Chlorination By-products Research Articles

Generation of chlorine by-products in simulated wash water

Free chlorine (FC) reacting with organic matter in wash water promotes the formation of chlorine by-products. This study aims to evaluate the dynamic impact of FC and organic load on the generation of haloacetic acids (HAAs) and trihalomethanes (THMs) in simulated wash water. Lettuce juice was sequentially added into FC solution with FC periodically replenished. Water samples were collected after each lettuce juice addition to measure water qualities and determine HAAs and THMs using US-Environmental-Protection-Agency (EPA) methods. Concentrations of 88–2103μg/l of total HAAs and 20.79–859.47μg/l of total THMs were detected during the study. Monobromoacetic, tribromoacetic, chlorodibromoacetic and trichloroacetic acid were the major HAAs components. Chloroform (trichloromethane) was the primary THMs present. A significant correlation of HAAs with chemical oxygen demand and THMs with FC was observed. Results indicated that optimizing wash water sanitizing systems to limit organic matters and maintain minimal effective FC concentration is critical.

Impact of UV disinfection on the potential of model organic-nitrogen precursors to form chlorination by-products in swimming pool water

The article presents the results of experiments on the potential of model solutions of urea, creatinine, glycine, histidine, and arginine to form several organic chlorination by-products. These precursors are the main organic-nitrogen compounds, whose sources in swimming pool water are sweat and urine of bathers. In the article, the formation potential of the following by-products has been presented and discussed: trichloromethane; monochloroacetic acid; dichloroacetic acid; trichloroacetic acid; trichloroacetonitrile; dichloroacetonitrile; 1,1-dichloropropanone; 1,1,1-trichloropropanone; chloral hydrate; and chloropicrin. The test on by-products formation potential was applied to conduct the experiments, and 24-h incubation time was applied for the swimming pool water samples, disinfected in three variants of treatment: (1) chlorination alone; (2) chlorination and Ultraviolet (UV) irradiation (cumulative dose 23.5 kJ/m2); and (3) chlorination and UV irradiation (cumulative dose 47 kJ/m2). The low-pressure UV lamp by Heraeus was used to irradiate the samples. The results of experiments have been discussed and analyzed to study the influence of UV radiation on the reactivity of individual model precursors and their potential to form halogenated organic chlorination by-products.

“STOP: Can You Drink That Water?” Microbiology, Chemistry, & Advocacy in an Inquiry-Based Water Quality Curriculum for 8th Graders

For many middle school students, connections between their lives and concepts like chemical reactivity, microbial contamination, and experimental sampling are not obvious. They may also feel that, even if there were connections, understanding the monitoring and quality of natural resources is something for grown-ups and beyond their responsibility. This curriculum highlights connections. Students characterize bacteria in a local untreated water source and investigate the mechanism, effectiveness, and byproducts of chlorine bleach as a water treatment. Working in groups, they use different growth and treatment conditions to characterize samples, thus collectively obtaining a more complete description of the system. The North Carolina 8th Grade Standard Course of Study Objectives were used during curricular development, and alignment to Next Generation Science Standards performance expectations is provided. Teacher-guided discussions, demonstrations, experimentation, and database investigation engage students as they develop informed and critical opinions about water quality and water treatment methods. The final activity connects scientific investigation to advocacy and civic engagement.

Chlorination and chloramination of bisphenol A, bisphenol F, and bisphenol A diglycidyl ether in drinking water

Bisphenol A (BPA), bisphenol F (BPF), and bisphenol A diglycidyl ether (BADGE) are common components of epoxy coatings used in food packaging and in drinking water distribution systems. Thus, leachates from the epoxy may be exposed to the disinfectants free chlorine (Cl2/HOCl/OCl−) and monochloramine (MCA, NH2Cl). Bisphenols are known endocrine disrupting chemicals (EDC) with estrogenic activity. Chlorination by-products have the potential to have reduced or enhanced estrogenic qualities, and are, therefore, of interest. In this work, chlorination reactions for bisphenols and BADGE were explored (via LC/MS/MS) and kinetic modeling (using a pseudo-first order approach) was conducted to predict the fate of these compounds in drinking water. The half-lives of BPA and BPF with 1 mg/L of free chlorine ranged from 3 to 35 min over the pH range from 6 to 11 and the temperature range of 10–25 °C. Half-lives for reactions of BPA and BPF with a nominal MCA concentration of 3.5 mg/L as Cl2 were from 1 to 10 days and were greater at higher pH and lower temperature. Formation of chlorinated bisphenol A by-products was observed during the kinetic studies. BADGE was found unreactive with either oxidant.

