The effects of riverside cities on microplastics in river water: A case study on the Southern Jiangsu Canal, China.

Microplastics, which are usually recognized as artificial polymer particles with a particle size <5 mm, have attracted much attention as new pollutants in recent years. Urban areas are a major contributor of microplastics to the environment, but their microplastic emission intensity and characteristics are not clear. In this paper, the microplastic abundances and characteristics in the Southern Jiangsu Canal were studied to reveal the effect of riverside cities on microplastics in river water. The results show that the microplastic abundance in the water body of the South Jiangsu Canal ranges from 3.41 to 19.07 particles L-1, with an average of 9.59 ± 3.95 particles L-1, which is at the same level as major urban agglomerations in the world. The top five polymers were polyethylene terephthalate (PET), polycarbonate (PC), polyethylene (PE), chlorinated polyethylene (CPE) and polyurethane (PU). Fragments accounted for the largest proportion (68.47 %), followed by beads and fibers. Most microplastics were <100 µm (83.87 %). Human life and industry in riverside cities contribute significantly to microplastics in the Southern Jiangsu Canal water. After flowing through the cities, the microplastic abundance in the canal water increased by 26 % ~ 211 %. The overall economic and social development of the city affects the occurrence characteristics of the canal water microplastics. The average abundance of microplastics was positively correlated with Regional Gross Domestic Product (GDP) per capita. Wastewater treatment plant effluent is an important point source of microplastics in canal water. The microplastic abundances downstream of WWTPs increased by 21.8 % ~ 64.6 % compared with those upstream.

Strategy of electron acceptors for ethanol-driven chain elongation from kitchen waste.

A two-phase kitchen waste (KW) fermentation was proposed in the current study to enhance medium-chain fatty acids (MCFAs) production from kitchen waste. In particular, effect of acetate to butyrate ratio (ABR) on MCFAs production was investigated which can be regulated by different pH and organic loading during the acidification phase. Medium ABR (1.00) was obtained when pH is 5.5 and organic loading is 20 g VS/L in FW acidification fermentation. Subsequent chain elongation fermentation demonstrated that the highest yield of caproate 9.67 g/L with selectivity of 79 %, and highest ethanol conversion efficiency of 1.11 was achieved in medium ABR system. Microbial community study showed that medium ABR significantly enrich the functional bacteria especially Clostridium kluyveri. The study provides a new method for chain elongation enhancement without addition of other additives in kitchen waste fermentation system and gives a guide for the regulation of the short-chain fatty acids distribution in its acidification phase.

Fugitive release and influencing factors of microplastics in urbanized watersheds: A case study of the central area of Suzhou City.

Urban areas are greatly affected by human activities that may result in the release of microplastics. Fugitive release of microplastics is the unorganized discharge of microplastics produced during plastic manufacturing and use. The microplastics enter the environment in a variety of ways. To investigate fugitively released microplastics and identify the major influencing factors in urban watersheds, the central area of Suzhou city was selected as a case study. This area has a dense network of canals without sources of organized release. The results show that the microplastic abundance in the urban canal of the area ranged from 8.29 to 40.63 particles L-1, with a mean of 14.75 ± 3.95 particles L-1. To better understand the relationship between microplastics and human activities, the main influencing factors, including water quality, water-related activities, dwelling type, urban landscaping, trash collection and land use type, were assessed. Water quality was not correlated with microplastic distribution in the urban watershed, as it is in larger watersheds. Water-related activities caused elevated fugitive release of microplastics. The abundance of microplastics discharged into the water environment in modern communities was significantly less than that discharged in an area of traditional residences. Traffic activities contributed to microplastic release, while urban landscaping physically blocked microplastics from flowing into urban waterbodies to some extent. Trash collection did not reduce the abundance of microplastic particles in the water, despite its ability to remove other types of plastic waste. The results also suggest that the contributions of different land use types to the abundance of microplastics in urban areas from highest to lowest were as follows: tourist districts > commercial areas > public areas > residential areas > roads. Moreover, fugitive release is an important source to be considered in future research on urban microplastic management. The renewal of urban construction to mitigate the influence of human activities on water ecology may play a positive role in controlling the fugitive release of microplastics.

