Nitrogen and Sulfur Concentrations and Flow Rates of Corn Wet‐Milling Streams

Nitrogen (N) and sulfur (S) concentrations can affect the market value of coproducts from corn wet‐milling. The composition of parent streams would be expected to affect composition of the resulting coproducts but there are few published data available to examine this relationship. Concentration and flow data are needed to determine which streams are important in modifying N and S coproduct concentrations. The objective was to measure concentrations and flows of N and S in corn wet‐milling streams. Samples were taken from 21 process streams from 3 wet‐milling plants during two periods of three weeks each; N and S concentrations of each sample were determined. There were large differences in N and S concentrations among processing streams; within most streams, N and S concentrations were similar among plants. Concentrations of N and S were related inversely to flow rates. Steepwater and gluten streams contained most of the N and S flow and provide an opportunity for modification. The process water stream carried large quantities of N and S and represents another opportunity for improving process efficiency and coproduct value.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141537/1/cche0260.pd

Anaerobic microbial community response to methanogenic inhibitors 2‐bromoethanesulfonate and propynoic acid

Methanogenic inhibitors are often used to study methanogenesis in complex microbial communities or inhibit methanogens in the gastrointestinal tract of livestock. However, the resulting structural and functional changes in archaeal and bacterial communities are poorly understood. We characterized microbial community structure and activity in mesocosms seeded with cow dung and municipal wastewater treatment plant anaerobic digester sludge after exposure to two methanogenic inhibitors, 2‐bromoethanesulfonate (BES) and propynoic acid (PA). Methane production was reduced by 89% (0.5 mmol/L BES), 100% (10 mmol/LBES), 24% (0.1 mmol/LPA), and 95% (10 mmol/LPA). Using modified primers targeting the methyl‐coenzyme M reductase (mcrA) gene, changes in mcrA gene expression were found to correspond with changes in methane production and the relative activity of methanogens. Methanogenic activity was determined by the relative abundance of methanogen 16S rRNA cDNA as a percentage of the total community 16S rRNA cDNA. Overall, methanogenic activity was lower when mesocosms were exposed to higher concentrations of both inhibitors, and aceticlastic methanogens were inhibited to a greater extent than hydrogenotrophic methanogens. Syntrophic bacterial activity, measured by 16S rRNA cDNA, was also reduced following exposure to both inhibitors, but the overall structure of the active bacterial community was not significantly affected.This manuscript reports a comprehensive approach to characterizing the effects of commonly used methanogenesis inhibitors on an anaerobic microbial community. We use mock and environmental communities and target two genes using DNA‐ and RNA‐based methods. Results from Illumina sequencing of the 16S rRNA gene, 16S rRNA cDNA, mcrA gene, and mcrA transcript cDNA highlight shifts in both methanogenic archaeal activity and syntrophic bacterial activity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134127/1/mbo3349.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134127/2/mbo3349_am.pd

An Environmental Science and Engineering Framework for Combating Antimicrobial Resistance

On June 20, 2017, members of the environmental engineering and science (EES) community convened at the Association of Environmental Engineering and Science Professors (AEESP) Biennial Conference for a workshop on antimicrobial resistance. With over 80 registered participants, discussion groups focused on the following topics: risk assessment, monitoring, wastewater treatment, agricultural systems, and synergies. In this study, we summarize the consensus among the workshop participants regarding the role of the EES community in understanding and mitigating the spread of antibiotic resistance via environmental pathways. Environmental scientists and engineers offer a unique and interdisciplinary perspective and expertise needed for engaging with other disciplines such as medicine, agriculture, and public health to effectively address important knowledge gaps with respect to the linkages between human activities, impacts to the environment, and human health risks. Recommendations that propose priorities for research within the EES community, as well as areas where interdisciplinary perspectives are needed, are highlighted. In particular, risk modeling and assessment, monitoring, and mass balance modeling can aid in the identification of “hot spots” for antibiotic resistance evolution and dissemination, and can help identify effective targets for mitigation. Such information will be essential for the development of an informed and effective policy aimed at preserving and protecting the efficacy of antibiotics for future generations

Considerations for reducing food system energy demand while scaling up urban agriculture

There is an increasing global interest in scaling up urban agriculture (UA) in its various forms, from private gardens to sophisticated commercial operations. Much of this interest is in the spirit of environmental protection, with reduced waste and transportation energy highlighted as some of the proposed benefits of UA; however, explicit consideration of energy and resource requirements needs to be made in order to realize these anticipated environmental benefits. A literature review is undertaken here to provide new insight into the energy implications of scaling up UA in cities in high-income countries, considering UA classification, direct/indirect energy pressures, and interactions with other components of the food–energy–water nexus. This is followed by an exploration of ways in which these cities can plan for the exploitation of waste flows for resource-efficient UA. Given that it is estimated that the food system contributes nearly 15% of total US energy demand, optimization of resource use in food production, distribution, consumption, and waste systems may have a significant energy impact. There are limited data available that quantify resource demand implications directly associated with UA systems, highlighting that the literature is not yet sufficiently robust to make universal claims on benefits. This letter explores energy demand from conventional resource inputs, various production systems, water/energy trade-offs, alternative irrigation, packaging materials, and transportation/supply chains to shed light on UA-focused research needs. By analyzing data and cases from the existing literature, we propose that gains in energy efficiency could be realized through the co-location of UA operations with waste streams (e.g. heat, CO2, greywater, wastewater, compost), potentially increasing yields and offsetting life cycle energy demands relative to conventional approaches. This begs a number of energy-focused UA research questions that explore the opportunities for integrating the variety of UA structures and technologies, so that they are better able to exploit these urban waste flows and achieve whole-system reductions in energy demand. Any planning approach to implement these must, as always, assess how context will influence the viability and value added from the promotion of UA

Quantifying the Impact of Wastewater Micronutrient Composition on in Situ Growth Activity of Acinetobacter spp.

