No abstract

In order to mitigate nutrient pollution in surface runoff more sustainably, the finite capacity for phosphorus (P) sequestration in best management practices (BMP) that rely heavily on sorption processes must be addressed. These BMP include sand filters, bioretention cells, and several types of constructed wetland. This study investigated facilitated microbial reduction of iron-based filtration substrates to promote controlled release of P previously sequestered by the BMP, P harvest for recycling, and rejuvenation of the substrate sorption capacity. Total dissolved P was well correlated with total dissolved iron during the reduction process, indicating that microbial iron reduction was capable of releasing previously sequestered P from substrates. Furthermore, results indicated that a sufficient carbon source was necessary but addition of a microbial culture was not necessary to facilitate iron reduction. While a large percentage of the previously sequestered P was removed, the process was much slower than initial sequestration of P by adsorption, and further research is needed to promote a more rapid release of P in order to optimize the rejuvenation process for field application.

Design and construction of full-scale anaerobic digesters that co-digest manure with other substrates, such as food processing wastes, is challenging because of the large number of potential mixtures that can be fed to the digester. In this work we examine the relationship between results from bench-scale methods such as biochemical methane potential assays (BMPs) and sub pilot-scale reactors. The baseline feedstock for this study was beef manure from concrete feedlot pens (open and covered) in eastern Iowa. Additional codigestion substrates tested were short-fiber cardboard, corn processing wastewater, enzyme processing wastewater and lagoon liquid. Substrates were characterized for total solids (TS), volatile solids (VS), chemical oxygen demand (COD), pH, alkalinity, and ammonia, after which BMPs were conducted on all substrates. Based on the BMP and anaerobic toxicity assay (ATA) results, a mixture was created and evaluated using BMPs and tested in 100-L sub pilot-scale reactors. This study showed that results from BMPs of feedstock co-digestion mixtures accurately estimated the range of methane produced from three 100-L, plug flow reactors.

Bench-scale methods such as Biochemical Methane Potential (BMP) assays and Anaerobic Toxicity Assays (ATAs) are useful tools in evaluating potential feedstocks for anaerobic digestion. The BMP method provides a preliminary indication of substrate biodegradability and methane production, while the ATAs provide an indication of substrate toxicity to anaerobic microbial consortia. Previous research using small (<20>L) reactors indicated that co-digestion of manures with small amounts of glycerin (ca. 1-2 %) can double methane production, but toxicity can result if glycerin exceeds 2% (volumetric basis). This paper investigated the relationship between bench-scale methods (BMPs and ATAs) and sub pilot-scale digester results, using glycerin as a test substrate mixed with a baseline feedstock (beef manure, corn processing wastewater, lagoon liquid, and short-fiber cardboard). The batch-fed, stirred ATAs indicated that glycerin was toxic to methane production at all inclusion levels. The batch-fed, stirred BMPs indicated no significant difference between methane production in the 0.0%to 4.0% addition levels; however at 8.0% addition, methane production tripled. The continuously fed, non-stirred, plug-flow sub pilot-scale reactors indicated toxicity effects in the 2.0% and 4.0% glycerin mixtures and no difference from the control in the 1.0% glycerin mixture. These results demonstrate the variations in scale performance of glycerin as a co-substrate and identify some serious challenges in extrapolating bench-scale assays to large-scale performance of mixed-waste anaerobic digestion systems.

been able to pursue my passion for solid waste engineering and have learned a great deal from him. I am very fortunate that Dr. D. Raj Raman was willing to step in and give me direction and guidance as my graduate career unfolded. With the help of Dr. D. Raj Raman and Dr. Robert P. Anex my graduate education was expanded beyond waste engineering, for that I am grateful.