Degradation Of Humic Substances Research Articles

Removal of dissolved organic matter (DOM) from water with activated carbon and effective microorganisms

Humic substances (HS) cause problems in water purification because of disinfection by-product (DBP) formation during chlorination. The efficiency of activated carbon (AC) adsorption as a method in drinking water treatment has been investigated in removing HS at different pH values (pH = 5; 6; 7; 8) in static equilibrium experiments. The degradation of HS was studied with an EM (effective microorganisms) bacteria community, and solutions of fulvic acid, sodium humate furthermore extracts of sandy soil were investigated. EM products are widely used but their effect on HS has not been investigated before. The combination of EM and AC methods in the case of fulvic acid resulted in higher performance than any of these methods alone. Humic substances were analyzed using a UV–VIS spectrophotometer and by total organic carbon (TOC) measurements. The carbon/nitrogen ratio was also determined, which enabled conclusions to be made for the nutrient supply. According to these results the degradation was efficient, especially in fulvic acid solutions.

Evaluation of photocatalytic degradation of a commercial humic acid in water using a simulated solar UV irradiation and monitoring the changes by size exclusion chromatography

Much research has been undertaken on the photocatalytic degradation of humic substances with titanium dioxide using commercial humic acids (HA), which are extracts from either peat or coal. Most of the research has been focused on the changes in dissolved organic carbon (DOC) and UV254 absorption. These parameters only give a general assessment. This work studies the changes in the physical and structural properties of a commercial humic acid by size exclusion chromatography with DOC and UV254 absorption detection (SEC-DOC, SEC-UV254), and the evolution of halogenated organic compounds (AOX) and trihalomethanes (THMs) during the photocatalytic degradation with simulated solar UV irradiation and Degussa P-25 TiO2. These changes are compared with those reported for natural organic matter (NOM). The photodegradation of commercial HA and NOM proceeds in a similar and sequential manner, initially with the preferential adsorption of larger molecules, then the degradation of these larger molecular size fractions and proceeding towards smaller molecular size fractions, while decreasing THMs and AOX formation potential.

Significant decomposition of riverine humic-rich DOC by marine but not estuarine bacteria assessed in sequential chemostat experiments

Humic substances (HS) are the most abundant natural organic compounds in aquatic and terrestrial environments. However, the bacterial degradation of HS in the estuarine salinity gra- dient and in coastal regions as a sink for HS, entering the open sea, is not well understood. Therefore, we studied the bacterial degradation of humic-rich dissolved organic carbon (DOC) at increasing salinities between 1 and 30 in an estuary of the southern North Sea (Weser). Three-stage chemostats, inoculated with natural brackish (salinity 5 and 15) and coastal marine (salinity 30) bacterial commu- nities fed 0.1 µm filtered natural humic-rich freshwater adjusted to the respective salinity, were run for up to 51 d at dilution rates of 0.1 and 0.15 d -1 . DOC concentrations, bacterial numbers, and pro- duction were assessed in each stage over the incubation time. In addition, the fulvic acid (FA), humic acid (HA), and hydrophilic acid (HPA) fractions of the HS were determined by XAD fractionation. At a salinity of 30, the humic-rich DOC was decomposed to more than 60%, whereas in the other 2 experiments at salinities of 15 and 5, no detectable decomposition occurred. At the highest salinity condition, all 3 HS fractions were reduced substantially, whereas at a salinity of 5, only the HA and HPA fractions decreased, and at 15, only the HA fraction decreased. In the latter experiments, con- centrations of the FA and HPA fractions in some chemostat stages increased despite unchanged DOC concentration. Our study provides evidence that the main bacterial decomposition, i.e. conversion into bacterial biomass and remineralization, of humic-rich DOC occurs in the polyhaline estuarine region and that at lower salinities, only some transformation of the humic fractions takes place, mod- ifying the adsorptive properties of the HS, but no bacterial DOC decomposition occurs. The sequen- tial chemostats were a useful approach to study the complex process of bacterial HS decomposition.

