Spirulina-based carbon materials as adsorbents for drinking water taste and odor control: Removal efficiency and assessment of cyto-genotoxic effects

The sensory quality of drinking water, and particularly its taste and odor (T&O) is a key determinant of consumer acceptability, as consumers evaluate water by their senses. Some of the conventional treatment processes to control compounds which impart unpleasant T&O have limitations because of their low efficiency and/or high costs. Therefore, there is a great need to develop an effective process for removing T&O compounds without secondary concerns. The primary objective of this study was to assess for the first time the effectiveness of spirulina-based carbon materials in removing geosmin (GSM) and 2-methylisoborneol (2-MIB) from water, two commonly occurring natural T&O compounds. The efficiency of the materials to remove environmentally relevant concentrations of GSM and 2-MIB (ng L-1) from ultrapure and raw water was investigated using a sensitive headspace solid-phase microextraction coupled with gas chromatography mass spectrometry (HS-SPME-GC/MS) method. Moreover, the genotoxic and cytotoxic effects of the spirulina-based materials were assessed for the first time to evaluate their safety and their potential in the treatment of water for human consumption. Based on the results, spirulina-based materials were found to be promising for drinking water treatment applications, as they did not exert geno-cytotoxic effects on human cells, while presenting high efficiency in removing GSM and 2-MIB from water.

Electronic nose application for detecting different odorants in source water: Possibility and scenario

The problem of taste and odor (T&O) in drinking water is a widespread societal concern and highlights substantial challenges related to the detection and evaluation of odor in water. In this study, the portable electronic nose PEN3, which is equipped with ten different heated metal sensors, was applied to analyze its applicability, feasibility and application scenarios for the detection of typical odorants, such as 2-methylisobornel (2-MIB), geosmin (GSM), β-cyclocitral, β-ionone, and other T&O compounds in source water, while avoiding uncertainties and instability related to manual inspection. All the T&O compounds could be effectively differentiated by principal component analysis (PCA). Linear discriminant analysis (LDA) showed that the odors varied greatly between different samples and could be effectively distinguished. As the odorant concentration increased, the sensor response intensity of the primary identification sensors R6 and R8 increased with a significant positive correlation. For Microcystis aeruginosa, an algae that produces odorants, PCA could distinguish the odors of algae at a series of densities at different concentrations. The responses of R10 showed a significant increase with increasing algae density, implying the production of more aliphatic hydrocarbons and other odor compounds. The results indicated that the electronic nose could provide a promising alternative to traditional unstable and complex detection methods for the detection of odorous substances in surface water and early warning of odor events. This study aimed to provide technical support for rapid monitoring and early warning of odorants in source water management.

Phosphorus accelerate the sulfur cycle by promoting the release of malodorous volatile organic sulfur compounds from Microcystis in freshwater lakes

Volatile organic sulfur compounds (VSCs) released by algae are of great significance in sulfur cycle, climate regulation and biological information transmission, and they also caused taste and odor in freshwaters. However, the categories, sources, and environmental regulatory factors of VSCs in freshwaters were less known. Here, we show that eight common freshwater cyanobacterium Microcystis, which bloom in freshwaters over the world, are found to be important producers of VSCs. Dimethyl sulfide (DMS), dimethyl disulfide (DMDS) and isopropyl methyl sulfide (IPMS) are the main VSCs with the highest concentrations 184.81 nmol/L, 162.01 nmol/L and 101.55 nmol/L, respectively. The amount of VSCs released from those Microcystis varied greatly, M. elabens, M. panniformis and M. flos-aquae released the largest amount of VSCs (1260.52 nmol S/L, 1154.75 nmol S/L and 670.58 nmol S/L), and M. wesenbergii had the smallest release amount. We also found for the first time that phosphorus (P) was one of the important factors for the regulation VSCs from most Microcystis. P can elevate the release of DMS by promoting the biomass and DMS yields of most Microcystis in the range 0.05 mg/L to 0.5 mg/L. Similar results were also found in 16 lakes at three different spatiotemporal scales. Overall, we revealed that the common freshwater Microcystis were able to release diverse thioethers, and the major VSCs were significantly influenced by water P concentrations. In the context of global freshwater eutrophication and Microcystis bloom, freshwater cyanobacteria driven sulfur cycle and water odor will probably be further strengthened.

