Spent lime, calcium water treatment residuals and application in stormwater
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Spent lime, calcium water treatment residuals and application in stormwater

This page provides information on calcium in water treatment residuals. The term spent lime is often used in place of calcium-water treatment residuals. Spent lime includes a wide range of products resulting from the use of calcium-based materials. This discussion focuses only on spent lime resulting from calcium used for treatment of drinking water. While providing extensive information on water treatment residuals, there is a section focused specifically on stormwater applications for aluminum and iron in water treatment residuals.

Overview and description

Drinking water is often treated with lime to soften water by removing carbonate and other anions that contribute to hardness (http://www.freepatentsonline.com/y2019/0256433.html). A typical chemical reaction for softening (removing calcium carbonate hardness) is given by

Ca²⁺ + 2HCO₃< +Ca(OH₂) = 2CaCO₃(s) + 2H₂O

This reaction shows the formation of calcium carbonate (CaCO₃). Precipitated CaCO3 is routinely referred to as spent lime. Spent lime as a hydrated slurry from water treatment is typically sent to landfills. However, lime materials precipitate out metals, perform anion exchange, and flocculate suspended and dissolved solids and may therefore have beneficial uses for pollutant removal or may have negative properties that would limit any beneficial use. https://www.graymont.com/en/markets/environmental/water-treatment

Stormwater runoff from urban areas contains relatively high concentrations of phosphorus (typically 0.2-0.4 mg/L). Furthermore, engineered media used in stormwater best management practices, such as bioretention practices, may export phosphorus due to high concentrations of organic matter in the media (multiple citations). This excess phosphorus negatively impacts receiving waters. Spent lime, added to engineered media in stormwater treatment practices such as bioretention, has the potential to retain phosphorus and reduce impacts to receiving waters provided it does not have other adverse effects, such as releasing contaminants associated with the treatment residual or having negative impacts to soil or vegetation. This page provides a discussion of spent lime, including information on its physical and chemical properties, capabilities for retaining phosphorus, and potential environmental effects. A discussion of applications beyond engineered media is included.

Applications in stormwater management

Spent lime has not been widely used in stormwater applications. The primary use is for retention of dissolved phosphorus. Most stormwater practices are effective at retaining other pollutants that spent lime could retain, such as metals, organic chemicals, and microorganisms. Dissolved phosphorus retention in many stormwater practices has been poor, however, including bioretention, constructed ponds, sand filters, and swales (multiple references).

Barr Engineering developed a spent-lime treatment cell for the Ramsey-Washington Metro Watershed District to reduce phosphorus loading to Wakefield Lake, an impaired lake located in Maplewood. The treatment cell, in operation for seven years, shows that the spent lime removes phosphorus and metals to low levels (removal of 74.4 percent of ortho-phosphate and 66 percent of particulate phosphate) (https://www.barr.com/Project/first-of-its-kind-spent-lime-stormwater-bmp-treatment-system).

In 2018, Barr Engineering began a study to evaluate the application of spent lime to pond sediments to reduce phosphorus release during warm summer months (https://www.wrc.umn.edu/pond-treatment-spent-lime-control-phosphorus-release-sediments). Additional projects where spent lime has been used or proposed include the following:

Willow pond: https://www.rwmwd.org/construction-to-begin-on-innovative-willow-pond-stormwater-filter/
Lake Cornelia: https://www.ninemilecreek.org/wp-content/uploads/Lake-Cornelia_DRAFT_2019_05-07_Rpt-Only.pdf
Spent lime reactors: https://www.ci.inver-grove-heights.mn.us/DocumentCenter/View/4573/IGHCWRFStormwaterProjectPlan?bidId=
Lake Susan spent lime treatment system http://rpbcwd.org/application/files/3115/4264/8313/EngineersReportLakeSusanWaterQualityImprovementProject_v1.0.pdf
Armstrong lake spent lime filter: https://www.swwdmn.org/wp-content/uploads/2018/09/Armstrong-Lake-Subwatershed-Retrofit-Analysis-Report.pdf

Production

Lime softening is a water treatment process that uses calcium hydroxide, or limewater, to soften water by removing calcium and magnesium ions. In this process, hydrated lime is added to the water to raise its pH level and precipitate the ions that cause hardness.

