Modelling of THM formation potential and DOM removal based on drinking water catchment characteristics

Hydrology Predominates Over Harvest History and Landscape Variation to Control Water Quality and Disinfection Byproduct Formation Potentials in Forested Pacific Coast Watersheds

Despite the global importance of forested watersheds as sources of drinking water, few studies have examined the effects of forestry on drinking water treatability. Relatively little is known about how the interaction between landscape variation and flow impacts source water quality and what this interaction means for drinking water treatability. To address this knowledge gap, we examined variability in sediments, dissolved organic matter, and disinfection byproduct formation potentials (DBP-FPs) across a range of flow conditions in four small watersheds with contrasting forest harvest histories and soil characteristics on Vancouver Island. Storm event-driven change in streamflow was the primary driver of water quality and DBP-FPs at our sites, with greater changes during stormflow (e.g., a 3-fold increase in dissolved organic carbon concentrations) than those across contrasting watersheds. Flow-driven changes in water quality and DBP-FPs were not significantly different across watersheds with different harvest histories; muted responses may be attributed to widespread second growth forests (i.e., recent harvesting effects may be confounded by historical harvest), forestry practices (e.g., slash burning), or soils with low organic carbon storage. This study suggests that variation in hydrology predominates over harvest history and soil characteristics to drive water quality and DBP-FPs on the east coast of Vancouver Island.

Characterization of DOM released from bacteria in response to chlorine in water based on indicator bacteria E. coli

ABSTRACTIn this study, Escherichia coli (E. coli) was used as an indicator bacterium treated with five different concentrations of chlorine (0.1; 0.5; 1.0; 2.0, and 5.0 mg/L) and without chlorine (0.0 mg/L) to evaluate the changes in the DOM characteristics. The dissolved organic carbon (DOC) concentration initially increased along with the chlorine concentrations and decreased after 24 h (0.0 and 0.1 mg/L) and 168 h (0.5; 1.0; 2.0 and 5.0 mg/L). Ultra-violet absorbance at 260 nm (UV260) showed that the absorbance decreased for control without chlorine (0.0 mg/L) and 0.1 mg/L chlorine, while increased for other concentrations of chlorine within 120 h. The DOC and UV260 results indicated that the high concentrations of chlorine initiated high contents of DOM which contained more humic-like molecules than the DOM released from E. coli without chlorine. Fluorescence excitation-emission matrix (EEM) analysis suggested that the DOM released from E. coli without chlorine enriched with protein-like substances, whereas the fulvic-like and humic-like substances more intensified in the DOM for the high concentrations of chlorine (>1.0 mg/L). The molecular weight distribution of DOM showed that the intensity of high molecular weight substances and polydispersity increased along with chlorine concentration and contact time, whereas the low molecular weight substances were relatively higher in the DOM for control without chlorine. The obtained results of this study would be useful for a better understanding of the variation of DOM during treatment and could be used as an important reference for optimizing the operation condition of the water treatment plants.

Assessing the effect of catchment characteristics to enhanced coagulation in drinking water treatment: RSM models and sensitivity analysis

Coagulation is the main process for removing natural organic matter (NOM), considered to be the major disinfection by-products (DBPs) precursor in drinking water production. In this work, k-means clusters analysis were used to classify influent waters from two different surface drinking water treatment plants (DWTPs) located in the Mediterranean region. From this, enhanced coagulation models based on response surface methodology (RSM) were then developed to optimise coagulation at two water catchments (river and reservoir). The cluster analysis classified the water quality of the raw waters into two groups related to baseline and peak organic loads. The developed enhanced coagulation models were based on the turbidity, total organic carbon (TOC) and UV₂₅₄ removals. Sensitivity analysis applied to the models (after predictors selection) determined the factors relative individual contributions for each DWTP scenario. Then, profile plots for enhanced coagulation were studied to identify the optimal levels for each case. Models mean R² were 0.85 and 0.86 in baseline and 0.85 and 0.84 in peak scenario for river and reservoir catchments, respectively. Results of this study indicate that the surface water quality variation in river DWTP is seasonal and is expressed by an increase of turbidity, while in the reservoir DWTP is related to extreme weather events showing high levels of dissolved organic load (TOC and UV₂₅₄). During baseline cases, where raw waters present low levels of organics, the three factors optimal adjustment should be ensured to optimise coagulation. Then, during peak scenarios, where influent waters present high organics, the optimal for enhanced coagulation relies on the correct adjustment of C_d. The presented work provides models for drinking water production aimed to propose the optimum conditions for enhanced coagulation, considering the influent water characteristics under different weather conditions.

