Inhibiting The Formation Of H₂S In Primary Sludge Digestion Using Wastes Containing Fe（Ⅲ）

Anaerobic digestion of primary sludge taken from the Fourth sewage treatmentplant in xi ’an was studied in a completely mixed reactor to investigate the processstability, efficiency and possibility to inhibit the formation of hydrogen sulfide usingFe（III）. Sulfur conversion rate in the process of digestion and the source of hydrogensulfide in gas were discussed by determining the sulfur content in sludge, digestedliquor and biogas. Main conclusions are as follows:（1）When the complete mixture anaerobic digestion experiments of primary sludgewere done under the condition of the moderate temperature, and the sludge batch ratewas5%, the average removal rate of VSS was37.4%, indicating that the activity ofdigested sludge was higher; The Daily biogas yields of primary sludge was1.92L, thedecomposition unit VSS gas production is0.96m³/kgVSS, gas production was0.35m³per kilogram of VSS, and7.68m³per cubic meter of sludge, primary sludge anaerobicdigestion ability and biogas production performance was very well.（2） The components of biogas produced from the primary sludge contains: CH₄:67.9%; CO₂:26.6%; H₂S:0.2861%; N₂:<1.9%; H₂is not detected. Methane content inthe gas is high, which showed that the reactor was operating normally.（3） Volatile fatty acids concentration in the digested liquor was200mg/l, alkalinitywas more than2000mg/l （as calcium carbonate）, which suggested that the system had agood buffer capacity, and was running stably.（4） The research proved that the addition of Fe（III） to digested sludge could inhibitthe generation of hydrogen sulfide well. When Fe（III） was dosed according to the Fe/Sratio0.8:1,37.4%of hydrogen sulfide removal rate could be achieved; When Fe（III） was dosed according to the Fe/S ratio2.4:1,55.3%of hydrogen sulfide removal ratecould be achieved; When Fe（III） was dosed according to the Fe/S ratio4.8:1, thehydrogen sulfide content of the biogas had dropped from2861.3ppm to272.9ppm,90.5%of hydrogen sulfide removal rate could be achieved.（5） The distribution and transfer of S forms in the sludge were determined by S balance.Total sulfur concentration in the sludge was395.1⁴14.7mg/L, among them,343.9³60.9mg/L （87.04%） being organic sulfur,47.7⁵0.1mg/L （12.08%） being inorganicsulfide, and3.5³.6mg/L （0.88%） being SO42--S. After sludge was digestedanaerobically, the total inorganic sulfide （including soluble sulphide, insoluble sulfideand gaseous H₂S-S） content had increased by54.0⁵6.7mg/l,94%of sulphurincreased were due to destruction of organic material, only6%of sulphur was camefrom the reduction of SO42--S; Only5.7%（3.1³.2mg/l） of inorganic sulfidetransformed by the organic sculpture compounds and SO42--S left the sludge as H₂S inthe biogas, the rest94.3%（50.9⁵3.0mg/l） of S were transformed into insolublesulfides.