Anaerobic treatment of landfill leachate by sulfate reduction

Abstract

The present study was conducted to investigate the effectiveness of the sulphate-reduction pathway in the anaerobic treatment of landfill leachate. The effects of several COD/SO4 ratios (keeping COD constant) and loadings on anaerobic filter performance were studied and compared with the results from anaerobic filters which followed the methanogenic pathway. Results indicated that the treatability of leachate by sulphate reducing bacteria (SRB) was dependent upon the leachate strength. With high strength leachate (COD = 15,000 mg/L) from the Keele Valley Landfill, it was found that at lower COD/SO4 ratios (< or = 1.6) toxic conditions developed in the system that were more inhibitory to the SRB than to the methane producing bacteria (MPB). As the COD/SO4 ratio increased, methanogenesis predominated. No predominance of SRB occurred at any COD/SO4 ratio with high strength leachate. The highest COD removal achieved was about 70% of which 20% was accomplished by the SRB at a COD/SO4 ratio of 1.6 and an organic loading rate (OLR) of 4 kg COD/m3.d. With low strength leachate (COD = 1500-3300 mg/L) from the Brock West Landfill, and a COD/SO4 ratio < or = 1, SRB became predominant. In these anaerobic filters in which SRB were predominant, the SRB reduced the COD as well as the MPB could. Sulphide inhibition did not take place at any loading in units treating low strength leachate. Consequently, both SRB and MPB should function at COD/SO4 ratios between 1 and 3. About 60% COD removal was achieved at a loading of 2.8 kg COD/m3.d and a COD/SO4 ratio of 1.0. However at a loading of 6 kg COD/m3.d only 27% COD removal was achieved, all of it through the sulphate-reduction pathway. These OLR values are comparable to those applied in systems where methanogenesis was dominant. It was also observed that once the methanogens were established in the units, it was not possible to displace them completely. However, where methanogenesis had not been previously established, it was found that sulphate-reduction could be the sole pathway for COD removal. From this study, it can be concluded that there is no advantage to the sulphate-reduction pathway in the anaerobic treatment of landfill leachate. The other options for increasing the loadings, i.e. the use of high surface/volume filter media (to achieve higher biomass concentrations) or high rate systems are likely to be more successful.

Biological treatment of highly contaminated acid mine drainage in batch reactors: Long-term treatment and reactive mixture characterization

“…Finally, other studies have attempted to link COD/SO 4 2− ratios with the suitability of a natural organic material to act as a substrate during biological treatment of AMD contaminated waters [19][20][21][22]. As in the case of C/N ratios, if the COD/SO 4 2− ratio is taken alone, data interpretation must consider the complexity of the organic carbon in the substrate used.…”

“…Thus, when ethanol is used as the substrate, the optimal COD/SO 4 2− ratio is 0.55-0.84 [21,22], whereas when organic wastes (e.g. municipal compost, activated sludge) are used as substrate, not all of the carbon present is used by the SRB and the optimal COD/SO 4 2− ratio has been reported to be 1.6 [20] or 5 [19].…”

Decomposition and mineralization of aquatic humic substances (AHS) in treating landfill leachate using the Anammox process

“…Landfill leachate usually contains a certain concentration of sulfate and anaerobic treatment of biodegradable organics in leachate by microbiological sulfate reduction has been researched (Henry and Prasad, 2000). In this study, despite the failure in the SRB isolation, the fact of sulfate reduction positively favored the deduction that sulfates functioned as electron receiver in the anaerobic respiration.…”

Effect of Sulfate Loading Rate and Organic Loading Rate on Anaerobic Baffled Reactors Used for Treatment of Sanitary Landfill Leachates

“…However, greater reactor performance has been observed at COD/SO 4 2-ratios over 0.67. In other cases, little, if any effect of sulfate concentration on anaerobic reactor performance was observed (Choi and Rim, 1991;Henry and Prasad, 2000).…”