PROBLEM: Rising sludge in the secondary clarifier of the conventional activated sludge plant. Indicators include slow settling MLSS in the settleability test with straggler floc in a cloudy supernatant. The sludge blanket rises before one hour in the settleability container. Microscopic exam shows numerous amoeba and flagellated protozoa. Effluent ammonia is high, nitrate near zero mg/L. Which dissolved gas is causing the rising sludge blanket? O Excess nitrogen gas released O Excess carbon dioxide gas released O Excess hydrogen sulfide gas released O Excess methane gas released