Nano zero-valent iron: A pH buffer, electron donor and activator for chain elongation.

Chain elongation produce medium chain carboxylates, which are important precursors to many pharmaceuticals, antimicrobials and biofuels. Results in the presented investigations show that the supply of nano zero-valent iron (NZVI) can enhance caproate production. The highest caproate concentration achieved amounted to 27.2 mmol/L when 5 g/L NZVI were added, which was about 100% higher than the control. The study also showed increase of ethanol oxidation and decrease of butyrate and butanol with NZVI addition. Mechanism study showed NZVI can stimulate caproate production by preventing pH to fall below 5.4 through displacement reaction. Electron balance analysis displayed that NZVI provides extra electron by promoting ethanol oxidation and its dissolution. H2 was the potential electron shuttle between NZVI and chain elongators; High throughput sequencing showed function of NZVI on reshaping of microbial communities, especially enriching Oscillibacter Marseille-P3260, a kind of chain elongator and Corynebacterium which possesses fatty acid biosynthesis and iron utilization.

Effect of nano zero-valent iron addition on caproate fermentation in carboxylate chain elongation system.

Carboxylate chain elongation is a burgeoning research area for producing added value bio-products from organic fraction of municipal solid waste. Effect of nano zero-valent iron (NZVI) on chain elongation and its possible mechanism was investigated. Highest caproate concentration, 28.0 mmol·L-1 was achieved with 2 g·L-1 NZVI amendment, which is about 16.7% higher than the control. Promoted ethanol utilization was considered as the main reason for the increment of caproate production and hydrogen generation. Electron balance analysis shows that NZVI did not improve the total electron recovery efficiency but favoured the electron flow toward longer carboxylate chain product, i.e. caproate. Finally, full-length 16s rRNA sequencing of bacterial community showed NZVI reshaped the bacterial community by exerting reduction selectivity. And Oscillibacter and Clostridium could be the potential functional species for carboxylate chain elongation.

Remediation of pyrene contaminated soil by double dielectric barrier discharge plasma technology: Performance optimization and evaluation.

Polycyclic aromatic hydrocarbons (PAHs) in soil are not only detrimental to environment but also to human health. Double dielectric barrier discharge (DDBD) plasma reactor used for the remediation of pyrene contaminated soil was studied. The performance of DDBD reactor was optimized with influential parameters including applied voltage, type of carrier gas, air feeding rate as well as pyrene initial concentration. The analysis of variance (ANOVA) results showed that input energy had a great effect on pyrene remediation efficiency followed by pyrene initial concentration, while, the effect of air feeding rate was insignificant. More specifically, the remediation efficiency of pyrene under air, nitrogen and argon as carrier gas were approximately 79.7, 40.7 and 38.2% respectively. Pyrene remediation efficiency is favored at high level of applied voltages and low level of pyrene initial concentration (10 mgkg-1) and air feeding rate (0.85 L/min). Moreover, computation of the energy efficiency of the DDBD system disclosed that an optimal applied voltage (35.8 kV) and higher initial pyrene concentration (200 mgkg-1) favored the high energy efficiency. A regression model predicting pyrene remediation under DDBD plasma condition was developed using the data from a face-centered central composite design (FCCD) experiment. Finally, the residual toxicity analysis depicted that the respiratory activity increased more than 21 times (from 0.04 to 0.849 mg O2 g-1) with a pyrene remediation efficiency of 81.1%. The study demonstrated the DDBD plasma technology is a promising method not only for high efficiency of pyrene remediation, but also recovering biological function without changing the physical-chemical properties of soil.

