Jeffrey A. Cunningham

Comparison of rhodamine WT and bromide in the determination of hydraulic characteristics of constructed wetlands

Abstract Hydraulic tracer tests were performed in the Prado Wetlands, Riverside County, California, USA. The goals of the tests were (1) to evaluate the suitability of rhodamine WT (RWT) as a tracer for wetlands studies, and (2) to determine the residence time distribution of the wetlands. The performance of RWT was evaluated by comparing the breakthrough curve (BTC) of RWT to that of bromide in a pilot-scale test. The BTCs of RWT and bromide indicated equal results. After the pilot test, a full-scale test was conducted by releasing a RWT pulse at the wetlands inlet and monitoring for RWT arrival near the wetlands outlet. The BTC indicated 10 and 90% (of the total mass recovered) breakthrough times of 25 and 112 h, respectively, but these must be considered approximations because only 29% of the injected RWT mass was recovered. Laboratory experiments suggest irreversible sorption to be the principal loss mechanism of RWT during transport through the wetlands. RWT is a suitable tracer in wetlands that are relatively small (less than 1 week residence time) and deep (at least 0.6 m) with limited sediment contact, but RWT yields only approximate results for the extended wetlands system.

Effects of grain-scale mass transfer on the transport of volatile organics through sediments 2. Column results

Trichloroethylene (TCE) elution profiles for purged and unswept columns are presented and simulated with the Distributed Dual Diffusion Model (DDDM) presented in the first of this two-paper series. Elution profiles were measured at 15, 22, 30, and/or 60°C for a silica gel, a Livermore sand fraction, a Livermore clay and silt fraction, a Santa Clara sediment, and/or a Norwood soil, all at 100% relative humidity. Advection and dispersion control TCE transport through the vapor phase of purged columns. Diffusion controls TCE transport through the vapor phase of unswept columns. For both purged and unswept columns a fast and a slow desorbing fraction of TCE were observed. The DDDM effectively simulated both of these fractions. For the fast fraction the DDDM predicted desorption with no fitting parameters. For the slow fraction the DDDM was not predictive but it simulated desorption using either a single (for silica gel) or a gamma distribution (for soil and sediments) of micropore diffusion rate constant(s) and a micropore capacity factor. Micropore capacity factors obtained by fitting the DDDM to purged column results were used to predict the onset of slow desorption in unswept columns of the same solid.

Effects of grain‐scale mass transfer on the transport of volatile organics through sediments: 1. Model development

In the first paper of this two-paper series, we present a new model that attributes nonequilibrium sorption of moderately hydrophobia, volatile organic compounds to intragranular diffusion. The model differs from those of previous researchers in that for the first time, it combines the following elements: (1) We account for two distinct intragranular rate-limiting diffusion processes, occurring in series and at widely different timescales; (2) we describe the slower of the two processes with a gamma distribution of diffusion rates; and (3) we use the disparity of timescales of the two processes to approximate a boundary condition for the distributed diffusion equation, allowing it to be solved analytically. The slower diffusion process is attributed to activated diffusion through very small pores, called micropores. In paper 2 [Werth et al., this issue] we evaluate the capabilities of the model and use it to interpret experimental results.

Use of temporal moments to investigate the effects of nonuniform grain‐size distribution on the transport of sorbing solutes

We use temporal moment analysis to examine the effects of nonuniform grain size on the transport of sorbing solute through porous media. We consider the case of advective-dispersive transport with sorption nonequilibrium governed by diffusion into spherical grains. For constant grain radius a and diffusion rate Da, the temporal moments for this problem are well known and have been reported elsewhere. In this paper, we consider the more realistic case, where there exists a distribution of diffusional timescales td ≡ a2/Da. The first and second temporal moments are unaffected by this distribution, but the third temporal moment is increased by a factor proportional to the variance of the distribution. This result holds regardless of the particular form of the distribution. Higher-order temporal moments depend on the higher-order moments of the distribution of td. Thus, even if the mean diffusion rate is relatively fast, higher-order temporal moments of the solute transport may exhibit significant nonequilibrium effects; hence it may not be possible to decide the validity of the “local equilibrium assumption” based solely on the second temporal moment. Also, our analysis shows that in simulation of aquifer remediation by pump-and-treat, the appropriate choice for the contaminant desorption rate depends upon the remediation goal.

