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There remains significant potential for improvement in oxygen transfer efficiency, which can account for 60% of water and wastewater treatment energy requirements. This research examined superoxygenation, or aerating water under pressure with high-purity oxygen gas. Examined were the effects superoxygenation has on five key aeration design parameters: the mass transfer coefficient ([K.sub.L]a), saturation concentration ([C.sup.*.sub.sat]), standard oxygen transfer rate (SOTR), standard aeration efficiency (SAE), and standard oxygen transfer efficiency (SOTE). This research compared values under pressures of 0,50,100,150, and 200 kPa using air and pressure swing adsorption (PSA) generated oxygen. It was found that with increasing pressure for both air and PSA oxygen: [K.sub.L]a decreased, [C.sup.*.sub.sat] increased, SOTR and SAE remained constant, and SOTE increased. While comparing air and PSA oxygen, oxygen was found to have a similar [K.sub.L]a, larger [C.sup.*.sub.sat], SOTR, and SOTE, and a lower SAE. It was concluded that superoxygenation is a viable method for increasing oxygen transfer and could potentially reduce oxygenation costs in water treatment processes. Key words: superoxygenation, reaeration, oxygen transfer, pressurized aeration, pure oxygen aeration. Il est encore possible de beaucoup ameliorer le transfert d'oxygene, lequel represente 60% de l'energie necessaire au traitement de l'eau et des eaux usees. La presente etude s'interesse a la superoxygenation de l'eau, c'est-a-dire l'aeration de l'eau par injection d'oxygene tres pur sous pression. On a examine les effets de la superoxygenation sur cinq parametres essentiels de l'aeration: le coefficient de transfert de masse ([K.sub.L]a), la concentration de saturation ([C.sup.*.sub.sat]), le taux standard de transfert d'oxygene (TSTO), le rendement standard de l'aeration (RSA) et rendement standard du transfert d'oxygene (RSTO). Dans la presente etude, on a compare les valeurs obtenues sous des pressions de 0, 50,100,150 et 200 kPa, en utilisant de l'air ou de l'oxygene produit par adsorption modulee en pression (AMP). On a constate que, lorsque la pression de l'air ou de l'oxygene produit par AMP augmentait, [K.sub.L]a diminuait, [C.sup.*.sub.sat] augmentait, le TSTO et le RSA restaient constants, et que le RSTO augmentait. En comparant l'air et l'oxygene produit pas AMP, on a decouvert que l'oxygene presentait un [K.sub.L]a similaire, une [C.sup.*.sub.sat], un TSTO et un RSTO plus eleves et un RSA plus faible. La conclusion de cette etude est que la superoxygenation est une methode fiable pour ameliorer le transfert d'oxygene et qu'elle pourrait permettre de reduire les couts de l'oxygenation dans les procedes de traitement des eaux. [Traduit par la Redaction] Mots-cles: superoxygenation, reaeration, transfert d'oxygene, aeration par injection d'air sous pression, aeration par injection d'oxygene pur., Introduction Anoxia, or low dissolved oxygen (DO) concentrations in aqueous environments adversely affects many species that are dependent upon oxygen for survival. The addition of dissolved oxygen into the hypolimnion [...]

Electrical conductivity (EC) is used for monitoring different types of aqueous systems. The measured EC value at any temperature needs to be corrected for a standard temperature, for reporting or comparison, since EC is dependent on temperature. A temperature compensation factor has been derived for conductivity correction from anaerobic digester supernatant/centrate samples of five different wastewater treatment plants in western Canada. For a temperature compensation factor of 0.0198[degrees][C.sup.-1], corresponding to the standard temperature at 25[degrees]C, the estimated [EC.sub.25] values were found to be reasonably accurate, with a maximum error of 2.01%. The estimated EC values, based on any standard temperature, were found to be statistically similar to each other. Considering the temperature dependence of EC, a relationship between EC and ionic strength was developed in this study for anaerobic digester supernatant/centrate samples. This relationship can be used to estimate the ionic strength of the solution in a system associated with struvite formation from anaerobic digester supernatant/centrate and effectively monitor the system performance. DOI: 10.1061/(ASCE)0733-9372(2009)135:11(122l) CE Database subject headings: Electrical conductivity; Monitoring; Temperature; Wastewater management.

Abstract: Autothermal thermophilic aerobic digestion (ATAD) is an exothermic process where sludge is subjected to temperatures greater than 55 °C for at least 4 hours, over 6-10 days. Organic solids [...]

Abstract: Increased legislative constraints have fuelled an interest in developing sustainable and economical methods for sludge digestion. Autothermal thermophilic aerobic digestion (ATAD) is a robust process that produces Class A [...]

Abstract: In advanced wastewater treatment plants (AWWTP), the recovery of phosphorus (P) has become a recent focus of the wastewater engineering industry. The potential economic savings behind improved sludge management [...]

