Wetlands receiving water treated with coagulants improve water quality by removing dissolved organic carbon and disinfection byproduct precursors

Spectral characterization of dissolved organic matter in groundwater to assess mixing with oil-field water near selected oil fields, southern California

Samples of oil-field water (oil wells, injectate, disposal ponds) and groundwater near selected oil and gas fields in southern California were analyzed for dissolved organic carbon (DOC) concentration and by optical spectroscopic techniques (i.e., absorbance and fluorescence) to assess whether these measurements can be used to distinguish between oil-field water (Oil Field), native groundwater (WGnat), and native groundwater mixed with oil-field water from surface (WGsurf) or subsurface sources (WGsub), and if so whether commonly reported optical measurements can be used as a screening tool to identify such water. Concentrations of DOC were significantly (p < 0.0001) higher (67 to 2934 mg C L-1) in oil-field water compared to native groundwater samples (<5.0 mg C L-1). Individual optical properties varied by water category and frequently overlapped. However, multivariate statistical analysis showed that when evaluated in combination, 10 optical properties were determined by discriminant analysis to be significant (p < 0.05) in distinguishing among water categories. Principal component analysis of those 10 optical properties showed that these properties can be used to successfully distinguish Oil Field samples from WGnat, WGsurf, and WGsub even when mixing fractions are low (approximately 10 %).

Enhanced coagulation for mitigation of disinfection by-product precursors: A review

The unintended formation of disinfection by-products (DBPs) has received considerable attention as it may pose risks to human health. Coagulation is the most common process for removing particulates as well as dissolved organic matter (DOM) (i.e., DBP precursors) during drinking water and wastewater treatments. With the improvement of water quality standards and the increased fluctuation in source water quality, conventional coagulation becomes challenging. Thus, significant efforts have been made to enhance coagulation to promote the removal of DOM in source water and mitigate the formation of DBPs in drinking water. This review provides a brief summary of the properties of DBP precursors and summarizes the effectiveness of enhanced coagulation involving three types of coagulants (metal-based coagulants, organic polymers, and organic-inorganic hybrid coagulants) in controlling the formation of DBPs during chlor(am)ination disinfection. Metal-based coagulants can achieve a reduction in DBP formation potential of approximately 20%-60% in natural water under enhanced coagulation conditions. Both the organic polymers (used as coagulant aids) and novel hybrid coagulants increase the removal of DOM and exhibit high potential for mitigating DBP formation. In addition, integrated treatments combining coagulation with other treatment processes (e.g., oxidation, membrane filtration, ion exchange, and adsorption) to enhance DBP precursor removal are evaluated in terms of performance, mechanisms, and features. Advanced treatments, such as membrane filtration and activated carbon adsorption, are effective coagulation-assisted processes, and can further control chlorinated DBPs; however, the elevated formation of bromate or highly brominated DBPs is of particular concern.

Spectroscopic fingerprinting of dissolved organic matter in a constructed wetland-reservoir ecosystem for source water improvement-a case study in Yanlong project, eastern China

The coupling between constructed wetlands and reservoir (CWs-R) afforded a novel ecosystem to improve the water quality and increase the emergency storage capacity of micro-polluted river drinking water source. In this study, spectroscopic characteristics of DOM in YL CWs-R ecosystem were first systematic studied based on a three-year field monitoring to investigate the chemical composition, sources and track the involved biogeochemical processes in the ecosystem. Three humic-like components (C1, C2, and C4, em >380 nm) and one protein-like component (C3, em < 380 nm) were identified by PARAFAC model. Significant spatiotemporal variations in concentration and composition of FDOM were observed in YL CWs-R ecosystem. The improved water transparency (SD) and, the increased hydraulic retention time (HRT) along YL CWs-R ecosystem enhance photochemical processes, leading to significant decreases in the intensities of humic-like components in effluent (P < 0.05) with lower degrees of aromaticity, molecular weights, and humification (decrease in HIX and increases in S_R and BIX). In contrast, no significant spatial difference was observed for protein-like component (P > 0.05), which implies that the biodegradation and production of protein-like component may balance each other in the CWs-R ecosystem. The ecological pond unit plays a major role in the removal and transformation of DOM, especially in summer, while wetland purification unit contributes little to DOM reduction. In addition, the decay of aquatic macrophytes in wetland purification unit and the risk of algal bloom in the ecological pond unit might become important autochthonous sources of DOM, especially in summer and autumn. These findings are critical for further understanding the transformation processes of DOM in large-scale CWs-R ecosystems, and could provide important implications to improve sustainable safety of drinking water sources.

