Fate and Modeling of Pentachlorophenol Degradation in a Laboratory-Scale Anaerobic Sludge Digester

Anaerobic pentachlorophenol (PCP) reductive dechlorination, commonly conducted in various media and systems, deprives chlorides from the PCP’s phenolic ring and has a great potential as an effective and harmless means in PCP removal. To evaluate the potential use of the anaerobic sludge digesters to treat PCP, two laboratory-scale sludge digesters, one reactive (with PCP) and one a control (no PCP), were operated in parallel in two modes: (1) a semicontinuous-fed mode to examine the available PCP congeners and sludge acclimation process over time; and (2) a batch-fed mode to show the effect of sludge acclimation to PCP. Two multiresponse models were also employed to determine the degradation rates and extent of the PCP and its by-products. The results of the semicontinuous-fed runs showed that it took 26?days to transform PCP to 3-monochlorophenol (3-MCP) by following two major PCP degradation pathways observed in series. It appeared that PCP’s orthochlorine was first removed followed by the para lastly the meta. In the batch-fed run using the acclimation sludge, the results showed the immediate PCP dechlorination to lower chlorinated intermediates (i.e., mono- and dichlorophenols) via diverse pathways. Two multiresponse models, one comprised of seven parameters and the other of nine parameters, were deemed adequate in terms of describing the kinetics of the observed chlorophenols degradation. On the other hand, the results of the batch-fed run using unacclimated sludge showed a four-day delay before the degradation of PCP, in which a single PCP degradation pathway and the absence of 3-MCP suggested the lack of microbial ability to remove the meta chlorine of the PCP.     

Effect of the Sonophotocatalytic Pretreatment on the Volume Reduction of Sewage Sludge and Enhanced Recovery of Methane and Phosphorus

In this study, the sonophotocatalytic process, i.e., combination of ultrasonic irradiation (US) and photocatalytic reaction, was proposed as a pretreatment process for the anaerobic digestion of organic sludge in order to drastically reduce the amount of sludge and promote the recovery of methane and phosphorus. Several series of experiments employing different techniques, i.e., sonophotocatalysis (SPC), US, photocatalysis (PC), and thermal treatment, were conducted by using a batch type apparatus. The results of the SPC treatment showed a decrease in sludge volume by about 50% and the synergetic effects of US and PC treatments which were clearly observed as increases in dissolved chemical oxygen demand of sludge filtrate and in phosphorus compounds dissolution from sludge particles. In the SPC process of sewage sludge, the photocatalytic reaction was enhanced by the sufficient disintegration of sludge flocks due to the US treatment. Any pretreatments applied promoted the anaerobic digestion process, however, there was little synergetic effect and the long time SPC treatment resulted in a decrease in the reaction rate.     

Effects of Pretreatments on Thermophilic Aerobic Digestion

In order to enhance the degradation efficiency of waste activated sludge (WAS) in thermophilic aerobic digestion (TAD), various pretreatment methods were investigated for the decomposition of WAS, including ultrasonic, thermal, alkaline, and mechanical treatments. Thermophilic aerobic digestion experiments using pretreated WAS were conducted to investigate the effects of the pretreatments on degradation efficiency in TAD. The pretreatment methods enhanced the degradation efficiency in the TAD process and thermal and mechanical pretreatments had the best efficacy from the viewpoint of solid particle decomposition. Based on the efficiencies of solid particle decomposition, the order of pretreatment efficacy was as follows: mechanical treatment > thermal treatment > alkaline treatment > ultrasonic treatment. Based on total suspended solids reduction and released compounds decomposition, the order of TAD efficacy was as follows: TAD with thermal pretreatment > TAD with mechanical pretreatment > TAD with alkaline pretreatment > TAD with ultrasonic pretreatment > control TAD (without pretreatment). Because the thermal process consumes a large amount of energy, mechanical pretreatment is considered the most practical pretreatment for the TAD process.     