β-Ionone causes endocrine disruption, hyperpigmentation and hypoactivity in zebrafish early life stages

In nature, the odorous substance β-ionone has been widely detected in aquatic ecosystems. However, little is known about its ecotoxicological effects on freshwater vertebrates. In this study, we aimed to assess the acute toxicity of β-ionone in zebrafish (Danio rerio) embryos from 2 to 120 h post fertilization (hpf) and investigate embryo development, locomotor behavior and pigmentation under different concentrations. The results showed that exposure to β-ionone had an acute toxicity to early life stages of zebrafish and induced a decrease in hatching rate and an increase in the mortality and malformation rate. The median lethal concentration (LC₅₀) of β-ionone at 96 h was observed as 1321 μg/L. In addition, β-ionone not only affected the body length of zebrafish larvae but also regulated the transcription of genes and the levels of hormones involved in the growth hormone/insulin-like growth factor (GH/IGF) and the hypothalamic-pituitary-thyroid (HPT) axes. Moreover, exposure to β-ionone induced significant decreases in locomotor activity and catecholamine neurotransmitters levels. Furthermore, β-ionone stimulated pigmentation via regulation of tyrosinase activity and melanin-related gene expression. Overall, this research could provide new insights into the potential risk of odorants to aquatic organisms.

Geosmin reduction by algaecide application to drinking water: field scale efficacy and mechanistic insights

Ten years of field data from an Oklahoma drinking water utility were analyzed for the effects of an acid-stabilized, ionic copper algaecide/bactericide called EarthTec on geosmin concentrations in the water traveling by pipeline from the source lake to a water treatment plant. The data show that geosmin already present in the raw water is reduced more during periods of applying algaecide than when not. Median reduction in geosmin concentration from pipe intake to pipe outfall by natural degradation without addition of algaecide was 5.6 ng/L removed (56.7% reduction) and improved to 126 ng/L removed (83% reduction) during periods the algaecide was being dosed at 1 μL/L, equivalent to 0.06 mg/L as copper. A laboratory study to replicate the phenomenon at bench-scale showed that either the algaecide itself or its copper-free acidic carrier can be used to depress pH and drive a reaction converting geosmin to an odorless dehydration product, argosmin. Algaecides intuitively reduce the organisms that produce geosmin, but this study shows that geosmin already present in the water is also being reduced through chemical conversion to the odorless argosmin, representing a novel means of geosmin removal in drinking water.

Effects of pre, post, and simultaneous loading of natural organic matter on 2-methylisoborneol adsorption on superfine powdered activated carbon: Reversibility and external pore-blocking

Three different natural organic matter (NOM)-loading methods were compared for the adsorptive removal of 2-methylisoborneol (MIB) by superfine powdered activated carbon (SPAC) and conventionally-sized powdered activated carbon (PAC). The three NOM-loading methods were: NOM adsorption followed by MIB (MIB adsorption on NOM-preloaded carbon), MIB adsorption followed by NOM (MIB adsorption on NOM post-loaded carbon), and simultaneous NOM and MIB loading (MIB adsorption on NOM-simultaneously loaded carbon). MIB removals were similar for the smaller-sized carbon (SPAC) at higher AC dosages and at lower initial NOM concentrations. The similar MIB removals indicate direct site competition between MIB and NOM with MIB adsorption reversibility (complete desorption of MIB by NOM). At lower AC doses, especially for PACs, and at higher initial NOM concentrations, the adsorption of MIBs depended on the sequence of MIB or NOM adsorption. MIB removal was lowest for the NOM-preloaded carbon, followed by NOM-simultaneously loaded carbon. The highest MIB removal was achieved by post-loading of NOM, indicating that the adsorption is irreversible. MIB adsorption on SPAC was more reversible than on PAC, although the pore size distributions of the two carbons were similar. The high degree of adsorption irreversibility for PAC compared with SPAC indicated that pore blocking occurs due to NOM loading at the PAC particle surface. Images of the external adsorption were obtained using isotope mapping and ¹⁵N-labeled effluent organic matter.

