Fate of Pharmaceuticals in the Environment and in Water Treatment Systems - Chapter 14 doc

339 14.5.3 Inhibition of Anaerobic Biodegradation by Antibiotics in Swine Lagoons ..... Land application of liquid slurry from anaerobic lagoons or storage basins, and anaerobic digester

in Swine Wastewater

Craig D Adams

14.1 INTRODUCTION

The formation and occurrence of antibiotic-resistant bacteria (especially pathogens)

in the environment are of significant concern to society, and are the specific focus of the scientific and regulatory communities In animal agriculture in the United States and elsewhere, antibiotics are provided to swine for therapeutic reasons, as well as for growth promotion Many antibiotics that are fed to or injected into swine may pass through the swine unmetabolized and, therefore, end up in the swine manure that is passed into the treatment system Accordingly, it is of considerable interest that an economical and effective means of treating these antibiotics prevent or minimize their introduction into the environment during their field application(Figure 14.1)

Contents

14.1 Introduction 331

14.2 Typical Manure Handling Systems for Swine 332

14.2.1 Interior Storage 332

14.2.2 Exterior Storage and Treatment 333

14.2.3 Multicell Lagoon Systems 334

14.2.4 Anaerobic Digestion 334

14.3 Sorption of Antibiotics in Swine Lagoons 336

14.4 Hydrolysis of Antibiotics in Lagoons 337

14.5 Biological Treatment of Antibiotics in Conventional Swine Treatment Systems 337

14.5.1 Anaerobic Biodegradation 338

14.5.2 Aerobic Biodegradation 339

14.5.3 Inhibition of Anaerobic Biodegradation by Antibiotics in Swine Lagoons 339

14.6 Chlorine Treatment for Antibiotics in Swine Wastewater 340

14.6.1 Antibiotic Removal 340

14.6.2 Simultaneous Disinfection 342

14.6.3 Comparison of Selected Classes of Antibiotics 345

14.7 Other Treatment Approaches 345

14.8 Concluding Remarks 346

References 347

14.2 TYPICAL MANURE HANDLING SYSTEMS FOR SWINE

Swine manure is a mixture of urine and feces, which often contains significant con-centrations of antibiotics and hormones Swine manure may typically contain only

10 to 20% solids and, therefore, is generally in slurry form Thus, swine manure gen-erally cannot be handled using solids handling equipment Lagoon slurry is usually discharged through direct land application to croplands While the slurry has sig-nificant nutrient value, it may also contain antibiotics, hormones, antibiotic-resistant organisms, as well as excessive phosphorus and other problematic contaminants Land application of liquid slurry from anaerobic lagoons or storage basins, and anaerobic digesters, is typically achieved by using irrigation-type equipment These systems include stationary spray guns, sprinkler systems, and controlled flooding

14.2.1 I NTERIOR S TORAGE

Swine manure from confined production facilities is often stored in either interior (underfloor) or exterior (lagoon) storage basins (Miner et al., 2000) The underfloor basin or pit is located directly beneath the slatted floor of the building housing the swine (Figure 14.2) The swine manure, along with excess food and other solids, falls or is periodically rinsed down into the underfloor pit Maximum storage time

in a typical underfloor pit may range from 5 to 12 months (Miner et al., 2000) Ven-tilation of the underfloor pits is critical to remove noxious gases such as hydrogen sulfide and ammonia, as well as carbon dioxide and methane, from the confinement building Prior to removal from the pit, the manure must be agitated to homogenize

it so that all of it can be completely removed from the pit, and to ensure that the

FIGURE 14.1 Sludge pump used to transfer lagoon slurry from lagoon to adjacent fields.

Treatment of Antibiotics in Swine Wastewater 333

removed manure has uniform nutrient characteristics Agitation is usually achieved using pumps placed in multiple locations along the pit wall (Miner et al., 2000) The discharge from underfloor storage is generally applied to surrounding fields as a fer-tilizer, although it is usually nonoptimal relative to nutrient p:n ratios

14.2.2 E XTERIOR S TORAGE AND T REATMENT

An alternative to an underfloor storage basin is the exterior storage basin, commonly referred to as a “lagoon.” Occasionally, exterior storage of manure is instead accom-plished by using a tank located outside the building; this is far less common, how-ever, than the use of a lagoon Generally, swine manure is collected using a slatted floor design, and then periodically (e.g., twice per day) flushed with water to move it from the building

In the simplest design, the manure flows to a single- or two-stage lagoon for stor-age and treatment, followed by periodic land application A variation of this system first provides for liquid-solid separation, after which the solids may be composted and the liquid passed to a lagoon for storage and treatment, prior to land application (Miner et al., 2000)

In a more sophisticated system, the waste from the barn is mixed and pumped into an anaerobic digester Methane generated in the process provides for energy recovery The effluent from the anaerobic digester is often pumped into an anaerobic lagoon for storage and treatment, followed by land application (Miner et al., 2000)

A variety of lagoon systems are used for swine wastewater treatment A lagoon system may be a single cell, or may contain multiple cells in series Generally, lagoons are not aerated and are, therefore, anaerobic In some cases an aerated cell

is used for enhancing ammonia removal

FIGURE 14.2 Inside a swine barn at a typical concentrated animal feed operation.