Determination of the apparent rate constants of the degradation of humic substances by ozonation and modeling of the removal of humic substances from the aqueous solutions with neural network

In this study, the degradation rate constants of humic substances by ozonation under the different empirical conditions such as ozone-air flow rate, ozone generation potential, pH, temperature, powdered activated carbon (PAC) dosage and HCO 3 − ions concentration were determined. The ozonation of humic substances in the semi-batch reactor was found to fit pseudo-first-order reaction. The values of apparent rate constant of humic substances degradation increased with the increase of initial ozone-air flow rates, ozone generation potential, pH, temperatures and PAC dosage, but decreased with the increase of HCO 3 − concentration of the solution. Using Arrhenius equation, the activation energy ( E a) of the reaction was found as 1.96 kJ mol −1. The reaction of ozonation of humic substances under the different temperatures was defined as diffusion control according to E a. The model based on artificial neural network (ANN) could predict the concentrations of humic substances removal from aqueous solution during ozonation. A relationship between the predicted results of the designed ANN model and experimental data was also conducted. The ANN model yielded determination coefficient of ( R 2 = 0.995), standard deviation ratio (0.065), mean absolute error (4.057) and root mean square error (5.4967).

The Degradtion of Humic Substance using Continuous Photocatalysis Systems

Photocatalytic oxidation is an emerging technology in water and wastewater treatment. Photocatalysis often leads to complete degradation of organic pollutants without the need for chemicals. This study investigated the degradation of humic substances in water using photocatalysis systems coupled with physio‐chemical processes such as adsorption and/or flocculation. Dissolved Organic Carbon (DOC) removal of PAC‐TiO2 was improved by a factor of two to three times compared with TiO2 alone. Solid Phase Micro Extraction (SPME)/Gas Chromatograph (GC) flame ionisation detector (FID) was used to investigate intermediates of photocatalytic oxidation in a batch reactor with TiO2 alone and with powder activated carbon (PAC) with TiO2. GC peaks showed that PAC‐TiO2 adsorbed some by‐products which were photo‐resistant and prevented the reverse reaction that occurred when TiO2 was used alone. The two other types of photocatalytic reactors used were the continuous photocatalytic reactor and recirculated photocatalytic reactor. The results show that the recirculated reactor had the highest efficiency in removing organic matter in a short photo‐oxidation (detention) time of less than 10 min. The use of PAC‐TiO2 in recirculated continuous reactor resulted in 80% removal of organic matter even when it was operated for a short detention time and allowed the use of a smaller dose of TiO2.

Electrolytic degradation of biorefractory organics and ammonia in leachate from bioreactor landfill

Electrochemical oxidation was applied to treat the effluent from bioreactor landfill with leachate recirculation, characterised as poor biodegradability and high NH3-N concentration. In this study, the effluent was electrolysed in a batch reactor with Ti/TiO2-IrO2-RuO2 anode and stainless steel cathode. The oxidation of dissolved organic matter (DOM) during electrolysis was evaluated based on the evolution of molecular weight grade, hydrophilic fractionation (humic acid, fulvic acid and hydrophilic fractions), specific ultraviolet absorbance (SUVA254) and AOX. The impact of the initial NH3-N concentration on the oxidation was discussed. The results showed that at a current density of 100 mA/cm2, electrolysis time of 1.5 h and electrode gap of 1 cm, NH3-N with an initial concentration of 1.2 g/L could be completely eliminated and 56% of COD with an initial concentration of 1.2 g/L could be removed, which illustrated that the electrolysis-produced chlorine preferentially oxidised ammonia. The electrolysis mainly resulted in the degradation of humic substances and other high molecular DOM, followed by the increase of BOD/COD ratio and decline of SUVA254 of the leachate. The current efficiencies for COD and ammonia oxidation gradually decreased during the electrolysis, with the latter obviously higher than the former. At the optimal electrolysis time of 1.5 h, NH3-N could be totally removed and the BOD/COD ratio could be enhanced to 0.3, which was also favourable to control the AOX at a reasonable level.

