Methane yields during anaerobic co-digestion of animal manure with other feedstocks: A meta-analysis.

Anaerobic co-digestion of animal manure with other feedstocks (aka co-digestion) is increasingly being used to enhance methane yield and organic waste management. The benefits accruing from co-digestions compared to mono-digestions, however, vary greatly in the literature. The goal of this research was to use meta-analysis to critically compare methane yields between mono- and co-digestions and identify relevant factors (co-substrate type, substrate dose, carbon to nitrogen (C/N) ratio, volatile solids (VS), substrate pH, organic loading rate (OLR), and hydraulic retention time (HRT)) contributing to methane yield. Published studies (n = 64 representing 384 case-studies) with sufficient detail on methane yield were identified for the meta-analysis. Analysis indicated that co-digestion of animal manure with other feedstocks significantly increased methane yield (249 L kg-1[VS]), compared with anaerobic mono-digestion of animal manure (171 L kg-1[VS]). Similar methane yields increases (47-57 L kg-1[VS]) were obtained from co-digestions in batch reactors of swine (238-287 L kg-1[VS]), poultry (213-260 L kg-1[VS]), and cattle manure (147-204 L kg-1[VS]). In continuous digesters of cattle manure (175-299 L kg-1[VS]) co-digestion had the greatest methane yield improvement of 124 L kg-1[VS], swine manure (212-322 L kg-1[VS]) co-digestion ranked second with 110 L kg-1[VS], and poultry manure ranked third with 70 L kg-1[VS]. Improved methane yield were obtained at optimum C/N ratio ranging from 26 to 34. The respective optimum OLR for co-digestion of swine, poultry, and cattle manure were 1.2, 1.4 and 3.4 kg VS m-3 d-1, while the recommended HRT was 30-40 d. Taken together, anaerobic co-digestion of animal manure with other feedstock significantly improved anaerobic digestion. Factors contributing to methane yields included: substrate-type and dose, VS, C/N, OLR, and HRT.

Effect of stearic or oleic acid on milk performance and energy partitioning when fed in diets with low and high rumen-active unsaturated fatty acids in early lactation.

This experiment was conducted to determine the effects of stearic acid (SA; C18:0) or rumen-protected oleic acid (OA; C18:1 cis-9) on milk performance and energy partitioning of early lactation cows when supplemented in diets with low and high level of rumen unsaturated fatty acids (RUFA). In low RUFA experiment (LRUFA), FA supplement rich in either SA or calcium salts OA was added to a basal diet with a low concentration of RUFA (0.75% vs. 1.4%, LRUFA-SA vs. LRUFA-OA). In high RUFA experiment (HRUFA), 2% soybean oil was added to the diet fed in the LRUFA experiment. In each experiment, 30 multiparous cows were blocked by parity and predicted transmitting ability for milk yield and were randomly fed 1 of 2 treatment diets from 2 to 13 wk postpartum. In the LRUFA experiment, LRUFA-SA had 2.4 kg/d more dry matter intake (DMI) (P < 0.01), 3.8 kg/d more energy-corrected milk (P < 0.01), and 0.3% units more milk fat percentage (P < 0.01) and 0.2 kg/d more milk fat yield (P < 0.01). Dietary treatments did not affect body weight, energy balance, and energy intake partitioning into milk, maintenance, and body tissues (P > 0.1). In the HRUFA experiment, HRUFA-SA had 1.4 kg/d more DMI (P = 0.03) but similar milk and milk components yields (P > 0.1). HRUFA-SA had a tendency to gain more body weight (P = 0.07) and had more positive energy balance (P = 0.01) and decreased gross feed efficiency (milk yield/DMI) (P = 0.01). Consistently, HRUFA-SA increased intake energy partitioning into body tissues (P = 0.02) and decreased energy partitioning into milk (P = 0.01). In summary, SA supplementation had more DMI relative to OA, but the effects on milk and milk fat production were different and affected by the level of RUFA in the basal diet. In application, SA supplementation was more effective to improve milk production when included in the basal diet with the low RUFA.

Nutrient contributions and biogas potential of co-digestion of feedstocks and dairy manure.

This study focused on collection of data on nutrient flow and biogas yield at a commercial anaerobic digester managed with dairy manure from a 1000 cow dairy and co-digestion of additional feedstocks. Feedstocks included: blood, fish, paper pulp, out of date beverages and grease trap waste. Mass flow of inputs and outputs, nutrient concentration of inputs and outputs, and biogas yield were obtained. It was determined that manure was the primary source of nutrients to the anaerobic digester when co-digested with feedstocks. The percentage of contribution from manure to the total nutrient inputs for total nitrogen, ammonia-nitrogen, phosphorus and total solids was 46.3%, 67.7%, 32.8% and 23.4%, respectively. On average, manure contributed the greatest amount of total nitrogen and ammonia-nitrogen. Grease trap waste contributed the greatest amount of phosphorus and total solids at approximately 50%. Results demonstrated that a reliable estimate of nutrient inflow could be obtained from the product of the nutrient analyses of a single daily composite of influent subsamples times the total daily flow estimated with an in-line flow meter. This approach to estimate total daily nutrient inflow would be more cost effective than testing and summing the contribution of individual feedstocks. Data collected after liquid-solid separation confirmed that the majority (>75%) of nutrients remain with the liquid effluent portion of the manure stream. It was demonstrated that the ash concentration in solids before and after composting could be used to estimate the mass balance of total solids during the compost process. This data confirms that biogas or methane yield could be accurately measured from the ratio of % volatile solids to % total solids.

