Simultaneous Removal of Phenol and Nitrate in an Anaerobic Bioreactor

Phenol and nitrate are two major pollutants simultaneously occurring in several industrial wastewaters. In this study, a 110-day gradual enrichment of an anaerobic culture has been carried out at 25°C in an anaerobic bioreactor for continuously treating a synthetic wastewater containing 600?mg/L phenol and 430?mg/L?NO3?–N. The results showed that the enriched culture can utilize phenol as a sole electron donor and nitrate as a sole electron acceptor. At the end of the enrichment (on Day 110), 93.3% of phenol and 98.0% of NO3?–N were simultaneously removed at a hydraulic retention time of 20.25?h in the anaerobic bioreactor. The removal of 1?g?NO3?–N required about 3.19?g chemical oxygen demand as the electron donor. Batch tests further revealed that cresol, nitrophenol, and monochlorinated phenol (MCP) could exert detrimental influences on the treatment abilities of the enriched culture. However, the inhibitory effects of cresol were impermanent, as compared to those of nitrophenol and MCP. In order to operate the anaerobic bioreactor steadily, high concentrations of cresol should be diluted before being fed while the existence of nitrophenol and MCP in the bioreactor should be avoided.     

Effect of the Composition of Anodic Purging Solutions on Electroosmosis

The objective of this study is to investigate the effect of the composition of anodic purging solutions on electroosmosis in an electrokinetic (EK) system. The effect of buffering capacity of anodic purging solutions on electroosmosis was first studied. With the increase of buffering capacity, soil pH and electric current increased, but the maximal cumulative electroosmostic flow (EOF) was achieved with 0.010?mol/L Na2CO3/NaHCO3 buffer. Na2CO3/NaHCO3 containing NaCl and Na2SO4, respectively, were used as anodic purging solutions to investigate the effect of cation concentration and anion type on electroosmosis. The increase of cation concentration led to the increase of soil pH and electric current but the decrease of EOF. At the same cation concentration, Na2SO4 resulted in higher electric current and greater EOF than NaCl, but similar distribution of soil pH. The present study provides useful information for the selection of purging solution in the EK remediation of contaminated soils.     

Nitrate Removal in Sulfur: Limestone Pond Reactors

The feasibility of using sulfur:limestone autotrophic denitrification (SLAD) pond reactors to treat nitrate-contaminated water or wastewater after secondary treatment was investigated with four lab-scale continuously fed SLAD ponds. The start-up period, temperature effects, and effects of different feed solutions were evaluated. With an influent concentration of 30 mg NO3?–N/L at an HRT of 30 days, the pond reactors had an overall nitrate removal efficiency of 85–100%. Effluent nitrite concentrations were <0.2 mg N/L in all tests. Aerobic conditions could result in a decrease of the SLAD pH of the pond by 2 to 3 units and a large increase in sulfate production ( ～ 1600–1800?mg-SO42?/L). Under unmixed (anoxic) conditions, the pH and sulfate produced were maintained at approximately 5.5 to 5.6 and 400–600?mg-SO42?/L, respectively, in all the SLAD ponds. Temperature affected the pond reactors adversely. By assuming that a first-order reaction occurred in a SLAD pond reactor, the temperature-activity coefficient, θ was found to be 1.068. Treatment of nitrate-contaminated surface water and wastewater using SLAD pond systems is feasible only if (1) the chemical oxygen demand (COD)/nitrate–N (COD/N) ratio is low (<1.2 with an initial NO3? concentration of 30 mg-N/L), (2) sulfur:limestone granules are not covered by sediment, and (3) sulfur-utilizing but nondenitrifying bacteria (SUNDB) are greatly inhibited due to the lack of DO in the pond systems. The SLAD ponds are not feasible for the treatment of raw wastewater or surface water if they contain high concentrations of organic matters due to the possible inhibition of sulfur-based autotrophic denitrifiers by heterotrophs (including heterotrophic denitrifiers). In addition, a high sulfate and low DO concentration as well as a low pH in the SLAD effluent of the pond (even when the pond is operated in an unmixed mode) also will limit the application of SLAD pond processes.     

Impact of Ethanol on Benzene Plume Lengths: Microbial and Modeling Studies

Recent legislation in several states has called for the removal of methyl tert-butyl ether (MTBE) from gasoline. In order to comply with Federal Clean Air Act requirements for carbon monoxide and ozone attainment, ethanol is being considered as a replacement for MTBE. The objective of this study is to evaluate the potential impact of ethanol on benzene plume lengths in subsurface environments following accidental spills of ethanol-blended gasoline. Two types of studies were conducted here. First, laboratory studies were performed using a pure culture indigenous to a gasoline-contaminated aquifer to evaluate the effect of ethanol on the rate of benzene biodegradation under aerobic conditions. Results from microbial studies showed that the biodegradation of 25 mg/L benzene was severely inhibited in the presence of 25 mg/L ethanol. While the enzymes responsible for benzene biodegradation by the culture were inducible, ethanol degradation appeared to be constitutive. Second, a two-dimensional model was developed to quantify the impact of ethanol on benzene plume lengths using weighted-average aerobic and anaerobic biodegradation rates for benzene in the presence and absence of ethanol. Model simulations indicated that benzene plume lengths are likely to increase by 16–34% in the presence of ethanol.     