微生物来源对餐厨垃圾厌氧消化产氢的影响

微生物来源对餐厨垃圾厌氧消化产氢的影响很大。单独一种接种物的条件下,剩余污泥的产氢效果是最好的,氢气的浓度和产量都最大,分别为47．1％和100．0mLH2／gVS,其次是矿化污泥和矿化垃圾,颗粒污泥体系氢气的产量最少,分别为88．6、57．8和36．8mLH2/gVS,但是颗粒污泥体系产生了甲烷气体。污泥和矿化污泥混合后,在实验时间内,能够提高氢气的产量到106．4mLH2／gVS,其余的混合体系的氢气的浓度和产量较单独的剩余污泥体系差。     

Radiation-Assisted Process Enhancement in Wastewater Treatment

Laboratory and pilot tests were conducted to investigate the use of ionizing radiation at an activated sludge wastewater treatment facility with residuals processing. Operational enhancements were investigated with respect to bulking control, thickening enhancement, and anaerobic stabilization processes. Radiation caused permanent effects in measured sludge parameters including solids content, chemical oxygen demand, ammonia-nitrogen, zeta potential, specific surface area, resistance to filtration, sludge volume index, pH, organic acid production, and digester gas evolution. Analysis of beneficial effects from preliminary studies and pilot tests demonstrated that a dose of 2–3 kGy would be potentially successful for bulking control and to a lesser degree, enhanced thickening and radiation-assisted anaerobic digestion. A cost analysis based on preliminary tests determined that a centralized electron beam irradiator could be applied economically in an integrated approach at an estimated annual savings of $0.2–2.7 million depending upon the application. Considering that the annual cost of operating an accelerator unit was estimated at $2.4 million ($2.16/m3), this might translate into an important savings for a large-scale wastewater treatment facility.     

Study of the reductive dechlorination of pentachlorophenol by a methanogenic consortium

Pentachlorophenol (PCP) dechlorination by a methanogenic consortium was observed when glucose, formate, lactate, or yeast extract was present in the mineral medium as a secondary carbon source. Acetate was not a good substrate to sustain dechlorination. The consortium was able to dechlorinate the different monochlorophenols, although the chlorine in position ortho and meta was removed more readily than in para position. Dechlorination was most efficient at 37 degrees C. At 45 degrees C, the first PCP dechlorination steps were very rapid, but 3,5-dichlorophenol (3,5-DCP) was not further dechlorinated. At 15 and 4 degrees C, dechlorination was very slow. The dechlorination of PCP to 3-chlorophenol (3-CP) was still observed after the consortium had been subjected to heat treatment (80 degrees C, 60 min), suggesting that spore-forming bacteria were responsible. The dechlorinating activity of the consortium was significantly reduced by the presence of hydrogen, 2-bromoethanosulfonic acid (BESA), or sulfate but not of nitrate. The dechlorination of 3-CP was completely inhibited by heat treatment or the presence of BESA, suggesting that a syntrophic microorganism would be involved. Vigorous agitation of the consortium stopped the dechlorination, but the presence of DEAE-Sephacel acting as a support was very efficient in restoring the activity, suggesting that association between certain members of the consortium was important.     

Aerobic mineralization of 2,6-dichlorophenol by Ralstonia sp. strain RK1

A new aerobic bacterium was isolated from the sediment of a freshwater pond close to a contaminated site at Amponville (France). It was enriched in a fixed-bed reactor fed with 2,6-dichlorophenol (2,6-DCP)as the sole carbon and energy source at pH 7.5 and room temperature. The degradation of 2,6-DCP followed Monod kinetics at low initial concentrations. At concentrations above 300 microM (50 mg.liter-1), 2,6-DCP increasingly inhibited its own degradation. The base sequence of the 16S ribosomal DNA allowed us to assign the bacterium to the genus Ralstonia (formerly Alcaligenes). The substrate spectrum of the bacterium includes toluene, benzene, chlorobenzene, phenol, and all four ortho- and para-substituted mono- and dichlorophenol isomers. Substituents other than chlorine prevented degradation. The capacity to degrade 2,6-DCP was examined in two fixed-bed reactors. The microbial population grew on and completely mineralized 2,6-DCP at 2,6-DCP concentrations up to 740 microM in continuous reactor culture supplied with H2O2 as an oxygen source. Lack of peroxide completely stopped further degradation of 2,6-DCP. Lowering the acid-neutralizing capacity of the medium to 1/10th the original capacity led to a decrease in the pH of the effluent from 7 to 6 and to a significant reduction in the degradation activity. A second fixed-bed reactor successfully removed low chlorophenol concentrations (20 to 26 microM) with hydraulic residence times of 8 to 30 min.     

