Thermophilic soil geobacilli isolated from cool temperate geographical zone environments have been shown to be metabolically inactive under aerobic conditions at ambient temperatures (-5 to 25 degrees C). It is now confirmed that a similar situation exists for their anaerobic denitrification activity. It is necessary therefore to determine the mechanisms that sustain the observed significant viable populations in these soils. Population analysis of thermophiles in rainwater and air samples has shown different species compositions which support the view that long distance global transport and deposition in rainwater is a possible source of replenishment of the soil thermophile populations. Survival experiments using a representative Geobacillus isolate have indicated that while cells lose viability rapidly at most temperatures, populations can increase only when the temperature allows growth to take place at a rate which exceeds death rate. Long term (9-month) experiments at 4 degrees C show population increases which can be accounted for by very slow growth rates complemented by negligible death rates. These results are interpreted in the context of current hypotheses on the biogeography patterns of bacteria.

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The effect of settling on mass balance and biodegradation characteristics of domestic wastewater and on denitrification potential was studied primarily using model calibration and evaluation of oxygen uptake rate profiles. Raw domestic wastewater was settled for a period of 30 minutes and a period of 2 hours to assess the effect of primary settling on wastewater characterization and composition. Mass balances in the system were made to evaluate the effect of primary settling on major parameters. Primary settling of the selected raw wastewater for 2 hours resulted in the removal of 32% chemical oxygen demand (COD), 9% total Kjeldahl nitrogen, 9% total phosphorus, and 47% total suspended solids. Respirometric analysis identified COD removed by settling as a new COD fraction, namely settleable slowly biodegradable COD (X SS ), characterized by a hydrolysis rate of 1.0 day 21 and a hydrolysis half-saturation coefficient of 0.08. A model simulation to test the fate and availability of suspended (X S ) and settleable (X SS ) COD fractions as carbon sources for denitrification showed that both particulate COD components were effectively removed aerobically at sludge ages higher than 1.5 to 2.0 days. Under anoxic conditions, the biodegradation of both COD fractions was reduced, especially below an anoxic sludge retention time of 3.0 days. Consequently, modeling results revealed that the settleable COD removed by primary settling could represent up to approximately 40% of the total denitrification potential of the system, depending on the specific configuration selected for the nitrogen removal process. This way, the results showed the significant effect of primary settling on denitrification, indicating that the settleable COD fraction could contribute an additional carbon source in systems where the denitrification potential associated with the influent becomes rate-limiting for the denitrification efficiency. Water Environ. Res., 81, 715 (2009).

BACKGROUND The study rationale was to explore the potential of particle size distribution (PSD) to support COD fractionation of sewage. Accordingly, the main aim focused on establishing the experimental relation between COD fractionation and PSD on two samples of a selected source, one representing the average character of the sewage and the other a weaker sample. PSD analyses were also conducted on effluent samples. RESULTS PSD profiles of COD yielded the typical bimodal distribution, one major peak representing 65% of COD, higher than 1600 nm and the second peak of 10% lower than 2 nm. Results were evaluated to underline the potential of PSD in complementing COD fractionation as related to biodegradation. PSD exhibited a close relationship with COD fractions with different biodegradation characteristics and defined all major COD fractions except the initial soluble and particulate inert COD fractions. CONCLUSION Selection of appropriate values for inert COD fractions together with default kinetic information available for sewage would enable modelling and designing of various biological treatment alternatives without the need for time consuming experiments on COD fractionation. Furthermore, PSD of biological treatment effluent provided concrete evidence for the generation of soluble residual products, which should be part of all modelling evaluations. © 2017 Society of Chemical Industry

The reductive transformation of pentachloronitrobenzene (PCNB), an organochlorine fungicide, was investigated with a mixed, methanogenic culture developed from a contaminated estuarine sediment. Batch assays performed with this enrichment culture resulted in the biotransformation of PCNB to pentachloroaniline (PCA), which was then sequentially dechlorinated as follows: PCA --> 2,3,4,5- and 2,3,5,6-tetrachloroaniline (TeCA) --> 2,4,5- and 2,3,5-trichloroaniline (TrCA) --> 2,4-, 2,5-, and 3,5-dichloroaniline (DCA) --> 3- and 4-chloroaniline (CA) (low levels). Glucose fermentation, methanogenesis, and dechlorination were not inhibited at an initial PCNB concentration up to 40 microM, which is 27 times higher than its aqueous solubility. The addition of 25 mM 2-bromoethanesulfonate (BES) to the PCNB-amended culture resulted in the complete inhibition of methanogenesis, but the biotransformation of PCNB to PCA and its sequential dechlorination pathway were not affected. The addition of sodium azide (200 mg/L) to the PCNB-amended culture resulted in complete inhibition of methanogenesis, but did not inhibit the transformation of PCNB to PCA; however, PCA dechlorination was not observed. PCNB was also abiotically transformed to PCA in autoclaved culture media but at much lower rates as compared to the biotic assays. In contrast, the rate of PCNB to PCA transformation in autoclaved culture controls was similar to the rates observed in the azide-amended culture and the active enrichment culture, indicating that biotically derived reductants facilitated the observed transformation of PCNB to PCA. Dechlorination of PCA was not observed in any of the abiotic controls. These findings have significant environmental implications in terms of the fate and transport of PCNB, PCA, and its dechlorination products in subsurface systems.