Joseph H. Harrison

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.

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.

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.

Phosphorus Removal by Struvite Crystallization in Various Livestock Wastewaters

Large dairies and swine farms using flush systems for animal waste management face increasing restrictions on over-application of phosphorus to cropland. The wastewater that the flush systems produce contains phosphorus, and is stored in lagoons for recycling in the flush system and for irrigation onto the cropland. Dairy wastewater in some cases in treated in digesters in concentrated form to produce biogas and reduce odor before being irrigated onto cropland. Struvite crystallization has been proposed for reducing the phosphorus content. The current study compares characteristics of three different wastewaters and relates them to differing phosphorus removal results achieved in applying a cone-shaped fluidized-bed struvite crystallizer system to the wastewaters. The three wastewaters were (1) swine lagoon wastewater; (2) dairy lagoon wastewater; and (3) dairy digester effluent.

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.

Field nitrogen budgets and post-harvest soil nitrate as indicators of N leaching to groundwater in a Pacific Northwest dairy grass field

Dairy farms in the U.S. are expected to use farm-field nitrogen (N) budgeting techniques to determine appropriate agronomic manure application rates for crops. As part of nutrient management, post-harvest soil nitrate sampling is often relied upon to indicate the amount of N not used for crop growth during the growing season. A 4–1/2-year study was conducted that quantified the major N inputs, outputs, and residuals (soil and groundwater) at a commercial dairy field overlying a shallow unconfined aquifer in the Pacific Northwest. The purpose of the study was to evaluate the relationships between two indicators, (1) N mass residuals estimated by farm-field N budget and (2) post-harvest soil nitrate residuals, against measured groundwater nitrate-N concentrations following high seasonal recharge. A mass balance mixing-box spreadsheet model that accounts for the hydrogeologic characteristics of the site was used to quantitatively predict the impact of excess farm-field N on underlying shallow groundwater nitrate-N concentrations. Despite intensive sampling of N balance components and post-harvest soil nitrate conditions, the N-budget-predicted groundwater nitrate-N was 37% of the average field-measured early winter groundwater concentration. The post-harvest soil nitrate-predicted groundwater nitrate-N concentration was 140% of that measured in the field. Neither indicator provided a reliable prediction of the groundwater quality response to land application of nutrients using the spreadsheet model in this poorly drained/high water table setting. The mixing-box model provides a basic tool for testing hypothetical nutrient management scenarios in a variety of conditions. However, groundwater nitrate monitoring data are needed to determine actual outcomes.

Phosphorus Reduction in Dairy Effluent through Flocculation

Previous studies by the investigators show that the majority of the phosphorus contained nin anaerobic digestion effluent from a concentrated dairy is in fine particle form. Therefore, nflocculation treatment with a polymer has the potential for enhancing the separation of solids from the nliquid manure. Cationic polyethylenimine (PEI) was used in the dairy effluent as a flocculant alone nwithout adding other chemicals for phosphorus and solids removal. PEIs with four different ncombinations of molecular weight and ethoxylation modification were evaluated. The PEI with nmedium molecular weight (750,000) had the highest removal of total phosphorus (TP) and total nsolids (TS) among the four PEIs. The PEI addition significantly increased the TP, TS and calcium nremoval by gravity settlement. The reductions of TP, calcium and TS increased with an increase of nthe polymer dosage, and achieved maximum values with the PEI dosage above 200 mg/L. The nmaximum reductions of TP, calcium and TS obtained were 77%, 68% and 58%, respectively. The nremoval efficiency of TP and TS was enhanced by wastewater dilution. PEI may be a new flocculant nchoice for phosphorus and solids removal from dairy effluent.