Novel Ag3PO4/ZnWO4-modified graphite felt electrode for photoelectrocatalytic removal of harmful algae: Performance and mechanism.

A novel Ag3PO4/ZnWO4-modified graphite felt electrode (AZW@GF) was prepared by drop coating method and applied to photoelectrocatalytic removal of harmful algae. Results showed that approximately 99.21% of chlorophyll a and 91.57% of Microcystin-LR (MCLR) were degraded by the AZW@GF-Pt photoelectrocatalytic system under the optimal operating conditions with a rate constant of 0.02617 min-1 and 0.01416 min-1, respectively. The calculated synergistic coefficient of photoelectrocatalytic algal removal and MC-LR degradation by the AZW@GF-Pt system was both larger than 1.9. In addition, the experiments of quenching experiments and electron spin resonance (ESR) revealed that the photoelectrocatalytic reaction mainly generated •OH and •O2- for algal removal and MC-LR degradation. Furthermore, the potential pathway for photoelectrocatalytic degradation of MC-LR was proposed. Finally, the photoelectrocatalytic cycle algae removal experiments were carried out on AZW@GF electrode, which was found to maintain the algae removal efficiency at about 91% after three cycles of use, indicating that the photoelectrocatalysis of AZW@GF electrode is an effective emergency algae removal technology.

Biomass conversion and radiocaesium (Rad-Cs) leaching behaviors of radioactive grass in anaerobic wet fermentation systems: Effects of pre-treatments.

Persistent concerns regarding environmental hazards arise from the difficulty in disposing of radioactive plant-based wastes originating from the nuclear accident at the Fukushima Daiichi Nuclear Power Plant (FNPP) in Japan in 2011. In this study, three anaerobic digestion (AD) strategies were proposed: Sole anaerobic wet fermentation, and wet fermentations with either alkaline-heat or ultrasonic pre-treatment, which were employed for long-term anaerobic treatment of a genuine radioactive grass stemming from the FNPP accident. The objectives of this work are to investigate the effects of pre-treatments on biomass conversion efficiency and to gain insight into the leaching behavior of radiocaesium (Rad-Cs) within AD processes. Experimental results indicate that by introducing alkaline-heat and ultrasonic pre-treatments to AD systems, the removal efficiencies of total solids (TS) from the raw grass increased by 60.8 % and 42.5 %, respectively, compared to sole wet fermentation. Pre-treatments have been shown to enhance the stability of AD systems, both in terms of enhancing methane production and mitigating pH fluctuations triggered by the accumulation of organic acids. Remarkably, even though the Rad-Cs leaching rate was highest when the AD system was fed with the alkaline-heat pre-treated grass, it remained unsatisfactory at only 5.77 %. We inadvertently isolated a soil-like component from the raw grass, and analyzed both its proportion in the raw grass and the radioactivity intensity. The results indicate that although the soil constituted only 9.51 % TS of the raw grass, it accounted for a significant 81.35 % of the total radioactivity. The soil, which has a pronounced affinity for ionic Cs, being mixed into the raw grass, was identified as the primary factor limiting the leaching efficiency of Rad-Cs throughout both the pre-treatment and wet fermentation phases.

Mechanistic insight into humic acid-enhanced sonophotocatalytic removal of 17ß-estradiol: Formation and contribution of reactive intermediates.

In this study, humic acid (HA) enhanced 17ß-estradiol (17ß-E2) degradation by Er3+-CdS/MoS2 (ECMS) was investigated under ultrasonic and light conditions. The degradation reaction rate of 17ß-E2 was increased from (14.414 ± 0.315) × 10-3 min-1 to (122.677 ± 1.729) × 10-3 min-1 within 90 min sonophotocatalytic (SPC) reaction with the addition of HA. The results of quenching coupled with chemical probe experiments indicated that more reactive intermediates (RIs) including reactive oxygen species (ROSs) and triplet-excited states were generated in the HA-enhanced sonophotocatalytic system. The triplet-excited states of humic acid (3HA*), hydroxyl radical (•OH), and superoxide radical (•O2-) were the dominant RIs for 17ß-E2 elimination. In addition, the energy- and electron-transfer process via coexisting HA also account for 12.86% and 29.24% contributions, respectively. The quantum yields of RIs in the SPC-ECMS-HA system followed the order of 3HA* > H2O2 > 1O2 > â€¢O2-> •OH. Moreover, the spectral and fluorescence characteristics of HA were further analyzed during the sonophotocatalytic reaction process. The study expanded new insights into the comprehension of the effects of omnipresent coexisting HA and RIs formation for the removal of 17ß-E2 during the sonophotocatalytic process.

[Effects of Aging on the Cd Adsorption by Microplastics and the Relevant Mechanisms].