Quicklime and hydrated lime are frequently used in water treatment. Quicklime, known as calcium oxide (CaO), is made through the thermal decomposition of limestone or other materials containing calcium carbonate in a lime kiln. The material is heated at high temperatures, and the remains are quicklime (https://bonesdontlie.wordpress.com/2013/08/08/new-morbid-terminology-quicklime/#:~:text=Quicklime%20is%20a%20chemical%20compound,and%20the%20remains%20are%20quicklime). Hydrated lime is the result of adding water to powdered quicklime, putting it in a kiln or oven, and then pulverizing it with water. The resulting lime is called calcium hydroxide.

Whether to use quicklime or hydrated lime in a particular situation is influenced by a number of factors, such as scale of operation, method cost, transportation cost, and availability. Material cost depends on whether bagged or bulk lime, hydrated or quicklime is used. The choice between purchasing lime in bags or in bulk is a direct function of rate of use. Where chemical requirements are small, bagged lime is preferred. Conversely, at larger treatment plants it is more efficient and economical to handle bulk lime.

The following table describes characteristics of quicklime and hydrated lime. Detailed information on the production and use of lime for water treatment can be found at the following links.

Properties

This section provides information on the physical and chemical properties of spent lime.

Physical

The following table summarizes some physical properties of spent lime.

Chemical

The following table summarizes chemical data for calcium water treatment residuals (WTRs). Data for calcium WTRs is limited to five studies. Data for aluminum WTRs and iron WTRs is included for comparison. The data indicate that chemical concentrations in Ca-WTRs are lower than for Al- and Fe-WTRs except for calcium, magnesium, and strontium. Soil reference values (SRVs) and soil leaching values (SLVs) are included and discussed in the next section. 1) Turner et al. 2019 2) Elliott et al 2002 3) Lang 4) Shrestha et al 5) Elliott et al. 6) Birikorang 7) EPA 8) Barr Engineering 9) Wang

Potential contaminants

Baker et al. (2005) summarized results of a USEPA study that examined removal of metals by lime sludge used for water softening. Removal rates, as a percent, varied with pH and are summarized in the following table.

Because of its sorptive properties, spent lime has the potential to contain chemicals that may be of environmental concern. The table in the previous section indicated that median concentrations of chemicals in spent lime do not exceed Tier 2 Soil Reference Values (SRVs) or Soil Leaching Values (SLVs). In computing the SLVs a separation distance of three feet was assumed between the bottom of a stormwater practice and an underlying water table, since this is the required minimum separation distance for stormwater practices. Concentrations of chemicals are a function of concentrations in the source water. Thus, although median concentrations are below levels of concern, source waters with elevated concentrations of specific chemicals, such as arsenic, could result in elevated concentrations in the spent lime. Barr Engineering conducted a study comparing aquatic toxicity of stormwater treated with spent lime to untreated stormwater. Two storm events were sampled and tested in a laboratory. Standard U.S. Environmental Protection Agency (EPA) methodologies were followed to test for chronic aquatic toxicity using a sensitive test species called Ceriodaphnia dubia (e.g., a zooplankton, often described as a water flea). For the May 21, 2012 test, mean young production was greater for treated stormwater than for untreated stormwater. This indicates that the treated stormwater was slightly less toxic than the untreated stormwater. For the June 19, 2012 test, mean young production was lower for treated stormwater than for untreated stormwater. In both cases, however, the spent lime material did not produce unwanted toxic conditions in the treated stormwater. Overall, these tests suggest that the use of spent lime will not cause unintended aquatic toxicity in water receiving spent lime-treated stormwater as long as the contact time is maintained at an appropriate level. Palizza et al. found that spent lime in leachate from bioretention plots did not affect heavy metal concentrations of Cu and Mn, reduced Al, Fe and Zn and slightly increased Ni (0.016 in spent lime vs. 0.013 mg L−1 in non-spent lime plots). Heavy metal concentrations of Cd, Cr and Pb in all treatments were <0.001 mg L−1. Barr Engineering conducted a field study to determine the retention of phosphorus and metals in a permeable reactive barrier containing spent lime. They observed removal rates of 57, 60, 86, 66, and 31 percent for aluminum, iron, lead, zinc, and copper respectively. DeBusk et al. found that use of limerock in a sand filter treating spiked stormwater runoff reduced concentrations of Cu, Cd, and Ni by 31, 81, and 31 percent, respectively. Adhikari et al. found spent lime reduced Cd and Pb concentrations to below detection (2 and 20 ug/L, respectively) in a column study with spiked stormwater runoff.

