Colloidal Organic Matter Research Articles

Size and polarity fractions of mobile organic matter from manure affect the sorption of sulfadiazine, caffeine and atenolol in soil

Waste-derived organics introduced to soils along with pharmaceutical active compounds (PhAC) are a crude mixture of compounds occurring in various size and polarity fractions. They affect the sorption of PhACs to soil; however, the relevant knowledge is still insufficient. The effects of different size and polarity fractions of manure-derived mobile organic matter (<63 µm) on the sorption of sulfadiazine, caffeine and atenolol to five topsoils were investigated. Mobilization of the PhACs was strongest in the presence of dissolved organic matter (mDOM, <0.45 µm), with a reduction of Kd of sulfadiazine, caffeine and atenolol by mean factors of 0.66, 0.57 and 0.41, respectively. The mobilizing effects of colloidal organic matter (0.45–10 µm) were slightly smaller. Fine particulate organic matter (10–63 µm) reduced the sorption of the PhACs in slightly acidic soils (pH 6.0), but increased it in strongly acidic soil (pH 4.3). Furthermore, hydrophobic (HO-mDOM) and hydrophilic (HI-mDOM) fractions of mDOM reduced the sorption capacity but increased the sorption nonlinearity of PhACs in soils. Effects of HO-mDOM and HI-mDOM were PhAC specific. It is suggested to consider the varying impacts of mobile fractions in animal manure and/or treated wastewater in evaluating the fate and environmental relevance of associated PhACs.

Compositions, sources, and bioavailability of colloidal organic matter in Lake Taihu

Colloidal organic matter (COM) exists ubiquitously in natural waters, and plays a pivotal role in biogeochemical cycles. Lake Taihu is confronted with severe eutrophication and algal blooms. Field investigations were carried out in Lake Taihu and two inflow rivers for two years to identify the source of COM and explore the bioavailability of COM to algae. Compositions and sources of COM were analyzed through UV absorption coefficients and parallel factor analysis of three-dimensional excitation emission matrix spectra (3D EEMs-PARAFAC). Absorption coefficient a(350) of COM in rivers surpassed that in the lake, SUVA254 exhibited noteworthy seasonal variations, and SR indicated a stable autochthonous characteristic. Three components were identified by PARAFAC analysis: tryptophan-like (C1), humic-like (C2), and tyrosine-like (C3). Fluorescence indexes showed that C1 and C3 were mainly autochthonously produced and C2 was derived from allochthonous inputs. The bioassays were conducted to assess the bioavailability of COM to the dominant species, Microcystis aeruginosa. The results showed that colloids supplied rich carbon sources and trace metals, supporting the growth of Microcystis aeruginosa. The specific growth rate, Chl a content, and biological increment of Microcystis aeruginosa in 50 % colloid-added treatment exceeded those in 20 % and 75 % treatments. Simultaneously, the effective quantum yield (Fv/Fm) and the apparent photosynthetic electron transport rate (ETRmax) demonstrated that the photosynthetic activity of Microcystis aeruginosa was higher in 20 % treatment. These findings help in understanding the intricate mechanisms of COM in lake ecosystems, and provide the robust scientific foundation for water management and protection in Lake Taihu.

Colloidal Filterable Bacteria Enhance Ammonia Nitrogen Enrichment in River Colloids under Different Turbidity Conditions: Bacterial Diversity, Assembly Mechanism, and Nitrogen Transformation

