Assessing the biosafety risks of pig manure for use as a feedstock for composting

Treatment of anaerobically digested pig manure by applying membrane processes for nutrient recovery and antibiotics removal

A combination of membrane processes was applied to treat the digestate produced after the anaerobic treatment of pig manure in a biogas plant, aiming towards the recovery of nutrients and effective water treatment for potential reuse. Initially, coarse filtration (sieving and microfiltration) was used to remove particles larger than 1 µm, followed by ultrafiltration, to reduce the suspended solids concentrations below 1 g/L. Subsequently, selective electrodialysis is employed to recover the main nutrient ions, primarily ammonium and potassium. The ion-depleted digestate is then fed to a reverse osmosis unit, where clean water was recovered, yielding a by-product (concentrate) stream enriched in phosphates and organics content. The presence of antibiotics and the concentrations of heavy metals were monitored during all treatment stages to assess their behavior/removal in the various membrane processes. The results indicate that almost 51% of the digestate could be recovered as water free from ions and antibiotics, suitable for reuse in the biogas plant for process needs and irrigation purposes. The selective electrodialysis process can recover 51% of initial NH4+ content (corresponding to 96% of the electrodialysis feed), while the remainder largely ended up in the ultrafiltration concentrate. A similar behavior was observed for the case of K+, while approximately 68% of the phosphates content was retained by the coarse filtration process, with another 24% remaining in the ultrafiltration concentrate and the remaining 8% in the reverse osmosis concentrate. Most of the antibiotics and heavy metals were retained by the coarse and ultrafiltration steps, with smaller amounts detected in the reverse osmosis concentrate.

Addition of plantation waste to the bioconversion of pig manure by black soldier fly larvae: Effects on heavy metal content and bioavailability

During the conversion of pig manure by black soldier fly larvae (BSFL), the accumulation and speciation changes of heavy metals (HMs) have adverse effects on the environment. In this study, corn straw, rice straw, bamboo chips (BC), wood chips, and rice husk char were added to a bioconversion system to study the accumulation, migration, speciation changes, and microbial correlations of HMs. The results indicated that the addition of BC was most beneficial for the accumulation of HMs (47-72 %) in the BSFL body. In the BC group, the accumulation effect of the BSFL body on zinc (Zn) and arsenic (As) was the most evident (72 and 71 %, respectively). The results of linear fitting (R2 > 0.90) and redundancy analysis (RDA; 90 %) indicated that the bacterium Bacillaceae (Bacillus) was beneficial for increasing the larval weight (LW) of BSFL, and a higher LW accumulated HMs. The addition of BC helped reduce the total amount (6-51 %) of available states (weak acid extraction and reducible states) in the BSFL residue. The RDA results indicated that bacteria (55-92 %) affected the transformation of HM speciation. For example, Zn and cadmium were mainly affected by Firmicutes, whereas copper and chromium were affected by Bacteroidetes. Proteobacteria and Pseudomonas formosensis affected the conversion of lead and As. This study provides important insights into the adsorption of HMs from pig manure by BSFL.

Developing a biogas centralised circular bioeconomy using agricultural residues - Challenges and opportunities

Anaerobic digestion (AD) can be used as a stand-alone process or integrated as part of a larger biorefining process to produce biofuels, biochemicals and fertiliser, and has the potential to play a central role in the emerging circular bioeconomy (CBE). Agricultural residues, such as animal slurry, straw, and grass silage, represent an important resource and have a huge potential to boost biogas and methane yields. Under the CBE concept, there is a need to assess the long-term impact and investigate the potential accumulation of specific unwanted substances. Thus, a comprehensive literature review to summarise the benefits and environmental impacts of using agricultural residues for AD is needed. This review analyses the benefits and potential adverse effects related to developing biogas-centred CBE. The identified potential risks/challenges for developing biogas CBE include GHG emission, nutrient management, pollutants, etc. In general, the environmental risks are highly dependent on the input feedstocks and resulting digestate. Integrated treatment processes should be developed as these could both minimise risks and improve the economic perspective.