Chlorination of polyvinyl pyrrolidone–polysulfone membranes: Organic compound release, byproduct formation, and changes in membrane properties

In this work, the release of organic compounds, the variations of membrane properties and the formation of toxic byproducts during chlorine treatment of polyvinyl pyrrolidone–polysulfone (PVP–PSF) membranes were investigated. Chlorine treatment decreased bovine serum albumin rejection, permeability and hydrophilicity of PVP–PSF membranes and resulted in the release of organic compounds as measured by total organic carbon (TOC). More organic compounds were released from the membranes at higher chlorine concentrations and higher initial values of chlorine contact pH. The presence of bromide that can be oxidized to bromine by chlorine also increased the release of organic matter from the membranes and contributed to the formation of high toxic brominated byproducts. Five toxic volatile chlorinated byproducts, chloroform, chloral hydrate, 1,1-dichloro-2-propanone, 1,1,1-trichloro-2-propanone and trichloronitromethane, were formed during chlorination of the organic compounds from the PVP–PSF membranes. Three brominated byproducts including bromodichloromethane, dibromochloromethane and bromoform were determined in the presence of bromide. The PVP appears to be more susceptible than PSF to chlorine destruction in the PVP–PSF membranes as analysis of the chlorinated byproducts derived from PVP precursors.

Impact of groundwater surface storage on chlorination and disinfection by-product formation

The change in water quality arising from the open storage of groundwater (GW) and its impact on chlorination and chlorination by-product formation were investigated. Water quality descriptors, such as temperature, pH, chlorophyll, and dissolved oxygen contents of GW undergo substantial alteration when stored in a reservoir. Dissolved organic content (DOC) measured in the two water sources studied, i.e., GW and open reservoir water (RW), varied from 0.41 mg/L to 0.95 mg/L and 0.93 mg/L to 2.53 mg/L, respectively. Although DOC demonstrated wide variation, UV absorbance at 254 nm (UVA254) values for GW (0.022-0.067) and RW (0.037-0.077) did not display reciprocal variations. The chlorine demand (CD) of RW was always higher than that of GW for the corresponding sampling period. Average trihalomethane (THM) formation for RW was 50-80% higher compared to GW and thus poses an enhanced health risk. Appreciable amounts of bromide present in these water sources (0.15-0.26 mg/L in GW and 0.17-0.65 mg/L in RW) have resulted in the non-selective distribution of the four THM species. The formation of more toxic brominated THM due to chlorination of these near-coast drinking water sources must be regarded as a decisive factor for the choice of water disinfection regime.

An outbreak of swimming-pool related respiratory symptoms: An elusive source of trichloramine in a municipal indoor swimming pool.

Several members of a swimming club complained of respiratory symptoms associated with attending a municipal indoor swimming pool. Trichloramine, a volatile chlorination by-product and a potent respiratory irritant, was the most probable culprit, but the exact cause for its presence in excessive concentrations remained elusive. Twenty-two competitive swimmers and six coaches were evaluated during the outbreak and nine swimmers and four coaches were re-evaluated one year later. Symptoms were recorded by non-standardized history taking; pulmonary function testing included spirometry, measurement of fraction of exhaled nitric oxide (FENO) and histamine provocation. Concentrations of trichloramine in air were measured repeatedly by the method of Héry. The most commonly reported symptoms consisted of cough (n=16), dyspnoea (n=13), tearing eyes (n=10) and blocked or runny nose (n=6). Mean FEV1% predicted was 109.1%. Mean FENO level was 19.7 ppb (higher than 25 ppb in 3 subjects). Airway hyperreactivity to histamine (PC20 ≤ 8 mg/ml) was detected in 22/26 subjects. Measured trichloramine concentrations in air exceeded the maximal concentration (WHO) of 0.5mg/m(3) four times between May and October 2011 and four times between January and March 2012. Polyamine compounds, present in glue used for repairing pipework, were identified as a probable external source of nitrogen resulting in increasing trichloramine concentrations. After the removal of the presumed cause of the excessive trichloramine concentrations, most subjects improved clinically, but several subjects remained symptomatic and had bronchial hyperreactivity. A high prevalence of airway hyperreactivity, accompanied by symptoms of upper and lower airways, was detected in swimmers who had been repeatedly exposed to high trichloramine concentrations. A glue containing polyamines, used to repair a pipework, was suspected to be the source of this excessive production of trichloramine.

