Progress 09/01/15 to 08/31/17
Outputs
Target Audience:The target audiences are those involved closely or remotely with CAFOs. These include, but are not limited to farmers, aggregators, meat producers, national and state animal associations (pork, poultry, cattle, etc.), regulators, policy makers, local communities, municipalities where CAFOs operate, technology providers, and consultants. Because this project was exploratory research, the above mentioned audience was not reached, but recommendations made include informing the target audiences about the outcome of this study. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
SUMMARY OF THE RESULTS Because of space limitations, the report is succinct. A more extensive report can be obtained from Dr. Deshusses (marc.deshusses@duke.edu). 1.1 SCWO and SCWG Comparison Comparison of supercritical water oxidation (SCWO) and gasification (SCWG) was conducted and concluded that SCWO was a superior technology to SCWG for animal waste treatment at CAFOs. SCWO provides cleaner effluent that does not require further treatment. The energy balances are more favorable for SCWO, and SCWO systems can be more compact than gasification ones (because of the shorter reaction time), thereby reducing CAPEX. 1.2 SCWO Treatment Performance A technical scale SCWO prototype designed by Dr. Deshusses and his team was used for the experiments reported in here. The system is housed in a standard 20 feet shipping container and can treat about 1 m3 of slurry per day. Typical animal wastes were found to be suitable for SCWO treatment, however many issues were experienced during high pressure pumping of manure. These were in part due to the small scale of our pilot, and also due to large particles, hair or feathers in the manure that was attempted to be treated. After these were resolved, treatment studies demonstrated that slurries could be very effectively treated (Table 1). Table 1. Typical steady-state performance of our SCWO treatment for animal waste. Here treatment of dog feces (10% dry solids content) augmented with 4% isopropanol (IPA) is reported. IPA was added to increase the calorific value of the slurry treated because we could not pump greater solids content (see text above). COD influent 192,000 mg/L Effluent 65-280 mg/L Removal >99.85% Total N influent 4,700 mg-N/L Effluent 220-420 mg-N/L Removal >91.1% Total P influent 14,500 mg-P/L Effluent 13.4-63.9 mg-P/L Removal >99.6% Examination of Table 1 reveals very high treatment levels across the board. Nitrogen in the manure left the system as harmless nitrogen gas while the phosphorous was precipitated as inert minerals and was easily recovered. Given increasing concerns about the release in the environment of trace contaminants such as antibiotics, pharmaceuticals, etc. spiking of three trace contaminants was conducted. These were acetaminophen (Tylenol), ibuprofen (Advil) and Triclosan (a common antimicrobial agent, e.g. in soap and hand sanitizers). Treatment performance shown in Table 2 indicates that these compounds were very well removed as all effluent concentrations were below our detection limit. Table 2. Treatment of trace contaminants spiked in fecal slurry in our SCWO prototype. Acetaminophen influent 10 mg/L Effluent <1 µg/L Removal >99.99% Ibuprofen influent 10 mg/L Effluent <1 µg/L Removal >99.99% Triclosan influent 100 µg/L Effluent <0.1 µg/L Removal >99.9% There were no odor emissions, and SOx, NOx and ammonia in the exhaust gas were always below our detection limit of 3, 10, and 3 ppmv, respectively. Because of the high temperature of the process, all pathogens were completely destroyed. This include all bacteria, virus, protozoa, prions. The complete elimination of antibiotic resistant bacteria is a clear asset of the SCWO technology. 1.3 Techno-economic evaluation A techno-economic study was conducted for two selected treatment capacities: 2000 head of swine and 10,000 head of swine (feeder to finish). Extrapolation to other animal CAFOs can be done using the specific manure production of various animals. Table 3. Techno-economic summary of SCWO treatment systems for CAFOs. Values are reported for small systems (2000 head of swine of 660 kg dry/day) /// large systems (10,000 head of swine or 3.3 tons dry/day) System footprint (ft2) 320 /// 960 CAPEX ($) $1.0M /// $2.5M OPEX1 ($/mo) $5.6k /// $8.1k Energy2 (kWh/d) +240 /// -300 Clean water generation (ga/d) 8,700 /// 49,000 1Not including CAPEX depreciation. 