Mechanism of the Hydrolysis of Endosulfan Isomers.

The objective of this study was to elucidate the mechanism of abiotic hydrolysis of ES isomers, i.e., Endosulfan-1 (ES-1) and Endosulfan-2 (ES-2), using a combination of experiments and density functional theory (DFT) calculations. Hydrolysis of both ES-1 and ES-2 resulted in the formation of Endosulfan Alcohol (ES-A). The rate of hydrolysis was first order in all cases and increased with both pH and temperature. Rate expressions describing the hydrolysis rates of ES-1 and ES-2 as a function of pH and temperature were obtained and validated with independent data sets. DFT calculations were performed using three functionals (M06-2X, B3LYP, and MPW1K) and both IEFPCM-UFF and SMD to introduce solvent effects. The geometry optimization of molecules ES-1 and ES-2 showed that the free energy of ES-1 was larger, and therefore, ES-2 was the more thermodynamically stable isomer. DFT calculations also supported a hydrolysis mechanism involving two successive attacks by OH- ions on C-O bonds resulting in the attachment of OH- and the elimination of SO3- from the ES molecule, but only the first attack was rate limiting. Calculations with all functionals and solvent effect combinations supported the experimentally observed result of faster hydrolysis of ES-2 than of ES-1. The MPW1K functional along with IEFPCM-UFF for solvent effect simulated the free energy of activation to be the closest for both ES-1 and ES-2 with less than 3% error with respect to the values computed from the experimental observations. The kinetic rate expression for ES hydrolysis derived on the basis of the proposed mechanism was identical to the rate expression derived from experiments. It was deduced that the hydrolysis rates of both ES isomers may vary over 3 orders of magnitude depending on the prevalent pH and temperature.

Challenges, opportunities and progress in solid waste management during COVID-19 pandemic.

At the end of December 2019, Wuhan City became the epicenter of the highly contagious virus known as the novel coronavirus. Now that mid-2020 has already passed, almost every country is adversely affected by Corona Virus Disease (COVID-19). The routine activities of people of all ages are overturned, which has led to a shift in the trends of waste created by households, streets, and most importantly, medical facilities and quarantine centers. Compulsive use of personal protection equipment such as masks, gloves, sanitizers, etcetera by the frontline workers from the medical sector, banks, daily need stores, waste collection industries, etc. and the use of masks by every common man stepping out has skewed the trend of waste generation to a different direction. Recently, the replacement of single-use plastic was accepted by the masses, and the pandemic suddenly rebounded to the previous situation, it is expected to be worse in the long run. Another secondary outcome is reduced waste collection and recycling due to lockdown, leading to a pile-up of wastes. But several nations are adopting strategies to break the transmission chain of the virus by trying to minimize human contact. The study discusses the effect of COVID-19 on the generation, recycling, and disposal of solid waste. A brief collection of different countries' efforts to restrict the transmission of virus through solid waste is also discussed.

A comprehensive mechanistic model for simulating algal-bacterial growth dynamics in photobioreactors.

A comprehensive mechanistic model with state of the art understanding and assumptions is presented to simulate major processes in a photobioreactor for describing the algal-bacterial growth dynamics. The model includes a total of 37 state variables that broadly cover all the essential physiological and physico-chemical processes in such a system. Model parameters are first calibrated with batch experimental data, and thereafter, extensive validation of the model is carried with long term independent experimental data in diverse conditions. The developed model is able to capture the complex system behavior with reasonable accuracy. Also, the comprehensive mathematical formulation with realistic assumptions make this model a valuable tool for gaining better insights into the complex system behavior.

The effect of ozonation on natural organic matter removal by alum coagulation.

