Source: UNIVERSITY OF ARKANSAS submitted to
DEVELOPMENT OF A SUSTAINABLE TREATMENT SYSTEM FOR POULTRY LITTER WITH MAXIMUM VALUE RECOVERY
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
EXTENDED
Funding Source
Reporting Frequency
Annual
Accession No.
1019978
Grant No.
2019-67021-29945
Project No.
ARK02648
Proposal No.
2018-07931
Multistate No.
(N/A)
Program Code
A1531
Project Start Date
Jul 1, 2019
Project End Date
Jun 30, 2023
Grant Year
2019
Project Director
Zhu, J.
Recipient Organization
UNIVERSITY OF ARKANSAS
(N/A)
FAYETTEVILLE,AR 72703
Performing Department
(N/A)
Non Technical Summary
The long-term goal of this project is to provide the poultry industry in the US a novel anaerobic digestion technology to treat raw poultry litter with minimal water usage to produce not only renewable energy (methane) but also a valuable fertilizer that can be used on farm or transported away to other nutrient deficient areas at reasonable costs. The viability of agriculture as a source for food, feed fiber and fuels will depend on our ability to reconcile agricultural production with environmental integrity. And research on sustainable production systems is thus crucial to developing the knowledge base to implement required agricultural innovations. This NIFA/AFRI project will focus on exploring and developing an innovative technology that will lead to a comprehensive utilization of agricultural production wastes including poultry litter in particular and crop residues such as rice/wheat straw to produce bioproducts and bioenergy through physical/chemical/electrical/biological conversions. Anaerobic digestion will be employed to co-treat poultry litter with wheat straw to overcome the low C/N content of poultry litter, with all the process parameters such as carbon/nitrogen ratio, pH, organic loading rate, etc., being optimized. In addition of methane, a slow release fertilizer (struvite) will be produced in this project. Use of forward osmosis/membrane distillation is the first of its kind endeavor to clean up digestion effluent for water reuse to reduce water consumption systemwide. The information and knowledge obtained from this project will be shared with the public through both refereed and non-refereed journal publications, extension/education events, classroom teaching, and among others. The ultimate goals of this research will be to protect the soil and water and natural resources in the nation by reducing the volume of wastes produced and maximizing the value-added products production and environmental benefits so the poultry industry in the US can be sustained in a long run.
Animal Health Component
0%
Research Effort Categories
Basic
20%
Applied
60%
Developmental
20%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
40332992020100%
Knowledge Area
403 - Waste Disposal, Recycling, and Reuse;

Subject Of Investigation
3299 - Poultry, general/other;

