Water Disinfection Techniques Research Articles

Biofouling characteristics of reverse osmosis membranes by disinfection-residual-bacteria post seven water disinfection techniques

Reverse osmosis (RO) is widely used in wastewater reclamation to alleviate the increasingly global water shortage. However, it has an inconvenient defect of biofouling. Some disinfection processes have been reported to select certain undesirable disinfection-residual bacteria (DRB), leading to severe long-term biofouling potential. To provide constructive guidance on biofouling prevention in RO systems, this study performed a 32-day experiment to parallelly compared the biofouling characteristics of RO membranes of DRB after five mature water disinfection methods (NaClO, NH2Cl, ClO2, UV, and O3) and two recently developed water disinfection methods (K2FeO4 and flow-through electrode system). As a result, the DRB biofilm of K2FeO4 and O3 caused a slight normalised flux drop (22.4 ± 2.4% and 23.9 ± 1.7%) of RO membrane compared to the control group (non-disinfected, ~27% normalised flux drop). FES, UV, NaClO and ClO2 caused aggravated membrane flux drop (29.1 ± 0.3%, 33.3 ± 7.8%, 34.6 ± 6.4%, and 35.5 ± 4.0%, respectively). The biofouling behaviour showed no relationship with bacterial concentration or metabolic activity (p > 0.05). The thickness and compactness of the biofilms and the organics/bacterial number ratio in the biofilm, helped explain the difference in the fouling degree between each group. Moreover, microbial community analysis showed that the relative abundance of typical highly EPS-secretory and biofouling-related genera, such as Pseudomonas, Sphingomonas, Acinetobacter, Methylobacterium, Sphingobium, and Ralstonia, were the main reasons for the high EPS secreting ability of the total bacteria, resulting in aggravation of biofouling degree (p < 0.05). All types of disinfection except for NaClO and ClO2 effectively prevented pathogen reproduction in the DRB biofilm.

WATER DISINFECTION TECHNIQUES: A REVIEW

Water pollution, inadequate water supply and poor waste treatment facilities have greatly contributed todiarrheal and other water borne disease conditions. Regular presence of Escherichia coli and other coliformsare probable indicators of water contamination. State of the art water disinfection methods of boiling andchlorination success has been limited due to inadequate germicidal effect and health risks. Frequent outbreaksof water borne illness in the rural areas of developing nations continue to exit despite the administration ofboiling, chlorination and use of herbs as water disinfection techniques among the residents. Solar waterdisinfection has emerged as alternative to back-up the existing water techniques. However, the acceptability andadoption potential has not been fully realized. Some of the solar water disinfection technologies have exhibiteddraw-backs of: Limited volume, post-disinfection regrowth, incomplete disinfection and pulsating flow rates. Inaddition, the experimented solar water disinfection technologies have mainly focused on indicators organismsuch as Escherichia coli and coliforms. The effect of solar water disinfection on diverse water borne pathogenshas not been fully established. Water disinfection techniques are reviewed here in with focus on sustainabledevelopment goal 6 (SDG).

Escherichia coli inactivation in water by sulfate radical-based oxidation process using FeCl3-activated biochar/persulfate system

Pathogenic microbes in water present great risks to environments, water resources, and human health. In the present study, for the first time, a FeCl3-activated bermudagrass-derived biochar (FA-BC) was applied to activate persulfate (PS) for E. coli inactivation. The PS activation was ascribed to the presence of Fe0 and Fe3O4 on the surface of FA-BC, and SO4·− radicals were proved to be the main role for E. coli inactivation using FA-BC activated PS system (FA-BC/PS). Decreasing the pH (5–9) and increasing the PS concentration (50–300 mg/L), reaction temperature (20–50 °C), and FA-BC dosage (100–500 mg/L) resulted in the enhancement of disinfection efficiency of E. coli using FA-BC/PS. 6.21 log reductions of E. coli were achieved within 20 min under the optimal conditions (500 mg/L FA-BC, 200 mg/L PS, pH 7, and 20 °C with 107 CFU/mL E. coli in DI water). The FA-BC/PS effectively eliminated various initial concentrations of E. coli (105–108 CFU/mL). The E. coli inactivation rate decreased from 0.1426 min−1 to 0.0883, 0.1268 min−1, and 0.1093 min−1 with the presence of 10 mg/L humic acid, 100 mg/L Cl−, and 100 mg/L HCO3−, respectively. In addition, after three cycles of disinfection tests using FA-BC/PS, the E. coli inactivation rate only slightly decreased from 0.1426 to 0.1288 min−1. The FA-BC/PS also effectively removed the E. coli in real stormwater with a 99.2 % inactivation efficiency within 180 min. The FA-BC/PS in fixed-bed column tests revealed the continuous and high inactivation of E. coli in water. Increasing the FA-BC amount (1.5 %–5 %) and PS concentration (50–200 mg/L) and decreasing the flow rate (2–4 mL/min) caused the lower E. coli concentration in effluent. Therefore, the FA-BC/PS can be considered as a promising and efficient technique for water disinfection.