Natural organic matter (NOM) was extracted from a moderately colored, eutrophic surface water source (Forge Pond, Granby, MA), and fractionated into quasi-homogeneous fractions. Fulvic acid (FA) and hydrophilic neutrals (HN) were the two most abundant NOM fractions that were isolated. Adsorption affinity of the isolated NOM fractions on preformed aluminum hydroxide flocs increased with increase in specific organic charge of the fractions, except for the two most highly charged fractions, FA and hydrophilic acids (HAA), which showed less adsorption affinity than expected based on their specific organic charge. Prior ozonation of FA and HN fractions resulted in a decline and an increase, respectively, in their adsorption affinity on aluminum hydroxide surface. Prior ozonation of Forge Pond raw water resulted in a progressive decline in dissolved organic carbon (DOC) removal by alum coagulation with increase in ozone dose. It appeared that ozone applied to raw water reacted preferentially with the humic fraction of NOM, resulting in the detrimental effects of ozonation on subsequent NOM removal by alum coagulation being magnified. Forge Pond raw water was pre-coagulated to remove humic substances. Ozonation of the pre-coagulated water demonstrated the beneficial effects of ozonation on the removal of non-humic NOM through alum coagulation. A strategy for staged coagulation with intermediate ozonation was proposed for waters containing both humic and non-humic NOM for maximum DOC and specific UV absorbance at 254nm (SUVA) removal.

Interaction of 2-chloronaphthalene with high carbon iron filings (HCIF): adsorption, dehalogenation and mass transfer limitations.

Interaction of 2-chloronaphthalene (2-CN) with high-carbon iron filings (HCIF) was studied in anaerobic batch systems, both under well-mixed and poorly-mixed conditions. In well-mixed conditions, partitioning of 2-CN between solid and aqueous phases was fast, resulting in rapid attainment of equilibrium. Equilibrium partitioning could be described by a Freundlich isotherm, C(s)=K x [C(a)](m), where C(s) (micromoles g(-1) iron) and C(a) (micromoles L(-1)) were the solid and aqueous phase 2-CN concentrations, respectively. Isotherm parameters, m and K were determined to be 0.76 and 5.6 x 10(-2) (micromole g(-1) iron)/(micromole L(-1)), respectively. Sorption (k(2)) and desorption (k(3)) rate constants were determined to be 5.60 x 10(-1) h(-1) g(-1) iron L and 10 h(-1), respectively. Reductive dehalogenation of aqueous phase 2-CN occurred concurrently but at a slower rate, and could be described by the expression (dC(T)//dt)= -k(1) x M x (C(a))(N), where C(T) (micromoles L(-1)) was the total 2-CN concentration and M (g iron L(-1)) the concentration of HCIF. The values of k(1) and N were determined to be 1.09 x 10(-2) h(-1) g(-1) iron L and 1.647, respectively. In poorly mixed conditions, adsorption (k(2)) and desorption (k(3)) rate constants were 3.92 x 10(-5) h(-1) g(-1) iron L and 7 x 10(-4) h(-1), respectively, i.e., several orders of magnitude less than in well-mixed systems. The dehalogenation rate parameters, k(1) and N were determined to be 2.22 x 10(-4) h(-1) g(-1) iron L and 0.986, respectively, suggesting slower dehalogenation. These results highlight how mass-transfer limitations during the interaction between HCIF and 2-CN in poorly mixed systems, such as permeable reactive barriers (PRBs), can potentially impact the dehalogenation process.

A comprehensive mechanistic model for simulating algal growth dynamics in photobioreactors.

A comprehensive mechanistic model for describing algal growth dynamics in a photobioreactor was developed in this work with state of the art understanding and realistic assumptions for major associated processes. The model included 27 state variables related to various algal processes. This model was validated with extensive experimental data obtained from independent growth experiments in batch reactors, and was able to simulate system performance reasonably well. The comprehensive nature of the formulation also highlights the complex inter-relationship between all processes, and provides a tool for gaining more systematic insights into algal behavior in photobioreactors and other such systems.

Impact of the composition of the bacterial population and additional carbon source on the pathway and kinetics of degradation of endosulfan isomers.

