FA) and free nitrous acid (FNA) exposure could effectively eliminate the Nitrospira (the NOB genus) while retaining the Nitosonomas (the AOB genus) community in the suspended sludge. NOB community rebounding was not detected even at the mainstream conditions with low nitrogen concentrations (Influent ammonium concentration=38±6 mg-NH4+-N/L) by intermittent aeration to control the system dissolved oxygen (DO) below 0.5 mg/L. The results of the mainstream treatment showed that the average effluent total nitrogen (TN) in the coupled process was generally lower than 10 mg-N/L, which meets the discharge limits of most prefectures in Japan. The investigated results of the in-situ anammox bacteria (AnAOB) growth kinetics suggested that the promoted start-up strategy of taking advantage of the warm months with higher mainstream temperature to achieve the rapid in-situ growth of the AnAOB is applicable in the investigated regions. From the perspective of the removal performance of the TN and organic substance, the AnMBR-PN/A process has great potential as the layouts of the carbon-neutral mainstream wastewater treatment plants.

Carbon nitride (C3N4) is a promising photocatalytic material to degrade various pollutants. However, the degradation activity is restricted by the limited light absorption and fast recombination of photoinduced carriers. Herein, a structure modification strategy by introducing a functional reagent during the polymerization process was adopted. The structure, composition and morphology of prepared materials were investigated by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. Benefiting from the implantation of oxygen and methyl groups in triazine unit of C3N4, enhanced light absorption and effective carrier separation are achieved. As a result, the modified C3N4 exhibits a significant enhanced degradation activity and the optimal rate constant of modified C3N4 for Acid Red 9 degradation is 5.83 times that of pristine C3N4. The work demonstrates the effect of structure modification in C3N4 for enhancing degradation activity.

The nitrogen (N) cascade in rural areas of Changshu County should be measured and evaluated due to the large increase in anthropogenic disturbances in China's Yangtze Delta. Here, we developed a village-scale N flow model using Changshu County and its towns as a case study. The model included four subsystems and was used to describe the driving forces behind the N cascade from agricultural food production and household consumption to the environment (agriculture-food-environment) system. It was found that from 1998 to 2018 the N input increased from 274.63 to 848.65 kg N ha-1. The cropland N use efficiency (NUEc) decreased by 10.35%, whereas the livestock feed N use efficiency (NUEa) increased by 51.84%. A relatively lower NUE, with a higher N input, was found in Shajiabang Town, which was attributed to hairy crab farming. Changes in dietary patterns led to the food N cost (FNC) being in the range of 4.59-7.74 kg kg-1. Over the past two decades, the N losses from the agriculture-food-environment system decreased by 45.40% from 12,436.60 t N yr-1 (1998). The contribution of the croplands, livestock-breeding, and household consumption to the N losses were 32.44%, 37.78%, and 29.78%, respectively. About 62.83% of the total N losses entered the water environment. Nitrogen emissions from the croplands accounted for 63.21% of the N losses into the atmosphere. Nitrogen oxide (NOx) emissions accounted for 38.50% of the gas emissions, followed by NH3 (28.36%) and N2O (2.81%). The total N losses decreased annually but losses to the water environment increased by 5.10% from 60.16% (1998). The contribution of food production to the total N loss displayed a decreasing trend, while that of food consumption exhibited an increasing trend. Population growth and increased volumes of domestic waste in the Changsu area were the main driving forces for the increased contribution of household food consumption. The significant decline in cropland area and increase in built-up and heavily trafficked areas indicated an overall increase in anthropogenic disturbances, stimulating the N cascade in the Yangtze Delta from 1998 to 2018.

