Kati W. Migliaccio

Contribution of Wastewater Treatment Plant Effluents to Nutrient Dynamics in Aquatic Systems: A Review

Excessive nutrient loading (considering nitrogen and phosphorus) is a major ongoing threat to water quality and here we review the impact of nutrient discharges from wastewater treatment plants (WWTPs) to United States (U.S.) freshwater systems. While urban and agricultural land uses are significant nonpoint nutrient contributors, effluent from point sources such as WWTPs can overwhelm receiving waters, effectively dominating hydrological characteristics and regulating instream nutrient processes. Population growth, increased wastewater volumes, and sustainability of critical water resources have all been key factors influencing the extent of wastewater treatment. Reducing nutrient concentrations in wastewater is an important aspect of water quality management because excessive nutrient concentrations often prevent water bodies from meeting designated uses. WWTPs employ numerous physical, chemical, and biological methods to improve effluent water quality but nutrient removal requires advanced treatment and infrastructure that may be economically prohibitive. Therefore, effluent nutrient concentrations vary depending on the particular processes used to treat influent wastewater. Increasingly stringent regulations regarding nutrient concentrations in discharged effluent, along with greater freshwater demand in populous areas, have led to the development of extensive water recycling programs within many U.S. regions. Reuse programs provide an opportunity to reduce or eliminate direct nutrient discharges to receiving waters while allowing for the beneficial use of reclaimed water. However, nutrients in reclaimed water can still be a concern for reuse applications, such as agricultural and landscape irrigation.

Removal of arsenic by magnetic biochar prepared from pinewood and natural hematite.

There is a need for the development of low-cost adsorbents to removal arsenic (As) from aqueous solutions. In this work, a magnetic biochar was synthesized by pyrolyzing a mixture of naturally-occurring hematite mineral and pinewood biomass. The resulting biochar composite was characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDS). In comparison to the unmodified biochar, the hematite modified biochar not only had stronger magnetic property but also showed much greater ability to remove As from aqueous solution, likely because the γ-Fe2O3 particles on the carbon surface served as sorption sites through electrostatic interactions. Because the magnetized biochar can be easily isolated and removed with external magnets, it can be used in various As contaminant removal applications.

Manganese oxide-modified biochars: Preparation, characterization, and sorption of arsenate and lead

This work explored two modification methods to improve biochars ability to sorb arsenic (As) and lead (Pb). In one, pine wood feedstock was pyrolyzed in the presence of MnCl2·4H2O (MPB) and in the other it was impregnated with birnessite via precipitation following pyrolysis (BPB). The resulting biochars were characterized using thermogravimetry, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-dispersive X-ray analyses. The dominant crystalline forms of Mn oxides in the MPB and BPB were manganosite and birnessite, respectively. Batch sorption studies were carried out to determine the kinetics and magnitude of As(V) and Pb(II) onto the biochars. As(V) and Pb(II) sorption capacities of MPB (0.59 and 4.91 g/kg) and BPB (0.91 and 47.05 g/kg) were significantly higher than that of the unmodified biochar (0.20 and 2.35 g/kg). BPB showed the highest sorption enhancement because of the strong As(V) and Pb(II) affinity of its birnessite particles.

Physicochemical and sorptive properties of biochars derived from woody and herbaceous biomass

It is unclear how the properties of biochar control its ability to sorb metals. In this work, physicochemical properties of a variety of biochars, made from four types of feedstock at three pyrolysis temperatures (300, 450 and 600°C) were compared to their ability to sorb arsenic (As) and lead (Pb) in aqueous solutions. Experimental results showed that both feedstock types and pyrolysis temperature affected biochars production rate, i.e., ratio of mass of biochar and biomass, thermal stability, elemental composition, non-combustible component (NCC) content, pH values, surface areas and thus their sorption ability to the two metals in aqueous solution. In general, the high temperature biochars had low O/C and H/C ratios, were more carbonized with larger surface area, and were more concentrated with alkaline cations. In addition, biochars made from woody feedstocks had larger surface area, but lower NCC contents than that made from grasses under the same conditions. Although all the tested biochars removed both As and Pb from aqueous solutions, they showed different sorption abilities because of the variations in properties. Statistical analyses suggested that feedstock type affected the sorption ability of the biochars to both As and Pb significantly (p<0.001). Pyrolysis temperature, however, showed little influence on biochar sorption of Pb in aqueous solutions. Statistical analyses also showed that electrostatic interaction played an important role in controlling the sorption of both As(V) and Pb(II) onto the biochar. Other mechanisms, such as precipitation and surface complexation, could also control the sorption of Pb(II) onto the biochars.

