Current/Recent Projects

• The role of chlorinated natural organic matter in stimulating dechlorination
• The cycling of nitrogen in oxidation ponds under conditions of low temperature and dissolved oxygen
• The development of novel materials to enrich and retain anammox bacteria
• Encapsulation for enhanced biological nutrient removal and high strength wastewater treatment  

The role of chlorinated natural organic matter in stimulating dechlorination

Given the extremely high cost associated with contaminated sediments in the United States, both in terms of human and ecological health and in terms of dollars, research on low-cost methods for sediment remediation is of critical importance. Although in situ bioremediation is promising, one major challenge that remains is how to effectively stimulate indigenous dehalorespirers (bacteria that physiologically respire halogenated compounds) in the presence of sorbed contaminants of limited bioavailability. The addition of alternative electron acceptors to contaminated sediment is able to successfully stimulate the growth of these organisms, encouraging the desorption and degradation of weathered contaminants. Nevertheless, the alternative electron acceptors used to date have also been toxic and/or bioaccumulative, precluding their use in the environment. Our past research has focused on better understanding the niche provided by naturally occurring chlorinated organic matter (Cl-NOM) for organohalide respiring bacteria in the environment and demonstrating that this Cl-NOM can serve as an electron acceptor for putative organohalide respiring bacteria. Our continuing research in this area focuses on studying how Cl-NOM can be used to best stimulate the dechlorination of contaminants. This research could facilitate the development of new remediation techniques designed to stimulate contaminant dechlorination with natural non-toxic alternative electron acceptors and will also provide important information regarding the global chlorine cycle.

Encapsulation for enhanced biological nutrient removal and high strength wastewater treatment 

This collaborative research is focused on developing models, methods, and treatment processes that will allow us to take advantage of encapsulated bacteria for enhanced biological nitrogen removal (BNR) from wastewater or improved high strength wastewater treatment. Encapsulating microorganisms provides benefits of increased microbial density and efficiency, reduced inhibition, and improved stability. We have been studying the growth, stability, and activity of a variety of microorganisms when encapsulated. This work will enable us to select communities for encapsulation that will perform well over time, develop models to predict changes in microbial numbers and activity given different input variables and time, and test encapsulation chemistries that will be simple to use and robust. Applications of this work include the encapsulation of (1) nitrifiers with a variety of nitrate and nitrite reducers (denitrifiers as well as anammox-containing communities) for enhanced BNR and (2) anaerobic communities for efficient high strength wastewater treatment from the food and beverage industry. 

This work is a joint effort with Prof. Bill Arnold (Civil, Environmental, and Geo- Engineering, UMN), Prof. Natasha Wright (Mechanical Engineering, UMN), Prof. Satoshi Ishii (Soil, Water, and Climate, UMN), Prof. Jeremy Guest (Civil and Environmental Engineering, University of Illinois at Urbana-Champaign), and Prof. Rob Nerenberg (Civil and Environmental Engineering, University of Notre Dame). 

The cycling of nitrogen in oxidation ponds under conditions of low temperature and dissolved oxygen

In Minnesota there are over 1,000 small communities with unmet wastewater management needs, ranging from no treatment to inadequate treatment. If inadequately treated, wastewater discharges can contain high concentrations of nitrogen species. Ammonia and nitrate can negatively impact surface and groundwater quality by decreasing oxygen levels in the receiving water body, causing eutrophication, and rendering well water unsafe to drink. It is important to remove these nitrogen species through efficient and effective treatment. An option for treating wastewater in small communities is treatment ponds, which are very simple to operate and relatively low-cost, relying on phenomena such as wind to provide oxygen, and thereby stimulate bacterial treatment of nitrogen species in the wastewater. Unfortunately, treatment ponds do not always remove nitrogen effectively, especially during the winter and spring months when the temperature drops and the ponds become ice-covered, limiting oxygen diffusion to the wastewater. We are studying how pond systems operate with respect to nitrogen cycling under conditions of low oxygen and/or low temperature with the goal of improving their management so that they can serve as a well-operating solution for Minnesota’s small communities in need of wastewater management. 

This work is a joint effort with Prof. Tim LaPara (Civil, Environmental, and Geo-Engineering, UMN). 

The development of novel materials to enrich and retain anammox bacteria 

Since its discovery, anammox has received attention for its potential utility to provide complete nitrogen removal from wastewater while simultaneously reducing oxygen requirements, supplemental carbon addition, and sludge production compared to traditional total nitrogen removal processes. Unfortunately, it has been extremely challenging to successfully implement anammox in traditional mainstream wastewater treatment. Anammox bacteria are slow growing, with ammonium concentrations in mainstream wastewater too low for high rates of anammox activity and biodegradable carbon concentrations too high to avoid competition from heterotrophs. This leads to low anammox activity and biomass washout. In addition, anammox require nitrite, which necessitates careful aeration control to facilitate ammonium oxidation to nitrite without subsequent nitrite oxidation to nitrate. In this research we are working collaboratively to develop new materials that can concentrate ammonium, and in one case also provide fine control of oxygen addition, to create localized niches for anammox enrichment and retention. This research has the potential to improve total nitrogen removal in wastewater while decreasing energy and chemical use.