Anaerobic digestion of decabromodiphenyl ether was carried out and compared in two continuously stirred anaerobic bioreactors for 210 days under thermophilic and mesophilic conditions. Results show that the degradation of decabromodiphenyl ether followed the first-order reaction kinetics, which exhibited a higher removal rate in the thermophilic reactor when compared to the mesophilic one, reaching its maximum of 1.1 μg·day−1. The anaerobic digestion of decabromodiphenyl ether was found to involve the replacement of bromines from polybrominated diphenyl ether by hydrogen atoms, gradually forming nona-, octa- and hepta-brominated diphenyl ether, respectively. Under the thermophilic condition, the reactors were dominated by Bacillus sp. and Methanosarcina sp. with high bioactivity and high concentrations of debromination microorganisms.

The application of biofilm-based processes such as up-flow anaerobic sludge blanket (UASB) reactors for saline wastewater treatment faces the problems of low strength and stability of granules cause by high salt concentration. In this study, the effect of biochar/Fe addition on biofilm formation was examined in anaerobic treatment of high salinity (10 g-Na+/L) wastewater with two parallel lab-scale UASBs. Higher removal efficiencies of soluble influent organics and methane production were achieved in the biochar/Fe seeded UASB reactor with an organic loading rate (OLR) ranging from 2.5 to 10 g-COD/L/d. The average SS concentration of the granular sludge in the biochar/Fe seeded UASB reactor reached 21.6 g/L while that in the non-biochar/Fe-seeded UASB one was 16.4 g/L. A higher extracellular polymeric substances (EPS) of 91.1 mg/g-VSS and medium particle size (D50) of 63.2 µm in the granular sludge with biochar/Fe addition were observed. All these results suggest that biochar/Fe addition can effectively improve biofilm formation under high salinity conditions.

This study investigated the effect of combination of pretreatment methods such as ultra-sonication and electrolysis for the minimum energy input to recover the maximal carbohydrate and solubilization (in terms of sCOD) from mixed microalgae biomass. The composition of the soluble chemical oxygen demand (COD), protein, carbohydrate revealed that the hydrolysis method had showed positive impact on the increasing quantity and thus enhanced methane yields. As a result, the combination of these 2 pretreatments showed the greatest yield of soluble protein and carbohydrate as 279 and 309mg/L, which is the recovery of nearly 85 and 90% in terms of total content of them. BMP tests showed peak methane production yield of 257mL/gVSadded, for the hydrolysate of combined pretreatment as compared to the control experiment of 138mL/gVS added.

Microbial electrolysis cell (MEC) holds the flexible potentials for waste biorefinery, pollutants removal, CO2 capture, and bioelectrosynthesis of clean and renewable electrofuels or valuable chemical commodities, dealing with the depletion of fossil fuels and environmental deterioration issues. Although substantial advances in process design and mechanisms exploration have greatly promoted the development of MEC platform from a concept to a technology, how to virtually utilize it in real-world scenario remains a big challenge. There are numerous technical issues ahead for MEC to be tackled towards up-scaling and real implementations. This review article presents a state-of-the-art overview of the fundamental aspects and the latest breakthrough results and accomplishments obtained from the MEC platform, with a special emphasis on mapping the key extracellular electron transfer (EET) mechanisms between electroactive microorganisms and electrode surface (including i: cells → e − anode ; and ii: cathode → e − cells ). A unified discussion of different process design: inoculation methods for rapid start-up, role of membranes, modification of cathode materials, cathodic catalysts (i.e. noble, un-noble metal catalysts and biocatalysts) as well as designs and configurations of versatile bioelectrochemical cells, is also involved. Finally, the major challenges and technical problems encountered throughout MEC researches are analyzed, and recommendations and future needs for the virtual utilization of MEC technology in real waste treatment are elaborated.

This research investigated the effects of various dilute acid (HCl, H 2 SO 4 , HNO 3 , H 3 PO 4 ) pretreatment on the solubilization of marine macroalgal biomass Gelidium amansii and subsequent hydrogen fermentation in a batch vials. The dry grounded biomass was hydrolyzed at temperature of 121 °C, solid/liquid (S/L) ratio of 5% (w/v), dilute acid concentration (1%) of various reagents, and reaction time of 30 min. The hydrolyzates obtained at these conditions were then fed to batch hydrogen fermentation. Results revealed that only H 2 SO 4 pretreatment method had a significant effect on improvement of biohydrogen production from Gelidium amansii , whereas the other pretreatment conditions were even worse than the control experiment. Dilute sulfuric acid (1%) provided a maximum hydrogen production of 52 mL-H 2 /g-dry biomass, whereas control experiment provided a hydrogen efficiency of 27 mL-H 2 /g-dry biomass. The results showed that selection of appropriate pretreatment method is essential for enhanced hydrogen production from macroalgal biomass.