Anaerobic Digestion of Food Industry Wastes: Effect of Codigestion on Methane Yield

Anaerobic treatability of two different wastes that represent the main refuse streams generated by a frozen food factory (fresh vegetable waste and precooked food waste) was assessed. Moreover, the sludge coming from agro-industrial wastewater treatment was codigested with the previously mentioned wastes. Batch tests were performed at different solids content both on the single wastes and on appropriate mixtures of them (also in order to simulate the seasonality of factory production). Both fresh vegetable and precooked food wastes strongly inhibited methanogenesis from unacclimated inoculum at 10% solids content (undiluted waste) and 5% solids content (eight- to nine-fold diluted waste), respectively. This was due to their high contents of potassium and lipids, respectively. The aerobic sludge from the wastewater treatment plant did not exert inhibitory effect up to 10% solids content (undiluted waste). Codigestion of the fresh vegetable waste and sludge (60 and 40% on wet basis) was more effective both in terms of rate and yield of methane production with respect to the single wastes (due to dilution and synergic effects). On the other hand, methanogenesis remained strongly inhibited from mixtures containing pre-cooked food waste (at 25 and 45%, on wet basis). Methanogenesis inhibition could be overcome by a long acclimation period. The results showed that fill-and-draw digestion in a 0.5 L lab-scale reactor of the fresh vegetable waste and sludge mixture after start up with acclimated inoculum allowed higher methane yields (37% at high organic load and 57% at low organic load). Better results were obtained in a 1.7 L micropilot fill-and-draw reactor (yield of 67%) fed at higher frequency.     

微波消解-氢化物发生原子荧光光谱法测定污泥中汞和砷

利用高压密闭微波消解技术消解样品, 建立了氧化物发生原子荧光光谱法测定污水处理厂污泥中汞和砷的方法。对消解酸和消解程序进行了优化, 同时讨论了硼氢化钾浓度对测定的影响。结果表明, 选用10 mL 硝酸-盐酸(4+6)可将0.25 g污泥样品消解完全;确定消解程序如下:消解功率为850 W, 发射率为80%, 第1步采用5 min内从室温升温至110 ℃, 保持5 min, 第2步采用10 min内继续升温至180 ℃, 保持20 min;在硼氢化钾浓度为20 g/L时进行测定, 效果最佳。汞和砷的方法检出限分别为0.001 6 mg/kg和0.002 2 mg/kg。方法应用于污泥样品中汞和砷的测定, 相对标准偏差(RSD, n=6)分别为2.7 %～3.8%和1.1%～2.0%, 汞和砷的加标回收率分别为96%～102%和98%～104%。方法应用于土壤标准样品GSS-25和GSS-26中汞和砷的测定, 结果与认定值一致, 汞和砷的RSD(n=6)分别为4.5%～7.4%和2.2%～2.4%。     

Formation of octa- and heptachlorodibenzo-p-dioxins during semi anaerobic digestion of sewage sludge

Octa- and heptachlorodibenzo-p-dioxins (OCDD and HpCDD) were formed during semi anaerobic digestion of sewage sludge at low temperature (20 degrees C). A twofold increase of OCDD and HpCDD was found after a digestion period of 192 days even if concentrations were corrected by corresponding accumulation factors caused by the degradation of biomass. Other polychlorinated dibenzo-p-dioxins and furans (PCDD/F) and polychlorinated biphenyls (PCB) were not increased. Under strictly anaerobic and aerobic conditions, however, no OCDD and HpCDD were formed. Semi anaerobic formation of OCDD and HpCDD may explain the prevalence of higher chlorinated PCDD in the homologues pattern typical for sewage sludge.     

