Water Treatment Residuals Application Research Articles

Potential Benefits and Disbenefits of the Application of Water Treatment Residuals from Drinking Water Treatment Processes to Land in Scotland: Development of a Decision Support Tool

Water Treatment Residuals (WTRs) are a by-product of the addition of chemical coagulants to water during the water treatment process and are a mixture of water and organic and inorganic matter that coagulates during the treatment process. WTRs often contain metals such as iron, aluminium, and manganese that have been oxidised as part of the process or are constituents of the coagulation chemicals used. The metals within WTRs are of interest with regard to applying these sludges to agricultural land. WTRs can also contain beneficial organic matter and nutrients (primarily nitrogen). The nature of the benefits delivered is largely dependent on the quality of the raw water and these beneficial components are generally found in much smaller quantities in WTRs than are found in sewage sludge produced from wastewater. However, WTRs can still be used to enhance the physical properties of soils. As urban populations increase in size, it is anticipated that the tonnage of WTRs will increase significantly in the future. At present, the majority of WTRs are disposed of in landfills; however, landfill charges are increasing significantly, making disposal of an increasing tonnage of WTRs financially unviable. In terms of a circular economy, the procedure of reusing WTRs for alternative applications satisfies the Scottish Government’s goals in terms of waste prevention and reducing the amount of material being sent to landfill as set out in the Proposals for Legislation in 2019. Given the potential benefits in terms of cost savings and compliance with government legislation, and the complexities of understanding where and when WTRs can be used in land applications, we developed a Decision Support Tool (DST) that uses data obtained from an extensive review of approaches in other countries to assist in decision making. We also conducted a pre-application analysis and provided guidance on when and where WTRs can be used in land applications and when they are not suitable, presented in a simplified format that requires few inputs from the user in order to simplify the process and removes the requirement for a specialist operator during pre-application analyses.

Application of modified water treatment residuals in water and wastewater treatment: A review

Large quantities of sludge known as water treatment residuals (WTRs) are generated from water treatment facilities across the world. Various attempts have been made to reuse these residuals. Among the different applications of WTRs, their reuse in water and wastewater treatment has received more attention. However, direct application of raw WTRs is associated with some limitations. In the last decade, in order to improve their characteristics, numerous investigators have modified WTRs by different methods. This paper reviews the different methods applied to WTRs to enhance their characteristics. The effects of these modifications on their characteristics are explained. The applications of modified WTRs as a filtration/adsorption medium for treating textile/dye wastewater, groundwater containing different anionic and cationic pollutants, storm water runoff, and as a substrate in constructed wetlands are presented in detail. Future research needs are highlighted. The review clearly indicates the potential of different modification methods to improve the removal of a variety of pollutants by WTRs from water and wastewater.

Water treatment residuals for ameliorating sandy soils: Implications in environmental, soil and plant growth parameters

Water treatment residuals (WTR) application may improve the quality of sandy soils; however, nutrient deficiency to plants and potentially toxic elements (PTEs) may be limiting. In contrast, adjusting the WTR pH, soil pH and WTR application rate might prevent adverse effects. This study aimed to evaluate the environmental safety and agronomic effectiveness of limed WTR for application in sandy soils. The tested treatments were increasing rates (0, 15, 30 and 60 Mg ha−1 of dry mass) of ground, dried and limed WTR in sandy soil under field conditions. Soil samples with disturbed and undisturbed structure were collected to determine selected soil physical, hydraulic and chemical parameters related to fertility, as well as the soil concentration of PTEs. Nutrients and PTEs content in plant tissue and the agronomic performance of maize and ryegrass were also evaluated. WTR were beneficial as they increased the content of fine and reactive particles (clay and silt). In general, WTR rates did not spoil soil chemical parameters related to soil fertility; did not increase aluminium saturation; and did not change soil PTE contents which were below the limits indicated by environmental legislations. The tested WTR rates did not cause negative effects on the agronomic variables of maize and ryegrass plants. Thus, waste application rates up to 30 Mg ha−1 are recommended. Liming WTR and soil makes this material safe and suitable for application in sandy and acidic agricultural soils.

