Browsing by Subject "Water--Purification--Biological treatment"
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Item Biological activated carbon: the relative role of metabolism and cometabolism in extending service life and improving process performance(2004) Putz, Andrea Robin Holthouse; Speitel, Gerald E.Granular activated carbon (GAC) is commonly used to remove synthetic organic chemicals (SOCs) from contaminated water. Replacement and subsequent disposal of spent GAC is expensive. By increasing the service life of the GAC, costs can be decreased. Encouragement of biodegradation (metabolism and cometabolism) where one or more of the SOCs are biodegradable can lengthen the GAC service life for some SOC mixtures. The service life increases because a biofilm that forms on the GAC can biodegrade SOCs, thereby reducing competition for GAC adsorption sites and allowing any remaining SOCs to adsorb onto the GAC to a greater extent than in the absence of biodegradation. SOCs in both the aqueous phase and adsorbed on the GAC are available to the microorganisms. Biodegradation of adsorbed SOCs (termed bioregeneration) renews the GAC’s capacity for SOC adsorption, while aqueous phase biodegradation slows the rate of GAC exhaustion, thereby lengthening the GAC service life and decreasing operation and maintenance costs. Adsorption isotherms and biological kinetic studies were performed to describe GAC column performance. Continuous-flow GAC bioregeneration experiments (preequilibrated and virgin) were conducted using a mixture of biodegradable (toluene) and either nonbiodegradable (perchloroethylene, PCE) or traditionally nonbiodegradable (trichloroethylene, TCE) SOCs. In the pre-equilibrated experiments, the GAC was saturated with respect to toluene and PCE or TCE to observe the biggest effect on bioregeneration performance. If no dissolved oxygen limitations occurred, the biodegradable SOC effluent concentration decreased over time and remained low, after which the nonbiodegradable or traditionally nonbiodegradable SOC effluent concentration also decreased because of the increased availability of adsorption sites on the GAC as well as the cometabolism of TCE, if present, by enzymes produced via toluene metabolism. Virgin column experiments were also run and allowed for direct measurement of the service life increase due to biodegradation. Toluene-and TCE-based bioregeneration ranged from 26 - 53% and 2.2 - 7.4%, respectively, of the initial loading after 11 to 20 days. Pre and post-experimental GAC loadings showed a decrease in the biodegradable SOC loading as well as an increase in the nonbiodegradable SOC loading. Greater degrees of bioregeneration were found for higher SOC concentrations and longer EBCTs.Item Biological pretreatment of produced water for reuse applications(2007-12) Kwon, Soondong, 1973-; Kinney, Kerry A.; Katz, Lynn EllenCo-produced water from the oil and gas industry represents a significant waste stream in the United States. Produced water is characterized by high levels of total dissolved solids (TDS), dissolved organics and oil and grease. Among the wide variety of organics present in the water, the concentration of hazardous substances such as benzene, toluene, ethylbenzene, and xylenes (BTEX) can reach 600 mg/L and the concentration of non-hazardous carboxylate can be as high as 10,000 mg/L (API, 2002). Regulations governing the disposal of produced water are tightening and the interest in reusing treated produced water is increasing in the United States particularly in regions with scarce water supplies. In order to reuse produced water, removal of both the inorganic dissolved solids and hazardous organics such as BTEX may be necessary. The main goal of this research was to investigate the feasibility of using a combined physicochemical/biological treatment system to remove the organic constituents present in saline produced water. In order to meet this objective, two separate biological treatment techniques were investigated: a vapor phase biofilter (VPB) to treat the regeneration off-gas from an upstream surfactant-modified zeolite (SMZ) adsorption system and a membrane bioreactor (MBR) to treat the carboxylate and BTEX constituents that penetrate an upstream SMZ system. Each of the biological pretreatment systems was investigated first in the laboratory treating synthetic produced water and then in the field coupled to an SMZ adsorption system treating produced water. Both of the biological treatment systems were capable of removing the BTEX constituents both in the laboratory and in the field over a range of operating conditions. For the VPB, separation of the BTEX constituents from the saline aqueous phase yielded high removal efficiencies. However, carboxylates remained in the aqueous phase and were not removed in the combined VPB/SMZ system. In contrast, the MBR was capable of directly treating the saline produced water and simultaneously removing the BTEX and carboxylate constituents. The major challenge of the MBR system was controlling membrane fouling, particularly when the system was treating produced water under field conditions.Item Cometabolism of trihalomethanes by nitrifying biofilters under drinking water treatment plant conditions(2006) Wahman, David Gerard; Speitel, Gerald E.This research studied the feasibility of THM cometabolism in laboratory-scale biofilters under conditions that reflect drinking water treatment practice. Initially, batch kinetic studies were conducted to determine whether nitrifying bacteria could reliably cometabolize all four THMs at a sufficient rate to make the process attractive to utilities. The kinetic experiments showed that nitrifier communities likely to be seen in drinking water treatment facilities can degrade THMs at a sufficient rate by themselves, without seeding a pure culture. These results also indicated that temperature sensitivity and product toxicity could be concerns if THM cometabolism by nitrifying bacteria was implemented as a treatment option in treatment facilities. In particular, as bromine substitution increases, both THM degradation kinetics and product toxicity increase. A series of laboratory-scale biofilter experiments was conducted to investigate the feasibility of THM cometabolism in the envisioned process configuration. The operating conditions of the mixed culture biofilters scaled to typical full-scale rapid filtration operating conditions seen in drinking water treatment practice. Overall, the biofilter experiments suggest that, for a 2 mg N/L TOTNH3 (the sum of ammonia-nitrogen and ammonium-nitrogen) removal, total THM removals might initially approach 32-38% (25- 31 μg/L total THMs). This initial removal might decline to 11-12% (9-10 μg/L total THMs) over time as bacteria are selected from THM product toxicity. Even if this decreased performance occurs, the 11-12% removal is potentially attractive in drinking water treatment practice. The allowable influent monochloramine concentration resides between 1 mg/L to 2.5 mg/L as Cl2, with the use of 1 mg/L as Cl2 being conservative. A simple kinetic model for THM cometabolism was incorporated into AQUASIM to describe biofilter performance under conditions where by-product toxicity is not a concern. Overall, total THM removal of 9 to 54% was projected in the full-scale simulations, which illustrates the potential of THM cometabolism to have a significant impact on treated water quality for utilities where their water quality will likely see a benefit from the proposed process. Even though these removals are modest, drinking water treatment plants might only require removals in this range to maintain compliance with existing and future regulations.