Turbidity has been one of the most typical problems in urban rivers, accompanied by eutrophication. Though the colloid is a nonnegligible factor associated with turbidity and nutrient enrichment in urban rivers, the characteristics of nitrogen enrichment and bacterial communities of colloids under different turbidity conditions of urban rivers have not been well understood. In this study, colloids of low and high molecular weights (LMW, 30 kDa–0.2 μm, and HMW, 0.2–1 μm) were separately collected from the bulk water (&lt;1 μm) of several typical urban rivers in China. Since the colloidal concentration presented the significantly highest correlation with turbidity, colloidal characteristics were further explored under three turbidity gradients with two cutoffs of 10 and 30 NTU. Results showed that colloidal organic matter in medium and high turbidity rivers was mainly sourced from the release of endogenous plankton and the proportion of colloidal organic carbon in dissolved organic carbon increased from 33% to 38% with increased turbidity. Colloidal ammonia nitrogen in medium turbidity accounted for the highest proportion (an average of 60%) in bulk water, which could be explained by the significantly positive correlation of colloidal ester groups and ammonia nitrogen (R2 = 0.47). Bulk water, HMW, and LMW colloids presented different dominant bacterial genera and LMW colloids also contained three unique dominant filterable genera: Flavobacterium, Acinetobacter, and Limnohabitans. LMW colloidal filterable bacteria under medium and high turbidities presented the greatest potential for dissimilatory nitrate reduction to ammonium, which might further enhance the enrichment of ammonia nitrogen in colloids. This study provides a primary understanding of the characteristics of colloids and colloidal bacterial communities in urban rivers from the perspective of turbidity and puts a new insight on the remediation of rivers under medium turbidity.

Co-transport of ferrihydrite–organic matter colloids with Sb(v) in saturated porous media: implications for antimony mobility

Schematic diagram of the mechanism of Fe–NOM–Sb(v) colloids formation and transport in the natural environment.

Characteristics and Comparison of Biofilm and Activated Sludge Sewage Treatment Technologies

Sewage treatment is a key environmental protection task and is of great significance to sustainable development. In this paper, biological filter method, rotating biological plate method, traditional push-flow activated sludge method and gradually reduced aeration method are selected to summarize and compare their principles, advantages and disadvantages, and removal objects. Biofilm method is similar to the principle of soil self-purification. It is a kind of aerobic biological treatment technology juxtaposed with activated sludge, and it is a fixed membrane process. The activated sludge is similar to the self-purification principle of water. It is an aerobic biological treatment method for sewage, removing dissolved and colloidal biochemical organic matter from the effluent, as well as suspended solids and other substances that can be adsorbed by activated sludge. It also removes some of the phosphorus and nitrogen. Both methods belong to wastewater biological treatment of suspended microorganisms in the water. They have their advantages, disadvantages and applicable conditions, so there is no competition between the two methods.

Role of colloids in the transfer and dispersion of trace elements into river waters through a former mining district

Characterizing the different chemical forms of trace elements in surface inland waters of mining regions is very important to understand the mechanisms underlying metal(loid) transport, their accumulation and toxicity, especially when waste storage areas are closely linked to the hydrographic network. This study focuses on the oldmining district of Salsigne in the Orbiel Valley (France), which was at one time the largest gold mine in Europe and the world’s largest arsenic mine. Our objective was to better understand the factors governing the transport of As and to investigate the role of colloidal matter as vector of major (Al, Ca, Fe, Mg) and trace (As, Pb, REE) elements in waters.A field sampling campaign was carried out during high water season to collect samples from the Orbiel River and its tributaries. In situ (ultra)filtrations at different cut-off thresholds (0.22 μm, 0.025 μm, 100 kDa and 3 kDa) were performed and physicochemical parameters (conductivity, pH, alkalinity, Dissolved Organic Carbon: DOC, anions, major cations, and metal(loid)s concentrations) of river water were assessed in all fractions.Results showed decreasing concentrations of DOC, Fe, Al and REE in the conventionally dissolved fraction (< 0.22 μm) from upstream to downstream. Arsenic concentration increased from upstream to downstream, especially at the exit of the old mining zone, and was mainly present in the truly dissolved fraction. However, arsenic in the colloid fraction was about 40% upstream and showed a clear decrease when going downstream. Upstream, Fe and Al were mostly present in the colloidal fraction (around 90%, but decreased to 30% downstream for Al). REE patterns suggested that colloidal organic matter played a significant role in metal transport. This was also inferred from the greater enrichment in middle REE as compared to light and heavy REE; this difference in enrichment progressively disappeared with decreasing cut-off filter size. The concentration variations along the length of the river were found to be a combined effect of the changes in lithology and input of contaminants from storage areas or alluvial table.