Effects of conductive carbon materials on dry anaerobic digestion of sewage sludge: Process and mechanism.

Dry anaerobic digestion of sewage sludge (SS-DAD) is often inhibited by excessive acidification due to low water content and high organic loading. The effects of conductive carbon materials including powdered activated carbon (PAC) and powdered graphite (PG) on SS-DAD under mesophilic condition (35℃) were investigated. The results demonstrated that the addition of PAC increased methane production of SS-DAD. The methane yield of PAC50% reactor (dosage of PAC is 50% of the volatile solids) amounted to 210 mL·gVSadded-1, which is 49% higher than that of control. PAC addition significantly enhanced the biodegradation process, as the reduction rate of total solids (TS) and volatile solids (VS) were increased by 36.4% and 34.1%, respectively, compared to the control. Inhibitory substrate adsorption experiments showed that PAC has significant adsorption (13.6 mg g-1) for VFAs, while PG showed almost no adsorption (0.81 mg g-1). Microbial community structure analysis showed hydrogenotrophic methanogens (Methanobrevibacter and Methanosphaera) were reduced in the PAC50% reactor, while methanogens (Methanobacterium) which can also use formate as electron donor were increased. PAC amendment reshaped the microbial community in the SS-DAD system which may result in shifting of the major electron carrier from hydrogen to formate and increasing electron transfer efficiency of the SS-DAD system.

Enhanced butyrate production by transition metal particles during the food waste fermentation.

Butyrate is an important precursor for fine chemicals and biofuels. The aim of this study is to investigate butyrate production as affected by transition metal addition of food waste fermentation including, nickel, Raney nickel and copper particles. Performance of fermentation showed nickel particles achieved the highest butyrate concentration, 7.3 g/L, which was 38.5% higher than that in the control trial. Raney nickel also showed similar effect on the enhancement of butyrate production. However, increased dosage of transition metal particle addition led to decreased butyrate production. The theoretical link between metal-assisted dark fermentation and butyrate production was tentatively explored. Redox potential affected by nickel addition was assumed to be an essential factor for butyrate production. Microbial community analysis found Clostridium sensu stricto 11 may be the dominant functional species for butyrate production. The study demonstrates that development on transition metal catalyst may contribute to waste biorefinery for added value products/energy production.

Volatile organic compounds (VOCs) removal in non-thermal plasma double dielectric barrier discharge reactor.

Non-thermal plasma (NTP) an emerging technology to treat volatile organic compounds (VOCs) present in unhygienic point source air streams. In present study, double dielectric barrier discharge (DDBD) reactors were used for the first time to evaluate the removal efficiency of VOCs mixture of different nature at constant experimental conditions (input power 16-65.8 W, VOCs mixture feeding rate 1-6 L/min, 100-101 ppm inlet concentration of individual VOC). Reactor A and B with discharge gap at 6 mm and 3 mm respectively, were used in current study. When treated at an input power of 53.7 W with gas feeding rate of 1 L/min in DDBD reactor A, removal efficiency of the VOCs were: tetrachloroethylene (100%), toluene (100%), trichloroethylene (100%), benzene (100%), ethyl acetate (100%) and carbon disulfide (88.30%); whereas in reactor B, the removal efficiency of all VOCs were 100%. Plasma-catalyst (Pt-Sn/Al2O3, BaTiO3 and HZSM-5) synergistic effect on VOCs removal efficiency was also investigated. Highest removal efficiency i.e 100% was observed for each compound with BaTiO3 and HZSM-5 at an input power 65.8 W. However, integrating NTP with BaTiO3 and HZSM-5 leads to enhanced removal performance of VOCs mixture with high activity, increase in energy efficiency and suppression of unwanted byproducts.

Fugitive halocarbon emissions from working face of municipal solid waste landfills in China.

