Louis-B. Jugnia

Methanotrophs and methanotrophic activity in engineered landfill biocovers.

The dynamics and changes in the potential activity and community structure of methanotrophs in landfill covers, as a function of time and depth were investigated. A passive methane oxidation biocover (PMOB-1) was constructed in St-Nicéphore MSW Landfill (Quebec, Canada). The most probable number (MPN) method was used for methanotroph counts, methanotrophic diversity was assessed using denaturing gradient gel electrophoresis (DGGE) fingerprinting of the pmoA gene and the potential CH(4) oxidation rate was determined using soil microcosms. Results of the PMOB-1 were compared with those obtained for the existing landfill cover (silty clay) or a reference soil (RS). During the monitoring period, changes in the number of methanotrophic bacteria in the PMOB-1 exhibited different developmental phases and significant variations with depth. In comparison, no observable changes over time occurred in the number of methanotrophs in the RS. The maximum counts measured in the uppermost layer was 1.5x10(9) cells g dw(-1) for the PMOB-1 and 1.6x10(8) cells g dw(-1) for the RS. No distinct difference was observed in the methanotroph diversity in the PMOB-1 or RS. As expected, the potential methane oxidation rate was higher in the PMOB-1 than in the RS. The maximum potential rates were 441.1 and 76.0 microg CH(4) h(-1) g dw(-1) in the PMOB and RS, respectively. From these results, the PMOB was found to be a good technology to enhance methane oxidation, as its performance was clearly better than the starting soil that was present in the landfill site.

Biocover Performance of Landfill Methane Oxidation: Experimental Results

An experimental passive methane oxidation biocover (PMOB) was constructed within the existing final cover of the St-Nicephore landfill. Its substrate consisted of a 0.80-m-thick mixture of sand and compost. The goal of this experiment was to evaluate the performance of the PMOB in reducing CH4 emissions when submitted to an increasing methane load. The CH4 load applied started with 9.3 g  CH4 m−2 d−1 . When the site had to be closed for the winter, the CH4 input was 820 g  CH4 m−2 d−1 . Throughout the study, practically all the CH4 input was oxidized; absolute removal rates were linearly correlated to methane loading; and the oxidation zone was established between 0.6–0.8 m. These results seem to indicate that the upper limit potential of this PMOB to oxidize CH4 was not necessarily reached during the study period. Surface CH4 concentration scans showed no signs of leaks. The substrate offered excellent conditions for the growth of methanotrophs, whose count averaged 3.91× 108  CFU g  dw−1 soil.

The microbial food web in the recently flooded Sep reservoir : Diel fluctuations in bacterial biomass and metabolic activity in relation to phytoplankton and flagellate grazers

The spatial distribution of the bacterial biomass and production and of potential heterotrophic activity (PHA) weree measured every 4 h between 23 July (10:00 h) and 25 July (10:00 h) 1997 in a recently flooded oligo-mesotrophic reservoir (the Sep Reservoir, Puy-de-Dôme, France), in relation to temperature, the phytoplankton biomass and production, and the abundance of heterotrophic flagellates. The temperature varied slightly with time during the study, but the well-established thermal stratification agreed well with vertical distribution of the biological variables that were measured. Only the bacterial production and the PHA showed significant diel changes (t-test,p<0.05), with maxima at 18:00 h and minima at 02:00 h. A significant positive relation was found between bacterial abundance and that of heterotrophic flagellates, which, rather than being an association related to the thermal stratification of the water column, was considered to reflect a trophic relation between these two communities. A carbon balance analysis suggested that at least 30% of the C from primary production measured during the sampling period was used by bacteria, and that 42% of this secondary production, or 6% of the primary production, would be used for the development of the heterotrophic flagellates present. We conclude that the bacterioplankton forms, at least occasionally, an important source of carbon for higher trophic levels, and reject the hypothesis that bacterial production in the Sep Reservoir depends exclusively on organic matter of allochthonous origin.

Effect of compost, nitrogen salts, and NPK fertilizers on methane oxidation potential at different temperatures

The effects of compost, nitrogen salts, and nitrogen–phosphorous–potassium (NPK) fertilizers on the methane oxidation potential (MOP) of landfill cover soil at various temperatures were assessed. For this, we used batch assays conducted at 5°C, 15°C, and 25°C with microcosms containing landfill cover soil slurries amended with these elements. Results indicated variable impacts dependent on the type of amendment and the incubation temperature. For a given incubation temperature, MOP varied from one compost to another and with the amount of compost added, except for the shrimp/peat compost. With this latter compost, independent of the amount, MOP values remained similar and were significantly higher than those obtained with other composts. Amendment with most of the tested nitrogen salts led to similar improvements in methanotrophic activity, except for urea. MOP with NPK fertilizer addition was amongst the highest in this study; the minimum value obtained with NPK (20–0–20) suggested the importance of P for methanotrophs. MOP generally increased with temperature, and nutrient limitation became less important at higher temperatures. Overall, at each of the three temperatures tested, MOP with NPK fertilizer amendments provided the best results and was comparable to those observed with the addition of the shrimp/peat compost. The results of this study provide the first evidence of the following: (1) compost addition to improve methanotrophic activity in a landfill cover soil should consider the amount and type of compost used and (2) the importance of using NPK fertilizers rather than nitrogen salts, in enhancing this activity, primarily at low temperatures. One can also consider the potential beneficial impact of adding these elements to enhance plant growth, which is an advantage for MOP.