Abundance of colloidal organic phosphorus in the Taiwan Strait

The Taiwan Strait is a coastal sea with dynamic hydrologic condition and dissolved organic matter (DOM) cycling. To better understand its phosphorus (P) transformation, phosphate and bulk dissolved organic phosphorus (DOP) concentrations were determined in the surface water of the Taiwan Strait during 2010 and 2011 summers. The bulk DOP was further fractionated into the low molecular weight (LMW) DOP and colloidal organic phosphorus (COP) with the application of the cross-flow ultrafiltration technique at a size cut-off of 10 kDa. The surface water in the Taiwan Strait generally showed higher bulk DOP concentration than phosphate excluding estuarine stations. This is similar to the surface waters in the subtropical gyres, implying a P-deficient condition in the Taiwan Strait. The LMW-DOP followed a constant permeation behavior in the ultrafiltration experiments, allowing the quantification of LMW-DOP and COP concentrations with the ultrafiltration permeation model. The average COP concentration was 0.044 ± 0.022 μmol/L and 0.042 ± 0.027 μmol/L during 2010 and 2011 summers, respectively. Accordingly, COP accounted for 35 ± 13% and 34 ± 16% of bulk DOP during 2010 and 2011 summers, respectively, suggesting a substantial occurrence of organic phosphorus in the colloidal fraction. The C/P ratio decreased from LMW-DOM to bulk DOM and to colloidal organic matter (COM), supporting the degradation pathway of bulk DOM from colloidal to LMW fractions and the lability of COP in the Taiwan Strait. The fractionation of C/P ratio between bulk DOM and COM in the Taiwan Strait, denoted by the fractionation factor (FC/D), was comparable to the open oceans, but significantly stronger than rivers and estuaries. It might indicate an autochthonous input and rapid turnover of bulk DOP pool in the Taiwan Strait in the context of low phosphate concentration. The FC/D also showed a spatial variability in the Taiwan Strait, high in the South China Sea Warm Current and upwelling occupied stations and low in inshore areas influenced by terrestrial input. This further supports the FC/D as an indicator of bulk DOM sources besides its application to decipher the diagenetic status of bulk DOM and biogeochemical cycles of bulk DOP in the coastal oceans.

Colloids facilitate cadmium and uranium transport in an undisturbed soil: A comparison of soil solution isolation methods

Accurate data of cadmium (Cd) and uranium (U) leaching are needed in the context of identifying their mass balances in agricultural soils. There is some controversy related to sampling methods and the contribution of colloid facilitated transport. Here, leaching was measured in undisturbed unsaturated soils and the impact of colloids was measured with due attention to solution sampling protocols. Soils were sampled in an arable, pH neutral silty loam soil. The columns (n = 8) were irrigated and PTFE suction plates (1 μm pores) at the bottom ensured unsaturated flow. New here is that both percolates and associated suction plates were collected, the elements in the plates were recovered with acid digestion and used as a lower estimate of colloidal forms. The fraction of elements collected in the plates were 33 % (Cd) and 80 % (U) of the total mobility (=percolates + plates), illustrating colloidal transport. Composition of pore water extracted by soil centrifugation varied largely between initial and final samples and showed that colloids increased as a result of reduced solution calcium after leaching two pore volumes with low calcium water. Flow Field-Flow Fractionation (FIFFF) of the pore water and percolates revealed co-elution of U with colloidal organic matter, oxyhydroxides and clay, illustrating colloidal transport of U by these vectors. Colloidal transport of Cd was less pronounced and was dominated by organic matter. Soil extracts with 0.01 M CaCl2 have lower colloid concentration and consequently underestimate mobile U. In contrast, Cd concentrations in 0.01 M CaCl2 extracts exceed that of percolates due to chloride complexation and higher calcium, mobilizing Cd. Soil leaching experiments better indicate potential leaching losses than a single pore water composition because the former yields the time integrated data. Suction plates and/or bottom filters need to be analysed in leaching studies to account for metal transport by colloids.