Field Of Science
2020 - Engineering;
Goals / Objectives
The long-term goal of this project is to provide an advanced, sustainable treatment system for poultry litter disposal. The system consists of an anaerobic digester, an electrolytic reactor with an anodic magnesium plate, and a forward osmosis (FO) or a membrane distillation (MD) reactor, purporting to recycle and reuse the digester effluent to liquefy the incoming litter for digestion to reduce water usage while still maintaining digester performance. The specific objectives of this proposal include1) develop and evaluate a specially designed anaerobic digester for loading solid materials and determine the operating parameters that matter most in biogas production and releases of magnesium and phosphate ions when co-digesting poultry litter with an external carbon source such as wheat straw;2) develop and evaluate an electrolytic reactor with an anodic magnesium plate to produce struvite from the anaerobic digester effluent to remove both nitrogen and phosphorus;3) develop, evaluate, and compare an FO and an MD process to further clean up the effluent from the electrolytic reactor so that it can be recycled back to the front for liquefying the feeding poultry litter to the anaerobic digester; and4) integrate the whole lab-scale system to evaluate its performance in treating poultry litter using the liquid anaerobic digestion technology.
Project Methods
The proposed system is mainly composed of three units, i.e., a liquid anaerobic digester, a novel electrolytic reactor with an anodic magnesium plate for struvite precipitation, and a forward osmosis or membrane distillation reactor for water cleaning so that the water coming out of the last unit can be recycled to the front to liquefy dry poultry litter for digestion. It is our belief that, based on limited preliminary work by the PD and co-PDs of this proposal and literature information, this proposed system can not only advance the liquid anaerobic digestion technology to treat a relatively dry waste stream such as poultry litter but also provide the very needed knowledge for further research to implement this technology on real poultry farms. The methods on each major unit in the proposed system are presented below.Methods for specific objective 1: Develop and evaluate a specially designed anaerobic digester for loading solid materials and determine the operating parameters that matter most in biogas production and magnesium and phosphate releases when co-digesting poultry litter with an external carbon source such as wheat straw (University of Arkansas)Experimental apparatus and feedstock materials: A lab-scale liquid anaerobic digester made of acrylic tubing will be built and set up in the Biological & Agricultural Engineering Department Lab at the University of Arkansas in Fayetteville, with a working volume of around 16.8L. The poultry litter used in the experiments will be collected from a commercial broiler house. After collection, the litter will be sieved through a 2.38 mm screen, and stored in a 4oC walk-in refrigerator prior to use. The wheat straw used will be collected from a local farm, which, after collection, will be processed using a Wiley mill to a size of 20 mesh (0.85 mm) and then be also stored in the walk-in refrigerator if not used immediately. Before experiments, the wheat straw will be analyzed for carbon and nitrogen content for adjusting the carbon to nitrogen ratio (C/N ratio) of the litter. Three parameters, with each having 5 levels, will be investigated in this study, i.e., substrate carbon to nitrogen ratio (C/N ratio: 10, 15, 20, 25, and 30), TS content (2, 4, 6, 8, and 10%), and hydraulic retention time (HRT: 10, 20, 30, 40, and 50 hour). a central composite design (CCD) coupled with response surface methodology will be adopted to build a second order (quadratic) model for the response variables.Methods for specific objective 2: Develop and evaluate an electrolytic reactor equipped with an anodic magnesium plate to produce struvite from the effluent of the anaerobic digester to remove both nitrogen and phosphorus (University of Idaho)Experimental apparatus: The electrolytic reactor with an anodic magnesium plate for continuous treatment of digested liquid of poultry litter will be fabricated, including an electrolytic unit, a DC power supply (CCB200, XP Power, Lake Hopatcong, New Jersey, USA), peristaltic pumps (Masterflex 07555-05 L/S, Cole-Parmer, Illinois, USA), and tubing. The electrolytic unit (total volume: 2 L), made of Plexiglas, consists of two identical chambers separated by a silicone pad with anion and cation exchange membranes attached. The dimension of all electrodes is 150x50x3 mm (length, width, and thickness), with an effective area of 45 cm2. High purity magnesium alloy and stainless steel are selected to be used as the anode and cathode materials. The distance between the anode and cathode plates is 3.5 cm, and the anodic magnesium plate and the cathodic stainless steel plate are connected to the positive and negative outlets of the power supply, respectively.Since the experiments with the electrolytic reactor in this stage will be conducted independently without the real digested liquid from the first unit, synthetic wastewater will be used, which is prepared by dissolving NH4Cl and NaH2PO4·H2O in deionized water according to a molar ratio of 1:1 for NH4+ and PO43-. The parameters that may affect the performance of the electrolytic reactor include solution pH at the anode, the current density applied (A/m2), and the hydraulic retention time (HRT) for continuous treatment. Therefore, the experimental design will also adopt CCD with RSM to determine the best condition for phosphate removal efficiency. All three parameters will be tested at five levels (current density: 10, 20, 30, 40, and 50 A/m2; pH: 7.5, 8.0, 8.5, 9.0, and 9.5; HRT: 10, 15, 20, 25, and 30 min).Methods for specific objective 3: Develop, evaluate, and compare an FO and an MD process to further clean up the effluent from the electrolytic reactor so that it can be recycled back to the front for liquefying the feeding poultry litter to the anaerobic digester (Virginia Tech)Experimental apparatus: The membrane unit is a commercial SEPA cell (GE Osmotnic, Trevose, PA, USA), which will be modified to have channels on both sides of the membrane. A flat-sheet, cellulose-based membrane from Hydration Technology Innovations (Albany, OR, USA) will be used for the FO process. The draw solution (DS) is flowing on the permeate side and the feed solution (digestate supernatant) will flow on the feed side. Concurrent flow will be used to reduce strains on the suspended membrane. Variable speed peristaltic pumps will be used to recirculate the feed and draw solutions. A heating mantel will be used to heat the returned DS while an analytical balance will be placed underneath to measure permeate production. The temperature of the influent feed and draw solution will be held at the same room temperature (20oC) during the FO tests. A 2L feed tank and a 2L permeate tank will be used to house the feed and draw solutions. The concentration (2, 4, 6, 8, and 10M) and temperature (35, 40, 45, 55, and 60oC) of the draw solution (NH4HCO3) in the permeate reservoir will be controlled, respectively, as individual variables in this study, thus consisting of a 5x5 factorial design (25 combinations of the DS concentration and temperature) to examine their effects on the water cleaning performance. The feed and draw solutions will be circulated at the rate of 0.12 L/min. The permeate volume will be continuously monitored along with the experimental time based on the analytical balance reading. The concentrations of COD, NH4+-N, TN, TP, and PO43- will be measured in both the feed and draw solutions before and after the FO treatment to estimate the rejection efficiencies of these substances. Each of these runs will last at least 24 hours.