A combined chemical and phytoremediation method for reclamation of acid mine drainage-impacted soils.

Production of acid mine drainage (AMD) and acid sulfate soils is one of the most concerning environmental consequences associated with mining activities. Implementation of appropriate post-mining AMD management practices is very important to minimize environmental impacts such as high soil acidity, soil erosion, and metal leachability. The objective of this study was to develop a cost-effective and environment-friendly "green" technology for the treatment of AMD-impacted soils. This study utilized the metal-binding and acid-neutralizing capacity of an industrial by-product, namely drinking water treatment residuals (WTRs), and the extensive root system of a metal hyper-accumulating, fast-growing, non-invasive, high-biomass perennial grass, vetiver (Chrysopogon zizanioides L.) to prevent soil erosion. Aluminum (Al)-based and calcium (Ca)-based WTRs were used to treat AMD-impacted soil collected from the Tab-Simco coal mine in Carbondale, IL. Tab-Simco is an abandoned coal mine, with very acidic soil containing a number of metals and metalloids such as Fe, Ni, Zn, Pb, and As at high concentrations. A 4-month-long greenhouse column study was performed using 5% and 10% w/w WTR application rates. Vetiver grass was grown on the soil-WTR mixed media. Turbidity and total suspended solid (TSS) analysis of leachates showed that soil erosion decreased in the soil-WTR-vetiver treatments. Difference in pH of leachate samples collected from control (3.06) and treatment (6.71) columns at day 120 indicated acidity removal potential of this technology. A scaled-up simulated field study was performed using 5% WTR application rate and vetiver. Soil pH increased from 2.69 to 7.2, and soil erosion indicators such as turbidity (99%) and TSS (95%) in leachates were significantly reduced. Results from the study showed that this "green" reclamation technique has the potential to effectively treat AMD-impacted soils.

Water treatment residuals as soil amendments: Examining element extractability, soil porewater concentrations and effects on earthworm behaviour and survival

Drinking water treatment residuals (WTRs), the by-product of water clarification processes, are routinely disposed of via landfill however there is a growing body of research that demonstrates the material has great potential for beneficial use in environmental applications. Application to agricultural land is one option showing great promise (i.e. a low cost disposal route that provides organic matter input to soils and other potential benefits), however questions remain as to the impact such applications may have on earthworm survival and behaviour and also on the potential effects it may have on soil porewater chemistry. This study examined the leachability of elements within two types of WTRs (one Al- and one Fe- based) from England via 0.001 M CaCl2 solution, at varying pH, and via the Community Bureau of Reference (BCR) sequential extraction scheme. Earthworm avoidance, survival, growth, reproduction and element concentrations were examined in WTR-amended sandy soils (0%, 5%, 10%, 20% w/w), while soil porewaters were also recovered from experimental units and examined for element concentrations. The results revealed leachable element concentrations to be very low in both types of WTRs tested and so element leaching from these WTRs would be unlikely to pose any threat to ecosystems under typical agricultural soil conditions. However, when the pH was lowered to 4.4 there was a substantial release of Al from the Al-WTRs (382 mg/kg). Soil porewater element concentrations were influenced to some degree by WTR addition, warranting further examination in terms of any potential implications for nutrient supply or limitation. Earthworm avoidance of WTR-amended soil was only observed for Al-WTRs and only at the maximum applied rate (20% w/w), while survival of earthworms was not affected by either WTR type at any application rate. Earthworm growth and reproduction (cocoon production) were not affected at a statistically significant level but this needs further examination over a longer period of exposure. Increased assimilation of Al and Fe into earthworm tissues was observed at some WTR application rates (maximum fresh weight concentrations of 42 mg/kg for Al and 167 mg/kg for Fe), but these were not at levels likely to pose environmental concerns.