Photocatalytic disinfection of extended-spectrum beta-lactamase producing Escherichia coli using Alumina/ZnO heterostructures

Spread of antibiotic resistant bacteria through water pose severe health risks to society. In this context, a systematic study is reported for photocatalytic removal of multidrug resistant (MDR) Escherichia coli and related genes from water by using Alumina/ZnO heterostructures under visible light. 500 mg/L of the photocatalyst could disinfect ≈ 106 CFU/mL of target bacteria in water within 240 min of visible light irradiation. Lipid peroxidation, DNA and protein leakage studies have suggested the compromisation of bacterial cell membrane which was further corroborated from electron microscopy images. MDR Escherichia coli has registered a loss of resistance towards fifteen antibiotics with a down-regulation in the antibiotic resistance genes after exposure to photocatalytic process. Proposed process was also validated for disinfection of MDR Staphylococcus haemolyticus and antibiotic susceptible Escherichia coli. Successful disinfection of fecal coliform was achieved in water samples collected from three major rivers and a waste water treatment plant. The in vivo toxicity study of the treated water on mice model has not revealed any remarkable impact on gut health. With high effectiveness in disinfecting bacteria coupled with biocompatibility of the treated water towards animal model may proffer the present technique as a propitious off-grid water disinfection technique for real-world applications.

Constructing a plasma-based Schottky heterojunction for near-infrared-driven photothermal synergistic water disinfection: Synergetic effects and antibacterial mechanisms

Developing green and highly efficient water disinfection technique is of great importance to public health. Herein, a near-infrared (NIR) light-triggerable thermo-sensitive defective molybdenum oxide-nitrogen doped carbon (MoO3-x/NCNs) composite was fabricated and applied to water disinfection. With the synergy of photodynamic and photothermal effects, the MoO3-x/NCNs achieve a rapid and effective inactivation of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as compared to photocatalytic treatment or thermal catalytic alone. Particularly, MONC-3 with optimal ratio can completely inactivate 7.6 log of E. coli and S. aureus within 60 min and 100 min, respectively. The MONC-3 hybrid exhibits efficient charge separation and migration ability due to the formation of Schottky heterojunction, resulting in the highly enhanced O2− (11.34 × 10−10 M) generation activity. Meanwhile, excellent NIR light absorption and photothermal conversion efficiency (52.6%) of MONC-3 can generate local high temperature to promote photocatalytic reaction rate and destruct the bacterial integrity. The monitoring of cell damage process confirmed the irreversible death of bacteria. Based on density functional theory (DFT) calculation, the antibacterial mechanism and Schottky effect were clarified. This work provides new insights for constructing a water disinfection strategy based on plasma-induced photothermal synergy catalysis.

Disinfection characteristics of an advanced rotational hydrodynamic cavitation reactor in pilot scale

Hydrodynamic cavitation is a promising technique for water disinfection. In the present paper, the disinfection characteristics of an advanced hydrodynamic cavitation reactor (ARHCR) in pilot scale were studied. The effects of various flow rates (1.4–2.6 m3/h) and rotational speeds (2600–4200 rpm) on the removal of Escherichia coli (E. coli) were revealed and analyzed. The variation regularities of the log reduction and reaction rate constant at various cavitation numbers were established. A disinfection rate of 100% was achieved in only 4 min for 15 L of simulated effluent under 4200 rpm and 1.4 m3/h, with energy efficiency at 0.0499 kWh/L. A comprehensive comparison with previously introduced HCRs demonstrates the superior performance of the presented ARHCR system. The morphological changes in E. coli were studied by scanning electron microscopy. The results indicate that the ARHCR can lead to serious cleavage and surface damages to E. coli, which cannot be obtained by conventional HCRs. Finally, a possible damage mechanism of the ARHCR, including both the hydrodynamical and sonochemical effects, was proposed. The findings of the present study can provide strong support to the fundamental understanding and applications of ARHCRs for water disinfection.