Progress 07/01/21 to 06/30/22

Outputs
Target Audience:The target audiences reached include the scientific community and the concerned industries through journal articles and the papers presented in the Annual Meeting of American Society of Agricultural and Biological Engineers and the17th IWA world conference on anaerobic digestion, Ann Arbor, MI on June 22, 2022. Also, the information generated from the research project is shared with farmers and companies in Arkansas who are interested in anaerobic digestion of poultry litter. Changes/Problems:The project has been granted for a one-year no-cost extension due to delays caused by the pandemic. What opportunities for training and professional development has the project provided?For University of Arkansas, a PhD grad student was trained heavily in anaerobic digestion technology for poultry litter digestion with wheat straw. For University of Idaho, one MS grad student was trained who did his thesis on the research. For Virginia Tech, a PhD grad student was trained for the design and operation of MD and FO. In addition, all grad students were trained to write scientific publications and/or oral presentations at conferences to disseminate research outcomes. How have the results been disseminated to communities of interest?The research results were mainly disseminated to the communities of interest through peer-reviewed journal articles and conference presentations. With the pandemic restriction on travel eased, attending conferences by PD/co-PD and grad students will return to pre-pandemic level, which can help increase the information dissemination. What do you plan to do during the next reporting period to accomplish the goals?For University of Arkansas, CCD/RSM analysis of the anaerobic sequencing digester for poultry litter co-digestion with wheat straw will be completed with the optimal running parameters determined. In the meantime, the microbial community structure in the digester may be to some extent determined, which can provide key information on properly operating the digester to maximize the treatment efficiency. For University of Idaho, the electrolytic reactor system with a magnesium plate anode will be subjected to tests with real poultry litter digester effluent, with the operating parameters adjusted if needed to achieve the best struvite yield and N and P removal. For Virginia Tech, next reporting period will be focused on the FO operational condition optimization when using NH4HCO3 as a draw solution. For example, other NH4HCO3 concentrations such as 2, 4, 8, and 10M will also be evaluated. The efficiency of NH4HCO3 separation from recovered water will also be evaluated at temperatures between 35, 40, 45, 55, and 60oC. For all institutions, assembling the entire system at University of Arkansas to be tested in the lab and on a poultry farm (TBD) may take place towards the end of the project.