Abiotic and bacterial degradation is presented for the two isomers α- and ß- of the organochlorine pesticide endosulfan, denoted as ES-1 and ES-2, respectively. Biodegradation studies were conducted with two indigenous species Pseudomonas putida (P. putida) and Rhodococcus sp. Both ES isomers rapidly hydrolyzed in water at pH ≥ 7 but the hydrolysis was inhibited in the presence of biomass. The pesticide partitioned onto the biomass making it unavailable for abiotic hydrolytic reaction. Spontaneous temperature dependent abiotic conversion of ES-2 to ES-1 was reported in the presence of dual air-water phases but was not observed in the abiotic aqueous phase. Biodegradation experiments with pure isomers showed a small amount of interconversion (∼5%) in either direction and ruled out any preferential interconversion of the ES-2 isomer to ES-1 or vice versa. Both the species were shown to degrade ES-2 at a higher rate compared to ES-1 which may lead to enrichment of ES-1 in agricultural fields in short-term following application of the pesticide. P. putida degraded both the ES isomers through oxidative and hydrolytic pathways while the Rhodococcus sp. used only the hydrolytic pathway. Since ES-S (product of the oxidative pathway) is orders of magnitude more toxic than the parent isomers, the short term toxicity of a field following the application of the pesticide may increase if the composition of the indigenous bacterial population is such that the oxidative pathway is preferred over the hydrolytic one. The presence of an additional carbon source increased the rates of degradation of both the isomers but the enhancement was greater for the degradation rate of ES-2 than ES-1.

Extent of oxidation of Cr(III) to Cr(VI) under various conditions pertaining to natural environment.

Calculations show that oxidation of chromium oxide (Cr2O3) by oxygen and oxidation of chromium hydroxide (Cr(OH)3) by manganese dioxide (MnO2) are thermodynamically feasible in both aerobic and mildly anoxic environments. Experiments were carried out to determine the rate and extent of chromium oxidation under various conditions, i.e., when Cr2O3 was heated in the presence of oxygen, when Cr(OH)3 and MnO2 mixtures were suspended in aerobic or anoxic aqueous media at various pH values, when Cr(OH)3 and MnO2 mixtures interacted in moist aerobic conditions and when chromium assumed to be Cr(OH)3 and manganese assumed to be MnO2 interacted in the presence of competing electron donors/acceptors, as is the case in chromium-contaminated sludge. Results indicate that trivalent chromium in Cr2O3 could be readily converted to hexavalent chromium at a temperature range of 200-300 degrees C, with conversion rates of up to 50% in 12 h. In aqueous media, Cr(OH)3 was slowly converted to dissolved Cr(VI) in the presence of MnO2, both in aerobic and anoxic conditions, with conversion rates of up to 1% in 60 days. In moist aerobic conditions and in the presence of MnO2, Cr(OH)(3) slowly converted to hexavalent chromium, with up to 0.05% conversion observed in 90 days. Chromium oxidation also occurred in sludge samples, especially under aerobic conditions. However, such transformation was found to be transitory, with the Cr(VI) formed being ultimately reduced back to Cr(III) due to the presence of various reducing agents in the sludge. Nevertheless since up to 17% conversion of Cr(III) to Cr(VI) occurred in sludge under aerobic conditions by 30 days, there is real danger under field conditions of spreading Cr(VI) pollution due to possible intervening rainfall, runoff and percolation.

Treatment of distillery spent-wash by ozonation and biodegradation: significance of pH reduction and inorganic carbon removal before ozonation.

This study is aimed at exploring strategies for mineralization of refractory compounds in distillery effluent by anaerobic biodegradation/ozonation/aerobic biodegradation. Treatment of distillery spent-wash used in this research by anaerobic-aerobic biodegradation resulted in overall COD removal of 70.8%. Ozonation of the anaerobically treated distillery spent-wash was carried out as-is (phase I experiments) and after pH reduction and removal of inorganic carbon (phase II experiments). Introduction of the ozonation step resulted in an increase in overall chemical oxygen demand (COD) removal, with the highest COD removals of greater than 95% obtained when an ozone dose of approximately 5.3 mg ozone absorbed/mg initial total organic carbon was used. The COD removal during phase II experiments was slightly superior compared with phase I experiments at similar ozone doses. Moreover, efficiency of ozone absorption from the gas phase into distillery spent-wash aliquots was considerably enhanced during phase II experiments.