This study investigated the potential and possibility of three mixed microalgae consortia collected from various ecological niches towards bioenergy production of H 2 and CH 4 in batch experiments under mesophilic conditions. Three different consortia collected from wastewater treatment plant, in an open pond system and in the lake bed possess different compositions and characteristics during their growth under a light intensity of 8000 lux and are referred as OP1, OP2 and LB. After 40 days of cultivation, collected wet biomass is directly used for H 2 and CH 4 fermentation and the results indicated that, consortia OP1 is good for H 2 production whereas consortia OP2 and LB showed nearly the similar CH 4 production performances. Peak hydrogen production rate (HPR) and methane production rate (MPR) were achieved as 289 mL/L-d and 97 mL/L-d, respectively from consortia OP1 and OP2. The energy production from this process could significantly contribute towards CO 2 emission reduction. Besides, this approach could be helpful in choosing the consortia towards which kind of biofuel (either H 2 or CH 4 ) production.

Biohydrogen production from lignocellulosic biomass (LCB) is an active research area. Several workers have tested a number of substrates under different operational conditions and brought forward the many positive process performance features and identified the main sources of inhibition. This review analyzes selected fermentative biohydrogen production processes by revisiting the core biohydrogen production performances in terms of gas production rates and yields and equally addresses the options for process enhancement by the application of through pretreatment methods and detoxification of process inhibitors. In addition, the issues related to continuous biohydrogen operation in different reactor configurations are highlighted. Lastly, future avenues of research which may be engendered and engineered to enhance the biohydrogen generation and process biokinetics are discussed. This review intends to provide the fundamental understanding of biohydrogen production and provides a perspective on future developments in this area of applied research.

Water eutrophication creates unfavorable environmental conditions for submerged macrophytes. In these situations, biotic interactions may be particularly important for explaining and predicting the submerged macrophytes occurrence. Here, we evaluate the roles of biotic interactions in predicting spatial occurrence of submerged macrophytes in 1959 and 2009 for Dianshan Lake in eastern China, which became eutrophic since the 1980s. For the four common species occurred in 1959 and 2009, null species distribution models based on abiotic variables and full models based on both abiotic and biotic variables were developed using generalized linear model (GLM) and boosted regression trees (BRT) to determine whether the biotic variables improved the model performance. Hierarchical Bayesian‐based joint species distribution models capable of detecting paired biotic interactions were established for each species in both periods to evaluate the changes in the biotic interactions. In most of the GLM and BRT models, the full models showed better performance than the null models in predicting the species presence/absence, and the relative importance of the biotic variables in the full models increased from less than 50% in 1959 to more than 50% in 2009 for each species. Moreover, co‐occurrence correlation of each paired species interaction was higher in 2009 than that in 1959. The findings suggest biotic interactions that tend to be positive play more important roles in the spatial distribution of multispecies assemblages of macrophytes and should be included in prediction models to improve prediction accuracy when forecasting macrophytes’ distribution under eutrophication stress.

