Volcanic trigger of ocean deoxygenation during Cordilleran ice sheet retreat.

North Pacific deoxygenation events during the last deglaciation were sustained over millennia by high export productivity, but the triggering mechanisms and their links to deglacial warming remain uncertain1-3. Here we find that initial deoxygenation in the North Pacific immediately after the Cordilleran ice sheet (CIS) retreat4 was associated with increased volcanic ash in seafloor sediments. Timing of volcanic inputs relative to CIS retreat suggests that regional explosive volcanism was initiated by ice unloading5,6. We posit that iron fertilization by volcanic ash7-9 during CIS retreat fuelled ocean productivity in this otherwise iron-limited region, and tipped the marine system towards sustained deoxygenation. We also identify older deoxygenation events linked to CIS retreat over the past approximately 50,000 years (ref. 4). Our findings suggest that the apparent coupling between the atmosphere, ocean, cryosphere and solid-Earth systems occurs on relatively short timescales and can act as an important driver for ocean biogeochemical change.

Organics alleviate the inhibition of sulfate on ANAMMOX sludge.

Anaerobic ammonium oxidation (Anammox) was an innovative process for nitrogen removal. In this study, the influence of sulfate in different concentrations (100, 200, 300, and 400 mg L-1) on Anammox process were investigated in nine identical sequential batch reactors, four of which were extra supplied for organics, to study the combined effect. The results indicated the obvious inhibition by sulfate which decreased the total nitrogen removal efficiency (TNRE) to 84.1%, 81.2%, 81.2%, and 72.5%, from the control results as 91.9%. Whereas, the organics addition alleviated the inhibitory effect, through consuming the oxygen in influent, promoting the secretion of protein, and inducing the denitrifying bacteria, for which the sulfate only slightly decreased the TNRE to 89.0%, 83.7%, 83.6%, and 75.7%, respectively. Candidatus Kuenenia and Denitratisoma could coexist in Anammox system and cooperatively contribute to the nitrogen removal, when treating the nitrogenous wastewater contains both sulfate and organics.

Silver nanowire network for flexible transparent electrodes based on spray coating at a low DC electric field and plasma treatment.

Flexible transparent electrodes have been fabricated successfully by using a metal nanowire network. Despite its higher conductivity and transparency, raw silver nanowire (AgNW) film suffers from the random arrangement and high surface roughness originating from the overlaps of a few tens of nanometer-thick AgNWs. In this work, a facile and environmentally friendly method is developed to form AgNW flexible transparent electrodes by spray coating at a low DC electric field (less than 6.0 V) and subsequent plasma treatment. The DC voltage, plasma power, and plasma treatment time of the AgNW network are optimized. The obtained electrodes fabricated by this technique exhibited excellent flexible, transparent, and flat junctions of AgNWs with a sheet resistance of 4.64 Ω · sq-1 and a specular transmittance of 87.3% at a wavelength of 550 nm. Furthermore, the AgNW electrodes are very flexible, highly durable, and moiré-free. The resistance remains almost unchanged over 500 cycles of mechanical deformation with a bending distance of 14 mm when its size is 20 × 20 mm. The as-prepared AgNW electrodes exhibited a root mean square roughness below 13.07 nm at a scan size of 5 × 5 µm. We propose that the improved properties can be attributed to the well-arranged AgNW network acheived by applying a DC electric field and a flat connection between the AgNW junctions induced by plasma treatment.

Impact of p-cresol on hydrogen sulfide and ammonia treatment by biotrickling filter and the production of nitrous oxide.

Biotrickling filter (BTF) is often used for purification of waste gas from swine houses, with vital information still needed regarding interaction effects among multiple gas pollutants removal and also the formation of byproducts especially nitrous oxide (N2O, a strong greenhouse gas) due to the relative high NH3 concentration level compared to other gases. In this study, gas removal and N2O production were compared between two BTFs, where the inlet gas of BTF-1 contained NH3 and H2S while p-cresol was additionally supplied to BTF-2. At inlet load (IL) between 3.67 and 18.91 g m-3 h-1, removal efficiencies of NH3 exceeded 95% for both BTFs. As alternative strategy, adding thiosulfate improved H2S removal. Interestingly, presence of p-cresol to some extent promoted H2S removal at IL of 0.56 g m-3 h-1possibly due to effect on pH value of circulating solution. Similar to NH3, removal efficiencies of p-cresol were higher than 95% at an average IL of 2.98 g m-3 h-1. Gas residence time, pH of circulating solution and inlet loading were identified as key factors affecting BTF performance, but the response of individual gas compound to these factors was not consistent. Overall, p-cresol enhanced N2O generation although the effects were not always significant. High-throughput sequencing results showed that Proteobacteria accounted for the largest proportion of relative abundance and BTF-2 had much richer microbial diversity compared to BTF-1. Thermomonas, Comamonas, Rhodanobacter and other bacterial genus capable of denitrification were detected in both BTFs, and their corresponding abundances in BTF-2 (10.9%, 8.7% and 5.2%) were all greater than those in BTF-1 (0.4%, 0.3% and 2.0%), indicating that more denitrification may occur within BTF-2 and higher N2O could have been generated. This study provided evidence that organic gas components, served as carbon source, may increase the N2O production from BTF when treating waste gases containing NH3.