Are Floodplain Soils a Potential Phosphorus Source When Inundated That Can Be Effectively Managed?

Core Ideas Dissolved phosphorus is released from floodplain soils when inundated. Phosphorus release rates are positively correlated with soil test and water‐extractable P in soil. Water treatment residuals decrease P release rates, providing a potential mitigation option. The growing concern over phosphorus (P) and water quality has led to questions as to where the loads originate and how to control landscape inputs from the watershed. We collected soil cores from two locations in the Illinois River watershed to examine the relationship between stored soil P and the amount of soluble reactive P (SRP) released into the water when soils are flooded. After inundation, P flux calculations for durations of ∼24 h ranged from less than 0.1 to 9.3 mg SRP m−2 h−1. Soil test P (STP), measured as water‐extractable P and Mehlich‐III P, correlated with SRP flux, where higher STP resulted in increased P flux to the overlying water. Floodplain soils have the potential to be a P source, potentially releasing more than 1600 mg m−2 yr−1 (>16 kg ha−1 yr−1) depending on length and frequency of inundation and on STP content. Applying water treatment residuals (WTRs) significantly reduced P flux from the cores. Hence, WTR application to critical source areas provides a mitigation strategy to manage floodplain soils and potential SRP release.

A method for determining the treatment dosage of drinking water treatment residuals for effective phosphorus immobilization in sediments

Drinking water treatment residuals (WTRs), non-hazardous by-products generated during treatment of drinking water, can be reused to immobilize phosphorus (P) in sediments for eutrophication control. Prior to application, it is necessary to determine the treatment dosage of WTR to immobilize P in sediments. In the present study, the dosage of Al/Fe based WTRs required to effectively immobilize P in lake sediments was determined in a laboratory setting as a function of the oxalate-extractable Al (Alox) and Fe (Feox) content of the WTRs by completely mixing Al/Fe based WTRs with Lake Baiyangdian sediments. The results showed that the capacity for immobilization of mobile P (Pm) in sediments by Alox and Feox in Al/Fe based WTRs ((Alox+Feox)WTR) can be described by the equation: (Alox+Feox)WTR=83*Pm–40 (where Alox, Feox and Pm are expressed in μmolg−1). This equation was successfully used to determine the respective quantities of three different Al/Fe based WTRs required to immobilize P in sediments from Lake Chaohu, Lake Taihu, the Changjiang River, the Haihe River, the Pear River and the Yellow River. Using the equation derived herein, the required Al/Fe based WTR application dose can easily be determined where the Pm content of the sediment and the Alox and Feox content of the WTR are known.

Use of drinking water treatment residuals to control the internal phosphorus loading from lake sediments: Laboratory scale investigation

This work investigated a novel approach of reusing drinking water treatment residuals (WTRs) to reduce the internal P loading from lake sediments under varied levels of dissolve oxygen (DO) in laboratory scale. The results showed that although the internal P loading increased as the DO level decreasing, WTRs can significantly reduce the internal P loading under different DO levels; in particular, under high DO level (5–8mgL−1), the internal P loading can be reduced by 100%. The results of P fractionation suggested that the retained-P by WTRs existed as the NaOH extractable P. The P nuclear magnetic resonance spectroscopy (31P NMR) analysis further demonstrated that the retained-P was the orthophosphate, orthophosphate monoesters, orthophosphate diesters and pyrophosphate. Moreover, application of WTRs had marginal effects on Fe and Al concentrations and pH of the overlaying water. Therefore, WTRs can be an ideal material for controlling the internal P loading for lake restoration in large scale.

Effects of drinking water treatment residuals on nickel retention in soils: a macroscopic and thermodynamic study

Purpose Recent research has focused on using water treatment residuals (WTRs) as cost-effective materials to remove potential environmental contaminants. To better understand and predict how WTRs affect the mobility and retention of nickel (Ni) in soils with time, it is crucial that the kinetics and thermodynamics of these reactions be understood. Such information is lacking in the literature and would aid in evaluating the suitability of WTR as a soil amendment for adsorbing Ni contaminant. Accordingly, we focused on investigating the retention of Ni in differing soils and the subsequent influence of WTR application on Ni retention.

