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Evaluation of wastewater treatment by-products as soilamendment: Growth of sorghum-sudan grass and traceelements concentrationsParamasivam Sivapatham a , Mariel C. Potts a , Jeffrey A. Delise a , Kenneth S. Sajwan b ,Ashok K. Alva c , Kuppuswamy Jayaraman a & Paromita Chakraborty aa Department of Engineering Technology and Mathematics, Savannah State University,Savannah, Georgia, USAb Department of Natural Sciences, Savannah State University, Savannah, Georgia, USAc USDA-ARS, Pacific West Area, Vegetable and Forage Crops Research Unit, Prosser,Washington, USAVersion of record first published: 15 Jun 2012.

To cite this article: Paramasivam Sivapatham , Mariel C. Potts , Jeffrey A. Delise , Kenneth S. Sajwan , Ashok K. Alva ,Kuppuswamy Jayaraman & Paromita Chakraborty (2012): Evaluation of wastewater treatment by-products as soil amendment:Growth of sorghum-sudan grass and trace elements concentrations, Journal of Environmental Science and Health, Part A:Toxic/Hazardous Substances and Environmental Engineering, 47:11, 1678-1686

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Journal of Environmental Science and Health, Part A (2012) 47, 1678–1686Copyright C© Taylor & Francis Group, LLCISSN: 1093-4529 (Print); 1532-4117 (Online)DOI: 10.1080/10934529.2012.687261

Evaluation of wastewater treatment by-products as soilamendment: Growth of sorghum-sudan grass and traceelements concentrations

PARAMASIVAM SIVAPATHAM1, MARIEL C. POTTS1, JEFFREY A. DELISE1, KENNETH S. SAJWAN2,ASHOK K. ALVA3, KUPPUSWAMY JAYARAMAN1 and PAROMITA CHAKRABORTY1

1Department of Engineering Technology and Mathematics, Savannah State University, Savannah, Georgia, USA2Department of Natural Sciences, Savannah State University, Savannah, Georgia, USA3USDA-ARS, Pacific West Area, Vegetable and Forage Crops Research Unit, Prosser, Washington, USA

Wastewater treatment by-products (WTBP), such as sewage sludge (SS) may be used to enhance soil chemical, physical, and biologicalproperties. These enhanced soil properties, in turn, could from its source of production to its site of application. These concerns maybe mitigated by incineration of the SS to produce ash (SSA) and dissolved in water and stored in ponds as contribute to an increasein plant growth, production, mineral nutrition. Some SS is difficult to handle due to bad odor in its raw state and has large mass,hence expensive for transportation weathered SSA (WSSA). A greenhouse study was conducted using Candler fine sand CFS; (CFS;pH = 6.8) and Ogeechee loamy sand OLS; (pH = 5.2) with application of either 0, 24.7, 49.4, 98.8, or 148.2 Mg ha−1 as either SS,SSA, or WSSA to evaluate the biomass production and elemental composition responses of sorghum-sudan grass (Sorghum vulgarisvar. Sudanese hitche). Shoot and root biomass were 2 to 3 fold greater in the soil amended with SS, than either SSA or WSSA.Concentrations of nutrient and trace elements in the shoots and roots increased with increasing rates of amendments. Application ofthese by-products up to 98.8 Mg ha−1 rate did not adversely affect growth or accumulation of trace elements in sorghum-sudan grass.Long-term field studies are recommended to investigate the potential leaching of various elements from the amended soils in additionto evaluation of plant growth and production responses to determine the acceptable rates of these by-products as amendments toagricultural soils.

Keywords: Chemical association, growth performance, sewage sludge, sewage sludge ash, soil amendment, sorghum-sudan grass,weathered sewage sludge ash.

Introduction

Sewage sludge (SS), also known as biosolids, is one of themajor solid organic by-products of wastewater treatmentfacilities in cities around the globe. Sewage sludge con-tains varying amounts of plant nutrients (C, N, P and K)and micronutrients and can be used as a soil amendmentto increase crop growth.[1] These by-products are rich inorganic materials which could improve the soil physical,chemical, and biological properties and ultimately enhancewater and nutrient retention capacity of agricultural soilsand crop production.