Impacts
What was accomplished under these goals? In this reporting period, substantial progress has been made in experiments. For Specific Objective 1 listed above, the digester startup process was meticulously studied because it was found difficult to fire up anaerobic digesters with diluted poultry litter supplemented heavily with wheat straw as a carbon source. The startup of the anaerobic co-digestion (ACoD) process of poultry litter (PL) and wheat straw (WS) was conducted by gradually increasing the organic loading rate (g VS/L/d) and significant variations in the process performance were observed when OLR was gradually increased with time. The results showed that during the startup operation from day 1 to day 16 when OLR was increased with time from 0.6 to 3.8 g VS/L/d, the ACoD process showed the gradually increasing daily biogas production (DBP), biogas methane content (MC), daily methane production (DMP). After a gradually increasing OLR, the process performance, represented by DBP, MC, DMP, and daily COD content in discharging liquid (DCOD), became relatively stable and varied within 5% in 5 consecutive days (day 26 to day 30), indicating that to reach a steady state of the ACoD process in the ASBR needed at least 26 days of operation. The increase of methane production with increasingOLR indicated that the metabolism of the microflora involved in the ACoD process was enhanced gradually. And it could be inferred that the gradually increased organics were efficiently consumed with rapid metabolism by the ACoD process during startup. Nonetheless, the steady state of the reactor had notbeen reached when OLR was increased to 3.8 g VS/L/d. At the steady state, the ACoD process had a DBP of 13.06 ± 0.21 L with a methane content of 54.38 ± 0.53 %, which resulted in a DMP of 116.80 ± 1.30 mL CH4/g VS added. And the DCOD was 4762.9 ± 42.9 mg/L, indicating a COD removal rate of 84.7 % compared to the feedstock data. After startup, five operating periods of the ACoD were carried out during the steady state using different OLRs (ranging from 1.6 to 5.2 g VS/Lreactor/day), with each period lasting 14 days after reaching the steady state. The results showed that at the lowest OLR, the average DMP of the ACoD process was 119.86 ± 9.34 mL CH4/g VS added. The highest average DMP (161.79 ± 12.20 mL CH4/g VS added) among the five periods was obtained with an OLR of 2.28 g VS/L/d. At the highest OLR of 5.20 g VS/L/d, the DMP only achieved an average value of 146.89 ± 7.34 mL CH4/g VS added. This indicated that a larger OLR in the regular operation did not guarantee a larger DMP at the steady state. Therefore, it can be concluded that using an appropriate OLR is critical to operating an ASBRto treatment poultry litter with wheat straw. For other parameters, the ACoD process has achieved reductions of COD, TN, NH4-N, TS, and TVS by 81%, 55%, 64%, 87%, and 91%, respectively. For Specific Objective 2, following the previous work reported in the last report, the operating conditions of the electrolytic reactor with a magnesium plate in terms of solution pH, mixing speed, and applied current on struvite yield and nutrients removal were studied and optimized using central composite design (CCD) coupled with response surface methodology (RSM). Synthetic wastewater, which was specially formulated according to the N and P content in the digested effluent of poultry litter, continued to be used as the substrate. The experimental design was divided into Part I and II. Since pH, mixing speed, and the current applied to the electrolytic reactor with a magnesium anode were influencing factors for struvite formation, a screening design was first adopted in Part I to determine the most significant two for the subsequent CCD/RSM optimization in Part II. Two levels for each parameter (pH: 8 and 9.5, mixing speed: 150 and 600 rpm, and the current applied: 0.1 and 0.5 A) and their combinations were examined. In Part II of the experiment, CCD coupled with RSM was employed to optimize the selected operating parameters from Part I to maximize struvite yield and NH4+ and PO43- removal efficiencies. Since pH was identified in Part I experiment as having the least impact on the response variables, the CCD design was thus focused on the two remaining independent variables, i.e., mixing speed and current applied, each tested at three levels (mixing speed: 150, 375, and 600 rpm; current applied: 0.1, 0.3, 10 and 0.5 A). The results from Part I experiments showed that there was a significant increase in struvite yield when the mixing speed increased from 150 rpm to 600 rpm, regardless of the amount of current applied and pH, and the mixing speed (intensity) had a significant impact on struvite yield. The reason that the high mixing speed (600 rpm) achieved the high struvite yield was that the sacrificial magnesium anode in the reactor continuously supplied Mg2+ ions for continuous struvite precipitation. According to the data obtained in this study, it may be concluded that when Mg2+ ions are present in a sufficient amount, raising mixing speed up to 600 rpm can improve the struvite yield by about 16-18%. The results from Part II experiments, i.e., CCD/RSM analysis, showed that the optimal values for the control parameters were 0.5 A and 413.9 rpm (~414 rpm), under which the optimal responses were 4.75 g/L, 93.0%, and 58.4% for struvite yield and NH4+ and PO43- removal efficiencies, respectively. The SEM-EDS, XRD, and FT-IR analysis confirmed the high purity and quality of the struvite produced by the electrolytic reactor system. For Specific Objective 3, the digestate composition in terms of COD, NH4+-N, NO3--N, NO2--N, and PO43- before and after anaerobic digestion and electrolytic reactor were characterized. Synthetic digestates were made accordingly to measure the rejection efficiencies of these substances by the MD and FO treatment to evaluate the membrane performance along with the water recovery efficiencies. For MD evaluation, two different types of hydrophobic membrane, namely PTFE 1 (SKU1121840, STERLITECH, USA) and PTFE 2 (RS40213, TISCH Scientific, USA), were compared. Although their rejection efficiencies of COD, NH4+-N, and PO43- were similarly good at almost 100% levels, the water flux of the latter was 30% better than the former. Therefore, PTFE 2 was selected as the hydrophobic membrane in the next round of MD transmembrane temperature effect evaluation. Transmembrane temperature measures the temperature gradient between the two sides of the membrane used in MD and act as the driving force for water diffusion and recovery. The transmembrane temperatures of 15, 20, and 40 oC were compared in this study. Results showed that the water flux achieved at 40 oC transmembrane temperature was around 4.6 L m-2 h-1, which was 14 and 3 times those obtained at transmembrane temperatures of 15 and 20 oC, respectively. This is in line with the linear correction between the driving force and water flux. For this established correlation, we didn't need to repeat the same experiment on 30 and 35 oC. For FO, we compared the effect of draw solution, namely 6M NH4HCO3 v.s. 1M NaCl, on the water flux through a Cellulose Triacetate (CTA) membrane. Results showed that rejection efficiencies of COD,NO3--N, NO2--N, and PO43- were similarly good at almost 100% levels. In terms of water flux, 6M NH4HCO3 obtained about 6 L m-2 h-1, which is higher than the 4.8 L m-2 h-1 obtained with 1M NaCl. These results exhibited that FO works better than MD, and NH4HCO3 works better than NaCl as a draw solution in FO in terms of water flux under this experimental setup. NH4HCO3 is actually a preferred draw solution in FO for its easy separation from recovered water via evaporation from 36 oC.

