No abstract

Halogenated organics are among the most commonly-encountered anthropogenic compounds accumulating in the environment. These compounds have many behavioral characteristics in common. Many are carcinogenic; many are toxic; almost all resist biodegradation; all undergo bioconcentration and concentration in sediments. One group of halogenated materials, the halogenated phenols, interact with microbial cell tissue and higher-life forms in a way not seen with the other compounds in this broad category. That is, they will uncouple oxidative phosphorylation, the energy transfer process which permits the accumulation of the energy of substrate oxidation as adenosine triphosphate which is subsequently used in synthesis. The present study reports on laboratory work which serves to quantify the various results of energy uncoupling. These are an increase in oxygen use, a decrease in synthesis and a decrease in the rate of normal substrate uptake. The work is carried out utilizing four common types of organics as growth substrates. The consequence of the phenomenon of uncoupling in full-scale treatment plants, based on experiences at one of the Phoenix wastewater treatment plants, is discussed.

Heavy metal contamination of soil frequently occurs at hazardous waste sites. The use of chelating agents to extract heavy metals from contaminated soils is seen as a treatment method. This research investigated the use of the chelator S‐carboxymethylcysteine (SCMC) to extract copper from a spiked soil. Batch equilibration experiments over 24‐hour periods tested the hypotheses that through a proper choice of chelator extraction could be made more selective toward heavy metals, and extracted metals could be readily recovered as precipitates by increasing the solution pH. The results showed that SCMC could extract and release copper reversibly and that SCMC prefers complexing with copper over competing Fe and Ca ions. Chemical equilibrium modeling was useful for selecting suitable chelating agents for the extraction and subsequent treatment conditions for metals recovery.

The relationship between chemical structure and the comparative rate of biodegradation (defined here as the biodegradation index) by unacclimated activated sludge has been studied. The findings of one model illustrate that the relationship between structure and biodegradability for a homologous series of aromatic compounds may be easily developed using techniques drawn from medical and pharmaco logical sciences, in this case, Hammett's constants. This is true when the biodegradation pathway is known. However, such a model is not broadly applicable to a diverse group of substances where such pathway infor mation is not available. A second model was developed using a newer technique-molecular connectivity indices-which does not require pathway information. The second model was calibrated with the data employed in the first model. This model did not contain specific pathway or directional information, but successfully predicted the rates at about the same confidence level as the first. Water Environ. Res., 65, 772 (1993).

This study developed a strategy to control effluent ammonia from an activated sludge system, using oxidation-reduction potential. By controlling effluent ammonia concentrations, disinfection of treated wastewater is more cost effectively achieved by chloramination rather than break-point chlorination. The system under consideration was an extended aeration oxidation ditch. The study takes into account the concepts of nitrification and denitrification, as well as intrinsic characteristics of oxidation-reduction potential, while also keeping ease of operation in mind. Data were gathered by varying the rate of aeration of the basin from two extremes, while collecting samples along the timeline. Oxidation-reduction potential, dissolved oxygen concentration and ammonia concentration data were collected for evaluation. Using these data a preliminary control strategy was developed. The control strategy focused on operating the system in a continuous flow and varying aeration scenario. Two attempts to control the oxidation ditch were made. Using oxidation-reduction potential as an indicator, adjustments were made to the aerator controls in order to accommodate changes in organic loading, and maintain a constant effluent ammonia concentration. The first attempt was met with success and used to fine tune the strategy for the second attempt. The second attempt experienced more success than the first in controlling effluent ammonia concentrations, thus confirming the original hypothesis of the study.