Halocarbons are important anthropogenic greenhouse gases (GHGs) due to their long lifetime and large characteristic factors. The present study for the first time assessed the global warming potential (GWP) of fugitive halocarbon emissions from the working face of landfills in China. The national emissions of five major halocarbons (CFC-11, CFC-113, CH2Cl2, CHCl3 and CCl4) from the working face of municipal solid waste landfills in China were provided through observation-based estimations. The fluxes of halocarbons from working face of landfills were observed much higher than covered cells in landfills hence representing the hot spots of landfill emissions. The annual emissions of the halocarbons from landfills in China were 0.02-15.6kt·y-1, and their GWPs were 128-60,948kt-CO2-eq·y-1 based on their characteristic factors on a 100-year horizon. CFC-113 was the dominant species owing to its highest releasing rate (i.e. 15.4±19.1g·t-1) and largest characteristic factor, resulting in a GWP up to 4036±4855kt-CO2-eq·y-1. The annual emissions of CFC-113 from landfills (i.e. 0.61kt·y-1) made up ∼76% of the total national CFC-113 emissions. The GWPs of halocarbons were estimated ∼14.4% of landfill methane emissions. Therefore, fugitive halocarbons emissions from working face are significant sources of GHGs in landfill sites in China, although they comprise a small fraction of total landfill gases.

Co-existence of Anaerobic Ammonium Oxidation Bacteria and Denitrifying Anaerobic Methane Oxidation Bacteria in Sewage Sludge: Community Diversity and Seasonal Dynamics.

Anaerobic ammonium oxidation (ANAMMOX) and denitrifying anaerobic methane oxidation (DAMO) have been recently discovered as relevant processes in the carbon and nitrogen cycles of wastewater treatment plants. In this study, the seasonal dynamics of ANAMMOX and DAMO bacterial community structures and their abundance in sewage sludge collected from wastewater treatment plants were analysed. Results indicated that ANAMMOX and DAMO bacteria co-existed in sewage sludge in different seasons and their abundance was positively correlated (P < 0.05). The high abundance of ANAMMOX and DAMO bacteria in autumn and winter indicated that these seasons were the preferred time to favour the growth of ANAMMOX and DAMO bacteria. The community structure of ANNAMOX and DAMO bacteria could also shift with seasonal changes. The "Candidatus Brocadia" genus of ANAMMOX bacteria was mainly recovered in spring and summer, and an unknown cluster was primarily detected in autumn and winter. Similar patterns of seasonal variation in the community structure of DAMO bacteria were also observed. Group B was the dominant in spring and summer, whereas in autumn and winter, group A and group B presented almost the same proportion. The redundancy analysis revealed that pH and nitrate were the most significant factors affecting community structures of these two groups (P < 0.01). This study reported the diversity of ANAMMOX and DAMO in wastewater treatment plants that may be the basis for new nitrogen removal technologies.

Health risk impacts analysis of fugitive aromatic compounds emissions from the working face of a municipal solid waste landfill in China.

Aromatic compounds (ACs) emitted from landfills have attracted a lot of attention of the public due to their adverse impacts on the environment and human health. This study assessed the health risk impacts of the fugitive ACs emitted from the working face of a municipal solid waste (MSW) landfill in China. The emission data was acquired by long-term in-situ samplings using a modified wind tunnel system. The uncertainty of aromatic emissions is determined by means of statistics and the emission factors were thus developed. Two scenarios, i.e. 'normal-case' and 'worst-case', were presented to evaluate the potential health risk in different weather conditions. For this typical large anaerobic landfill, toluene was the dominant species owing to its highest releasing rate (3.40±3.79g·m-2·d-1). Despite being of negligible non-carcinogenic risk, the ACs might bring carcinogenic risks to human in the nearby area. Ethylbenzene was the major health threat substance. The cumulative carcinogenic risk impact area is as far as ~1.5km at downwind direction for the normal-case scenario, and even nearly 4km for the worst-case scenario. Health risks of fugitive ACs emissions from active landfills should be concerned, especially for landfills which still receiving mixed MSW.