In the present study, milled wood
lignin (MWL) and organosolv lignin
isolated from red oak (hardwood), loblolly pine (softwood) and corn
stover (herbaceous biomass) were characterized by TGA, elemental analyzer,
GPC, FTIR, 2D-HSQC NMR, and then pyrolyzed in the absence and presence
of a zeolite catalyst. For all three biomass species, organosolv lignins
contained fewer volatiles in comparison to the corresponding MWLs.
Red oak lignin was affected most by the organosolv process, evident
by the greatest decrease in volatile content and increase in carbon
content of the organosolv lignin. Compared to the corresponding MWLs,
organosolv lignins produced more char and less phenolic oil upon pyrolysis.
Organosolv lignins also convert to catalytic coke and light hydrocarbons
in higher selectivity in comparison to the MWLs during catalytic pyrolysis.
When pyrolyzed, corn stover MWL produced 16.26% of phenolic monomers,
which is a significantly higher yield compared to 8.61% from red oak
MWL and 9.51% from loblolly pine MWL. During catalytic pyrolysis,
corn stover lignins also produced higher yields of aromatic hydrocarbons
in comparison to red oak or loblolly pine derived lignins. Overall,
corn stover lignin had the highest potential for volatilization because
it retains highly branched polymer structure enriched in tricin, ferulate
and coumarate groups.
Quantitative estimates of denitrification are needed in designing artificial wetlands to optimize nitrate (NOj-) removal. Acetylene blockage and ~SN-tracer methods were employed to quantify denitriflcation in constructed wetlands receiving agricultural tile drainage, using plastic tubes to enclose in situ mesocosms. Estimates were also made through NO;-disappearance from mesocosm water columns. The ~SN and CzHz methods yielded comparable rates. At 4 to 25°C, and with 9 to 20 mg NO~-N L-1 initially in the mesocosm water columns, denitrification rates by the CzHz technique ranged from 2.0 to 11.8 mg N m-z h-1. In the June-August lSN experiment, when wetland NOj-was below detection, a time series of denitrification rates followed a bell-shaped curve after a pulse input of NOj-(-15 mg N L-~, 70 atom% ~SN). The maximal denitrification rate (9.3 mg N m-~ h-1) was observed 5.4 d after the pulse. After 33 d, 58% of the ~SNOj-had been evolved as N2, only ~0.1% as N~O; 6 to 10% was recovered in plant shoots and as organic N in the upper 5 cm of sediment. From 32 to 36% of the ~NO~-spike was not recovered, and presumably seeped into the sediments. The NO3 disappearance rates in the water column ranged from 12 to 63 mg N m-~ h-~ at 11 to 2T'C. Because water infiltration carries NO~-through the anaerobic sedimenl/water interface for denitrification, a subsurface-flow wetland may denitrify more NO~-than a surface-flow wetland.
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