Challenges of pathogen inactivation in animal manure through anaerobic digestion: a short review

Animal manure is the main source of bioenergy production by anaerobic digestion (AD). However, the pathogenic bacteria in manure may pose a high risk to human health by contaminating the environment if not effectively inactivated during AD. Worldwide, more than 20,000 biogas plants are running for the treatment of animal manure. AD has been playing the important role in establishing a circular economy in the agricultural sector and may contribute to the United Nations sustainable development goal (UN SDG). Nevertheless, whether AD is a reliable approach for pathogens inactivation has been challenged. A comprehensive understanding of the coping mechanisms of pathogens with adverse conditions and the challenges of establishing the AD process to inactivate effectively pathogens are yet to be analyzed. In this review, the diversity and resistance of pathogens in animal manure are summarized. The efficiencies and the difficulties of their inactivations in AD are also analyzed. In particular, three forms of pathogens i.e. sporing-forming pathogens, viable but non-culturable (VBNC) pathogens, and persistent pathogens are discussed. The factors influencing the pathogens’ inactivation and AD efficiencies are analyzed. The trade-off between energy production and pathogens inactivation in an AD system was consequently pointed out. This review concluded that the development of anaerobic processes should meet the goals of high efficient bioenergy production and deep hygienization.

A Bayesian inference approach to quantify average pathogen loads in farmyard manure and slurry using open-source Irish datasets

Farm-to-fork quantitative microbial risk assessments (QMRA) typically start with a preliminary estimate of initial concentration (C_initial) of microorganism loading at farm level, consisting of an initial estimate of prevalence (P) and the resulting pathogen levels in animal faeces. An average estimation of the initial concentration of pathogens can be achieved by combining P estimates in animal populations and the levels of pathogens in colonised animals' faeces and resulting cumulative levels in herd farmyard manure and slurry (FYM&S). In the present study, 14 years of data were collated and assessed using a Bayesian inference loop to assess the likely P of pathogens. In this regard, historical and current survey data exists on P estimates for a number of pathogens, including Cryptosporidium parvum, Mycobacterium avium subspecies paratuberculosis (MAP), Salmonella spp., Clostridium spp., Campylobacter spp., pathogenic E. coli, and Listeria monocytogenes in several species (cattle, pigs, and sheep) in Ireland. The results revealed that Cryptosporidium spp. has potentially the highest mean P (P_mean) (25.93%), followed by MAP (15.68%) and Campylobacter spp. (8.80%) for cattle. The P_mean of E. coli is highest (7.42%) in pigs, while the P_mean of Clostridium spp. in sheep was estimated to be 7.94%. C_initial for Cryptosporidium spp., MAP., Salmonella spp., Clostridium spp., and Campylobacter spp. in cattle faeces were derived with an average of 2.69, 4.38, 4.24, 3.46, and 3.84 log₁₀ MPN g ^-1, respectively. Average C_initial of Cryptosporidium spp., Salmonella spp., Clostridium spp., and E. coli in pig slurry was estimated as 1.27, 3.12, 3.02, and 4.48 log₁₀ MPN g ^-1, respectively. It was only possible to calculate the average C_initial of Listeria monocytogenes in sheep manure as 1.86 log₁₀ MPN g ^-1. This study creates a basis for future farm-to-fork risk assessment models to base initial pathogen loading values for animal faeces and enhance risk assessment efforts.