Batch growth studies with pure cultures of Acinetobacter johnsoniiT and Acinetobacter johnsonii strain 210 on various media formulations were used to examine the effects of micronutrient composition on the growth rate of microbial populations in wastewater treatment systems. On nutrient rich Luria-Bertani medium, both strains of A. johnsonii grew with a doubling time of approximately 30 min. On a defined, minimal medium with acetate as the sole carbon source, the doubling time of A. johnsoniiT was 9.62 h and the doubling time of strain 210a was 2.6 h. Using a synthetic wastewater as a growth medium, the type strain had a doubling time of 56 h and strain 210a had a doubling time of 9.62 h. The concentration and redox state of iron appeared to be the principle growth limiting factors with higher doubling times occurring in media containing ferric iron as compared to ferrous iron. Additionally, grab samples from batch growth experiments were analyzed with oligonucleotide hybridization probes targeting the mature 16S ribosomal RNA (rRNA) and precursor 16S rRNA of Acinetobacter spp. Results showed that the precursor 16S rRNA levels responded more rapidly and to a greater extent than total 16S rRNA levels to changes in the micronutrient composition of the growth media. Precursor 16S rRNA levels increased in both strains when overnight cultures were diluted with fresh media and when micronutrient supplements were added to growing cultures. Our results show that the micronutrient composition of the influent wastewater can have a significant impact on the microbial community structure in wastewater treatment systems

Who Eats What? Classifying Microbial Populations Based on Diurnal Profiles of rRNA Levels

Identifying the relationships between various bacterial populations and the substrates they consume is central to the understanding of population dynamics and to the development of process control in activated sludge. However, linking a heterotrophic population to its activity in situ is difficult because ribosomal RNA (rRNA) techniques, while allowing the rapid identification of populations, provide little information about their heterotrophic activity. Activated sludge models describe biodegradation kinetics by classifying substrates into two types: readily and slowly degradable substrates. Assuming that bacterial populations specialize in degrading one type of substrate, their growth rate should be affected differently if the COD loading rate varies diurnally as for a municipal activated sludge system. Modeling results suggested that the growth rates of populations consuming readily degradable substrates vary according to variations in COD loading rate. On the other hand, the growth rates of populations consuming slowly degradable substrates do not change despite the variation in COD loading rate. Since the cellular rRNA level is positively correlated with the growth rate, we hypothesized that the rRNA levels of some populations in municipal activated sludge should increase throughout the day, while they should stay constant for other populations. This hypothesis was verified by monitoring the rRNA level of Acinetobacter (a model population consuming readily degradable substrates) and Gordonia (a model population consuming slowly degradable substrates) in the mixed liquor of a full-scale municipal activated sludge reactor for three weeks

Oligonucleotide Probe Hybridization and Modeling Results Suggest that Populations Consuming Readily Degradable Substrate have High Cellular RNA Levels

Analyses based on ribosomal RNA (rRNA)-targeted hybridization performed in our laboratory identified two types of bacterial populations: a population with a high RNA level per biomass and a population with a low of RNA per biomass. To extend these descriptions, the diurnal dynamics of the RNA pool were monitored by rRNA-targeted oligonucleotide probe membrane hybridization. Under the typical diurnal variation in COD loading rate experienced by municipal wastewater treatment plants, the RNA level of the bacterial population with a high level of RNA per biomass varied with changs in the COD loading rate. Under the same conditions, the RNA level of the population with low RNA level per biomass remained constant. A structured biomass model was developed to describe these data. Substrate COD was divided into a readily biodegradable and a slowly biodegradable COD fraction. It was assumed that two specialized populations coexist in municipal activated sludge treatment systems. One population consumes readily degradable COD and the other consumes slowly degradable COD. According to model simulations, the population consuming readily degradable COD has a high level of RNA per biomass under variable substrate concentrations. Comparatively, the population consuming slowly degradable COD has a low level of RNA level per biomass. Furthermore, model simulations reproduced the two diurnal RNA profiles observed in a full-scale municipal activated sludge system. Therefore, we suggest that two populations can be distinguished in municipal activated sludge systems: a population consuming readily degradable substrate and a population consuming slowly degradable substrate

Interfacing Phylogenetic Oligonucleotide Probe Hybridizations with Representations of Microbial Populations and Specific Growth Rates in Mathematical Models of Activated Sludge Processes

Accurate estimates of microbial population concentrations and the direct, in situ determination of kinetic parameters could improve the calibration and validation of existing mechanistic mathematical models of biological nutrient removal activated sludge systems. Oligonucleotide probe hybridizations show promise for measuring concentrations and in situ specific growth rates of microbial populations. The most common targets for oligonucleotide probes are the phylogenetically conserved ribosomal RNA molecules. Recent advances in hybridization techniques have improved the quantitative nature of ribosomal RNA based assays. However, correlations between concentrations of \u27theoretical\u27 microbial populations predicted by mechanistic models and quantitative information obtained with oligonucleotide probe hybridizations are not yet developed. Future work should develop such correlations, while addressing the limitations of the molecular assays