Occurrence of halogenated transformation products of selected pharmaceuticals and personal care products in secondary and tertiary treated wastewaters from southern California.

Final effluent samples from 10 southern California (United States) wastewater treatment facilities, employing four distinct treatment schemes, were surveyed for selected pharmaceuticals, personal care products (PPCPs), alkylphenols, and 21 of their halogenated disinfection byproducts. Chlorinated and brominated standards and isotopically labeled internal standards were synthesized and purified to confirm and more accurately quantify selected disinfection byproducts of salicylic acid, bisphenol A, gemfibrozil, naproxen, diclofenac, technical 4-nonylphenol, and 4-tert-octylphenol using high-performance liquid chromatography and tandem mass spectrometry. Concentrations of parent compounds ranged from <10 to 3830 ng/L (gemfibrozil), and those of chloro/bromo byproducts ranged from <4 to 370 ng/L (dibromo nonylphenol). The highest concentrations of parent compounds were measured in effluent that was not subjected to tertiary treatment. The chlorinated and brominated byproduct concentration may be affected by the influent concentration of parent compounds, hydraulic retention times, and chlorine contact times. Salicylic acid was readily halogenated, which is evident from the ratio of halogenated to nonhalogenated species. There were no measured chlorinated byproducts of bisphenol A despite occasionally high concentrations of the parent compound. Not surprisingly, higher concentrations of most brominated species were measured in the treatment plant with the highest bromide concentrations. These results demonstrate the occurrence of novel halogenated byproducts of PPCPs that have limited toxicological data and significant uncertainty with regard to their risk to ecological systems.

Damage-associated molecular pattern and innate cytokine release in the airways of competitive swimmers.

Daily intensive exercise by elite athletes can result in exercise-induced asthma especially in elite swimmers and this may be linked to epithelial damage. To study airway epithelial damage and release of damage-associated molecular patterns (DAMPs) after intensive exercise in elite athletes and controls. We recruited competitive swimmers (n=26), competitive indoor athletes (n=13) and controls (n=15) without any history of asthma. Lung function was measured before, immediately after and 24h after a 90-min intensive exercise protocol. Sputum induction was performed at baseline and 24h after exercise. Exercise-induced bronchoconstriction (EIB) was assessed by the eucapnic voluntary hyperventilation test. Baseline sputum uric acid, high mobility group box-1, CXCL8 mRNA, sputum neutrophils and serum Clara cell protein-16 (CC-16) were significantly higher in competitive swimmers compared with controls. Intensive swimming for 90min resulted in an increase of sputum IL-1β, IL-6 and TNF mRNA in competitive swimmers, and of sputum IL-6 mRNA and sputum neutrophils in controls. Although all participants were asymptomatic, seven competitive swimmers, one indoor athlete and one control met the criteria for EIB. Our findings show that the intensive training combined with exposure to by-products of chlorination induces airway epithelial damage in competitive swimmers. This is associated with increased damage-associated molecular patterns, innate cytokine release and neutrophilic airway inflammation.

Colon and Rectal Cancers and Chlorination By-Products in Treated Water:A Strategy for Management Based on Hormonal Studies

Colon and Rectal Cancers and Chlorination By-Products in Treated Water:A Strategy for Management Based on Hormonal Studies

Colon and Rectal Cancers and Chlorination By-Products in Treated Water:A Strategy for Management Based on Hormonal Studies

Colon and Rectal Cancers and Chlorination By-Products in Treated Water:A Strategy for Management Based on Hormonal Studies

