Mary Hummerick

Design and Preliminary Evaluation of a Novel Gravity Independent Rotating Biological Membrane Reactor

The integration of membrane-aeration technology with biological water processors has direct application to wastewater treatment in microgravity because of the ability to diffuse gases across the membrane without two-phase interactions (gas-liquid). Membrane-aeration bioreactors have demonstrated the ability to deliver a terminal electron acceptor (O 2 ) and substrates (CH 4 and H 2 ) to biofilms attached to the membrane surface. However, the process performance of these systems has been limited by mass transfer constraints. A novel bubbleless membrane-aeration bioreactor was design and tested at Kennedy Space Center. The Aerobic Rotational Membrane System (ARMS) consists of a rotational membrane module inside of a pressurized reactor vessel. Rotation of the membrane module enables a reduction in the mass transfer resistance coefficients associated with both the membrane/liquid boundary layer (k La ) and constituents in the bulk liquid, and it equalizes the concentration gradient across the bioreactor allowing for uniform biofilm formation and decreased bulk liquid O 2 transfer. Preliminary engineering tests have been conducted to determine the effect of key operational parameters (i.e. rotational speed, superficial velocity) on O 2 flux rates and hydrodynamic characteristics within the ARMS. This paper presents the ARMS design and results of the preliminary engineering tests.

Genome-wide expression analysis of reactive oxygen species gene network in Mizuna plants grown in long-term spaceflight

BackgroundSpaceflight environment have been shown to generate reactive oxygen species (ROS) and induce oxidative stress in plants, but little is known about the gene expression of the ROS gene network in plants grown in long-term spaceflight. The molecular response and adaptation to the spaceflight environment of Mizuna plants harvested after 27 days of cultivation onboard the International Space Station (ISS) were measured using genome-wide mRNA expression analysis (mRNA-Seq).ResultsTotal reads of transcripts from the Mizuna grown in the ISS as well as on the ground by mRNA-Seq showed 8,258 and 14,170 transcripts up-regulated and down-regulated, respectively, in the space-grown Mizuna when compared with those from the ground-grown Mizuna. A total of 20 in 32 ROS oxidative marker genes were up-regulated, including high expression of four hallmarks, and preferentially expressed genes associated with ROS-scavenging including thioredoxin, glutaredoxin, and alternative oxidase genes. In the transcription factors of the ROS gene network, MEKK1-MKK4-MPK3, OXI1-MKK4-MPK3, and OXI1-MPK3 of MAP cascades, induction of WRKY22 by MEKK1-MKK4-MPK3 cascade, induction of WRKY25 and repression of Zat7 by Zat12 were suggested. RbohD and RbohF genes were up-regulated preferentially in NADPH oxidase genes, which produce ROS.ConclusionsThis large-scale transcriptome analysis revealed that the spaceflight environment induced oxidative stress and the ROS gene network activation in the space-grown Mizuna. Among transcripts altered in expression by space conditions, some were common genes response to abiotic and biotic stress. Furthermore, certain genes were exclusively up-regulated in Mizuna grown on the ISS. Surprisingly, Mizuna grew in space normally, as well as on the ground, demonstrating that plants can acclimate to long-term exposure in the spaceflight environment by reprogramming the expression of the ROS gene network.

Effect of hydraulic retention time on inorganic nutrient recovery and biodegradable organics removal in a biofilm reactor treating plant biomass leachate

A fixed-film (biofilm) reactor was designed and its performance was determined at various retention times. The goal was to find the optimal retention time for recycling plant nutrients in an advanced life support system, to minimize the size, mass, and volume (hold-up) of a production model. The prototype reactor was tested with aqueous leachate from wheat crop residue at 24, 12, 6, and 3 h hydraulic retention times (HRTs). Biochemical oxygen demand (BOD), nitrates and other plant nutrients, carbohydrates, total phenolics, and microbial counts were monitored to characterize reactor performance. BOD removal decreased significantly from 92% at the 24 h HRT to 73% at 3 h. Removal of phenolics was 62% at the 24 h retention time, but 37% at 3 h. Dissolved oxygen concentrations, nitric acid consumption, and calcium and magnesium removals were also affected by HRT. Carbohydrate removals, carbon dioxide (CO2) productions, denitrification, potassium concentrations, and microbial counts were not affected by different retention times. A 6 h HRT will be used in future studies to determine the suitability of the bioreactor effluent for hydroponic plant production.

Heat Melt Compaction as an Effective Treatment for Eliminating Microorganisms from Solid Waste

