Following the route of veterinary antibiotics tiamulin and tilmicosin from livestock farms to agricultural soils

Veterinary antibiotics (VAs) are not completely metabolized in the animal body. Hence, when animal excretes are used as soil manures, VA residues are dispersed with potential implications for environmental quality and human health. We studied the persistence of tiamulin (TIA) and tilmicosin (TLM) along their route from pig administration to fecal excretion and to agricultural soils. TLM was detected in feces at levels folds higher (4.27-749.6 μg g^-1) than TIA (0.55-5.99 μg g^-1). Different administration regimes (feed or water) showed different excretion patterns and residual levels for TIA and TLM, respectively. TIA and TLM (0.5, 5 and 50 μg g^-1) dissipated gradually from feces when stored at ambient conditions (DT₅₀ 5.85-35.9 and 23.5-49.8 days respectively), while they persisted longer during anaerobic digestion (DT₉₀ >365 days) with biomethanation being adversely affected at VA levels > 5 μg g^-1. When applied directly in soils, TLM was more persistent than TIA with soil fumigation extending their persistence suggesting microbial degradation, while soil application through feces increased their persistence, probably due to increased sorption to the fecal organic matter. The use of TIA- and TLM-contaminated feces as manures is expected to lead to VAs dispersal with unexplored consequences for the environment and human health.

Effects of organic loading rate and hydraulic retention time on bioaugmentation performance to tackle ammonia inhibition in anaerobic digestion

Three continuously stirred-tank reactors fed with manure operating under high ammonia levels (5.0 g NH3-N L-1) and with increased organic loading rate (OLR), (2.09 R1, 3.02 R2 and 4.0 R3 g VS L-1 d-1), achieved through glucose amendment in R2 and R3, were inoculated with an ammonia-acclimatized microbial culture. Successful bioaugmentation was endured only in R2 and R3, both reactors characterized by high OLR, resulting in 19.6 and 24.5% increase in methane production, respectively. The high OLRs in these reactors favored the co-occurrence of the hydrogenotrophic (Methanobacteriaceae), methylotrophic (Methanomethylophilaceae) and aceticlastic methanogenic pathways. The latter was supported by the successful establishment of ammonium-tolerant Methanosarcina, prevailing in the inoculum. Oppositely in R1, the low OLR prevented the establishment of Methanosarcina, leading to an exclusive hydrogenotrophic methanogenesis and reduced methane production. HRT shortening resulted in limited effect on biomethane performance, indicating a well establishment of the introduced bioaugmentation culture in the reactors.

Ammonia-induced inhibition of manure-based continuous biomethanation process under different organic loading rates and associated microbial community dynamics

Three Continuously Stirred Tank Reactors (CTSRs) were operating at steady state conditions with Organic Loading Rates (OLR) of 2.09, 3.024 and 4.0 g VS L^-1 d^-1. Glucose was used as the sole factor for increasing the OLR, linking the increase of the OLR with the C/N ratio increase. The reactors were stressed by increasing the ammonia concentration to 5 g L^-1 from 1.862 g L^-1. The results showed elevating inhibition of the anaerobic process by increasing the C/N ratio just by increasing the OLR, under the high ammonia concentration. A different response of the bacterial and archaeal community under ammonia stressed conditions was also observed. Under the high ammonia concentration, hydrogen-depended methylotrophic was the dominant methanogenesis route at OLR of 2.09 g VS L^-1d^-1, while the hydrogenotrophic route was the dominant at the high OLR of 4 g VS L^-1d^-1, which coincided with high acetate and propionate concentrations.

Anaerobic co-digestion of cattle manure and alternative crops for the substitution of maize in South Europe

In this study alternative agricultural substrates are investigated as potential substitutes of maize for biogas production in the region of South Europe. Crop silages of cardoon, maize, milk thistle and sorghum as well as bedding straw from cattle farm were examined in the anaerobic co-digestion procedure with cattle manure. Milk thistle crop was further investigated in a naturally sun dried form and the effect of mechanical, thermal and thermo-chemical pretreatments on fiber composition and methane yield was evaluated. Pretreatment with NaOH increase the solubilization by 77.7%. The co-digestion experiment was carried out in 28 batch reactors at 37°C. The highest methane yields of 308, 271 and 267LCH4kg(-1) of volatile solids were obtained by co-digestion of cattle manure with cardoon silage, thermo-chemical pretreated milk thistle stalks with NaOH and maize silage, respectively. Furthermore, co-digestion of bedding straw and cattle manure had similar methane yield with maize silage.