A Systematic Review on Advancements in Drinking Water Disinfection Technologies: A Sustainable Development Perspective

The Sustainable Development Goal 2015-30, which is the blueprint to achieve a better and sustainable future for all includes goal number six, aiming at the provision of clean water and sanitation by 2030 worldwide. But still the rural areas in developing nations are predominantly facing the scarcity of pathogen-free drinking water, which creates an urgent need for research in the area of water disinfection. The paper presents a systematic literature review of the conventional and novel water disinfection techniques supported by a bibliometric analysis based on the data from Scopus and Web of Science data from the year 1980 to 2020 for all the disinfection techniques. The novel and latest water disinfection technology in the literature studied by few researchers are also discussed and it can be concluded that the research related to these latest technologies is fewer and real-life usage is very scanty. The detailed literature review indicates the need for novel, decentralized, low-cost water disinfection technology for providing clean and pathogen-free water to all, overcoming the problems related to access of safe drinking water to rural communities. The paper also identifies the research gaps related to new technologies for water disinfection which needs to addressed in further studies.

ENERGY-EFFICIENT WATER DISINFECTION SYSTEM BASED ON LED LIGHT SOURCES

In the article the energy-efficient technology of disinfection of drinking water which is based on the use of LED light sources for generating ultraviolet radiation. Some theoretical and experimental models of water disinfection have been developed and investigated. The structure of the system of water disinfection technique and algorithm for calculating the light distribution of LED light sources that provide efficient use of electricity in the disinfection of water. The fragmentation algorithm is attached for the development of the bactericidal anti-infection system. The authors have devised a methodology for the synthesis of light on the basis of the distorted power of a single light switch of a light switch. The problem associated with the need to improve the efficiency of water disinfection at the stages of it treatment in an increasingly unfavorable trend of deterioration of microbiological parameters in the reservoirs of the first category is considered. Historical facts of development and the application of this technology in the water treatment system are described.

2D g-C3N4 monolayer for amino acids sequencing

An analog of graphene, graphitic carbon nitride (g-C3N4), is a promising metal-free conjugated polymer, owing to its excellent performance in biosensing and photocatalysis. We have demonstrated the adsorption of twenty-five amino acids (AA) employing DFT-D3 correction method of Grimme's dispersion and the non-equilibrium Green's function (NEGF) for describing the coherent transport in molecular devices coupled with adsorption energies, substrate-adsorbate distances, the density of states, charge transfer mechanism, molecular dynamics, work function, and bonding patterns. We have also depicted the current-voltage (I–V) characteristics where the curves of current vs. bias voltage (I–Vb) display a distinct response for each AA. Furthermore, we have illustrated the anti-bacterial mechanism of g-C3N4 utilizing bioinformatics study and compared it with DFT studies. We found evidence of a difference in transport, electronic as well as molecular mechanisms reinforcing the possibility of g-C3N4 applications based on sensors for AA sequencing of proteins, water-disinfection technique, and microbial control.

Water disinfection by orifice-induced hydrodynamic cavitation.

Hydrodynamic Cavitation (HC) is considered as a promising water-disinfection technique. Due to the enormous complexity of the physical and chemical processes at play, research on HC reactors is usually carried out following an empirical approach. Surprisingly, past experimental studies have never been designed on dimensional-analysis principles, which makes it difficult to identify the key processes controlling the problem, isolate their effects and scale up the results from laboratory to full-scale scenarios. The present paper overcomes this issue and applies the principles of dimensional analysis to identify the major non-dimensional parameters controlling disinfection efficacy in classical HC reactors, namely orifice plates. On the basis of this analysis, it presents results from a new set of experiments, which were designed to isolate mainly the effects of the so-called cavitation number (σv). Experimental data confirm that the disinfection efficacy of orifice plates increases with decreasing σv. Finally, in order to discuss the significance of the results presented herein and frame the scope of future research, the present paper provides an overview of the drawbacks associated with dimensional analysis within the context of HC.

