Computerized Methodology for Evaluating Drinking Water Treatment Technologies: Part II

The previously described computer based system, Best Available Technology Evaluator (BATE), is used for least cost comparison of AST and AST with GPGAC and LPGAC processes. The underlying LPGAC cost and process dynamics simulation models are complex and need to be modified and coupled in an efficient manner in order to yield useful preliminary design data. This paper discusses a technique for such model combination and a method for finding the LPGAC least cost. Sensitivity analysis of LPGAC cost and performance with respect to common operating parameters such as empty bed contact time (EBCT), hydraulic loading rate (HL), and process configuration is discussed in light of this efficient model combination and least cost finding technique. This study shows that there is an optimal combination of EBCT and LPGAC process configuration for which its cost is comparable to that of AST alone and AST with GPGAC. Such optimal combinations are discussed for some VOC scenarios.     

Control of odors arising from the thickening of surplus activated sludge in the dissolved air flotation unit

This paper reports on investigations carried out to determine the feasibility of using various types of adsorbent medium to remove odors emitted during the thickening of surplus activated sludge by the dissolved air flotation (DAF) process. The performances of four different commercial grades of granular activated carbon and a grade of activated alumina were evaluated using a pilot facility set up at a local wastewater treatment plant. The odorous air directly above the DAF unit was pumped simultaneously through a set of columns each filled with the appropriate test adsorbent until odor breakthrough occurred. Air samples were collected at the inlet and outlet of each column and also at intermediate sampling ports located along the column. The odor concentration of air samples was assessed by dynamic olfactometry and the capacity of the various media for removing sewage odor was evaluated and compared. Results revealed that the odor concentration of the influent column air averaged 35 son m^?3. Of the four activated carbon grades tested, the alkali impregnated carbon that is frequently recommended for used at sewerage facilities was found to be least effective in the treatment of odors from the DAF unit. The capacity of the various media tested ranged from about 2650 son kg^?1 for the worst activated carbon grade to 37 510 son kg^?1 for the activated alumina which was the most cost effective adsorbent used. It is estimated that the cost for treating a given volume of odorous air at the DAF unit with activated alumina will be less than 65 % of the most economic activated carbon grade.     

Optimal design of single and multiple stage activated sludge processes

The present paper describes a rational approach to minimum cost design of an integrated activated sludge process which includes activated sludge reactor, secondary clarifier and sludge recycle. The cost of anaerobic digestion of excess sludge produced is also considered. Procedures for optimal design of both single and multiple stage activated sludge processes, considering construction and operational costs are developed. Biomass concentration in aeration tank and return sludge are utilized as the primary independent design variables to which system performance is related for single stage process. In the multiple stage process, additional design variables (flow and volume fractions for each stage) are included in design vector. Liquid-biomass separation is based on the batch solids flux theory. The optimization problem is framed as minimization of capital and operating cost subject to the constraints determined by effluent quality criteria and process variables affecting the performance. The interior penalty function method is used. Results definitely favor the application of multiple stage process over single stage. The major factor which appears to be contributing to reduction in cost is the biological solids retention time and hence the aeration tank volume.     

VOC emissions from primary clarifier weirs

Volatile organic compounds (VOCs) are emitted from wastewater treatment processes via stripping and volatilization. Significant progress has been made in modeling these emissions, but questions remain regarding operative mass transfer mechanisms in certain processes. In the case of flow over weirs and drop structures, two approaches have been presented: mass transfer is modeled as taking place either (1) entirely in the nappe, or (2) entirely in air bubbles entrained by falling water in the tailwater pool. In the present work, these two very different modeling approaches are evaluated using experimental results on liquid-side concentrations of chlorinated solvents above and below a primary clarifier weir. The model locating the primary emission mechanism within entrained air bubbles in the tailwater pool is found to predict observed liquid-side VOC concentrations better than the model which considers only emissions from the weir nappe.     

Evaluating Binary Sorption of Phenol/Aniline fromAqueous Solutions onto Granular Activated Carbon and Hypercrosslinked Polymeric Resin (MN200)

Sorption equilibrium of phenol and aniline onto the granular activated carbon and hyperreticulated un-functionalized polymeric resin (MN200) was investigated in single and binary component aqueous systems. Higher loading was obtained for aniline than phenol onto both sorbents, which is probably due to hydrophobic difference between both solutes and the greater electronic density of the aromatic ring of the aniline. Granular activated carbon reported larger uptake than resin MN200 for both solutes, which may be attributed to the better physical properties of the granular activated carbon, for instance, larger surface area. The experimental sorption could be properly described by the Langmuir and Freundlich isotherms. Five models for predicting the binary equilibrium sorption isotherm were compared in order to determine the best fit model to correlate binary experimental data: the extended Langmuir isotherm with and without a constant interaction factor, a simplified model based on the single equilibrium factors, the empirical extended Freundlich isotherm and the modified extended Langmuir equation, which considers the synergistic interactions between sorbate–sorbate and not only the competition between them defined by the extended Langmuir model. The modified extended Langmuir model provides the best agreement between predicted and experimental data indicating that the synergistic interactions between solutes play an important role in the binary phenol/aniline sorption system.     