Elliott et al. (1990) conducted laboratory studies to determine water soluble fractions of metals in Al- and Fe- water treatment residuals. They found water-soluble fractions of 5.8, 1.0, 1.0, 0.6, 4.2, and 0.5% for Cd, Cu, Cr, Ni, Pb, and Zn, respectively, indicating these metals are relatively strongly sorbed to lime.

These studies indicate concentrations of metals are typically below concentrations of concern in spent lime and that lime-amended media adsorb metals from stormwater runoff.

Effects on physical and chemical properties of soil and engineered media

This section provides a summary of the effects of spent lime on soil and engineered media.

Physical properties

Lang observed that freeze thaw cycles caused the reduction of compressive strength for both natural soils and soils treated by lime sludge but that lime sludge treated soil specimens have much higher strength than natural soil specimens even after freeze-thaw cycles. These observations point to the positive effects of lime sludge treatment in improving the soil mechanical performance properties as well as improving the durability under freeze-thaw cycles.

Baker et al. (2005) observed that lime-amended soils exhibited similar soil bulk densities and increased water-holding capacity compared to non-amended soils.

From Tran et al.: A number of works on lime treatment showed that there are two distinct processes that take place when lime is added in wet soil: modification and stabilisation (Sherwood, 1993, Rogers and Glendinning, 1996, Boardman et al., 2001). The modification corresponds to a cation exchange process where the calcium ions (Ca2+) from hydrated lime migrate to the surface of the clay particles and displace water and other ions. This process gives rise to soil “flocculation and agglomeration” and lasts for a few hours depending on the clay mineral involved (Rogers and Glendinning, 1996). The soil becomes friable and granular after this phase. If quicklime is used, another process, i.e. hydration of quicklime, occurs before the modification process. This process is an exothermic reaction which occurs immediately between quicklime and water to form hydrated lime. The stabilisation refers to the pozzolanic reaction which occurs more slowly over a long period of time and depends on temperature, soil chemistry and mineralogy (Hunter, 1988, Wild et al., 1993). During this process, the high pH value in soil causes silica and alumina to be dissolved and to combine with calcium producing cementitious compounds, calcium silicate hydrates (CSH) and calcium aluminate hydrates (CAH) (Choquette et al., 1987, Locat et al., 1996).

Barr Engineering observed the hydraulic conductivity of spent lime is high even when wet and does not readily clog.