Virus infection of phytoplankton increases average molar mass and reduces hygroscopicity of aerosolized organic matter

Viral infection of phytoplankton is a pervasive mechanism of cell death and bloom termination, which leads to the production of dissolved and colloidal organic matter that can be aerosolized into the atmosphere. Earth-observing satellites can track the growth and death of phytoplankton blooms on weekly time scales but the impact of viral infection on the cloud forming potential of associated aerosols is largely unknown. Here, we determine the influence of viral-derived organic matter, purified viruses, and marine hydrogels on the cloud condensation nuclei activity of their aerosolized solutions, compared to organic exudates from healthy phytoplankton. Dissolved organic material derived from exponentially growing and infected cells of well-characterized eukaryotic phytoplankton host-virus systems, including viruses from diatoms, coccolithophores and chlorophytes, was concentrated, desalted, and nebulized to form aerosol particles composed of primarily of organic matter. Aerosols from infected phytoplankton cultures resulted in an increase in critical activation diameter and average molar mass in three out of five combinations evaluated, along with a decrease in organic kappa (hygroscopicity) compared to healthy cultures and seawater controls. The infected samples also displayed evidence of increased surface tension depression at realistic cloud water vapor supersaturations. Amending the samples with xanthan gum to simulate marine hydrogels increased variability in organic kappa and surface tension in aerosols with high organic to salt ratios. Our findings suggest that the pulses of increased dissolved organic matter associated with viral infection in surface waters may increase the molar mass of dissolved organic compounds relative to surface waters occupied by healthy phytoplankton or low phytoplankton biomass.

Boosting butyrate and hydrogen production in acidogenic fermentation of food waste and sewage sludge mixture: a pilot scale demonstration

Within the urban scenario, the application of a biorefinery technology value chain can foster the conversion of different organic substrates into marketable and added-value products. In this work, a pilot-scale dark fermentation (DF) process has been carried out as a key step for volatile fatty acids (VFA) and hydrogen production from the liquid fraction of sewage sludge and food waste mixture. Six operating conditions have been monitored in terms of yield and process stability, by changing the hydraulic retention time (HRT) from 4 to 6 days and applying a short-term hyper-thermophilic hydrolysis (70 °C, 8 h) on the same feedstock mixture. A tubular centrifugation was utilized to remove part of the biosolids (driven to biogas production) before the DF step, which was applied on the soluble and/or colloidal organic matter only. The hydrolysis step favored the following acidification process, in which a fermentation yield up to 0.42 g CODVFA/g VS0 was achieved at 5 days as HRT. Hydrogen production (up to 34.4% v/v and 0.046 m3 H2/kg VS0) was positively affected by the hydrolysis application and by the decrease of the HRT, highlighting the possibility to produce biohythane in the modeled two-phases anaerobic bioprocess. On the other hand, without the application of the hydrolysis, a selective production of butyric acid (up to 75% COD basin) was achieved, furnishing a different valorization route for the chosen urban organic feedstock. Changes in operating conditions and performances were also reflected by the adaptation of the microbial community, whose characterization highlighted the occurrence of several fermentative microorganisms (e.g., Clostridiaceae, Ruminococcaceae).