Simultaneous removal of ammonia and sulfur odorants in biotrickling filters and N2O production.

Research on the stability evaluation of biotrickling filters (BTFs) under harsh conditions and the bacterial adaptation process still needs to be improved. Herein, BTFs with polypropylene plastic (PP) and ceramic raschig rings (CRR) were investigated for a better understanding of the biodegradation of ammonia (NH3), hydrogen sulfide (H2S), and dimethyl sulfide (DMS). The results showed an excellent performance in removal efficiency (RE) for NH3 (91.6 %-99.9 %), H2S (RE: 55.3 %-99.5 %), and DMS (RE: 10.6 %-99.9 %). It was found that a more apparent positive correlation between N2O emission and pressure drop in CRR BTF (R2 = 0.92) than in PP BTF (R2 = 0.79) (P < 0.01). Low temperature promotes an increase in the abundance ofComamonasandBacillus. The polysaccharides in PP and CRR reactors decreased by 78.6 % and 68.1 % when temperature reduced from 25℃ to 8℃. This work provides a novel insight into understanding bacterial survival under harsh BTF environments.

The key role of unsaturated olefin content on polysulfides prepared via inverse vulcanization of waste plant oils for mercury removal from wastewater.

Three waste plant oils (olive oil, coconut oil, and soybean oil) were utilized as monomer crosslinking agents to synthesize polysulfides by inverse vulcanization with elemental sulfur, for mercury removal from wastewater. NMR analysis showed that 92.1% of the olefins participated in the inverse vulcanization reaction, indicating that the quantity of unsaturated olefins in plant oil mainly affects the ring-opening ratio of sulfur for the formation of sulfur-based polymers. The experimental results showed that olive oil polysulfide (S-r-olive) achieved 100% Hg2+ removal within 2 h at a pH of 6. The S-r-olive, S-r-soybean, and S-r-coconut exhibited adsorption capacities of 130.23, 42.72, and 28.08 mg/g, respectively. The kinetic and adsorption isotherm illustrated that the Hg2+ adsorption by polysulfides conformed to the pseudo-second-order and Freundlich models, showing that the reaction rate constant of S-r-olive is approximately 14 times and 4.6 times greater than that of S-r-soybean and S-r-coconut, respectively. The adsorption mechanism is concluded that Hg2+ first enters the suspended S-r-olive by physical adsorption, then combined with sulfur to form HgS by chemical action and fixed in the S-r-olive adsorbent. This study demonstrates that utilizing waste plant oils as monomer crosslinking agents to synthesize adsorbents for Hg2+ removal is feasible and effective.

Dominance of benthic fluxes in the oceanic beryllium budget and implications for paleo-denudation records.

The ratio of atmosphere-derived 10Be to continent-derived 9Be in marine sediments has been used to probe the long-term relationship between continental denudation and climate. However, its application is complicated by uncertainty in 9Be transfer through the land-ocean interface. The riverine dissolved load alone is insufficient to close the marine 9Be budget, largely due to substantial removal of riverine 9Be to continental margin sediments. We focus on the ultimate fate of this latter Be. We present sediment pore-water Be profiles from diverse continental margin environments to quantify the diagenetic Be release to the ocean. Our results suggest that pore-water Be cycling is mainly controlled by particulate supply and Mn-Fe cycling, leading to higher benthic fluxes on shelves. Benthic fluxes may help close the 9Be budget and are at least comparable to, or higher (~2-fold) than, the riverine dissolved input. These observations demand a revised model framework, which considers the potentially dominant benthic source, to robustly interpret marine Be isotopic records.

Investigation on operational parameters and membrane fouling performance in treating synthetic aquaculture wastewater via forward osmosis with sucrose as draw solution.