Land application of some source of SS may have neg-ative effects such as offensive odor, high acidity, or high

Address correspondence to Paramasivam Sivapatham, Depart-ment of Engineering Technology and Mathematics, SavannahState University, P.O. Box 20089, Savannah, GA 31404, USA;E-mail: siva@savannahstate.eduReceived January 6, 2012.

levels of some heavy metals, and pathogens. Compostingof raw organic wastes leads to reduction in material massand water content, pathogens, seed viability, and produc-tion of stabilized organic material that is easier to spreadon agricultural lands.[2,3] Composted organic wastes andSS materials were successfully tested as a soil amendmentfor variety of crops.[4–6] Some wastewater treatment plantshave adapted to incinerate the SS to produce sewage sludgeash (SSA) and store this ash by dissolving it in ash ponds asweathered sewage sludge ash (WSSA). The SSA and WSSAhave the following advantages: (i) reduced mass, which re-duces landfill space; (ii) less offensive odor; and (iii) a lowercost of transportation to the field where it could be used assoil amendment. Wastewater treatment plants in Savannahproduce all three by-products (SS, SSA, and WSSA).

Depending on the source of origin of the wastewater usedin treatment plants, some SS may contain excessive levelsof trace elements which can cause phytotoxicity and ani-mal toxicity if any of these plants were used for grazing.[7]

Phyto-toxicity of trace elements in SS is dependent on the

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relative partitioning of various forms of metals.[8] The dy-namics and release of various nutrients and trace elementsin the SS are also dependent on the origin of the wastewater used in the treatment plant, the soil type, moisturecontent of the soil, and other plant related parameters.The dynamics of sludge organic carbon can influence thefate of trace elements in the soil.[9]

The dynamics and release of various nutrients and traceelements in the SS are also dependent on the origin of thewaste water used in the treatment plant, the soil type, mois-ture content of the soil, and other plant related param-eters.[10] Bioavailability and leachability of various traceelements in SSA and WSSA, however, depend on the spe-ciation of trace elements and their portioning into variousforms of residues leaving the incinerator. The effect of op-erating conditions (temperature and gas composition, resi-dence time and the presence of reactive compounds such aschlorine, sulfur, and or alumino-silicates) would also deter-mine speciation and partitioning of trace elements presentin raw SS.[11–13]

Reactive compounds, such as chlorine, have a strong in-fluence on the trace element partitioning because all chlo-rides of trace elements generally have higher vapor pressurethan that of their corresponding oxides. Morf et al.[14] no-ticed greater loss of Cu, Cd, and Pb with combustion fluegas than Zn when the raw SS with greater sulfur was incin-erated. Raw SS with greater moisture content and excessivemineral matter greatly reduces the volatilization of traceelements during incineration.[15]

Because WSSA is produced by dissolving SSA and stor-ing it in an ash pond for a long time, elemental concentra-tion in WSSA would be substantially different from thatof the original SS. Therefore, we conducted a pot experi-ment to evaluate the effect of application of different ratesof either SS, SSA, or WSSA to two soils on the dry matteryield of sorghum-sudan grass, and tissue concentration ofvarious plant nutrients and trace elements.

Materials and methods

Soils and rates of amendments

Two soils were sampled from the surface horizon (0–15 cm)for greenhouse pot experiment: (i) Candler fine sand CFS;(sandy, hyperthermic, uncoated, Typic Quartzipsamments)from the University of Florida, Citrus Research and Edu-cation Center, Experimental Farm in Lake Alfred, FL, and(ii) Ogeechee loamy sand OLS; (silicious, thermic TypicOchragult) from a fallow land in Savannah, GA. Watertreatment residuals (SS, SSA, and WSSA) were collectedfrom city of Savannah President Street Wastewater Treat-ment Plant, Savannah, GA and air-dried and stored beforeuse.