Cyanobacteria derived taste and odor characteristics in various lakes in China: Songhua Lake, Chaohu Lake and Taihu Lake

In recent years, increasing eutrophication in large freshwater lakes, which are an important drinking water source for cities in China, have been resulted in substantial cyanobacteria blooms that could cause serious taste and odor (T&O) problems. In this investigation, three typical lakes (Songhua Lake, Chaohu Lake and Taihu Lake) as drinking water sources located in different geographical areas in China, were selected to study the problems of cyanobacteria-derived T&O (i.e., 2-methylisobornoel, geosmin, β-ionone, 2-isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, and 2-methylbenzofuran). The occurrence of T&O in target lakes was compared across various nutrition states and geographic locations, to get more information for early warning for algal bloom and T&O occurrence, being useful lake water management and purification. Results show that the occurrence of T&O in Songhua Lake was the poorest for the lowest nutrient state, as a first report in T&O research field in China. This is a lake located in Northeast China at high latitude, with lower water temperatures. The occurrence of T&O in Chaohu Lake was ranked in the middle. That in Taihu Lake was the most intensive. Finally, the relationship between water quality, T&O and its origin was analyzed by multivariate statistical methods (correlation analysis, principal component, and cluster analyses).

Causality analysis and prediction of 2-methylisoborneol production in a reservoir using empirical dynamic modeling

2-Methylisobornel (MIB) is one of the most widespread and problematic biogenic compounds causing taste-and-odor problems in freshwater. To investigate the causes of MIB production and develop models to predict the MIB concentration, we have applied empirical dynamic modeling (EDM), a nonlinear approach based on Chaos theory, to the long-term water quality dataset of Kamafusa Reservoir in Japan. The study revealed the dynamic nature of MIB production in the reservoir, and determined causal variables for MIB production, including water temperature, pH, transparency, light intensity, and Green Phormidium. Moreover, EDM established that the system is three-dimensional, and the approach found elevated nonlinearity (from 1.5 to 3) across the whole study period (1996-2015). By taking only one or two candidate predictors with varying time lags, multivariate models for predicting MIB production (best model: r = 0.83, p < 0.001, root mean squared error = 3.1 ng/L) were successfully established. The modeling approach used in this study is a powerful tool for causality identification and odor prediction, thus making important contributions to reservoir management.

Early warning method for cyanobacteria toxin, taste and odor problems by the evaluation of fluorescence signals

Permanganate and ozone are often used in drinking water treatment plants for the oxidation of taste and odor compounds, toxins, and algae as well as the reduction of mussel activity. The disadvantage of an overuse of such oxidants is the potential lysis of cyanobacterial cells. Cell lysis causes taste and odor components as well as toxins to be released into the water, which results in the need for even more treatment to remove these compounds completely. Our research in the CLIENT-SIGN project investigated an innovative method to monitor the lysis of cyanobacteria cells: increases in a specific fluorescence emission spectrum of the cyanobacteria pigment phycocyanin were used as a proxy for cell lysis and other compounds (taste/odor, toxins) leaving the cells. We call this form of phycocyanin "free phycocyanin" or "unbound phycocyanin". By monitoring free phycocyanin via a relatively fast and inexpensive measurement, water utilities will be better able to optimize the dosage of pre-oxidation compounds to remove extracellular compounds while preventing the lysing of cells. Laboratory studies and a case study at Yangcheng Lake (adjacent to Lake Taihu, Yangcheng Lake Water Treatment Plant, Suzhou Industrial Park, China) are presented herein. An online surveillance system that monitors incoming raw water and the water after pre-oxidation is proposed to better cope with changing water conditions.

Slow-releasing permanganate ions from permanganate core-manganese oxide shell particles for the oxidative degradation of an algae odorant in water

In this work, potassium permanganate particles (KMnO₄) were modified with a manganese oxide (MnOx) shell comprising passages for the slow release of permanganate ions (MnO₄^-) in aquatic systems. The bare particle (KMnO₄) and KMnO₄ core-MnOx shell particles (CP-60) were characterized by attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The CP-60 were evaluated as a slow source of MnO₄^- for the oxidative treatment of pure and lake water containing dimethyl trisulfide (DMTS), a water odorant produced by cyanobacteria in many eutrophic waters. XPS and ATR-FTIR results confirmed the presence of MnOx surface shell (diameter ∼ 1 μm) on CP-60. SEM images revealed cracks on CP-60, which serve as outlets for MnO₄^-. Approximately 0.76 ± 0.07 g KMnO₄/g of CP-60 was released from the core of CP-60 after 120 min. The CP-60 degraded 88.9 ± 2.5% and 70.8 ± 6.3% of DMTS in pure water and lake water matrix within 120 min, respectively. The degradation was slightly more effective than the degradation using aqueous KMnO₄ (74.2%) reported in literature. The release kinetics of the particles is consistent with a pseudo-first order equation with correlation coefficients of 0.99 and 0.97 in pure water and lake water matrix, respectively. The CP could serve as low cost slow-release particles for the degradation of micropollutants, even in cyanobacteria laden water. Notably, the in situ MnOx formed during the KMnO₄ oxidation reaction can facilitate adsorption of organics and metal ions, improving water quality.

