Managing biosolids runoff phosphorus using buffer strips enhanced with drinking water treatment residuals

Washing and Heat Treatment of Aluminum-Based Drinking Water Treatment Residuals to Optimize Phosphorus Sorption and Nitrogen Leaching: Considerations for Lake Restoration

Drinking water treatment residuals (DWTRs) generated during drinking water treatment have been proposed for use in lake restoration as a solid-phase sorbent to inactivate phosphorus (P) in lake sediment. However, treatments that minimize leaching of nitrogen (N) and optimize P sorption capacity may be necessary prior to use. This study assessed seven different treatment methods, including washing and heat treatments at different temperatures and with and without oxygen limitation, among two DWTRs from Thailand. Results showed that oxygen-limited heat treatment at 600 °C substantially reduced N leaching (<0.2 mg/kg TKN) while also improving P sorption capacity (increase of 18–32% compared to untreated DWTR) to a maximum of 45.7 mg P/kg. Washing with deionized water reduced N leaching if a sufficient volume was used but did not improve P sorption. Heating at 200 °C with or without the presence of oxygen did not improve N leaching or P sorption. Regression of P sorption parameters from a two-surface Langmuir isotherm against physio-chemical properties indicated that oxalate-extractable (i.e., amorphous) aluminum and iron were significantly associated with total P sorption capacity (R2 = 0.94), but micropores and oxalate-extractable P modulated the P sorption from high-affinity to low-affinity mechanisms. In conclusion, this study confirmed the importance of amorphous aluminum in DWTRs for inactivating P, and the results suggest that high-temperature treatment under oxygen-limited conditions may be the most reliable way to optimize DWTRs for environmental remediation applications.

Design and Preliminary Testing of an In-Field Passive Treatment System for Removing Phosphorus from Surface Water

It is well documented that excess phosphorus in source waters is a major contributor to harmful algal bloom formation. While there are many approaches to controlling algal populations in reservoirs, including a variety of phosphorus reduction approaches (e.g., sequestration of legacy phosphorus with alum or clay products), addressing physical phosphorus loading upstream is considered less often. Water treatment residuals (WTR) containing alum, a common waste product of conventional surface water treatment, have been shown to retain the ability to capture phosphorus even after the WTR ‘sludge’ is formed and removed from the sedimentation process. This research designed and tested a refillable, reusable in-stream phosphorus cartridge system which beneficially reutilizes WTR ‘sludge’ to sequester instream phosphorus and remove it from the water when spent media is replaced. This reduces in-stream phosphorus entering into the reservoir without permanently adding additional materials to the waterbody and provides measurable results as to the amount of phosphorus removed. The ten sampling events during the first year’s field assessment indicated that the gates removed a total of 556.31 g of reactive phosphorus (PO43−) and it is anticipated that the actual phosphorous removal was even greater. Other watershed managers can implement the same approach using their own WTR to capture in-stream phosphorus.

Influence of pH on hydrothermal treatment of swine manure: Impact on extraction of nitrogen and phosphorus in process water

This study investigates the influence of pH on extraction of nitrogen and phosphorus from swine manure following hydrothermal treatment. Conditions include thermal hydrolysis (TH) at 120°C and 170°C, and hydrothermal carbonisation (HTC) at 200°C and 250°C in either water alone or in the presence of 0.1M NaOH, H2SO4, CH3COOH or HCOOH. Phosphorus extraction is pH and temperature dependent and is enhanced under acidic conditions. The highest level of phosphorus is extracted using H2SO4 reaching 94% at 170°C. The phosphorus is largely retained in the residue for all other conditions. The extraction of nitrogen is not as significantly influenced by pH, although the maximum N extraction is achieved using H2SO4. A significant level of organic-N is extracted into the process waters following hydrothermal treatment. The results indicate that operating hydrothermal treatment in the presence of acidic additives has benefits in terms of improving the extraction of phosphorus and nitrogen.

Nitrogen and Phosphorus Loss Potential from Biosolids-Amended Soils and Biotic Response in the Receiving Water

Application of municipal biosolids to agricultural soil can improve soil quality and improve crop yields. However, runoff or tile leachate from biosolids-applied fields may contribute to localized eutrophication of surface water. A laboratory experiment was conducted to determine loss potential of nutrients from soils amended with two different biosolids (anaerobically digested and chemically stabilized) relative to loss from a reference soil and to determine response in freshwater microcosms to nutrients lost from soils. Total phosphorus (TP) and total nitrogen (TN) were measured in runoff, and equivalent amounts were added to reference microcosms to determine if aquatic systems would respond similarly to TN and TP loading in bioavailable forms (PO, NH, NO) simulating loading related to inorganic fertilizer application. Nutrient concentrations (TP, TN, PO, NH, NO, and organic P and N) were similar in the runoff from the two biosolids-amended soils and higher than those in the runoff from the reference soil. Runoff from biosolids-amended soils stimulated algal growth and production (chlorophyll a and dissolved oxygen) relative to runoff from reference soil, but the response was weaker than in microcosms receiving equivalent amounts of inorganic N and P. Nutrient runoff from land-applied biosolids does have potential to increase algal production in receiving waters; however, this experiment suggests receiving waters may absorb a single large nutrient loading event associated with runoff from biosolids-amended soil without substantial impact. Moreover, the response to N and P in biosolids versus inorganic nutrient additions suggests biosolids may contribute relatively less to eutrophication than inorganic fertilizers, assuming equivalent TN and TP loading to aquatic systems.

