Degree Type

Dissertation

Date of Award

2006

Degree Name

Doctor of Philosophy

Department

Civil, Construction, and Environmental Engineering

First Advisor

Hans (J) van Leeuwen

Second Advisor

Anthony L. Pometto, III

Abstract

High organic strength food-processing wastewaters are typically treated with conventional aerobic systems such as an activated sludge process that produces substantial quantities of low value bacterial sludge. Treatment and disposal of bacterial sludge place a huge burden on wastewater plants. Industrial wastewaters with high organic content treatment are also often treated with bacterial processes. The research in this dissertation focuses on using fungi to treat food-processing wastewater to produce biomass that is a good source of valuable byproducts (e.g. enzymes, protein, and other bio-chemicals). The recovery of value added products derived from the fungal biomass could generate additional revenue for the industry. However, controlling bacterial domination is critical in non-aseptic fungal wastewater treatment. An attached growth fungal system was employed in this study to prevent the bacterial contamination by maintaining the high fungal density in the reactor. Plastic composite support (PCS) tubes, composed of 50% (w/w) polypropylene (PP) and 50% (w/w) agricultural products, were used as a support medium to grow Rhizopus oligosporus on corn wet milling wastewater. The effects of sterile operation, nutrient supplementation, support medium composition, pH, hydraulic retention time (HRT) and airflow rate on PCS biofilm continuous-reactor were evaluated;The results proved that supplementation of nutrients (nitrogen and phosphorus) under aseptic conditions enhanced the chemical oxygen demand (COD) removal and biomass yield from 50% and 0.11 g(dry-weight)/gCODremoved to 55% and 0.16 g(dry-weight)/gCODremoved, respectively. Under non-aseptic operation, total biomass production of 0.32 g volatile suspended solids (VSS)/gCOD removed was obtained with no significant improvement in COD removal (~53%), whereas with nutrient supplementation, COD removal improved significantly to 85% with a high biomass production of 0.56 gVSS/gCODremoved. Significantly lower COD removals and biomass yields were observed in the control bioreactors with PP tubes alone and suspended growth, which confirmed that the PCS medium with agricultural components was essential for better biofilm formation and organic removal;COD removal and biomass yield were maximal at pH 4.0 with minimal bacterial competition. Highest COD removal of 78% was achieved at a 5 h HRT with a biomass yield of 0.44 gVSS/gCODremoved. At 3.75 and 2.5 h HRT, the biomass yield increased to 0.45 and 0.48 gVSS/gCODremoved while COD removal reduced to 76 and 70%, respectively. An HRT of 5 h was most suitable for COD removal because of the longer contact time of wastewater with biomass. Maximum biomass yield was achieved at 2.5 h HRT due to higher substrate availability rate, but the biofilm was more sensitive to wastewater composition changes. Therefore, 3.75 h HRT was recommended as a compromise for bench-scale operation. Competitive bacterial growth was reduced with shorter HRTs. The shortest HRT of 1.25 h led to biomass wash out from the reactor. The wastewater composition proved to have significant effect on the biofilm reactor performance;Supply of air at a rate of 1.0 Lmin-1 (0.8 vvm) was found optimal. Increase in the airflow rates improved COD removal as well as biomass production. In-situ dissolved oxygen concentrations indicated an oxygen limiting condition in the reactor. Fungal biomass exhibited better settleability at higher airflows. Detailed study on hydrodynamic properties and mass transfer characteristics in a pilot scale reactor is warranted for better optimization of the aeration system;The results of this study showed that an attached growth fungal treatment system with PCS medium was effective in treating nutrient supplemented corn wet milling wastewater with simultaneous recovery of high value fungal biomass and suppression of bacterial competition.

DOI

https://doi.org/10.31274/rtd-180813-11427

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Nagapadma Jasti

Language

en

Proquest ID

AAI3243571

File Format

application/pdf

File Size

139 pages

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