USE OF ALKALINE STABILIZED BIOSOLIDS AS AN AGRICULTURAL LIMING AGENT

Transcription

1 US OF ALKALIN STABILIZD BIOSOLIDS AS AN AGRICULTURAL LIMING AGNT William Rogers*, Scott Carr, Dr. Fred Cox, Dr. Robert Holman, and Trille Mendenhall ABSTRACT A number of utilities are implementing alkaline stabilization systems for biosolids to achieve a Class A Product. Application of biosolids to agricultural land is the predominant I method of disposal. Due to low nitrogen concentrations and high calcium carbonate equivalence (CC), application rates need to be based on the neutralizing capacities of the materials. This research compared alkaline stabilized biosolid (ASB) with a standard agricultural dolomitic lime to determine the chemical properties of the ASB, reaction rates of the material, how long these reactions would continue, and how plant nutrition may be affected. Three types of experiments were initiated: incubation, greenhouse, and field. Soils selected for studies contained a range in clay and organic matter content. The ASB neutralized soil acidity as well as the agricultural lime at the same CC application rates. ASB reacted more quickly than agricultural lime in the greenhouse and field studies. This was due to the finer particle size of the ASB. The ASB was able to supply more calcium, but considerably less magnesium, than agricultural lime. The deficiency of magnesium will be of concern when ASB is applied on soils that are naturally deficient in magnesium. INTRODUCTION Increasingly stringent state and federal regulations for the management of wastewater biosolids have forced many utilities to develop alternative methods for disposal of biosolids. For example, the state of North Carolina no longer allows utilities to dispose of wastewater biosolids in unlined landfills. In addition, recent federal regulations, 40 CFR Part 503-Standards for the Use or Disposal of Sewage Sludge (Part 503), established new quality standards that utilities did not have to meet prior to One new method of biosolids treatment that is becoming more prevalent across the country is alkaline stabilization. The resulting product can possibly be used by the agricultural community as a liming material. Alkaline stabilization is a proven method that can readily meet the pathogen and vector attraction reduction standards of Part 503. Many methods of utilization for this alkaline stabilized biosolid have been proposed. They include use as a daily and final landfill cover, fill, soil conditioner, and as an agricultural liming agent. Alkaline stabilized biosolids can have a calcium carbonate equivalent (CC) of 75-85%, just slightly less than traditionally used agricultural lime, 90-95%. With this relatively high CC, ASB is an adequate liming material for use in the agricultural community. The treated wastewater biosolid can also supply small quantities of phosphorus and potassium for crop use. However, only a limited quantity of nitrogen would be available due to the loss of. William Rogers and Dr. Fred Cox, Dept. Soil Science, North Carolina State University, Raleigh, N.C.; Scott Carr, Black and Veatch, Charlotte, N.C.; Dr. Robert Holman, Water Resources Research Institute of The University of North Carolina, Raleigh, N.C.; Trille Mendenhall, Charlotte-Mecklenburg Utility Department, Charlotte, N.C. *Corresponding Author