Adsorbability and photocatalytic degradability of humic substances in water on Ti-modified silica

From the viewpoint of development of a removal agent for humic substances, we prepared Ti-modified silica gel, SiO 2–Ti, from titanium alkoxide and microsized silica gel. The prepared silica agent was investigated in adsorption and photocatalytic degradation of humic substances in water. In these experiments, four humic substances, commercially available Wako humic acid (Wako-HA), Nordic aquatic humic acid (Nordic-HA), Nordic aquatic fulvic acid (Nordic-FA), and Suwannee river fulvic acid (Suwannee-FA), were used, and Freundlich constants ( K F and 1 / n ) and photodegradation rates were evaluated. Wako-HA, which has the highest aromaticity ratio [Ar–OH]/[COOH] and molecular weight, had the highest adsorbability ( K F = 17.5 ( mg / g ) ( L / mg ) 1 / n , 1 / n = 0.67 ) but the lowest photodegradability (<80%). On the other hand, Suwannee-FA, which has the lowest aromaticity, [Ar–OH]/[COOH] ratio, and molecular weight, afforded lesser adsorbability ( K F = 7.1 ( mg / g ) ( L / mg ) 1 / n , 1 / n = 0.39 ) but the highest photodegradability (>99%). Nordic-HA and Nordic-FA afforded adsorbabilities similar to that for Suwannee-FA, and medium photodegradabilities between those for Wako-HA and Suwannee-FA. Adsorption and photodegradation capacities of SiO 2–Ti were improved with increased Ti content and phosphorescence emission amount, respectively. From XRD analysis, we found that the structure of anatase-type TiO 2 features the Ti modifiers of SiO 2–Ti. Therefore, humic substance molecules effectively interact with the Ti modifiers and are decomposed by OH radicals generated in situ. We hope that SiO 2–Ti will be used as a photodegradation catalyst in water purification plants.

A comparative study on the photocatalytic degradation of humic substances of various origins

The photocatalytic removal of model humic and fulvic acids of different origins (terrestrial and aquatic) was investigated using TiO 2 Degussa P-25 as the photocatalyst. The results were presented comparatively based on pseudo-first-order and the Langmuir-Hinshelwood kinetic models. The reaction rates calculated for the UV-vis parameters follow the general trend: IHSS soil humic acid > Aldrich humic acid > IHSS humic acid > Roth humic acid > IHSS fulvic acid. However, the rate constants show differences depending on the UV-vis absorption parameters. The evaluation of the Langmuir-Hinshelwood kinetic model reveals that, in all cases, Roth humic acid has the lowest Langmuir-Hinshelwood rate, rate constant and adsorption coefficient, and the ordering of the rates follows the same trend with that of pseudo-first order. Furthermore, data related to the molecular size distribution profiles of raw and treated humic acids suggest that the photocatalytic degradation occurs irrespective of the molecular size fractions.

Effects of UV-B radiation on molecular weight distribution and fluorescence from humic substances in riverine and low salinity water

Light degradation is very likely an important removal process for humic substances (HS) in the aquatic environment, and thus of importance for the cycling of organic carbon. For this reason, laboratory experiments under artificial conditions using UV-B radiation (λ max =313 nm) , to study light degradation of HS were carried out on natural untreated Baltic Sea water samples and, for reference, on humic (HA) and fulvic acid (FA) isolates from the Göta River. During these experiments, the molecular weight distribution, fluorescence, UV-absorbance and total organic carbon concentration were monitored over a period of 3 weeks. In the natural seawater samples the higher molecular weight part was more easily degraded than the lower molecular weight part. The results indicate that FA and HA were more resistant towards UV-B irradiation than natural seawater. Irradiation caused formation of lower molecular weight substances in the case of FA and HA whereas for natural seawater this process was less obvious.

Utilization and transformation of aquatic humic substances by autochthonous microorganisms.