The effect of water treatment unit processes on cyanobacterial trichome integrity

Many toxic and/or noxious cyanobacteria appear in nature with a filamentous, stacked cell arrangement called trichomes. Although water treatment can be optimized to keep cyanobacterial cells intact and avoid the release of toxic and/or noxious compounds, many physical and chemical stresses encountered during the treatment process may result in trichome truncation, decreasing treatment efficiency by allowing single cells or short trichomes to reach the product water. This makes it possible for harmful/noxious compounds as well as organic matter to enter the distribution system. Investigations in a pilot and three full-scale water treatment plants were carried out in order to elucidate the degree of trichome truncation across different unit processes. It was found that genera (Pseudanabaena, Planktolyngbya) with short trichomes (<10-12 cells per trichome), are hardly affected by the unit processes (loss of one to four cells respectively), while genera (Planktothrix, Geitlerinema, Dolichospermum) with longer trichomes (30+ cells per trichome) suffer from high degrees of truncation (up to 63, 30, and 56 cells per trichome respectively). The presence of a rigid sheath and/or mucilaginous layer appears to offer some protection from truncation. It was observed that certain unit processes alter the sensitivity or resilience of trichomes to disruption by physical stress. Some genera (Planktothrix, Geitlerinema) were sensitive to pre-oxidation making them more susceptible to shear stress, while Dolichospermum sp. appears more robust after pre-oxidation. While the potential of toxicogenic genera breaking through into the product water is a real danger, in the current study no toxicogenic cyanobacteria were observed. This work stresses the need for plant operators to study the incoming cyanobacterial composition in the raw water in order to adjust treatment parameters and thus limit the potential of toxic/noxious compound breakthrough.

The relationships between odors and environmental factors at bloom and non-bloom area in Lake Taihu, China

Lake Taihu has been experiencing taste and odor (T&O) events recently. And for the purpose of seeking the environmental factors having great influences on T&O compounds and supplying theory information for preventing the occurrence of T&O problems, Redundance analysis (RDA) was conducted for the dissolved and particle-bound forms of T&O compounds. And the whole lake was divided into the blooming and non-blooming areas. Results indicated that environmental factors, including biotic and abiotic factors, made great contributions to the variation of T&O compounds in Lake Taihu. The key biotic factors included Microcystis, Oscillatoria and chlorophyll-a. Microcystis made great contribution of these compounds in the blooming area and had close relationship with those particulate forms of odorants in Taihu. Oscillatoria made great and absolute contribution to odorants in the non-blooming area. Chlorophyll-a influenced greatly the odorants in the blooming area and had significant relationship with the particle-bound fractions in the whole lake. Dissolved oxygen and water temperature were the dominant abiotic factors with large contributions.

Succession and interaction of surface and subsurface cyanobacterial blooms in oligotrophic/mesotrophic reservoirs: A case study in Miyun Reservoir

Subsurface cyanobacterial blooms, are a significant source of odor problems in source water and have been recorded in many oligotrophic/mesotrophic drinking water reservoirs. In this study, we explored the key driving forces responsible for the succession between surface and subsurface cyanobacteria using ecological niche modelling based upon a case study in Miyun Reservoir, China. The results suggest a negative effect of water depth and surface light irradiance (I₀) on subsurface Planktothrix sp. growth (p-values < 0.001), and a unimodal effect of surface water temperature (T₀) with the optimum at 23 °C (p-value < 0.001). While the surface Microcystis spp. shows a strong positive relationship with temperature (T₀; p-value < 0.001), and significant effects for the interaction between T₀ and I₀ (p- value < 0.01). In addition, we identified the extent and type of interaction between subsurface and surface cyanobacteria and conclude that the high irradiance surface water combined with sufficient nutrients at the pre-bloom stage are key factors responsible for the preferential growth of surface cyanobacteria, while the gradual decline of the surface cyanobacteria in post-bloom stage is associated with nutrient reduction. This decline and loss of surface populations enhanced underwater irradiance and thus promoted the growth and allowed for succession of subsurface cyanobacteria in deeper layers where the nutrient supply was still adequate. Based upon this, the growth potentials for the subsurface and surface cyanobacteria are different under different environmental conditions: the subsurface cyanobacteria have greater growth potential than surface cyanobacteria in shallow oligotrophic and deep eutrophic reservoirs during median light irrigation seasons.