Removal of Hydrophobic Volatile Organic Compounds in an Integrated Process Coupling Absorption and Biodegradation—Selection of an Organic Liquid Phase

Since usual processes involve water as absorbent, they appear not always really efficient for the treatment of hydrophobic volatile organic compound (VOC). Recently, absorption and biodegradation coupling in a two-phase partitioning bioreactor (TPPB) proved to be a promising technology for hydrophobic compound treatment. The choice of the organic phase, the non-aqueous phase liquid (NAPL) is based on various parameters involved in both steps of the process, hydrophobic VOC absorption in a gas?Cliquid contactor, and biodegradation in the TPPB. VOC solubility and diffusivity in the selected NAPL, as well as NAPL viscosity, seems to be the main parameters during the absorption step, while biocompatibility, namely the absence of toxic effect of the NAPL towards microorganisms, non-biodegradability and VOC partition coefficient between NAPL and water were revealed as the key factors during the biodegradation step. The screening of the various NAPL available in the literature highlighted two families of compounds matching the required conditions for the proposed integrated process, silicone oils and ionic liquids.     

Adsorption-desorption of trichloroethylene in granular media

Sorption studies were conducted to determine the adsorption and desorption characteristics of a common synthetic chemical, trichloroethylene (TCE) in four granular media; sandy loam soil, organic top soil, peat moss and granular activated carbon (GAC). The results showed that the Freundlich Isotherm satisfactorily represents adsorption and desorption of dissolved TCE in these media and that the organic carbon content is an important factor in both processes. The soil-water partition coefficient (K _oc) for TCE suggests that it will migrate quickly through soil.     

Evaluation of Activated Carbon-Coated Electrode in Electrostatic Precipitator and Its Regeneration for Volatile Organic Compounds Removal

Activated carbon-coated electrode was developed and applied in electrostatic precipitator to remove volatile organic compound gases simultaneously with dust particles from a contaminated air. The activated carbon coating mixture was made up of powdered activated carbon (AC), carbon black (CB), and polyvinyl acetate (PVA), and methanol was added as a solvent to control the thickness of the mixture for best coating performance. During the coating process, the Brunauer-Emmett-Teller (BET) surface decreased to 86% of the original AC while pore volume percentages of macro pore increased, compared to micro- and meso-sized pores. The adsorption isotherm of benzene, toluene, ethyl benzene, and xylene (BTEX) gases onto the original AC and AC coating mixture (AC thoroughly mixed with PVA and methanol for coating and powdered again after dry) were tested and compared to each other, and it was found that both isotherm were best fitted to Freundlich and Langmuir isotherm with the order of adsorption capacities; ethyl benzene?>?m-xylene?>?toluene?>?benzene. The difference between adsorption capacities was clearer with the absorbent AC but became little with the AC coating mixture. In removing BTEX at increasing linear velocities up to 6.7 cm/s, it appeared that the surface area of AC electrode was directly proportional to its removal rate of BTEX. The thermal desorption was applied to regenerate the AC electrode, and 200 °C was found to be most efficient for benzene desorption, but higher temperature would be required for entire BTEX gases desorption.     

倒伏超级稻割前摘脱台试验

针对目前倒伏超级稻霜前机械化收获存在的问题,设计了一种新型气吸式摘脱台。为优化该摘脱台的设计、确定其关键参数最佳匹配,以倒伏型水稻割前摘脱总损失为评价指标,回收率为参考指标,对摘脱滚筒齿尖线速度、喂入速度、喂入口水平开度与喂入口风速等进行了单因素和正交试验。单因素试验表明：影响摘脱台损失的主要因素是喂入速度、摘脱滚筒齿尖线速度、喂入口风速和喂入口水平开度。正交试验表明：最佳组合为摘脱滚筒齿尖线速度23 m/s,喂入速度0.9 m/s,喂入口水平开度100 mm与喂入口气流速度14 m/s,割前收获顺向倒伏超级稻总损失1.52%。试验结果表明所设计的摘脱台满足倒伏超级稻收获要求,并为超级稻割前摘脱联合收割机摘脱台的设计提供依据。     