Publications

  • Type: Journal Articles Status: Published Year Published: 2022 Citation: Ndeddy Aka Robinson Jr., Sarah (Xiao) Wu, Jun Zhu, Yuanhang Zhan. 2022. Optimization of a dual-chamber electrolytic reactor with a magnesium anode and characterization of struvite produced from synthetic wastewater. Environmental Technology https://doi.org/10.1080/09593330.2022.2077131.
  • Type: Journal Articles Status: Published Year Published: 2022 Citation: Zhan, Y., X. Cao, Y. Xiao, X. Wei, S. Wu, J. Zhu. 2022. Start-up of co-digestion of poultry litter and wheat straw in anaerobic sequencing batch reactor by gradually increasing organic loading rate: methane production and microbial community analysis. Bioresource Technology 354:127232.
  • Type: Journal Articles Status: Published Year Published: 2022 Citation: Zhan, Yuanhang, Yiting Xiao, Leland C. Schrader, and Jun Zhu. 2022. A float meter-based system for self-regulated discharging and feeding in a laboratory semi-CSTR for anaerobic digestion of chicken litter. J. ASABE 65(3): 481-490. https://doi.org/10.13031/ja.14804.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Zhang X.Y., Zhu J., Wu X., and Wang Z.W. 2022. Application of Low-energy membrane technologies for closing the water loop of poultry litter anaerobic digestion, 17th IWA world conference on anaerobic digestion, Ann Arbor, MI, June 17-22