Contribution of filamentous fungi to the musty odorant 2,4,6-trichloroanisole in water supply reservoirs and associated drinking water treatment plants

In this study, the distribution of 2,4,6-trichloroanisole (2,4,6-TCA) in two water supply reservoirs and four associated drinking water treatment plants (DWTPs) were investigated. The 2,4,6-TCA concentrations were in the range of 1.53-2.36 ng L^-1 in water supply reservoirs and 0.76-6.58 ng L^-1 at DWTPs. To determine the contribution of filamentous fungi to 2,4,6-TCA in a full-scale treatment process, the concentrations of 2,4,6-TCA in raw water, settled water, post-filtration water, and finished water were measured. The results showed that 2,4,6-TCA levels continuously increased until chlorination, suggesting that 2,4,6-TCA could form without a chlorination reaction and fungi might be the major contributor to the 2,4,6-TCA formation. Meanwhile, twenty-nine fungal strains were isolated and identified by morphological and molecular biological methods. Of the seventeen isolated fungal species, eleven showed the capability to convert 2,4,6-trichlorophenol (2,4,6-TCP) to 2,4,6-TCA. The highest level of 2,4,6-TCA formation was carried out by Aspergillus versicolor voucher BJ1-3: 40.5% of the original 2,4,6-TCP was converted to 2,4,6-TCA. There was a significant variation in the capability of different species to generate 2,4,6-TCA. The results from the proportions of cell-free, cell-attached, and cell-bound 2,4,6-TCA suggested that 2,4,6-TCA generated by fungi was mainly distributed in their extracellular environment. In addition to 2,4,6-TCA, five putative volatile by-products were also identified by gas chromatography and mass spectrometry. These findings increase our understanding on the mechanisms involved in the formation of 2,4,6-TCA and provide insights into managing and controlling 2,4,6-TCA-related problems in drinking water.

Reducing production of taste and odor by deep-living cyanobacteria in drinking water reservoirs by regulation of water level

Abatement and control of algae, producing toxins and creating taste & odor (T&O) in drinking water sources, is a major challenge for water supply. In this study we proposed a strategy based on water level regulation for the control of odor-producing cyanobacteria in source water. Miyun Reservoir, the main surface water source for Beijing, has been suffering from 2-methylisoborneol (2-MIB) induced T&O problems caused by deep-living Planktothrix sp. since 2002. The biomass of deep-living Planktothrix in Miyun Reservoir was found to be mainly governed by the water depth above its sediment habitat. An algorithm for water level regulation aiming to minimize the risk for T&O in different types of reservoirs is proposed. The study demonstrates that risk for T&O can be minimized by increasing the water level in Miyun Reservoir. The high-risk area can be reduced by about 2.91% (0.61% to 5.76%) of surface area for each meter increase in the water level, when the water level is lower than 145m. More specifically, the water level needs to be raised to higher than 147.7ma.s.l. from 131.0m in order to obtain an acceptable risk level (ARL) of 10%. This management strategy to abate T&O problems is simpler and cheaper to implement compared to traditional physical, chemical and biological techniques. Moreover, it has no apparent negative impact on water quality and aquatic organisms.