Coupled flow and transport modelling of a large-scale in situ migration experiment with 14 C-labelled natural organic matter colloids in Boom Clay

Abstract Twenty-five years ago, a unique long-term and large-scale in situ experiment with 14 C-labelled natural organic matter (NOM) was set up at the HADES underground research facility in Mol (Belgium) to study its migration behaviour. Natural organic matter plays an important role in the mobility of various safety-relevant radionuclides, which is critical in the context of Safety &amp; Performance Assessment (SA/PA) calculations for a possible nuclear waste repository. The objective of this work is to enlarge the confidence in current NOM transport models by validating them with the in situ experiment, which is still continued to this day. Stepwise adding more complexity to the model resulted in a 10-parameter model with which excellent fits to the data are obtained. The model considers two different fractions that are transported by advection and diffusion and can be subject to both irreversible and reversible immobilization processes. The associated fitted parameter values compare well with values determined on small-scale migration experiments. This builds confidence in the NOM transport model, which in turn contributes to the confidence in the outcome of the radionuclide migration calculations performed in the context of SA/PA. These results again highlight the incredible value of such long-running experiments at underground research facilities like HADES.

Influence of colloidal iron oxide and natural organic matter fouling on nanofiltration membrane performance: role of feed composition and membrane properties

Iron oxide colloids and natural organic matter in the presence of divalent cations cause irreversible fouling for commonly used drinking water nanofiltration membranes.

Composition of Colloidal Organic Matter in Phytoplankton Exudates

The colloidal organic matter (COM) was isolated from the exudates of three cultured phytoplonkters, namely the chlophyte nanoflagellate Tetraselmis sp., the diatom Chaetoceros socialis and the dinoflagellate Prorocentrum minimum, from the Gulf of Trieste (northern Adriatic Sea). The isolation of COM was performed by ultrafiltration with molecular weight cut-off membranes of 5 kDa and final desalinisation by dialysis. The composition of the COM was characterised using C elemental analysis and 1H NMR spectroscopy and compared with COM isolated from a marine sample from the same area (Gulf of Trieste). By using 1H NMR spectroscopy, it was possible to semi-quantitatively determine the concentrations of the main biochemical constituents present in the COM samples. The results showed that the phytoplankton COM was predominantly composed of polysaccharides, with minor contributions from proteins and especially lipids. Therefore, the phytoplankton COM mainly contributes to the marine COM pool in the polysaccharide fraction and less in the protein and lipid fractions.

Passive water sampling and air–water diffusive exchange of long-range transported semi-volatile organic pollutants in high-mountain lakes

The concentrations of legacy and currently emitted organic pollutants were determined in the freely dissolved phase of water from six high-mountain lakes in the Pyrenees (1619–2453 m) by passive water sampling. Low-density polyethylene (LDPE) and silicone rubber (SR) sheets were exposed for three consecutive periods lasting each one year between 2017 and 2020 for the study of polychlorinated biphenyls (PCBs), organophosphate esters (OPEs), polycyclic aromatic hydrocarbons (PAHs), and other organochlorine compounds (e.g., hexachlorobenzene, HCB). HCB concentrations (1.0–14 pg L−1) remained essentially the same as those measured with pumping systems over two decades ago in the same area. ƩPAHs (35–920 pg L−1) were around half of those observed in the past, which agrees with reductions in European atmospheric emissions. ƩPCB concentrations (1.2–2.2 pg L−1) were substantially lower, although unexpectedly large differences could be due to comparing yearly averages from the present study to seasonally variable (i.e., affected by snowmelt, stratification, and colloidal organic matter) episodic pumping measurements from previous studies. ƩOPEs (139–2849 pg L−1) were measured for the first time in this area and were found at high concentrations in some sites. Concentrations of most compounds obtained with LDPE and SR samplers agreed with each other by ratios generally lower than three or four times, except for a few PAHs and OPEs. Diffusive exchange flux calculations between the atmospheric gas phase and the freely dissolved water phase revealed net deposition of pollutants from air to water, except for some OPEs and PCBs presenting equilibrium conditions, and HCB with volatilization fluxes. Atmospheric degradation fluxes of PAHs and OPEs pointed at competing removal mechanisms that support the air-to-water direction of their diffusive exchange, while PCBs and organochlorines were not affected by photodegradation. In their current state, these remote lakes accumulate many emerging and legacy pollutants subject to long-range atmospheric transport.