Evaluating, interpreting, and communicating performance of hydrologic/water quality models considering intended use: A review and recommendations ☆

Abstract Previous publications have outlined recommended practices for hydrologic and water quality (H/WQ) modeling, but limited guidance has been published on how to consider the projects purpose or models intended use, especially for the final stage of modeling applications – namely evaluation, interpretation, and communication of model results. Such guidance is needed to more effectively evaluate and interpret model performance and more accurately communicate that performance to decision-makers and other modeling stakeholders. Thus, we formulated a methodology for evaluation, interpretation, and communication of H/WQ model results. The recommended methodology focuses on interpretation and communication of results, not on model development or initial calibration and validation, and as such it applies to the modeling process following initial calibration. The methodology recommends the following steps: 1) evaluate initial model performance; 2) evaluate outliers and extremes in observed values and bias in predicted values; 3) estimate uncertainty in observed data and predicted values; 4) re-evaluate model performance considering accuracy, precision, and hypothesis testing; 5) interpret model results considering intended use; and 6) communicate model performance. A flowchart and tables were developed to guide model interpretation, refinement, and proper application considering intended model uses (i.e., Exploratory, Planning, and Regulatory/Legal). The methodology was designed to enhance application of H/WQ models through conscientious evaluation, interpretation, and communication of model performance to decision-makers and other stakeholders; it is not meant to be a definitive standard or a required protocol, but together with recent recommendations and published best practices serve as guidelines for enhanced model application emphasizing the importance of the models intended use.

Landscape Models for Simulating Water Quality at Point, Field, and Watershed Scales

In the last four decades, a plethora of models has been developed to simulate nonpoint-source (NPS) pollutant fate and transport at point, field, and watershed scales. Developed by experts in various disciplines, these models tend to reflect the needs of those disciplines. For example, the original intent of the solute transport models was to determine impact of water, nutrient, and salts on plant growth. Later, these models were extended to examine solute transport in the vadose zone to assess possible contamination of soil and groundwater. Similarly, a number of field- and watershed-scale models have been developed by linking together submodels of system components to quantify best management practice (BMP) effectiveness and watershed-level impact. New model users are often unaware of the suite of models available and are often uncertain about the appropriateness of models for their situation. The goals of this article are to discuss why NPS pollutant models were developed at various spatial scales (i.e., scale issues), briefly review commonly used models, and reflect on the future of landscape NPS models. Since the computational power of computers has significantly increased, automated data acquisition systems that can capture and transmit data at high resolution are being used, software that can handle large volumes of data has been developed, and improved chemical analysis capabilities are being developed, we conclude this article with the projection that development of a scale-independent model that can address complex issues of the next century by coupling state-of-the-art understanding of multiple hydrogeological, geochemical, and microbiological processes is possible. Future improvement in these models will result in a more scientific and robust approach for managing NPS pollutants.

Nutrient discharges to Biscayne Bay, Florida: trends, loads, and a pollutant index.

Changes in land use, management practices, and environmental conditions may all lead to detectable differences in nutrients transported to aquatic systems. Biscayne Bay, an oligotrophic estuary in southeastern Florida, requires minimal phosphorus and nitrogen inputs and here we quantified the effects of continued watershed development. Nutrient (nitrate/nitrite-nitrogen [NO(X)-N], total ammonia nitrogen [NH(3)-N], and total phosphorus [TP]) water quality data (1992-2006) from six monitoring sites were evaluated using trend analysis, load estimation, and a new Pollutant Empower Density (PED) index. The PED index assesses the effect of discharged pollutants relative to the background productivity of aquatic environments. NO(X)-N, NH(3)-N, and TP concentrations declined or exhibited no change at most sites, with only six instances of significantly (p<0.1) increasing trends. Load estimates revealed higher NO(X)-N loads in the southern, agricultural section of the watershed and higher NH(3)-N and TP loads in the urbanized northern and central areas. NO(X)-N loads from site MW04 (south) were the highest for all sites while site LR06 (north) had the highest NH(3)-N and TP loads. Of the evaluated canal discharges, PED index values also suggested that canal discharges from these two sites (MW04 and LR06) had the greatest potential for impact in the bay. Overall, water quality is generally improving but canal discharges are coupled with land use activities in adjacent drainage areas. Trend analysis, load estimation, and the PED index can be used together to provide a more holistic interpretation of water quality, which is necessary for optimizing resources to meet watershed management goals.

