The rapid infiltration (RI) land treatment process is a reliable, cost effective method for secondary and/or tertiary treatment of municipal wastewaters. When properly designed and operated, RI systems can achieve a significant level of nitrogen removal via coupled biological processes, namely nitrification-denitrification. Generally, it is believed that lower overall nitrogen levels can be achieved when influent wastewater is fully nitrified. However, at a specific RI facility located in Colton, CA higher nitrogen removals were observed when non-nitrified influent wastewaters were introduced. As a result, it was first hypothesized that an abiotic mechanism, ammonium adsorption, to the soils was occurring. This hypothesis, led to the conduct of an initial effort to evaluate the sorptive phenomenon that was occurring at this site. As a result of that initial effort, it was determined that ammonium adsorption was not occurring and that no nitrogen removal was observed under abiotic (sterile) conditions. Nitrogen removal was observed only under biotic conditions.

Subsequent to that initial effort, a second study was conducted in an effort to confirm and better understand the biological nitrogen removal mechanisms that are occurring at the Colton RI facility. In addition, experiments were conducted to evaluate whether nitrogen removal could be enhanced at the facility via organic carbon amendment to the influent wastewater. For design purposes, a 2:1 mass ratio of organic carbon to nitrogen is recommended for nitrogen removal in RI systems. The normal organic carbon to nitrogen ratio at the Colton RI facility is 1:3, highly organic carbon deficient. Experimental systems were amended with additional organic carbon in the form of methanol. Additional organic carbon in the Colton RI facility influent water may improve the denitrification rate within some portions of the soil column.

Perchlorate (ClO4-) has gained attention recently due to its interference with thyroid gland function. In infants and unborn children, inadequate thyroid hormone production can cause mental retardation and thyroid tumors. Since new perchlorate standards will be proposed in 2013, and if a stricter standard is imposed, cost effective technologies will be in high demand. The overall objective of this research was to evaluate two perchlorate bioremediation strategies using indigenous soil bacteria: 1) an autotrophic strategy using zero-valent iron (ZVI) to generate hydrogen as the electron donor and alkalinity in the form of (bi)carbonate as the carbon source for cell growth and maintenance and 2) a heterotrophic strategy using organic substrates as the electron donor and the carbon source for cell growth and maintenance.

The first strategy was evaluated on perchlorate-contaminated groundwater from West Valley Water District Well #2 located in Rialto, CA (Chapter III). A mobile treatment system consisting of a water holding tank, a ZVI packed bed and two parallel sand filters was placed at the site. In the first three months, the system experienced excellent performance, as measured by the tested parameters meeting the California drinking water standards. The effluent concentration of perchlorate was non-detectable (below 4 µg/L), nitrate effluent concentration was less than 0.01 mg/L as N, effluent iron ranged from 0 to 0.05 mg/L. Coliforms, fecal coliforms and E. coli in the reactor effluent were below the detection limit of 2 MPN/100mL. However, significant loss of perchlorate performance was observed after 3 months operation. The reason was attributed to the reduction of hydraulic conductivity and flow channeling.

A laboratory column experiment was conducted to investigate the hydraulic condition change in the ZVI beds (Chapter IV). Effects of flow rate and (bi)carbonate on hydraulic condition were evaluated by performing hydraulic conductivity tests, SEM examination, and tracer tests. The results indicated that the decrease of hydraulic conductivity was more pronounced in the low flow reactors than in the higher flow reactors. This result appeared to contradict the hypothesis that increasing the flow rate will accelerate the hydraulic conductivity reduction. (Bi)carbonate was determined to be the primary cause of the hydraulic conductivity reduction. The decrease in hydraulic conductivity was most severe in the segment receiving the higher concentration of NaHCO3. Hydraulic conductivity decreased from 10-2.73 cm/s to 10 -7.33 cm/s after constantly feeding 24 mM of NaHCO3 for 41 days. The reduction of hydraulic conductivity was caused by the formation of mineral precipitates.

