Wastewater Reuse and Organic Nitrogen

As a result of population growth and limited water supplies, wastewater recycling programs for indirect potable reuse have been initiated in the American Southwest and are spreading to other areas of the country. The passage of wastewater-derived contaminants through advanced technology treatment units (e.g., reverse osmosis) at these facilities into drinking water supplies has caused great consumer concern. However, more disturbing is a recent US Geological Survey study that points to the presence in streams that may be used as drinking water supplies of contaminants likely derived from conventional wastewater treatment plant discharges.  These findings indicate that unintentional potable reuse of wastewater may be common.

Wastewater effluents contain higher concentrations of organic nitrogen than do pristine water supplies.  Unfortunately, specific constituents of dissolved organic nitrogen in wastewater have rarely been identified. Recent evidence indicates that tertiary alkyl amines are common constituents of wastewater effluents that resist biodegradation.

Our research intends to:

1. Develop analytical methods for the bulk identification of particular varieties of tertiary amines (e.g., tertiary amines with specific functional groups).  These methods will be more specific and quantitative than the current state-of-the-art NMR techniques.
2. Assess the biodegradation of tertiary amines.  Tertiary amines may persist in the environment to foster eutrophication of receiving waters or to negatively impact downstream drinking water supplies.  Laboratory and field studies will assess these possibilities.

Emerging Disinfection By-Product Formation Mechanisms

As a result of population growth, wastewater effluents will increasingly impact drinking water supplies.  Although public concern has focused on pharmaceutical concentrations in wastewater-impacted drinking water sources, there is no evidence that the low concentrations present in these waters represent a health risk.  In contrast, toxicology studies indicate that certain families of nitrogen-containing disinfection by-products (DBPs), such as N-nitrosamines, halonitromethanes and nitriles, exhibit far higher toxicities than currently regulated trihalomethane and haloacetic acid DBPs.  These compounds may be more likely to form during chlorination of wastewater-impacted drinking water supplies due to the higher concentrations of dissolved organic nitrogen precursors.

Our research intends to:

1. Identify precursors for these disinfection by-products.
2. Define reaction mechanisms for the formation of these compounds.

Understanding the important reaction pathways for the formation of these compounds will enable us to identify operational strategies to prevent the formation of these compounds during disinfection or to design treatment technologies to remove these compounds prior to disinfection.

Advanced Oxidation of Reverse Osmosis Brines Containing Emerging Contaminants

Reverse osmosis treatment is becoming a favored treatment technology for the removal of emerging contaminants during wastewater reuse operations due to the blanket removal of various classes of contaminants (e.g., hormones, pharmaceuticals and pesticides).  Unfortunately, the reverse osmosis results in the creation of a concentrated brine containing these contaminants.  The disposal of this brine is problematical.

Our research will assess the feasibility of advanced oxidation techniques (i.e., hydroxyl radical treatments) for the removal of contaminants in the brine.  This research involves:

1. Assessing clean-up technologies to remove humic substances and other radical scavengers prior to advanced oxidation
2. Assessing the affect of high concentrations of dissolved salts on advanced oxidation performance.

Environmental Fate of Phthalates

Phthalates are common plasticizing agents in polyvinyl chloride and other plastics.  Although these compounds are potential carcinogens and endocrine disrupting compounds, information about their occurrence and fate in the environment is lacking because their prevalence results in their common occurrence as laboratory contaminants.

Our research intends to:

1. Develop a "clean lab" enabling the accurate detection of these compounds
2. Assess their fate in wastewater and water treatment and streams.  This research will attempt to define the most important removal mechanisms for these compounds

Photolysis and Hydrolysis of DEET

Diethyltoluamide (DEET) is a common constituent of bug repellent.  A recent survey of US streams indicated that it was one of the top five contaminants detected.  DEET is structurally similar to several pesticides such as carbaryl.  The main degradation mechanisms responsible for its removal from the environment have not yet been identified.

Our research intends to:

1. Determine the hydrolysis rate of DEET to compare with similar rates determined for structurally related pesticides.
2. The structure of DEET indicates that this compound may be more susceptible to photolysis than structurally related pesticides. Our research will assess the relative photolysis rate of this compound compared to structurally related pesticides.

The results of our research could lead to the design of pesticides that are more amenable to degradation.

Wastewater Treatment Technologies for Mid-Size Cities in the Third World

Non-profit groups often provide inexpensive, low-technology solutions for wastewater treatment or disposal that is deemed appropriate for small villages in the developing world.  On the other hand, mid-size cities in the developing world often have installed wastewater collection systems to convey sewage to streams used as drinking water supplies by downstream communities (e.g., Uruapan, Mexico), but lack sufficient funds to install the conventional treatment systems common in the developed world. Such cities represent an opportunity to devise inexpensive, but technically challenging wastewater treatment processes that limit wastewater impacts on drinking water supplies. 

We hope to initiate a chapter of Engineers Without Borders at Yale.  This chapter will provide engineering design services for sanitary services for a mid-size sister city in the developing world.  This chapter will capitalize on the extensive interdisciplinary resources available at Yale (e.g., the Yale School of Forestry and Environmental Studies).

Organohalogen Formation in Marine Aerosol

Water soluble organics, often of biogenic origin, can constitute nearly 20% of marine aerosol mass during the summer and may accumulate at the air-aerosol interface.  Hydroxyl radicals (OH*) have been assumed to constitute one of the primary mechanisms for organic compound destruction in aqueous aerosols.  Recent research has focused on the autocatalytic generation of reactive halogen species, including X* (e.g., Br*), X2*- (e.g., ClBr*-), X2 (e.g., ClBr), HOX (e.g., HOCl), and X3- (e.g., Cl3-), initiated by reactions of oxidants such as OH* with the elevated halide concentrations in these aerosols.  Reactive halogens emitted from aerosols have important impacts on O3, NOx and dimethylsulfide mixing ratios in the marine boundary layer.  Because reactive halogen concentrations may exceed those of OH* by several orders of magnitude, and because rate constants for reactions of several reactive halogens (e.g., Cl*) with organic compounds approach those of OH*, processing of water soluble organics in these aerosols may be dominated by reactions with reactive halogens, resulting in organohalogen formation.  Natural, abiotic pathways for organohalogen formation have not been previously identified.

Our research aims to use a series of model organic precursors to define the relationships between the structure of the organic precursor, the reaction conditions, and the stable products formed from reactions with OH* in the presence of elevated halide concentrations in aqueous solution.  By elucidating the principles underlying organohalogen formation, the results will enable the prediction of organic structures most susceptible to halogenation and the associated products.  Future studies can target the detection of these products in environmental samples. 

We’re looking for a few good engineers!