It has been verified that, as an emerging contaminant, microplastics are capable of adsorbing certain traditional contaminants like the heavy metal Cd. However, the majority of previous studies only focused on certain types of virgin microplastics, especially for PE and PS. In addition, this adsorption process might be affected by microplastics inevitably undergoing aging and consequent changes in the natural environment. Unfortunately, the relevant reports on aging effects were mainly about organic pollutants, rather than heavy metals. By far, there have been few comprehensive and mechanistic studies on the key aging effects on the Cd adsorption by various types of microplastics. In this study, five representative types of microplastics (i.e., PS, ABS, PP, PVC, and PET) were selected for aging by ultraviolet radiation, and the physicochemical properties of virgin and aged microplastics were thoroughly compared, including specific surface area, crystallinity, surface functional groups, and surface elements. Accordingly, the changes in adsorption isotherms of Cd by microplastics were discussed. The results showed that:① aging induced non-significant changes in specific surface area but a significant decrease in crystallinity. Surface functional groups also changed, including the emergence of a C=O functional group on PS and ABS, the decrease in C=C absorption peak intensity on ABS, and the increase in absorption peak intensities of C=O, C-O, and polar ester groups on PET. Regarding surface C content, C=C/C-C decreased, whereas C-O and O-C=O increased. The total O content and O/C significantly increased as well. ② The Langmuir model well-fitted the adsorption isotherms of Cd by virgin and aged microplastics. Aging significantly expanded the adsorption capacity of Cd by microplastics, as the order of saturated adsorption capacity before aging was ABS (0.2284 mg·g-1)>PVC (0.1360 mg·g-1)>PS (0.1286 mg·g-1)>PP (0.1005 mg·g-1)>PET (0.0462 mg·g-1) and then became PS (0.2768 mg·g-1)>ABS (0.2586 mg·g-1)>PVC (0.1776 mg·g-1)>PP (0.1721 mg·g-1)>PET (0.0951 mg·g-1) after aging. ③ Both crystallinity and surface functional groups played key roles in the adsorption of Cd by microplastics. As for virgin microplastics, crystallinity was negatively correlated with the saturated adsorption capacity of Cd, because the amorphous regions contributed most to Cd adsorption. Aging brought about the decrease in crystallinity and the increase in amorphous regions, which further promoted the oxidation reaction on microplastics. Consequently, oxygen-containing functional groups increased on the surface and eventually expanded the adsorption capacity of Cd by microplastics. Note that certain specific functional groups of various microplastics also had impacts on the adsorption process. These results provide valuable information about the environmental behaviors and interactions of microplastics and heavy metals in nature.

Enhanced anaerobic digestion of tar solution from rice husk thermal gasification with hybrid upflow anaerobic sludge-biochar bed reactor.

Tar generated as a by-product during biomass gasification contains a high concentration of refractory organic matters. In this study, a hybrid upflow anaerobic sludge-biochar bed reactor was established for tar treatment, and the methane yield was 120-154 NmL-CH4/g-CODinf, 20-30% higher than the control reactor. COD removal and methane production significantly decreased in both reactors when the influent tar concentration was doubled from 4954 mg-COD/L to 9964 mg-COD/L. When the influent concentration was reduced, the biochar packed reactor showed a faster recovery. Batch tests confirmed that higher tar concentration inhibited methane production and induced longer lagphase. Biochar addition effectively relieved the inhibition and prolonged the retention of organic matters. SEM observation and 16S rRNA analysis suggested that biochar also acted as the microbe's carrier, and promoted the growth of some microbes. The results of this study provide new ideas for tar treatment.

A successful start-up of an anaerobic membrane bioreactor (AnMBR) coupled mainstream partial nitritation-anammox (PN/A) system: A pilot-scale study on in-situ NOB elimination, AnAOB growth kinetics, and mainstream treatment performance.

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.

Comparison of decabromodiphenyl ether degradation in long-term operated anaerobic bioreactors under thermophilic and mesophilic conditions and the pathways involved.

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.

Improved stability of up-flow anaerobic sludge blanket reactor treating starch wastewater by pre-acidification: Impact on microbial community and metabolic dynamics.

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.

Nutrient augmentation enhances biogas production from sorghum mono-digestion.

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.

Bioleaching and removal of radiocesium in anaerobic digestion of biomass crops: Effect of crop type on partitioning of cesium.

Cultivation of biomass crops for energy production is a promising land-use for farmland abandoned owing to radionuclide fallout. However, radionuclides in soil are easily taken up in the crop. To understand phase partitioning of radiocesium Cs (RCs) during anaerobic digestion (AD) of crops, semi-continuous AD experiments were carried out using two types of RCs-contaminated crops. Analysis of fractionated digestate effluent revealed that AD of the crops released RCs into the water phase (up to 82 %), and the efficiency of RCs solubilization depended on crop biodegradability. Adsorption treatment for removal of RCs from the water phase of the digestate indicated a water-zeolite partition coefficient of 0.287 L/g. The efficiency of removal from the water phase was 90 % at an adsorbent dose of 30 g/L.

The role of rice husk biochar addition in anaerobic digestion for sweet sorghum under high loading condition.