Removal of Iron and Manganese from Water with a High Organic Carbon Loading. Part II: The Effect of Various Adsorbents and Nanofiltration Membranes

This paper describes the second part of an investigation into the removal of iron and manganese from water with a high dissolved organic carbon (DOC) loading. This investigation focused on the use of ferrichloride as coagulant in conjunction with hydrogen peroxide as an oxidant and different physical treatment processes, such as adsorption and nanofiltration, to reduce dissolved iron and manganese in water with a high DOC loading. It was found that nanofiltration employing H₂O₂ is the only treatment capable of producing drinking water within the set requirements of the treatment facility. Both fly ash and powdered activated carbon (PAC) used as adsorbents yielded a low percentage removal of DOC, while all the treatment methods evaluated accomplished high removals of the metallic ions Fe(II) and Mn(II). From the results a staggered treatment approach is recommended to obtain the best results at the lowest cost.     

Coal sorbent system for the extraction and disposal of heavy metals and organic compounds

The Coal Sorbent System (CSS) utilizes a newly developed coal-based sorbent, which has the combined characteristics of an activated carbon and ion exchange resin. The low cost and excellent combustion characteristics (including very low sulfur and ash) of the coal sorbent enabled the development of a system to extract metals and organics from aqueous streams, concentrate them on the sorbent and encapsulate the metals (destroy organics) utilizing developed incineration or vitrification processes. Coal Sorbent is produced by the chemical leaching of ordinary coal using the TRW Molten Caustic Leaching (MCL) process. The coal sorbent produced from the MCL process is much like activated carbon with a large internal surface area (up to 1000 m²/g). In addition to its high surface area, the coal sorbent, unlike activated carbon, has inherent carboxyl groups much like ion exchange resins that can remove heavy metals from wastewater. Heavy metal capacities up to 70 mg/g (7%) of coal sorbent have been demonstrated. The coal sorbent has both a high surface area and a large concentration of carboxyl groups on the surface. These two features enable the Coal Sorbent to be used as a wastewater treating medium to remove both organics (high carbonaceous surface area) and heavy metals (carboxyl ion exchange groups). Once the heavy metals and organics are adsorbed on the virtually sulfur and ash-free coal sorbent, the spent coal sorbent can be processed by commercially available combustion/vitrification processes to encapsulate the metals and destroy the organics. Waste volume reductions as high as 420,000:1 have been demonstrated for uranium groundwater applications at an estimated costthrough disposal of < $0.001/gallon water treated.     

Photolysis, Sonolysis, and Photosonolysis of Trichloroethane (TCA), Trichloroethylene (TCE), and Tetrachloroethylene (PCE) Without Catalyst

Photolysis, sonolysis, and photosonolysis of common groundwater contaminants, namely 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene, were investigated using a flow-through photosono reactor system. Simulated groundwater containing the chlorinated volatile organic compounds (VOCs) was exposed to ultraviolet light (UV), ultrasonication (US), and UV and US concurrently (UVUS), without a photo catalyst. VOC removal efficiencies of the UV, US, and UVUS treatment processes were computed from the VOC concentrations in influent and effluent of the reactor. The process using UVUS exhibited larger degradation efficiencies than that with UV and US separately in most cases; however, statistical analysis showed that the UVUS treatment efficiency is likely to be additive of the UV and US treatment efficiencies. The results also showed that the increase of the detention time from 26 to 60 min had no significant effect on the VOC removal efficiencies in these processes.     

寒地超级稻摘脱台设计参数的试验研究

为进一步改善寒地超级稻霜前收获摘脱台的性能,降低梳脱损失,通过对影响摘脱台工作性能的主要参数和结构特点的分析,在4ZTL-1800型气吸式割前摘脱稻麦联合收割机研究基础上,设计了一种具有可更换3种滚筒的摘脱台。以摘脱台的总损失为评价指标,对摘脱滚筒线速度、喂入速度、喂入口开度与喂入口风速进行了单因素和多因素正交试验。单因素试验表明：摘脱滚筒线速度、喂入速度和喂入口风速三因素对摘脱损失有显著影响。正交试验表明：最佳组合为滚筒线速度23 m/s,喂入速度1.1 m/s,喂入口开度120 mm,喂入口气流速度14 m/s,此技术条件下摘脱损失不大于1%。所设计的摘脱台满足超级稻收获要求,并为超级稻割前摘脱联合收割机摘脱台的设计提供依据。     

Comparison of Activated Carbon and Physic Seed Hull for the Removal of Malachite Green Dye from Aqueous Solution

