Dechlorination Agent Research Articles

Phosphotungstic Acid as a Dechlorination Agent Collaborates with CeO2 for Synergistic Catalytic Elimination of NOx and Chlorobenzene.

The development of efficient technologies for the synergistic catalytic elimination of NOx and chlorinated volatile organic compounds (CVOCs) remains challenging. Chlorine species from CVOCs are prone to catalyst poisoning, which increases the degradation temperature of CVOCs and fails to balance the selective catalytic reduction of NOx with the NH3 (NH3-SCR) performance. Herein, synergistic catalytic elimination of NOx and chlorobenzene has been originally demonstrated by using phosphotungstic acid (HPW) as a dechlorination agent to collaborate with CeO2. The conversion of chlorobenzene was over 80% at 270 °C, and the NOx conversion and N2 selectivity reached over 95% at 270-420 °C. HPW not only allowed chlorine species to leave as inorganic chlorine but also enhanced the Bro̷nsted acidity of CeO2. The NH4+ produced in the NH3-SCR process can effectively promote the dechlorination of chlorobenzene at low temperatures. HPW remained structurally stable in the synergistic reaction, resulting in good water resistance and long-term stability. This work provides a cheaper and more environmentally friendly strategy to address chlorine poisoning in the synergistic reaction and offers new guidance for multipollutant control.

Reversible capture and release of I2 with dechlorinated porous organic polymer

In recent years, porous organic polymers (POPs) possess a remarkable potential as adsorbents for heavier halogen (I2 and Br2) capture in the fields of environmental treatment and industrial production. How to improve iodine adsorption properties through efficient molecular structure design is still worth exploring. In this work, a novel nitrogen-rich POP, defined as POP-TT, for iodine capture is designed and easily obtained by reacting 2,4,6-trichloro-1,3,5-triazine (TCT) and tris(4-aminophenyl) amine (TAPA) with the aid of dechlorination agent under mild condition, inspired by the significant enhancement of iodine capture with N-rich heterocyclic structure. The proposed POP-TT shows good stability and porosity even in high-salt solutions. Profiting from the nitrogen-rich skeleton and phenyl groups of POP-TT and strong charge-transfer interaction between polymer framework and adsorbed iodine, the proposed POP-TT exhibits excellent affinity with uptake capacity of 4.62 g g−1 for iodine vapor and removal efficiency of 86.8 % for iodine aqueous solution. Good retention behavior and recycling capacity are also observed for POP-TT. This work provides a practical guide for designing heavier halogen adsorbents by using dechlorinated porous organic polymers.

High temperature reduction of divalent mercury to elemental mercury for Hg-CEMS

The high temperature reduction (HTR) of flue gas divalent mercury to elemental mercury is the core technology for the mercury continuous emission monitoring system (Hg-CEMS). In this work, the high temperature reduction of HgCl2 to Hg0 was systematically investigated. The results show that HgCl2 can entirely decompose to Hg0 at 800 °C, but Cl, ClO, Cl2, and HCl can easily oxidize Hg0 at low temperature. A new efficient alkaline dechlorination agent for eliminating these Cl species was proposed firstly. The dechlorination agent can efficiently capture the HCl, Cl, and ClO but fail to completely adsorb Cl2. Consequently, a scheme was created that a pair of dechlorination agents were filled in inlet and outlet of the HTR furnace respectively. It features that the upper layer removes HCl and prevents the generation of Cl2 because HCl is the precursor of Cl2, and the lower layer adsorbs the Cl and ClO generated by the HTR process. The feasibility of the method was successfully verified in both a fixed-bed reactor and a Hg-CEMS pretreatment device. DFT calculation indicates that the adsorption of Cl, ClO, and HCl on CaO falls into the category of strong chemisorption while Cl2 is weakly chemisorbed.