Trihalomethane precursors: Land use hot spots, persistence during transport, and management options

To meet drinking water regulations, rather than investing in costly treatment plant operations, managers can look for ways to improve source water quality; this requires understanding watershed sources and fates of constituents of concern. Trihalomethanes (THMs) are one of the major classes of regulated disinfection byproducts, formed when a specific fraction of the organic carbon pool-referred to as THM precursors-reacts with chorine and/or bromine during treatment. Understanding the source, fate, timing and duration of the organic compounds that react to form THMs will allow identification of targeted and effective management actions. In this study we evaluated THM precursor contributions from multiple land use categories and hydrologic contexts, including novel data for urban land uses that demonstrate strong potential to release water with high THM formation potential (THMFP; median 618 μg L^-1): greater than storm runoff integrated across a mixed-use (1/3 natural, 2/3 agricultural) watershed (median 460 μg L^-1), irrigation runoff from agricultural systems (357 μg L^-1), or runoff from a natural forested (median 123 μg L^-1) and shrubland/grassland (median 259 μg L^-1) watersheds. While individual storm events released high THM precursor concentrations over short periods, dry season agricultural irrigation as well as urban landscapes have the potential to release water high in THM precursors for several months. Experimental bioassays and sampling along 333 miles of the California Aqueduct confirmed bioavailability and photooxidation potential of less than 10% for THM precursors, suggesting that rivers with residence times of days to weeks may act as THM precursor conduits, shuttling THM precursors from hundreds of miles away to drinking water intakes with minimal degradation. This finding has considerable implications for water managers, who may therefore consider THM precursor management strategies that target even sources located far upstream.

Wetlands for wastewater treatment

This article presents an update on the research and practical demonstration of wetland treatment technologies for wastewater treatment. Applications of wetlands in wastewater treatment (as an advanced treatment unit or a decentralized system) and stormwater management or treatment for nutrient and pollutant removal (metals, industrial and emerging pollutants including pharmaceutical compounds and pathogens) are highlighted. A summary of studies involving the effects of vegetation, wetland design and operation, and configurations for efficient treatment of various municipal and industrial wastewaters is also included. PRACTITIONER POINTS: Provides an update on current research and development of wetland technologies for wastewater treatment. Effects of vegetation, pathogens removal, heavy metals and emerging pollutants removal are included. Wetland design and operation is a key factor to improve water quality of wetland effluent.

A comparison of trichloromethane formation from two algae species during two pre-oxidation-coagulation-chlorination processes

Microcystis aeruginosa (M. aeruginosa) commonly blooms in summer while Cyclotella meneghiniana (C. meneghiniana) outbreaks in fall in water reservoirs of Southeast China. Pre-oxidation has been demonstrated to enhance the algae removal from chemical coagulation processes. However, excessive dosage of pre-oxidant can increase the disinfection by-products formation potential (DBPsFP). Additionally, the DBPs formation mechanisms from algae during the pre-oxidation-coagulation-chlorination processes have not well elucidated. In this study, the objectives were to investigate the trichloromethane (TCM) formation, the changes of water quality indexes, and the morphology changes of algal cells from M. aeruginosa or C. meneghiniana contaminated water during potassium permanganate (KMnO₄) or chlorine (Cl₂) pre-oxidation-coagulation-chlorination disinfection. The results showed that the TCM yield for two algal species decreased with the dosage increase of KMnO₄ pre-oxidation, but increased with the dosage increase of pre-chlorination. Therefore, the 2.0 mg/L KMnO₄ or 0.5 mg/L Cl₂ was proposed as the optimal dosage for preventing both M. aeruginosa blooms in summer and for C. meneghiniana outbreaks in fall. M. aeruginosa exhibited a slightly higher TCM yield than C. meneghiniana in these treatment processes. Based on the release of potassium (K) ion and SEM analysis, KMnO₄ had less damage on cell integrity than Cl₂ at the dosage ≤2.0 mg/L. In addition, C. meneghiniana was easier to be disrupted by both pre-oxidants than M. aeruginosa, combining with subsequent coagulation led to different value of dissolved organic carbon (DOC), UV-visible absorbance (UV₂₅₄) and turbidity.