Pilot Plant Study of Simultaneous Sewage Sludge Digestion and Metal Leaching

This research is related to a preindustrial pilot scale study of the performance of the simultaneous sewage sludge digestion and metal leaching (SSDML) process for decontamination and stabilization of sewage sludge. Ten batch tests were carried out in two 4?m3 bioreactors under various conditions of operation. Results indicated that the addition of 1.0 to 1.5?g?S0/L, which is the equivalent of approximately 30 to 50?kg?S0 per tons dry sludge, is sufficient to obtain conditions of acidity (pH<2.5) and oxido-reduction potential greater than 500 mV necessary for an effective solubilization of toxic metals. The final average of metal solubilization in the output sludge during the SSDML process varied in the following ranges: 25–78% Cd, 9–32% Cr, 48–100% Cu, 77–99% Mn, 15–53% Ni, 12–47% Pb, and 66–100% Zn. The N, P, and K contents were also preserved in the decontaminated sludge. Moreover, the use of low concentrations of elemental sulfur makes it possible to obtain decontaminated sludge with a low total sulfur content (1.4–1.5% S) compatible with agricultural use. The suspended solids removal calculated for the SSDML process was slightly lower, (2.5±0.4)% volatile suspended solids per day, than those reached using standard aerobic digestion. Finally, the SSDML process was found to be effective in removing bad odors and in the destruction (99–100%) of indicator bacteria.     

Improved Anaerobic Degradation of Phenol with Supplemental Glucose

In this study, phenol degradation was investigated, with and without glucose as a cosubstrate, in batch and continuous studies. The two 2-L lab upflow anaerobic sludge blanket reactors were operated at a constant hydraulic retention time of 12 h with a gradual stepwise increase in phenol concentration from 105 to 1,260 mg∕L. Batch studies showed that a 1,000-mg∕L glucose supplement provided the fastest phenol removal and sludge acclimation. The effect of the glucose supplement was assessed based on microbial acclimation and granulation, phenol degradation, and resistance to shock loading. The reactor with the 1,000-mg∕L glucose supplement had a shorter start-up and granulation period (4 months, compared to 7 months for the reactor without glucose supplement), larger granule size (2.76 mm, compared to 1.77 mm), and higher phenol removal efficiency under steady-state operation at 6-kg phenol-COD∕L?day (98% compared to 88%). The reactor with the glucose supplement also exhibited a higher resistance to shock load or temperature change and faster recovery than the reactor without a glucose supplement.     

