Organic Carbon Removal Rate Research Articles

Propham mineralization in aqueous medium by anodic oxidation using boron-doped diamond anode: Influence of experimental parameters on degradation kinetics and mineralization efficiency

This study aims the removal of a carbamate herbicide, propham, from aqueous solution by direct electrochemical advanced oxidation process using a boron-doped diamond (BDD) anode. This electrode produces large quantities of hydroxyl radicals from oxidation of water, which leads to the oxidative degradation of propham up to its total mineralization. Effect of operational parameters such as current, temperature, pH and supporting electrolyte on the degradation and mineralization rate was studied. The applied current and temperature exert a prominent effect on the total organic carbon (TOC) removal rate of the solutions. The mineralization of propham can be performed at any pH value between 3 and 11 without any loss in oxidation efficiency. The propham decay and its overall mineralization reaction follows a pseudo-first-order kinetics. The apparent rate constant value of propham oxidation was determined as 4.8×10 −4 s −1 at 100 mA and 35 °C in the presence of 50 mM Na 2SO 4 in acidic media (pH: 3). A general mineralization sequence was proposed considering the identified oxidation intermediates.

TiO 2 nanowire membrane for concurrent filtration and photocatalytic oxidation of humic acid in water

A novel TiO 2 nanowire membrane was successfully fabricated using hydrothermal synthesis-filtration method. The fabricated TiO 2 membrane had uniform thickness and was flexible to form into other shape modules. These nanowires were of 20–100 nm in diameter and had typical length in the range of several micrometers to tens of micrometers. The pore size of the TiO 2 nanowire membrane was about 0.05 μm. The TiO 2 nanowire membrane exhibited similar photocatalytic activity as commercial TiO 2 powder (P25) on degradation of humic acid in water. In continuous experiment, TiO 2 nanowire membrane achieved near 100% and 93.6% removal rate of humic acid and total organic carbon (TOC), respectively, via a concurrent filtration and photocatalytic oxidation. The TiO 2 nanowire membrane also showed excellent anti-fouling ability owing to the photodegration of foulants by the TiO 2 nanowire membrane.

Enhanced electrochemical oxidation of phenol by introducing ferric ions and UV radiation

The mineralization of phenol in aerated electrochemical oxidation has been investigated. The results show that a cathodic Fenton process can occur when the Ti-0.3Mo-0.8Ni alloy material is used as cathode in solution containing ferric or ferrous ions; moreover, the reinforcement of cathodic Fenton process on the total organic carbon (TOC) removal rate of phenol is quite distinct. Among the metallic ions investigated, the ferric ion is the best catalyst for the electrochemical mineralization of phenol at initial pH 2.0, and the optimal concentration range is from 50 to 200 mg/L. The favorable pH range and supporting electrolyte (Na2SO4) concentration for mineralization of phenol in solution containing ferrous ions are 1.8-2.3 and below 0.10 mol/L, respectively. UV radiation can improve the TOC removal rate of phenol, but the enhanced effect varies in different solutions. In the solution containing ferric ions, an equal sum or synergetic effect can be observed. The optimal effect of electrolysis system under UV radiation is achieved in the solution containing 50 mg/L Fe3+ with a final removal percentage of 81.3%.

Kinetics and mechanism of degradation of p-chloronitrobenzene in water by ozonation

