Fate of Antibiotics and Antibiotic Resistance during Digestion and Composting: A Review.

Antibiotics and antibiotic-resistant bacteria (ARB) enter the environment through municipal and agricultural waste streams and pose a potential risk to human and livestock health through either direct exposure to antibiotic-resistant pathogens or selective pressure on the soil microbial community. This review summarizes current literature on the fate of antibiotics, ARB, and antibiotic resistance genes (ARGs) during anaerobic digestion and composting of manure and wastewater residuals. Studies have shown that removal of antibiotics varies widely during mesophilic anaerobic digestion, even within the same class of antibiotics. Research on ARB shows a wide range of removal under mesophilic conditions, with nearly complete removal under thermophilic conditions. Research on 16 antibiotics in 11 different studies using both bench-scale and farm-scale composting systems demonstrates that composting significantly reduces levels of extractable antibiotics in livestock manure in nearly all cases. Calculated half-lives ranged from 0.9 to 16 d for most antibiotics. There is more limited evidence that levels of ARB are also reduced by composting. Studies of the fate of ARGs show mixed evidence for removal during both mesophilic and thermophilic anaerobic digestion and during thermophilic composting. Antibiotic resistance genes are DNA structures, so they may persist until the DNA structure is degraded, yet the bacterium may have been rendered nonviable long before the DNA is completely degraded. Additional research would be of value to determine optimum anaerobic digestion and composting conditions for removal of ARB and to increase understanding of the fate of ARGs during anaerobic digestion and composting.

Intermittent rainstorms cause pulses of nitrogen, phosphorus, and copper in leachate from compost in bioretention systems.

Bioretention systems rely on vegetation and mixtures of soil, sand, and compost to filter stormwater runoff. However, bioretention systems can also leach metals and nutrients, and compost may be a major contributor to this leaching. To safely implement bioretention systems, it is crucial to determine the composition of compost leachate. We characterized and quantified the leachate composition of compost following intermittent, simulated storm events. Columns of municipal compost were irrigated to simulate 6-month, 24-hour rain storms in the Seattle-Tacoma region. Outflow was analyzed for pH, electrical conductivity (EC), particulate concentration, surface tension, dissolved organic carbon (DOC), nitrogen, phosphorus, and copper. Results indicate a decrease of chemical concentrations over the course of individual storms and following repeated storms, but each new storm released another peak of constituents. The decrease in phosphorus, copper, and DOC concentrations with repeated storms was slower than for nitrate and EC. Nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR) showed that the DOC consisted mainly of aliphatic and aromatic components typical of fulvic and humic acids. Less than 3% of the original copper content from the compost leached out even after nine storm events. Nonetheless, copper concentrations in the leachate exceeded regulatory discharge standards. Our results show that compost can serve as a sustained source of leaching of nutrients and metals.

Biosolids applications to tall fescue have long-term influence on soil nitrogen, carbon, and phosphorus.

Repeated applications of biosolids provide long-term benefits by increasing soil organic matter and N supply but can cause excess accumulation of P. Our objective was to determine the residual effects of repeated surface applications of biosolids on N availability and fate, tall fescue ( Schreb.) response, soil C, and P. A field experiment was started in 1993 to compare two biosolids products, each applied at three rates (6.7, 13.4, and 20.1 Mg ha yr), with synthetic N fertilizer (0 and 403 kg N ha yr as ammonium nitrate). Treatments were surface applied for 10 yr, followed by a 9-yr residual period where all plots received a reduced rate of inorganic N (202 kg N ha yr). Annual measurements included forage yield, N uptake, and soil nitrate N. Soil samples collected in 2002 and 2011 were analyzed for total C and N and Bray-1 P. Cumulative apparent N recoveries in harvested grass (1993-2010) were 51% for biosolids N and 72% for ammonium nitrate. Net fall soil nitrate N summed for the period 1993-2002 ranged from <1 to 3% of N applied. The N applied that was accounted for in forage and soil averaged 74% for biosolids and 73% for ammonium nitrate. Soil C increased in the biosolids treatments, and the increase was equivalent to 27% of biosolids C. Bray-1 P remained at excessive levels (338-629 mg P kg soil) 9 yr after the last biosolids application.