Aerobic Thermophilic and Anaerobic Mesophilic Treatment of Sludge

The objective of this research was to investigate the effectiveness of aerobic thermophilic treatment in enhancing conventional anaerobic mesophilic digestion in terms of pathogen reduction. vector attraction reduction, volatile solids (VS) reduction, gas production, and product sludge dewaterability. Lab-scale two-stage experiments were conducted with the aerobic thermophilic stage as pretreatment (AerTAnM) or as posttreatment (AnMAerT) to mesophilic anaerobic digestion. The lab-scale AerTAnM and AnMAerT systems were operated at system sludge residence times (SRTs) of 15 and 15.5 days, thermophilic reactor temperature = 62°C, and mesophilic reactor temperature = 37°C. The control anaerobic digester was operated at a system SRT of 15 and 15.5 days and temperature = 37°C. The AerTAnM and AnMAerT systems and control anaerobic digester operated at a system SRT of 15 days were able to achieve VS reductions of >38% (Class A sludge vector attraction reduction requirement). The VS reductions by the AerTAnM and AnMAerT systems (～65%) were higher than the VS reduction in the control (～51%) by 14%. The AerTAnM and AnMAerT systems reduced fecal coliform density in the feed sludge from 108 most probable number (MPN) per gram of total solids (TS) to <103 MPN∕g TS (Class A sludge fecal coliform density limit), whereas the control reduced the same feed sludge fecal coliform density to about 106 MPN∕g TS. The AerTAnM and AnMAerT systems and control can reduce Salmonella density in the feed sludge from 5 to 12 MPN∕4 g TS to <1 MPN∕4 g TS. Average methane gas production by the AerTAnM system anaerobic mesophilic digester (0.61 m3∕kg VS destroyed) was higher than those of the AnMAerT system (0.50 m3∕kg VS destroyed) and control (0.52 m3∕kg VS destroyed) anaerobic mesophilic digesters. Average H2S content of the AerTAnM [133 ppm volume-to-volume ratio (v∕v)] system anaerobic thermophilic digester gas was significantly lower than those in gas from the AnMAerT system (249 ppm v∕v) and control (269 ppm v∕v) anaerobic mesophilic digesters. The dewaterabilities of the product sludge (measured as time-to-filter, s) from the AerTAnM system (237 s) and AnMAerT system (203 s) were significantly better than that of the product sludge from the control (346 s).     

Combined Anaerobic/Aerobic Secondary Municipal Wastewater Treatment: Pilot-Plant Demonstration of the UASB/Aerobic Solids Contact System

Anaerobic pretreatment followed by aerobic posttreatment of municipal wastewater is being used more frequently. Recent investigations in this field using an anaerobic fluidized bed reactor/aerobic solids contact combination demonstrated the technical feasibility of this process. The investigation presented herein describes the use of a combined upflow anaerobic sludge bed (UASB)/aerobic solids contact system for the treatment of municipal wastewater and attempts to demonstrate the technical feasibility of using the UASB process as both a pretreatment unit and a waste activated sludge digestion system. The results indicate that the UASB reactor has a total chemical oxygen demand removal efficiency of 34%, and a total suspended solids removal efficiency of about 36%. Of the solids removed by the unit, 33% were degraded by the action of microorganisms, and 4.6% accumulated in the reactor. This low solids accumulation rate allowed operating the UASB reactor for three months without sludge wasting. The long solids retention time in this unit is comparable to the one normally used in conventional sludge digestion units, thus allowing the stabilization of the waste activated sludge returned to the UASB reactor. Particle flocculation was very poor in the UASB reactor, and therefore, it required postaeration periods of at least 100?min to proceed successfully in the aerobic unit. Polymer generation, which is necessary for efficient biological flocculation, was practically nonexistent in the anaerobic unit; therefore, it was necessary to maintain dissolved oxygen levels greater than 1.5?mg/L in the aerobic solids contact chamber for polymer generation to proceed at optimum levels. Once these conditions were attained, the quality of the settled solids contact chamber effluent always met the 30?mg BOD/L, 30?mg SS/L secondary effluent guidelines.     

Examination on Process Configurations Incorporating Thermal Treatment for Anaerobic Digestion of Sewage Sludge

This study aimed to examine the process configurations for mesophilic anaerobic digestion of sewage sludge, when incorporated with thermal treatment of 120°C for 1?h. Four types of process configurations were designed: control (no thermal treatment), pretreatment and posttreatment configurations of the single-stage process, and an interstage-treatment configuration of the two-stage process. The lab-scale digesters were operated at 35°C with the sewage sludge of 4.5% total solids, and were equally set at the total hydraulic retention time of 20 days. At the steady state, the control digester showed 35.3% of volatile solids (VS) destruction and 0.168?L/g VS fed of methane production. Compared to the control, the VS destruction in the pre-, post-, and interstage-treatment configurations was increased by 4.5, 6.6, and 9.9%, respectively, while the methane production in the post- and interstage-treatment configurations was improved by 0.036 and 0.028?L/g VS fed, respectively. The pretreatment configuration yielded identical methane production to the control. Therefore, it is more effective on anaerobic digestibility to apply the moderate thermal treatment after sewage sludge is digested once. On the other hand, the increase in soluble chemical oxygen demand and deterioration of dewaterability were observed, when solids destruction was improved.     