Abstract: Autotrophic ammonia oxidizing bacteria (AOB) are capable of generating nitrous oxide ([N.sub.2]O), via nitrite reduction, in oxygen-limited environments. The recognition of the environmental fate and effects of [N.sub.2]O, as [...]

A laboratory scale enhanced biological phosphorus removal process was operated in the University of Cape Town configuration to study the variations in alpha and oxygen transfer efficiency ([OTE.sub.f]) under different process conditions. As part of this investigation, process oxygen transfer parameters were determined using the steady state oxygen uptake rate (OUR) and the nonsteady state hydrogen peroxide addition (HPA) methods, as per the American Society of Civil Engineers guidelines. The results indicated that the oxygen transfer parameters [volumetric mass transfer coefficient ([K.sub.L][a.sub.f]), oxygen transfer rate ([OTR.sub.f]), ct and [OTE.sub.f])] were higher when both methods were applied on the same day, compared to the subsequent period, when only the steady state OUR method was employed, under similar operating conditions. The difference in the oxygen transfer parameters appears to be due to the addition of [H.sub.2][O.sub.2] that generates reactive oxygen species in the nonsteady state HPA test. Based on the findings, it was concluded that the HPA test was not a suitable technique to measure oxygen transfer under process conditions. Further, a conceptual model hypothesizing the impacts of [H.sub.2][O.sub.2] addition on activated sludge process is presented. DOI: 10.1061/(ASCE)0733-9372(2005)131:12(1684) CE Database subject headings: Phosphorus; Oxygen transfer; Abatement and removal; Biological treatment; Activated sludge.

In this study, a laboratory scale Univ. of Cape Town enhanced biological phosphorus removal process was operated under controlled conditions at a solids retention time of 15 days. Results are presented for the process performance and oxygen transfer parameters determined by applying the steady state oxygen uptake rate (OUR) and the changing power level (CPL) techniques, as per ASCE standard guidelines. The testing periods were temporally separated to eliminate interference of the tests. During the application of the CPL method, the sludge volume index gradually increased and higher values of the oxygen transfer rate and alpha were measured, in comparison to the data from the steady state OUR method, under similar process performance. Furthermore, the mass transfer rate decreased as the CPL method of testing continued. In contrast, the oxygen transfer parameters remained uniform during the time when the OUR method was applied. The data indicated that the CPL method resulted in higher and variable oxygen transfer parameters, even though the process performance remained unchanged. Therefore, a more rigorous evaluation of the CPL method is recommended to clarify the validity of the test. CE Database subject headings: Phosphorus; Oxygen transfer; Abatement and removal; Sludge treatment.

The use of pH profiles simultaneously with oxidation-reduction potential (ORP) profiles as control strategies will lead to better cyclic control of aerobic-anoxic sludge digestion. The linear ring-buffer concept used on the anoxic part of the oxidation-reduction potential (ORP) profile should be utilized to determine the presence of dissolved-oxygen (DO) breakthrough, thereby preventing the occurrence of incomplete nitrification failures.

This research documents the use of oxidation-reduction potential (ORP) to control two lab-scale aerobic-anoxic sludge digesters. The reactors were operated in sequencing batch reactor fashion, and one reactor had the ratio of air-on/air-off arbitrarily 'fixed' at 3 h for each portion of the cycle. The other reactor operated in a real-time manner with 3 h of air-on and the air-off time determined by computer detection of the nitrate breakpoint in the orp-time profile. Reactor performances were evaluated from a chemical (mass balance) removal perspective (total and volatile suspended solids (TSS and VSS), nitrogen, and phosphorus) coupled with a consideration of the control stability achieved when the reactors were subjected to spikes of sodium nitrate, ammonium chloride, and hydrogen peroxide. The reactors showed comparable chemical removals, however the real-time control reactor displayed a greater ability to accommodate the disturbances investigated.

A pilot-scale, first-stage, autothermal thermophilic aerobic digestion reactor was used to study the effect of microaerophilic conditions on sludge solids destruction, volatile fatty acids (VFA) production, and phosphorus release. For the aeration rates of 0-100 mL/min and the reactor sludge volume of 72 L, with a primary to secondary sludge ratio of 35:65, the solids destruction efficiency ranged between 19.5 and 23.8%, as measured by total suspended solids (TSS). The maximum increase in VFA concentration (483 mg/L as acetic acid) occurred at the low airflow rate of 25 mL/min. The unit VFA production ranged from 0.009 to 0.183 mg of-VFA generated/mg of TSS destroyed, with the dominance of acetic acid. The milligrams of phosphorus released per milligrams of TSS destroyed was from 0.018 to 0.0312, with the maximum measured when no air (nitrogen) was supplied; but the maximum ratio of VFA to [PO.sub.4] (equal to 8.2) was measured when the air supply was at 25 mL/min.