Mineralization of some natural refractory organic compounds by biodegradation and ozonation.

The objective of this study was to explore the extent of mineralization, reduction in color and reduction of COD of gallic acid, tannin and lignin by ozonation and a combination of aerobic biodegradation and ozonation. Ozonation of pure aliquots (phase I experiments) resulted in the decline in TOC, COD, COD/TOC ratio, UV absorbance at 280 nm and color of the three model compounds investigated, with COD removals of greater than 80% and high removals (>90%) of UV absorbance at 280 nm and color observed in all cases at an ozone dose of 6 mg ozone/mg initial TOC or higher. Aerobic biodegradation of pure gallic acid, tannin and lignin aliquots resulted in COD decline of approximately 36-38%. Subsequent ozonation (phase II experiments) resulted in further decline in TOC, COD, COD/TOC ratio, and increase in UV absorbance at 280 nm and color removals. COD and TOC removals comparable to phase I experiments were obtained with 30-40% lower ozone absorption in phase II experiments. The biodegradation step was quite effective in removing specific UV absorbance at 280 nm, with up to 75% removal observed. Subsequent ozonation increased overall specific UV absorbance at 280 nm to greater than 90%.

Use of pyrite for pH control during hydrogenotrophic denitrification using metallic iron as the ultimate electron donor.

Maintenance of stable pH through provision of adequate buffering is of importance to many pollutant removal processes where either acid or base is produced as a reaction product. The objective of this study was to evaluate the suitability of pyrite (FeS2) as an in situ buffering agent for arresting pH increase during metallic iron assisted hydrogenotrophic denitrification. Pyrite is considered promising for this purpose because it is a mineral which is unstable under moderately reducing, i.e., anoxic conditions, where such denitrification takes place, and therefore expected to consume hydroxide ions produced due to hydrogenotrophic denitrification reactions and get oxidized to ferrous hydroxide Fe(OH)2. The theoretical basis for this buffering action was established through chemical speciation studies using the chemical speciation software, MINEQL+. Experimental evaluation of the buffering efficiency of pyrite showed that it was effective in arresting pH increase associated with denitrification in both batch systems and during flow through reactive porous media. Further, addition of pyrite had no demonstrable toxic effect on the denitrifying microorganisms, though elevated sulfate concentration was seen in the effluent after denitrification.

Oxidation of Cr(III) in tannery sludge to Cr(VI): field observations and theoretical assessment.

Sludge, soil and leachate samples collected from a chromium-contaminated tannery waste dumping site in Kanpur, India, were found to contain considerable amounts of Cr(VI), despite the fresh tannery sludge containing little or no Cr(VI). Literature reports suggested that dry Cr(III) precipitates could be converted to Cr(VI) when heated in the presence of oxygen. Also, Cr(III) in aqueous phase could be oxidized through interaction with manganese dioxide (MnO2) surface to Cr(VI). Measurement of manganese in the sludge samples collected from the site showed concentrations up to 0.6 mg/g. Based on equilibrium calculations, it was determined that both dry phase Cr(III) oxidation by atmospheric oxygen and aqueous phase Cr(III) oxidation by MnO2 surface were thermodynamically feasible. It was further suggested that in aqueous phase, manganese may act effectively as an electron transporter between Cr(III) and dissolved oxygen during Cr(III) oxidation, leading to regeneration of MnO2 solid phase. Further, as dissolved Cr(III) is oxidized, dissolution of Cr(OH3) will take place to maintain the equilibrium between the dissolved and solid phases of Cr(III). In the pH range of 3-10, and at oxygen partial pressure (P(O2)) of 10(-6) atm or higher, equilibrium conditions stipulate nearly complete conversion of Cr(III) to Cr(VI). At P(O2) of 10(-20) atm or lower, very little Cr(VI) is expected to be present under equilibrium conditions. In the intermediate P(O2) regions, incomplete dissolution of the Cr(OH3) solid phase and only partial conversion of chromium from +3 to the +6 oxidation state is expected, especially at lower pH values.