Anaerobic Thermophilic/Mesophilic Dual-Stage Sludge Treatment

Conventional anaerobic mesophilic (AnM) digestion coupled with anaerobic thermophilic (AnT) pretreatment (AnTAnM system) and anaerobic thermophilic posttreatment (AnMAnT system) of mixed sludge (thickened waste activated sludge and primary sludge) was investigated. The main objectives were to investigate the ability of AnTAnM and AnMAnT systems to produce a product sludge that can meet Class A sludge requirements and to enhance sludge treatment in terms of volatile solids (VS) destruction, gas production, sludge supernatant chemical oxygen demand (COD) reduction, and sludge dewaterability. Lab-scale AnTAnM and AnMAnT systems were operated at a system sludge residence time of 15 days and temperature of 62°C in AnTAnM and AnMAnT thermophilic reactors. A lab-scale control anaerobic digester was operated at a system sludge residence time of 15 days and temperature of 37°C. The AnTAnM and AnMAnT systems and control achieved VS reductions of >38% (Class A sludge vector attraction reduction requirement). Average VS reductions by the AnTAnM (61%) and AnMAnT (63%) systems were significantly higher than VS reduction by the control (50%). The fecal coliform densities in the AnTAnM and AnMAnT system product sludges were below 1,000 most probable number (MPN) per gram total solids (TS) (Class A sludge fecal coliform density limit) compared to 106 MPN∕g TS in the control product sludge. The product sludge from the AnTAnM and AnMAnT systems and the control anaerobic digester met the Class A sludge Salmonella density limit (<3 MPN∕4 g TS) when fed with feed sludge containing 2–12 MPN∕g TS. Average methane production by the AnTAnM mesophilic digester (0.66 ± 0.10 m3∕kg VS destroyed) was higher than those of the AnMAnT (0.51 ± 0.06 m3∕kg VS destroyed) and the control anaerobic mesophilic digesters (0.52 ± 0.03 m3∕kg VS destroyed). The average supernatant CODs in the AnTAnM system product sludge (10,500 ± 200 mg∕L) and AnMAnT system product sludge (10,200 ± 150 mg∕L) were approximately the same and were significantly lower than the supernatant COD in the control anaerobic digester (14,100 ± 350 mg∕L). All three systems were fed with feed sludge containing an average supernatant COD of 22,500 mg∕L. Dewaterability of the product sludges, measured as time to filter, was 244 and 207 s for AnTAnM and AnMAnT systems, respectively, whereas it was 364 s for the control anaerobic digester product sludge.     

生活污泥用于焦化废水处理的培养驯化

介绍了用生活污水厂的干污泥做菌种,进行焦化废水处理的培养驯化过程。采用连续曝气、间歇进水的方式对污泥进行驯化,通过调整温度、pH值、磷酸三钠和萄葡糖的投加量等工艺参数,32d内使污泥恢复了活性并完全适应了焦化废水环境,使废水中酚的去除率达到99.8%以上,CODcr去除率达到60%以上。     

Improved Anaerobic Process Efficiency Using Mesophilic and Thermophilic Elutriated Phased Treatment

