Progress 10/01/01 to 09/30/05

Outputs
This study addressed preliminary optimization (biogas production and organic strength reduction) of an ASBR treating dilute swine slurries from pit-recharge manure management systems commonly found in confined swine housing. Based on the results, optimum biogas yields from anaerobic digestion of low-strength swine waste (0.3 to 0.4 percent total solids) were approximately 0.14 mL/mg chemical oxygen demand (COD) and 0.16 mL/mg COD at 5.25 and 6 days hydraulic retention time (HRT) at digestion temperatures of 20 C and 35 C, respectively. Higher operational temperature improved the specific biogas yield, but the qualities of biogas produced at the two temperatures, although high (65 to 70 percent CH4 and 17 to 20 percent CO2), were not significantly different. Maximum COD reductions of approximately 90 percent and 84 percent would be achieved at 7.2 and 9.1 days HRT at digestion temperatures of 20 C and 35 C, respectively. Higher COD reduction (implying more bio-stabilization of slurry) in the lower-temperature digester was attributed to less biomass washout, which is likely due to more efficient solids settling. The volatile fatty acids at both reactor temperatures were reduced from a mean of 639 (plus or minus 75) mg/L in the influent to mean values of 74 (plus or minus 12) and 85 (plus or minus 17) mg/L in the effluents at 20 C and 35 C, respectively, which significantly mitigated the potential of odor generation from the effluents. Additionally, it was observed that the nutrient (both nitrogen and phosphorus) levels in the effluents remained about the same as in the influent.

Impacts
Use of anaerobic digestion for the treatment and recovery of biogas from concentrated animal waste effluents is a technically viable approach, but widespread acceptance has been limited due to poor economics. This challenge is magnified several-fold when considering anaerobic digestion of low-strength or dilute animal slurries because of the larger digester volumes and the corresponding high energy input requirements. These constraints could be mitigated by using an anaerobic sequencing batch reactor (ASBR). This technology has shown tremendous potential to improve the economics for the treatment of dilute animal waste effluents.

Publications

• Ndegwa, P.M., Hamilton, D.W., Lalman, J.A., and Cumba, H.J. 2005. Optimization of anaerobic sequencing batch reactors treating dilute swine slurries. Transactions of the ASAE 48(4):1575-1583.

Progress 10/01/03 to 09/30/04

Outputs
The operational processes of the two 12-L ASBR reactors were automatically controlled once the reactors were acclimated with raw swine manure at the experimental organic loadings. Digital timers and peristaltic pumps were used to control daily feeding, mixing, and decanting effluent. Collected raw manure was placed in a 5-gallon plastic bucket inside a refrigerator that has a side opening for pumping manure to the reactors. Biogas production was monitored using a tipping-bucket meter. The organic loading rates were set at 400, 600, 800, and 1200 mg COD/L-d which corresponded to 12, 8, 6, and 4 days HRT. These loadings were investigated using one feeding per day, but ongoing studies looks for gradually increasing the feeding sequence to four loading per day with different combinations of organic loadings and HRTs at 20 degrees C and 35 degrees C. Preliminary results using one feeding per day indicates that the maximum COD reduction were approximately 84% to 90%, at 7.2 and 9.1 days HRT, at 20 degrees C and 35 degrees C. The optimum biogas yield is approximately 0.14 mg/mg COD at 5.25 days HRT. Also, the effluent VFA and nutrients (N&P) were low, resulting from an efficient biodegradation of high organic materials into digested solids and methane and CO2 gases. Two kinetics trials were conducted: a 28-day unseeded trial and a 42-day seeded trial. Each trial included 24 reactors. Research variables were % Total Solids (0.25, 0.50, and 0.75%) and Temperature (20 degrees C and 35 degrees C). Due to a prolonged storage time, microbiological populations were dormant during the unseeded trial, and a decision was made to end the trial. Anaerobic sludge was obtained from the City of Tulsa Northside Wastewater Treatment Plant, and each reactor was seeded with approximately 10% seed sludge. All %TS and T schemes provided significant degradation, with the most substantial consumption of substrate occurring at 35 degrees C with a TS loading of 0.75%. The results from the kinetic studies are currently being used to develop an anaerobic model applicable for ASBR treating swine waste.

Impacts
Experiments to determine the impact of ASBR to treat swine waste are currently in progress.

Publications

• Cumba, Hector. Short Term Kinetic Study of Anaerobic Microbiological Properties of Diluted Swine Slurry. 2004.

Progress 10/01/02 to 09/30/03

Outputs
The bench scale anaerobic sequencing batch reactors (ASBRs) built at OSU were seeded with anaerobic biomass obtained from an anaerobic digestors located at the wastewater treatment plant of the City of Stillwater, OK. Two-stage acclimation period was performed since the seeded biomass and the experimental swine wastewater have different organic strength characteristics. During the first stage, the reactors were fed with city wastewater. After one month of acclimation, the reactors were gradually fed with characterized swine wastewater. Throughout the acclimation period, the reactors were constantly monitored for biogas composition, organic acid production, and biosolids composition. Biogas and organic acids were analyzed using a gas chromatography and ion chromatography, respectively. Both instruments are equipped with a thermal conductivity detector. After five months of biomass and swine wastewater acclimation, the first series of experiment started by operating the reactors at different organic loading rates with constant hydraulic retention time (HRT) and solid retention time (SRT). Mixing pattern was kept constant throughout the experiment. These parameters are going to be evaluated one at a time on a series of experiments to determine the optimum operating parameters of the ASBR. At OSU-Tulsa the preparation for the ASBR kinetic experimentation has been ongoing using serum bottles to simulate the bench reactors built at OSU. A dedicated gas chromatography has been set up and calibrated to run biogas samples produced in the serum bottles. The kinetic experiments involve triplicates of 18 serum bottles at 20 degrees C and 35 degrees C.

Impacts
Experiments to determine the impact of ASBR to treat swine waste are currently in progress.

Publications

• No publications reported this period

Progress 10/01/01 to 09/30/02

Outputs
The overall scope of the proposed work was to investigate the use of anaerobic sequencing batch reactors (ASBRs) for treating swine waste in Oklahoma. Choice of a suitable treatment technology depended on simplicity for farm implementation, energy recovery and nutrient recycling. A graduate student has been recruited to conduct the bench-scale studies to determine the ASBR operational parameters for maximizing methane production and nutrient uptake into biosolids. This student is funded by a competitive grant from the Environmental Institute at Oklahoma State University (OSU). This grant is also funding the purchase of equipment and two graduate students at the OSU-Tulsa campus. Within the reporting period, design and construction of the lab-scale ASBRs were completed together with purchase of relevant instrumentation needed for the reactors. In addition, most of the necessary laboratory analytical methods and procedures have been developed. It is, therefore, expected that seeding of the reactors will commence soon followed by the approximately four-months biomass acclimation to the swine waste needed before the start of initial studies. After acclimation, the reactors will be operated under increasing organic loading conditions. Additionally, the impact of operational variables such as hydraulic retention time (HRT) and solids retention time (SRT) will be investigated. Mechanistic modeling studies will examine the impact of different operational conditions on nitrogen and phosphorus uptake into the biosolids. Several models have been discussed, and work is progressing on compiling an overall model comprising the anaerobic digestion aspects along with N and P cycling in the ASBR process.

Impacts
The proposed work to examine the impact of using an anaerobic process to treat animal waste is under investigation. This research will examine the use of an anaerobic technology for nutrient removal and energy recovery from swine waste.

Publications

• No publications reported this period