The dispersion of granules in upflow anaerobic sludge blanket (UASB) reactor represents a critical technical issue in methanolic wastewater treatment. In this study, the potentials of coupling a microbial electrolysis cell (MEC) into an UASB reactor for improving methanolic wastewater biodegradation, long-term process stability and biomethane recovery were evaluated. The results indicated that coupling a MEC system was capable of improving the overall performance of UASB reactor for methanolic wastewater treatment. The combined system maintained the comparatively higher methane yield and COD removal efficiency over the single UASB process through the entire process, with the methane production at the steady-state conditions approaching 1504.7 ± 92.2 mL-CH4 L−1-reactor d−1, around 10.1% higher than the control UASB (i.e. 1366.4 ± 71.0 mL-CH4 L−1-reactor d−1). The further characterizations verified that the input of external power source could stimulate the metabolic activity of microbes and reinforced the EPS secretion. The produced EPS interacted with Fe2+/3+ liberated during anodic corrosion of iron electrode to create a gel-like three-dimensional [-Fe-EPS-]n matrix, which promoted cell-cell cohesion and maintained the structural integrity of granules. Further observations via SEM and FISH analysis demonstrated that the use of bioelectrochemical stimulation promoted the growth and proliferation of microorganisms, which diversified the degradation routes of methanol, convert the wasted CO2 into methane and accordingly increased the process stability and methane productivity.

Restaurant grease trap waste (GTW) is a potentially feasible energy source that can be used as an alternative to liquid fossil fuels and natural gas. However, GTW must be collected from many different resources for energy production because restaurants in Japan only produce an average of 486 kg GTW per year. This study investigated the variation in oil properties and methane generation potential of 44 GTW samples from 13 types of restaurants during different seasons. The GTW samples had high variation in oil content and oil properties. Biofuel oil was extracted from most GTW samples at a high efficiency (more than 80 wt%). In contrast, the methane yield varied little among de-oiled GTW samples. All types of GTWs are potential sources of biomethane generation. GTW samples are classified into five major oil property clusters according to solid chemical stability. Oil properties depend little on the season and heavily on the restaurant type.

In this chapter, the perspective needed for examining graded impact statements is described. Such an evaluation is comprised of the examinations of various culture conditions for standardizing the microcosm N-system, the two-species cultures, the microcosm, and the mesocosm.

Accurately measuring and estimating trends and variations in nutrient levels is a significant part of managing emerging eutrophic lakes in developing countries. This study developed an integrated approach containing Seasonal Trend Decomposition using Loess (STL) and a dynamic nonlinear autoregressive model with exogenous input (NARX) network to decompose and estimate the nutrient concentrations in Lake Erhai, a preliminary eutrophic lake in China. The STL decomposition results indicated that total nitrogen (TN) concentration of Lake Erhai progressively descended from 2006 to 2014, except for some agriculture area. The total phosphorus (TP) concentration showed an increasing trend from 2006 to 2013 and then decreased in 2014, but in the area near the tourist attractions, TP increased continuously from 2011 to 2014. Seasonal variations in TN and TP indicated that the lowest water quality of Lake Erhai occurred from July to October. Based on results obtained with STL, TP was selected as the sensitive parameter, as it showed a significant deterioration trend, and the area near the tourist attractions was selected as the sensitive area. Three variables (DO, pH, and water temperature) were selected as input parameters to estimate TP using the dynamic NARX model. The NARX modeling results demonstrated that it can accurately estimate TP concentrations with low root-mean-square error (0.0071 mg/L). The study establishes a new approach to better understand trends and variations in nutrient levels and to better refine estimates by identifying more easily accessible physical parameters in a preliminary eutrophic lake.