In a standard anaerobic lagoon, swine manure is stored until the time of year that

is amenable for field application, that is, when the nutrients are needed and the ground

is not frozen Additionally, some treatment of the manure is achieved in the lagoon and the quality of the slurry changes with time In general, solids are decreased, which makes the slurry much more amenable to field application (Miner et al., 2000) Key differences between an anaerobic digester and an anaerobic lagoon for swine waste treatment are that lagoons have no temperature control and cannot capture methane for energy recovery (unless appropriately covered) Depending on the region, in the colder winter months, anaerobic activity in a lagoon may be very low relative to that

in the warmer summer months As temperatures increase during the transition from winter to summer, the excess stored organic matter may cause enhanced anaerobic activity until stored organic loads are reduced (Miner et al., 2000)

14.2.3 M ULTICELL L AGOON S YSTEMS

Two- and three-celled lagoon systems, in series, are also used at some facilities Typically, the first cell is operated as in a single-cell system Most solids are retained

in the first cell, which provides for additional solids decomposition In the final cell, algae often may thrive, allowing better slurry treatment (Miner et al., 2000) Addi-tionally, aeration is sometimes added to the final cell to improve effluent quality Multicelled systems are more common when the lagoon water is to be used as the flushing water for the barns

As an example of typical treatment parameters, characteristics of swine barn wastewater in two different lagoon systems studied by Qiang et al (2006) are pre-sented inTable 14.1 For Lagoon System A, comparison of the influent (A-INF) and effluent (A-EFF) from the first of two anaerobic cells showed a significant reduction

in soluble chemical oxygen demand (SCOD) and dissolved organic carbon (DOC), while ammonia, alkalinity, pH, and UV adsorption all increased (Table 14.1) Com-parison of the influent into the second (overflow) cell and its bulk concentration (A-OV) (which is periodically land applied), showed a further reduction of SCOD and COD, as well as ammonia (Table 14.1)

A second two-cell lagoon system was also studied (Lagoon B) that was similar to Lagoon System A, except that the first cell of the lagoon was aerated Similar treat-ment was achieved for SCOD and DOC However, a much lower ammonia concen-tration was achieved in the effluent of the first (aerated) cell (B-EFF), which helped achieve a very low final ammonia concentration (B-OV) in the second (nonaerated) cell The slurry from this second cell is periodically land applied

14.2.4 A NAEROBIC D IGESTION

Swine manure is also amenable to treatment in an anaerobic digester An anaerobic digester is enclosed so as to capture product gases (e.g., hydrogen sulfide, ammonia, methane, and carbon dioxide) and to allow efficient treatment of the swine waste However, because this level of efficient waste treatment is not required in the United States for CAFO wastes, the perceived cost associated with anaerobic digesters has limited their use for swine manure treatment in the United States The use of

TABLE 14.1

Mean Physical-Chemical Properties of Wastewaters from Two Swine Lagoons

Properties

Lagoon A Raw Waste from Barn (AINF)

Lagoon A Bulk Slurry from 1st (Anaerobic) Cell (A-EFF)

Lagoon A Bulk Slurry from 2nd (Anaerobic) Cell (A-OV)

Lagoon B Raw Waste from Barn (BINF)

Lagoon B Bulk Slurry from 1st (Aerated) Cell (B-EFF)

Lagoon B Bulk Slurry from 2nd (Anaerobic) Cell (B-OV)

Soluble COD (mg/L) 1102 302 145 104 248 126

Dissolved Organic Carbon (mg/L) 385 117 73 359 80 42.7±5.2

Alkalinity (mg/L) 513 1405 620 539 723 2351

Total Dissolved Solids (mg/L) 1370 2510 1360 1430 1570 680

Conductivity (uS) 2060 3760 2035 2140 2350 1030

Specific UV Absorbance (L/mg-m) 0.5 1.9 1.6 0.5 1.8 1.5

Source: Qiang et al., Ozone Science and Engineering 26, 1–13, 2006 (With permission.)