Physicochemical water quality of the Mfoundi River watershed at Yaoundé, Cameroon, and its relevance to the distribution of bacterial indicators of faecal contamination.

Water quality of the Mfoundi River and four of its tributaries was studied by assessing some physicochemical variables (temperature, pH, conductivity, chlorides, phosphates and nitrogen ammonia, dissolved oxygen and carbon dioxide, organic matter content and Biological Oxygen Demand) and their influence on the distribution of bacterial indicators of faecal contamination (total coliform, faecal coliform and faecal streptococci). For this, standard methods for the examination of physicochemical parameters in water were followed, and statistical analysis (Pearson correlations) used to establish any relationships between physicochemical and biological variables. Our results revealed that almost all of the examined physicochemical variables exceeded World Health Organization (WHO) guidelines for recreational water. This was in agreement with a previous microbiological study indicating that these waters were not safe for human use or primary contact according to water quality standards established by the WHO. Results of our correlation analysis suggested that physicochemical and biological variables interact in complicated ways reflecting the complex processes occurring in the natural environment. It was also concluded that pollution in the Mfoundi River watershed poses an increased risk of infection for users and there exists an urgent need to control dumping of wastewater into this watershed.

An assessment of the impact of Mingoa Stream input to the bacteriological quality of the Municipal Lake of Yaoundé (Cameroon)

To investigate the deteriorating bacteriological water qualityof Municipal Lake of Yaoundé, the degree of pollution of theMingoa Stream, the main tributary of the lake, was evaluated fortotal coliforms, thermotolerant coliforms, and fecal streptococci. Concentrations of these bacterial indicators inMingoa Stream were higher than those allowed by international norms for the bacteriological quality of recreational water. Thus, this stream contributes to the high levels of bacteria number in the water column of the Municipal Lake.

Enhancing the Potential for in situ Bioremediation of RDX Contaminated Soil from a Former Military Demolition Range

ABSTRACT Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a toxic, mobile groundwater contaminant common to military sites. Biodegradation of RDX is an alternative, cost effective and environmentally friendly remediation approach. The effects of carbon amendments (waste glycerol and cheese whey) used alone or with a potential electron shuttle (ammonium lignosulfonate) on RDX biodegradation were assessed. These substrates are readily available waste materials that can be used as nutrients to promote oxygen consumption, creating a more reducing environment. Nutrient amended batch assays were conducted using RDX spiked contaminated demolition range soil under anaerobic conditions. The amendments that improved RDX mineralization the most were subsequently tested in a scaled up repacked soil column study to verify if this strategy could be effectively implemented on-site. Microcosm results indicated that RDX mineralization by indigenous anaerobic microorganisms was enhanced the most by the low carbon amendment concentration. The use of ammonium lignosulfonate was not effective, exhibiting an inhibitory effect on RDX biodegradation that was stronger at higher concentrations. The soil column study showed that the low concentration of waste was the most promising treatment scenario. These results offer good prospects for the use of waste glycerol for in situ treatment of soils contaminated with energetic-materials, such as RDX.

Bacteria—phytoplankton relationships in a recently formed reservoir (Sep, France)

The role ofbacterioplankton in the cycling of carbon and nutrients in pelagic systems is increasingly recognized as important. lndeed, heterotrophic planktonic bacteria mediate a significant conversion of poor-quality dissolved organic carbon imo highquality particulate organic carbon available to higher trophic levels, and so, occupy a pivotal position in aquatic ecosystems (AzAM et al. 1983). Bacteria are generally considered as the principal decomposers of organic carbon and generators of minerals in aquatic systems. A number of studies from natural or artificial stabilized lakes have shown dose coupling between heterotrophic bacterial activity and growth and phytoplankton primary production, presumably related to the production of dissolved organic carbon by autotrophs (e.g. COLE et al. 1988, WHITE et al. 1991). However, the absence of or weak (i.e. nonsignificant) coupling between bacteria and autotrophs is sometimes reported in plankton, especially in coastal and inland waters where carbon fixed within the systems can play a minor role in plankton dynamics, compared to the impact of allochthonous substrate inputs from the catchment (CoFFIN & SHARP 1987, LAVANDIER 1990, FINDLAY et al. 1991, JuGNIA et al. 1998).