Drinking Water Treatment Residuals: A Review of Recent Uses

Coagulants such as alum [Al2(SO4)3 x 14H2O], FeCl3, or Fe2(SO4)3 are commonly used to remove particulate and dissolved constituents from water supplies in the production of drinking water. The resulting waste product, called water-treatment residuals (WTR), contains precipitated Al and Fe oxyhydroxides, resulting in a strong affinity for anionic species. Recent research has focused on using WTR as cost-effective materials to reduce soluble phosphorus (P) in soils, runoff, and land-applied organic wastes (manures and biosolids). Studies show P adsorption by WTR to be fast and nearly irreversible, suggesting long-term stable immobilization of WTR-bound P. Because excessive WTR application can induce P deficiency in crops, effective application rates and methods remain an area of intense research. Removal of other potential environmental contaminants [ClO4-, Se(+IV and +VI), As(+III and +V), and Hg] by WTR has been documented, suggesting potential use of WTR in environmental remediation. Although the creation of Al plant toxicity and enhanced Al leaching are concerns expressed by researchers, these effects are minimal at circumneutral soil pH conditions. Radioactivity, trace element levels, and enhanced Mn leaching have also been cited as potential problems in WTR usage as a soil supplement. However, these issues can be managed so as not to limit the beneficial use of WTR in controlling off-site P losses to sensitive water bodies or reducing soil-extractable P concentrations.

Water Treatment Residuals and Biosolids Long‐Term Co‐Applications Effects to Semi‐Arid Grassland Soils and Vegetation

Water treatment residuals (WTRs) and biosolids are byproducts from municipal water treatment processes. Both byproducts have been studied separately for land application benefits. There are possible environmental benefits of WTRs and biosolids co‐application but these studies are limited. Our objectives were to determine relative long‐term (13–15 yr) effects of a single and short‐term (2–4 yr) effects of repeated WTR‐biosolids co‐applications on soil chemistry, microbiology, and plant community structure in a Colorado semiarid grassland. Only relative changes associated between co‐applications were studied, as we assumed WTR application would only occur if used as a management practice. Three WTR rates (5, 10, and 21 Mg ha−1) were surface co‐applied (no incorporation) with a single biosolids rate (10 Mg ha−1) once in 1991 (long‐term plots) and again in 2002 (short‐term plots). Soil 0‐ to 8‐, 8‐ to 15‐, and 15‐ to 30‐cm depth pH, electrical conductivity (EC), NO3–N, NH4–N, total C, and total N were not affected by WTR application in 2004, 2005, or 2006. Ammonium‐bicarbonate diethylenetriaminepentaacetic acid (AB‐DTPA)‐ extractable soil Al was unaffected by WTR application, but extractable P and Mo decreased with increasing WTR rate because of WTR adsorption. Plant tissue P and Mo content decreased with specific plant species and years due to adsorption to WTR; no deficiency symptoms were observed. Plant community composition and cover were largely unaffected by WTR application. Soil microbial community structure was unaffected by WTR co‐application rate (total ester‐linked fatty acid methyl ester [EL‐FAME] concentrations ranged from 33.4 to 54.8 nmol g−1 soil), although time since biosolids‐WTR application affected a subset of microbial community fatty acids including markers for Gram‐positive and Gram‐negative bacteria. Overall, WTR‐biosolids co‐applications did not adversely affect semiarid grassland ecosystem dynamics.