2 nitrogen from the increased ph and temperature within the product. In the alkaline stabilization process a large amount of the nitrogen is driven off due to ammonia volatilization. Land application of wastewater biosolids has traditionally been based on the nitrogen availability from the material. Due to the limited amount of nitrogen present a new method of determining application rates needs to be evaluated. Soils used for agriculture production in North Carolina tend to be acidic. Of all the soils submitted to the Soil Testing Division of The North Carolina Department of Agriculture (NCDA) in 1994, 33% of the Piedmont, 5% of the Coastal Plain, and 43% of the Mountain soils needed lime applications. Also, 750,000 tons of lime were sold in North Carolina in 1993 and NCDA expects close to 1,000,000 tons of lime to be sold in The Urban Water Consortium of North Carolina decided to evaluate the possibility of using the alkaline stabilization practice for North Carolina utilities. In 199, the Water Resources Research Institute of The University of North Carolina was engaged by the consortium to perform a three- year investigation into the viability of alkaline stabilization. The research compared ASB with a standard agricultural dolomitic lime to determine the chemical properties of ASB, reaction rates of the materials, how long these reactions will continue, and how plant nutrition may be affected. MATRIALS AND MTHODS Alkaline stabilized biosolids used in all of the studies were provided by the Charlotte- Mecklenburg Utility Department (CMUD), a member of the Urban Water Consortium. In January 199, CMUD began operation of a 0 dry ton per day pilot alkaline stabilization facility at its McAlpine Creek Wastewater Management Facility. The pilot facility blends qr lick! ime (calcium oxide) with dewatered anaerobically digested biosolids. The biosolids are dewatered using centrifuges to reach a final product with approximately 0% total solids. Quicklime is blended with the biosolids using a Leopold Plowblender at approximately 1.4: 1.O on a dry weight basis. After blending, ASB is allowed to sit in a stockpile for a minimum of three days to promote cooling and allow for the volatilization of ammonia. The stockpile is periodically moved during this period. When the stabilized biosolids are ready for distribution, the total solid concentration ranges from 40 to 55 percent. Three types of studies were initiated to evaluate the effectiveness of ASB when compared to standard agricultural lime: incubation, greenhouse, and field. In the incubation study two soils were used to evaluate the effects of ASB and agricultural lime. These soils were selected to establish a range of clay and organic matter contents. Three soils were used in two greenhouse studies to examine the plant uptake of calcium and magnesium along with changes in soil ph. Lastly, three field experiments were conducted to evaluate changes in soil ph and elemental plant uptake from both liming sources over time. In the incubation study ASB and agricultural lime were applied at CC rates of 0,000, 4000, and 8000 lbs/acre to both a Cecil (clayey, kaolinitic, thermic Typic Kanhapludult) and a Goldsboro(fine-loamy, siliceous, thermic Aquic Paleudult) soil. lemental composition of both ASB and agricultural lime is given in Table 1. Soils were then wet to field capacity and placed in plastic bags on a laboratory bench at room temperature. Sub-samples were collected at 1,, 4, 8, and 16 weeks after application of liming materials. Soil samples were oven dried at 0" C and then ground to pass a mm sieve. ach sample was analyzed for ph, Ca, Mg, P, K, Cu,

3 8 Mn, and Zn. Soils were analyzed for ph using a water to soil ratio of 1 : 1. Cations and metals were extracted with the Mehlich I11 soil extracting solution (Mehlich, 1984) for Ca, Mg, K, Mn, Cu, and Zn and read by Atomic Absorption Spectrophotometry. Phosphorus was also extracted with Mehlich 111, then analyzed colorimetrically following the methods of Murphy and Riley, (196). Two greenhouse experiments were completed using both liming materials. In both greenhouse experiments the liming materials were applied to three soils: Cecil, Goldsboro, and Portsmouth (fine-loamy, mixed, thermic Typic Umbraquult). Both liming materials were applied at rates of 0, 000, 4000, and 8000 lbdacre. The ASB and agricultural lime were I incorporated into 8" pots lined with plastic bags. The rowcrop experiment had a rotation of corn (Zea mays L.), wheat (Triticum aestivum L.), and soybeans (Glycine ma L.). The corn and wheat were grown for six weeks and the soybeans for eight weeks. At the end of each period the crop was harvested. During harvest both soil and plant samples were collected; soil samples were analyzed as in the incubation experiment, while plant samples were dried in a forced-draft oven at 70" C for 48 hours, ground to pass a 1 mm sieve, dry ashed for 1 hours at 500" C in a muffle furnace, and dissolved in 6 M HCl. Phosphorus, Ca, Mg, K, Cu, Zn, Fe, Al, B, S, Cd, Cr, Pd, and Ni were determined by ICP (Inductively Coupled Plasma Spectrophotometer). The fescue greenhouse experiment used similar procedures as the first with the only variation being in the crop grown. Fescue (Festzrca arundinacea Schreb) was planted and harvested through cutting once every six weeks and analyzed to evaluate the elemental uptake from both liming sources. Plant samples were evaluated as in the previous greenhouse experiment. The first field experiment was located at the Fountain farm of the Upper Coastal Plain Research Station near Rocky Mount on a Roanoke loam (clayey, mixed, thermic Typi Ochraquult). The other two studies were initiated at the Piedmont Research Station near Salisbury on a Wilkes sandy loam (loamy, mixed, thermic, shallow Typic Hapludalc Goth ASB and agricultural lime were applied at calcium carbonate equivalency (CC) rates of 0, 1000, 000, and 4000 Ibdacre. In the Rocky Mount field study the materials were incorporated to a depth of 8" and corn was planted. Soil samples were collected to a depth of 8" in both the spring and fall of each year. Whole plant samples were collected six weeks after planting; earleaf samples were collected at anthesis, and grain samples were collected at harvest. Soil and plant samples were evaluated using the same methods as in the incubation and greenhouse studies. At the Piedmont Research Station two field studies were initiated to evaluate the effectiveness of ASB when compared to agricultural lime. In one experiment the liming materials were incorporated to a depth of 8". Following incorporation corn was planted. Soil and plant samples were collected and analyzed using the same procedures as in the study at Rocky Mount. In the second experiment the liming materials were topdressed onto an established pasture. A fescue harvest was conducted in both the spring and fall of each year. Plant and soil samples were collected with each harvest. Soil samples were taken to a depth of 4". Soil and plant samples were analyzed using the same procedures as in the incubation and greenhouse studies. RSULTS AND DISCUSSION CMUD's alkaline stabilized biosolids have metal concentrations well below the Pollutant