Progress 07/01/20 to 06/30/21

Outputs
Target Audience:The target audiences reached include the scientific community and the concerned industries throughjournal articles and the papers presented in the Annual Meeting of American Society of Agricultural and Biological Engineers. Although effort was exercised, the level of outreachinthis reporting period from this project is not extensive due to the impact of covid-19 pandemic that caused difficulties to conduct normal research and outreach activities. It is expected that, with the vaccination rate increasing, all activities on campus will return to normal in the fall of 2021 and the outreach activities will be intensified. Changes/Problems:As reported in the last round, the project inception was delayed due to the unsuccessful recruiting of graduate students timelyand the covid-19 pandemic that shut down the operation of labs and facilities on campus. Therefore, a one-year, no cost extension of the project will be requested before the current ending date, which is 6/30/2022. What opportunities for training and professional development has the project provided?On top of the two graduate studentshiredin U of AR and U of ID last year, respectively, another grad student was finally hired recentlyin VirginiaTech. Therefore, this project starts to provide training opportunities for graduate students to prepare them for theircareer development in the respective areas described in this proposal. How have the results been disseminated to communities of interest?Due to the covid-19 pandemic, conference/symposium activities were at the historically low level. Despite that, one conference paperwas produced in 2020 and presented in the American Society of Biological and Agricultural Engineers Annual International meeting, in which the early results of this project were shared with the scientific community. What do you plan to do during the next reporting period to accomplish the goals?The three participating institutions will have respective goals to accomplish in the next reporting period. For University of Arkansas (specific objective 1), according to the experimental design in the proposal, there are a total of 20 experiments needing to be completed to determine the optimal operating condition forthe anaerobic digester co-digesting poultry litter and wheat straw for biogas production and magnesium release. Currently only six out of the 20 experiments have been completed and data collected. Therefore, in the next year, the remaining 14 experiments will be expected to be completed with data collected and analyzed. At the end of the next reporting period, the anaerobic digester developed will be ready for incorporation with the other two units developed in University of Idaho and Virginia Tech to form a complete system for poultry litter treatment. For University of Idaho (specific objective 2), three goals are expected to be accomplished. First, the reactor design and electrode configuration will be improved toimprovenitrogen and phosphorus recovery through struvite precipitation. Second,the optimal operational factors will be identifiedand evaluated toimprovestruvite purity in terms of precipitate composition. And third, real poultry litter digestate will be used to test the nitrogen and phosphorus recovery rates for struvite precipitation. To achieve these goals, the full CCD/RSM experimental design proposed will be executed for three parameters all at five levels, i.e., current density: 10. 20, 30, 40, and 50A/m2; pH: 7.5, 8.0, 8.5, 9.0, and 9.5; and HRT: 10, 15, 20, 25, and 30 min, to determine the optimal operating condition for the electrolytic reactor in removing ammonium nitrogen and phosphorus and producing struvite. At the end of next period, the electrolytic reactor will be ready for system assembly to treat poultry litter. For Virginia Tech (specific objective 3), a 5x5 factorial design with theconcentration(2, 4, 6, 8, and 10M)andtemperature(35, 40, 45, 55,and60oC)of thedraw solution(NH4HCO3) in the permeate reservoirwill be controlled to examine their effects on the water cleaning performance.The concentrationsof COD,NH4+-N,TN, TP, andPO43-will be measured before and after the FO treatment to estimate the rejection efficiencies of these substances.Likewise, in MD, the feed solution temperature (35, 40, 45,50,55,and60oC) will be varied as the only variable in this studywhile the permeatetemperature will be kept at 20oC to examine their effects on the water cleaning performance. For all institutions, at least one manuscript will be produced from each participating institution in the due course.