The kinetics and mechanism of p-chloronitrobenzene ( pCNB) degradation by ozone were investigated. With reference compounds, nitrobenzene (NB) and chlorobenzene (CB), reaction rate constants of pCNB with O 3 and OH were measured by means of competition kinetics (mixtures of pCNB and NB, or pCNB and CB), with the rate constants being, 1.6 L mol −1 s −1, 2.6 × 10 9 L mol −1 s −1, respectively. During the ozonation process of pCNB, an increase of chloride and nitrate ions in the water sample solution was observed, which is consistent with the decrease in pCNB concentration. But the total organic carbon (TOC) removal rate is not consistent with the pCNB elimination rate indicating only part of pCNB was mineralized and thus presumably some intermediate products were formed. The pCNB degradation intermediate products were analyzed by gas chromatography–mass spectrometry (GC–MS), liquid chromatography–mass spectrometry (LC–MS), high performance liquid chromatography (HPLC) and ion chromatography (IC). The main intermediate products were phenol, p-chlorophenol, p-nitrophenol, 2-chloro-5-nitrophenol, 5-chloro-2-nitrophenol, 5-nitro-catechol, para-benzoquinone, 5-nitro-1,2,3-trihydroxy phenol, trihydroxy semiquinone, glycolic acid, oxalic acid, hydroxybutanoic acid, mesoxalic acid, tartrouic acid, malonic acid, maleic acid, hydroxymalonic acid, tartaric acid, malic acid, ketoglutaric acid and muconic acid. From the identified reaction products, a possible degradation pathway for the ozonation of pCNB has been proposed.

Photocatalytical degradation of 1,3-dichloro-2-propanol aqueous solutions by using an immobilized TiO 2 photoreactor

The photocatalytic oxidation of 1,3-dichloro-2-propanol (1,3-DCP) was studied by following the target compound degradation, the total organic carbon removal rate and by identifying the oxidation products. The reaction was performed in a batch recycle reactor, at room temperature, using UV radiation, H 2O 2 as oxidant, and immobilized TiO 2 as catalyst. 1,3-Dichloro-2-propanone, chloroacetyl-chloride, chloroacetic acid, formic and acetic acid were detected as reaction intermediates and a possible pathway for the oxidation of 1,3-dichloro-2-propanol is proposed. The effect of the oxidative agent's initial concentration was investigated and it was established that higher concentrations of H 2O 2 slow down the reaction rate. The investigation of the effect of the 1,3-DCP initial concentration showed no influence on the degradation process. The carbon and chloride ion mass balance calculations confirmed the fact that chlorinated intermediates are formed and that they degrade with a lower rate than 1,3-DCP.

DEGRADATION OF MALACHITE GREEN IN AQUEOUS SOLUTIONS WITH A NOVEL CATALYST OF HYPERCROSSLINKED RESIN

Due to the high concentration,thicken color,great toxicity and bad degradation of the dye wastewater,its treatment is always a difficult subject.Attention has been paid to the application of porphyrin and PcS as photo-catalyst for wastewater treatment.As a bionic compound,the structure of phthalocyanine sulfonic iron(FePcS)(like P-450) is similar to that of porphyrin modified metal.In this paper,A novel catalyst of hypercrosslinked resin,named as C-FePcS,was synthesized by using the Friedel-Crafts reaction between FePcS and post-crosslinked beads of chloromethylated polyvinylbenzene-styrene.The catalyst was characterized by diffuse reflectance absorption spectra,and essential conditions of photo reaction were discussed.Upon visible light irradiation in the presence of(H_2O_2,)this catalyst was found to be highly effective for the degradation of nonbiodegradable malachite green(MG) in aqueous solutions with decolorness rate of near 100% and total organic carbon(TOC) removal rate of 72%.The influence factors of degradation of MG with visible light at different conditions including acidity,dosage of catalyst were investigated.This catalyst was hardly affected by pH of the solution.A possible reaction mechanism was also proposed.