Effects of Co‐Application of Biosolids and Water Treatment Residuals on Corn Growth and Bioavailable Phosphorus and Aluminum in Alkaline Soils in Egypt

The co-application of biosolids and water treatment residuals (WTRs) has been previously trialed to reduce excessive bioavailable P in the soil treated with biosolids. However, uncertainty still exists regarding the environmental consequences of the co-application of biosolids and WTRs, especially in alkaline soils in Egypt or the Middle East region. A greenhouse pot study was conducted with Egyptian alkaline soils to (i) quantify the effects of co-application of biosolids and drinking WTRs on biomass production of corn (Zea mays L. cultivar single hybrid 10), (ii) determine the co-application effects on Olsen-P and KCl-extractable Al in relation to their accumulation in plant tissues, and (iii) optimize the co-application ratio of biosolids to WTRs for the best yield and effective reduction of soil bioavailable P. The results show that, among the studied soils treated with 1% biosolids along with various rates of WTRs, the corn yield increased significantly (P < 0.01) with increasing WTR application rate from 0 to 3% (w/w), but decreased at 4% application rate. The corn yield also significantly correlated with soil water holding capacity that increased with the addition of WTRs. Phosphorus uptake by plants significantly (P < 0.01) increased when the biosolid application rate was increased from 1 to 3% in the three studied soils that were treated with 1, 2, or 3% WTRs. The application of 4% WTRs in the biosolid-amended soils resulted in a significant reduction in soil Olsen-P values, but without having observable phytotoxicity of metals (such as Al) to corn during the growth period. The effective co-application ratio of biosolids to WTRs, for increasing corn yield and minimizing the potential for bioavailable P in runoff, was approximately 1:1 at the application rate of 3% biosolids and 4% WTRs in the alkaline soils.

Water Treatment Residuals and Biosolids Co‐applications Affect Phosphatases in a Semi‐arid Rangeland Soil

Co‐application of biosolids and water treatment residuals (WTR) land has not been extensively studied but may be beneficial by sorbing excess biosolid‐borne or soil phosphorus (P) onto WTR, reducing the likelihood of off‐site movement. Reduction of excess soil P may affect the role of specific P‐cleaving enzymes. The research objective was to understand the long‐term effects of single co‐applications and the short‐term impacts of repeated co‐applications on soil acid phosphomonoesterase, phosphodiesterase, pyrophosphatase, and phytase enzyme activities. Test plots were 7.5 × 15 m with treatments consisting of three different WTR rates with a single biosolids rate (5, 10, and 21 Mg WTR ha−1; 10 Mg biosolids ha−1) surface co‐applied once in 1991 or reapplied in 2002. Control plots consisted of those that received no WTR–biosolids co‐applications and plots that received only 10 Mg biosolids ha−1. Plots were sampled to a 5‐cm depth in 2003 and 2004, and soil phosphatases and phytase enzyme activities were measured. Soil phosphodiesterase activity decreased in WTR‐amended plots, and pyrophosphatase activity decreased with increasing WTR application rates. In contrast, acid phosphatase and phytase activity increased with WTR addition, with WTR application possibly triggering a deficiency response causing microorganisms or plants to secrete these enzymes. Biosolids and WTR co‐applications may affect enzymatic strategies for P mineralization in this study site. Reductions in phosphodiesterase activity suggest less P mineralization from biomass sources, including nucleic acids and phospholipids. Increased acid phosphatase and phytase activities indicate that ester‐P and inositol‐P may be important plant‐available P sources in soils amended with WTR.

Land application of Water Treatment Residuals: effect on wheat yield and the availability of phosphorus and aluminium

Water Treatment Residuals (WTR) can be a potential source for available phosphorus (P) and Al, but the influence of WTR rates on the dynamics of available P and Al and plant uptake in alkaline soils are not well documented. Our objective was to evaluate the effects of WTR (Alum-sludge) on the agronomic performance of wheat crop grown in alkaline soils as well as P and Al availability and extractability. Wheat (Triticum aestivum L) plants were grown in three alkaline soils amended with WTR at five rates. After 13 weeks, plant shoots, panicles and roots were harvested separately and P and Al were measured. Increases of 246, 32% and 43% in total dry matter yield were achieved as a result of applying 30 g kg−1 WTR to sandy, clay and calcareous soils respectively. The trend of P concentration in different parts of wheat plants in response to applied WTR was negative quadratic (P 6 mg Al kg−1. Therefore, slight increases in available Al from application of WTR should not have adverse effects on soils or plants.