两种含氯消毒副产物对草履虫急性毒性效应初探

氯化消毒是我国普遍采用的城市污水消毒措施，然而，氯化消毒的同时，氯与水中的有机物发生反应生成一系列的卤代烃类化合物，即氯化消毒副产物。经研究证实大部分氯化消毒副产物具有致癌、致突变、生殖毒性效应。为研究消毒废水中一些副产物的毒性，本研究采用消毒废水中的有害副产物三氯甲烷(CHCl3)和三溴甲烷(CHBr3)为毒物材料，以草履虫为受试生物，对其种群进行单一急性毒性和联合毒性实验，探究CHCl3和CHBr3对草履虫的急性毒性和联合毒性。实验结果表明，两种毒物单独作用时，随着浓度增大，毒性作用也增大，CHCl3的1 h半致死浓度(LC50)为1585.27 μg/L，CHBr3的1 h半致死浓度(LC50)为656.37 μg/L，两种毒物共同作用时表现为协同作用。由于草履虫对两种毒物毒性较为敏感，其可作为CHCl3和CHBr3的毒性评价生物。 Chlorination is widely applied to disinfect drinking water in China. However, a series of chlori-nated disinfection by-products (CDBPs) are formed when chlorine reacts with organic matters in water health. Many CDBPs can cause health hazards for human, for example, cancers and mutagenic and reproductive toxicity. For the study of disinfection by-products in some wastewater toxicity, this study used the harmful by-products, chloroform (CHCl3) and methyl bromide (CHBr3) in disinfection wastewater, as poison materials. In single acute toxicity test and joint toxicity test, the acute toxicity and joint toxicity of CHCl3 and CHBr3 to paramecium were studied. The results show that, when the two toxicants work separately, toxic effects increase along with the increasing concentration. The median lethal concentration (LC50) of CHCl3 in 1 h was 1585.27 μg/L and that of CHBr3 was 656.37 μg/L, and it showed a synergistic effect when combining two poisons. Since paramecium is sensitive to the toxicity of the two poisons, it can be used to evaluate the toxicity of CHCl3 and CHBr3.

Removal of Trihalo Methanes Using Activated Carbon Prepared from Agricultural Solid Wastes

High chlorine dosages are used in some drinking water plants to overcome the deficiencies in the treatment to at least ensure a supply of microbiologically safe water to the population. This fact and the increment of natural organic matter (NOM) in the aquatic resources due to rainfall increases and anthropogenic activities are becoming a critical concern, due to the formation of chlorination by-products such as trihalomethanes (THM), which are carcinogenic substances. Egypt drinking water system using new treatments is essential to meet the quality guidelines. Trihalomethanes are carcinogenic by-products of disinfection that are present in drinking water. In the present research, adsorption was employed for the removal of THMs found in water supply systems. The effects of pH, contact time, adsorbents and adsorbate concentration on the adsorption system were investigated. The Langmuir and Freundlich adsorption isotherm models were used to analyse the resulting adsorption data. The kinetics of THM removal was found to follow the pseudo-second-order model rather than the Langmuir–Hinshelwood pseudo-first-order model.

High catalytic performances of CeO2–CrOx catalysts for chlorinated VOCs elimination

A series of porous CeO2–CrOx mixed oxides are synthesized using different precipitants (NaOH, NH4OH, (NH4)2CO3 and urea) and evaluated for deep oxidation of various chlorinated VOCs (CH2Cl2, C2HCl3, C2H4Cl2 and C6H5Cl). The results show that all these materials represent porous structures and small particle sizes (2–8nm). Part of Cr element can go into the lattice of CeO2, resulting in the formation of Ce–Cr–O mixed oxide. Compared with pure CeO2 and Cr2O3, the amount of Cr6+ species and oxygen vacancies in CeO2–CrOx mixed oxides are significantly increased, due to the strong interaction between CeO2 and CrOx. Thus, all the CeO2–CrOx mixed oxides exhibit high catalytic activity and good durability for deep oxidation of chlorinated VOCs, especially the CeO2–CrOx prepared using (NH4)2CO3 as precipitant. Moreover, only slight chlorinated byproducts are detected in the process of chlorinated VOCs oxidation, and the surface accumulation of coke and Cl species as well as the loss of Cr element is slight during the long-term reaction at 265°C, indicating that these CeO2–CrOx materials possess interesting fundamental result, deserving more research before conclusion on practical value.