Dechlorination and fuel gas generation in chemical looping conversion of waste PVC over inherently Na/Ca/K-containing bauxite residue-based oxygen carriers

The inert atmosphere in chemical looping (CL) technology can considerably inhibit the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans during the thermal treatment of polyvinyl chloride plastic (PVC) waste. In this study, PVC was innovatively converted to dechlorinated fuel gas via CL gasification under a high reaction temperature (RT) and the inert atmosphere by applying an unmodified bauxite residue (BR) as both a dechlorination agent and oxygen carrier. The dechlorination efficiency reached 49.98% at an oxygen ratio of only 0.1. Furthermore, a moderate RT (750 °C in this study) and an increased oxygen ratio enhanced the dechlorination effect. The highest dechlorination efficiency (92.12%) was achieved at an oxygen ratio of 0.6. Iron oxides in BR improved the generation of syngas from CL reactions. The yields of the effective gases (CH4, H2, and CO) increased by 57.13% to 0.121 Nm3/kg with an increase in oxygen ratio from 0 to 0.6. A high RT improved the production of the effective gases (an 809.39% increase to 0.344 Nm3/kg from 600 to 900 °C). Energy-dispersive spectroscopy and X-ray diffraction were used to study the mechanism, and formation of NaCl and Fe3O4 was observed on the reacted BR, indicating the successful adsorption of Cl and its capability as an oxygen carrier. Therefore, BR eliminated Cl in situ and enhanced the generation of value-added syngas, thereby achieving efficient PVC conversion.

Dechlorination during pyrolysis of plastics: Effect of municipal plastic waste composition

In order to close the loop in chemical recycling via pyrolysis, products must meet strict limits for halogen content to be used in conventional petrochemical processes. By integrating dechlorination as an integral part of pyrolysis, results show that the efficiency of dechlorination, both via stepwise pyrolysis and dechlorination agents, is significantly decreased in the presence of PET or cellulose in the feedstock. Product analysis showed that Cl reacts with formed oxygenated substances, some of which remain in the reactor during the 1st step at 350 °C and subsequently pass into the final liquid product. This increases the requirements for applied dechlorinating agents during the 2nd pyrolysis step. Novel agents have to therefore cope with a wide range of chlorinated hydrocarbons. By combining acidic β-zeolite with alkali hydrotalcite in a 1:1 ratio, a synergic effect towards dechlorination was observed, increasing individual efficiency by about 12% and 6%, respectively. Combining stepwise pyrolysis, which removed 38% of Cl on average, with the mentioned mixture of agents, 95% efficiency and 12.2 ± 1.2 ppm of Cl were obtained in the final liquid product. Such a level of dechlorination may be sufficient, considering that the pyrolysis liquid will be diluted in conventional petrochemical feedstocks.

Study of Efficiency and Reaction Rates Dechlorination of Nata De Coco Wastewater Using Sodium Thiosulfate

Chemical reduction with sodium thiosulfate is commonly used to dechlorinate chlorinated waste. U.S. Environmental Protection Agency recommends sodium thiosulfate (Na2S2O3) as a dechlorinating agent for waste samples containing residual chlorine before being released into the environment or entering the distribution system. However, sodium thiosulfate's efficiency and chlorination kinetics at different concentrations are still unknown due to a lack of information on chlorination kinetics. The study was conducted by determining the number of efficient doses of sodium thiosulfate and observing chlorination kinetics using sodium thiosulfate as a dechlorination agent observed at different stoichiometric ratios (1x, 1.5x, and 2x). Sodium thiosulfate at a stoichiometric dose of 2x can reduce chlorine residue by up to 0.4 ppm. The regression analysis of and constant rate are used in the kinetic analysis of sodium thiosulfate dechlorination processes. The kinetics of the chlorination process employing sodium thiosulfate is first order to the total concentration of chlorine in solution at a stoichiometric dosage of 2x, according to the findings.

Comparison of Commercial Dechlorination Chemicals used in Reverse Osmosis Processes

Objectives : The objective of this study was to find a promising dechlorination chemical which can replace sodium bisulfite (SBS), which is mainly used as a dechlorination agent in reverse osmosis processes but can cause odor issues.Methods : Candidate chemicals were selected in consideration of economic feasibility, ease of use, and toxicity. These included sodium metabisulfite (SM), sodium thiosulfate (ST), and sodium sulfite (SS). We investigated the effect of organic matters in water on residual chlorine decomposition and compared the appropriate injection amounts for each dechlorination chemicals. Also, the effect of the pH of treated water upon dechlorination was assessed.Results and Discussion : Upon injection of dechlorination chemicals at the theoretical chlorine removal point, the chlorine was not completely removed but 10% to 40% remained. In ultrapure water, it was possible to completely dechlorinate by injecting 1.6 to 2.6 times more than the theoretical injection amount: 1.8, 2.2, and 3.1 times more for ST, SM, and SS, respectively. Considering only the injection amount, ST is an efficient dechlorination chemical for water with pH 9 or higher, and SM is for pH 9 or lessConclusion : Considering the product price and user convenience, it is feasible to use ST, which can resolve the odor problem.