Inactivation of Salmonella during dry co-digestion of food waste and pig manure

Extremely high volatile fatty acids (VFAs) and ammonia concentrations can accumulate during dry co-digestion of organic wastes, which may inactivate pathogenic microorganisms. In this study, inactivation of Salmonella during dry co-digestion of pig manure (PM) and food waste (FW), which are both reservoirs of zoonotic pathogens, was examined. The effects of pH, VFAs, ammonia and their interactions were assessed on three inoculated Salmonella serotypes. The results show that dry co-digestion significantly decreased the Salmonella inactivation time from several months (in wet digestion) to as short as 6-7 days. A modified Weibull distribution was proposed to simulate Salmonella reduction and to calculate or predict the minimum inhibitory concentrations (MIC) of VFAs and ammonia. Statistical analysis showed that all the factors (pH, VFA type, VFA/ammonia concentration and Salmonella serotype) significantly impacted Salmonella inactivation (P < 0.01). The inhibitory effect sequence was pH > VFA concentration > VFA type > Salmonella serotype in VFA MIC tests, and ammonia concentration > pH > Salmonella serotype in ammonia MIC tests. The toxicity of VFAs was much greater than that of ammonia, and an antagonistic effect was found between VFAs and ammonia on Salmonella inactivation. Apart from the toxicity of free VFAs and free ammonia, the inhibitory effects of pH alone, ionized VFAs and ammonium were also observed.

Bioleaching of heavy metals from pig manure with indigenous sulfur-oxidizing bacteria: effects of sulfur concentration

The purpose of this work was to study the sulfur concentration on bioleaching of heavy metals from pig manure employing indigenous sulfur-oxidizing bacteria. Also, the variations in physicochemical properties of pig manure before and after bioleaching were investigated. The results showed that sulfur concentration significantly affected the rate of acidification, sulfate production and metal solubilization during pig manure bioleaching process. A Michaelis–Menten type equation was utilized to interpret the relationships between sulfur concentration, sulfate production and metal solubilization in the bioleaching process. The rates of metal solubilization during pig manure bioleaching were well described by a first order kinetic equation related to time. After 12 days of bioleaching, 93%–97% of Zn, 96%–98% of Mn and 48%–94% of Cu were leached out from pig manure, respectively. The metals remaining in the pig manure residual were mainly existed in stable forms. In addition, elemental analysis showed that bioleaching process could significantly modify the dewaterbility and organic composition of pig manure. However, fertility analysis found that 9.0%–19.1% of nitrogen, 68.5%–71.0% of phosphorus, 76.5%–78.8% of potassium and 47.5%–49.4% of the total organic carbon (TOC) were lost from pig manure in the bioleaching process. Therefore, bioleaching process used in this study could be applied to remove heavy metals effectively from the pig manure, but more detailed studies need to be done to decrease the nutrients loss from pig manure.

Inactivation of enteric indicator bacteria and system stability during dry co-digestion of food waste and pig manure

Provision of digestate with satisfactory biosafety is critical to land application of digestate and to the anaerobic digestion approach to treating manure and food waste (FW). No studies have been conducted on digestate biosafety in dry co-digestion systems. The aim of this study was to assess the inactivation efficiency and possible inactivation mechanism for three enteric indicator bacteria and the system stability during dry mesophilic anaerobic co-digestion of FW and pig manure (PM). The effects of two different inocula were examined at a rate of 50% based on volatile solids (VS): digestate taken from existing dry co-digestion digesters and dewatered anaerobic sludge from a local wastewater treatment plant. The FW/PM ratios of 50:50 and 75:25 on a VS basis were also assessed. The results showed that using digestate as the inoculum and a FW/PM ratio of 50:50 led to stable dry co-digestion, with the specific methane yield (SMY) of 252mL/gVS_added. Total volatile fatty acid (VFA) concentration was a significant inhibition factor for methane production during dry co-digestion (P<0.001). The data also showed that dry co-digestion of FW and PM effectively inactivated enteric indicator bacteria. E. coli and total coliforms counts decreased below the limit of detection (LOD, 10²CFU/g) within 4-7days, with free VFA identified as a significant inactivation factor. Enterococci were more resistant but nonetheless the counts decreased below the LOD within 12days in the digestate inoculum systems and 26-31days in the sludge inoculum systems. The residence time was the most significant inactivation factor for enterococci, with the free VFA concentration playing a secondary role at high FW/PM ratio in the sludge inoculum system. In conclusion, digestate as inoculum and the FW/PM ratio of 50:50 were preferable operation conditions to realize system stability, methane production and enteric indicator bacteria inactivation.