Potential application of Alcaligenes faecalis strain No. 4 in mitigating ammonia emissions from dairy wastewater.

This research examined the potential mitigation of NH3 emissions from dairy manure via an enhanced aerobic bio-treatment with bacterium Alcaligenes faecalis strain No. 4. The studies were conducted in aerated batch reactors using air and pure oxygen. Aeration with air and oxygen removed approximately 40% and 100% total ammoniacal nitrogen (TAN), respectively. Intermittent oxygenation (every 2 or 4 h) reduced oxygen consumption by 95%, while attaining nearly identical TAN removal to continuous aeration. The results revealed that adequate oxygen supply and supplementing dairy wastewater with carbon are essential for this bioprocess. Based on the nitrogen mass balance, only 4% of TAN was released as NH3 gas, while the majority was retained in either the microbial biomass (58%) or converted to nitrogen gas (36%). The mass balance results reveal high potential for environmentally friendly bio-treatment of dairy wastewater using A. faecalis strain No. 4 with respect to NH3 emissions.

Reliable low-cost devices for monitoring ammonia concentrations and emissions in naturally ventilated dairy barns.

This research investigated the use of two relatively cost-effective devices for determining NH3 concentrations in naturally ventilated (NV) dairy barns including an Ogawa passive sampler (Ogawa) and a passive flux sampler (PFS). These samplers were deployed adjacent to sampling ports of a photoacoustic infrared multigas spectroscope (INNOVA), in a NV dairy barn. A 3-day deployment period was deemed suitable for both passive samplers. The correlations between concentrations determined with the passive samplers and the INNOVA were statistically significant (r = 0.93 for Ogawa and 0.88 for PFS). Compared with reference measurements, Ogawa overestimated NH3 concentrations in the barn by ∼ 14%, while PFS underestimated NH3 concentrations by ∼ 41%. Barn NH3 emission factors per animal unit (20.6-21.2 g d(-1) AU(-1)) based on the two passive samplers, after calibration, were similar to those obtained with the reference method and were within the range of values reported in literature.

Reduction of volatile fatty acids and odor offensiveness by anaerobic digestion and solid separation of dairy manure during manure storage.

Volatile fatty acids (VFA) play an important role in the biodegradation of organic wastes and production of bioenergy under anaerobic digestion, and are related to malodors. However, little is known about the dynamics of VFA during dairy manure storage. This study evaluated the characteristics of VFA in dairy manure before and after anaerobic co-digestion in a laboratory experiment using eight lab-scale reactors. The reactors were loaded with four different types of dairy manure: (1) liquid dairy manure from a freestall barn, (2) mixture of dairy manure and co-digestion food processing wastes at the inlet of an anaerobic digester, (3) effluent from the digester outlet, and (4) the liquid fraction of effluent from a solid separator. Four VFA (acetic, propionic, butyric, and 2-methylbutyric acids) were identified and quantified in weekly manure samples from all reactors. Results showed that the dominant VFA was acetic acid in all four manure sources. The off-farm co-digestion wastes significantly increased the total VFA concentrations and the proportions of individual VFA in the influent. The dairy manure under storage demonstrated high temporal and spatial variations in pH and VFA concentrations. Anaerobic digestion reduced the total VFA by 86%-96%; but solid-liquid separation did not demonstrate a significant reduction in total VFA in this study. Using VFA as an indicator, anaerobic digestion exhibited an effective reduction of dairy manure odor offensiveness.

Releasing phosphorus from calcium for struvite fertilizer production from anaerobically digested dairy effluent.

Being a non-renewable resource and a source of potential water pollution, phosphorus could be recovered from animal manure in the form of struvite (MgNH4PO4.6H2O) to be used as a slow-release fertilizer. It was found recently that the majority of phosphorus in anaerobically digested dairy effluent is tied up in a fine suspended calcium-phosphate solid, thus becoming unavailable for struvite formation. Acidification and use of a chelating agent were investigated for converting the calcium-associated phosphorus in the digested effluent to dissolved phosphate ions, so that struvite can be produced. The results demonstrated that the phosphorus in the effluent was released into the solution by lowering the pH. In addition, the phosphorus concentration in the solution increased significantly with increased ethylenediaminetetraacetic acid (EDTA) concentration, as EDTA has a high stability constant with calcium. Most of the phosphorus (91%) was released into the solution after adding EDTA. Further, the freed phosphorus ion precipitated out as struvite provided that sufficient magnesium ions (Mg2+) were present in the solution. Furthermore, the phase structure of the solid precipitate obtained from the EDTA treatment matched well with standard struvite, based on the data from X-ray diffraction analysis. These results provide methods for altering the forms of phosphorus for the design and application of phosphorus-removal technologies for dairy wastewater management.