Dechlorination performance in chemical looping conversion of polyvinyl chloride plastic waste using K/Na/Ca-modified iron ore oxygen carriers

The reducing atmosphere of chemical looping conversion (CL) can greatly limit the emission of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) during the heat treatment of polyvinyl chloride plastics waste (PPW). Loading alkali metals and alkaline earth metals (AAEM) on iron ore OC can remove chlorine in situ, reduce HCl corrosion, and further reduce the emission of other harmful chlorine pollutants. In this work, iron ore OC was modified by K, Na, and Ca. The three modified OCs showed good dechlorination and catalytic gasification performances, while the pristine iron ore OC only exhibited weak dechlorination effects. The dechlorination activity of the three OCs was found to decrease in the order K- > Na- > Ca-modified OC. Decreasing the reaction temperature in the range of 750–900 °C and increasing the dechlorination agent loading improved the dechlorination efficiency. The AAEM conversion of K- and Na-modified OCs could reach or approach 100%, while that of Ca-modified OC reached only about 30%. Scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD) results showed that the corresponding alkali and alkaline earth metal chlorides were formed on the surface of the OCs during the CL processes.

Green and circular method for chloride separation from acid wastewater: Application in zinc smelter

• A circular dechlorination process was proposed. • Dechlorination rate of bismuth absorbing materials exceeded 90%. • The elution rate of the dechlorination residue reached 93.64%. • Bismuth antichlor exhibits excellent cyclic performance. • Chlorine in the wastewater was converted to sodium chloride eventually. A circular method for dechlorination of acid wastewater and application in a zinc smelter was proposed based on thermodynamic calculations, where bismuth oxide was used as the dechlorination agent, and the entire process comprised bismuth oxide acidification–adsorptive dechlorination – alkaline washing – regeneration. First, bismuth oxide (Bi 2 O 3 ) was converted to clusters of rod-like bismuth sulfate or basic bismuth sulfate by sulfuric acid maturation, after which Clin the acid solution was adsorbed and formed a BiOCl precipitate. The rate of Clremoval from the zinc smelter wastewater reached more than 90% under the following optimum conditions: initial pH of 1.5, reaction temperature of 40 °C, 10-fold concentration of bismuth relative to the amount of Cl and reaction time of 1 h. BiOCl was then subjected to alkaline washing for dechlorination and regeneration of Bi 2 O 3 . The morphology of the dechlorination residue was rod-like, and a high concentration of NaCl solution was obtained at a temperature of 90 °C, reaction time of 1 h, NaOH concentration of 80 g/L, and liquid–solid ratio of 5:1, where the chlorine elution rate reached 93.64%. Finally, the bismuth oxide was acidified again with sulfuric acid and again dechlorinated. Tests showed that the dechlorination rate of regenerated bismuth oxide was still over 90% after 10 cycles. The process actually consumes only cheap sodium hydroxide due to the reuse of bismuth oxide, thus reducing the production costs and has potential industrial application given its simplicity.

Effects of dechlorination conditions on the developmental toxicity of a chlorinated saline primary sewage effluent: Excessive dechlorination is better than not enough.

Chlorine-disinfected sewage effluents are typically dechlorinated by using NaHSO3, Na2SO3, or Na2S2O3, as chlorine residual could be harmful to aquatic organisms upon discharge of sewage effluents into receiving marine water. In this study, we systematically investigated the effects of dechlorination-related factors on the developmental toxicity of a chlorinated saline primary sewage effluent, via direct exposure of the embryos of a marine polychaete to the effluent. The results showed that dechlorination ratio (i.e., the ratio of the dosed amount to the requisite stoichiometric amount of a dechlorination agent) and mixing condition were critical factors affecting the toxicity of the effluent. The toxicity of the effluent under insufficient dechlorination conditions was mainly caused by residual chlorine, especially monochloramine. Although the three dechlorination agents generally performed similarly, dechlorination with Na2S2O3 required a more vigorous mixing condition than that with NaHSO3 or Na2SO3, as the relatively high density of Na2S2O3 might affect the mixing efficiency. Under insufficient mixing conditions, a prolonged dechlorination time was beneficial to achieving complete dechlorination and thus lowered the toxicity of the effluent. Moreover, because disinfection byproducts (DBPs) may have chronic effects on aquatic organisms, the developmental toxicity of the DBP mixtures in the chlorinated effluent in different dechlorination scenarios was also evaluated. The results indicated that increasing the dechlorination ratio reduced the developmental toxicity of the DBP mixture in the chlorinated saline sewage effluent, which might be ascribed to the decrease of the levels of overall brominated and iodinated DBPs; the dechlorination agent (NaHSO3 or Na2S2O3) might act as a nucleophile in the nucleophilic substitution and cause the substitution of bromine or iodine atoms in brominated and iodinated DBPs. The results from this study might aid in the design and operation of dechlorination facilities in sewage treatment plants.