* ND = Not Detected

© 2008 by Taylor & Francis Group, LLC

anaerobic digesters may increase, however, as more emphasis is placed on energy recovery, odor control, and more effective waste treatment than is provided by open storage basins or lagoons

14.3 SORPTION OF ANTIBIOTICS IN SWINE LAGOONS

Sorption of antibiotics to biosolids is an important mechanism that affects whether an antibiotic would likely be in the aqueous phase vs sorbed to biosolids Furthermore, antibiotics that strongly sorb to biosolids may tend to exist in the settled solids, while weakly sorbed antibiotics may tend to exist predominantly in the slurry If a lagoon is not mixed prior to land application, only the antibiotics in the slurry may be predomi-nantly introduced to the environment If the lagoon is mixed prior to land application, all antibiotics in the lagoon may, in that case, be released to the environment The linear sorption coefficient (KD) (L/kg) between an antibiotic and biosolids

in a treatment process represents the concentration of an antibiotic sorbed (µg/kg) relative to its concentration in the liquid phase (µg/L) The linear KDmodel is very often used to model sorption of pharmaceuticals in sediment, solids, and soils due

to the linearity of isotherms at low adsorbate concentrations Because there are a variety of mechanisms for sorption of pharmaceuticals on the organic and inorganic solids in treatment processes, prediction of KDis complex Sorption onto solids can involve a variety of mechanisms, including absorption into organic carbon, adsorp-tion to mineral surfaces, ion exchange, and chemical reacadsorp-tions (Schwarzenbach et al., 2003) Similarly, equilibrium solubility of the antibiotic in the aqueous phase can

be affected by many factors, including temperature, dissolved solids, and pH Kurwadkar et al (2007) investigated the effects of sorbate speciation on the sorption of selected sulfonamides in three loamy soils Sulfonamides predominantly exist as anions at pH levels above their respective pK2values (5.3–7.5) (Qiang and Adams, 2004), as neutral species at pH between their respective pK2and pK1values (1.9–2.1) (Qiang and Adams, 2004), and as cations below their respective pK1values

An effective KDcan be estimated using a weighted KDvalue approach

(Schwarzen-bach et al., 2003; Kurwadkar et al., 2007), that is:

KD,effective=Bcationic·KD,cationic+Bneutral·KD,neutral+Banionic·KD,anionic

where KD,cationic, KD,neutral, and KD,anionicare the linear partition coefficients for the cationic, neutral, and anionic species, respectively, andBcationic,Bneutral, andBanionic are the fractions of each species present at a specific pH While this study addressed sorption to soils rather than biosolids, the same general principles are likely to apply

in biosolids Extrapolating to biosolids, sulfonamides may be expected to sorb much less at a higher pH (above their pK2) due to the predominance of the anionic form and much more at a lower pH (between their pK1and pK2) where the neutral form predominates and sorption to organic carbon in biosolids may be more significant Typical values for log KD are 4 tetracyclines, 3 for tylosin, and 1 for sulfon-amides (Loftin et al., 2004) Therefore tetracyclines and tylosin would tend to sorb strongly to settled biosolids in a lagoon, whereas sulfonamides may appear in the aqueous phase to a much larger degree

Treatment of Antibiotics in Swine Wastewater 337

Related work by Vieno et al (2007) examined removal of antibiotics, as well as other pharmaceuticals, in a municipal wastewater treatment plant in Finland The study concluded that the ciprofloxacin is readily “eliminated” from wastewater by sorption to biosolids due to high KDor KOWvalues (e.g., >4)

14.4 HYDROLYSIS OF ANTIBIOTICS IN LAGOONS

Antibiotics have opportunities to hydrolyze in storage basins, anaerobic lagoons, and other treatment systems Hydrolysis studies by Loftin et al (2007) were conducted

in deionized lab water and filtered lagoon slurry as a function of pH (2−11), tem-perature (7 to 35°C), and ionic strength This study showed that lincomycin (LNC), trimethoprim (TRM), sulfadimethoxine (SDM), sulfathiazole (STZ), sulfachlorpyr-idazine (SCP), and tylosin A (TYL) were recalcitrant to hydrolysis in lagoon slurry for pH 5, 7, and 9 At a higher pH of 11, limited hydrolysis of TYL was observed