Effect of feeding sodium butyrate in the late finishing period on Salmonella carriage, seroprevalence, and growth of finishing pigs

Pork is an important source of human salmonellosis and low-cost on-farm control measures may provide a useful element in reducing the prevalence of this pathogen in food. This study investigated the effectiveness of dietary supplementation with sodium butyrate administered to finisher pigs for ∼4-weeks prior to slaughter to control Salmonella shedding on highly contaminated farms. Two trials (A and B) were conducted on two commercial pig farms, which had a history of high Salmonella seroprevalence. In both trials, pens (14 pens of 12 pigs/pen in Trial A and 12 pens of 12-17 pigs/pen in Trial B) were randomly assigned to a control (finisher feed without additive) or a treatment group (the same feed with 3kg sodium butyrate/t) for 24-28days, depending on the trial. Faeces were collected from each pig on days 0, 12 and 24/28, and blood, caecal digesta and ileocaecal/mesenteric lymph nodes were collected from the slaughterhouse. Pigs were weighed at the start and end of the trials, feed intake was recorded, and carcass quality parameters were recorded at slaughter. In Trial A, Salmonella shedding was reduced in the treatment compared to the control group at the end of the trial (30% versus 57% probability of detecting Salmonella in faeces, respectively; p<0.001). This reflected the serology results, with detection of a lower seroprevalence in the treatment compared to the control group using the 20% optical density cut-off (69.5% versus 89%; p=0.001). However, no effect on faecal shedding or seroprevalance was observed in Trial B, which may be explained by the detection of a concomitant infection with Lawsonia intracellularis. No significant differences in Salmonella recovery rates were observed in the caecal digesta or lymph nodes in either trial. Furthermore, feed intake, weight gain, and feed conversion efficiency (FCE) did not differ between groups (p>0.05) in either trial. Numerical improvements in weight gain and FCE were found with sodium butyrate treatment, which gave a cost benefit of €0.04/kg of live-weight gain. Overall, results suggest that strategic feeding of sodium butyrate, at 3kg/t of feed, to finishing pigs for 24-28days prior to slaughter was effective in reducing Salmonella shedding and seroprevalance but perhaps only in the absence of co-infection with other pathogens. However, sodium butyrate supplementation at this rate did not influence intestinal carriage, nor did it reduce seroprevalence to below the cut-off used for the high Salmonella risk category in Ireland (50%), or significantly improve growth performance.

Persistence of bacterial indicators and zoonotic pathogens in contaminated cattle wastes

BACKGROUND

Manure can provide a favourable environment for pathogens' survival. De-contamination may be conducted by extended storage, until field conditions are suitable for application to land as source of agricultural nutrients.

RESULTS

The hygienic evaluation of manure and slurry coming from a plant that collects cattle livestock wastes from a big slaughterhouse was carried out. Samples were even collected from spillages in the area around the plant. Microbial analyses highlighted the massive presence of faecal indicators in all samples: mean counts of Escherichia coli and enterococci were always above EU limits for marketable processed manure products. Cultures referable to the genus Brucella spp. were recorded in two samples of fresh manure but not in the aged ones. Conventional isolation techniques failed to detect members of the Mycobacterium genus, while by means of IS900 and F57 PCR real-time system on DNA directly extracted from environmental samples, the pathogen was detected in all cases.