Influence of blast furnace top gas composition and dust on HCl removal with low temperature Ca-based dechlorination agent

Using fixed-bed reaction method and changing the gas composition and dust content, the influence of blast furnace top gas composition and dust on HCl removal with low temperature Ca-based antichlor was studied. It was found that, when the content of CO2 in blast furnace top gas increased, the dechlorination efficiency was getting worse obviously; when the contents of CO and N2 increased, the dechlorination efficiency was getting better to a certain extent; when the content of H2 changed, the dechlorination efficiency got no significant change; as the content of dust increased, the dechlorination efficiency got better obviously when the content was less than 15 g/m3, but it would be got worse quickly when the content was more than 20 g/m3, and the best content was 15–20 g/m3; the suitable site of the process of dechlorination was after gravity dust collector and before bag dust collector.

Thermodynamic Analysis on the Thermal Treatment of Electric Arc Furnace Dust-PVC Blends

This work reports a thermodynamic assessment of EAFD chlorination products stem from thermal decomposition products of PVC. Upon PVC pyrolysis, HCl gas is liberated in conjunction with several volatile organic matters leaving solid carbonaceous residue. EAFD contains appreciable quantities of zinc, iron and lead oxides. These react with HCl to form metal chlorides, if EAFD is added to the PVC as a dechlorination agent. Selective chlorination of zinc and lead present in EAFD leaving iron in its oxide form is of an apparent commercial value. Detailed thermodynamic analysis of EAFD chlorination by HCl was performed considering the effects of several variables. These include temperature, amount of chlorination agent, presence of oxidizing agent and the effect of presence of other EAFD constituents such as sodium, potassium, calcium, silicon and sulfur. It was found that 100% recovery of both zinc and lead can be achieved for mixture containing 50% EAFD and 50% PVC when pyrolyzed under inert conditions, but contaminated with at least 20% of the iron chloride. However, when thermal treatment is performed in the presence of oxygen, the 100% zinc and lead recoveries were achieved at lower temperature with a minimal iron contamination (< 2.6%). Removal of sodium and potassium chloride from EAFD prior to pyrolysis by washing, under oxidizing condition, has also resulted in great selectivity in zinc and lead chlorination. The behavior of other elements during chlorination process was also discussed. The results obtained shall be instrumental in efforts aiming to achieve optimum recycling operations for both categories of pollutants.

Factors that affect carbothermal synthesis of nanoscale zero-valent iron supported activated carbon and its use as dechlorination agent of hexachlorobenzene

Factors that affect carbothermal synthesis of nanoscale zero-valent iron supported activated carbon and its use as dechlorination agent of hexachlorobenzene

ZnO-promoted dechlorination for hierarchically nanoporous carbon as superior oxygen reduction electrocatalyst

The dechlorination of unconventional carbon source: polyvinyl dichloride (PVDC) by ZnO at the presence of melamine was used to prepare hierarchically Porous N-doped nanoCarbon (PDC). ZnO played the multirole of dechlorination agent, mesopore templates, and most importantly, ZnCl2 generation source. ZnCl2, at latter high temperature treatment, could promote carbonization and lead to hierarchical micro- and mesopore formation, which facilitated mass transportation for electrocatalytic oxygen reduction reaction (ORR). The 900°C-annealed PDC exhibited ultrahigh activity which comprehensively surpassed the commercially available 20wt% Pt/C.

