Anaerobic Decomposition and Denitrification during Plant Decomposition in an Organic Soil.

Nitrate concentrations in groundwater have been shown to be reduced during passage through riparian soils and a possible mechanism for this reduction is bacterial denitrifieation. For denitrification to occur there must be sufficient available C as an energy source. We examined the competition for organic substrate between microbial processes during the anaerobic decomposition of plant matter in a laboratory study. Fresh and senescent pine needles (Pinus radiata D. Don) and watercress leaves (Rorippa nasturtium-aquaticum L.Hayek) were added to an organic riparian soil, incubated anaerobically for 90 d and production of CO2 and CH4 measured. At 9-d intervals NO3 and acetylene were added to a replicate and production of CO2 , CH4 , and N2 O was followed. In the absence of NO3 , watercress produced the most CO2 and CH4 (21% of added C), followed by fresh pine needes (10%), and senescent pine needles (6%). First-order rate constants calculated for gaseous C production were 0.033 d-1 , 0.0088 d-1 , and 0.0071 d-1 for watercress, fresh, and senescent pine needles, respectively. As plant tissue became increasingly decomposed via fermentation, less N2 O and CO2 was produced following NO3 addition, presumably because the remaining plant matter was more resistant to further degradation. Denitrification and CO2 production in the watercress and fresh pine needle treatments were up to 5 times higher than that measured in the senescent pine needle treatment. As the same amount of C was added to all treatments, these results suggested that the lability of added C was of greater importance than the quantity of C added in regulating microbial response. The response of denitrifying bacteria to the addition of NO3 was rapid, even after 99 d of incubation in the absence of either NO3 or oxygen as an electron acceptor. This suggested that denitrifying bacteria could survive and compete for C in riparian soils where NO3 concentrations fluctuate.

Anaerobic digestion of wood ethanol stillage using upflow anaerobic sludge blanket reactor.

The anaerobic digestion of wood ethanol stillage in a UASB reactor was studied. At organic loading rates be low 16 kg COD/m(3) day the reactor performed effectively, achieving soluble COD and BOD removals in excess of 86 and 93%, respectively. Removal of color averaged 40%. At a loading rate of 16 kg COD/m(3) day the methane yield was 0.302 L CH(4) (STP)/g COD removed, and the observed cell yield was 0.112 g VSS/g COD removed. Operation of the reactor at higher loading rates was unsuccessful. Nitrogen, phosphorus, and alkalinity were supplemented. No additions of the essential trace elements Fe, Co, and Ni were required.