Quantifying Biological Organic Carbon Removal in Groundwater Recharge Systems

This paper presents a novel approach to study and predict the removal of organic carbon in groundwater recharge systems by combining microbial community description with advanced methods for organic carbon characterization. Soil microbial biomass was characterized using three methods: dehydrogenase activity (general heterotrophic activity), substrate induced respiration (rapid mineralization potential), and phospholipid extraction (total viable biomass). These methods proved to be sensitive, robust, and relatively simple in their application for soils of various groundwater recharge sites. Findings indicated that microbial biomass was positively correlated to the organic carbon removal capacity of different laboratory-scale test systems. Organic carbon seems to be a limiting factor for biomass growth in recharge systems. Organic carbon removal rates are increased by higher initial organic carbon concentrations. The removal of three organic carbon fractions (natural organic matter, effluent organic matter, and glucose and glutamic acid) in soil column studies followed a first-order kinetic with distinctly different rate constants and correlated positively with respective total viable biomass in the column systems. These results supported the assumption that during groundwater recharge organic carbon is preferably removed by biological processes. The transformation of organic carbon fractions during travel through the subsurface became apparent in size-exclusion chromatograms indicating a shift to smaller molecular weight. The presented approach showed promise to reveal new insights into removal mechanisms of organic carbon and to serve as a tool to predict organic carbon removal in groundwater recharge systems to improve design and operation of vadose zone treatment.

Total RNA concentration as an index of microbial activity and oxygen supply in an oxidation ditch

Total RNA and chromosomal DNA concentrations at a municipal wastewater treatment plant with an oxidation ditch (OD) were monitored for 1.5 years using commercial extraction kits for DNA and RNA. No parameters correlated with the chromosomal DNA concentration. The total RNA concentration exhibited better correlation than the solids retention time and the mixed liquor suspended solids with the removal rate of total organic carbon, and can be regarded as an index of microbial activity. The total RNA concentration varied with a cycle of one year and increased at lower water temperatures in this OD. When diffusion theory was taken into account, it was found that the oxygen dissolution rate increased at lower temperature, and a small change in the oxygen dissolution rate caused a large variation in microbial activity and also affected nitrification and denitrification. The information was insufficient to clarify the various reaction relationships, but total RNA concentration will likely be useful as an index of microbial activity in actual wastewater treatment reactors.

Adsorption / reduction of bromate from drinking water using GAC: effects on carbon characteristics and long-term pilot study

This study investigated the feasibility of using granular activated carbon (GAC) to remove bromate (BrO3-) from drinking water through batch experiments, rapid small-scale column tests (RSSCT) and a pilot-scale study. The results indicated that the GAC capacity for BrO3- removal was dependent on the GAC surface characteristics and empty-bed contact time (EBCT). The GAC with a high number of basic groups and higher pHpzc values showed an increased BrO3- removal capacity. On the other hand, BrO3- removal was improved by increasing EBCT. In the GAC pilot plant, a GAC column (operating with 15 min EBCT) preload for 12 months achieved a BrO3- and assimilable organic carbon (AOC) removal rate ranging between 7 and 96 % and between 41 and 85 %, respectively. The amount of BrO3- removed was found to be proportional to the influent BrO3- concentration. Based on the results of our long-term experiment, the BrO3- and AOC removal rate during the transition from initial GAC to biological activated carbon (BAC) was calculated as 0.12 % w/w and 0.27 % w/w, respectively. However, the BrO3- removal rate apparently decreased with increasing operating time (after 3 months). This may be a result of the contribution of the bacterial biomass being adsorbed on the GAC surface which hindered BrO3- reduction by GAC, either by blocking the pores or adsorbing on the activated sites for BrO3- reduction. WaterSA Vol.30 (3) 2004: 369-375

Effects of dissolved gas species on ultrasonic degradation of (4-chloro-2-methylphenoxy) acetic acid (MCPA) in aqueous solution

Sonochemical degradation of MCPA ((4-chloro-2-methylphenoxy) acetic acid) in dilute aqueous solutions was studied using ultrasound with a frequency of 500 kHz. The effect of gas atmosphere on MCPA degradation was investigated in nitrogen (N 2), air (O 2/N 2), oxygen (O 2), argon (Ar) and Ar/O 2 (60/40% v/v) atmospheres. For sonochemical degradation of MCPA in N 2, air (O 2/N 2), O 2 and Ar atmospheres, the rate enhancement of MCPA decomposition by sonolysis was found to be more effective in an O 2-enriched atmosphere compared to Ar atmosphere. It was considered that a higher amount of oxidants was formed in a higher O 2 partial pressure, which accelerated MCPA decomposition in a radical reaction system. On the other hand, both dechlorination and total organic carbon (TOC) removal rates were higher in Ar atmosphere, compared to those in O 2/N 2 atmosphere. It was found that, MCPA was most effectively decomposed by sonication in Ar/O 2 (60/40% v/v) atmosphere, with higher rates of decomposition, dechlorination and TOC removal.

