Possibilities of anaerobic processing of substrates rich in sulphur were studied. High concentrations of sulphur cause problems when contained in biogas, as well as inhibition by sulphides in anaerobic processes. The impact of ferrous chloride on anaerobic processes, directly dosed to the anaerobic reactor was studied. This sulphur removal method is commonly known, though the objective of our study was to identify problems when it is applied on substrates rich in sulphur. Waste biomass from cystine production was used as substrate, which is produced in large quantities (17000 t/y) by Biotika, a.s. Slovenská Ľupča and requires processing; sulphur content range from 4 up to 5 % in the biomass. Specific biogas production was 0.410 m3/kg COD i.e. 0.737 m3/kg VSS, while 77 % sulphide inhibition occurred after several dose repetitions. Inhibition decreased to 25.4 % during long-term processing of cystine biomass in a mixed anaerobic reactor. Ferrous chloride dosing, however, resulted in high excess sludge generation, lower organic content in the sludge and high concentration of dissolved inorganic salts. These factors may lead to secondary problems in long-term processing of cystine biomass.
Waste biomass from the industrial production of the amino acid L-cystine contains above-average concentrations of organic pollutants and significant concentrations of nitrogen and sulfur. The specific biogas production (SBP) of waste biomass was monitored in parallel suspended-growth laboratory anaerobic bioreactors. After severe inhibition was observed, three different procedures were applied to inhibited reactor sludge to counter-attack the inhibitory effects of sulfides, respectively hydrogen sulfide: micro-aeration, dilution with water and precipitation by ferrous iron cations. The performance of bioreactors was weekly monitored. Organic loading rates (as chemical oxygen demand, COD) ranged from 1.07 to 1.97 g L(-1) d(-1). At the end of the experimentation, SBP averaged 217, 300 and 320 l kg(-1) COD with a methane content of 21%, 52% and 54%; specific sludge production averaged 133, 111 and 400 g total solids kg(-1) COD, and inhibition was 49%, 27% and 25%; for the applied procedures of micro-aeration, dilution and precipitation respectively.
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