Aquatic humic substances (HS) from a bog lake water, a riverwater, and a groundwater were isolated after enrichment on XAD 8 columns and added to a Czapek-Dox nutrient broth which was used either in full strength or without glucose and/or NaNO3. The individual flasks were inoculated with natural microbial populations of corresponding water samples or with a Pseudomonas fluorescens strain isolated from groundwater. The presence of HS resulted in an increase of bacterial numbers in nearly all cultures incubated for 3 weeks at 25 degrees C on a shaker. HS reisolated from cultures without glucose or NaNO3 showed no or only minor quantitative differences as compared to those from sterile controls. In full strength nutrient broth up to 27% of HS were utilized. Data obtained by spectroscopic methods (UV/vis/FTIR) and elemental analysis indicated a decrease in particle size and a loss in aromaticity and aliphatic carbon in HS reisolated from the microbial cultures. Simultaneously an increase in the N content of HS was observed, which probably originated from some constituents of microbial biomass such as proteins and amino sugars. The NMR data also documented that significant transformations of HS occurred in the individual microbial cultures. After incubation, increased amounts of aromatic acids were detected in some liquid media and residual HS by GC/MS or capillary electrophoresis. 1H NMR spectroscopy was less effective in indicating structural differences in the HS than 13C NMR but revealed considerable detail of the microbial degradation of riverine HS, when limited sample was available. The newly developed NMR increment analysis provided substantial detail of aromatic structures in a microbially altered HS. The microbial degradation of HS strongly depended on the composition of the HS, the species selection of the microorganisms, and to a lesser extent on the culture conditions. For any series of identical inoculum and HS, full broth media initiated the most extensive alteration of HS.

Electrochemical degradation of humic acid

The treatment of natural water for drinking water production goes through the degradation of humic substances. In this study, humic acid, extracted from a peat area located at the margins of the Mogi Guaçu River at São Paulo State, Brazil, was used to perform electro-oxidation essays in order to evaluate the possibilities of electrochemical methods in the degradation of humic substances. The working electrodes were dimensionally stable anodes (DSA) type with the following compositions: Ti/Ir 0.3Ti 0.7O 2; Ti/Ru 0.3Ti 0.7O 2; and Ti/Ir 0.2Ru 0.2Ti 0.6O 2. The electrolyses were performed by using a solution composed of an electrolyte support (0.1 mol l −1 KCl) and 30 mg l −1 of the humic acid. Samples were taken during the electrolyses and analysed by the pH, transmittance, UV-vis spectra and chromatography. The results show that the Ti/Ru 0.3Ti 0.7O 2 electrode presents the best performance considering the elimination of most of the electro-oxidation products after approximately 2 h of electrolysis at 40 mA cm −2.

Source indicators of humic substances: an elemental composition, solid state 13C CP/MAS NMR and Py-GC/MS Study

Humic substances (HS) isolated from swamp water, surface soil, peat and brown coal were characterized using elemental composition, solid state 13C CP/MAS NMR and Py-GC/MS analysis. A substantial amount of information with regard to the source, maturity, depositional environment and degree of degradation of humic substances was obtained. The elemental composition, atomic ratio, 13C NMR spectra and Py-GC/MS results indicated that vascular plant matter is the main contributor to humic substances. Humic substances from swamp water and from soil in the surrounding area of the swamp were found to be identical, suggesting that the swamp humic substances are derived from surrounding soils. Humic substances from brown coal were characterized by a higher degree of humification, including loss of polysaccharides, degradation in lignin content and increase in aromaticity. Compared with humic substances from brown coal, the humic substances from peat showed a lower degree of humification and were considerably more aliphatic in nature.

Soil management system effects on size fractionated humic substances

The humic substances (HS) of two Brazilian Oxisols, one under native grassland (NG) and the other submitted to a long-term (19-year) tillage systems experiment including no-tillage (NT), minimal tillage (MT) and an adjacent eucalyptus-planted forest (F), were extracted with sodium pyrophosphate, analysed and fractionated by exclusion chromatography on controlled pore glass (CPG). Chromatographic analysis of HS was performed at 400 nm (visible region), the resulting chromatograms deconvoluted and statistical analysis of data made using multivariate methods (factor and Pearson correlation analysis). Increase of tillage intensity, estimated by factor analysis, resulted in a general HS content decrease, not affecting soil C content. Tillage increased the relative proportion of small molecular size HS, determined directly by CPG and indirectly by the relative increase of fulvic acids (FA) content (increase of fulvic acids/humic acids ratio). This suggests that tillage caused preferential degradation of large molecular size HS and/or a neo-synthesis of small HS due to increased fresh-carbon input partially induced by liming and fertilisation. The HS fractionation method on CPG permitted gray humic acids (GHA) separation into two distinct fractions. The larger molecular size fraction showed an unusual high E 4/E 6 ratio, possibly due to a small conjugation of aromatic rings.