The soils were air dried and passed through a 2-mmsieve. Each pot (30-cm diameter and 30-cm height) was

lined with 3 Whatman No. 42 filter papers and filled with3 kg of soil. The top 2.5-cm soil was amended with fourrates (24.7, 49.4, 98.8, and 148.2 Mg ha−1) of SS, SSA, orWSSA. An unamended treatment was included for eachsoil as a control. Each treatment was replicated three times.The pots were incubated for eight weeks at field capacitymoisture content and fifteen seeds of sorghum sudan grass(Sorghum vulgaris var. Sudanese hitche) were planted ineach pot. After two weeks, the pots were thinned to 7 plantsper pot and growth response was evaluated for 65 days atfield capacity moisture content.

The soil moisture content was monitored regularly withthe help of soil moisture probes prior to water application(Portable Soil Moisture Meter, Lincoln Irrigation, Profes-sional Equipment Company, Janesville, WI, USA). Exper-iment was conducted under greenhouse conditions duringlate spring to summer (May–July) months without any sup-plemental light. Average day light variation during thesemonths was in the range of 13.5 to 14 hours a day. The rangeof high and low temperature variations during these monthsinside greenhouse were 95–100◦F and 30–38◦F, respectivelyand humidity variation were in the range of 70–100.

Harvest of plant materials and analysis

At the end of 65 days, plants were harvested by clipping at1-cm above the soil surface. The roots were separated fromsoil by washing. Harvested plant parts from each pot werewashed (separately) in detergent solution by rubbing withcheese cloth, rinsed in deionized water, soaked in dilute(5%) HCl acid bath for about 30 seconds and followedby four successive rinses in deionized water baths. Washedplant parts were placed on brown paper sheets to dry atroom temperature for 24 h and then transferred to paperbags and placed in a draft oven at 70◦C for 72 h. Dryweights were recorded to the nearest 0.01 g.

The dried samples were ground to pass through 40-mmmesh and stored in labeled vials until further analysis. Theground plant samples were dry-ashed in a muffle furnaceat 550◦C for 6 h, allowed to cool and then dissolved in20 mL of 1M HNO3

[16] and analyzed for elemental com-position by Inductively-Coupled Plasma Optical EmissionSpectrophotometer (ICP-OES; Perkin Elmer RL 3100).Standard reference plant samples from National Instituteof Standards and Technology (NIST) were used to checkand confirm the analytical quality of ICP-OES.

Soil analysis at the end of sorghum-sudan grass harvest

Residual soils in pots were sampled for pH and electricalconductivity measurements in soil suspension (10 g soil/20 mL deionized water). The ionic strength (I; in mM) wasestimated by multiplying EC (µS cm−1) values by 0.013i.e., I = 0.013 EC as described by Griffin and Jurinak[17]

and Alva et al.[18] Concentrations of total elements in soilsamples at the end of 65-d sorghum-sudan grass growth

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were determined using ICP-OES (Perkin Elmer 3100 RL)on acid digested soil sample (1 g soil / 12 mL 16 M HNO3)using Kjeltec block digester and diluting the sample to500 mL with deionized water.

Statistical analysis

The experiment was a completely randomized design witha with factorial treatment arrangement (2 soil x 3 sourcesof amendment × 5 rates of application) with 3 replicatesper treatment combination. Analysis of variance was con-ducted as randomized complete block design (RCBD) byconsidering replicates as block with SAS software (Version8.1; SAS 2000). Means and standard errors for dry matteryield and elemental concentrations of shoots and roots ofsorghum-sudan were computed and compared for signif-icance at 0.05 probability level. Mean comparisons weredone with the help of Duncan Multiple Range Test. Sim-ilar statistical analyses were also performed for the resultsof elemental concentrations, pH and ionic strength of soilsamples at the end of plant growth.