Because of the lack of long-term perchlorate reduction in the autotrophic ZVI-based system, an alternative strategy that utilized organics as both the electron donor and carbon growth source was tested for perchlorate bioremediation (Chapter V). Laboratory microcosm and column tests were employed to assess the effectiveness of selected organic substrates on reducing perchlorate from two different locations of a real perchlorate-contaminated site. One location (source area) had 70 mg/L of perchlorate in groundwater, and another one (plume edge, referred to "biobarrier") had 500 µg/L of perchlorate. The effect of adding nutrients was also examined. For the high concentration source area treatment, emulsified oil substrate (EOS) and glycerin were determined to be the most effective organics from the microcosm testing. Hence, they were selected for column testing. The results revealed that amending soil with EOS had significant advantages over using glycerin as a soil amendment. After a single injection of EOS, perchlorate can be reduced to less than 4 µg/L for 4 months. Perchlorate reduction was not initiated in glycerin-amended soil. Glycerin had to be constantly added into the influent to treat perchlorate to non-detectable level. For the low concentration biobarrier treatment, compost/mulch, EOS, and EHC (a combination of carbon plant-based carbon source and zero-valent iron) had similar perchlorate removal rates in microcosm tests. EOS appeared to have greater longevity than EHC in the column tests. The addition of nutrients had minor benefit on both sites treatments.

Comparing the two strategies, using organic substrate was more feasible for perchlorate bioremediation in terms of overall performance and longevity.

Historical, uncontrolled disposal practices have made perchlorate a significant threat to drinking water supplies in the United States. In-situ bioremediation (ISB) technologies are cost effective and provide an environmental friendly solution for treating contaminated groundwater and soil.

In situ bioremediation was considered as an option for treatment of perchlorate in groundwater and soil in Lockheed Martin Corporation's Beaumont Site 2 (Beaumont, CA). Based on the perchlorate distribution and concentration in the ground, in-situ remediation within the site was divided into three parts (groundwater plume, source area groundwater remediation and vadose zone soil remediation). In both groundwater remediation studies, biological reduction of perchlorate was readily achieved within one week by amending electron donating substrates. In both column studies, perchlorate reductions were observed within two weeks operation and emulsified oil substrate (EOS) had the best performance as electron donor in terms of effectiveness and longevity in both column studies. In the vadose zone remediation study, perchlorate degradation did not occur in 20% moisture content microcosms. However, perchlorate reduction occurred under saturated conditions with the same soil and both EOS and glycerin as electron donors.

To investigate the impact of soil moisture condition on perchlorate remediation, soil microcosm studies were conducted with different soils under different mass water contents. Optimum soil moisture content for perchlorate bioremediation varied significantly in different soils. Anaerobic respiration processes other than denitrification were all limited by unsaturated moisture condition in the soil. Dominant electron acceptor in the unsaturated microcosms was oxygen. However, eliminating oxygen in the soil system using an anaerobic chamber did not result in perchlorate reduction. Addition of humic acid as an electron shuttling mediate reduced soil redox potential significantly but was not able to promote perchlorate reduction under unsaturated condition.

In-situ bioremediation of perchlorate was readily achieved in groundwater but it was more challenging in vadose zone. Soil moisture was identified as a key factor in perchlorate remediation and optimum moisture condition in different soil had large variation. The results from this research provide basis for designing and optimization of in-situ bioremediation of perchlorate in different soils and groundwater.

The fate of pathogens upon excretion to natural environments from initial hosts is not fully understood. Often overlooked is the fact that pathogens either cannot survive or lose their virulent characteristics upon exposure to environmental stress. However, problematic pathogens such as Salmonella are very resilient and acclimate well in secondary habitats; therefore requiring comprehensive studies to understand the mechanisms of fitness and survival in external environments. Additionally, despite the widespread knowledge of Salmonella and its interaction with targeted hosts, the deposition and transport behavior of this important food- and waterborne pathogen is not commonly studied. The objective of this research was to understand the fate and transport of Salmonella under a framework of environmentally relevant groundwater conditions. Therefore several Salmonella enterica serovars with different phenotypes were selected and the depositions of these pathogens onto solid surfaces were examined over a range of solution chemistries. Packed bed column and radial stagnation point flow (RSPF) systems were utilized for the transport experiments. Several batch experiments were designed to simulate the stress conditions in aquatic environments to understand the fate of Salmonella in terms of fitness, survival and virulence. These experiments were complemented by a wide range of cellular characterization techniques. Transport experiments of Salmonella in comparison to another important pathogen, E. coli O157:H7 has shown that Salmonella can be transported further than E. coli in saturated packed bed column systems. Additionally, this transport behavior was shown to be affected by different solution chemistries and cell injection concentrations. Deposition and transport behavior of three Salmonella enterica serovars with different motility phenotypes were studied in packed bed column and RSPF systems. Results have shown that flagellated strains deposit more than nonflagellated strains, concluding that nonmotile cells can be transported further than motile cells.