In the present work, the effectiveness of physic seed hull, PSH (Jatropha curcas L.), as an alternative low-cost adsorbent for the removal of malachite green (MG) dye from simulated wastewater has been studied. It has been observed that PSH has remarkable adsorption capacity compared to granular activated carbon. The PSH adsorbent was characterized by SEM-EDX, BET, CHNS, zeta potential, and FTIR techniques. The adsorption behaviors such as adsorption kinetics, adsorption dynamics, and adsorption isotherms of PSH for the removal of MG dye from aqueous solution were studied in detail. The kinetic data fitted well with the pseudo second-order kinetic model for MG adsorption. Langmuir isotherm was found to be the model best fitted to describe the adsorption process.     

The Potted-Plant Microcosm Substantially Reduces Indoor Air VOC Pollution: I. Office Field-Study

Volatile organic compounds (VOCs) are major contaminants of indoor air, with concentrations often several times higher than outdoors. They are recognized as causative agents of “building-related illness” or “sick-building syndrome”. Our previous laboratory test-chamber studies have shown that the potted-plant/root-zone microorganism microcosm can eliminate high concentrations of air-borne VOCs within 24 hours, once the removal response has been induced by an initial dose. However, the effectiveness of the potted-plant microcosm in ‘real-world’ indoor spaces has never previously been tested experimentally. This paper reports the results of a field-study on the effects of potted-plant presence on total VOC (TVOC) levels, measured in 60 offices (12 per treatment), over two 5–9 week periods, using three planting regimes, with two ‘international indoor-plant’ species. Fourteen VOCs were identified in the office air. When TVOC loads in reference offices rose above 100 ppb, large reductions, of from 50 to 75% (to <100 ppb), were found in planted offices, under all planting regimes The results indicate that air-borne TVOC levels above a threshold of about 100 ppb stimulate the graded induction of an efficient metabolic VOC-removal mechanism in the microcosm. Follow-up laboratory dose-response experiments, reported in the following paper, confirm the graded induction response, over a wide range of VOC concentrations. The findings together demonstrate that potted-plants can provide an efficient, self-regulating, low-cost, sustainable, bioremediation system for indoor air pollution, which can effectively complement engineering measures to reduce indoor air pollution, and hence improve human wellbeing and productivity.     

Feasibility Assessment of Chromium Removal from Groundwater for Drinking Purposes by Sorption on Granular Activated Carbon and Strong Base Anion Exchange

The goal of this study was to compare the performances of strong base anion (SBA) exchange and activated carbon adsorption in the removal of hexavalent chromium, Cr(VI), from a real groundwater matrix exploited for drinking purposes. Two SBA resins and three granular activated carbons (GAC) were tested by batch experiments for kinetics and equilibrium isotherm determination. SBA resins showed higher affinity toward Cr(VI) (present in raw water at about 20 μg L^?1) with respect to the GACs, with faster kinetics and higher equilibrium adsorption capacities. Among GACs, vegetal-based carbons showed higher Cr(VI) removal efficiencies than the mineral-based carbon, which can be related to the more developed textural properties. SBA resins also displayed relevant removal capacities towards nitrate and sulfate (present at mg L^?1 concentration levels), while boron (present at about 60 μg L^?1) was effectively removed by GACs. Batch experiment results were elaborated to estimate the chromium throughputs for the studied materials, to preliminary compare their performances in a real-scale application. The monitoring of a real-scale GAC adsorption stage permitted to validate throughputs estimation and confirmed that, despite being effective toward synthetic organics, GAC adsorption is a not feasible solution for Cr(VI) removal, with extremely early breakthrough. SBA exchange process resulted to be the most suitable solution, providing the best sorbent usage rates. However, SBA resin usage rates can strongly increase when considering the removal of nitrate and sulfate ions, requiring much shorter cycle times.     

Activated Sludge Acclimation for Hydrophobic VOC Removal in a Two-Phase Partitioning Reactor

The effect of activated sludge acclimation on the biodegradation of toluene and dimethyldisulphide (DMDS) in the presence of a non-aqueous phase liquid, polydimethylsiloxane (PDMS), in a two-phase partitioning bioreactor was characterized. The influence of the presence of PDMS, at a ratio of 25% (v/v), and acclimation of activated sludge on two hydrophobic VOC biodegradation was studied. Activated sludge were acclimated to each VOC and in the presence of the non-aqueous phase liquid, namely in the emulsion of PDMS in water. Using acclimated cells, 97.9% and 108.7% improvement of the mean biodegradation rates were recorded for toluene and DMDS, respectively, if compared to the values recorded in the absence of acclimation. While and in agreement with the lower solubility in water of DMDS if compared to toluene, a most significant effect of PDMS addition on the rate of DMDS removal was recorded, 87.0% and 153.6% for toluene and DMDS, respectively. In addition and if both biomass acclimation and PDMS addition were considered, overall improvements of the removal rates were 204% and 338% for toluene and DMDS.     