P-Nitrosodimethylaniline (RNO)-Based Evaluation of Enhanced Oxidative Potential During Electrochemical Treatment of High-Salinity Wastewater

The electrochemical bleaching of p-nitrosodimethylaniline (RNO) was investigated in order to apply its reactions to evaluating electrochemical oxidation. The bleaching rate of RNO during electrochemical treatment was accelerated by the presence of chloride ions. The initial bleaching rate of RNO was found to be accelerated during the electrolysis of NH4Cl, suggesting that electrochemically generated chloramines are sufficiently strong oxidants to convert RNO. A method of evaluating direct or indirect oxidative potential for electrochemical treatment was proposed, provided that the initial bleaching rate of RNO is consistent with low concentrations of RNO. The saline wastewater of Japanese pickle production processes (brown mustard and Japanese radish) was electrochemically treated. The ammonium ion (18 and 8 mg L−1) was almost completely removed after 1h of treatment in the presence of NaCl (3%). The removal rate of total organic carbon (TOC) exceeded 90% for 7 mg L−1 and 60% for 352 mg L−1, indicating that electrochemical treatment is useful in removing ammonium ions and organic substances from high-salinity wastewater.

Anaerobic digestion of desizing wastewater: influence of pretreatment and anionic surfactant on degradation and intermediate accumulation

Sizing agents like starch or partly hydrolyzed starch are applied to yarn for an efficient weaving process. The corresponding desizing wastewater makes up about 50% of the organic load in wastewater from textile wet-processing. During the size preparation and desizing process, the degree of polymerization of the starch is reduced. The degradation of starch products (with a decreasing degree of polymerization) with and without surfactant was studied in a series of batch experiments. Glucose, two different dextrines, soluble and native starch were used as model compounds. Decyl sulfate served as model compound for surfactants used in the desizing process. Without surfactant, the rate of the total organic carbon removal from the solution was nearly independent of the degree of polymerization (as long it was sufficient soluble). The period of intermediate degradation was about 100 h for glucose, but 300 h for potato starch. The accumulation of intermediates was comparable after 1 day with and without surfactant (substrate: glucose) and slightly lower where carbohydrates with higher degrees of polymerization were used. In contrast to experiments without surfactant, these intermediates were accumulated for a long period of time as the surfactant inhibited the degradation of the intermediates. The experiments demonstrate that the design of an anaerobic digestion process for this wastewater must take into account the finishing process as well as the material used.

Removal of Benzoic Acid Derivatives from Aqueous Effluents by the Catalytic Decomposition of Hydrogen Peroxide

The batch catalytic oxidation of a synthetic effluent containing benzoic acid derivatives (p-hydroxybenzoic, gallic and vanillic acids) using hydrogen peroxide and Cu2+ ions at temperatures from 25 to 80 °C, hydrogen peroxide concentrations from 0.22 to 9.3 gl−1, catalyst concentrations from 6 to 300 mgl−1 and initial pH values from 1.7 to 10 has been investigated. At the conditions under consideration, total organic carbon (TOC) removal rates generally increased with increasing temperature, hydrogen peroxide and catalyst concentrations. Alkaline or strongly acidic conditions (i.e. pH values outside the range 3–7) appeared to have a detrimental effect on total oxidation rates. The Cu2+/H2O2 system was found to be capable of removing most of the organic carbon at relatively short times and moderate temperatures with 85% and nearly 100% TOC removal being recorded after 120min at 60 °C and 60 min at 80 °C, respectively. In this respect, the Cu2+/H2O2 system was found to be more effective than the typical Fenton's reagent (Fe2+/H2O2). The hydrogen peroxide catalytic decomposition (in the absence of organics) has also been investigated. Copper and iron ions were both capable of rapidly decomposing hydrogen peroxide; at temperatures higher than ambient, Cu2+-catalysed decomposition was always faster than the Fe2+-catalysed one.

