European legislation imposes tough restrictions on the quality of landfill leachate discharges, of which a major component is ammonia. Thus, there is a pressing need, particularly for oper ators who will have to meet these discharge standards, for a greater understanding of the origin and transformations of ammonia and other nitrogenous compounds from landfills. Moreover, with the concept of 'sustainability' being applied to landfilling, the industry will need to meet the challenge of accelerating the rate of refuse decomposition. Ammonia is both a potentially toxic product of refuse degradation and an essential nutrient for the bacteria responsible for this. The quantities present in municipal solid waste (MSW) are known but prediction of the amounts released during decom position is hampered by the lack of long term data on amino nia concentrations in leachate either from landfills or exper imental systems with a measured initial nitrogen content. For the treatment of ammonia from landfill regimes designed to accelerate refuse degradation, it is vital to under stand the nitrogen requirements of the degradation processes, in order to minimise potential ammonia toxicity while ensur ing sufficient concentrations to support the rate of decompo sition. The authors found little experimental evidence to sup port current views on the nitrogen transformations that occur in MSW, although new experimental data support the hypothesis that denitrification occurs in landfill sites. It is generally considered that the high ammonia concentrations in leachate provide evidence that ammonia is released from the decomposition of protein in refuse, even though the con centrations of the various nitrogenous components in refuse during decomposition are not known. Although the concen trations of nitrogenous components in leachate have been characterised, these do not necessarily reflect the degradation of MSW.

1998) The carbon and hydrogen stable isotope composition of bacteriogenic methane: A laboratory study using a landfill inoculum, Geomicrobiology Journal, 15:3, 157-169,

Sterilised and non-sterilised soils contaminated with pentachlorophenol (PCP) were inoculated with solid substrate cultures of Lentinula edodes LE2 ("shiitake" mushroom) to simulate monoculture bioremediation treatments and treatments in which the fungus competes with natural microflora. With monocultures of L. edodes, rates of PCP depletion were rapid for the initial 4 weeks and, although thereafter the rate decreased, 99% biotransformation was obtained in 10 weeks. In mixed culture, PCP biotransformation by L. edodes was markedly slower and only 42% of the PCP was depleted after 10 weeks. Maximal rates of PCP transformation, biomass (ergosterol) accumulation and oxidative enzymes (phenol oxidase and manganese-peroxidase) production were observed after 2 weeks of incubation. In monocultures, phenol oxidase activity was 195.5 U g-1 and Mn-peroxidase 138.4 U g-1. In mixed cultures, fungal enzyme activities were markedly lower: 70.33 U g-1 for phenol oxidase and 85.0 g-1 for Mn-peroxidase. Analyses of soil metabolites after 10 weeks revealed that monocultures of L. edodes had eliminated both PCP and pentachloroanisole. Pentachloroanisole, however, was detected in soils with the mixed microflora. Both dechlorination and mineralisation of the xenobiotic compound were effected by L. edodes LE2.

The recirculation of nitrified leachate through landfill sites, followed by in situ denitrification, represents a novel and more sustainable approach for the removal of ammonia from leachate, prior to discharge. The effects of nitrate and leachate supplementation on methanogenesis in Municipal Solid Waste (MSW) were studied in batch cultures. The addition of a range of nitrate concentrations to MSW samples had an inhibitory effect on methanogenesis. The effects were dose-dependent, such that recovery of methane production was recorded within 5 and 23 days with added 100 and 750 mg NO 3 dm −3 , respectively. Even after 24 days, no recovery was observed in cultures challenged with 1000 mg NO 3 dm −3 . The enumeration of denitrifying bacteria in a range of fresh, actively methanogenic and aged, welldecomposed MSW confirmed the potential of MSW for rapid denitrification. Methanogenesis was not inhibited by the addition of leachate (20-100% strength) that contained high concentrations of VFAs. However, when the same leachate was supplemented with nitrate (250 mg NO 3 dm −3 ), methanogenesis was inhibited by the addition of leachate concentrations ≥20%, which was attributed to inhibition of denitrification by VFAs. Propionate accumulated, confirming the importance of methanogenesis as an electron sink. With the removal of nitrate and the recovery of methanogenesis, net propionate concentrations decreased.

The influences of temperature, soil moisture potential and initial pH on the biotransformation of pentachlorophenol (PCP) by the lignicolous fungi Lentinula edodes and Phanerochaete chrysosporium were examined. At 10 degrees C, L. edodes was more effective in degrading PCP (P < 0.05) than P. chrysosporium. At 15 degrees C similar results were obtained for the two fungi. The highest levels of degradation occurred for both fungi at 25 degrees C. With P. chrysosporium, the extent of PCP elimination was directly related to soil moisture content and optimal at approximately 47%. With L. edodes, in contrast, the process was inversely related to moisture content and maximal at 26%. The initial soil pH also had a marked influence, and pH 4.0 was optimal for both fungi.