CONCLUSIONS

Thoughtful design of manure storage infrastructure is critical to prevent spills and over-topping of an open structure. The documented overload situation seems to lay the basis for an ongoing environmental contamination by enteric organisms and opportunistic pathogens circuit faecal-oral route. Moreover, the type of wastes analysed during this study, namely a mixture of fresh cattle manure, bedding and rumen content, needs a longer storage period or, alternatively, of specific chemical, biological or thermal treatments for stabilization.

An investigation into the removal of Salmonella and enteric indicator bacteria from the separated liquid fraction of raw or anaerobically digested pig manure using novel on-farm woodchip biofilters

The objective was to investigate the removal of Salmonella and enteric indicator bacteria from the liquid fraction of raw and anaerobically digested (AD) pig manure in woodchip biofilters over a 14 week (98 day) period. Antibiotic susceptible Salmonella Infantis was detected in one influent material (liquid fraction of raw manure) on two occasions but was not found in the effluent at any time point. Furthermore, mean coliform reductions of 56% were observed in the biofilters treating the liquid fraction of raw manure. However, a mean increase of 228% was found in those treating the liquid from AD manure, despite the fact that the microbial challenge to these biofilters was lower. In addition, relatively high coliform counts were still present in the effluent from both biofilter treatments, especially in the systems treating the liquid fraction of AD manure. However, findings for Escherichia coli and Enterococcus were more promising, with reductions observed for both treatments (10 and 18.5% for E. coli and 71 and 87% for Enterococcus). Moreover, E. coli and Enterococcus were at, or just above, the limit of detection in the final effluents. Overall, although, there are no microbial limits for discharge or washwaters, the woodchip filter effluent would appear safe for discharge to waterways or use on-farm as regards Salmonella, E. coli and Enterococcus but not coliform. In conclusion, woodchip biofilters offer potential as a low-cost sustainable novel treatment option for the removal of pathogens from the liquid fraction of pig manure.

An assessment of Salmonella survival in pig manure and its separated solid and liquid fractions during storage

The objective of this study was to examine Salmonella survival in pig manure and its separated fractions during storage. Salmonella declined, but significant reductions were not observed in the manure and liquid until day 56, whereas counts in the solids were lower by day 7. The Salmonella inoculum initially impacted counts but not after days 28-56. By day 112 Salmonella was undetectable in the manure and liquid but was recovered from the solids. There was no clear dominance of particular serotypes and antibiotic resistance transfer was not found. Storage duration and pH impacted Salmonella counts in all samples, with duration having the greatest effect. Of the nutrients, nitrate had the greatest impact in the manure and, together with phosphate, it also affected counts in the liquid fraction. This study demonstrates that if pig manure or its separated fractions are stored under controlled conditions at 10.5°C for 84-112 days Salmonella is reduced or eliminated, irrespective of the initial load.

The analysis of animal faeces as a tool to monitor antibiotic usage

The analysis of antibiotics in animal faeces is important to obtain more insight in the possible formation of bacterial resistance in the animals׳ gut, to learn about the dissemination of antibiotics to the environment, to monitor trends in antibiotic usage and to detect the illegal and off-label use of antibiotics. To facilitate these studies a comprehensive method for the analysis of trace levels of 44 antibiotic compounds including tetracyclines, quinolones, macrolides and sulfonamides in animal faeces by liquid chromatography in combination with tandem mass spectrometric (LC-MS/MS) detection is reported. The method is fully validated according to European regulation and showed satisfactory quantitative performance according to the stringent criteria adopted, with the exception of some of the macrolide compounds, which can be analysed with somewhat high measurement uncertainty. A large survey was carried out monitoring swine and cattle faeces and the outcomes were striking. In 55% of the swines, originating from 80% of the swine farms and in 75% of the calves, originating from 95% of the cattle farms, antibiotics were detected. Oxytetracycline, doxycycline and sulfadiazine were the most detected antibiotics, followed by tetracycline, flumequine, lincomycin and tylosin. Over 34% of the faeces samples contained two or more different antibiotics with a maximum of eight. Possible explanations for these findings are given and the effects are discussed.