Vincent H. Varel

Carvacrol and Thymol Reduce Swine Waste Odor and Pathogens: Stability of Oils

An incomplete anoxic fermentation of livestock waste results in offensive odor emissions. Antimicrobial additives may be useful in controlling odor emissions and pathogens. Natural antimicrobial compounds, carvacrol or thymol at 16.75 mM (2.5 g/l) completely inhibited the production of the offensive odor compounds, isobutyrate, valerate, isovalerate, and cresol, and significantly reduced other short-chain volatile fatty acids and gas emissions from swine waste. Fecal coliforms were reduced from 6.3 × 106 to 1.0 × 103 cells per ml 2 days after treatment with carvacrol (13.3 mM) and were not detectable within 14 days. Total culturable anaerobic bacteria were reduced from 12.4 × 1010 to 7.2 × 108 cells per ml after 2 days and were suppressed below this level for 28 days. Lactate production was not prevalent in untreated swine waste indicating that the microbial populations differ from those in cattle waste. Carvacrol and thymol were stable in swine waste under anoxic conditions for 62 days with 90 to 95% of the additive being recovered in the waste solids. In conclusion, carvacrol and thymol are not metabolized in anoxic swine waste and they are potentially useful in controlling odor emissions and pathogens in swine waste.

Plant-Derived Oils Reduce Pathogens and Gaseous Emissions from Stored Cattle Waste

ABSTRACT Carvacrol and thymol in combination at 6.7 mM each completely inhibited the production of short-chain volatile fatty acids and lactate from cattle waste in anoxic flasks over 23 days. Fecal coliforms were reduced from 4.6 × 106 to 2.0 × 103 cells per ml 2 days after treatment and were nondetectable within 4 days. Total anaerobic bacteria were reduced from 8.4 × 1010 to 1.5 × 107 cells per ml after 2 days and continued to be suppressed to that level after 14 days. If the concentration of carvacrol or thymol were doubled (13.3 mM), either could be used to obtain the same inhibitory fermentation effect. We conclude that carvacrol or thymol may be useful as an antimicrobial chemical to control pathogens and odor in stored livestock waste.

Use of urease inhibitors to control nitrogen loss from livestock waste

Abstract Current waste management systems for cattle feedlots and swine facilities result in nitrogen losses of approx. 75%. Most of this loss occurs through the rapid hydrolysis of urinary nitrogen (urea) to ammonia, which volatilizes into the atmosphere. This contributes to odor, environmental problems, and loss of a valuable fertilizer resource. Urease inhibitors cyclohexylphosphoric triamide (CHPT) and phenyl phosphorodiamidate (PPDA) were used to control the hydrolysis of urea in duplicate one-liter slurries of cattle and swine wastes (1:1 g:g feces to urine). With cattle waste (3·3 g urea l−1) and swine waste (4·8 g urea l−1), both inhibitors at 10 mg l−1 of waste prevented hydrolysis of the urea for 4–11 days, and then a gradual hydrolysis occurred until complete at day 28. Hydrolysis of urea in untreated cattle or swine waste (controls) was complete within one day. Addition of the inhibitors once per week was the most effective method of preventing urea hydrolysis. Weekly additions of 10, 40 or 100 mg of PPDA per liter of cattle waste (5·6 g urea l−1) prevented 38, 48 and 70% of the urea from being hydrolyzed after 28 days, respectively. With swine waste (2·5 g urea l−1) these PPDA concentrations prevented 72, 92 and 92% of the urea from being hydrolyzed after 28 days, respectively. PPDA additions were stopped after 49 days, and all urea at the three PPDA concentrations was hydrolyzed after 70 and 84 days for the cattle and swine wastes, respectively. These results offer a strategy for significant control of ammonia emissions from livestock facilities and increasing the fertilizer value of wastes by improving the nitrogen to phosphorous ratio for plant growth. Published by Elsevier Science Ltd.

Eugenol stimulates lactate accumulation yet inhibits volatile fatty acid production and eliminates coliform bacteria in cattle and swine waste

Aim:  To determine how eugenol affects fermentation parameters and faecal coliforms in cattle and swine waste slurries stored anaerobically.

Combination of a urease inhibitor and a plant essential oil to control coliform bacteria, odour production and ammonia loss from cattle waste.

Aim:  To evaluate urea hydrolysis, volatile fatty acid (VFA) production (odour) and coliforms in cattle waste slurries after a urease inhibitor N‐(n‐butyl) thiophosphoric triamide (NBPT) and a plant oil component (thymol) were added.

Enhanced Reduced Sulfur Emission from Manures of Beef Cattle Fed Distiller’s Byproducts

Reduced sulfur compounds (H2S and methyl sulfides) are normal products of manure decomposition which are emitted from confined animal feeding operations (CAFO). These compounds not only contribute to nuisance odors, but with recent EPA regulations, H2S emissions in excess of 100 lbs per day must be reported by the livestock operation. Feeding distiller’s byproducts, which can be very high in sulfur, has recently become very common in large feedlots. Two studies were conducted to evaluate the relative impact of feeding wet distiller’s grain plus solubles (WDGS), which can be high in sulfur, to beef cattle. In the first study, beef cattle in sixteen small-scale pens were fed varying amounts (0%, 20%, 40%, and 60%) of WDGS. Fresh manure composites were collected four times from each pen during the study, and the relative emissions were measured using a laboratory wind tunnel chamber. The relative emission of reduced sulfur was significantly greater (4 to 22-fold) in the 40% and 60% WDGS manures for all time periods compared to the 0% manure composite. A second follow up study in eight production-scale feedlot pens feeding either 0% or 40% WDGS demonstrated that reduced sulfur emissions were consistently larger (up to 2.6-fold) from the feedlot surface near the feed bunk when cattle were fed the 40% diet. Largest reduced sulfur emissions were detected when the feedlot surface was wet. Spatially, relative emission from the feedlot surface after animals were removed from the pens came principally from the wetter edges of the pen. Taken together, the results indicate that very large CAFO need to consider both the sulfur content and the feeding level of WDGS in order to comply with EPA’s reduced sulfur emission guidelines. More intensive manure management of the edges of pens may minimize emissions, but further research is needed to demonstrate whether this management practice is truly effective.