The objective of this study was to operate a novel, field-scale, aerobic bioreactor and assess its performance in the ex situ treatment of groundwater contaminated with gasoline from a leaking underground storage tank in Pascoag, RI. The groundwater contained elevated concentrations of MTBE (methyl tert-butyl ether), TBA (tert-butyl alcohol), TBF (tert-butyl formate), BTEX (benzene, toluene, ethyl benzene, and xylene isomers), and other gasoline additives (tert-amyl methyl ether, di-isopropyl ether, tert-amyl alcohol, methanol, and acetone). The bioreactor was a gravity-flow membrane-based system called a Biomass Concentrator Reactor (BCR) designed to retain all biomass within the reactor. It was operated for six months at an influent flow rate that ultimately reached 5 gpm. The goal was to achieve a removal of all contaminants to <5 μg/L, which is the California Drinking Water advisory for MTBE. The concentration of TBA, an MTBE biodegradation byproduct, was consistently lower than that of MTBE. The other daughter compound detected in the influent, TBF, was degraded to concentrations below the detection limit of 0.02 μg/L. BTEX were consistently degraded to significantly lower levels in the effluent throughout the duration of the study (<1 μg/L). A similar high removal efficiency of the other gasoline oxygenates present in the groundwater (TAME, DIPE, and TAA) was also achieved. Dissolved organic carbon analysis demonstrated the ability of the bioreactor to produce high quality effluents with nonpurgeable organic carbon (NPOC) averaging approximately 50% lower than the NPOC concentrations in the influent contaminated groundwater.
ABSTRACT Wetlands are among the most sensitive of habitats to oil spills. A field experiment was conducted on a salt marsh in Atlantic Canada to determine the significance of bioremediation by nutrient enrichment in enhancing wetland restoration. Six experimental treatments were monitored: (1) unoiled control (2) unoiled control + nutrients, (3) oil with no treatment (natural attenuation), (4) oil + nutrients, (5) oil + nutrients with plants cut back, (6) oil + nutrients with disking (tilling) to enrich oxygen penetration. Remediation success was quantified by determining changes in the composition and concentration of the residual oil, plant recovery and reduction in sediment toxicity. The experimental results advocate natural attenuation as the clean-up strategy for the ecotype under study. Within the untreated plots, significant recovery of the predominant plant species within the marsh (Spartina alterniflora) was observed after 20 weeks and approximately 90% of the resolved n-alkanes and 70% of the parent and alkyl-substituted polyaromatic hydrocarbons (PAH) were biodegraded.
Abstract Wastewater results from mankind's use of water in all aspects of daily life. Historically, increasing population density forced mankind to abandon localized disposal (cesspools, septic tanks, etc.) toward collection and conveyance of contaminated water away from population centers for prevention of disease and protection of water. The aggregate of these contaminated waters has become known as wastewater or sewage. The first sewer system in a major city in the U.S. was constructed in New York City in 1895. Storm water conveyance has been documented as the major reason for the construction of sewers. This article describes the treatment of wastewater and public vulnerability to disruptions of wastewater collection. Most of the modern large treatment plants are comprised of primary settling, or clarification (primary treatment), and secondary biological treatment consisting of biological oxidation, followed by separation of solids, The liquid treatment sequence is followed by one or more tertiary treatments (to reduce control nutrients and solids in final effluent). Effluent disinfection is the final step in order to reduce pathogenic potential. Although disruptions in wastewater collection and treatment are of secondary nature and not as critical as disruptions to drinking water, power, communications, and public health system, there can be severe implications associated with wastewater collection disruption. Impacts on human health, economic effects, and longer term ecological effects are discussed.
A comprehensive wastewater treatment plant mathematical model is developed. The model includes primary sedimentation followed by a singlestage activated sludge system for both BOD reduction and nitrification. Primary and waste activated sludges are assumed to be mixed, chemicaly‐conditioned prior to vacuum filtration and the cake incinerated. Capital, materials, and operating and maintenance costs are utilized in arriving at a least cost system design. The sensitivity of the optimum design to selected values of various model constants and effluent constraints is evaluated to establish which variables most significantly affected system design.
Wetlands are among the most sensitive of habitats to oil spills. To determine the significance of nutrient enrichment in enhancing wetland restoration in the presence and absence of plants, an intentional spill was conducted on a salt marsh in Atlantic Canada. The study evaluated 6 experimental treatments: unoiled, unoiled with nutrients (nitrate and phosphate fertilizer), natural attenuation, nutrient addition with intact plants, nutrient addition with plants cut back, and nutient addition with intact plants and tilling to enrich oxygen penetration. Remediation success was quantified by determining the rates of oil loss, plant recovery and reduction in sediment and interstitial water toxicity. Based on the experimental results, on an operational scale, natural attenuation is the recommended clean-up strategy for the ecotype under study. Significant plant recovery was observed after 20 weeks and approximately 90°/0 of the resolved nalkanes and 70°A of the parent and alkyl-substituted polyaromatic hydrocarbons (PAH) were biodegraded.
The performance of two pelletized media biofilters, highly loaded with toluene, was evaluated in this study. Both biofilters were operated at the same influent concentration of 250 ppmv toluene. Biofilter `A` was operated at 1 minute EBRT and biofilter `B` at 0.67 minute EBRT. The impact of backwash duration on performance was studied for both biofilters, primarily the stability of performance between backwashings. This biofilter behavior indicated that increasing the backwash period from 1 to 2 hours was effective in improving the performance stability of both biofilters. This improved performance stability is due to reduction of short circuiting within the media, caused by accumulating biomass.
An innovative energy efficient process has been developed for the effective degradation of phenolic compounds. The treatment process, which consists of an anaerobic filter with granular activated carbon serving as a contact medium, effectively reduces the phenolic content of a synthetic catechol bearing wastewater. Degradation of another phenolic compound, o-cresol, was not realized. The o-cresol exhibited no inhibition to the formation of methane as a result of the breakdown of other organic cosubstrates—glucose, sodium citrate and an ethanol vitamin extract. The potential of the treatment process in the treatment of coal conversion wastewaters is currently under investigation.