Phosphorus

Phosphorus can be precipitated from a system by calcium, either through incorporation into a calcium phosphate salt, or adsorbed onto calcium carbonate. A typical reaction is given by the following. 2H3PO4+3 + CaCO3(ag) → Ca3(PO4)2(s) + 3CO3−2 + H+ 2H+ + CO3−2 → H2O + CO2 There are many forms of calcium phosphate , the most stable being hydroxyapatite. Initial reactions between calcium and phosphate are very quick, with phosphate solutions coming into equilibrium with calcium carbonate within 20 minutes except at very high phosphate concentrations (5 mg/L or greater). These initial rapid reactions typically result in the formation of metastable species such as tricalcium phosphate, octacalcium phosphate, anhydrous dicalcium phosphate, and dicalcium phosphate dihydrate. The rate of formation for hydroxyapatite is very slow and results from “aging” of these intermediate precipitates (Birdsey, Clark and Turner). Most studies in the literature examined the removal of phosphorus from wastewater or from biosolids applied to soil. Phosphate removal rates reported in the literature vary from about 60 to as high as 95 percent (Yanamadala. Birdsey, Clark and Turner, Wandruszka). Factors affecting phosphorus retention include the following.

Retention increases as surface area of the carbonate material increases
Retention increases as the charge differential increases between the liquid solution and solid surface
Retention by calcium decreases as iron and clay concentration increases
Retention may increase or decrease in media with organic matter depending on the nature of the organic material

Shrestha et al. studied sorption of phosphate in bioretention media containing varying amounts of compost and amended with coir or spent lime WTRs. The study included a field-based mesocosm experiment and a laboratory study, both which assessed the effect of spent lime amendments on leachate nutrient. Spent lime significantly reduced leachate PO43− concentrations (upwards of 50%) in both the field and lab mesocosm studies compared to treatments without spent lime. While leachate P concentration increased significantly with increasing compost levels in the absence of spent lime, leachate P concentrations remained relatively uniformly low across this gradient when spent lime was added to substrate.

Elliott et al. (2002) studied phosphorus leaching in laboratory and greenhouse plots receiving biosolids application and amended with water treatment residuals (iron, aluminum, and calcium WTRs). With no WTRs, 11-21% of P leached over 4 months, compared to a loss of 2.5% for calcium-WTRs.

Barr Engineering conducted laboratory and field studies to examine phosphorus removal by spent lime. The laboratory study included column tests whereby stormwater was passed through different lime configurations. The pilot-scale field study included site identification, design, permitting, construction, and monitoring of a pilot-scale lime treatment cell. Three years of monitoring the test spent lime system showed total phosphorus removal of 60% and total dissolved phosphorus removal of 70% in this test. Adhikari et al. observed a 76% reduction in phosphorus concentrations from water samples spiked with high concentrations of phosphorus (25 and 80 mg/L). Adsorption was 90 percent complete within 60 minutes.

In a column study DeBusk observed a 42% decrease in P concentrations in stormwater effluent containing0.40 mg/L P. Yanamadala, studying the effects of lime in aquatic systems, observed that calcium carbonate was highly successful (p < 0.0001) in decreasing phosphates from 1.5 ppm, on average, to 0.4 ppm, an average decrease of approximately 70%. Other pollutants in runoff

Barr Engineering observed removal rates of 57.1, 57.2, 25.5, 60.2, 86.4, 66.4, and 31.4 percent for TSS, Al, Ca, Fe, Pb, Zn, and Cu, respectively.

RoyChowdhury et al. (2018) conducted laboratory batch sorption studies to determine removal of acidity and metals from acid mine drainage-impacted water using calciumwater treatment residuals. The filter media removed more than 99% of the initial Fe, Al, Zn, Pb, As, Mn, and 44% of the initial SO4-2. pH increased from 2.27 to 7.8. Desorption experiments showed that the metals were irreversibly bound to the WTRs and were not released back to the water.

Shrestha observed reductions in NH4+ concentrations were also observed due to spent lime but with variable significance across the different compost levels, whereas NO3− concentrations were higher in plots with spent lime than plots without spent lime.

Increase in pH.