This study employed high-throughput quantitative PCR and 16S rRNA sequencing to evaluate the effect of temperature and residual antibiotics on the dynamics of antibiotic resistance genes (ARGs) and microbial communities during anaerobic digestion of swine manure. The abundances of total ARGs and 16S rRNA genes significantly decreased in all of four treatments (25°C, 37°C, and 37°C with 50 mg of wet weight antibiotics of body weight, and 55°C). The abundances of most ARG types were significantly correlated with those of the 16S rRNA gene and transposase gene (P < 0.01). However, the abundances of total ARGs at 55°C were much higher than those of other treatments. Meanwhile, the microbial communities at 55°C, where the Streptococcus pathogen remained at a relatively high abundance and cellulose degraders and hydrogen producers, such as Ethanoligenens and Coprococcus bacteria, increased, were markedly different from those of other treatments. Redundancy analysis indicates that temperature, pH, and the genus Streptococcus had the highest explanation for ARG variation among experimental factors, chemical properties, and representative genera, respectively. Network analysis further showed that the genus Streptococcus contributed greatly to the higher ARG abundance at 55°C. The moderate antibiotic residue only caused a slight and transitory inhibition for microbially diverse populations and promotion for ARG abundance, probably due to the degradation of antibiotics and microbial adaptability. Our results clarify the cooperativity of gene transfer-related items on ARG variation and intensively prove that higher temperature cannot always achieve better ARG removal in anaerobic digestion unless pathogens and gene transfer elements are more efficiently inhibited. IMPORTANCE Antibiotic resistance genes (ARGs) are frequently detected with high abundance in manure-applied soils. Anaerobic digestion is one of widely used processes for animal waste treatment. Thus, it is critical to understand the potential of anaerobic digestion to attenuate ARGs. Although some previous studies recommended thermophilic digestion for ARG removal, they did not get sufficient evidence to support this view. The antibiotics applied to animals are mostly excreted through feces and urine because of incomplete metabolism. It is indispensable to know whether residual antibiotics in manure will hinder ARG attenuation in anaerobic digesters. The significance of our research is in comprehensively understanding the evolution and mechanism of ARGs in anaerobic digestion of swine manure affected by temperature and residual antibiotics, which will allow the development of an ARG elimination strategy before their release into the environment.

The molecular structure of soil organic matter (SOM) is closely related to the structure and functions of the rhizosphere community. In this study, a microcosm experiment was conducted to investigate the effect of straw-derived biochar on the structural differentiation of SOM and rhizosphere bacterial communities. 13C NMR spectra showed that the relative abundance of carboxyl, alkyl, N-alkyl, O-alkyl and methoxyl groups decreased by 22%, 31%, 27%, 27% and 27%, respectively, and the relatively stable structure of aryl and O-aryl groups increased by 213% and 41%, respectively. In addition, network-based analysis showed that biochar amendment not only improved the network connectivity of the rhizosphere bacteria, but also enhanced the linkage between bacteria and the molecular structure of SOM. The topological properties of the network, including the number of edges, network density, and average clustering coefficient, were increased by 79%, 15% and 22%, respectively. Moreover, modularization analysis and structural equation model indicated that rhizosphere bacterial network was the important bio-factor affecting the content of labile carbon.

Co-composting of solid manure (SM) and liquid manure (LM) is a new practice in livestock wastes recycling process and management. However, this practice is laced with various challenges including undesired leachate production, greenhouse gas emissions and characteristics poor nutrient quality of the final compost. Pragmatic utilization of the resource potential availed by combined LM and SM co-composting will be a game changer strategy for direct recycling of livestock wastes and reducing environmental contamination. By adapting a recently proposed LM addition model, we systematically investigated the promoting factors (thermophilic duration, organic matter (OM) degradation, and so on) necessary for successful co-composting of SM and LM, and for the first time examined the nutrient enrichment model essential to achieving final compost recyclability. Compared to the conventional SM co-compost, the proposed SM and LM controlled co-composting process elongated the thermophilic duration, reduced leachate generation, enhanced OM degradation, and simultaneously induced potential nutrients enrichment as evidenced by the nutrient balance analysis. The concentrations of TN, TP, TK, Cu and Zn in the controlled final compost were relatively enriched by 21.7 ± 2.16%, 12.1 ± 0.14%, 12.6 ± 0.16%, 11.0 ± 0.16% and 11.3 ± 1.24%, respectively. In addition, the controlled co-composting technique allowed for reduction in nutrients loss due to volatile N, estimated at 28.8% decrease in N loss rate relative to the conventional SM co-compost, and approximately 1.8 t/day of livestock wastewater can be effectively managed. The study conclusively demonstrated that concomitant utilization of liquid and solid manure presents an environmental friendly and unique advantage for simultaneous management and recycling of livestock wastes.