Several batch experiments were designed to simulate a wide range of groundwater conditions to study the fate of Salmonella upon short and long term exposure to environmental stress. Both phenotypical (antibiotic resistance, in vitro and in vivo virulence) and genotypical (gene screening in silico) evaluations of Salmonella fitness, survival, and pathogenicity were conducted. The findings of this research suggest that Salmonella successfully remains viable and virulent under a wide range of groundwater environments.

Excess nutrients, particularly nitrogen, from wastewater discharged into waterways lead to eutrophication, hypoxia, and oceanic red tide that threaten public and environmental health. Anaerobic Ammonium Oxidation or Anammox is a relatively new treatment approach used to remove nitrogen from wastewater. Compared to conventional multi-stage nitrification-denitrification nitrogen (N) removal systems, the Anammox process utilizes less energy and eliminates the need for organic carbon additives in wastewater treatment plants. However, the process has encountered a number of pragmatic challenges that has impeded its widespread adoption as a practical treatment alternative. Foremost among these challenges is the very slow growth rate of the Anammox bacteria, which necessitates long start-up times before high nitrogen removal efficiencies can be obtained on a steady-state basis. Attempts to reduce start-up times are challenged by inadequate seed biomass and bacteria washout during operation. As such, efforts are needed to promote faster bacterial growth and system retention. One approach is to amend bioreactors with materials that have beneficial surface and chemical properties that are capable of concentrating growth factors (e.g., ammonium, NH4+), while enabling selective colonization of Anammox bacteria on the materials’ surfaces. This strategy could reduce start-up time and minimize biomass effluent losses. With evidence of higher cation exchange capacity (CEC) and better ammonium ion exchange (IX) rates than natural clinoptilolites (zeolite, group 7), chabazite material (zeolite, group 4) is hypothesized to be a better choice for enhancing Anammox culture development. Therefore, it was proposed to amend Anammox SBR with chabazite particles to accelerate the startup period and to enhance culture development. Nonetheless, bacterial activity in the amended process risk inhibition from cations released during NH4+-IX. In relation, the study also sought to investigate the effect of chabazite sub-species (-Ca & -K), target cation (NH4+), and competing cation (i.e. K+) on the ammonium oxidation rate.

Anammox culture was developed from atypical thermophilic anaerobic digester (TAD) mixed-sludge added proportionately in three bench-scale reactors. All the reactors exhibited phenotypic Anammox activities at approximately 90% total nitrogen removal with varying start-up times. Increased amount of TAD mixed-sludge in the reactors led to fast start-up time, within 59 days, improved specific anammox activity (SAA) at high nitrogen loading rate, and increased Anammox bacteria population. The Anammox bacteria species in the reactors was identified as “Candidatus Brocadia sinica.” Enhanced culture development in terms of increased gene copy numbers was attributed to less competition among the bacteria involved in the process during start-up. In adding appropriate doses of chabazite to SBRs seeded with fresh return activated sludge (RAS), it was determined that chabazite particles had minimal influence on the Anammox process start-up time since both the amended (with chabazite) and non-amended reactors exhibited evidence of Anammox activity after 69 days. However, chabazite mitigated the effect of high feed concentration variability resulting in optimum feed concentration needed by the Anammox bacteria for development. The quick recovery from influent shock-loads exhibited by chabazite amended reactor was attributed to chabazite concentration of NH4+ on the surface leading to increased Anammox bacteria population. Different chabazite sub-species including the Bowie chabazite A ZUB (Na/Ca), AZLB-Na, and AZLB-Ca were studied to investigate the effective chabazite type for Anammox process amendment. In the order of NH4+ removal efficiencies, reactor amended with chabazite-Ca > Na/Ca > Na > non-amended (control) = sand (attached control).

For the two common chabazite forms in the bioreactors, the reactor containing chabazite-Na was impacted adversely to a greater extent at high feed concentrations compared to the chabazite-Ca reactor with ammonium removal efficiencies decreasing from >95% to 53.5% and >95% to 88%, respectively.