Numerous crops, including turf grass as susceptible to damage when soil pH values are excessively acidic. Characteristics of turf pH imbalance are excess weed growth, patchy growth, yellowing, or a combination of thereof. One of the primary methods of correcting this problem is to add lime to turf to restore depleted nutrients and repair the damage. Soil pH is affected by a variety of factors that illustratively include rainfall, organic matter decay, fertilizers applied, pesticides applied, and pollution; and as such can drift from desired levels over time. ( http://www.freepatentsonline.com/y2019/0256433.html)

Barr report: Examining the data provided in Appendix C, one can observe that for certain constituents the treatment cell appeared to behave differently in 2012—the year immediately following the placement of spent lime in the cell—compared to 2013. In 2012, the treatment cell removed predominantly dissolved othophosphorus while it removed very little particulate phosphorus. In that year, it did not appear that much TSS, calcium, aluminum, or iron were removed. It appears that in 2012, most of the calcium, aluminum, and iron entering the treatment cell was dissolved. In 2013, the treatment cell removed suspended solids, both total and dissolved phosphorus, calcium, aluminum, iron, copper, lead, and zinc. There was a strong correlation between total suspended solids and metals (i.e., calcium, aluminum, iron, copper, lead, and zinc) concentration. It is possible that the maintenance performed on the treatment system (see Figure 6-1) had the effect of changing the structure of the lime in the barrier, leading to greater filtration capacity. An additional hypothesis is that when the material was initially placed with the backhoe, the open spaces between lime chunks were large. After periods of wetting and drying, settling time, and mixing with maintenance, the pore spaces perhaps decreased, causing the lime to act as a better filter.

Effects on plant growth and microbial function

Wandruszka demonstrated that excess lime in soil can inhibit phosphorus uptake by plants, but this is unlikely to be a concern in most stormwater applications due to relatively high concentrations of phosphorus in stormwater runoff.

Limestone is routinely spread on a target crop if the soil pH is too low. Limestone, often referred to synonymously as agricultural lime, or calcic limestone that is predominantly the chemical calcium carbonate, CaCO3; and is applied as a fine powder. The other conventional types of materials applied to crops include burnt lime, often referred to synonymously as quick lime, or caustic lime that is predominantly the chemical calcium oxide, CaO; and hydrated lime, often referred to synonymously as slaked lime that is predominantly the chemical calcium hydroxide, Ca(OH)2. Natural limestones also vary in the relative amounts of calcium and magnesium, with calcium limestones referred to as calcitic, and mixed limestones referred to as dolomitic. While conventional, treating soil with the aforementioned lime materials has several problems including the caustic nature of some the products, comparatively high cost, slow action to raise pH, a potential for localized caustic burning of the target crop, and fouling of spreader equipment. While some of these problems are more pronounced for a given material as compared to another, there remains a complexity to application and the possibility for harm to the target crop.( http://www.freepatentsonline.com/y2019/0256433.html)

Standards and classification

No standards or classification were found in the literature.

Distributors

If possible, list facilities that use lime for softening and generate spent lime. Quantities would also be useful if available.

Test methods

Standard test methods for spent lime were not found in the literature. Test methods are described in several reports ().

Aging

Spent lime should not undergo structural or chemical changes over time, though there is insufficient data in the literature on this topic. The phosphorus binding capacity of media amended with spent lime can be calculated knowing the concentrations of calcium (Brock et al., 2007). Adhikari calculated a sorption capacity of 44 mg-P/g-lime.

Storage, handling, and field application

Storage

Keep quick lime dry until used. Normal temperatures and pressures do not affect the material.