4 Concentration (PC) limits established in Part 503 (Table ). In addition to meeting the PC limits, CMUD's product meets the Class A pathogen reduction requirements and a vector attraction reduction requirement. Therefore, the product is considered to be of exceptional quality under Part 503 standards. In the incubation study there was a significant increase in soil ph from both the additions of ASB and agricultural lime. Figure 1 illustrates the change in soil ph over time with the addition of 8000 lbs/acre of ASB and agricultural lime at the same CC rate. The majority of the reaction was completed within the first week. Within the Goldsboro soil there was no significant difference between materials in the time needed to neutralize soil acidity. In contrast, ASB appeared not to have the same neutralizing capacity when compared to agricultural lime in the higher clay Cecil soil. The rowcrop greenhouse experiment also demonstrated no significant difference between the two materials in their ability to change soil ph (Figure ). In contrast to the incubation study however, there was not as rapid a change in soil ph over time. In the incubation study a large amount of the reaction occurred in the first week. However, in the greenhouse study it required 1 weeks for a significant amount of the reaction to occur. This is most likely due to the optimal conditions that were maintained in the incubation study, while in the greenhouse study there was a fluctuation in soil temperature and moisture. Also, in contrast with the incubation study, ASB tended to reduce soil acidity slightly better than did the agricultural lime. This was probably due to the particle size differences between the two materials. ASB has finer size particles than does the agricultural lime, thus allowing it to react more quickly than agricultural lime. In the rowcrop greenhouse study with the addition of ASB there was an increase in the plant calcium concentrations, but a decrease in the plant magnesium concentrations when compared to agricultural lime. As seen in Figure 3 the magnesium concentrations of the Cecil soil were above a critical level of.0 g/kg. But, in the Portsmouth soil these corn and soybean plant magnesium levels were below the critical level for optimal plant growth. These differences can be explained by the fact that Cecil soils are higher in natural magnesium than the coastal plain Portsmouth soil, and that ASB contains little magnesium. There was a significant difference in the plant calcium and magnesium concentrations of the fescue greenhouse experiment in each of the four cuttings (Figure 4). With the addition of ASB there was an increase in plant calcium and decrease in plant magnesium when compared to agricultural lime, Figure 5 illustrates the calcium and magnesium plant concentrations at the different stages of corn growth in the field study at Rocky Mount. Again there was an increase in plant calcium and a decrease in plant magnesium with the addition of ASB when compared to agricultural lime. The plant magnesium was again found to be below.0 g/kg with the addition of ASB but not with the addition of agricultural lime. Agricultural lime seems to be able to provide sufficient magnesium for optimal plant growth. However, the pasture study at Salisbury had the same plant nutrient concentration trends as the study at Rocky Mount. But, the magnesium concentrations are not below.0 g/kg (Figure 6). The Wilkes soil in the Piedmont at Salisbury is naturally higher in soil magnesium than the Roanoke soil in the Coastal Plain at. Rocky Mount. Figure 7 represents the change in soil ph over time for the pasture study at Salisbury. This is representative of the other two field studies. ASB was able to neutralize soil acidity more rapidly than agricultural lime. Near the end of this sampling period agricultural lime is slowly beginning to be able to neutralize the same amount of soil acidity as ASB. The