2The "+" indicates energy consumption, while the "-" indicates net surplus electricity produced. Highlights of Table 3 include the very small footprint of the systems. This will free up land for either more animal barns or planting cash crops. CAPEX values are high compared to lagoons, but SCWO provides complete treatment with many associated advantages. OPEX require further validation. The results suggest that building a single system to handle the waste of multiple farms should be investigated. Comparison with selected swine waste treatment technologies is shown in Table 4. SCWO treatment would be very competitive with an annual cost of $166/1000 lbs. steady state live weight (SSLW). This estimate takes into account revenues of $77/1000 Lbs SSLW/year, some of which are highly volatile. For instance, swine RECs in North Carolina could sell for as much as $100/REC, although even without revenues, SCWO treatment is competitive. Table 4 Comparison of selected swine waste management systems with SCWO treatment. Lagoon and sprayfield: Traditional practice. Simple process. Odorous, releases greenhouse gases and NH3, large footprint, requires land for spraying, breeds flies, possibly antibiotic resistant bacteria. Subject to changing regulations. 87 $/1000 Lbs SSLW/year. Composting ("SuperSoils"): Aerobic process primarily for dry matter (e.g. dewatered manure). Relatively simple process, makes low value product, releases odors and NH3, requires dewatering of the manure (and liquid waste management) and often addition of high C waste for co-composting. 83 $/1000 Lbs SSLW/year (for the dewatered fraction only). Anaerobic digestion + post-treatment (Loyd Ray Farms & AgriClean): Slow biological process for partial conversion of organics to biogas. Moderately complex, recovers some energy in the form of biogas, does not provide N or P management or pathogen control, usually requires post treatment (aerobic or land application). 210 - 221 $/1000 Lbs SSLW/year. SCWO (this study): High-tech engineered system for complete treatment. No odor or greenhouse gas emissions, complete elimination of all pathogens, small footprint, produces renewable energy. 166 $/1000 Lbs SSLW/year (See note #2) 1Costs for Loy Ray Farms are from Adair et al. (2016) Trans. ASABE 59: 1009-1018. All other costs are from NCSU 2006. Dev. of environm. superior technologies: Phase 3 report. https://projects.ncsu.edu/cals/waste_mgt/smithfield_projects/phase3report06/pdfs/report%20summary.pdf. 2Without any revenue, cost is $243/1000 lbs. SSLW/year. 2 RECOMMENDATIONS This project demonstrated the feasibility of using supercritical water oxidation (SCWO) for the complete treatment of organics, nutrients, trace contaminants and pathogens in manure. A techno-economic evaluation revealed that the cost would be very competitive. The environmental benefits of SCWO, reduction in land requirement and secondary benefits (e.g., possible animal health) will make SCWO treatment even more attractive. Recommendations include: Further examination of the applicability of SCWO at CAFOs is recommended, in particular through a feasibility study at a CAFO with a sufficiently large SCWO unit to enable identification of CAFO specific issues. A detailed study of the specific regulations and market place and generation of renewable energy credits (RECs) and carbon offsets is recommended. This location-specific information will enable to identify states where SCWO can generate income and possibly make manure treatment a cash positive operation. Further study and quantification of the secondary benefits (odor, environmental emissions, costs, animal and worker's health) of SCWO treatment at CAFOs is recommended. Finally, informing the target audiences about the outcome of this study is recommended. These include but are not limited to farmers, aggregators, meat producers, national and state animal (pork, poultry, cattle, etc.) associations, regulators, policy makers, local communities, municipalities where CAFOs operate, technology providers, and consultants.
Publications
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