Results and discussion

Dry matter yield of shoots

Shoot dry weight of sorghum-sudan grass increased withincreasing rates of SS in both soils (Fig. 1). This was fol-lowed by a decreased shoot dry weight at the highest rate ofSS. This suggests potential negative effects of high SS rate,perhaps, associated with some phyto-toxicities. However,the similar negative effect was not evident for the SSA andWSSA amendments (Fig. 1). Mean dry weights of shoot

Fig. 1. Sorghum-sudan grass top biomass response to differentrates of amendments (sewage sludge: SS; sewage sludge ash: SSA;and weathered sewage sludge ash: WSSA) to a Candler fine sand(CFS) or an Ogeechee loamy sand (OLS). Error bar on each pointrepresents standard error of the means of 3 replicates.

Table 1. Selected properties of sewage sludge (SS), sewage sludgeash (SSA) and weathered sewage sludge ash (WSSA) and soilsused in this study.

Properties† SS‡ SSA‡ WSSA‡ CFS¶1 CLS¶2

pH (1:1water: soil)

6.6 8.0 7.7 6.8 5.5

(mS cm−1)EC 3.4 1.6 0.3 0.1 0.1

(g kg−1)C 395.0 10.5 11.0 5.0 12.0N 45.7 1.5 0.2 0.4 0.6S 11.1 2.0 0.1 0.1 0.2P 13.3 2.9 0.3 0.1 0.2K 2.0 6.0 0.7 1.3 1.2Ca 16.0 13.3 7.2 0.2 0.3Mg 1.7 1.6 1.1 0.1 0.1Fe 10.4 9.3 6.2 0.6 0.7

(mg kg−1)Mn 191.0 139.0 83.0 14.5 14.1Cu 219.0 210.0 24.0 38.4 1.2Zn 542.0 526.0 69.0 72.6 4.4Pb 37.0 29.0 10.0 20.9 4.9Cd 4.0 1.0 0.4 0.7 0.4Ni 16.0 14.0 8.5 nd ndCr 27.0 17.0 8.0 7.4 4.3

(g kg−1)Sand 967.0 860.0Silt 8.0 100.0Clay 25.0 40.0Texture fine sand sandy loam

†Elemental compositions were determined by ICP-OES on acid-digest.‡Collected from the President Street water quality control plant inSavannah, Georgia, USA. ¶1Collected from Polk County, Lake Alfred,Florida, USA. (CFS = Candler fine sand).

were significantly lower for the SSA (10.1 g) and WSSA(7.4 g) treatments compared with the SS treatment (20.8 g).This is somewhat expected considering substantial reduc-tion in C, Ca, N and P contents in the SSA and WSSA wascompared to those in the SS (Table 1). This observationcould also be explained by the loss plant nutrients follow-ing the destruction of organic components of SS duringincineration.

Mean shoot dry weight was significantly greater across allrates of amendments for the sorghum-sudan grass grownin the Ogeechee loamy sand (16.5 g) compared with theCandler fine sand (9.0 g). This effect was mainly evidentin the SS amendment only. Shoot dry weight of sorghum-sudan grass grown in unamended Ogeechee loamy sand wasgreater than sorghum-sudan grass grown in unamendedCandler fine sand (Fig. 1). The difference in shoot dryweight between soils could be attributed to differences inC and N contents because the differences in the amounts

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Fig. 2. Sorghum-sudan grass root biomass response to differentrates of amendments (sewage sludge: SS; sewage sludge ash: SSA;and weathered sewage sludge ash: WSSA) to a Candler fine sand(CFS) or an Ogeechee loamy sand (OLS). Error bar on each pointrepresents standard error of the means of 3 replicates.

of other macronutrient elements such as P, K, Ca, and Mgwere insignificant (Table 1).