Photochemical release of biologically available nitrogen from aquatic dissolved organic matter

DISSOLVED organic material in marine and freshwater ecosystems constitutes one of the Earth's largest actively cycled reservoirs for organic matter1. The bacterially mediated turnover of chemically identifiable, low-molecular-mass components of this pool has been studied in detail for nearly three decades, but these compounds constitute less than 20% of the total reservoir2. In contrast, little is known about the fate of the larger, biologically more refractory molecules—including humic substances—which make up the bulk of dissolved organic matter. Here we report results from bacterial bioassays and photochemical studies indicating that exposure to sunlight causes dissolved organic matter to release nitrogen-rich compounds that are biologically available, thus enhancing the bacterial degradation of humic substances. We demonstrate that ammonium is among the nitrogenous compounds released and is produced most efficiently by ultraviolet wavelengths. Photochemical release of ammonium from dissolved organic matter has important implications for nitrogen availability in many aquatic ecosystems, including nitrogen-limited high-latitude environments and coastal oceans, where inputs of terrestrial humic substances are high.

A degradation procedure for determination of halogenated structural elements in organic matter from marine sediments

This study showed that an oxidative degradation method originally developed to study lignin structures can be used to investigate the presence of halogenated structures in high-molecular-weight organic matter from marine sediments. When the sediment sample itself, or the organic matter isolated from the sediment, was properly desalted prior to the degradation, remaining halides did not cause any halogenation reactions that interfered with the analysis of halogenated phenolic structures. Gas chromatography — atomic emission detection (GC-AED) and gas chromatography - mass spectrometry (GC-MS) analyses of degraded and methylated organic matter from Baltic Sea sediments showed that chlorinated, brominated, and iodinated analogues of 4-ethoxybenzoic acid methyl ester were present in all analysed samples. The chlorinated species have previously been identified upon degradation of humic substances from unpolluted freshwaters. The identification of brominated and iodinated structural elements represents the first indication of a large-scale bromination and iodination of high-molecular-weight organic matter in marine environments.

Degradation of humic substances by UV irradiation

Aqueous solutions of humic substances (humic and fulvic acids) were irradiated with light at λ = 254 nm followed by analyses of total organic carbon (TOC), ultraviolet (UV) absorbance and molecular weight distribution. A degradation of the dissolved humic compounds by up to 50% after 6 h was observed. The average molecular weight decreased (from 1800 to approx. 300) as well as the UV absorbance of the remaining organic fraction. Low molecular weight organic acids were formed during the irradiation and tentatively identified by capillary electrophoresis (formic, acetic, succinic, and oxalic acids). The low molecular organic acids continued to degrade by further irradiation; the loss of TOC is assumed to be due to CO 2 formation. Indications of a large-scale photo degradation process in nature was observed as a seasonal variation of the ratio humic substances/TOC related to the length of the day. Weekly sampling and analysis of UV absorbance and TOC in the Kalix River in northern Sweden indicate a higher humic fraction of the TOC during winter (dark period) than during summer.

