High Free Ammonia Concentrations Research Articles

The influence of reactor mixing characteristics on the rate of nitrification in the activated sludge process

The effect of longitudinal mixing on nitrification was evaluated in two bench scale activated sludge reactors of equal volume, one approximating complete mixing ( ∂ = 0.62) and one approximating plug-flow mixing ( ∂ = 0.07). The onset of nitrification was more rapid under plug-flow conditions and a higher rate constant for nitrification was observed. Both the numbers and species of nitrifying bacteria were the same in both reactors and thus this did not contribute to the observed differences. Lower reaction rates in the complete mix reactor were shown to result from a high concentration of free ammonia in the mixed liquor, which gave rise to inhibition of nitrifying bacteria. Over an extended operating period, the plug flow reactor produced a sludge which demonstrated superior settling properties to that of the complete mix reactor. In addition incidences of sludge bulking were absent, whereas they were a regular feature of the complete mix system.

Interactive effect of ammonia and pH on viability and 14C-labeled exudation from fungal propagules

The effect of ammonia on exudation and viability of 14C-labeled propagules of Cochliobolus victoriae, Cochliobolus sativus, and Macrophomina phaseolina was studied in a model fungistatic system with nutrient-independent or nutrient-dependent propagules or in soil amended with urea from which ammonia was generated. In soil, ammonia stimulated exudation of 14C-labeled compounds, but their metabolism by the soil microbiota was suppressed. Short-term exposures of a few hours in a model fungistatic system with high free ammonia concentrations (up to 10 000 mg/L) stimulated a burst of exudation which was usually associated with death of the propagules. Lower concentrations increased exudation less, but exudation tended to be maintained at a level greater than that in nontreated controls. Viability was reduced when the propagules were continuously exposed to long-term doses which were nonlethal for shorter durations. High pH by itself increased exudation, but it did not account for the greater exudation effected by ammonia, nor for its lethal effects. In a fixed-volume system, which imposed low nutrient stress, ammonia (10–100 mg/L) had a sparing effect on the increased exudation brought on by high pH alone; as ammonia concentration was increased (100–1000 mg/L), the sparing effect was lost and exudation increased, accompanied by decreased viability.

Thermophilic and mesophilic anaerobic fermentation of swine manure

The effects of temperature (35° and 55°C), influent Volatile Solids (VS) concentration (S o = 50·4 and 62·5 kg VS m −3) and hydraulic retention time (HRT = 5, 10, 15 and 25 days) on methane (CH 4) production from swine manure were evaluated using 3-dm 3 laboratory scale fermentors. The highest CH 4 production rate achieved was 3·12 m 3 CH 4 per m 3 fermentor per day at 55°C, 5-day HRT and S o = 50·4 kg VS m −3. Batch fermentations showed an ultimate CH 4 yield (B 0) of 0·49 m 3 CH 4 kg VS fed. Extreme fermentation instability was experienced by the thermophilic (55°C) fermentors at 25-day HRT and S 0 = 62·5 kg VS m −3. This instability was attributed to free-ammonia and influent-substrate inhibitions. After a significant period for adaptation (over 170 days), the thermophilic fermentors adapted to the high free-ammonia concentrations and operated satisfactorily.