Impacts
What was accomplished under these goals? In this reporting period, substantial progress has been made in terms of experimental setup and execution. For specific objective 1 listed above, two anaerobic digesters were built, extensively tested, and now in normal operating condition. Experiments have started according to the experimental design described in the proposal to determine the best operating parameters to produce biogas and release magnesium ions for the next treatment unit, i.e., the electrolytic reactor with a magnesium plate. Partial CCD/RSM results from co-digestion of poultry litter and wheat straw were obtained. Under C/N ratio of 20 and TS 6%, the average CH4 production efficiency was around 124 ml/g VS when HRT was 16 days. No change in CH4 production efficiency was observed when HRT increased to 24 days; however, for HRT = 7.5 days, the production efficiency increased to 139 ml/g VS. The highest CH4 production effiency was seen for C/N ratio of 15, TS 4%, and HRT11 days, which was 162 ml/g VS. In terms of magnesium ion release, it was interesting to see that the highest release of 236.8 mg/l happened also under the same operating condition as forthe highest CH4 production efficiency, i.e., C/N = 15, TS = 4%; and HRT = 11 days. The magnesium concentration in the feeding substrate was around 79 mg/l, while was 236.8 mg/l in the digester effluent (aroughly 3-fold increase achieved). Therefore, our hypothesis that anaerobic digestion can increase magnesium release is verified. The experiments are ongoing now and more data will be collected to determine the optimal operating condition for specific methane production and magnesium ion release bythe anaerobic digester, which will be reported in our next progress report. One manuscript was developed and under internal review based on the experimental data obtained thus far. For specific objective 2, substantial progress has also been made. In this period, a synthetic wastewater solution was used to investigate the characteristics of the dual chamber reactor. The composition of the synthetic digestate was obtained following the typical components of the digestate from anaerobic digestion of poultry manure. The wastewater solution was prepared by dissolving appropriate amounts of analytical grade NaH2PO4.12H2O and NH4Clin deionized water to obtain an initial PO43--P and NH4+-N concentration of 1.5 g/L. The initial pH was then adjusted to the desired pH using 1M NaOH or HCl solutions while stirring at. 120 rpm for 5 minutes. In the last report, we mentioned that a better magnesium alloy material needed to be selected. Therefore, in this phase of experiment, a high purity magnesium alloy (AZ91, not AZ31 that was used early) was used as the sacrificial anode with stainless steel as the cathode material.The dimension of all electrodes was 150x50x3 mm (length, width, and thickness), with an effective area of 45 cm2. Pretreatment of the electrodes was carried out to remove metal oxides, which coulddeactivate the reaction when existing on the electrode surface. After polishing with sandpaper, both electrodes were acid washed with 2.0 M HCl solution. After pretreatment, all electrodes were rinsed with DI water. A cation exchange membranewas used to separate the cathode from the anode chamber to prevent the migration of anions from anode to cathode and also to induce a bulk phase pH increase in the cathode chamber. The electrodes were then placed symmetrically on the different sides of membranes with the total distance of 4 cm and a constant voltage was applied across the electrodes using a DC power supply. Partial results indicated that pH change from 8 to 9.5had little impact on NH4-N removal efficiency by the electrolytic reactor, but it significantly reduced the PO4 removal efficiency (from 52% to 38%). This means that high liquid pH will negatively affect PO4 precipitation. Increasing the electrical current to the reactor was able to significantly increase the removal efficiencies for both NH4 and PO4 in the liquid, especially for NH4 removal. When the current increased from 0.1 to 0.5 A, the removal rate for NH4 was increased from 18% to 82%, while that for PO4 was from 16% to 51%. Obviously, increasing current has led to increase in magnesium ion release which helps precipitate more NH4 and PO4 to form struvite, thus increasing both removal rates. One manuscript is under preparation from the results obtained thus far. For specific objective 3, the international student recruited managed to join us in her new position and started her experiment in spring 2021 right after the university lab re-opening. So far, she has established the performance baselines of the FO and MD with synthetic wastewater. In the FO using CTA (Cellulose Triacetate) membrane (flat sheet, Sterlitech corporation), water in feed solution containing 4000 mg/L chemical oxygen demand (COD) was able to permeate at a flux of 3.11 mL/m2/h across the membrane into the draw solution made of 70 g/L sodium chloride. Meanwhile, 89.6% of the COD was rejected by the membrane in the feed solution. These transmembrane flux and COD rejection values are comparable to the values reported in literature using similar FO setup. For MD using PTFE membrane (flat sheet with 0.2micro pore size, Sterlitech corporation), water in feed solution containing 4000 mg/L COD was able to permeate at a flux of 6.46 mL/m2/h across the membrane when being heated at 60 oC. Meanwhile, 99.96% of the COD and 99.97% of the salts were rejected by the membrane in the feed solution. Again, these transmembrane flux and COD rejection values are comparable to the values reported in literature using similar MD setup. With these successful FO and MD system test runs and baseline information verified, the comparative study in the next step will be straightforward by varying the temperature and draw solution composition.

Publications

  • Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Zhu, J. 2020. Solids, Ammonia, and Carbon\Nitrogen Ratio on Anaerobic Co-Digestion of Poultry Litter and Wheat Straw, and Kinetics Modeling of Continuous Operation Using Batch Experimental Data. ASABE Annual International Meeting paper#: 2001666. July 10-13. Virtual.


