The bacterial rhizosphere communities of three host plants of the pathogenic fungus Verticillium dahliae, field-grown strawberry (Fragaria ananassa Duch.), oilseed rape (Brassica napus L.), and potato (Solanum tuberosum L.), were analyzed. We aimed to determine the degree to which the rhizosphere effect is plant dependent and whether this effect would be increased by growing the same crops in two consecutive years. Rhizosphere or soil samples were taken five times over the vegetation periods. To allow a cultivationindependent analysis, total community DNA was extracted from the microbial pellet recovered from root or soil samples. 16S rDNA fragments amplified by PCR from soil or rhizosphere bacterium DNA were analyzed by denaturing gradient gel electrophoresis (DGGE). The DGGE fingerprints showed plant-dependent shifts in the relative abundance of bacterial populations in the rhizosphere which became more pronounced in the second year. DGGE patterns of oilseed rape and potato rhizosphere communities were more similar to each other than to the strawberry patterns. In both years seasonal shifts in the abundance and composition of the bacterial rhizosphere populations were observed. Independent of the plant species, the patterns of the first sampling times for both years were characterized by the absence of some of the bands which became dominant at the following sampling times. Bacillus megaterium and Arthrobacter sp. were found as predominant populations in bulk soils. Sequencing of dominant bands excised from the rhizosphere patterns revealed that 6 out of 10 bands resembled gram-positive bacteria. Nocardia populations were identified as strawberry-specific bands.

Triclosan (TCS; 5-chloro-2-[2,4-dichloro-phenoxy]-phenol) is a widely used antimicrobial agent. To understand its fate during sewage treatment, the biodegradation and removal of TCS were determined in activated sludge. In addition, the effects of TCS on treatment processes were assessed. Fate was determined by examining the biodegradation and removal of TCS radiolabeled with 14C in the 2,4-dichlorphenoxy ring in laboratory batch mineralization experiments and bench-top continuous activated-sludge (CAS) systems. In batch experiments with unacclimated sludge, TCS was mineralized to 14CO2, but the total yield varied as a function of test concentration. Systems that were redosed with TCS exhibited more extensive and faster mineralization, indicating that adaptation was a critical factor determining the rate and extent of biodegradation. In a CAS study in which the influent level of TCS was incrementally increased from 40 microg/L to 2,000 microg/L, removal of the parent compound exceeded 98.5% and removal of total radioactivity (parent and metabolites) exceeded 85%. Between 1.5 and 4.5% of TCS in the influent was sorbed to the wasted solids, whereas >94% underwent primary biodegradation and 81 to 92% was mineralized to CO2 or incorporated in biomass. Increasing levels of TCS in the influent had no major adverse effects on any wastewater treatment process, including chemical oxygen demand, biological oxygen demand, and ammonia removal. In a subsequent experiment, a CAS system, acclimated to TCS at 35 microg/L, received two separate 4-h shock loads of 750 microg/L TCS. Neither removal of TCS nor treatment processes exhibited major adverse effects. An additional CAS study was conducted to examine the removal of a low level (10 microg/L) of TCS. Removal of parent equaled 94.7%, and biodegradation remained the dominant removal mechanism. A subsequent series of CAS experiments examined removal at four influent concentrations (7.5, 11, 20, and 50 microg/L) of TCS and demonstrated that removal of parent ranged from 98.2 to 99.3% and was independent of concentration. Although TCS removal across all experiments appeared unrelated to influent concentration, removal was significantly correlated (r2 = 0.87) with chemical oxygen demand removal, indicating that TCS removal was related to overall treatment efficiency of specific CAS units. In conclusion, the experiments show that TCS is extensively biodegraded and removed in activated-sludge systems and is unlikely to upset sewage treatment processes at levels expected in household and manufacturing wastewaters.

Laboratory models of wastewater treatment plants (WWTP) provide controlled systems for studying chemical biodegradability and removal as well as WWTP microbial ecology and engineering. In this study, Continuous Activated Sludge (CAS, 3-L) and Semi-Continuous Activated Sludge (SCAS, 2.5-L) units were maintained for up to 17 weeks using feedstocks of either fresh WWTP sewage, a complex synthetic wastewater, or a simple glucose/peptone feed (SCAS only). The goal of this research was to evaluate the microbial communities of the WWTP and the CAS and SCAS units to determine which laboratory models, and which feedstocks, were able to maintain the complexity of the WWTP microbial communities in the laboratory. One endpoint evaluated in this study was microbial community metabolic profiles, as measured using Biolog MicroPlates. Biolog Microplates contain 95 different pre-dried carbon sources and a tetrazolium dye used to spectrophotometrically measure oxidation of carbon sources. The Biolog carbon source utilization patterns of the CAS communities were similar to the SCAS communities when both were fed WWTP sewage. In addition, the profiles for these laboratory models remained similar to the WWTP microbial communities, even over an extended cultivation time (16 weeks) in the CAS systems. Amendment with a complex synthetic wastewater (25% by chemical oxygen demand) did not affect microbial metabolic response in the CAS systems, but amendment (100% by chemical oxygen demand) with a simple glucose-peptone wastewater in the SCAS system resulted in a measurable shift in microbial metabolic response.

The temperature-phased anaerobic biofilter (TPAB) process is a new high-rate anaerobic treatment system that includes a thermophilic biofilter connected in series to a mesophilic biofilter providing for two-temperature. two-phase treatment.Three TPAB systems with thermophilic:mesophilic reactor size ratios of 1:7, I:3. and I: I were operated at system hydraulic retention times (HRTs) of 24. 36. and 48 hours at temperatures of 56°C in the thermophilic phase and 35°C in the mesophilic phase. The three TPAB systems achieved soluble and total chemical oxygen demand (COD) reductions in excess of 97% and 90%. respectively, for a synthetic milk substrate over a range of system COD loadings from 2 to 16 g COD/L/ d. There was little difference in performance between the three TPAB systems based on COD reduction and methane production, making it feasible to use a smaller thermophilic first phase in the TPAB system.At the 48-hour system HRT, the 6-hour thermophilic phase biofilter reached saturation loading at a COD load of 48 gil/d. After further increases in organic loading, the methane production decreased in the thermophilic first phase and increased in the corresponding mesophilic second phase while levels of n-valeric and butyric acids increased significantly. It is proposed that a microbial population shift occurred in the thermophilic first phase at high organic loadings at low HRTs. Although a decrease in methane production from the thermophilic phase was observed, the performance of the overall two-stage TPAB system did not decline.The TPA B systems were observed to outperform single-stageanaerobic filters operated at equivalent HRTs and organic loadings. Water Environ. Res .. 67, 1095Res .. 67, (1995.