Forward osmosis (FO), a membrane separation process driven by a natural concentration gradient, is served as a potential strategy in the aspect of wastewater treatment. In this work, a worthy attempt at aquaculture wastewater treatment using a self-made FO system was conducted, confirming it was a promising approach to treating aquaculture wastewater. Optimization of operational parameters of the FO system, including draw solution (DS) concentration, cross-flow velocity, and DS temperature, was systematically investigated to enhance the running efficiency. Different selected parameters highly influenced the water flux during the single-factor experiments, and the findings indicated that the optimal conditions were DS of 1.5 M, cross-flow velocity of 15 cm/s, and temperature of 32 °C with consideration of FO performance and economical cost. An excellent linear relationship between chemical oxygen demand (COD) changing multiples and operational parameters was obtained from experimental results, offering a great interception performance of organic contamination. On the basis of optimal operating conditions, membrane fouling experiments with different running time were conducted, and the microscopic morphology and element composition of the fouled membrane were also analyzed. The results demonstrated that a layer of cake was coated on the surface of the membrane, and the main elements in the fouling cake included C, O, Na, and S, which were highly determined by the component of the feed solution (FS) and working time. Afterward, the 60-h FO fouled membrane was cleaned under the method which combined hydraulic power and chemical agents, and the water flux recovered to 12.79 Lm-2 h-1, proving a good performance for the recovery of water flux. This investigation showed that employing sucrose as DS was effective for reducing wastewater volume, and it provided an alternative choice and a sustainable way for the separation of organic pollutants from water resources.

Study on removal of phosphorus as struvite from synthetic wastewater using a pilot-scale electrodialysis system with magnesium anode.

Struvite precipitation may become ineffective in removing phosphorus due to the low concentration of phosphate in the liquid. In this study, electrolysis with a magnesium anode was applied to recovering phosphorus and ammonia as struvite from wastewater. A novel electrodialysis process (ED) with a magnesium anode was developed, and its feasibility to treat synthetic wastewater with low phosphate concentration was demonstrated in a pilot-scale experimental system. To achieve high phosphate removal efficiency in the product stream, the optimal initial pH and flow rate were found to be 8.8 and 200 L h-1, respectively, for the ED system at a constant current of 0.1 A. The pilot-scale ED system under the consecutive batch mode removed 65% phosphate from the synthetic wastewater containning 10 mg L-1P, and the phosphate concentration in the product stream was kept at 30 mg L-1 after 280 min. The running cost of the ED system was estimated to be $31.27 kg-1 P for synthetic wastewater with 10 mg L-1 P, mainly resulting from the cost of the loss of the magnesium anode. The precipitates generated from the product stream were confirmed as struvite by XRD analysis.

The role of Northeast Pacific meltwater events in deglacial climate change.

Columbia River megafloods occurred repeatedly during the last deglaciation, but the impacts of this fresh water on Pacific hydrography are largely unknown. To reconstruct changes in ocean circulation during this period, we used a numerical model to simulate the flow trajectory of Columbia River megafloods and compiled records of sea surface temperature, paleo-salinity, and deep-water radiocarbon from marine sediment cores in the Northeast Pacific. The North Pacific sea surface cooled and freshened during the early deglacial (19.0-16.5 ka) and Younger Dryas (12.9-11.7 ka) intervals, coincident with the appearance of subsurface water masses depleted in radiocarbon relative to the sea surface. We infer that Pacific meltwater fluxes contributed to net Northern Hemisphere cooling prior to North Atlantic Heinrich Events, and again during the Younger Dryas stadial. Abrupt warming in the Northeast Pacific similarly contributed to hemispheric warming during the Bølling and Holocene transitions. These findings underscore the importance of changes in North Pacific freshwater fluxes and circulation in deglacial climate events.

Phasing of millennial-scale climate variability in the Pacific and Atlantic Oceans.

New radiocarbon and sedimentological results from the Gulf of Alaska document recurrent millennial-scale episodes of reorganized Pacific Ocean ventilation synchronous with rapid Cordilleran Ice Sheet discharge, indicating close coupling of ice-ocean dynamics spanning the past 42,000 years. Ventilation of the intermediate-depth North Pacific tracks strength of the Asian monsoon, supporting a role for moisture and heat transport from low latitudes in North Pacific paleoclimate. Changes in carbon-14 age of intermediate waters are in phase with peaks in Cordilleran ice-rafted debris delivery, and both consistently precede ice discharge events from the Laurentide Ice Sheet, known as Heinrich events. This timing precludes an Atlantic trigger for Cordilleran Ice Sheet retreat and instead implicates the Pacific as an early part of a cascade of dynamic climate events with global impact.