Dry matter yield of roots

The root dry weight showed a negative response to thehighest rate of SS amendment only (Fig. 2). Similar toshoots, the root dry weight increased with an increase inSSA and WSSA rates over the entire range of amendmentrates and in both the soils. The difference between the two

Fig. 3. Sorghum-sudan grass tissue calcium concentration re-sponse to different rates of amendments (sewage sludge: SS;sewage sludge ash: SSA; and weathered sewage sludge ash:WSSA) to a Candler fine sand (CFS) or an Ogeechee loamysand (OLS). Error bar on each point represents standard error ofthe means of 3 replicates.

soils was less apparent for the mean root dry weight (2.0 gcompared to 1.7 g) than for mean shoot dry weight (16.5 gcompared to 9.0 g), across all amendment rates. Still, therewas very little difference in dry matter yield of roots couldbe observed in sorghum-sudan grass grown in unamendedsoils. This insignificant difference of root dry weight couldbe attributed to the variation in C and N contents of thesetwo soils (Table 1 and Fig. 2).

Concentrations of Ca, Mg, P, and K in shoots and roots

Irrespective of types of amendments and plant parts, con-centrations of Ca, Mg, P, and K in plant tissues increasedwith increasing rates of amendment application (Figs. 3–6).The concentrations of Ca, Mg, P, and K were significantlygreater in the shoots compared with roots. The concentra-tions of Ca, Mg, and P in both plant parts decreased in thefollowing order in both soils and at all rates of amendments:SS > SSA ≥ WSSA (Figs. 3–5). However, these differencesare not always statistically significant. In general, concen-tration differences of Ca, Mg, and P in plant tissues grownin SSA and WSSA amended soils were insignificant forall the application rates. In contrast, concentration of Kfor both the plant parts in both soils and at all rates ofamendments decreased in the following order : SSA > SS> WSSA (Fig. 6). Concentration difference of K in planttissues grown in soils amended with SS and WSSA wereinsignificant across all the application rates (Fig. 6).

Concentrations of P and K in plant tissues were ap-parently greater in the plants grown in WTBP amendedCandler fine sand compared to that in WTBP amended

Fig. 4. Sorghum-sudan grass tissue magnesium concentrationresponse to different rates of amendments (sewage sludge: SS;sewage sludge ash: SSA; and weathered sewage sludge ash:WSSA) to a Candler fine sand (CFS) or an Ogeechee loamysand (OLS). Error bar on each point represents standard error ofthe means of 3 replicates.

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Fig. 5. Sorghum-sudan grass tissue phosphorus concentrationresponse to different rates of amendments (sewage sludge: SS;sewage sludge ash: SSA; and weathered sewage sludge ash:WSSA) to a Candler fine sand (CFS) or an Ogeechee loamysand (OLS). Error bar on each point represents standard error ofthe means of 3 replicates.

Ogeechee loamy sand. This may be due to greater but steadydecomposition of organic amendments in sandy soil (Can-dler fine sand) compared to that in the Ogeechee loamysand. In addition, this is also due to comparatively lesserdry matter yield obtained from sorghum-sudan grass grownin Candler fine sand than that from Ogeechee loamy sand(Figs. 1–2).

However, the tissue concentrations of Ca and Mg donot show difference between the soils. Concentrations ofCa and Mg in plant shoots of sorghum-sudan grass grownin unamended soils were greater in the Ogeechee loamysand compared to that of in the Candler fine sand (Figs.3–4). In contrast, the concentration of P and K in plantshoots of sorghum-sudan grass grown in both unamendedsoils showed negligible differences (Figs. 5–6). None of theobserved concentration variation of these elements in planttissue could be related to inherent nutrient (Ca, Mg, P andK) status of unamended soils as presented in Table 1.

Concentrations of trace elements in the shoots and roots

Concentrations of Zn, Mn, and Fe in the shoots ofsorghum-sudan grass were greater in the plants grown inOgeechee loamy sand compared to those of the plantsgrown in Candler fine sand (Table 2). Concentrations ofthese trace elements in the shoots and roots increased withincreasing rates of amendment in both soils. Concentra-tions of Zn, Fe, and Cu in the roots were greater comparedwith shoots across all sources of amendments and soil types(Table 2).