Progress 07/01/19 to 06/30/20

Outputs
Target Audience:The intended target audiences include the scientific community and the concerned industries, which will be reached through journal articles and the papers presented in the Annual Meeting of American Society of Agricultural and Biological Engineers. However, as of this reporting period, outreaching effort from this project is minimal due to the slow start of the project affected by both the difficulties in hiring graduate students in fall 2019 and the nationwide campus lockdown due to covid-19 in spring and summber 2020. Changes/Problems:Due to the delay of project startup caused by the various reasons stated above, the current project may not be completed in the originally proposed time frame (7/1/2019-6/30/2022). Requesting a no-cost extension at the end of the current project ending date is thus anticipated, i.e., the project ending date most likely will be changed to 6/30/2023. This is the only potential change to the best of our knowledge by now. What opportunities for training and professional development has the project provided?Two graduate students have been hired so far in U of AR and U of ID, respectively, and one more will come on board in fall 2020 in V Tech. Therefore, this project starts to provide training opportunities for graduate students to prepare them for their career development in the respective areas described in this proposal. 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?We plan to accomplish these goals as assigned to the three institutions in the proposal. Progress will be made progressively to accomplish individual goals in a stepwise manner. In the next reporting period, the separate working plans for each institution are presented below. University of Arkansas: In the next reporting period, experiments will be conducted with the anaerobic digester for different running regimes to determine the best combination on maximizing Mg2+ and PO43- releases for struvite precipitation. University of Idaho: The next step is to select a better magnesium alloy material for the anode, and optimize the extraction of phosphorus from wastewater as a function of pH, current density, mixing speed, and study the effect of foreign ions (Ca2+ and humic acid) on struvite recovery to prepare the use of this reactor for the effluent of digested poultry litter. Virginia Tech: After completing the construction of FO and MD modules, experiments will be run with the membrane modules to test the effect of different variable combinations on the maximum water recovery. Data will be collected and analyzed to develop publishable materials.

Impacts
What was accomplished under these goals? Due to the delay in hiring graduate students in all three institutions involved in this project (one student was hired in spring 2020 in UofAR, one in May 2020 in UofID, and one in fall 2020 in V. Tech) and the covid-19 pandemic leading to shutdown of campuses and labs, only limited accomplishments are available in this reporting period, which are presented below according to the results from each institution. University of Arkansas One graduate student came on board in spring 2020 and was immediately involved in initiating the project. However, just before taking off, covid-19 hit and the university campus was completely locked down with no access to labs whatsoever, leading to the halt of the project. As the campus reopened in stage I and II, labs became accessible starting from June 2020 and project work was restarted at a limited level immediately. Up to this point, an anaerobic digester for the project was constructed and ready for experiments. Raw materials such as poultry litter and wheat straw were collected and processed. With the campus continuing to reopen, it is expected that research activity will return to normal this coming fall and more experimental results from the project will be obtained, which will be presented in the next reporting period. University of Idaho Similar delayed scenario was seen in University of Idaho. With a graduate student hired in May 2020, the project was jump-started immediately. An electrolytic reactor (working volume of 1 liter) with an anodic magnesium plate was fabricated, assembled, and trial experimented in batch operational mode with synthetic wastewater to determine the feasibility of struvite precipitation. The system included an electrolytic unit, a DC power supply, a peristaltic pump, and a mixer. High purity magnesium alloy AZ31 and stainless steel are used as the anode and cathode materials. The distance between the anode and cathode plates is 3.5 cm, and the anodic magnesium plate and the cathodic stainless-steel plate are connected to the positive and negative outlets of the power supply, respectively. Preliminary results showed that higher current density resulted in a higher rate of precipitate formation, while the magnesium anode dissolved significantly at high current density of 45.4 A/m2. The AZ31 alloy could not withstand higher current densities as the rate of dissolution was too fast, which led to disintegration of large pieces of Mg particles from the electrode surface. Precipitate scale formation was also observed on the surface of the Mg anode, which slowed down the overall process considerably. Formal experiments are planned when the University goes back to normal business operations, and data will be collected and analyzed, which will be reported in the next reporting period. Virginia Tech The project has been delayed because of both COVID-19 and the time it took to recruit a new graduate student for doing this project. An international Ph.D. student has been successfully recruited and will report to the position by Fall 2020 if his travel is not further impacted by the COVID-19 pandemic. Despite that, purchasing materials and supplies was initiated and is ongoing to prepare for the assembly of the forward osmosis (FO) and membrane distillation (MD) modules in order to kick off the project immediately after the new hire is on board. With the experiments up and running starting fall 2020, it is expected that we will have substantial results to report during the next reporting period.

Publications