Enhanced anaerobic bioremediation of groundwater contaminated by fuel hydrocarbons at Seal Beach, California.

Enhanced anaerobic biodegradation of groundwater contaminated by fuel hydrocarbons has been evaluated at a field experiment conducted at the Naval Weapons Station, Seal Beach, California. This experiment included the establishment of three different remediation zones in situ: one zone was augmented with sulfate, one was augmented with sulfate and nitrate, and the third was unaugmented. This enables a comparison of hydrocarbon biodegradation under sulfate-reducing, sequential denitrifying/sulfate-reducing, and methanogenic conditions, respectively. In general, the results from the field experiment are: (1) Certain fuel hydrocarbons were removed preferentially over others, but the order of preference is dependent upon the geochemical conditions; and (2) In the zones that were augmented with sulfate and/or nitrate, the added electron acceptors were consumed quickly, indicating that enhancement via electron acceptor injection accelerates the biodegradation process. More specifically, in the sulfate-reducing zone, sulfate was utilized with an apparent first-order rate coefficient of approximately 0.1 day-1. In the combined denitrifying/sulfate-reducing zone, nitrate was utilized preferentially over sulfate, with an apparent first-order rate coefficient of 0.1–0.6 day-1. However, the data suggest that slow sulfate utilization does occur in the presence of nitrate, i.e., the two processes are not strictly sequential. With regard to the aromatic BTEX hydrocarbons, toluene was preferentially removed under intrinsic conditions; biodegradation of benzene was slow if it occurred at all; augmentation with sulfate preferentially stimulated biodegradation of o-xylene; and ethylbenzene appeared recalcitrant under sulfate-reducing conditions but readily degradable under denitrifying conditions.

Effect of solids retention time on the bioavailability of organic carbon in anaerobically digested swine waste

Anaerobic digestion (AD) can be used to stabilize and produce energy from livestock waste; however, digester effluents may require further treatment to remove nitrogen. This paper quantifies the effects of varying solids retention time (SRT) methane yield, volatile solids (VS) reduction and organic carbon bioavailability for denitrification during swine waste AD. Four bench-scale anaerobic digesters, with SRTs of 14, 21, 28 and 42 days, operated with swine waste feed. Effluent organic carbon bioavailability was measured using anoxic microcosms and respirometry. Excellent performance was observed for all four digesters, with >60% VS removal and CH4 yields between 0.1 and 0.3(m(3)CH4)/(kg VS added). Organic carbon in the centrate as an internal organic carbon source for denitrification supported maximum specific denitrification rates between 47 and 56(mg NO3(-)-N)/(g VSS h). The digester with the 21-day SRT had the highest CH4 yield and maximum specific denitrification rates.

Lead (Pb) contamination of self-supply groundwater systems in coastal Madagascar and predictions of blood lead levels in exposed children.

Thousands of households in coastal Madagascar rely on locally manufactured pitcher-pump systems to provide water for drinking, cooking, and household use. These pumps typically include components made from lead (Pb). In this study, concentrations of Pb in water were monitored at 18 household pitcher pumps in the city of Tamatave over three sampling campaigns. Concentrations of Pb frequently exceeded the World Health Organizations provisional guideline for drinking water of 10 μg/L. Under first-draw conditions (i.e., after a pump had been inactive for 1 h), 67% of samples analyzed were in excess of 10 μg/L Pb, with a median concentration of 13 μg/L. However, flushing the pump systems before collecting water resulted in a statistically significant (p < 0.0001) decrease in Pb concentrations: 35% of samples collected after flushing exceeded 10 μg/L, with a median concentration of 9 μg/L. Based on measured Pb concentrations, a biokinetic model estimates that anywhere from 15% to 70% of children living in households with pitcher pumps may be at risk for elevated blood lead levels (>5 μg/dL). Measured Pb concentrations in water were not correlated at statistically significant levels with pump-system age, well depth, system manufacturer, or season of sample collection; only the contact time (i.e., flushed or first-draw condition) was observed to correlate significantly with Pb concentrations. In two of the 18 systems, Pb valve weights were replaced with iron, which decreased the observed Pb concentrations in the water by 57-89% in one pump and by 89-96% in the other. Both systems produced samples exclusively below 10 μg/L after substitution. Therefore, relatively straightforward operational changes on the part of the pump-system manufacturers and pump users might reduce Pb exposure, thereby helping to ensure the continued sustainability of pitcher pumps in Madagascar.