Evaluation of approaches for consumers to eliminate chlorine off-flavors from drinking water at point-of-use

Chlorine off-flavors of tap water have caused dissatisfaction and distrust from some consumers, placing pressure on operators concerning water disinfection. Evaluating practical approaches for eliminating chlorinous off-flavors by consumers at point-of-use while avoiding production of toxic byproducts is a practical concern. Three recognized dechlorination methods: ultraviolet (UV) irradiation, ascorbic acid (AA) and hydrogen peroxide (HP), were evaluated for chlorinated and chloraminated waters. AA is the most efficient for removing free chlorine and chloramine from water samples. Three new chlorine-containing compounds were detected and identified from the reaction between AA and chlorine. High doses of UV irradiation at 254 nm virtually eliminated chlorine. HP could effectively remove free chlorine but was not effective for chloramine elimination. AA shows promise as a practical household dechlorination agent. However, to assure consumers about drinking water safety, further investigation is needed to evaluate any potential toxicity concerns for reaction products in treated water.

Comparison of Reaction Rates and Relative Efficiencies for Various Dechlorination Chemicals

Dechlorination of chlorinated water and wastewater is most often achieved by chemical reduction through the addition of sulfur-IV compounds before discharge into the aquatic receiving environment or upon entry in the distribution system. However, reasonable doubts subsist about the efficiency of sulfur-IV compounds as dechlorination mediators for the reduction of chlorine and organic chloramines. As a consequence, alternative treatments have been investigated over the past few years but little information remains available on the kinetics of dechlorination at different dosages. In this study, the kinetics of dechlorination promoted by five selected dechlorination agents were observed at different stoichiometric ratios (1x, 3x, and 10x), and ANOVA was applied to the results in order to assess their statistical significance. Hydrogen peroxide (HP) was shown to promote faster than expected dechlorination; ascorbic acid and calcium thiosulfate also presented viable alternatives to treatment by sulfur-IV compounds represented by sodium sulfite and bisulfite in this study. This study challenges the common perception that HP dechlorination is slow and provides a comparative analysis for dechlorination kinetics using regression analysis, half-life values, and rate constants.

SiO2-Al2O3-P2O5무기복합체를 이용한 LiCl-KCl 방사성 폐기물의 안정화/고형화: Part 1. LiCl-KCl의 탈염화 반응거동 및 고형화특성

사용후 핵연료내 우라늄 및 초우란원소를 회수하는 파이로프로세싱 공정에서 배출되는 금속염화물계 방사성 폐기물은 높은 휘발특성과 붕규산계 유리와의 낮은 상용성으로 인해 고화처리가 쉽지 않은 폐기물이다. 이를 위해, 본 연구에서는 고화처리의 한 방법으로 탈염화 반응을 통한 고화체제조 개념을 채택하였다. 솔젤법을 이용하여 탈염화물질, <TEX>$SiO_2-Al_2O_3-P_2O_5$</TEX> (SAP)을 합성하였으며 이를 이용하여 탈염화 반응거동 반응생성물의 고형화 특성을 조사하였다. LiCl계 폐기물과 달리, LiCl-KCl폐기물의 반응은 두 개의 온도범위에서 반응이 진행되며, <TEX>$400^{\circ}C$</TEX>의 경우에는 LiCl이, 약 <TEX>$700^{\circ}C$</TEX>에서는 KCl이 주로 반응하는 것으로 확인되었다. 여러 가지 반응실험을 통하여 LiCl-KCl의 탈염화 반응에 가장 적합한 물질은 SAP 1071 (Si/Al/P=1/0.75/1 in molar)인 것으로 확인되었다. 4가지 종류의 고형화 실험을 통하여 고화체의 bulk shape과 densification은 SAP/Salt의 비에 영향 받는 것을 확인하였다. 제조된 고형화 시료는 Product Consistency Test-A법을 이용하여 기본적인 내구성을 평가하였다. 본 연구는 <TEX>$SiO_2$</TEX>, <TEX>$Al_2O_3$</TEX>, <TEX>$P_2O_5$</TEX>로 이루어진 탈염화 물질을 이용하여 반응특성과 고형화 특성에 대한 기본적인 정보를 제공하였으며, 이와 같은 실험을 통하여, 본 연구에서 제안된 탈염화 고화처리방법이 휘발특성이 높고 기존 유리매질과 상용성이 낮은 금속염화물계 폐기물에 적용이 가능함을 확인하였다. The metal chloride wastes from a pyrochemical process to recover uranium and transuranic elements has been considered as a problematic waste difficult to apply to a conventional solidification method due to the high volatility and low compatibility with silicate glass. In this study, a dechlorination approach to treat LiCl-KCl waste for final disposal was adapted. In this study, a <TEX>$SiO_2-Al_2O_3-P_2O_5$</TEX> (SAP) inorganic composite as a dechlorination agent was prepared by a conventional sol-gel process. By using a series of SAPs, the dechlorination behavior and consolidation of reaction products were investigated. Different from LiCl waste, the dechlorination reaction occurred mainly at two temperature ranges. The thermogravimetric test indicated that the first reaction range was about <TEX>$400^{\circ}C$</TEX> for LiCl and the second was about <TEX>$700^{\circ}C$</TEX> for KCl. The SAP 1071 (Si/Al/P=1/0.75/1 in molar) was found to be the most favorable SAP as a dechlorination agent under given conditions. The consolidation test revealed that the bulk shape and the densification of consolidated forms depended on the SAP/Salt ratios. The leaching test by PCT-A method was performed to evaluate the durability of consolidated forms. This study provided the basic information on the dechlorination approach. Based on the experimental results, the dechlorination method using a <TEX>$SiO_2-Al_2O_3-P_2O_5$</TEX> (SAP) could be considered as one of alternatives for the immobilization of waste salt.

