RESUMEN
Denitrification beds are containers filled with wood by-products that serve as a carbon and energy source to denitrifiers, which reduce nitrate (NO(3)(-)) from point source discharges into non-reactive dinitrogen (N(2)) gas. This study investigates a range of alternative carbon sources and determines rates, mechanisms and factors controlling NO(3)(-) removal, denitrifying bacterial community, and the adverse effects of these substrates. Experimental barrels (0.2 m(3)) filled with either maize cobs, wheat straw, green waste, sawdust, pine woodchips or eucalyptus woodchips were incubated at 16.8 °C or 27.1 °C (outlet temperature), and received NO(3)(-) enriched water (14.38 mg N L(-1) and 17.15 mg N L(-1)). After 2.5 years of incubation measurements were made of NO(3)(-)-N removal rates, in vitro denitrification rates (DR), factors limiting denitrification (carbon and nitrate availability, dissolved oxygen, temperature, pH, and concentrations of NO(3)(-), nitrite and ammonia), copy number of nitrite reductase (nirS and nirK) and nitrous oxide reductase (nosZ) genes, and greenhouse gas production (dissolved nitrous oxide (N(2)O) and methane), and carbon (TOC) loss. Microbial denitrification was the main mechanism for NO(3)(-)-N removal. Nitrate-N removal rates ranged from 1.3 (pine woodchips) to 6.2 g N m(-3) d(-1) (maize cobs), and were predominantly limited by C availability and temperature (Q(10) = 1.2) when NO(3)(-)-N outlet concentrations remained above 1 mg L(-1). The NO(3)(-)-N removal rate did not depend directly on substrate type, but on the quantity of microbially available carbon, which differed between carbon sources. The abundance of denitrifying genes (nirS, nirK and nosZ) was similar in replicate barrels under cold incubation, but varied substantially under warm incubation, and between substrates. Warm incubation enhanced growth of nirS containing bacteria and bacteria that lacked the nosZ gene, potentially explaining the greater N(2)O emission in warmer environments. Maize cob substrate had the highest NO(3)(-)-N removal rate, but adverse effects include TOC release, dissolved N(2)O release and substantial carbon consumption by non-denitrifiers. Woodchips removed less than half of NO(3)(-) removed by maize cobs, but provided ideal conditions for denitrifying bacteria, and adverse effects were not observed. Therefore we recommend the combination of maize cobs and woodchips to enhance NO(3)(-) removal while minimizing adverse effects in denitrification beds.
Asunto(s)
Bacterias/crecimiento & desarrollo , Carbono/farmacología , Desnitrificación/efectos de los fármacos , Nitratos/aislamiento & purificación , Purificación del Agua/instrumentación , Purificación del Agua/métodos , Bacterias/efectos de los fármacos , Bacterias/genética , Desnitrificación/genética , Dosificación de Gen/genética , Genes Bacterianos/genética , Efecto Invernadero , Metano/análisis , Nitrato-Reductasa/genética , Nitrógeno/aislamiento & purificación , Óxido Nitroso/análisis , Oxidorreductasas/genética , ARN Ribosómico 16S/genética , Solubilidad/efectos de los fármacos , TemperaturaRESUMEN
Denitrifying woodchip bioreactors (denitrification beds) are increasingly used to remove excess nitrate (NO3â») from point-sources such as wastewater effluent or subsurface drains from agricultural fields. NO3â» removal in these beds is assumed to be due to microbial denitrification but direct measurements of denitrification are lacking. Our objective was to test four different approaches for measuring denitrification rates in a denitrification bed that treated effluent discharged from a glasshouse. We compared these denitrification rates with the rate of NO3â» removal along the length of the bed. The NO3â» removal rate was 8.73 ± 1.45 g m⻳ d⻹. In vitro acetylene inhibition assays resulted in highly variable denitrification rates (DR(AI)) along the length of the bed and generally 5 times greater than the measured (NO3â»-N removal rate. An in situ push-pull test, where enriched ¹5N-NO3â» was injected into 2 locations along the bed, resulted in rates of 23.2 ± 1.43 g N m⻳ d⻹ and 8.06 ± 1.64 g N m⻳ d⻹. The denitrification rate calculated from the increase in dissolved N2 and N2O concentrations (DR(N2) along the length of the denitrification bed was 6.7 ± 1.61 g N m⻳ d⻹. Lastly, denitrification rates calculated from changes in natural abundance measurements of δ¹5N-N2 and δ¹5N-NO3â» along the length of the bed yielded a denitrification rate (DR(NA)) of 6.39 ± 2.07 g m⻳ d⻹. Based on our experience, DR(N2) measurements were the easiest and most efficient approach for determining the denitrification rate and N2O production of a denitrification bed. However, the other approaches were useful for testing other hypotheses such as factors limiting denitrification or may be applied to determine denitrification rates in environmental systems different to our study site. DR(N2) does require very careful sampling to avoid atmospheric N2 contamination but could be used to rapidly determine denitrification rates in a variety of aquatic systems with high N2 production and even water flows. These measurements demonstrated that the majority of NO3â» removal was due to heterotrophic denitrification.
Asunto(s)
Reactores Biológicos , Nitratos/análisis , Eliminación de Residuos Líquidos/métodos , Purificación del Agua/métodos , Desnitrificación , Nueva ZelandaRESUMEN
Gutta percha, the trans-isomer of polyisoprene, is being used for several technical applications due to its resistance to biological degradation. In the past, several attempts to isolate micro-organisms capable of degrading chemically pure poly(trans-1,4-isoprene) have failed. This is the first report on axenic cultures of bacteria capable of degrading gutta percha. From about 100 different habitats and enrichment cultures, six bacterial strains were isolated which utilize synthetic poly(trans-1,4-isoprene) as sole carbon and energy source for growth. All isolates were assigned to the genus Nocardia based on 16S rRNA gene sequences. Four isolates were identified as strains of Nocardia nova (L1b, SH22a, SEI2b and SEII5a), one isolate was identified as a strain of Nocardia jiangxiensis (SM1) and the other as a strain of Nocardia takedensis (WE30). In addition, the type strain of N. takedensis obtained from a culture collection (DSM 44801(T)) was shown to degrade poly(trans-1,4-isoprene). Degradation of poly(trans-1,4-isoprene) by these seven strains was verified in mineralization experiments by determining the release of CO(2). All seven strains were also capable of mineralizing poly(cis-1,4-isoprene) and to use this polyisoprenoid as a carbon and energy source for growth. Mineralization of poly(trans-1,4-isoprene) after 80 days varied from 3 % (strain SM1) to 54 % (strain SEI2b) and from 34 % (strain L1b) to 43 % (strain SH22a) for the cis-isomer after 78 days. In contrast, Gordonia polyisoprenivorans strain VH2, which was previously isolated as a potent poly(cis-1,4-isoprene)-degrading bacterium, was unable to degrade poly(trans-1,4-isoprene). Scanning electron microscopy revealed cavities in solid materials prepared from poly(trans-1,4-isoprene) and also from poly(cis-1,4-isoprene) after incubation with N. takedensis strain WE30 or with N. nova strain L1b, whereas solid poly(trans-1,4-isoprene) material remained unaffected if incubated with G. polyisoprenivorans strain VH2 or under sterile conditions.