Release kinetics of volatile organic compounds from roasted and ground coffee: online measurements by PTR-MS and mathematical modeling

The present work shows the possibilities and limitations in modeling release kinetics of volatile organic compounds (VOCs) from roasted and ground coffee by applying physical and empirical models such as the diffusion and Weibull models. The release kinetics of VOCs were measured online by proton transfer reaction-mass spectrometry (PTR-MS). Compounds were identified by GC-MS, and the contribution of the individual compounds to different mass fragments was elucidated by GC/PTR-MS. Coffee samples roasted to different roasting degrees and ground to different particle sizes were studied under dry and wet stripping conditions. To investigate the accuracy of modeling the VOC release kinetics recorded using PTR-MS, online kinetics were compared with kinetics reconstituted from purge and trap samplings. Results showed that uncertainties in ion intensities due to the presence of isobaric species may prevent the development of a robust mathematical model. Of the 20 identified compounds, 5 were affected to a lower extent as their contribution to specific m/z intensity varied by <15% over the stripping time. The kinetics of these compounds were fitted using physical and statistical models, respectively, the diffusion and Weibull models, which helped to identify the underlying release mechanisms. For dry stripping, the diffusion model allowed a good representation of the release kinetics, whereas for wet stripping conditions, release patterns were very complex and almost specific for each compound analyzed. In the case of prewetted coffee, varying particle size (approximately 400-1200 microm) had no significant effect on the VOC release rate, whereas for dry coffee, the release was faster for smaller particles. The absence of particle size effect in wet coffee was attributed to the increase of opened porosity and compound diffusivity by solubilization and matrix relaxation. To conclude, the accurate modeling of VOC release kinetics from coffee allowed small variations in compound release to be discriminated. Furthermore, it evidenced the different aroma compositions that may be obtained depending on the time when VOCs are recovered.     

Treatment of High Ammonium–Nitrogen Wastewater from Composting Facilities by Air Stripping and Catalytic Oxidation

Composting municipal wastewater sludge may generate composting wastewater (acid washer water and tunnel wastewater) with high ammonium–nitrogen (NH₄–N) concentration; this kind of wastewater is usually generated in a rather small daily amount. A procedure of air stripping with catalytic oxidation was developed and tested with pilot-scale and full-scale units for synthetic disposal of the high NH₄–N wastewaters from composting facilities. In air stripping, around 90% NH₄–N removal efficiency was reliably achieved with a maximum of 98%. A model to describe the stripping process efficiency was constructed, which can be used for process optimization. After catalytic oxidation, the concentrations in the outlet gas were acceptable for NH₃, NO_X, NO₂, and N₂O, but the NH₃ and N₂O concentrations limited the feasible loading range. The treatment costs were estimated in detail. The results indicate that air stripping with the catalytic oxidation process can be applied for wastewater treatment in composting facilities.     

Removal of Arsenic from Aqueous Solutions by Sorption onto Sewage Sludge-Based Sorbent

This study aimed at evaluating and comparing the removal of arsenic from solutions by a low-cost waste-based sorbent, produced by pyrolysing sewage sludge under appropriate conditions, and by a commercially activated carbon. Batch sorption experiments were performed under isothermal conditions (20°C), in order to evaluate the effect of pH on the arsenic sorption kinetics and on the equilibrium sorption capacity of the materials under study. Kinetic data revealed that the arsenic sorption was faster onto the activated carbon than onto the pyrolysed sludge. The sorption process was well described by both the pseudo-first and pseudo-second-order kinetics equations for both materials. Changes in the initial solution pH have distinct effects on the removal of arsenic onto pyrolysed sludge and activated carbon. While for pyrolysed sludge, pH affects essentially the equilibrium time, for activated carbon it affects the sorption capacity. Equilibrium results were well described by both Freundlich and Langmuir isotherm models, although fittings corresponding to the Langmuir isotherm were slightly better. The Langmuir maximum sorption capacity determined for the pyrolysed sludge was 71???g?g^?1, while for activated carbon was 229???g?g^?1. Despite the relative lower capacity of the pyrolysed sludge, the considerable lower cost and the valorisation of the sludge may justify further research on its use for water decontamination.