Manuel L. Cano

Transfers and transformations of zinc in constructed wetlands: mitigation of a refinery effluent.

Abstract Two pilot-scale wetlands were constructed to facilitate transfers and transformations of Zn in a secondary refinery wastewater effluent. The wetlands (6.1×30.5 m, width×length) were planted with Scirpus californicus and were operated with 24-h nominal hydraulic retention times (HRT). To evaluate wetland performance in terms of Zn removal at two water depths, one wetland was amended with a nominal concentration of 4.0 mg Zn/l as ZnCl2 for 144 days at an operational water depth of 0.3 m, and for an additional 22 days at a water depth of 1 m. The second wetland served as an unamended control. From wetland inflow to outflow, approximately 38% of total recoverable and 65% of soluble Zn was removed during the experiment at the 0.3-m water depth. During the flooded period (1.0-m water depth), approximately 18% of total recoverable and 66% of soluble Zn was removed from the effluent. Toxicity of effluent to Ceriodaphnia dubia Richard and Pimephales promelas Rafinesque decreased from inflow to outflow by ∼54 and 73%, respectively, at the 0.3-m water depth, and by at least 100% at the 1.0-m water depth. These data illustrate successful construction of wetlands for transfers and transformations of Zn from the water column and for decreases in associated toxicity.

Sorption of two model alcohol ethoxylate surfactants to sediments

Abstract We have examined the sorption of two radiolabeled alcohol ethoxylate surfactants (AE) (C13 alcohols with exactly 3 or 9 moles of ethylene oxide (EO) per mole of alcohol) to natural sediments. Formalin was included in the sediment/surfactant/water mixtures to prevent biodegradation. Four sediments with 0.3 to 2.2 % organic carbon content were used in equilibrium experiments to determine the effect of various sediment properties and EO chain length on the sorption process. The equilibrium sorption isotherms were determined to be non-linear and described by the Freundlich model, and distribution ratios (ratio of surfactant concentration on sediment to aqueous concentration) at 1 mg/L surfactant ranged from 110 to 590 L/kg. These distribution ratios indicated that the AEs did not sorb strongly to the tested sediments. The amount of sorption was better correlated to the percent clay content of the sediment than to the percent organic carbon content of the sediment.

Impact of Heat Aging on Sediment Toxicity of Ester/Olefin-Based Drilling Fluids to Leptocheirus Plumulosus

Abstract Synthetic-based drilling fluids (SBF) have been used in a variety of drilling applications and are an important component of deepwater drilling operations. One of the applications of SBF is high-temperature wells. In order to address regulatory concerns about SBF in high temperature applications, an inter-industry study was conducted to examine the effects of temperature and time on the sediment toxicity (to Leptocheirus plumulosus) of synthetic-based fluids used for high-temperature wells. Four factors were examined: (1) ester content, (2) time, (3) temperature, and (4) alkalinity (absence or presence of green cement). Three base-stock fluids were tested, a 100% internal olefin (C1618 IO) and two traditional ester/olefin blends (10%/90% and 30%/70%). The base fluids were blended into drilling fluids and subjected to temperatures ranging from 275 to 350°F and time of exposures to temperature ranging from 16 to 160 hr. Phase 1 toxicity results indicated that temperature and time parameters bracketed the region where ester/olefin drilling fluids transitioned from passing to failing the sediment toxicity limitation. Phase 2 used a statistical experimental design to identify significant factors impacting toxicity, and a statistical model was developed to predict sediment toxicity ratios (STR). 2-Ethyl hexanol, an indicator of ester hydrolysis, was positively correlated with increased STR and could be used to screen for potential sediment toxicity. The sediment toxicity tests, analytical measurements, and the statistical STR model supported the hypothesis that, for the types of muds studied, toxicity increased for ester/olefin blends under downhole conditions of increased time and temperature. The data from this study support caution in the use of drilling fluids containing the type of esters (traditional esters) used in this study when temperatures exceed a threshold of ~300°F. Above 300°F, these materials may break down and result in increased sediment toxicity for the drilling fluids.

A direct comparison of U.S. Environmental Protection Agency's Method 304B and batch tests for determining activated-sludge biodegradation rate constants for volatile organic compounds

Biodegradation rate constants for volatile organic compounds (VOCs) in activated-sludge systems are needed to quantify emissions. One current U.S. Environmental Protection Agency method for determining a biodegradation rate constant is Method 304B. In this approach, a specific activated-sludge unit is simulated by a continuous biological treatment system with a sealed headspace. Batch experiments. however, can be alternatives to Method 304B. Two of these batch methods are the batch test that uses oxygen addition (BOX) and the serum bottle test (SBT). In this study, Method 304B was directly compared to BOX and SBT experiments. A pilot-scale laboratory reactor was constructed to serve as the Method 304B unit. Biomass from the unit was also used to conduct BOX and modified SBT experiments (modification involved use of a sealed draft-tube reactor with a headspace recirculation pump instead of a serum bottle) for 1,2-dichloroethane, diisopropyl ether, methyl tertiary butyl ether, and toluene. Three experimental runs-each consisting of one Method 304B experiment, one BOX experiment, and one modified SBT experiment-were completed. The BOX and SBT data for each run were analyzed using a Monod model, and best-fit biodegradation kinetic parameters were determined for each experiment, including a first-order biodegradation rate constant (K 1 ). Experimental results suggest that for readily biodegradable VOCs (i.e., K 1 > 10 L/g volatile suspended solids [VSS].h) the two batch techniques can provide improved means of determining biodegradation rate constants compared with Method 304B. In particular, these batch techniques avoid the Method 304B problem associated with steady-state effluent concentrations below analytical detection limits. However, experimental results also suggest that the two batch techniques should not be used to determine biodegradation rate constants for slowly degraded VOCs (i.e., K 1 < 0.1 L/g VSS.h).