High ammonium removal efficiency observed in chabazite-Ca reactor was attributed to high NH4+ ion-exchange rate compared to chabazite-Na. The effect of chabazite form on ammonium removal depended on the extent to which NH4+ ion-exchange impacted the partial nitrification step of the Anammox process that is mediated by the ammonium oxidizing bacteria. Despite lower reactor activity than the chabazite-Ca reactor, chabazite-Na reactor total specific bacteria population was the highest among the various chabazite amended reactors. High bacteria population in the chabazite-Na reactor resulted from higher NH4+ ion-exchange rate that accelerated bacteria biofilm formation and growth over a prolonged period. The results imply that while chabazite-Ca greatly mitigates the effect of high feed variability on Anammox activities compared to other chabazite sub-species, chabazite-Na exhibits high bacteria population attributed to high NH4+ ion-exchange rate at start-up.

Lastly, sequencing batch reactors with active Anammox biomass were amended with appropriate doses of chabazite-Na, chabazite-Ca, and non-amended (control) to investigate the effect of competing cation (K+) on ammonium oxidation rate and to determine the effect of competing cation (K+) on feed substrates (NH4+ and NO2-) utilization rates in Anammox processes amended with different chabazite sub-species. Upon spiking the feed media with different K+ concentrations that ranged from 0 to 5.12 meq/L, it was determined that the NH4+ and NO2-utilization rates were higher in chabazite-Na reactor compared to chabazite-Ca reactor at high K+ concentration. Further, the effect of NH4+ ion-exchange on partial nitrification was mitigated at increased K+ concentration, which led to improved substrates utilization at increased Anammox bacteria population resulting in higher Anammox removal rates in chabazite-Na reactor than that in chabazite-Ca reactor

Iron nanomaterials including nanoscale zero valent iron (NZVI), NZVI-based bimetallic reductants (e.g., Pd/NZVI) and naturally occurring nanoscale iron mineral phases represent promising treatment tools for impaired water supplies. However, questions pertaining to fundamental and practical aspects of their reactivity may limit their performance during applications.

For NZVI treatment of pollutant source zones, a major hurdle is its limited reactive lifetime. In Chapter 2, we report the longevity of NZVI towards 1,1,1,2-tetrachloroethane (1,1,1,2-TeCA) and hexavalent chromium [Cr(VI)] in oxygen-free systems with various anionic co-solutes (e.g., Cl^-, SO^2-, ClO^-, HCO^-, NO^-). Trends in longevity provide evidence that surface-associated Fe(II) species are responsible for Cr(VI) reduction, whereas 1,1,1,2-TeCA reduction depends on the accessibility of Fe(0) at the NZVI particle surface.

In Chapter 3, we show that dithionite, previously utilized for in situ redox manipulation, can restore the reducing capacity of passivated NZVI treatment systems. Air oxidation of NZVI at pH &ge 8 quickly exhausted reactivity despite a significant fraction of Fe(0) persisting in the particle core. Reduction of this passive layer by low dithionite concentrations restored suspension reactivity to levels of unaged NZVI, with multiple dithionite additions further improving pollutant removal.

In Chapter 4, measurements of solvent kinetic isotope effects reveals that optimal Pd/NZVI reactivity results from accumulation of atomic hydrogen, which only occurs in NZVI-based systems due to their higher rates of corrosion. However, atomic hydrogen formation only occurs in aged Pd/NZVI suspensions for ~2 weeks, after which any reactivity enhancement likely results from galvanic corrosion of Fe(0).

Finally, the activity of hybrid nanostructures consisting of multi-walled carbon nanotubes decorated with of hematite nanoparticles (&alpha-Fe₂O₃/MWCNT) is explored in Chapter 5. Sorption of Cu(II) and Cr(VI) is enhanced in hybrid nanostructure systems beyond what would be expected from simple additive sorption capacities of their building blocks. The enhanced sorption capacity is in part derived from the greater surface area of hematite nanoparticles immobilized on MWCNTs relative to aggregated hematite suspensions. The hybrid &alpha-Fe₂O₃/MWCNT may also exhibit unique surface chemistry, as supported by the tunable values of zeta potential measured as a function of the mass of &alpha-Fe₂O₃ deposited on the MWCNTs.