Strong wastewater from the animal breeding industry threatens the environmental and human health, while the widely used anaerobic digestion treatment is insufficient. To achieve the reclamation and reuse of the effluent containing an excessively high amount of nutrients (N, P and K) and a certain extent of biochemical oxygen demand (BOD), an original CO2-enhanced natural treatment system was put forward, which was composed of trickling filter and soil-plant units installed inside an elaborate greenhouse with an elevated CO2 concentration. On the basis of previous feasibility studies, an investigation on the system’s limitations and potential were carried out for further optimisation, in which red ball earth-Kentucky bluegrass column tests were conducted at the recommended CO2 concentration of 1,400 ppm for two specific scenarios, i.e. high BOD concentration and increasing hydraulic and nutrient loading rates. N is the most critical factor determining the effect and efficiency of the system, and results confirmed that, to establish a satisfactory nitrification function in the soil for N removal, adequate BOD reduction prior to land application was indispensable. Optimal operational strategies and parameters, as well as design information for scale-up, are also discussed. By means of nutrient balance approximation, the system’s significant capabilities of removing and recovering waterborne nutrients are further presented, specifically complete removal of both N and P, and 8%, 18% and 18% recovery rates for N, P and K, respectively. Meanwhile, carbon balance analysis reveals its potential for substantially reducing greenhouse gas emission, as 9% of the input waterborne C is sequestrated for establishing plant biomass and maintaining greenhouse CO2 concentration at the designated level. More importantly, the above are realised in a highly profitable manner, as the value of the high-quality turf product can be an order of magnitude higher than the cost for system operation and maintenance. This original system provides an innovative way for rural communities worldwide to achieve sustainable development via wastewater reclamation and reuse.

Behavior of veterinary antibiotics, the corresponding resistant genes in soil layer of constructed wetlands (red soil), and their response to different hydraulic loading rates (HLR) (2, 5, and 10 cm/d) were investigated. Results indicated that the soil layer had perfect performance for oxytetracycline and ciprofloxacin, yet sulfamethazine removal was unsatisfactory. Detection rates of oxytetracycline, ciprofloxacin and sulfamethazine in the effluent of simulation systems of soil layer were 8.33-36.36%, 8.33-47.83% and 100%, respectively. The model analysis of adsorption and hydrolysis indicated that physical adsorption, which was controlled by exchange reaction process based on diffusion, was the primary adsorption mechanism of target antibiotics in red soil, and the hydrolysis half-life values of antibiotics in the water of soil layer were shorter than them in wastewater. The removal response of oxytetracycline and ciprofloxacin to change of HLR was insignificant, yet the respective effluent concentrations of sulfamethazine at HLR of 2-10 cm/d were 41.90, 61.35 and 73.54 μg/L during treating synthetic livestock wastewater, which revealed significant positive correlation (P 0.05). The relative abundances of each target resistance genes in soil showed significant increase after treating wastewater (10

This study investigated the effects of pretreatment methods (such as autoclave, ultrasonication and electrolysis) of mixed microalgae consortia (predominantly composed of Scenedesmus followed by Chlorella species) from natural ecological niche. In addition, the cultivated biomass (wet) was subsequently utilized for fermentative H2 production in mesophilic regime. The results showed that peak hydrogen production rate (HPR) and hydrogen yield (HY) were achieved from electrolysis pretreated algal consortia as 236 ± 14 mL/L-d and 37.7 ± 0.4 mL/g (volatile solids) VSadded, whereas the untreated algal consortia resulted in the turnout as 64 ± 5 mL/L-d and 9.5 ± 0.0 mL/g VSadded, respectively. The significant increment observed in HPR and HY values were nearly 4 times higher. The solubilization of organic matter during the pretreatment showed positive correlation with the H2 production. The energy generation rate and yield of the corresponding pretreatment methods were as follows, 1.44, 1.79 and 2.65 kJ/L-d for autoclave, ultra-sonication and electrolysis, the corresponding yields also fell in the range of 0.32, 0.41 and 0.43 kJ/g VSadded, respectively.