Photolysis of mixtures of UV filters octocrylene and ethylhexyl methoxycinnamate leads to formation of mixed transformation products and different kinetics

The treatment with ultraviolet (UV) light is a well-known technique for water disinfection. Photodegradation by UV light is in discussion as measure for advanced water treatment that could provide a potential removal option for micropollutants. Micropollutants such as ingredients from personal care products are also present in grey water. Grey water gets increasingly attention as a source for water reuse. For that purpose it has to be treated. UV-treatment is an option. However, the knowledge on the fate of micropollutants within such a treatment is little. Therefore, we investigated the fate of the UV filters ethylhexyl methoxycinnamate (EHMC), and octocrylene (OCR) as for both UV filters the presence in grey water was reported. OCR as a single compound was investigated with regard to its degradation kinetics and possible photo-transformation products (photo-TPs). These results were compared with those of EHMC previously reported in literature. The mixture of the two UV filters was also investigated to reveal if mixture effects occur regarding the elimination of the UV filters and the formation of TPs. A medium pressure mercury vapor lamp (200–400 nm) was employed for photolysis. This study shows that OCR itself was eliminated below the limit of detection after 256 min and that photo-TPs were formed. The photolysis of the mixture demonstrated alterations of the degradation rates and patterns. Additional TPs were formed by the reaction of the UV filters or TPs with each other. The study shows that more attention should be paid to mixture-effects and mixture-TPs that may cause further follow-up effects.

Using simulation model to determine the regulation and to optimize the quantity of chlorine injection in water distribution networks

Water can be disinfected by various techniques. Chlorination is the most prevalent and the cheapest method in this regard. One of the most significant factors in chlorination is the location and the amount of chlorine injections, both of which must be chosen in a way that the amount of chlorine remaining in all sections of a city’s water distribution network is within the standard range, and the associated costs are reduced to a considerable extent. Therefore, in this research, we have implemented a technique which takes both of those issues, i.e., the amount of residual chlorine in pipes and the quantity of chlorine consumed in diverse sections of the water distribution network into account leading to a much more cost-effective water disinfection technique. Our technique shows that municipal water distribution network, are effectively in tune with the current highest standards set in the water disinfection procedure for the lowest possible cost. For modeling the water allocation network, the WaterGems software was used. Using this software, the network was modeled into two practical methods, i.e., gravity and direct pumping methods. The productivity of gravity as well as direct pumping methods was shown to control the optimal chlorine injection rate by resolving the two applied models of water distribution networks. The results showed that the residual chlorine content in 70% of the direct pipe network was within the standard range and in 100% of the tubes in the gravity distribution network lower than the standard. Also, the chlorine which was consumed in the direct pumping network was 7% lesser than that in the gravity distribution network. This research showed that the adjusting of chlorine injection into direct-pumped networks compared with gravity distribution networks was more feasible and also required less chlorine consumption.

Mechanistic insight into the disinfection of Salmonella sp. by sun-light assisted sonophotocatalysis using doped ZnO nanoparticles

The vulnerability of human life to gastrointestinal diseases of infectious origin in developing countries is increasing due to water contamination by enteric bacteria. So, there is an immediate need to search for novel techniques for the elimination of water borne pathogenic microorganisms. In this context, here we report the sun-light aided sonophotocatalytic (SPC) disinfection of a common enteric bacterium, Salmonella sp. using Iron (Fe) doped ZnO nanoparticles (ZnO:Fe NPs). ZnO:Fe NPs were found to be more effective than ZnO for SPC disinfection. Complete disinfection was not achieved with TiO2 NPs under the same experimental conditions. Fluorescence microscopy images have suggested the complete bacterial cell death after SPC. Electron microscopy has confirmed the evidences for compromised bacterial cell membrane. Our investigation has indicated that OH and O2 radicals might be acting as the crucial component in disinfecting Salmonella Typhimurium (S. Typhimurium) in SPC process. Based on the results obtained from Resazurin assay, it is expected that reactive oxygen species (ROS) produced during SPC may have interfered with the oxido-reductase protein system of the bacteria and hence hindered its metabolic activity. Solar-SPC process using ZnO:Fe NPs demonstrated successful disinfection of S. Typhimurium in water samples collected from various sources such as river, pond, lake and municipal tap. Also, SPC treated water was found to have supportive effects on the germination of Zea mays seeds compared to that of water infected with S. Typhimurium. With high effectiveness of SPC under sunlight in disinfecting bacteria, it may have a very promising outcome as a water disinfection technique for real world applications.