Role of iron in controlling speciation and mobilization of arsenic in subsurface environment.

Widespread arsenic contamination of groundwater has been reported of late in Bangladesh and West Bengal state of India. On the basis of arsenic geochemistry, three probable mechanisms have been cited for arsenic mobility in aquifers of West Bengal and Bangladesh. First, mobilization of arsenic due to the oxidation of arsenic-bearing pyrite minerals. Second, dissolution of arsenic-contaminated iron oxy-hydroxides (FeOOH) due to onset of reducing conditions in the subsurface. Third, due to the release of arsenic sorbed to aquifer minerals by competitive exchange with phosphate ions, that migrates into aquifers due to application of fertilizer to surface soil. Based on the review of field data from the affected region, it appears that the second mechanism described above is the most probable. Two reduction processes associated with this mechanism were investigated, viz., reduction of iron oxy-hydroxide to iron (II), which results in the mobilization of arsenic, and reduction of arsenic (V) to arsenic (III), which may enhance mobility of arsenic under certain conditions. These reactions, in the opinion of some researchers, are possible in subsurface environments mainly through microbial intervention. However, through the data presented in this paper, it has been demonstrated that above red-ox reactions involving iron and arsenic are also possible through predominantly abiotic pathways. While these results do not necessarily imply that abiotic red-ox processes are dominant in all subsurface environments containing iron and arsenic, it is entirely possible that abiotic interactions as described here may be responsible for a substantial amount of transformations involving iron and arsenic in anoxic subsurface environments.

Analysis of photosynthetic activity in the most polluted stretch of river Ganga.

As a result of the increasing anthropogenic activities in the gangetic plain, Ganga water quantity as well as quality has declined over the years. A major effort to clean Ganga, named Ganga Action Plan (GAP) was instituted by the Government of India in 1984. The emphasis in GAP was on the reduction of organic load on the river through interception, diversion and treatment of wastewater reaching the river, thus maintaining the biochemical oxygen demand (BOD) and dissolved oxygen (DO) levels of river within the acceptable limits. A major criticism of GAP is that the significance of river ecology has not been addressed adequately during its conception and implementation. One of the important aspects from this perspective is the photosynthetic activity in the river Ganga. It has been postulated that photosynthetic activity plays an important role in maintaining high levels of DO in Ganga, and as a result the river can assimilate high organic loads without appreciable depletion in dissolved oxygen levels. Objective of the present study was to assess the photosynthetic activity and oxygen production rates in the river and correlate these values with various water quality parameters. Most polluted stretch of Ganga, which is known as the Kannauj-Kanpur stretch was chosen for this study. Based on the results of the study, it was concluded that despite implementation of phase I of GAP, and consequent diversion and reduction of organic loading to the river, both BOD and DO levels in the river has increased in the entire Kannauj-Kanpur stretch, except at Jajmau, where anaerobically treated effluent is discharged to the river. The nitrogen levels have also increased in the entire Kannauj-Kanpur stretch. Dissolved oxygen (DO) and alkalinity in the river water vary diurnally at all sites. Chlorophyll-a levels and oxygen production rates due to photosynthesis appear to be positively influenced by phosphate levels in the river water. Chlorophyll-a levels appear to be negatively correlated to the Ammonical and total Total Kjeldahl Nitrogen (TKN) content in the river water, suggesting the possibility of release of nutrients due to algal death and decomposition under certain circumstances.

Case studies on biological treatment of tannery effluents in India.