Remote sensing of temperature variations around major power plants as point sources of heat

Variations in land surface temperature (LST) around major point sources of heat were studied using the Tampa Bay region as a case study. LST in the Tampa Bay region, FL, USA, was retrieved from Landsat Thematic Mapper (TM) 6 and Enhanced Thematic Mapper Plus (ETM+) 6 high-gain thermal bands. The TM6 image data were obtained on 29 January (winter season) and 3 April 2007 (spring season). The ETM+6 data were obtained on 11 April 2007 (spring season). Spatial profiles of LST around four major fossil-fuelled power plants (FFPPs) were considered in this study. Temperatures were found to be highest at power plants and to decay to an average background temperature within 1.2–2.0 km from the FFPPs. The average background temperatures obtained in January and April were 17°C and 29°C, respectively. Results indicate that LST in close proximity to the FFPPs could be up to 10°C hotter than the surrounding areas. These findings suggest that FFPPs are significant heat sources and populations living within 1–2 km from an FFPP might be at significantly higher risk of heat-related illnesses and mortality.

Viability and fate of Cryptosporidium parvum and Giardia lamblia in tubular anaerobic digesters.

In many developing countries where pathogenic diseases of animal waste origin, such as giardiasis and cryptosporidiosis, are often prevalent, facilities are limited to treat livestock waste. However, household-scale anaerobic digesters are currently being promoted for bioenergy production from livestock manure. Since the effluent is often used as a fertilizer for food crops, it is critical to understand the effect of environmental conditions within household-scale digesters on the viability of Cryptosporidium parvum oocysts and Giardia lamblia cysts. In this study, key environmental parameters affecting (oo)cyst inactivation were measured in four tubular anaerobic digesters, which are a type of household-scale digester promoted for treatment of swine waste in rural Costa Rica. Interviews and participant observations were used to understand digester operation and maintenance procedures. Ambient temperatures (21-24°C), near-neutral pH, total ammonia nitrogen (TAN) concentrations<250 mg/L and hydraulic retention times (HRTs) between 23 and 180 days were observed. Laboratory (oo)cysts inactivation studies were performed in bench-scale digesters, which were maintained under conditions similar to those observed in the field. Apparent first-order inactivation rate coefficients for Giardia lamblia and Cryptosporidium parvum were 0.155 ± 0.041 and 0.054 ± 0.006 day(-1), respectively. Temperature and volatile fatty acids were the main factors contributing to Cryptosporidium parvum and Giardia lamblia inactivation. A mathematical model was developed that predicts the concentration of (oo)cysts in the liquid effluent of tubular digesters like those observed in Costa Rica. A mathematical model was developed that predicts the concentration of (oo)cysts in the liquid effluent of tubular digesters like those observed in Costa Rica. Two dimensionless groups can be used to predict the performance of the digesters for inactivating pathogens; both dimensionless groups depend upon the average HRT in the digester. This is the first study to combine mathematical modeling with qualitative analysis, field and laboratory studies to predict the concentrations of (oo)cysts in tubular digester effluents.

Soil treatment by solvent extraction and catalytic hydrodehalogenation

We investigated the extraction of halogenated hydrophobic organic contaminants (HHOCS) from soil, and the subsequent catalytic hydrodehalogenation of extracted HHOCs. We used water/ethanol mixtures as the solvent and pentachlorophenol and 1,2,4,5-tetrachlorobenzene as target contaminants. The efficiency of extraction improved with increasing contact time and/or increasing ethanol fraction in the solvent, but, surprisingly, did not improve with increasing solvent volume. Tetrachlorobenzene extracted from the contaminated soil could be dehalogenated catalytically, with no apparent interference or inhibition caused by the extraction process. This suggests that a proposed new remediation technology (called remedial extraction and catalytic hydrodehalogenation, or REACH) should be technically viable.