Chlorination of model drinking water biofilm: implications for growth and organic carbon removal

The influence of chlorine on biofilm in low organic carbon environments typical of drinking water or industrial process water was examined by comparing biomass and kinetic parameters for biofilm growth in a chlorinated reactor to those in a non-chlorinated control. Mixed-population heterotrophic biofilms were developed in rotating annular reactors under low concentration, carbon-limited conditions (<2 mg/L as carbon) using three substrate groups (amino acids, carbohydrates and humic substances). Reactors were operated in parallel under identical conditions with the exception that chlorine was added to one reactor at a dose sufficient to maintain a free chlorine residual of 0.09–0.15 mg/L in the effluent. The presence of free chlorine resulted in development of less biofilm biomass compared to the control for all substrates investigated. However, specific growth and organic carbon removal rates were on the average five times greater for chlorinated biofilm compared to the control. Observed yield values were less for chlorinated biofilm. Although chlorinated biofilm's specific organic carbon removal rate was high, the low observed yield indicated organic carbon was being utilized for purposes other than creating new cell biomass. The impacts of free chlorine on mixed-population biofilms in low-nutrient environments were different depending upon the available substrate. Biofilms grown using amino acids exhibited the least difference between control and chlorinated kinetic parameters; biofilm grown using carbohydrates had the greatest differences. These findings are particularly relevant to the fundamental kinetic parameters used in models of biofilm growth in piping systems that distribute chlorinated, low-carbon-concentration water.

Catalytic Ozonation of Sulfosalicylic Acid

The investigation of heterogeneous catalytic ozonation of sulfosalicylic acid (SSal) in aqueous solution is reported in this paper. It was found that catalytic ozonation in the presence of V-O supported on silica gel had a more positive effect on the removal rate (62% in 30 min) of total organic carbon (TOC) than that of ozonation alone (20% in 30 min), and the catalyst supported on TiO2 had similar results. The experimental results also showed that the ozone dosage should be sufficient for achieving the catalytic effect. Efficient removal of TOC in catalytic ozonation was probably attributed to producing more powerful oxidants than molecular ozone.

Effect of light/dark cycles on wastewater treatments by microalgae

Chlorella kessleri was cultivated in artificial wastewater using diurnal illumination of 12 h light/12 h dark (L/D) cycles. The inoculum density was 105 cells/mL and the irradiance in light cycle was 45 μmol m2 s−1 at the culture surface. As a control culture, another set of flasks was cultivated under continuous illumination. Regardless of the illumination scheme, the total organic carbon (TOC) and chemical oxygen demand (COD) was reduced below 20% of the initial concentration within a day. However, cell concentration under the L/D lighting scheme was lower than that under the continuous illuminating scheme. Thus the specific removal rate of organic carbon under L/D cycles was higher than that under continuous illumination. This result suggested thatC. kessleri grew chemoorganotrophically in the dark periods. After 3 days, nitrate was reduced to 136.5 and 154.1 mg NO3 −-N/L from 168.1 mg NO3 −-N/L under continuous illumination and under diurnal cycles, respectively. These results indicate nitrate removal efficiency under continuous light was better than that under diurnal cycles. High-density algal cultures using optimized photobioreactors with diurnal cycles will save energy and improve organic carbon sources removal.

Homogeneous Catalytic Wet‐Air Oxidation for the Treatment of Textile Wastewater

An extensive series of experiments was performed to identify suitable catalysts to increase the reaction rate of wet‐air oxidation of textile wastewater at relatively mild temperatures and pressures. Wastewater types treated included natural‐fiber desizing wastewater, synthetic‐fiber desizing wastewater, and printing and dyeing wastewater. Experimental results indicated that all catalysts tested in this investigation significantly increased the chemical oxygen demand (COD) and total organic carbon (TOC) removal rates and total COD and TOC removals. Of all catalysts tested, copper salts were the most effective. Anions in the salt solutions played a role in the catalytic process. Nitrate ions were more effective than sulfate ions. Similarly, copper nitrates were more effective than copper sulfates. A mixture of salts containing different metals performed better than any single salt.