Use of Ozone in the Citrus Industry

The use of ozone for postharvest sanitation and decay control of fruits, vegetables and their products during handling, processing and storage has been investigated for commercial applications. Due to their significant contribution to world trade and human nutrition, citrus fruits are thought to be important commodities. Decay can be observed in these products because of microbial activity and ethylene accumulation throughout storage. Residues of pesticides and other compounds in citrus fruit and food-borne illness outbreaks caused by consumption of contaminated citrus juice are important health issues. In this study, the possible uses of ozone in citrus industry for all these problems, and efficacy, benefits and/or detrimental effects of these applications are discussed.     

Design and Operation of Point-of-Use Treatment System for Arsenic Removal

A point-of-use (POU) system was designed and constructed using commercially available activated alumina to remove arsenic from drinking water. Testing with City of Albuquerque chlorinated tap water containing an average of 23 ug/L arsenic found that 1 L of adsorbent would provide water for direct consumption by a family of four for 435 days. It was estimated that the POU system constructed for this study could be sold for $162, and the arsenic adsorption columns were estimated to cost $4. A monthly cost to the customer of $10/month was estimated to purchase, install, and operate this POU system, assuming annual replacement of adsorption media cartridges. The implications of relying upon POU systems to comply with a new drinking water standard for arsenic are discussed.     

Allocation of CO2 emission permits—Economic incentives for emission reductions in developing countries

The economic impacts on developing regions following a global cap and trade system for carbon dioxide are assessed through the use of an energy-economy systems model. Both an equal per capita allocation and a contraction and convergence allocation with convergence of the per capita emissions by 2050 are shown to offer economic incentive for Africa, India and probably also Latin America to accept binding emissions commitments under a 450 ppm carbon dioxide stabilization scenario. The gain for Latin America is mainly a result of increased export revenues from sales of bio-fuels as a result of the climate policy. It is, on the other hand, unlikely that these allocation approaches would offer an economic incentive for China to join the regime because of its high economic growth, present higher per capita emissions than India and Africa, and more costly mitigation options than Latin America. A more stringent allocation for developing countries such as contraction with convergence of the per capita emissions by the end of this century is estimated to generate reduced net gains or increased net losses for the developing regions (though Africa is still expected to gain).     

Role of Bioflocculation on Chemical Oxygen Demand Removal in Solids Contact Chamber of Trickling Filter/Solids Contact Process

The trickling filter/solids contact (TF/SC) process was developed in the late 1970s to improve the quality of the final effluent from existing trickling filter plants, to be able to meet stricter Environmental Protection Agency effluent requirements. Although this process has successfully achieved this objective, it is still not completely understood, there is limited information regarding the flocculation phenomena occurring in the solids contact chamber (SCC), and no information could be found on the relationship between flocculation and organic matter removal kinetics. To better understand the kinetics of biological flocculation in a continuous flow SCC, a long-term experimental program was conducted using a TF/SC pilot plant constructed at the Marrero, La., wastewater treatment plant. This program started in January 1998 and has continued through date. The present article will focus on two major areas: (1) the kinetics of bioflocculation in the SCC; and (2) effect of bioflocculation on chemical oxygen demand (COD) removal. Analysis of the wastewater composition revealed that, on the average, only 18.7% of the total COD in the SCC influent is truly dissolved. Therefore, most of the total COD removal observed in the SCC must be due to a physical process, such as flocculation. The experimental data confirmed that flocculation of the particulate COD contained in the trickling filter effluent explains the high total COD removal observed at the SCC. Both total and colloidal COD removals are well explained by the first-order flocculation model.     

Plasma-Assisted Process for Removing NO/NOx from Gas Streams with C2H4 as Additive

NOx removal from gas streams via dielectric barrier discharges (DBDs) has been experimentally evaluated. This paper investigates the effect of injecting C2H4 as an additive with respect to the De–NOx chemistry and the effect of gas composition on NO/NOx removal efficiencies. Experimental results indicate that both removal efficiencies of NO and NOx are enhanced with increasing applied voltage, gas temperature, and water vapor. Water vapor in gas streams has a distinct influence on NOx removal by generating OH radicals to convert NO2 to form HNO3. NOx removal decreases with increasing oxygen content although NO removal increases with increasing oxygen content. As high as 100% of NO and 57% of NOx are removed at 140°C for the gas stream containing [NO]:[C2H4]:[H2O(g)]:[O2]:[N2] = 0.05:0.2:3.0:5.0:91.75. Major mechanisms for NO and NOx removals in DBD processing with C2H4 as an additive are described in the text.     

Removal of Immiscible Contaminants from Sandy Soils Monitored by Means of Dielectric Measurements

The main objective of this paper is to explore the potential application of electromagnetic waves to evaluate the effect of contaminant removal in granular soils. Thus, various specimens of saturated silica sand were prepared using paraffin oil and lubricant oil as contaminants. Four flushing fluids were used to remove the contaminants from sand columns: Deionized water, water-detergent, water-detergent-alcohol solution, and water vapor. Dielectric permittivity was measured at different stages of the removal process at the frequency from 20?MHz?to?1.3?GHz. The measured permittivity was compared with that determined for clean and fully contaminated specimens. A theoretical mixture formula was calibrated and implemented to estimate the volume fraction of contaminant present in the pore fluid. It is concluded in this work that dielectric parameters reflect the contamination level of the soil for the nonpolar organic compounds used here. Measurement of permittivity allows us to determine that the inclusion of alcohol and detergent in the displacing fluid improved the removal efficiency. However, water vapor was the most efficient removal agent.