On the other hand, the tetracyclines—oxytetracycline (OTC), chlorotetracycline (CTC), and tetracycline (TET)—were all readily hydrolyzed under anaerobic lagoon conditions at pH levels of 5, 7, 9, and 11 (Figure 14.3) Researchers, including Loftin

et al (2007), have noted that a wide range of hydrolysis byproducts of the tetra-cyclines occur under different conditions, including epi-, iso-, epi-iso-, anhydro-, and epi-anhydro-analogues More study is warranted of the partitioning behavior

of these compounds to estimate their mobility relative to the corresponding parent tetracyclines For a temperature of 22°C or greater, half-lives of OTC, CTC, and TET were 16 hours or less (Loftin et al., 2007) At colder temperatures (e.g., 7°C), nearly an order-of-magnitude slower hydrolysis was observed Due to the significant seasonal temperature fluctuations observed in many swine lagoons, a wide range of hydrolysis rates for tetracyclines would be expected, depending on both tempera-ture and pH However, due to long holding times, on the order of months, complete hydrolysis to below detection would often be expected

Tylosin underwent no hydrolysis in the pH range 5 to 9, but was readily degraded

or labile at alkaline pH (>11) at temperatures of 22°C or greater Thus, tylosin would not be expected to undergo appreciable hydrolysis in swine lagoon pH levels These results suggest that tylosin, lincomycin, and the sulfonamides would be expected

to be recalcitrant to abiotic degradation (hydrolysis) in swine lagoons In warmer seasons or locations, oxytetratracycline and related compounds might be expected to hydrolyze to some greater or lesser degree

14.5 BIOLOGICAL TREATMENT OF ANTIBIOTICS

IN CONVENTIONAL SWINE TREATMENT SYSTEMS

When antibiotics enter a treatment lagoon, there are many potential transforma-tion and partitransforma-tioning reactransforma-tions that can potentially occur Transformatransforma-tion reactransforma-tions include anaerobic or aerobic biodegradation depending on redox conditions, hydro-lysis, and photolysis Partitioning reactions for antibiotics in a common treatment lagoon are primarily to suspended and settled solids In the subsequent sections, these potential removal mechanisms are discussed in more detail

14.5.1 A NAEROBIC B IODEGRADATION

Very few studies have investigated the biodegradation of antibiotics in anaerobic swine lagoons Anaerobic biodegradation in swine lagoon slurry was studied by Lof-tin et al (2004) in laboratory microcosm experiments In this work, soluble COD was readily removed In these microcosms, sulfathiazole exhibited little degradation over a 2-month period (half-life = 222 days), suggesting that sulfathiazole would likely be biorecalcitrant under anaerobic conditions This persistence also suggests overall concerns with sulfonamides in swine lagoons, that is, their presence in slurry applied to the environment Similarly, lincomycin also was persistent with a half-life

of 78 days in one slurry and no degradation in another

Oxytetracycline, on the other hand, appears much more readily biodegradable under anaerobic conditions with half-lives of approximately 1 month in two different slurries For example, with a 3-month treatment time, the concentrations of oxytetra-cycline decreased to only 12% of its initial value Tylosine was observed to degrade even more readily under anaerobic conditions with a half-life of approximately 1 day

OH

HO Cl

OH

OH

NH2 OH

O

N

HO

HO

OH

NH2 HO

N H

HO

OH

NH2 OH

N H

FIGURE 14.3 Structures of chlorotetracycline (top), oxytetracycline (middle), and

tetracy-cline (bottom) (Courtesy of ChemFinder 2004, Cambridgesoft Corp.)

Treatment of Antibiotics in Swine Wastewater 339

in both swine lagoon slurries studies Abiotic degradation rates were much slower (i.e., approximately 2 weeks) in the same autoclaved slurries

Thus, the amount of anaerobic biodegradation treatment of antibiotics that would

be expected is highly dependent on the nature of the antibiotics While the sulfonamide and lincosamide were relatively recalcitrant, the tetracycline and macrolide were rela-tively easily degraded More studies are needed in order to be able to realistically estimate and model the anaerobic biodegradation of antibiotics in swine lagoons

14.5.2 A EROBIC B IODEGRADATION

Relatively little information is available on aerobic biodegradation of antibiotics in acti-vated sludge, aerated lagoons, or other processes Work by Ingerslev et al (2001) suggests that antibiotics may generally degrade much more rapidly under aerobic conditions than under anaerobic conditions They examined tylosin, oxytetracycline, metronidazole, and olaquindox in laboratory microcosms and demonstrated that for these antibiotics, aerobic biodegradation was significantly more rapid than anaerobic biodegradation The use of aerated lagoons, and aerated “caps” (an aerobic zone as the surface layer) on anaerobic lagoons, is a potentially viable option for more effectively treat-ing antibiotics in swine wastewater treatment systems An aerated “cap” is created by oxygenating the surface layer sufficiently to maintain dissolved oxygen at the surface

on an otherwise anaerobic lagoon More research in needed to better develop, opti-mize, and implement this technology