This paper presents a comparative assessment of the cost and quality of treatment of tannery wastewater in India by two common effluent treatment plants (CETPs) constructed for two tannery clusters, at Jajmau (Kanpur) and at Unnao in the state of Uttar Pradesh, India. The Jajmau plant is upflow anaerobic sludge blanket (UASB) process-based, while the Unnao plant is activated sludge process (ASP)-based. Investigations indicated that the ASP-based plant was superior in all respects. Total annualized costs, including capital and operation and maintenance costs, for the UASB and ASP plants were Rs. 4.24 million/million liters per day (MLD) and Rs. 3.36 million/MLD, respectively. Land requirements for the two CETPs were 1.4 hectares/MLD and 0.95 hectares/ MLD, respectively. Moreover, the treated UASB effluent had higher biochemical and chemical oxygen demand (BOD/ COD) and considerable amounts of other undesirable constituents, like chromium (Cr) and sulfide, as compared with the ASP effluent, which had lower BOD/COD and negligible concentration of sulfide and Cr. Sludge production from the UASB-based plant was also higher at 1.4 t/day/MLD, in comparison to the sludge production of 0.8 t/day/MLD for the ASP-based plant. Also, the entire sludge produced in the UASB-based plant was Cr-contaminated and, hence, hazardous, while only a small fraction of the sludge produced in the ASP-based plant was similarly contaminated. The results of this study are at variance with the conventional wisdom of the superiority of anaerobic processes for tannery wastewater treatment in tropical developing countries like India.

Modeling of 2-chloronaphthalene interaction with high carbon iron filings (HCIF) in semi-batch and continuous systems.

Unrusted high carbon iron filings (HCIF) were contacted sequentially with successive aliquots of aqueous 2-chloronaphthalene (2-CN), i.e., in semi-batch mode, both in well-mixed and poorly-mixed conditions. Aqueous concentration of 2-CN and the dehalogenation by-product naphthalene (N) were monitored at the beginning and end of each 2-CN addition cycle. Experimental data was modeled using the 2-CN dehalogenation and adsorption/desorption rate constants determined from batch experiments involving 2-CN and a similar HCIF sample. Model predictions for the semi-batch experiments matched quite well with the experimental data in both well-mixed and poorly-mixed cases. Further, it was experimentally demonstrated that adsorption and hence accumulation of N on HCIF surface did not substantially hinder either 2-CN adsorption or dehalogenation under the conditions examined in this study. Continuous transport of water containing 0.5 µmol L(-1) 2-CN through a 1.0-m thick unrusted HCIF layer was simulated at superficial velocities of 0.01 and 0.10 m h(-1). Both simulations indicated nearly complete removal of 2-CN in the HCIF layer. This study suggests that HCIF can be used as a potential reactive material in permeable reactive barriers (PRBs) for in situ remediation of groundwater contaminated with 2-CN.

Nutrient removal using algal-bacterial mixed culture.

Simultaneous nitrate (N), phosphate (P), and COD removal was investigated in photobioreactors containing both algae and bacteria. The reactors were operated in the semi-batch mode with a hydraulic retention time of 2 days. Reactors were operated in two phases, (1) with 33 % biomass recycle and (2) with no biomass recycle. In both phases, more than 90 % of N and P and 80 % of COD present in synthetic wastewaters with initial N and P concentrations of up to 110 and 25 mg/L, respectively, and initial COD of 45 mg/L could be removed. Biomass growth in reactors did not increase with the increase in initial N and P concentration in either phase. However, biomass growth was slightly more in reactors operated with no biomass recycle. In both phases, N and P uptake was greater in reactors with greater initial N and P concentrations. Also in all cases, N and P uptake in the reactors was far in excess of the stoichiometric requirements for the observed biomass growth. This "luxury uptake" of nitrogen and phosphorus by biomass was responsible for excellent nitrogen and phosphorus removal as observed. However, based on the results of this study, no advantage of biomass recycling could be demonstrated.

Impact of addition of amendments on the degradation of DDT and its residues partitioned on soil.