Fig. 6. Sorghum-sudan grass tissue potassium concentration re-sponse to different rates of amendments (sewage sludge: SS;sewage sludge ash: SSA; and weathered sewage sludge ash:WSSA) to a Candler fine sand (CFS) or an Ogeechee loamysand (OLS). Error bar on each point represents standard error ofthe means of 3 replicates.

Plant uptake of trace elements from the soil, particu-larly with organic amendments is affected by bioavailabilitywhich in turn affected by the pH of the growth medium,[19]

type of amendments, and relative mobility of various traceelements within the part of sorghum-sudan grass.[20] Con-centrations of these trace elements (Fe, Mn, Cu and Zn)are generally elevated in the plants grown on soils amendedwith municipal biosolids (depends on the source) whichoften contain high levels of these elements.

Similar observations were also reported by other re-searchers who studied the effect of application of com-posted sewage sludge as soil amendment for broccoli[6] andturf grass. [5] In some wastewater treatment plants inorganicsalts of Fe and Zn are used which results in elevated con-centrations of these elements in the residuals of WTBP.Therefore, the application of Fe and Zn enriched WTBPmay contribute to the elevated concentrations of these ele-ments in plant tissues of sorghum-sudan grass or any otherplants. However, characterization data for the WTBP usedin this study do not support any addition of Zn or Feand these values are substantially lower than the averageconcentration of Fe and Zn we generally found in sewagesludge materials.[21]

Irrespective of type of soil and amendments, higher con-centrations of Pb was found in roots of sorghum-sudangrass than in shoots (Table 3). Sorghum-sudan grass grownin the Candler fine sand, Pb concentration in the shootswere above the detection limits across all 3 amendmenttypes. However, this was true only for the SSA and WSSAamendments for the plants grown in the Ogeechee loamysand. Results also indicated greater concentration of Cr

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Table 2. Concentration ranges of Mn, Fe, Zn, and Cu in the tops and roots of sorghum-sudan grass grown in two soils amended withdifferent rates (0, 24.7, 49.4, 98.8, and 148.2 Mg ha−1) of sewage sludge (SS), sewage sludge ash (SSA) or weathered sewage sludgeash (WSSA).

Concentrations of trace elements in sorghum-sudan grass(µg g−1)

Tissue type Amendment type Mn Fe Zn Cu

Candler fine sandTops SS 113–249 119–182 21–450 2–4 0

SSA 243–376 35–69 21–29 1–6.2WSSA 42–138 26–52 17–26 nd–0.2Control 29 19 11 nd

Roots SS 74–130 878–2287 97–181 93–126SSA 67–244 350–1022 83–156 27–67WSSA 43–206 437–627 25–74 9–57Control 24 142 18 8

Ogeechee sandy loamTops SS 186–405 128–198 64–221 nd

SSA 164–345 48–94 37–49 nd–4.5WSSA 26–230 32–51 22–45 ndControl 25 29 9 nd

Roots SS 102–178 549–644 185–274 8–30SSA 134–274 969–2120 147–363 10–69WSSA 16–219 532–1046 82–272 7–28Control 16 161 48 4

Mean concentrations of elements in plant parts of sorghum-sudan grass are expressed as ranges within the range of amendment application rates.nd: non-detectable amount. Elemental compositions were determined by ICP-OES on acid-digest.

Table 3. Concentration ranges of Cr, Cd, Ni, and Pb in the tops and roots of sorghum-sudan grass grown in two soils amended withdifferent rates (0, 24.7, 49.4, 98.8, and 148.2 Mg ha−1) of sewage sludge (SS), sewage sludge ash (SSA) or weathered sewage sludgeash (WSSA).