14.5.3 I NHIBITION OF A NAEROBIC B IODEGRADATION

BY A NTIBIOTICS IN S WINE L AGOONS

Swine manure consists of a complex mixture of fats, carbohydrates, and proteins Anaerobic biodegradation of swine manure occurs by a series of metabolic steps, specifically: (1) conversion of complex organics to volatile fatty acids by fermenta-tive organisms; (2) conversion of volatile fatty acids to acetate and hydrogen by fatty-acid oxidizing organisms; and (3) conversion of acetate and hydrogen to methane by methanogens (archea) Because antibiotics may often be present in swine manure and, hence, in the swine lagoon slurry, there is potential for the antibiotics to nega-tively impact the anaerobic biodegradation of other waste constituents in a lagoon Work by Loftin et al (2005) investigated the inhibition of anaerobic biological activity in swine lagoon slurry in lab-scale microcosm experiments This work mon-itored the impacts of varying concentrations of sulfonamides, tetracycline, linco-mycin, and tylosin on the production of methane, hydrogen, and volatile fatty acids, including acetate

These studies showed a significant (20 to 50%) inhibition of methane production for all of the antibiotics studied Furthermore, antibiotic dosages of 1, 5, and 25 mg/L

of a specific antibiotic all caused similar inhibitions, which in general plateaued at approximately 20 to 45% Sanz et al (1996) also saw a plateauing effect for ampi-cillin, novobiocin, peniampi-cillin, kanamycin, gentamicin, spectinomycin, streptomycin, tylosin, and tetracyclines over a wide range of inhibition (from 0 to 100%) This rapid plateauing in the inhibition of methane productions suggested that there exist certain

bacterial subpopulations within the slurry that are greatly inhibited by antibiotics (even at low antibiotic concentrations [e.g., 1 mg/L]), while others are resistant to the effects of the antibiotics

In the work by Loftin et al (2004), no buildup of acetate or hydrogen was observed, suggesting that the methanogens were the microbial population most sig-nificantly inhibited as might most commonly be anticipated Similarly, volatile fatty acids were not observed to build up in concentration, suggesting that the fatty-acid oxidizing organisms were not the most inhibited population Thus this work sug-gested, but did not prove, that the fermentative organisms were the most significantly inhibited microbial population

A key consequence of this observed inhibition of anaerobic metabolism in lagoons is that the presence of antibiotics may reduce the amount of manure degra-dation achieved in a swine waste treatment system Furthermore, these findings sug-gest that if the amount of antibiotics entering a lagoon could be reduced then more effective treatment might be achieved Finally this reduction in antibiotics could potentially be attained by pretreating the wastewater between a barn and the bio-logical treatment system to remove antibiotics, or by reducing the application rate of antibiotics given to the swine For example, by eliminating the use of antibiotics for growth promotion (where it is still practiced), the problem could possibly be mini-mized or reduced

14.6 CHLORINE TREATMENT FOR ANTIBIOTICS

IN SWINE WASTEWATER

14 6.1 A NTIBIOTIC R EMOVAL

Chlorine treatment of wastewater from a barn, prior to discharge into a treatment process, is a potential means of removing antibiotics that could promote antibiotic-resistant bacterial growth within the lagoon, or may inhibit anaerobic activity within the lagoon Chlorine treatment of treated wastewater (e.g., lagoon slurry) prior to field application is, similarly, a potential method for removing antibiotics, thereby preventing their introduction into the environment Chlorine treatment prior to field application may also have potential for removing antibiotic-resistant bacteria, thereby preventing their release into the environment

The pH has been shown to have a highly significant effect on the oxidation rates

of selected antibiotics due to the speciation of the stronger hypochlorous acid (HOCl)

to the weaker hypochlorite ion (OCl-) (Chamberlain and Adams, 2006) Because the acid dissociation constant for HOCl/OCl-is approximately 7.6, at pH levels greater than 7.6, hypochlorite will be the most prevalent oxidant species of the two Oxidation of antibiotics and disinfection of antibiotic resistant bacteria by indi-vidual addition of free chlorine or monochloramine were studied by Qiang et al (2006) The study looked at the oxidation of sulfonamides (sulfamethizole [SML], STZ, sulfamethazine [SMN], sulfamethoxazole [SMX], and SDM) in influents and effluents from two lagoon systems Both lagoon systems had two cells in series, with one of the lagoons utilizing aeration in its first cell In laboratory experiments,