Direct electrochemical oxidation of ammonia on graphite as a treatment option for stored source-separated urine

Electrolysis can be a viable technology for ammonia removal from source-separated urine. Compared to biological nitrogen removal, electrolysis is more robust and is highly amenable to automation, which makes it especially attractive for on-site reactors. In electrolytic wastewater treatment, ammonia is usually removed by indirect oxidation through active chlorine which is produced in-situ at elevated anode potentials. However, the evolution of chlorine can lead to the formation of chlorate, perchlorate, chlorinated organic by-products and chloramines that are toxic. This study focuses on using direct ammonia oxidation on graphite at low anode potentials in order to overcome the formation of toxic by-products. With the aid of cyclic voltammetry, we demonstrated that graphite is active for direct ammonia oxidation without concomitant chlorine formation if the anode potential is between 1.1 and 1.6 V vs. SHE (standard hydrogen electrode). A comparison of potentiostatic bulk electrolysis experiments in synthetic stored urine with and without chloride confirmed that ammonia was removed exclusively by continuous direct oxidation. Direct oxidation required high pH values (pH > 9) because free ammonia was the actual reactant. In real stored urine (pH = 9.0), an ammonia removal rate of 2.9 ± 0.3 gN·m−2·d−1 was achieved and the specific energy demand was 42 Wh·gN−1 at an anode potential of 1.31 V vs. SHE. The measurements of chlorate and perchlorate as well as selected chlorinated organic by-products confirmed that no chlorinated by-products were formed in real urine. Electrode corrosion through graphite exfoliation was prevented and the surface was not poisoned by intermediate oxidation products. We conclude that direct ammonia oxidation on graphite electrodes is a treatment option for source-separated urine with three major advantages: The formation of chlorinated by-products is prevented, less energy is consumed than in indirect ammonia oxidation and readily available and cheap graphite can be used as the electrode material.

Dichloroacetate treatment accelerates the development of pathology in rodent autosomal recessive polycystic kidney disease.

Dichloroacetate (DCA) is a toxicant by-product from the chlorination disinfection process for municipal water. The levels would not affect people with normal renal and liver function. However, people with impaired renal or liver function may have an increased susceptibility to DCA toxicity as those are the organs affected by DCA. People (and rodents) with polycystic kidney disease (PKD) are polyuric, drink more fluids, and have both renal and liver pathology. In PKD, renal tubules and biliary epithelial cells proliferate to form cysts, which can eventually cause renal and/or liver dysfunction. Therefore, PKD may be a predisposing condition with an increased sensitivity to DCA toxicity. PCK rats are an orthologous model of human autosomal recessive PKD and were treated with 75 mg/l DCA in their drinking water. Male and female PCK and male Sprague-Dawley rats were treated from 4 to 8 wk of age, after which the severity of the renal and liver pathology induced by DCA were assessed. Only male PCK rats were adversely affected by DCA treatment, with an increase in the severity of renal cystic disease evinced by an increase in cystic enlargement and proteinuria. In conclusion, the chlorination byproduct DCA may adversely affect those with a preexisting renal disease, especially those who are polydipsic, like those with PKD.

The relationship between chlorine consumption and trihalomethane formation from hydrophobic and transphilic fractions: a comparative study between two dams of east Algeria

In Algeria, the use of chlorine in drinking water treatment is a widespread practice. When chlorine combines with natural organic matter (NOM), it forms various chlorine by-products such as trihalomethanes (THMs). In this work, we studied the relationship between chlorine consumption and THM formation, by chlorination of hydrophobic and transphilic (TRS) fractions. We compared the kinetic behavior and the THM formation potential of two major dams in east Algeria. A nonlinear regression modeling study showed a good correlation of the specific chlorine consumption and the specific THM formation. In the case of Ain Zeda dam and at pH = 7, the specific THM yield coefficients αS were: 6.57 and 10.22 μg-THM/mg-Cl2.mg-C.L−1 for hydrophobic and TRS fractions, respectively, while at the same pH, they were 12.07 and 23.66 μg-THM/mg-Cl2.mg-C.L−1 for Ain Dalia dam. Although the NOM concentration of Ain Zeda dam was higher than that of Ain Dalia dam, the THM formation potential of Ain Dalia dam was greater than that of Ain Zeda dam. It seems clear that the water source origin and characteristics play a key role in this case. They affect the THM formation due to the complex composition of humic substances which differs from one source to another.