One of the technologies being tested at Ames Research Center as part of the logistics and repurposing project is heat melt compaction (HMC) of solid waste to reduce volume, remove water and render a biologically stable and safe product. Studies at Kennedy Space Center have focused on the efficacy of the heat melt compaction process for killing microorganisms in waste and specific compacter operation protocols, i.e., time and temperature required to achieve a sterile, stable product. The work. reported here includes a controlled study to examine the survival and potential re-growth of specific microorganisms over a 6-month period of storage after heating and compaction. Before heating and compaction, ersatz solid wastes were inoculated with Bacillus amyloliquefaciens and Rhodotorula mucilaginosa, previously isolated from recovered space shuttle mission food and packaging waste. Compacted HMC tiles were sampled for microbiological analysis at time points between 0 and 180 days of storage in a controlled environment chamber. In addition, biological indicator strips containing spores of Bacillus atrophaeus and Geobacillus stearothermophilus were imbedded in trash to assess the efficacy of the HMC process to achieve sterilization. Analysis of several tiles compacted at 180deg C for times of 40 minutes to over 2 hours detected organisms in all tile samples with the exception of one exposed to 180deg C for approximately 2 hours. Neither of the inoculated organisms was recovered, and the biological indicator strips were negative for growth in all tiles indicating at least local sterilization of tile areas. The findings suggest that minimum time/temperature combination is required for complete sterilization. Microbial analysis of tiles processed at lower temperatures from 130deg C-150deg C at varying times will be discussed, as well as analysis of the bacteria and fungi present on the compactor hardware as a result of exposure to the waste and the surrounding environment. The two organisms inoculated into the waste were among those isolated and identified from the HMC surfaces indicating the possibility of cross contamination.

Development of a Fixed-Film Bioreactor for Recycling of Inedible Plant Nutrients in Controlled Biological Systems

Controlled ecosystems, including coupled hydroponic and bioreactor systems, are being developed for long-term space missions, in order to reduce the need to resupply food, water, and oxygen. Food crops grown in such systems (e.g. wheat) can be greater than 60% by weight inedible matter: stalks, leaves, roots, and chaff. Significant levels of inorganic nutrients can be leached from this material and recycled back to the plant growth system; however, leaching also extracts organics including soluble carbohydrates, which can reduce plant growth. A fixed-film system, consisting of a floating bead reactor in a loop with an oxygenation cone, was designed for BOD reduction in the smallest practicable volume. Temperature and pH are controlled, and the bead bed is mechanically agitated and backwashed. BOD reductions range from 93% to 68% for retention times from 1 day to 90 minutes. At the shorter retention times, severe fouling occurs on all surfaces. The system has been modified to try to combat these problems, including installing redundant flow switches and placing sensors in a separate loop.

A hazard analysis critical control point plan applied to the Lada vegetable production units (VPU) to ensure the safety of space grown vegetables

The Lada Vegetable Production Unit (VPU), flight hardware currently deployed on the Russian module of the International Space Station (ISS), is being used to validate the food safety of fresh “space-grown” crops. The final objective of this project is the development of a hazard analysis and critical control point (HACCP) plan for Lada grown crops to minimize potential microbial risks to the astronauts. Following FDA guidelines for the development of a HACCP plan, the identification of hazards and critical control points associated with the production of consumable crops grown in the Lada VPU and the establishment of preventative procedures to minimize risk were performed through the collection of baseline microbiological data and testing of pre and post harvest sanitization protocols. Microbiological data collected from both plant tissue and hardware (e.g., root modules) returned from a variety of crops grown on ISS and ground based experiments have been done to define normal microbial loads and understand the fate and survival of human associated pathogens in the Lada VPU. Protocols have been tested to determine the effectiveness of a sanitizer approved by the FDA and USDA (Pro-San) to achieve acceptable levels of microbes on VPU surfaces and vegetables. These data have been used to develop the HACCP plan outlined here for crops grown in a VPU designed for a space environment.

Continuous Leaching (Bio)reactor

A continuous leaching device was designed to extract inorganic nutrients from ALS solid wastes for recycling back to hydroponic plant growth systems. The system consists of a conveyor that carries the waste under a water spray. The leacher was used to extract nutrients from hydroponic rice crop residues. The highly aerated and nutrient-rich recirculation liquid supports microbial growth on all surfaces, which leads to biofouling that causes maintenance difficulties. However, it may be better than the standard leaching protocol, as it produces leachate with significantly reduced BOD. This would make it possible to use the leachate from this reactor in hydroponic plant systems without further processing.

The effect of plant cultivar, growth media, harvest method and post harvest treatment on the microbiology of edible crops.

Systems for the growth of crops in closed environments are being developed and tested for potential use in space to provide a source of fresh food. Plant growth conditions, growth media composition and harvest methods can have an effect on the microbial population of the plant, and therefore should be considered along with the optimization of plant growth and yields to ensure a safe and palatable food crop. This work examined the effect of plant cultivar, growth medium, and harvest method on plant microbial populations. Twelve varieties of leafy greens and herbs were grown in a mixture of Fafard #2 and Arcillite using the “pillow” root containment system currently being considered for the VEGGIE plant growth unit developed by Orbitec. In addition, Sierra and Outredgeous lettuce varieties were grown in three different mixtures (Fafard #2, Arcillite, and Perlite/Vermiculite). The plants were analyzed for microbial density. Two harvest methods, “multiple cuttings” and single harvestwere also compared in separate experiments. Red leaf lettuce and mizuna were grown in pots in a Biomass Production System for Education (BPSe) chamber and harvested every two weeks by either method. Another set of experiments was performed using the rooting pillows to grow five varieties of leafy greens and cut harvest at different time intervals. Radishes were harvested and replanted at two-week intervals. Results indicate up to a 3 log 10 difference in microbial counts between some varieties of plants. Lettuce grown in arcillite rooting medium resulted in an approximately 2 log 10 lower count than those grown in the other mixtures. Harvest method and frequency had less impact on microbial counts only showing a significant increase in one variety of plant. Post harvest methods to decrease the bacterial counts on edible crops were investigated in these experiments.