SULFIDE TOXICITY IN ANAEROBIC SYSTEMS FED SULFATE AND VARIOUS ORGANICS

Upflow anaerobic filters fed acetate and propionate, and completely mi xed, suspended growth reactors fed acetate, propionate, lactate, and g lucose were used to investigate the effect of electron donor and react or type on the interaction between sulfate-reducing bacteria (SRB) and methanogens. Organic loading rates of 0.25-0.50 g chemical oxygen dem and (COD)/L.d were used in suspended growth systems and 1.0-5.0 g COD/ L.d in filters. COD/sulfur ratios ranged from 20/1 to 2/1 for complete ly mixed reactors, and 20/1 to 8/1 for anaerobic filters. Results indi cated that organisms involved in the conversion of lactate and glucose into simpler products were not affected by sulfide toxicity. Levels o f 60-75 mg sulfur/L of hydrogen sulfide and 150-200 mg/L of dissolved sulfide (DS) caused stress in all suspended growth reactors; 100-150 m g sulfur/L of hydrogen sulfide and 200-400 mg DS/L could be tolerated in lactate and glucose systems, although with diminished COD and sulfa te removal. For similar loading conditions, lactate and glucose system s had higher DS levels than acetate and propionate systems. A cyclic p attern of variation of DS and hydrogen sulfide with volatile-acids COD (VACOD) was observed in long-term experiments with suspended growth r eactors. Anaerobic filters were able to tolerate higher DS and hydroge n sulfide levels than suspended growth reactors. A propionate-fed filt er could withstand more than 150 mg hydrogen sulfide/L of hydrogen sul fide and 1000 mg DS/L, and an acetate-fed filter could tolerate more t han 125 mg sulfur/L of hydrogen sulfide and 400 mg DS/L.