Comparison of Hyperspectral Versus Traditional Field Measurements of Fractional Ground Cover in the Australian Arid Zone

The collection of high-quality field measurements of ground cover is critical for calibration and validation of fractional ground cover maps derived from satellite imagery. Field-based hyperspectral ground cover sampling is a potential alternative to traditional in situ techniques. This study aimed to develop an effective sampling design for spectral ground cover surveys in order to estimate fractional ground cover in the Australian arid zone. To meet this aim, we addressed two key objectives: (1) Determining how spectral surveys and traditional step-point sampling compare when conducted at the same spatial scale and (2) comparing these two methods to current Australian satellite-derived fractional cover products. Across seven arid, sparsely vegetated survey sites, six 500-m transects were established. Ground cover reflectance was recorded taking continuous hyperspectral readings along each transect while step-point surveys were conducted along the same transects. Both measures of ground cover were converted into proportions of photosynthetic vegetation, non-photosynthetic vegetation, and bare soil for each site. Comparisons were made of the proportions of photosynthetic vegetation, non-photosynthetic vegetation, and bare soil derived from both in situ methods as well as MODIS and Landsat fractional cover products. We found strong correlations between fractional cover derived from hyperspectral and step-point sampling conducted at the same spatial scale at our survey sites. Comparison of the in situ measurements and image-derived fractional cover products showed that overall, the Landsat product was strongly related to both in situ methods for non-photosynthetic vegetation and bare soil whereas the MODIS product was strongly correlated with both in situ methods for photosynthetic vegetation. This study demonstrates the potential of the spectral transect method, both in its ability to produce results comparable to the traditional transect measures, but also in its improved objectivity and relative logistic ease. Future efforts should be made to include spectral ground cover sampling as part of Australia’s plan to produce calibration and validation datasets for remotely sensed products.

Interrelationship among the pollutants in stormwater in an urban catchment and first flush identification using UV spectroscopy

Assessing urban stormwater quality by investigation and characterisation of pollutants is a prerequisite for its effective management, for reuse and safe discharge. The stochastic nature of rainfall, dry weather periods, topology, human activities and climatic conditions generate and wash-off pollutants differently from event to event. This study investigated the major physico-chemical pollutants in stormwater runoff collected from an urban catchment over a period of two years. The aim of this study was to explore the use of UV spectroscopy to identify the first flush. In this study, the variation of pollutants during the passage of a rain event and the relationships among the measured pollutants was analysed to help broaden the application of UV spectroscopy beyond the detection of organic matter. Correlation analysis and principal component analysis (PCA) were performed to identify the possible relationship among measured pollutants. Although correlation analysis revealed some relationships between pollutants, in general they were not strong enough and was not helpful. PCA biplots suggested a few groups and revealed that the two components model could explain nearly 72% of the variability between pollutants. Pollutants in the group that included dissolved organic carbon (DOC) behaved in a similar manner. UV spectroscopy was applied to identify the first flush by comparing the recorded spectrum of consecutive samples that were collected in an event. Analysis of the spectra was able to isolate the point when first flush ends for DOC and pollutants that behave similar to it.

Evaluating Water Resource Assets Based on Fuzzy Comprehensive Evaluation Model: A Case Study of Wuhan City, China

With the rapid development of China’s economy, the demand for water resources continues to sharply increase, which has gradually contributed to serious environmental problems. The Chinese government has proposed establishing a natural resource balance sheet, which is expected to solve this problem by assessing the value of water resources. The main purpose of this study was to assess the value of water resources in Wuhan from 2013 to 2017. Based on a fuzzy mathematical evaluation model, 15 indicators were chosen considering the three main aspects of resources, society, and the environment to construct a water resource evaluation indicator system. In addition, the analytic hierarchy process (AHP) and entropy weight methods were combined to determine the index weight. Based on this, we calculated the value of water resources in Wuhan from 2013 to 2017. The results demonstrated that the values of water resources in Wuhan from 2013 to 2017 were US$2.910 billion, US$5.006 billion, US$9.223 billion, US$14.167 billion, and US$7.189 billion, respectively. Therefore, this paper provides a scientific foundation for the rational establishment of water prices, the assessment of local natural resource assets, and the preparation of natural resource balance sheets.