Characteristics of dissolved organic matter in urban road runoff under different traffic densities in Beijing, China.

The characteristics of dissolved organic matter (DOM) in road runoff under different traffic densities were compared using resin fractionation, molecular weight distribution analysis, three-dimensional excitation-emission matrix fluorescence spectroscopy, and UV-visible spectroscopy. Heavy traffic density strongly increased the concentration of DOM in road runoff, resulting in higher dissolved organic carbon. The distribution of molecular weights in DOM was not influenced by the traffic. DOM was dominated by colloidal organic matter with molecular weight in the 1kDa to 0.45μm size range. Hydrophobic fractions accounted for a large proportion than hydrophilic fractions in DOM, and hydrophobic acids increased with higher traffic density. Traffic density did not alter the fluorescent substances in DOM, including fulvic-like UV fluorescent substances and protein-like substances. However, more tryptophan-like protein substances were found in DOM from road runoff with heavy traffic. Moreover, the aromatization degree of DOM was not affected by heavy traffic, while the degree of humification decreased.

Efficient direct membrane filtration (DMF) of municipal wastewater for carbon recovery: Application of a simple pretreatment and selection of an appropriate membrane pore size

Considerable attention has been paid in recent years to the recovery and effective utilization of organic matter in municipal wastewater for the establishment of a circular economy. Direct membrane filtration (DMF) of municipal wastewater using microfiltration (MF) or ultrafiltration (UF) membranes to retain and concentrate the organic matter in municipal wastewater could be a practical option for this purpose. However, severe membrane fouling and high concentrations of organic matter remaining in the DMF permeate are concerns to be addressed. Application of a simple pretreatment using fixed biofilms was investigated to address these issues. In this study, experiments were carried out at an existing municipal wastewater treatment plant. A moving bed biofilm reactor (MBBR) process operated under a very short HRT of 1 h and DO concentration of 0.5 mg/L selectively degraded low-molecular-weight dissolved organic matter in municipal wastewater without degradation of membrane-recoverable suspended and colloidal organic matter. Application of the pretreatment did not reduce the amount of organic carbon recovered by DMF using an MF membrane (approximately 70% of the influent COD being recovered), while it dramatically mitigated the membrane fouling probably due to the alteration of characteristics of dissolved organic matter in wastewater. The pretreatment also reduced the concentration of organic matter in the DMF permeate by 41%: COD concentration in the DMF permeate was as low as 40 mg/L. With the established MBBR pretreatment, performances of MF (0.1 µm) and UF (molecular weight cut-off: 150,000) membranes for DMF were compared in parallel. It was found that the increase of the recoverable amount of organic matter by using UF was marginal (about 5%), whereas fouling in UF was much more severe than that in MF. The severe fouling in UF was caused by inorganic colloids such as FeS that could pass through MF membranes but be retained by UF membranes. Based on the results obtained in this study, it is concluded that MF is more suitable than UF for efficient DMF.

Enhanced organic degradation and biogas production of domestic wastewater at psychrophilic temperature through submerged granular anaerobic membrane bioreactor for energy-positive treatment

This study deals with the conversion of organic matter into methane at ambient temperature, during anaerobic digestion of domestic wastewater combined with a submerged ultrafiltration membrane with no gas-sparging. A one-stage submerged granular anaerobic membrane bioreactor (G-AnMBR) and a control anaerobic digester (UASB type) were operated during four months, after 500 days of biomass acclimatization to psychrophilic and low loading rate conditions. Membrane barrier led to the retention of biomass, suspended solids and dissolved and colloidal organic matter which greatly enhanced total COD (tCOD) removal (92.3%) and COD to methane conversion (84.7% of tCOD converted into dissolved and gaseous CH4). G-AnMBR overcame the usual long start-up period and led to a higher sludge heterogeneity, without altering the granular biomass activity. The feasibility of the G-AnMBR without gas-sparging was also assessed and the net positive energy balance was estimated around + 0.58 kWh.m−3.