Emerging contaminants in urban groundwater sources in Africa

The occurrence of emerging organic contaminants within the aquatic environment in Africa is currently unknown. This study provides early insights by characterising a broad range of emerging organic contaminants (n > 1000) in groundwater sources in Kabwe, Zambia. Groundwater samples were obtained during both the dry and wet seasons from a selection of deep boreholes and shallow wells completed within the bedrock and overlying superficial aquifers, respectively. Groundwater sources were distributed across the city to encompass peri-urban, lower cost housing, higher cost housing, and industrial land uses. The insect repellent DEET was ubiquitous within groundwater at concentrations up to 1.8 μg/L. Other compounds (n = 26) were detected in less than 15% of the sources and included the bactericide triclosan (up to 0.03 μg/L), chlorination by-products – trihalomethanes (up to 50 μg/L), and the surfactant 2,4,7,9-tetramethyl-5-decyne-4,7-diol (up to 0.6 μg/L). Emerging contaminants were most prevalent in shallow wells sited in low cost housing areas. This is attributed to localised vulnerability associated with inadequate well protection, sanitation, and household waste disposal. The five-fold increase in median DEET concentration following the onset of the seasonal rains highlights that more mobile compounds can rapidly migrate from the surface to the aquifer suggesting the aquifer is more vulnerable than previously considered. Furthermore it suggests DEET is potentially useful as a wastewater tracer in Africa. There was a general absence of personal care products, life-style compounds, and pharmaceuticals which are commonly detected in the aquatic environment in the developed world. This perhaps reflects some degree of attenuation within the subsurface, but could also be a result of the current limited use of products containing emerging contaminants by locals due to unaffordability and unavailability. As development and population increases in Africa, it is likely a wider-range of emerging contaminants will be released into the environment.

Multiobjective optimization of water quality and rechlorination cost in water distribution systems

To comprehensively describe the effect of residual chlorine and disinfection by-products (DBPs) on water quality in water distribution systems (WDS) and optimize rechlorination cost, this study developed a multi-objective optimization model of water quality and rechlorination cost. Firstly, chlorine decay and DBPs formation were simulated using EPANET_MSX. An improved non-dominated sorting genetic algorithm II (NSGA-II) with real code was used to optimize the multiobjective model and Pareto fronts could be obtained under different conditions. The results showed that Pareto fronts obtained by average value were better than those obtained by standard deviation and multiplication. Moreover, with the number of boosters increased, maximum value of water quality increased and rechlorination cost decreased. Wall chlorine decay constants were the most important on Pareto fronts, followed by the number of chlorination nodes, proportional coefficients of trihalomethanes (THMs) generation based on residual chlorine consumption, and THMs concentration.

Challenges with Industrialization of Atomic Layer Deposition of Silicon Nitride

Scaling of next generation logic and memory semiconductor devices requires conformal thin films on high aspect ratio features at low deposition temperatures (<500ºC). Atomic layer deposition (ALD) is an ideal method for depositing these films and is currently being used in high volume manufacturing (HVM) to deposit high-k dielectric materials (HfO2, ZrO2, etc.) as well as the more traditional dielectrics silicon oxide (SiO2) and silicon nitride (SiNx). With the notable exception of silicon nitride, all of these films can be deposited at sufficiently low temperatures to satisfy the integration requirements while maintaining reasonable throughput and cost. In the HVM environment, silicon nitride ALD has historically been deposited in large furnaces operating at high temperatures, and although both plasma and thermal deposition of silicon nitride have been reported at low temperatures1-2, translation of these low temperature R&D films into HVM films has been challenging.In this presentation, we discuss some of the challenges faced with addressing the requirements associated with bringing low temperature ALD SiNx into HVM, which include achieving high wafer throughput and low per wafer cost, while simultaneously keeping the resistance of the film to multiple downstream etches and cleans, which may include exposure to hydrofluoric acid (HF). Generic to all ALD processes is the high cost of the precursors relative to traditional chemical vapor deposition (CVD); in the case of SiNx, this is exacerbated by the relative low “reactivity to cost ratio” of available silicon precursors. Cost can partially be addressed with chlorosilane precursors, but the chlorine byproducts create challenges with deposition chamber materials and effluent management. Low reactivity of the silicon precursors poses challenges with respect to process design; the choice of spatial ALD vs. temporal ALD and isobaric vs. non-isobaric deposition sequences affects the final cost and throughput. Lastly, the use of plasmas in ALD poses challenges for achieving isotropic film properties over the complex topography on today’s semiconductor substrates.