Photochemical aspects related to humic substances

Dissolved humic substances (HS) show yellow color and relatively strong absorption in the UV range [ a(254 nm) ca. 0.04 cm −1 for c (DOC)= 1 mg/L]. This is the basis for photochemical reactions in the photic zone of aquatic systems and in water treatment using UV sources. Even though understanding the mechanisms involved in the energy transfer and the resulting reactions is hampered by the poorly defined structure of HS, reliable information has been gathered on some typical aspects of their photochemistry. The luminescence of HS can be influenced and partly quenched by molecular interactions with other water constituents (e. g., heavy metals and organic micropollutants). The presence of oxygen may lead to the sensitized production of singlet oxygen ( 1O 2), that can react specifically with substances containing diene structures or low valent sulfur. Because of the presence of these structures in HS, humic molecules will also react with the sensitized products. As a consequence, their biological, chemical, and physical properties are influenced. In addition, HS have a significant impact on the photochemical treatment of organic micropollutants in water. This has to be kept in mind when using photochemical steps for water treatment. The results from model experiments reflecting the conditions in surface water and in water treatment are given and discussed. In the presence of H 2O 2, irradiation led to a transformation and partial degradation of HS. The rate of photochemical degradation of pesticides (e. g., atrazine) was decreased in the presence of HS. Fe and Mn quenched the luminescence. From this, a decrease of excited states of HS for sensitizing reactions can be deduced. The results suggest the manyfold and significant influences of HS on the photochemistry of aquatic systems.

Solar UV‐light penetration and photodegradation of humic substances in peaty lake water

The in situ photodegradation of aquatic humic substances by underwater UV light (300–400 nm) in peaty lake water was studied. The photodegradation of aquatic humic substances (HS) occurred at depths where UV light with wavelengths &lt;320 nm can penetrate. The daily photodegradation rate of aquatic HS under a cloudless summer sky in the northern Netherlands appeared to be of the same order of magnitude as that of the mean daily pelagic photosynthetic fixation of dissolved inorganic C in typically oligotrophic humic lakes. However, the measured UV degradation of aquatic HS on a yearly basis is small compared to the approximate annual primary production of temperate lake phytoplankton (8%) and submerged macrophytes (3%) under fertile conditions. The measured UV‐light‐driven HS degradation implies a higher turnover of organic C in humic lakes than believed so far.

Humic substances, a possible source of environmental goitrogens

The by-products of humic substances (HS), resorcinol, orcinol, phloroglucinol, pyrogallol, 3,4- and 3,5-dihydroxybenzoic acids, and ortho- and meta-phthalic acids, have been tested for antithyroid and goitrogenic activities. By two in vitro assays all compounds, except the phthalic acids, were potent inhibitors of the thyroid peroxidase enzyme, and of thyroidal 125I uptake and/or its incorporation into thyroid hormones using thyroid slices. Resorcinol in drinking water was goitrogenic as indicated by in vivo assay in rats. These findings, the identification of resorcinol in the water supply of an endemic goiter district in western Colombia, where increased goiter prevalence is associated with watersheds rich in organic matter, and results of elemental analysis of goitrogenic water extracts from the same district showing a composition similar to that of aquatic HS, suggest that HS degradation by-products may play an important role in the etiology of endemic goiter.

Chemical and GC-MS characterization of marine dissolved lipids

The chloroform-extractable ‘lipid’ fraction of dissolved organic matter in seawater was analyzed by gravimetry, liquid chromatography, gas chromatography (GC), and gas chromatography—mass spectrometry (GC—MS). Gravimetric concentrations of dissolved lipids in the Gulf of Mexico were in the range of 60–160 μg 1 −1 in near-surface waters and 61–116 μg 1 −1 in near bottom waters and accounted for ∼4% of the dissolved organic carbon. Over a 12-h sampling period and a 5-d sampling period extensive variability in dissolved lipid quantity and quality were observed. The major percentage of extractable weight was collected in the polar liquid chromatographic fraction (55–95%). Gas chromatographic concentrations of the aliphatic fractions were in the range of 0.014-0.187 μg 1 −1. Concentrations derived from gas chromatography were consistently lower than gravimetrically-derived concentrations. A number of compounds were tentatively identified by a combination of GC, GC—MS, and authentic standards. The major components of the analyzable dissolved lipids were n-alkanes (C 16C 32), pristane, phytane, methyl, ethyl and propyl esters of fatty acids. Minor components included olefins and cycloalkanes, aromatics, short-chained acids, and possibly a lactone and an alcohol. All concentrations and compounds were indicative of a fairly pristine environment. The n-alkane distribution appears to be the result of marine and terrestrial inputs superimposed on a chronic low-level background of oil pollution. It is suggested that the fatty acid esters and other fragment molecules are the résult of the degradation of humic substances. A number of potential indicators of source were isolated.