Controlled Application Rate of Water Treatment Residual for Agronomic and Environmental Benefits

Water treatment residuals (WTR) are useful soil amendments to control excessive soluble phosphorus (P) in soils, but indiscriminate additions can result in inadequate control or excessive immobilization of soluble P, leading to crop deficiencies. We evaluated the influence of application rates of an Al-WTR and various P-sources on plant yields, tissue P concentrations, and P uptake and attempted to identify a basis for determining WTR application rates. Bahiagrass (paspalum notatum Fluggae) was grown in a P-deficient soil amended with four P-sources at two application levels (N- and P-based rates) and three WTR rates (0, 10, and 25 g kg(-1) oven dry basis) in a glasshouse pot experiment. The glasshouse results were compared with data from a 2-yr field experiment with similar treatments that were surface applied to an established bahiagrass. Soil P storage capacity (SPSC) values increased with application rate of WTR, and the increase varied with sources of P applied. Soil soluble P concentrations increased as SPSC was reduced, and a change point was identified at 0 mg kg(-1) SPSC in the glasshouse and the field studies. A change point was identified in the bahiagrass yields at a tissue P concentration of 2.0 g kg(-1), corresponding to zero SPSC. Zero SPSC was shown to be an agronomic threshold above which yields and P concentrations of plants declined and below which there is little or no yield response to increased plant P concentrations. Applying P-sources at N-based rates, along with WTR sufficient to give SPSC value of 0 mg kg(-1) SPSC, enhanced the environmental benefits (reduced P loss potential) without negative agronomic impacts.

Land Application of Water Treatment Residuals: Effects on Heavy Metals Availability

Land Application of Water Treatment Residuals: Effects on Heavy Metals Availability

Lability of Drinking Water Treatment Residuals (WTR) Immobilized Phosphorus

Time constraints associated with conducting long-term (>20 yr) field experiments to test the stability of drinking water treatment residuals (WTR) sorbed phosphorus (P) inhibit improved understanding of the fate of sorbed P in soils when important soil properties (e.g., pH) change. We used artificially aged samples to evaluate aging and pH effects on lability of WTR-immobilized P. Artificial aging was achieved through incubation at elevated temperatures (46 or 70 degrees C) for 4.5 yr, and through repeated wetting and drying for 2 yr. Using a modified isotopic ((32)P) dilution technique, coupled with a stepwise acidification procedure, we monitored changes in labile P concentrations over time. This technique enabled evaluation of the effect of pH on the lability of WTR-immobilized P. Within the pH range of 4 to 7, WTR amendment, coupled with artificial aging, ultimately reduced labile P concentrations by > or = 75% relative to the control (no-WTR) samples. Soil samples with different physicochemical properties from two 7.5-yr-old, one-time WTR-amended field sites were utilized to validate the trends observed with the artificially aged samples. Despite the differences in physicochemical properties among the three (two field-aged and one artificially aged) soil samples, similar trends of aging and pH effects on lability of WTR-immobilized P were observed. Labile P concentrations of the WTR-amended field-aged samples of the two sites decreased 6 mo after WTR amendment and the reduction persisted for 7.5 yr, ultimately resulting in > or = 70% reduction, compared to the control plots. We conclude that WTR application is capable of reducing labile P concentration in P-impacted soils, doing so for a long time, and that within the commonly encountered range of pH values for agricultural soils WTR-immobilized P should be stable.

Mathematical Model to Predict Solids Content of Water Treatment Residuals during Drying

Dewatering and drying of residuals are extremely energy intensive processes, which are necessary to reduce the quantity of wet residuals produced from the water and wastewater treatment operations. Meteorological conditions are a major factor in the drying of residuals, which can greatly affect the drying period. A mathematical model is developed for the process of drying of water treatment residuals. A steady-state heat-balance equation is applied for a control volume of residuals that takes into account the heat transfer by radiation, convection, and evaporation. The mathematical model was validated using drying experiments conducted in a wind tunnel as well as other experiments conducted in an open environment equipped with a weather monitoring station. Good agreement was obtained between model predictions and experimental observations. The model can be used to predict the drying time of a given application of water treatment residuals with the knowledge of meteorological conditions.