Long-term crop and soil response to biosolids applications in dryland wheat.

Biosolids have the potential to improve degraded soils in grain-fallow rotations. Our objectives were to determine if repeated biosolids applications in wheat ( L.)-fallow could supply adequate but not excessive N for grain production and increase soil C without creating a high risk of P loss. A replicated on-farm experiment was established in 1994 in central Washington, comparing anaerobically digested biosolids with anhydrous NH and a zero-N control. Biosolids were applied at 5, 7, and 9 Mg ha every fourth year through 2010 and incorporated 10 cm deep, while anhydrous NH plots received 56 kg ha N every second year. Grain yield and protein were determined. Soil chemical, biological, and bulk density analyses were made in 2012. Medium and high biosolids rates significantly increased grain yield (3.63 vs. 3.13 Mg ha) and protein (103 vs. 85 g kg) compared with anhydrous NH averaged across all crops. The medium biosolids rate had significantly lower bulk density (1.05 vs. 1.22 g kg) and greater total C (0-10-cm depth) (16.9 vs. 9.4 g kg), mineralizable N (156 vs. 52 mg kg), and extractable P (114 vs. 16 mg kg) than anhydrous NH. The P index site vulnerability increased from low for anhydrous NH to medium for the biosolids treatments. Soil NO-N was nearly always <10 mg N kg soil (0-30-cm depth). Medium and high biosolids rates significantly increased bacteria/fungi ratios, Gram-negative bacteria, and anaerobic bacteria markers compared with anhydrous NH. Biosolids can be an agronomically and environmentally sound management practice in wheat-fallow systems.

Gaseous nitrogen and bacterial responses to raw and digested dairy manure applications in incubated soil.

A study was conducted under laboratory conditions to compare rates of nitrous oxide (N(2)O) and ammonia (NH(3)) emissions when soil was amended with anaerobically digested dairy manure slurry containing <30% food byproducts, raw dairy manure slurry, or urea. Slurries were applied via surface and subsurface methods. A second objective was to correlate genes regulating nitrification and denitrification with rates of N(2)O production, slurry treatment, and application method. Ammonia volatilization from incubated soil ranged from 140 g kg(-1) of total N applied in digested slurry to 230 g kg(-1) in urea. Subsurface application of raw dairy manure slurry decreased ammonia volatilization compared with surface application. Anaerobic digestion increased N(2)O production. Cumulative N(2)O loss averaged 27 g kg(-1) of total N applied for digested slurry, compared with 5 g kg(-1) for raw dairy slurry. Genes of interest included a 16S rRNA gene selective for ß-subgroup proteobacterial ammonia-oxidizers, amoA, narG, and nosZ quantified with quantitative polymerase chain reaction (qPCR) and real-time polymerase chain reaction (RT-PCR). Application of anaerobically digested slurry increased nitrifier and denitrifier gene copies that correlated with N(2)O production. Expression of all genes measured via mRNA levels was affected by N applications to soil. This study provides new information linking genetic markers in denitrifier and nitrifier populations to N(2)O production.

Validation of a 2 percent lactic acid antimicrobial rinse for mobile poultry slaughter operations.

Poultry processing antimicrobial interventions are critical for pathogen control, and organic, mobile operations in Washington seek alternatives to chlorine. Laboratory and field studies (three replications each) evaluated lactic acid efficacy as a chlorine alternative. For the laboratory study, retail-purchased, conventionally processed chicken wings inoculated with Salmonella were randomly assigned to the following treatments: Salmonella inoculation followed by no treatment (10 wings) or by 3-min rinses of water, 50 to 100 ppm of chlorine, or 2% lactic acid (20 wings for each rinse treatment). Wings were sampled for Salmonella enumeration on xylose lysine desoxycholate agar. During pastured poultry processing at mobile slaughter units for each field study replication, 20 chicken carcasses were randomly assigned to each treatment: untreated control or 3-min immersion in lactic acid or chlorine. Whole-carcass rinses were examined for aerobic plate count (APC) on tryptic soy agar and coliforms on violet red bile agar. Untreated controls were also examined for Salmonella. In the laboratory study, lactic acid produced a significant (P < 0.01) Salmonella reduction compared with the inoculated no-rinse, water, and chlorine treatments, which were statistically similar to each other. In the field study, no Salmonella was detected on untreated controls. Lactic acid produced significant >2-log (P < 0.01) reductions in APC and coliforms, whereas chlorine resulted in slight, but significant 0.4-log reductions (P < 0.01) and 0.21-log reductions (P < 0.05) in APC and coliforms compared with untreated controls. Considering laboratory and field studies, lactic acid produced greater reductions in Salmonella, APC, and coliforms, validating its effectiveness as a chlorine alternative in mobile poultry slaughter operations.