Market-grade DDT used for mosquito control and other purposes is a mixture of 4,4-DDT, 2,4-DDT and smaller amounts of 4,4-DDD, 2,4-DDD, 4,4-DDE and 4,4-DDMU. All above components (together known as DDTr) are strongly hydrophobic and hence are present in the environment predominantly in the soil/sediment phases. The persistence of DDTr and the feasibility of attenuation of DDTr concentration in soil matrix through addition of amendments is a subject of ongoing interest. The objective of this study was to compare the decline of soil-partitioned DDTr concentration through, (1) the natural attenuation process, (2) enhanced aerobic and anaerobic biodegradation processes involving addition of acclimatized seed and co-metabolites and (3) Nanoscale Zero Valent Iron (NZVI) addition. The extent of decline in soil DDTr concentration in control experiments, where biodegradation and photolysis were excluded, was around 10-15% in ∼100d. Extent of DDTr decline in natural attenuation experiments was 25-30% and 15-20% under aerobic and anaerobic conditions respectively. In enhanced biodegradation experiments, addition of acclimatized seed and/or co-metabolites did not enhance the extent of DDTr attenuation over and above the natural attenuation rates both in aerobic and anaerobic conditions. It thus appeared that biodegradation of DDTr adsorbed on soil was severely limited and controlled by desorption and consequent bioavailability of DDTr in the aqueous phase. In case of NZVI addition, the rate of DDTr degradation was much faster, with 40% decrease in DDTr concentration within 28h of NZVI addition. Here, the faster DDTr degradation may be through direct electron transfer between NZVI particles and DDTr molecules adsorbed on soil. Increase in the concentration of 4,4-DDD and 2,4-DDD during NZVI addition suggest that these compounds are either intermediate or end products of DDT degradation process.

Interaction of 2,4,6-trichlorophenol with high carbon iron filings: Reaction and sorption mechanisms.

Reductive dehalogenation of 2,4,6-trichlorophenol (2,4,6-TCP) by two types of high carbon iron filings (HCIF), HCIF-1 and HCIF-2 was studied in batch reactors. While the iron, copper, manganese and carbon content of the two types of HCIF was similar, the specific surface area of HCIF-1 and HCIF-2 were 1.944 and 3.418m(2)g(-1), respectively. During interaction with HCIF-1, 2,4,6-TCP adsorbed on HCIF-1 surface resulting in rapid reduction of aqueous phase 2,4,6-TCP concentration. However, reductive dehalogenation of 2,4,6-TCP was negligible. During interaction between 2,4,6-TCP and HCIF-2, both 2,4,6-TCP adsorption on HCIF-2, and 2,4,6,-TCP dechlorination was observed. 2,4,6-TCP partitioning between solid and aqueous phase could be described by a Freundlich isotherm, while 2,4,6-TCP dechlorination could be described by an appropriate rate expression. A mathematical model was developed for describing the overall interaction of 2,4,6-TCP with HCIF-2, incorporating simultaneous adsorption/desorption and dechlorination reactions of 2,4,6-TCP with the HCIF surface. 2,4-Dichlorophenol (2,4-DCP), 2-chlorophenol (2-CP) and minor amounts of 4-chlorophenol (4-CP) evolved as 2,4,6-TCP dechlorination by-products. The evolved 2,4-DCP partitioned strongly to the HCIF surface. 4-CP and 2-CP accumulated in the aqueous phase. No transformation of 2-CP or 4-CP to phenol was observed.

Autotrophic denitrification using hydrogen generated from metallic iron corrosion.

Hydrogenotrophic denitrification was demonstrated using hydrogen generated from anoxic corrosion of metallic iron. For this purpose, a mixture of hydrogenated water and nitrate solution was used as reactor feed. A semi-batch reactor with nitrate loading of 2000 mg m(-3) d(-1) and hydraulic retention time (HRT) of 50 days produced effluent with nitrate concentration of 0.27 mg N L(-1) (99% nitrate removal). A continuous flow reactor with nitrate loading of 28.9 mg m(-3) d(-1) and HRT of 15.6 days produced effluent with nitrate concentration of approximately 0.025 mg N L(-1) (95% nitrate removal). In both cases, the concentration of nitrate degradation by-products, viz., ammonia and nitrite, were below detection limits. The rate of denitrification in the reactors was controlled by hydrogen availability, and hence to operate such reactors at higher nitrate loading rates and/or lower HRT than reported in the present study, hydrogen concentration in the hydrogenated water must be significantly increased.