Handling

MSDS

http://www.gpreinc.com/uploads/10-3-SDS/GHS-SDS_Lime-Sludge_2017-09_Rev-7.pdf – spent lime. It is concluded that the use of calcium hydroxide in the treatment of wastewater has no adverse effect on the aquatic ecosystem in “Draft human and environmental risk assessment of calcium hydroxide” report prepared by the Washington State Department of Ecology in March 2005. Not a hazardous waste either by listing or characteristic. : Corrosive material; avoid any release of dust during transportation, by using tight tanks for powders and covered trucks for pebbles. Following neutralization either at the spill site or at a waste management facility, the resultant sludge can be disposed of to a secure landfill. Or consult with environmental regulatory agencies for guidance on acceptable disposal practices. Handling is similar to lime products described below.
https://assets.greenbook.net/M105512.pdf - hydrated lime
https://ehs.cranesville.com/msds.pdfs/MSDS(L012).pdf – quick lime: Exposure to quick lime may cause irritation or caustic burns to the moist mucous membranes of the nose, throat, and upper respiratory system. Exposure of sufficient duration to wet quick lime can cause serious, potentially irreversible tissue (skin or eye) destruction in the form of chemical (caustic) burns. Promptly remove dusty clothing or clothing which is wet with cement fluids and launder before reuse. Wash thoroughly after exposure to dust or quick lime mixtures or fluids. Where prolonged exposure to quick lime products might occur, wear QuickLime MSDS (2).doc impervious clothing and gloves to eliminate skin contact. Wear sturdy boots that are impervious to water to eliminate foot and ankle exposure. Avoid actions that cause dust to become airborne. Use local or general exhaust ventilation to control exposures below applicable exposure limits. Use NIOSH/MSHA approved (under 30 CFR 11) or NIOSH approved (under 42 CFR 84) respirators in poorly ventilated areas, if an applicable exposure limit is exceeded, or when dust causes discomfort or irritation. (Advisory: Respirators and filters purchased after June 10, 1998 must be certified under 42 CFR 84.) Ventilation Use local exhaust or general dilution ventilation to control exposure within applicable limits. Eye Protection Where potentially subject to splashes or puffs of quick lime, wear safety glasses with side shields or goggles. In extremely dusty environments and unpredictable environments wear unvented or indirectly vented goggles to avoid eye irritation or injury. Contact lenses should not be worn when working with quick lime.

Application

There are few studies that provide design information for spent lime in stormwater applications. There are numerous studies in the literature describing use of lime for agricultural and other soil applications. Lime is primarily used to adjust soil pH in acidic soils, thereby improving uptake of specific elements and reducing potential toxicity associated with other elements, particularly metals. Since phosphorus can be limiting in soils, these studies typically have the goal of increasing pH to neutral values. For stormwater applications, phosphorus will not be limiting because of constant inputs of phosphorus from stormwater runoff. Raising the pH is therefore less of a concern except for the potential to impact vegetation. An appropriate plant assemblage should therefore be selected based on the final pH in the amended media. The primary concern with lime additions is on reduced hydraulic conductivity associated with excess lime application. Shrestha mesocosm study: The residuals were air dried in the sun and 124 mechanically pounded and crushed into powder form (maximum grain size≤ 5 mm) before 125 application. Upper layer of engineered media with compost and an underlying 13 cm layer consisting of 60% WTR and 40% sand. Shrestha column study: WTR was crushed and sieved through a 2 mm mesh screen. Layered system. RoyChowdhurey: WTR samples were airdried, ground, and sieved through a 1-mm sieve prior to use. WTRs were uniformly mixed with sand at ten mass ratios ranging from 1:1 to 1:10. One of the major disadvantages of WTRs is their low porosity. Filter media 1 was prepared by mixing sand and WTRs at 1:6 ratio. Barr: Annual maintenance has consisted of removal of accumulated material on the top of the cell and mixing the top 1-foot of the lime material with a shovel. Mixing takes about 1 to 2 hours. Other mixing tools may be useful such as a compost aeration tool. Rototillers have not been used successfully. It is expected that spent lime can be used in a wide range of treatment designs and configurations. Future designs should consider the use of a pond or plunge pool to settle out sand, leaves, and sticks. This may help minimize the accumulation of material on the surface of the spent lime and also reduce the frequency of maintenance.

Sustainability

Since spent lime is a byproduct produced from water softening, it is a sustainable product for stormwater applications. Salih et al. (2019) estimated water utilities across the United States are currently generating approximately 3.2 million tons of lime sludge per year. Several cities in Minnesota soften their municipal water with lime, and the number of facilities using lime is increasing as a means of reducing demand for water softening in individual homes.

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