Concentrations of trace elements in sorghum-sudan grass(µg g−1)

Tissue type Amendment type Cr Cd Ni Pb

Candler fine sandTops SS nd nd nd 0.0–0.8

SSA nd–1.4 nd–1.2 158–236 0.4–9.0WSSA nd nd 138–177 nd–0.4Control nd nd 17 nd

Roots SS 0.9–6.6 nd nd 15.0–22.0SSA 0.5–1.5 0.2–2.9 125–231 3.5–18.9WSSA nd–1.4 nd 92–134 0.8–9.0Control nd nd 21 0.7

Ogeechee sandy loamTops SS nd nd nd nd

SSA nd–0.8 nd–0.7 133–165 nd–1.4WSSA nd nd 99–110 nd–0.1Control nd nd 18 nd

Roots SS 0.3–2.0 nd nd 2.2–4.7SSA 2.5–6.8 0.3–1.0 147–363 4.0–20.0WSSA 2.1–4.5 nd 82–272 3.3–9.7Control nd nd 48 1.3

Mean concentrations of elements in plant parts of sorghum-sudan grass are expressed as ranges within the range of amendment application rates.nd: non-detectable amount. Elemental compositions were determined by ICP-OES on acid-digest.

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Table 4. Mean concentration ranges of Mn, Fe, Zn, Cu, Cr, and Pb at the end of 65-d sorghum-sudan grass growth in two soilsamended with different rates (0, 24.7, 49.4, 98.8, and 148.2 Mg ha−1) of sewage sludge (SS), sewage sludge ash (SSA) or weatheredsewage sludge ash (WSSA).

Concentrations of trace elements in sorghum-sudan grass(µg g−1)

Amendment type Mn Fe Zn Cu Cr Pb

Candler fine sandSS 54–153 373–1243 11–137 25–94 1.1–1.8 12.4–23.9SSA 16–37 211–484 16–128 16–56 0.3–0.5 4.0–4.3WSSA 9–31 95–523 14–129 12–21 0.1–0.2 2.4–2.9Control 6 36 20 11 0.1 2.3

Ogeechee sandy loamSS 41–168 818–3400 170–515 39–105 1.7–3.8 7.0–12.2SSA 35–61 268–2600 34–306 17–63 0.9–1.2 6.7–7.0WSSA 12–46 71–1197 31–194 13–48 0.6–0.8 3.4–4.2Control 9 60 12 2 0.4 3.1

Mean concentrations of elements in soil at the end of 65-d sorghum-sudan growth experiment are expressed as ranges within the range of amendmentapplication rates. Elemental compositions were determined by ICP-OES on acid-digest. Concentrations of Cd and Ni were below the detectionlimits.

in roots compared with shoots of sorghum-sudan grass inboth type of soils (Table 3). Observed higher concentra-tions of Cr and Pb in roots of sorghum-sudan grass com-pared with shoots in our study concurred with the reportof Piechalak et al.,[22] which indicated that roots were mainaccumulation site of Pb in several plant species.

The concentrations of Ni were rather high in both shootsand roots of sorghum-sudan grass grown in both soilsamended with SSA and WSSA compared with that ofin SS amended soils. The concentrations of Ni were non-detectable in both shoots and roots in both soils amendedwith SS (Table 3). In contrast, the concentrations of Cdwere in detectable amount in both shoots and roots ofsorghum-sudan grass grown in both soils amended onlywith SSA. But the results also indicated that non-detectableamount of Cd was in both top and root tissues of sorghum-sudan grass grown in both soils amended with either SS orWSSA.

Wallace and Romney[20] reported the general distributiontrend of trace elements within different parts. Accordingly,the trace elements can be placed into three groups, basedon their relative distributions in different plants parts:(i) more uniform distribution of elements between rootsand shoots, e.g., Zn, Mn, Ni, and B, (ii) greater amountsin shoots than in roots, with moderate to some timeslarge quantities in the shoots, e.g., Cd, Co, and Mo, and(iii) mostly greater amounts in roots and very little amountsin shoots, e.g., Pb, Ag, Cr, Cu, and V. This generalizedgrouping however, can change according to plant species,soil and environmental conditions. Results of this study in-dicated the following exceptions to the above generalizedtrends: (i) greater concentrations of Mn in the shoots thanthose in the roots, and (ii) vice versa for Cu, and Zn (Ta-ble 2). It is important to note that high concentrations of

trace elements in the shoots can be toxic if it is used asanimal feed.[22]

Soil reaction and ionic strength of soil at the end ofsorghum-sudan growth

Application of different types of WTBP had effect on thesoil reaction (pH) at the end sorghum-sudan growth. Fora given source of amendment, changes in soil pH weresignificant across all rates in both soils (Fig. 7). For a givenrate of amendment, soil pH was lower for the SS treatmentas compared to that for the SSA or WSSA irrespective ofsoil type.