Contact stabilization process for hospital wastewater treatment: effects of colloidal organic matter

Abstract In this study, the treatability of hospital wastewater was investigated using a contact stabilization process on a laboratory scale. A detention time of one hour was selected for sludge settling and separation of treated effluent, and removal efficiency was measured at contact times of 30, 60, and 90 min, and stabilization times of 4.5 and 5.5 h. Based on the different detention times, 6 series of experiments were designed. Results showed that after an initial rapid COD removal in the first 30 min, COD values fluctuate in the time range of 30–90 min. However, in the case where COD values reduce in the second stage, this recovery is negligible; thus, the time of 30 min is considered as the optimal detention time for the contact reactor. Sludge volume index (SVI) values of 119.20 and 109.17 mL/g were obtained for stabilization times of 4.5 and 5.5 h, respectively. Therefore, the longer the stabilization time, the closer the SVI is to 100 mL/g. Moreover, lower settled sludge volume (SSV) value at 5.5 h of stabilization shows better characteristics compared to 4.5 h of stabilization. Furthermore, COD removal efficiency at the optimum contact time is higher when 5.5 h is selected for stabilization.

Past fires and post-fire impacts reconstructed from a southwest Australian stalagmite

Speleothem records of past environmental change provide an important opportunity to explore fire frequency and intensity in the past, and the antecedent climatic conditions leading to fire events. Here, fire sensitive geochemical signals in a stalagmite from Yonderup Cave, a shallow cave in Western Australia, are compared to well-documented wildfire events that occurred in recent decades. The results are extended to identify wildfires during the growth interval of the speleothem (1760 CE–2005 CE). Principal component analysis of the stalagmite time-series revealed distinct peaks in a combination of phosphorus and metal (aluminium, zinc, copper and lead) concentrations in response to known fire events, which are interpreted to have come from ash. Varying responses in the geochemical signal in the pre- and post-European colonisation period are likely linked to changes in land management, fire frequency and fire intensities. Of note is what we infer to be a particularly intense fire event concluded to have occurred in 1897 ± 5 CE, which climate sensitive proxies (δ18O and bedrock-derived elements) indicate was preceded by a multi-decadal dry period that began in the late 1860s. The intensity of the deduced fire event is supported by a peak in P that is 6.3 times higher than elsewhere in the speleothem, accompanied by a peak in Zn. It was also inferred that changes to the surface-cave hydrology occurred as a result of this event, indicated by increased input of colloidal organic material onto the stalagmite that was interpreted to be caused by shallow karst bedrock fracturing from the heat-induced deformation that is observed after intense fires. These findings show the potential for speleothems to provide dated records of fire intensity and recurrence intervals. Further development could lead to a better understanding of the climate-fire relationship and the effects of land-management practices on wildfire frequency and intensity.

Impact of Pre-Ozonation during Nanofiltration of MBR Effluent.

This study aimed to investigate the impact of real MBR effluent pre-ozonation on nanofiltration performances. Nanofiltration experiments were separately run with non-ozonated real MBR effluent, ozonated real MBR effluent and synthetic ionic solution mimicking the ionic composition of the real MBR effluent. The specific UV absorbance and the chemical oxygen demand were monitored during ozonation of real effluent, and the mineralization rate was calculated through the quantitative analysis of dissolved organic carbon. The membrane structure was characterized using SEM on virgin and fouled membrane surfaces and after different cleaning steps. The results confirm the low effect of the ozonation process in terms of organic carbon mineralization. However, the chemical oxygen demand and the specific UV absorbance were decreased by 50% after ozonation, demonstrating the efficiency of ozonation in degrading a specific part of the organic matter fraction. A benefic effect of pre-ozonation was observed, as it limits both fouling and flux decrease. This study shows that the partial mineralization of dissolved and colloidal organic matter by ozonation could have a positive effect on inorganic scaling and decrease severe NF membrane fouling.