HYDROLOGIC COMPONENTS OF WATERSHED-SCALE MODELS

This article briefly reviews the hydrologic components of prominent models used in agricultural and mixed land use watersheds and presents the current state-of-the-art in agricultural watershed modeling. The models included are Annualized Agricultural Nonpoint Source (AnnAGNPS), Areal Nonpoint Source Watershed Environment Response Simulation (ANSWERS-2000), Hydrologic Simulation Program - Fortran (HSPF), Soil and Water Assessment Tool (SWAT), Watershed Assessment Model (WAM), and Water Erosion Prediction Project (WEPP). Hydrologic components (e.g., precipitation, potential evapotranspiration (PET), infiltration-surface runoff, groundwater, and stream flow) are discussed for each of these models. Simulation of PET differs among selected watershed models, with some offering multiple PET options and others providing one method. The primary difference in the infiltration and surface runoff algorithms among watershed models is their empirical (e.g., curve number (CN) and Green-Ampt) or physical (e.g., Philips) basis and their simulation time step. Groundwater components (such as interflow, tile drainage, shallow aquifer, and deep aquifer) may be one of the most variable hydrologic components among watershed models. Stream flow was routed predominantly by the selected models using the continuity equation and Mannings equation; other algorithms used were the Muskingum routing method, finite difference integration, and kinematic wave. The use of watershed models by agricultural and biological engineers continues to expand as new technologies, such as the integration of remote sensing and Geographic Information Systems (GIS), and computer capabilities improve and the expectations for high-quality results (including uncertainty analyses and multi-objective functions) increase.

Surface water quality evaluation using multivariate methods and a new water quality index in the Indian River Lagoon, Florida

[1] Appropriate assessment of long-term water quality monitoring data is essential to evaluation of water quality and this often requires use of multivariate techniques. Our objective was to evaluate water quality in the south Indian River Lagoon (IRL), Florida using several multivariate techniques and a comprehensive water quality index (WQI). Clustering was used to cluster the six monitoring stations into three groups, with stations on the same or characteristic-similar canals being in the same group. The first five factors from exploratory factor analysis (EFA) explain around 70% of the total variance and were used to interpret water quality characterized by original constituents for the purpose of data reduction. Nutrient species (phosphorus and nitrogen) were major variables involved in the construction of the principal components (PCs) and factors. Seasonal and spatial differences were observed in compositional patterns of factors and principal water quality constituents. Positive or negative trends were detected for different factor at different monitoring groups identified by clustering during different seasons. The composite WQI was developed based on principal water quality constituents greatly contributing to the construction of factors which were derived from EFA. The WQI showed significant difference among the three clustering groups with the greatest WQI median in group 1 stations (C23S48, C23S97, and C24S49). Medians of WQI were significantly greater in the wet than in the dry season, which implied more natural nutrient water status during the dry than the wet season probably due to the different contribution of nonpoint sources between two seasons.

Water savings, nutrient leaching, and fruit yield in a young avocado orchard as affected by irrigation and nutrient management

This project was designed to determine the effect of fertilizer rate and irrigation scheduling on water use, nutrient leaching, and fruit yield of young avocado trees (Persea americana Mill. cv. Simmonds). Seven nutrient and irrigation management practices were evaluated: (1) irrigation based on crop evapotranspiration (ET) with 50% fertilizer at a standard rate (FSR); (2) ET irrigation with FSR (typical for avocado production in the area); (3) ET irrigation with 200% FSR; (4) irrigation based on exceedance of 15-kPa (SW) soil water suction with 50% FSR; (5) SW with FSR; (6) SW with 200% FSR; and (7) irrigation at a set schedule (based on timing and frequency typically used in local avocado production) with FSR. The SW with FSR treatment saved 87% of the water volume applied and reduced total phosphorus leached by 74% compared to the set schedule irrigation with FSR. The SW with FSR treatment had higher avocado fruit production, tree water-use efficiency, and fertilizer-use efficiency than the other six treatments. Thus, the use of soil water monitoring for irrigation management can substantially increase sustainability of young avocado orchards in southern Florida.