Ionic strength of soil suspension is a direct measure ofamount of ions present in the soil. At the time of endof crop growth ∼ 65 d), ionic strength increased with anincrease in the rate of amendment (Fig. 7). Ionic strength ofthe soil suspension was strikingly greater for the Ogeecheeloamy sand as compared to that for the Candler fine sand,particularly for the SS amendment at the application ratesof 98.8 and 148.2 Mg ha−1 (Fig. 7). Even though similarincrease was noted with other types of WTBP amendment,the difference was not strikingly greater like the one notedwith SS.

Trace element contents of residual soil at the end ofsorghum-sudan growth

Results of total trace elements analysis conducted on ho-mogenously mixed soil samples collected at the end ofsorghum-sudan grass growth are presented as range of con-centration in Table 4. Concentrations of trace elements insoils increased with increasing rates of amendments, and

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Evaluation of wastewater treatment by-products as soil amendment 1685

Fig. 7. Relationship of application rates of wastewater treatmentby-products and ionic strength and pH of residual soil at the endof 65-d sorghum-sudan grass growth in light-textured Candlerfine sand (CFS) from Lake Alfred, FL and in medium-texturedOgeechee loamy sand (OLS) from Savannah, GA. Error bar oneach point represents standard error of the means of 3 replicates.

in general these concentrations decreased in the follow-ing order: SS > SSA > WSSA amended treatments. Con-centrations of Cd and Ni in soils at the end of 65d cropgrowth were non-detectable in both soils irrespective oftypes and rates of amendments. This observation was in-teresting since Cd and Ni were introduced into the soil inthe form of WTBP amendments and at least a portion ofintroduced should be left in the soil unless these elementsare removed by plant uptake and/or leaching. Because theleaching losses were not monitored simultaneously withplant uptake in this greenhouse, it is difficult to provideproper accounting on these two elements.

Conclusions

Results of this study demonstrated that biomass productionof sorghum-sudan grass increased with an increased rate ofSS amendment up to 98.8 Mg ha−1. The application of SSAor WSSA also had positive effects on growth of sorghum-sudan grass up to the highest rate (148 Mg ha−1) evaluatedin this study. However, at a given rate of amendment theplant biomass was greater with SS as compared to that withSSA or WSSA amendments.

The concentrations of Ca, Mg, P, and K in the topsand roots increased with increasing rates of all amend-ments in both the soils. The concentrations of Ca, Mg, andP were greater in the plants which received SS, as com-pared to those of the plants which received either SSAor WSSA amendments. However, the concentrations ofK were greater in plants which received SSA, as com-

pared to those of the plants received either SS or WSSAamendments.

The concentrations of trace elements were greater in theplants that received SSA or WSSA amendments as com-pared to those of the plants received SS amendment. Incin-eration of the SS appeared to transform the trace elementsinto more available form as compared to those in the SS.

Results of the soil analysis at the end of (65-d) plantgrowth study indicated a greater amount of trace elementspresent in soil amended with SS as compared to those soilswhich received SSA or WSSA amendment. Additional fieldplot studies in different soil types need to be conductedto draw comprehensive results with respect to crop per-formance and leaching losses prior to make recommen-dations regarding types and rates of wastewater treatmentby-products as soil amendments.

Acknowledgments

Authors appreciate the financial support for this studythrough Title III program and the Department of Ed-ucation and Environmental justice, community educa-tion, and advisory project of the Department of Energy/Environmental Protection Agency. We appreciate the assis-tance and cooperation of the President Street wastewatertreatment plant staff, Savannah, GA.

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