An innovative anaerobic digestion elutriated phased treatment (ADEPT) has been evaluated at mesophilic (M-ADEPT) (35°C) and thermophilic (T-ADEPT) (55°C) temperatures in which the organic loading rate (OLR) was increased until reactor failure (pH<5.5). Single-stage continuously stirred tank reactors (CSTRs) at both temperatures were also operated as controls (M-CSTR for 35°C and T-CSTR for 55°C). The T-CSTR failed at an OLR of 7.4 g volatile solid (VS)/L?day and the M-CSTR at an OLR of 10 g VS/L?day while the M-ADEPT continued until an OLR of 18 g VS/L?day and the T-ADEPT reached an OLR of 24 g VS/L?day before system failure. The T-CSTR produced the poorest effluent quality as manifested by high propionate concentrations (1,500–2,500 mg/L) while both M-ADEPT and T-ADEPT produced much better quality of effluent with propionate concentrations below 100 mg/L. Thus it appears that the T-ADEPT design may solve effluent quality problems associated with normally high propionate concentrations produced during thermophilic anaerobic digestion. Superior effluent quality, reduced reactor volume requirements, more stable methanogenesis due to the extended solids retention time, and uncoupling of the methanogen wasting from the refractory sludge wasting process resulted in stable and efficient processing at both temperatures for the innovative ADEPT design. Because the higher amounts of volatile fatty acids produced in the acid elutriation phase of the ADEPT system can be a favorable carbon source for biological nutrient removal in wastewater treatment plants, this positive aspect should be considered in future applications of the ADEPT system.     

Integrated System for Remediation of Contaminated Soils

A pilot-scale study was conducted to evaluate an integrated system for the remediation of soils contaminated primarily with pentachlorophenol (PCP), a wood preserver. The integrated soil remediation system consisted of three unit processes: (1) Soil solvent washing; (2) solvent recovery; and (3) biotreatment of the contaminant residual. Pilot-scale countercurrent solvent washing was carried out using a 95% ethanol solution—a solvent that in an earlier bench-scale study was found to be effective in removing PCP and hydrocarbons (HCs) from soils. Three-stage countercurrent solvent washing of a field-contaminated soil was performed using batches of 7.5 kg of soil and 30 L of solvent (1 kg:4 L soil-to-solvent contact ratio). The washed soil was rinsed with water in a single stage after three countercurrent wash stages. Pilot-scale, three-stage countercurrent solvent washing with 95% ethanol reduced the PCP and HC contamination on the soil by 98 and 95%, respectively. The spent solvent and the spent rinse water were combined as the spent wash fluid for further treatment. A pilot-scale distillation unit was used to recover the ethanol from the spent wash fluid. The HC constituents of the spent wash fluid were removed by pH adjustment prior to feeding the spent wash fluid to a distillation unit. Greater than 96% of the ethanol in the spent wash fluid was recovered in the distillate stream, whereas PCP was captured in the bottoms stream. The bottoms stream was treated sequentially in anaerobic and aerobic granular-activated carbon fluidized-bed reactors. Complete mineralization of PCP was achieved using this treatment train.     

Treating Soil PCP at Optimal Conditions Using Heme and Peroxide

The environmental impact of pentachlorophenol (PCP) has been the subject of extensive research in recent years. Investigations of PCP degradation using both biotic and abiotic methods are extensively reported in literature. Based on some preliminary tests (not shown), an abiotic method was found for oxidative PCP degradation in soil under unsaturated conditions and a neutral pH. Reagents used were heme (a catalyst) and peroxide (an oxidant). From two screening tests (not shown), the heme and peroxide were identified as the most important factors on PCP degradation in highly PCP-contaminated soil. The objective of this study was to determine the optimum doses of heme and peroxide for PCP degradation in soil. Using a statistical method, known as response surface methodology, a quadratic function was fit to the data and used to estimate the optimum doses of heme and peroxide at 0.035?g/2?g-soil and 0.105?g/2?g-soil, respectively, in treating PCP-contaminated soil. The model also was used to determine the region in which the response was within the 95% confidence region of the optimum. The lowest heme and peroxide doses required to achieve a response within the 95% confidence region of the optimum were found to be 0.017?g/2?g-soil and 0.095?g/2?g-soil, respectively. Based on the results of the optimization studies, kinetic studies were conducted to examine the rate and extent of PCP degradation in soil over time. The results showed that about 50% of PCP was degraded within the first 30?min, and up to ～ 80% of PCP was degraded within 4?h.