Immobilization of phosphorus in cow manure during hydrothermal carbonization

The surplus of manure phosphorus (P) with increasing livestock production might pose a risk of P loss to the environment due to the high mobility of P in manure. Thus, there is an increasing need to mitigate P loss from manure. This study aimed to investigate the effect of hydrothermal carbonization (HTC) on the immobilization of P in cow manure. The results demonstrated that the P content in cow manure was increased substantially by ∼20% after HTC, while the water-extractable P (WEP) and Mehlich-3-extractable P (MEP) in manure was reduced significantly by >80% and 50%, respectively. The decrease in P solubility might result from the increased apatite P (increased by >85%) and decreased soluble Ca (decreased by ∼50%) after HTC. These results suggested that HTC could be an efficient strategy to immobilize P in cow manure, thereby potentially mitigating the P loss problem from cow manure.

Long-term effects of drinking-water treatment residuals on dissolved phosphorus export from vegetated buffer strips

The export of dissolved phosphorus (P) in surface runoff from agricultural land can lead to water quality degradation. Surface application of aluminium (Al)-based water treatment residuals (Al-WTRs) to vegetated buffer strip (VBS) soils can enhance P removal from surface runoff during single runoff events. However, the longer-term effects on P removal in VBSs following application of products such as Al-WTR remain uncertain. We used field experimental plots to examine the long-term effects of applying a freshly generated Al-WTR to VBSs on dissolved P export during multiple runoff events, occurring between 1 day and 42 weeks after the application of Al-WTR. Vegetated buffer strip plots amended with Al-WTR significantly reduced soluble reactive P and total dissolved P concentrations in surface runoff compared to both unamended VBS plots and control plots. However, the effectiveness of Al-WTR decreased over time, by approximately 70% after 42 weeks compared to a day following Al-WTR application. Reduced performance did not appear to be due to drying of Al-WTR in the field. Instead, the development of preferential flow paths as well as burying of Al-WTR with freshly deposited sediments may explain these observations. Better understanding of the processes controlling long-term P removal by Al-WTR is required for effective management of VBSs.

An anaerobic incubation study of metal lability in drinking water treatment residue with implications for practical reuse

Drinking water treatment residue (WTR) is an inevitable by-product generated during the treatment of drinking water with coagulating agents. The beneficial reuse of WTR as an amendment for environmental remediation has attracted growing interest. In this work, we investigated the lability of Al, As, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Sr, V and Zn in Fe/Al hydroxide-comprised WTR based on a 180-day anaerobic incubation test using fractionation, in vitro digestion and a toxicity characteristic leaching procedure. The results indicated that most metals in the WTR were stable during anaerobic incubation and that the WTR before and after incubation could be considered non-hazardous in terms of leachable metal contents according to US EPA Method 1311. However, the lability of certain metals in the WTR after incubation increased substantially, especially Mn, which may be due to the reduction effect. Therefore, although there is no evidence presented to restrict the use of WTR in the field, the lability of metals (especially Mn) in WTR requires further assessment prior to field application. In addition, fractionation (e.g., BCR) is recommended for use to determine the potential lability of metals under various conditions.

Targeting treatment technologies to address specific stormwater pollutants and numeric discharge limits

Stormwater treatment is entering a new phase with stormwater management systems being required to meet specific numeric objectives, as opposed to the historic approach of meeting guidance-document-provided percent removal rates. Meeting numeric discharge requirements will require designers to better understand and apply the physical, chemical, and biological processes underpinning these treatment technologies. This critical review paper focuses on the potential unit treatment operations available for stormwater treatment and outlines how to identify the most applicable treatment options based on the needed pollutant removal goals.

Phosphorus mitigation during springtime runoff by amendments applied to grassed soil

Permanent grass vegetation on sloping soils is an option to protect fields from erosion, but decaying grass may liberate considerable amounts of dissolved reactive P (DRP) in springtime runoff. We studied the effects of freezing and thawing of grassed soil on surface runoff P concentrations by indoor rainfall simulations and tested whether the peak P concentrations could be reduced by amending the soil with P-binding materials containing Ca or Fe. Forty grass-vegetated soil blocks (surface area 0.045 m, depth 0.07 m) were retrieved from two permanent buffer zones on a clay and loam soil in southwest Finland. Four replicates were amended with either: (i) gypsum from phosphoric acid processing (CaSO × 2HO, 6 t ha), (ii) chalk powder (CaCO, 3.3 t ha), (iii) Fe-gypsum (6 t ha) from TiO processing, or (iv) granulated ferric sulfate (Fe[SO], 0.7 t ha), with four replicates serving as untreated controls. Rainfall (3.3 h × 5 mm h) was applied on presaturated samples set at a slope of 5% and the surface runoff was analyzed for DRP, total dissolved P (TDP), total P (TP), and suspended solids. Rainfall simulation was repeated twice after the samples were frozen. Freezing and thawing of the samples increased the surface runoff DRP concentration of the control treatment from 0.19 to 0.46 mg L, up to 2.6-3.7 mg L, with DRP being the main P form in surface runoff. Compared with the controls, surface runoff from soils amended with Fe compounds had 57 to 80% and 47 to 72% lower concentrations of DRP and TP, respectively, but the gypsum and chalk powder did not affect the P concentrations. Thus, amendments containing Fe might be an option to improve DRP retention in, e.g., buffer zones.

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.