Occurrence and distribution of taste and odor compounds in subtropical water supply reservoirs and their fates in water treatment plants

Taste and odor (T&O) problems in surface water supplies attract growing environmental and ecological concerns. In this study, 10 T&O compounds, 2-methylisoborneol (2-MIB), geosmin, β-ionone, 2-isopropyl-3-methoxypyrazine (IPMP), 2-isobutyl-3-methoxypyrazine (IBMP), 2,4,6-trichloroanisole (2,4,6-TCA), 2,3,6-trichloroanisole (2,3,6-TCA), 2,3,4-trichloroanisole (2,3,4-TCA), 2,4,6-tribromoanisole (2,4,6-TBA), and trans-2,cis-6-nonadienal (NDE) were investigated in 13 water supply reservoirs and 2 water treatment plants (WTPs) in S City of China. 2-MIB, geosmin, and β-ionone were detected in most of the reservoirs and WTPs. The highest concentrations in reservoirs reached 196.0 ng L^-1 for 2-MIB, 11.4 ng L^-1 for geosmin, and 39.7 ng L^-1 for β-ionone. Canonical correspondence analysis (CCA) was used to examine the relationship between the 3 T&O compounds and environmental parameters of the reservoirs. The results showed that TP was strongly positively correlated with 2-MIB in wet season and negatively correlated in dry season. It was suggested that controlling nutrient (TP, TN/TP, and NH₃-N) inputs was required for better management of drinking water reservoirs. Furthermore, the maximum concentrations in raw water of WTPs was kept at 82.1 ng L^-1 for 2-MIB, 5.6 ng L^-1 for geosmin, and 66.1 ng L^-1 for β-ionone. β-Ionone could not be detected in the post-filtration and finished water of two WTPs, and both 2-MIB and geosmin significantly decreased in the water of XWTP. It was indicated that T&O compounds could be removed partly or completely by the filtration of conventional treatment processes.

Source-water odor during winter in the Yellow River area of China: Occurrence and diagnosis

Yellow River source water has long suffered from odor problems in winter. In this study, odor characteristics, potential odorants, and algae in the source water of six cities (Lanzhou, Yinchuan, Hohhot, Zhengzhou, Jinan and Dongying) along the Yellow River were determined in winter (February to March 2014). According to flavor profile analysis (FPA), moderate to strong fishy odors occurred in all cities, except for Lanzhou. At the same time, mild earthy/musty odors and septic/swampy odors were also detected. The strong fishy odor (FPA intensity, 8.5) in Yinchuan was attributed to the abnormal growth of Dinobryon (cell density, 5.7 × 10⁴ cells/mL), while the fishy odors in Hohhot, Zhengzhou, Jinan, and Dongying might be caused by Melosira and Cyclotella, Cryptomonas, Dinobryon, and Synedra, respectively. Unsaturated aldehydes, which have been reported to cause fishy odors, were not detected in all samples. However, some saturated aldehydes, including hexanal, heptanal, nonanal, decanal, and benzaldehyde, were detected with a total concentration range of 690 ng/L to 2166 ng/L, and might have partly contributed to the fishy odors. In addition, 2-MIB (5.77-21.12 ng/L) and geosmin (2.26-9.73 ng/L) were responsible for the earthy/musty odors in the Yellow River source waters, and dimethyl disulfide (648.2 ng/L) was responsible for the rancid/swampy odor (FPA intensity, 8.0) episode in Yinchuan. This is a comprehensive study reporting on the occurrence and possible reasons for the odor issues in the Yellow River source water during winter.

An alternative method to quantify 2-MIB producing cyanobacteria in drinking water reservoirs: Method development and field applications

2-Methylisoborneol (2-MIB) is a commonly detected cyanobacterial odorant in drinking water sources in many countries. To provide safe and high-quality water, development of a monitoring method for the detection of 2-MIB-synthesis (mibC) genes is very important. In this study, new primers MIBS02F/R intended specifically for the mibC gene were developed and tested. Experimental results show that the MIBS02F/R primer set was able to capture 13 2-MIB producing cyanobacterial strains grown in the laboratory, and to effectively amplify the targeted DNA region from 17 2-MIB-producing cyanobacterial strains listed in the literature. The primers were further coupled with a TaqMan probe to detect 2-MIB producers in 29 drinking water reservoirs (DWRs). The results showed statistically significant correlations between mibC genes and 2-MIB concentrations for the data from each reservoir (R²=0.413-0.998; p<0.05), from all reservoirs in each of the three islands (R²=0.302-0.796; p<0.01), and from all data of the three islands (R²=0.473-0.479; p<0.01). The results demonstrate that the real-time PCR can be an alternative method to provide information to managers of reservoirs and water utilities facing 2-MIB-related incidents.