An MINLP model for biofouling control in seawater-cooled facilities

The use of seawater as a cooling agent in industrial plants is becoming a common practice in regions with water scarcity. One of the main problems of this approach is the heat transfer reduction due to biofouling in the heat exchangers. Biocide agents and scheduled maintenances are commonly used to control the biofilm growth. Dechlorination agents are also used to reduce the biocide concentration in the water discharge. In this work, a mathematical programming approach to develop optimal policies of biocide continuous dosing, dechlorination agents continuous dosing and maintenance scheduling for a seawater-cooled power desalination plant is presented. The resulting mixed integer nonlinear programming model can be used to test different dosing policies to detect a superior one. For the case study presented, results show that daily dosing policies offer an optimum economic policy, although biweekly and monthly dosing policies might provide a suitable compromise between economic and operating issues.

Potential Aquatic Health Impacts of Selected Dechlorination Chemicals

Abstract Municipal wastewater effluents are one of the largest single effluent discharges in Canada. Chlorination of wastewater effluents is a widespread practice throughout Canada (excluding Quebec), the United States and parts of Europe. As chlorine in wastewater effluents is toxic to aquatic biota, dechlorination chemicals may be used to reduce residual chlorine concentrations to below 0.02 mg/L (as Cl2) as mandated by Canadian law. However, the potential aquatic health impacts of residual dechlorination chemicals must also be determined. Seven dechlorination agents (ascorbic acid, hydrogen peroxide, calcium thiosulfate, sodium sulfite, sodium thiosulfate, sodium metabisulfite, sodium bisulfite) were evaluated with regards to their 48 hour acute toxicity. Tests were conducted using Daphnia magna to identify the acute (48 h) toxicity affects of the dechlorination chemicals over a range of concentrations (0-200 mg/L). Sodium sulfite and thiosulfate were found to have the least aquatic mortality effects while hydrogen peroxide and calcium thiosulfate had the most deleterious effects.

Transcriptional Regulation of the pdt Gene Cluster of Pseudomonas stutzeri KC Involves an AraC/XylS Family Transcriptional Activator (PdtC) and the Cognate Siderophore Pyridine-2,6-Bis(Thiocarboxylic Acid)

In order to gain an understanding of the molecular mechanisms dictating production of the siderophore and dechlorination agent pyridine-2,6-bis(thiocarboxylic acid) (PDTC), we have begun characterization of a gene found in the pdt gene cluster of Pseudomonas stutzeri KC predicted to have a regulatory role. That gene product is an AraC family transcriptional activator, PdtC. Quantitative reverse transcription-PCR and expression of transcriptional reporter fusions were used to assess a role for pdtC in the transcription of pdt genes. PdtC and an upstream, promoter-proximal DNA segment were required for wild-type levels of expression from the promoter of a predicted biosynthesis operon (P(pdtF)). At least two other transcriptional units within the pdt cluster were also dependent upon pdtC for expression at wild-type levels. The use of a heterologous, Pseudomonas putida host demonstrated that pdtC and an exogenously added siderophore were necessary and sufficient for expression from the pdtF promoter, i.e., none of the PDTC utilization genes within the pdt cluster were required for transcriptional signaling. Tests using the promoter of the pdtC gene in transcriptional reporter fusions indicated siderophore-dependent negative autoregulation similar to that seen with other AraC-type regulators of siderophore biosynthesis and utilization genes. The data increase the repertoire of siderophore systems known to be regulated by this type of transcriptional activator and have implications for PDTC signaling.