Mercury sequestration and transformation in chemically enhanced treatment wetlands

Mercury (Hg) pollution is a concern to human and wildlife health worldwide, and management strategies that reduce Hg inputs to aquatic systems are of broad interest. Using a replicated field-scale study in California's Sacramento-San Joaquin Delta, we tested the effectiveness of chemically enhanced treatment wetlands (CETWs) under two coagulation treatments, polyaluminum chloride (Al treatment) and ferric sulfate (Fe treatment), in their initial removal and longer-term sequestration of Hg compared to untreated control wetlands. The primary mechanism for Hg removal by CETWs was the transfer of Hg from filtered forms to insoluble particulate forms and enhanced settling of particles. CETWs resulted in total Hg annual load removals of 63 ng m^-2 yr^-1 (71%) and 54 ng m^-2 yr^-1 (54%) for the Al and Fe treatments, respectively. Control wetlands removed significantly less at 13 ng m^-2 yr^-1 (14%). Load removals indicate that Fe treatment wetlands more effectively reduced filtered and total methylmercury (MeHg) exports, while Al treatment wetlands more effectively reduced particulate MeHg and total Hg exports. These differences in Hg species load reductions possibly indicate different mechanisms of Hg sequestration; current data suggest more effective floc formation and particle settling was likely responsible for the Al treatment behavior, while either preferential MeHg sequestration or methylation suppression was potentially responsible for Fe treatment behavior. Differences in Hg sequestration behavior post-coagulation between the flocs formed by different coagulants indicate the importance of in-situ studies and the need for careful selection of coagulant treatment depending on the Hg species requiring remediation.

Effects of ferric sulfate and polyaluminum chloride coagulation enhanced treatment wetlands on Typha growth, soil and water chemistry

Land surface subsidence is a concern in many deltas worldwide as it contributes to water quality degradation, loss of fertile land and increased potential for levee failure. As a possible solution to these concerns, on-site coagulation enhanced treatment wetlands (CETWs), coagulation water treatment followed by wetland passage serving as a settling basin, were implemented in a field-scale study located on a subsided island of the Sacramento-San Joaquin Delta in northern California under three treatments; coagulation with polyaluminum chloride (PAC), coagulation with ferric sulfate and an untreated control. Because CETWs offer a relatively novel solution for water quality improvement and subsidence reversal due to its low-infrastructure requirements and in-situ nature, effects from these systems remain uncharted and they may have adverse effects on plant biomass production that also contribute to sediment accretion. This study focuses on the effect CETWs had on the growth of Typha spp.; the dominant vegetation in the wetlands. Plant growth parameters and nutrient content were measured in conjunction with soil, pore water and surface water chemistry. Soil analysis indicated there was no intermixing of newly formed flocs and original soil material. Where there was significant deposition of floc, PAC treatment reduced phosphate concentrations and ferric sulfate treatment increased total Fe concentrations in surrounding water compared to the control. Results indicated coagulation treatments had no negative effects on Typha leaf nutrient content, Typha growth or allometric parameters. Additionally, no signs of plant toxicity such as necrosis, wilting or chlorosis were observed in any of the treatments. Overall, this study suggests that CETWs are viable treatment option for water quality improvement and sediment accretion while having no negative impact on the growth of Typha plants.