Disinfection with neutral electrolyzed oxidizing water to reduce microbial load and to prevent biofilm regrowth in the processing of fresh-cut vegetables

Product decontamination is one of the most important processes of the hygienic practice in food industries such as Minimally Processed Vegetables (MPV) plants and sodium hypochlorite (NaOCl) solutions are commonly used as a biocide for disinfection. Although it may be corrosive and irritating when compared to alternative biocides, this biocide is frequently applied at high concentrations. This work aims at studying the use of lower concentrations of chlorine by testing neutral electrolyzed oxidizing water (NEOW) as a chlorine-source disinfectant in fresh-cut salad processing. Assays were performed at industrial and laboratory scale. Results showed that lower doses of chlorine from NEOW (30ppm) are as effective as higher concentrations of the traditional chlorine from NaOCl (80ppm) in the reduction of total microbial population at industrial scale. Moreover, in laboratory studies, the NEOW chlorine was also more effective in biofilm eradication, as well as a biofilm preventive agent. NEOW can thus be a successful alternative water disinfection technique, reducing the free chlorine concentration needed to sanitize salads, also decreasing water consumption whilst taking into account environmental and food quality impacts.

Clean Water for Developing Countries.

Availability of safe drinking water, a vital natural resource, is still a distant dream to many around the world, especially in developing countries. Increasing human activity and industrialization have led to a wide range of physical, chemical, and biological pollutants entering water bodies and affecting human lives. Efforts to develop efficient, economical, and technologically sound methods to produce clean water for developing countries have increased worldwide. We focus on solar disinfection, filtration, hybrid filtration methods, treatment of harvested rainwater, herbal water disinfection, and arsenic removal technologies. Simple, yet innovative water treatment devices ranging from use of plant xylem as filters, terafilters, and hand pumps to tippy taps designed indigenously are methods mentioned here. By describing the technical aspects of major water disinfection methods relevant for developing countries on medium to small scales and emphasizing their merits, demerits, economics, and scalability, we highlight the current scenario and pave the way for further research and development and scaling up of these processes. This review focuses on clean drinking water, especially for rural populations in developing countries. It describes various water disinfection techniques that are not only economically viable and energy efficient but also employ simple methodologies that are effective in reducing the physical, chemical, and biological pollutants found in drinking water to acceptable limits.

Comparative study of homogeneous and heterogeneous photo-oxidative treatment on bacterial cell via multianalytical techniques

• Heterogeneous photocatalyst, nano-titania is proved to be an effective antibacterial agent over the homogeneous neutral Photo-Fenton system. • The different mode of bactericidal activity was evaluated by cultivability, viability, cell permeability, extent of inner cell components release and morphological studies. • The heterogeneous photocatalyst causes disinfection through more of cell permeability unlike the homogeneous photocatalyst. The present article demonstrates the comparative efficiency of homogeneous and heterogeneous photocatalyst on cell membrane destruction using electron microscopy and spectroscopy techniques to understand the mechanism and evolve an effective water disinfection technique. The antibacterial activity of a heterogeneous photocatalyst nano-TiO 2 was compared with a homogeneous neutral Photo-Fenton reagent (Fe 2+/3+ , H 2 O 2 ) against Salmonella typhimurium , a gram negative water borne bacterium. To confirm the extent of both types of photooxidation treatment on bacterial cell, production of MDA, release of RNA, DNA and protein were carefully studied and analyzed. Based on the above experimental results, heterogeneous photocatalyst shows better performance than homogeneous neutral Photo-Fenton system and the difference is attributed to the mode of disinfection in the two systems. The damage of cell membrane and release of inner cell components is higher in heterogeneous system in contrast to the neutral Photo-Fenton system which causes disinfection through both cell membrane and internal cell damage. The entrapped RNA/DNA within the cell up to 80% in Fe 2+ treated bacteria substantiates destruction via internal cell damage.