Nowadays there is a huge demand for new and sustainable technologies aiming the reduction of the greenhouse gas, in particular carbon dioxide emission. In this work, enzymatically-boosted supported ionic liquid membrane (EB-SILM) was developed to permeate carbon dioxide with improved efficiency. Firstly, the selected biocatalyst, carbonic anhydrase (CA) was prepared and purified from spinach, a cheap plant biomass containing the enzyme of our interest. Afterwards, the CA enzyme preparation was used for SILM fabrication in order to test the properties towards enhanced carbon dioxide permeation over CH 4 , H 2 and N 2 . The results indicate basically that EB-SILMs possess an increased ability to permeate CO 2 in comparison with enzymeless controls and therefore, may be viewed as a promising approach e.g. towards enhanced CO 2 -capture bioprocesses.

The use of liquid fraction of pressed municipal solid waste (LPW) for hydrogen production was evaluated via electrohydrogenesis in a single-chamber microbial electrolysis cell (MEC). The highest hydrogen production (0.38 ± 0.09 m3 m−3 d−1 and 30.94 ± 7.03 mmol g−1 CODadded) was achieved at an applied voltage of 3.0 V and pH 5.5, increasing by 2.17-fold than those done at the same voltage without pH adjustment (pH 7.0). Electrohydrogenesis was accomplished by anodic oxidation of fermentative end-products (i.e. acetate, as well as propionate and butyrate after their acetification), with overall hydrogen recovery of 49.5 ± 11.3% of CODadded. These results affirm for the first time that electrohydrogenesis can be a noteworthy alternative for hydrogen recovery from LPW and simultaneous organics removal. Electrohydrogenesis efficiency of this system has potential to improve provided that electron recycling, electromethanogenesis and deposition of non-conductive aggregates on cathode surface, etc. are effectively controlled.

Continuous primary energy consumption has motivated the scientists of the world to search for renewable energy sources that could substitute fossil fuels. Microalgae can be an alternative substrate for renewable energy recovery. In this study, biochemical methane potential (BMP) assays were used as a tool to examine the technical potential of methane production from microalgae (MA) through co-digesting with food waste (FW) at different MA: FW ratios on volatile solids (VS). Three mathematical models (i.e. first-order kinetic, modified Gompertz, and Cone models) were also utilized to fit the experimental data, with the purpose of elucidating the biological degradation and principle kinetics of the co-digestion. The results showed that supplementing food waste significantly improved microalgae digestion performance, with the highest methane yield of 639.8 ± 1.3 mL/g VSadded obtained at a MA:FW ratio of 0.2:0.8, which was 4.99-fold increase with respect to that (106.9 ± 3.2 mL/g VSadded) of the microalgae alone. Cone model had the best fitness and reliability to the experimental results and could describe the co-digestion kinetics more reasonably. Parameter analysis and synergistic impact evaluation together revealed that the improvement in methanogenesis potential (fd) caused by the synergy of co-digestion might be the fundamental cause for the upgraded methane production. These results validated the superiority of co-digestion as a step towards maximizing methane production from microalgae, aiding the development of multi-biomass co-disposal and ultimately bioenergy recovery techniques.

This review portrays the status and perspectives of bioaugmented hydrogen fermentation, an emerging strategy of process intensification. Firstly, the paper introduces the potentials and limitations of dark fermentative hydrogen production and describes the technologies available for its enhancement including bioaugmentation. The theoretical background and practical features of augmentation methods for biohydrogen generation are subsequently assessed and surveyed in details. Furthermore, a throughout evaluation of the recent and novel achievements reported in the concept of “augmented hydrogen fermentation” is given in association with (i) bioreactor start-up, (ii) utilization of solid wastes, wastewaters, (iii) the feasibility in continuous systems as well as in complementary – integrated – applications. The article is intended to provide an insight to the advancements made for realizing more viable biohydrogen formation via bioaugmentation and hence it might be encouraging for further studies in the field.