5 longer overall reaction period for agricultural lime was due to the slower reacting, coarser particles. CONCLUSIONS The alkaline stabilized biosolid was found to meet all State and Federal regulations, making it a usable product by the agricultural community. ASB was able to neutralize soil acidity as well as agricultural lime at the same CC application rate. ach different batch of ASB will need to be evaluated for its CC, and application rates adjusted accordingly. Due to. the finer particle size of ASB it reacts more quickly than agricultural lime under greenhouse and field conditions. This quicker reaction time may be of interest to farmers who are renting land and need a quicker reacting liming material than the standard dolomitic lime. The alkaline stabilized biosolid was able to supply more calcium but less magnesium to plants than. agricultural lime. In soils not deficient in magnesium, ASB will neutralize soil acidity and supply large amounts of calcium. But, in magnesium deficient soils there will be a need to add supplemental magnesium for optimal plant growth. RFRNCS Mehlich, A Mehlich-3 soil test extractant: A modification of Mehlich- extractant. Commun. Soil Sci. Plant Anal. 15: Murphy, J. and J.P. Riley A modified single solution method for the determination of phosphate in natural waters. Anal. Chem. Acta 7: Table 1. Calcium carbonate equivalency (CC) and elemental composition of alkaline stabilized biosolid and agricultural lime. CC N Ca Mg P K S Fe Mn Zn Cu B ~ ~~ na = not analyzed

6 Table. Metal composition of alkaline stabilized biosolid and Part 503 regulations. As Cd Cr Cu Hg Mo Ni Pb Se Zn Alkaline stabilized biosolid Figure 1. ffects of ASB and agricultural lime on soil ph over time on (A) Cecil and (B) Goldsboro soils in the incubation experiment 6.5 I =e a m * lb/acre Ag Lime 8000 lb/acre ASB Check.... * *.""'... I I I I I I

7 Figure. ffects of ASB and agricultural lime on soil ph with time when applied to (A) Cecil, (B) Goldsboro, and (C) Portsmouth soils in the greenhouse Figure 3. Magnesium concentrations of com. wheat. and soybeans grown in the greenhouse with applications of ASB and agricultural lime on (A) Cecil and (B) portsmouth soils (A) 7.5, I ~ P 1 So00 Iblacre ASB 0 SOOOIb/acrc AgLime 0 Check J 14 a Check 1, Ib/acrc Ag Lime -- CUI $,8 0 ^^ I (C) t

8 Figure 4. Calcium and magnesium concentrations in fescue grown for 4 weeks in the greenhouse on (A) Cecil and (B) Goldsboro soils. (A) n 10 v s 8 ' 6 (A) : 5 0 Check J 8000 Ib/acre Ag Lime Iblacre ASB t 1 n 10- ' 5 v 8: 6; n- " r i 8 8t Z 6 v 4 n "

9 .- e I m v1 8 IA.- e 1.w v1 e, C M I ml 1 "- x N* e?.- 1 M LL I I I I d- M r4 d 0 ck e M cr 0 Y l o m i I f r: q!.i 3 U ce 8 c rn e, C tq 3 : CQ 3 IW

10 Figure 7. Changes in soil ph over time for the pasture study at S a1 is bury t W 4000 lb/acre ASB 6.6 z.- P, m I, I I I I I I I I Days after application