Low-Cost Sustainable Technologies for the Production of Clean Drinking Water—A Review

Water has always been an important and life-sustaining drink to humans and is essential to the survival of all known organisms. Over large parts of the world, humans have inadequate access to drinking water and use water contaminated with disease vectors, pathogens or unacceptable levels of toxins or suspended solids. Drinking such water or using it in food preparation leads to widespread, acute and chronic illnesses and is a major cause of death and misery in many countries. The UN estimates that over 2.0 billion people have limited access to safe water and nearly 800 million people lack even the most basic supply of clean water. The main issue is the affordability of water purifying systems. Many people rely on boiling water or bottled water, which can be expensive. Therefore, technologies that are cost effective, sustainable, ease of operation/maintenance and the treatment processes with locally available materials are required. In this article, some unique low-cost sustainable technologies available/or in-use, i.e. natural filtration, riverbank filtration, biosand filtration, membrane filtration, solar water disinfection technique, biologically degradable materials such as moringa powder, scallop powder treatment, and biosand pitcher treatments have been discussed.

Comparing electrochemical disinfection with chlorination for inactivation of bacterial spores in drinking water

Drinking water disinfection techniques without the dosage of chemicals are regarded as more advantageous in terms of costs and practical use. Here we investigated the efficacy of electrochemical disinfection for inactivation of Bacillus subtilis spores – a model microorganism of highly resistant pathogens. The effect of electrochemical disinfection with TinO2n−1 ceramic electrodes which generate active chlorine from chloride in situ, was compared to the traditional chlorination in which active chlorine was produced from addition of sodium hypochlorite. Research was performed on a batch scale with a synthetic buffered drinking water containing 35.5 mg/l of chloride ions. Spore viability was analysed with both cultivation and cell potential for dividing (direct viable count method). The results showed that at similar residual disinfectant concentrations x contact time (CT value), electrochemical disinfection was over three times more effective in neutralizing both cultivable B. subtilis spores and those with cell potential for dividing than traditional chlorination. As in chlorination, electrochemical disinfection was shown to be water-pH dependent and the lowest CT value of 112 mg/l min−1 (2-log removal) was obtained at pH 6. The lowest efficiency for both techniques was observed at pH 8. In conclusion, electrochemical disinfection is a viable in situ method even at low levels of chlorides in drinking water and appears to be more effective than simple chlorination with the addition of the active chlorine species when highly resistant microbial forms are analysed, however, to apply the technology on a large scale additional studies on potential formation of disinfection by-products must be performed.

Water disinfection by pulsed atmospheric air plasma along water surface

An above water‐pulsed nonthermal plasma technique for water disinfection is reported. Experiments are performed with a 2.5 L plasma reactor and Escherichia coli. When its initial number density is less than 106 cfu/mL, up to six orders reduction can be achieved within 0.5–2.5 min and at a plasma energy density of less than 2 J/mL. The disinfection performance is always effective by controlling water conductivity of below 1.5 mS/cm, which significantly affects plasma generation. Aqueous hydrogen peroxide, ozone, and nitric acid are continuously accumulated inside the reactor by the processing. Plasma generated UV radiation plays an important role in the cell inactivation. Inactivated cell morphology almost remains the same shape, their intracellular protein like green fluorescent protein, however, is destructed according to fluorescence observation. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1458–1467, 2013

QSPR for predicting chloroform formation in drinking water disinfection

Chlorination is the most widely used technique for water disinfection, but may lead to the formation of chloroform (trichloromethane; TCM) and other by-products. This article reports the first quantitative structure–property relationship (QSPR) for predicting the formation of TCM in chlorinated drinking water. Model compounds (n = 117) drawn from 10 literature sources were divided into training data (n = 90, analysed by five-way leave-many-out internal cross-validation) and external validation data (n = 27). QSPR internal cross-validation had Q 2 = 0.94 and root mean square error (RMSE) of 0.09 moles TCM per mole compound, consistent with external validation Q2 of 0.94 and RMSE of 0.08 moles TCM per mole compound, and met criteria for high predictive power and robustness. In contrast, log TCM QSPR performed poorly and did not meet the criteria for predictive power. The QSPR predictions were consistent with experimental values for TCM formation from tannic acid and for model fulvic acid structures. The descriptors used are consistent with a relatively small number of important TCM precursor structures based upon 1,3-dicarbonyls or 1,3-diphenols.