Use of Drinking Water Treatment Residuals as a Potential Best Management Practice to Reduce Phosphorus Risk Index Scores

The P risk index system has been developed to identify agricultural fields vulnerable to P loss as a step toward protecting surface water. Because of their high Langmuir phosphorus adsorption maxima (P(max)), use of drinking water treatment residuals (WTRs) should be considered as a best management practice (BMP) to lower P risk index scores. This work discusses three WTR application methods that can be used to reduce P risk scores: (i) enhanced buffer strip, (ii) incorporation into a high soil test phosphorus (STP) soil, and (iii) co-blending with manure or biosolids. The relationship between WTR P(max) and reduction in P extractability and runoff P was investigated. In a simulated rainfall experiment, using a buffer strip enhanced with 20 Mg WTR ha(-1), runoff P was reduced by from 66.8 to 86.2% and reductions were related to the WTR P(max). When 25 g kg(-1) WTR was incorporated into a high STP soil of 315 mg kg(-1) determined using Mehlich-3 extraction, 0.01 M calcium chloride-extractable phosphorus (CaCl(2)-P) reductions ranged from 60.9 to 96.0% and were strongly (P < 0.01) related to WTR P(max). At a 100 g kg(-1) WTR addition, Mehlich 3-extractable P reductions ranged from 41.1 to 86.7% and were strongly (P < 0.01) related to WTR P(max). Co-blending WTR at 250 g kg(-1) to manure or biosolids reduced CaCl(2)-P by >75%. The WTR P(max) normalized across WTR application rates (P(max) x WTR application) was significantly related to reductions in CaCl(2)-P or STP. Using WTR as a P risk index modifying factor will promote effective use of WTR as a BMP to reduce P loss from agricultural land.

An Alum‐Based Water Treatment Residual Can Reduce Extractable Phosphorus Concentrations in Three Phosphorus‐Enriched Coastal Plain Soils

The accumulation of excess soil phosphorus (P) in watersheds under intensive animal production has been linked to increases in dissolved P concentrations in rivers and streams draining these watersheds. Reductions in water dissolved P concentrations through very strong P sorption reactions may be obtainable after land application of alum-based drinking water treatment residuals (WTRs). Our objectives were to (i) evaluate the ability of an alum-based WTR to reduce Mehlich-3 phosphorus (M3P) and water-soluble phosphorus (WSP) concentrations in three P-enriched Coastal Plain soils, (ii) estimate WTR application rates necessary to lower soil M3P levels to a target 150 mg kg(-1) soil M3P concentration threshold level, and (iii) determine the effects on soil pH and electrical conductivity (EC). Three soils containing elevated M3P (145-371 mg kg(-1)) and WSP (12.3-23.5 mg kg(-1)) concentrations were laboratory incubated with between 0 and 6% WTR (w w(-1)) for 84 d. Incorporation of WTR into the three soils caused a near linear and significant reduction in soil M3P and WSP concentrations. In two soils, 6% WTR application caused a soil M3P concentration decrease to below the soil P threshold level. An additional incubation on the third soil using higher WTR to soil treatments (10-15%) was required to reduce the mean soil M3P concentration to 178 mg kg(-1). After incubation, most treatments had less than a half pH unit decline and a slight increase in soil EC values suggesting a minimal impact on soil quality properties. The results showed that WTR incorporation into soils with high P concentrations caused larger relative reductions in extractable WSP than M3P concentrations. The larger relative reductions in the extractable WSP fraction suggest that WTR can be more effective at reducing potential runoff P losses than usage as an amendment to lower M3P concentrations.