Prediction of powdered activated carbon doses for 2-MIB removal in drinking water treatment using a simplified HSDM approach

The addition of powdered activated carbon (PAC) is an effective measure to cope with seasonal taste and odor (T&O) problems caused by 2-methylisoborneol (2-MIB) and trans-1, 10-dimethyl-trans-9-decalol (geosmin) in drinking water. Some T&O problems are episodic in nature, and generally require rapid responses. This paper proposed a simplified approach for the application of the homogenous surface diffusion model (HSDM) to predict the appropriate PAC doses for the removal of 2-MIB. Equilibrium and kinetic experiments were performed for 2-MIB adsorption onto five PACs in three source waters. The simplified HSDM approach was compared with the experimental data, by assigning the Freundlich 1/n value in the range of 0.1-1.0 and obtaining the Freundlich equilibrium parameter K value through a 6-hr adsorption kinetic test. The model describes the kinetic adsorption data very well for all of the tested PACs in different source waters. The results were validated using the data obtained from one full scale water treatment plant, and the differences between the predicted and observed results were within 10% range. This simplified HSDM approach may be applied for the rapid determination of PAC doses for water treatment plants when faced with 2-MIB episodes in source waters.

Adsorption capacities of activated carbons for geosmin and 2-methylisoborneol vary with activated carbon particle size: Effects of adsorbent and adsorbate characteristics

The adsorption capacities of nine activated carbons for geosmin and 2-methylisoborneol (MIB) were evaluated. For some carbons, adsorption capacity substantially increased when carbon particle diameter was decreased from a few tens of micrometers to a few micrometers, whereas for other carbons, the increase of adsorption capacity was small for MIB and moderate for geosmin. An increase of adsorption capacity was observed for other hydrophobic adsorbates besides geosmin and MIB, but not for hydrophilic adsorbates. The parameter values of a shell adsorption model describing the increase of adsorption capacity were negatively correlated with the oxygen content of the carbon among other characteristics. Low oxygen content indicated low hydrophilicity. The increase of adsorption capacity was related to the hydrophobic properties of both adsorbates and activated carbons. For adsorptive removal of hydrophobic micropollutants such as geosmin, it is therefore recommended that less-hydrophilic activated carbons, such as coconut-shell-based carbons, be microground to a particle diameter of a few micrometers to enhance their equilibrium adsorption capacity. In contrast, adsorption by hydrophilic carbons or adsorption of hydrophilic adsorbates occur in the inner pores, and therefore adsorption capacity is unchanged by particle size reduction.

Simultaneous assessments of occurrence, ecological, human health, and organoleptic hazards for 77 VOCs in typical drinking water sources from 5 major river basins, China

Owing to the growing public awareness on the safety and aesthetics in water sources, more attention has been given to the adverse effects of volatile organic compounds (VOCs) on aquatic organisms and human beings. In this study, 77 target VOCs (including 54 common VOCs, 13 carbonyl compounds, and 10 taste and odor compounds) were detected in typical drinking water sources from 5 major river basins (the Yangtze, the Huaihe, the Yellow, the Haihe and the Liaohe River basins) and their occurrences were characterized. The ecological, human health, and olfactory assessments were performed to assess the major hazards in source water. The investigation showed that there existed potential ecological risks (1.30 × 10 ≤ RQtotals ≤ 8.99 × 10) but little human health risks (6.84 × 10(-7) ≤ RQtotals ≤ 4.24 × 10(-4)) by VOCs, while that odor problems occurred extensively. The priority contaminants in drinking water sources of China were also listed based on the present assessment criteria.

A review on advanced oxidation processes for the removal of taste and odor compounds from aqueous media

In view of the global concern about the occurrence of taste and odor (T&O) compounds in waters for drinking water supply and the necessity for the development of more innovative and efficient technologies for water treatment and depuration, the focus of this study is to provide a state of the art overview on current knowledge for the application of advanced oxidation technologies for the treatment of T&O compounds in aquatic media. The most representative and newly emerging compounds belonging to the major groups of T&O compounds, such as geosmin, methylisoborneol, benzothiazoles, mercaptans and sulfides as well as aromatic and other miscellaneous T&O compounds, are included in the systematic overview. The current data has been compiled and extensively discussed in terms of the degree of degradation, reaction kinetics, effect of operational parameters and water quality, identity of intermediate and final products and possible transformation pathways.