Estimating plant-available nitrogen release from manures, composts, and specialty products.

Recent adoption of national rules for organic crop production have stimulated greater interest in meeting crop N needs using manures, composts, and other organic materials. This study was designed to provide data to support Extension recommendations for organic amendments. Specifically, our objectives were to (i) measure decomposition and N released from fresh and composted amendments and (ii) evaluate the performance of the model DECOMPOSITION, a relatively simple N mineralization/immobilization model, as a predictor of N availability. Amendment samples were aerobically incubated in moist soil in the laboratory at 22 degrees C for 70 d to determine decomposition and plant-available nitrogen (PAN) (n = 44), and they were applied preplant to a sweet corn crop to determine PAN via fertilizer N equivalency (n = 37). Well-composted materials (n = 14) had a single decomposition rate, averaging 0.003 d(-1). For uncomposted materials, decomposition was rapid (>0.01 d(-1)) for the first 10 to 30 d. The laboratory incubation and the full-season PAN determination in the field gave similar estimates of PAN across amendments. The linear regression equation for lab PAN vs. field PAN had a slope not different from one and a y-intercept not different than zero. Much of the PAN released from amendments was recovered in the first 30 d. Field and laboratory measurements of PAN were strongly related to PAN estimated by DECOMPOSITION (r(2) > 0.7). Modeled PAN values were typically higher than observed PAN, particularly for amendments exhibiting high initial NH(4)-N concentrations or rapid decomposition. Based on our findings, we recommend that guidance publications for manure and compost utilization include short-term (28-d) decomposition and PAN estimates that can be useful to both modelers and growers.

Decomposition and plant-available nitrogen in biosolids: laboratory studies, field studies, and computer simulation.

This research combines laboratory and field studies with computer simulation to characterize the amount of plant-available nitrogen (PAN) released when municipal biosolids are land-applied to agronomic crops. In the laboratory studies, biosolids were incubated in or on soil from the land application sites. Mean biosolids total C, organic N, and C to N ratio were 292 g kg(-1), 41.7 g kg(-1), and 7.5, respectively. Based on CO2 evolution at 25 degrees C and optimum soil moisture, 27 of the 37 biosolids-soil combinations had two decomposition phases. The mean rapid and slow fraction rate constants were 0.021 and 0.0015 d(-1), respectively, and the rapid fraction contained 23% of the total C assuming sequential decomposition. Where only one decomposition phase existed, the mean first order rate constant was 0.0046 d(-1). The mean rate constant for biosolids stored in lagoons for an extended time was 0.00097 d(-1). The only treatment process that was related to biosolids treatment was stabilization by storage in a lagoon. Biosolids addition rates (dry basis) ranged from 1.3 to 33.8 Mg ha(-1) with a mean value of 10.6 Mg ha(-1). A relationship between fertilizer N rate and crop response was used to estimate observed PAN at each site. Mean observed PAN during the growing season was 18.9 kg N Mg(-1) or 37% of the biosolids total N. Observed PAN was linearly related to biosolids total N. Predicted PAN using the computer model Decomposition, actual growing-season weather, actual analytical data, and laboratory decomposition kinetics compared well with observed PAN. The mean computer model prediction of growing-season PAN was 19.2 kg N Mg(-1) and the slope of the regression between predicted and observed PAN was not significantly different from unity. Predicted PAN obtained using mean decomposition kinetics was related to predicted PAN using actual decomposition kinetics suggesting that mean rate constants, actual weather, and actual analytical data could be used in estimation of PAN. There was a linear relationship between predicted N mineralization for the growing season and for the first year. For this study, the mean values for the growing season and year were 27 and 37% of the organic N, respectively.