Biochar is a carbon rich product made from the biomass pyrolysis process. Recently, biochar addition in anaerobic digestion processes has attracted attention for its possible functions to act as pH stabilizing agent, microbial carrier, and interspecies electron transfer. In this study, the effects of rice husk biochar addition in sorghum anaerobic digestion were investigated in batch tests. Under high F/M (food to microorganism) ratio conditions, obvious pH decreases and volatile fatty acids (VFA) accumulation was observed. Addition of 15 g/L biochar was found effective to increase the sorghum maximum methane production rate by 25 % and shorten the lag phase time by 44 %. Further biochar concentration increase showed little effects. Alkalinity increase brought by biochar addition contributed to the performance enhancement. Moreover, the promotive effects of biochar addition on degradation of acetic acid, propionic and butyric acid were not obvious under neutral pH conditions.

An integrated anaerobic system for on-site treatment of wastewater from food waste disposer.

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.

Simple solvatochromic spectroscopic quantification of long-chain fatty acids for biological toxicity assay in biogas plants.

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.

[Performance of an Aerobic Granular Reactor Treating Biogas Slurry from Pig Farm].

This research investigated the performance of an aerobic granular reactor treating biogas slurry from pig farm. Results indicated that the granular structure of aerobic sludge was not affected by the high pollution concentrationsin the biogas slurry. Although a low removal rate of phosphate was found in this study (about 16%±2%), organic matter and ammonia nitrogen showed stable removal and transformation in the granular system, and the effluent concentrations of those components were (267±81)mg·L-1 and(62±12)mg·L-1, respectively. In addition, the removal rate of sulfamethazine and tetracycline was 98%±2% and 65%±16%, respectively. During the process biogas slurry treatment, bacterial communities in the aerobic granular reactor remained stable, and Comamonadaceae was the dominant bacteria (relative abundance ofapproximately 16.66%).

Anaerobic degradation of deca-brominated diphenyl ether contaminated in products: Effect of temperature on degradation characteristics.

In this study, a 200-day deca-brominated diphenyl ether (deca-BDE) degradation activity experiment was carried out, using consumer-use curtain material as the substrate. During the degradation process, polybrominated diphenyl ether (PBDE) products with fewer bromine atoms were gradually generated by the debromination of deca-BDE. The influences of temperature, initial substrate dosing mass, and pH were also investigated. Interestingly, thermophilic conditions proved more beneficial for deca-BDE degradation than mesophilic conditions. The results also demonstrate that the debromination rate increased with the initial deca-BDE dosing mass, and that pH 7 was the most suitable for the reaction.

Distribution characteristics of poly-brominated diphenyl ethers between water and dissolved organic carbon from anaerobic digestate: Effects of digestion conditions.

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.

Effects of light intensity on biomass, carbohydrate and fatty acid compositions of three different mixed consortia from natural ecological water bodies.

This study investigated the effect of light intensity on three various microalga consortia collected from natural ecological water bodies (named A, B and C) towards their fatty acid profiling and fractions, carbohydrate and protein production at different light intensities of 100, 200 and 300 µmol m-2 s-1. The results indicating that increasing light intensity positively correlated with the lipid production than carbohydrate and protein. Irrespective to the solids (Total and Volatile Solid) content, lipids and carbohydrate has varied significantly. Consortia C showed higher productivity toward lipids, whereas consortia A and B accumulated more carbohydrate and protein, respectively. The microscopic images revealed the breakdown of cells during the increase in light intensity, in spite, the similar algal species were observed in all consortia experimented. Principal component analysis (PCA) revealed that low light intensity aid relatively in high protein, Total Nitrogen and Total Phosphorus, meanwhile high intensity attributed carbohydrates and unsaturated fatty acids (USFA) contents.

Effects of lipid concentration on thermophilic anaerobic co-digestion of food waste and grease waste in a siphon-driven self-agitated anaerobic reactor.

To investigate the influence of lipid concentration (of total solids, w/w) on anaerobic treatment of food waste under thermophilic condition, a siphon-driven self-agitated anaerobic reactor was operated for 220 days. The average lipid concentration was changed from 12.8% to 59.3% (w/w) step by step. The gas production rate increased from 1.97 to 2.31 L/L/d with lipid concentration increased from 12.8% to 19.7% (w/w), whereas decreased sharply to 0.78 L/L/d when the concentration further increased to 59.3% (w/w). The COD recovery from output at different lipid concentration was analyzed in this study. With the concentration increased from 12.8% to 59.3% (w/w), the percentage of COD recovered as methane gas decreased from 80.9% to 35.4%, while the percentage of COD remained in the effluent was also decreased significantly from 15.5% to 2.60%. The lipid concentration under 40% (w/w) was recommended in the co-digestion of food waste and grease trap waste.

Impact of cationic substances on biofilm formation from sieved fine particles of anaerobic granular sludge at high salinity.

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.

Effect of temperature and organic loading rate on siphon-driven self-agitated anaerobic digestion performance for food waste treatment.

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 ±â€¯1 °C) and thermophilic condition (55 ±â€¯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.