Removal of Natural Organic Matter (NOM) from Drinking Water Supplies by Ozone-Biofiltration

Removal of natural organic matter (NOM) in biofilters can be affected by many factors including NOM characteristics, use of pre-ozonation, water temperature, and biofilter backwashing. Laboratory experiments were performed and a biofilter simulation model was developed for the purpose of evaluating the effects of each of these factors on NOM removal in biofilters. Four sources of NOM were used in this study to represent a broad spectrum of NOM types that may be encountered in water treatment. In batch experiments with raw NOM, the removal of organic carbon by biodegradation was inversely proportional to the UV absorbance (254 nm)-to-TOC ratio and directly proportional to the percentage of low molecular weight material (as determined by ultrafiltration). The extent and rate of total organic carbon (TOC) removal typically increased as ozone dose increased, but the effects were highly dependent on NOM characteristics. NOM with a higher percentage of high molecular weight material experienced the greatest enhancement in biodegradability by ozonation. The performance of laboratory-scale continuous-flow biofilters was not significantly affected by periodic backwashing, because backwashing was unable to remove large amounts of biomass from the filter media. Model simulations confirmed our experimental results and the model was used to further evaluate the effects of temperature and backwashing on biofilter performance.

Removal of natural organic matter (nom) from drinking water supplies by ozone-biofiltration

Removal of natural organic matter (NOM) in biofilters can be affected by many factors including NOM characteristics, use of pre-ozonation, water temperature, and biofilter backwashing. Laboratory experiments were performed and a biofilter simulation model was developed for the purpose of evaluating the effects of each of these factors on NOM removal in biofilters. Four sources of NOM were used in this study to represent a broad spectrum of NOM types that may be encountered in water treatment. In batch experiments with raw NOM, the removal of organic carbon by biodegradation was inversely proportional to the UV absorbance (254 nm)-to-TOC ratio and directly proportional to the percentage of low molecular weight material (as determined by ultrafiltration). The extent and rate of total organic carbon (TOC) removal typically increased as ozone dose increased, but the effects were highly dependent on NOM characteristics. NOM with a higher percentage of high molecular weight material experienced the greatest enhancement in biodegradability by ozonation. The performance of laboratory-scale continuous-flow biofilters was not significantly affected by periodic backwashing, because backwashing was unable to remove large amounts of biomass from the filter media. Model simulations confirmed our experimental results and the model was used to further evaluate the effects of temperature and backwashing on biofilter performance.

Fate of adsorbable organic halides from bleached laundering in septic tank systems

A study was conducted to assess the fate of adsorbable organic halide (AOX) formed from the use of household bleach during laundering in a septic system. Experiments were conducted using laboratory-scale septic tanks and leachfield systems. Addition of feed water containing 20% of bleached or unbleached laundry wash water did not affect the performance of the septic tanks or the leach fields. Overall chemical oxidation demand (COD) and total organic carbon (TOC) removal rates through the septic systems were in the range of 90%. Adsorbable organic halide from unbleached laundry wash water with concentrations between 0.13 and 0.21 mg/L appeared to be removed in the septic tank but not in the leach field. The average overall AOX removal rate using unbleached laundry wash water was approx. 43%. In contrast, the overall removal rate of AOX generated from the use of sodium hypochlorite in bleached laundry wash water was between 87 and 94%. About one-third of the AOX was removed in the septic tank, and the rest was removed in the leach field. Analysis of the septic tank sludge and the soil in the leach field showed no accumulation of AOX from the use of hypochlorite, and the AOX was most likely removed by biodegradation and/or chemical degradation.