Total Ammonia Concentration Research Articles

Effects of changes in plasma pH, CO2 and ammonia on ventilation in trout

We investigated ventillatory responses to a plasma alkaloids and hypocapnia,a nd the basis for the ventilatory response to sodium bicarbonate (NaHCO3) infusion in rainbow trout. Plasma alkalosis and hypocapnia created by infusion of sodium hydroxide (NaOH) did not cause hypoventilation, whereas infusion of hydrochloric acid (HCl) caused vigorous hyperventilation, associated with an acidosis, a reduction in blood O2 content (CaO 2) and a release of circulating catecholamines. Infusion of NaHCO3 stimulated ventilation and caused an increase in plasma pH, total carbon dioxide content (CaCO 2) and catecholamine levels, and a reduction in oxygen tension (PaO 2). Infusion of ammonium bicarbonate (NH 4HCO3) caused hyperventilation and was associated with an increase in CaCO 2 and plasma total ammonia (Camm) and ammonia gas (NH3) concentration. Infusion of sodium chloride (NaClI) and Cortland's saline had no effect on ventilation. The results indicate that trout do not exhibit the ventilatory sensitivity to pH seen in terrestrial vertebrates. Ventilatory responses to NaHCO3 appear to have been a result of reductions in PaO 2, a release of catecholamines and an increase in CaCO 2 whereas responses to NH4HCO3 appear to have been a result of increases in CaCO 2 and Camm.

Total Ammonia Concentration and PH of Haemolymph, Pleon Fluid and Maxillary Urine in Porcellio Scaber Lattreille (Isopoda, Oniscidea): Relationships to Ambient Humidity and Water Vapour Uptake

ABSTRACT Ammonia levels and pH were studied in body fluids of Porcellio scaber with special reference to ambient humidity and the timing of pleon fluid secretion and pleopodal ventilation. In high humidity (approximately 96.7%), concentrations of total ammonia (NH3+NH4+) in haemolymph display pronounced episodic changes, ranging from less than 1mmol l−1 to more than 50mmol l−1. Elevated concentrations (>5mmol l−1) occur in discrete bouts lasting from 40min to more than 2h. Concomitant changes in total ammonia levels are seen in pleon fluid and maxillary urine. Overall, mean ammonia concentrations in pleon fluid, but not maxillary urine, are significantly higher than in the haemolymph, which may indicate active secretion of NH4+ in the pleon. Elevated ammonia concentrations are not observed in reduced ambient humidities (85% and 30%). Evidence supports a physiological coupling between pleon NH3 volatilization and active water vapour absorption. Pleon fluid and haemolymph pH values are similar, discounting a role of alkalization in NH3 volatilization. Published rates of ammonia excretion are compatible with intermittent volatilization from pleon fluid and with measured NH3 levels during elevations in ammonia concentration.

Chronic hyperkalemia impairs ammonium transport and accumulation in the inner medulla of the rat.

Previously we demonstrated in rats that chronic hyperkalemia had no effect on ammonium secretion by the proximal tubule in vivo but that high K+ concentrations inhibited ammonium absorption by the medullary thick ascending limb in vitro. These observations suggested that chronic hyperkalemia may reduce urinary ammonium excretion through effects on medullary transport events. To examine directly the effects of chronic hyperkalemia on medullary ammonium accumulation and collecting duct ammonium secretion, micropuncture experiments were performed in the inner medulla of Munich-Wistar rats pair fed a control or high-K+ diet for 7-13 d. In situ pH and total ammonia concentrations were measured to calculate NH3 concentrations for base and tip collecting duct and vasa recta. Chronic K+ loading was associated with significant systemic metabolic acidosis and a 40% decrease in urinary ammonium excretion. In control rats, 15% of excreted ammonium was secreted between base and tip collecting duct sites. In contrast, no net transport of ammonium was detected along the collecting duct in high-K+ rats. The decrease in collecting duct ammonium secretion in hyperkalemia was associated with a decrease in the NH3 concentration difference between vasa recta and collecting duct. The fall in the NH3 concentration difference across the collecting duct in high-K+ rats was due entirely to a decrease in [NH3] in the medullary interstitial fluid, with no change in [NH3] in the collecting duct. These results indicate that impaired accumulation of ammonium in the medullary interstitium, secondary to inhibition of ammonium absorption in the medullary thick ascending limb, may play an important role in reducing collecting duct ammonium secretion and urinary ammonium excretion during chronic hyperkalemia.

A Survey of Water Quality Characteristics of Effluent from Hawaiian Aquaculture Facilities

AbstractTen water quality parameters were measured in influent and effluent water at 11 aquaculture facilities in Hawaii. The data were grouped into four categories based on the types of organisms cultured: freshwater fish, freshwater prawn, marine fish, and marine shrimp. Within each category, concentrations of most parameters were lognormally distributed and spanned one to two orders of magnitude. Geometric mean concentrations of suspended materials, total nitrogen, total phosphorus, and pigments were highest in effluent from freshwater prawn ponds and lowest in marine fish pond effluent. Nitrate/Nitrite and total ammonia concentrations were higher in fish pond effluent than in crustacean pond effluent. Parameter concentrations were generally higher in effluent than in influent water, with freshwater fish and prawn ponds exhibiting the greatest increases in suspended materials and pigments. In contrast, nitrate/nitrite concentrations were lower in effluent than in influent waters. These data provide a basis for analyzing the environmental impacts of warm‐water aquaculture effluent discharges.

Investigation of Batchwise Nitrite Build-Up by an Enriched Nitrification Culture

Nitrite build-up within biological wastewater treatment systems has generally been attributed to unsuitable environmental and process conditions. In this study, an enriched nitrifying culture was used to investigate the cause of nitrite build-up by controlling dissolved oxygen (DO) and total ammonia concentrations as well as pH level in a batch system. At pH 7.5, nitrite build-up was observed with a low DO level (0.5 mg/L), while no nitrite accumulation was found in the system with a high DO level (6.0 mg/L). However, nitrite peaks were found in both the high and low DO systems at pH values of 8.0 and 8.5. Conversely, at pH 7.0, no nitrite accumulated in either such system. Hence, DO level did not appear to be the dominant factor behind a nitrite build-up, and the correlation with free ammonia (FA) was erratic. On the other hand, hydroxylamine, an intermediate in nitritification by Nitrosomkonas, has been found to inhibit nitratification by Nitrobacter. Indeed, based strictly on the mechanistic pathways of nitritification, hydroxylamine appeared likely to accumulate in a nitrifying system subjected to deficient oxygen. The results of this research showed that variable levels of hydroxylamine would accumulate in a batch system under all conditions. Relative to nitrite build-up, the presence of unionized or so called free hydroxylamine (FH) fraction (as opposed to ‘total') appeared to have a consistent correlation with incomplete nitrification. In turns, FH was believed to be a major, if not principal, factor behind nitrite build-up in these batch nitrifying systems.

Effect of defaunation and hay:concentrate ratio on fermentation, fibre digestion and passage in the rumen of sheep

Two rumen-cannulated wethers were used to study the effect of defaunation and dietary carbohydrate composition on fermentation, fibre digestion and passage in the rumen. According to a crossover design, sheep were either free of ciliate protozoa or had a type B protozoal population, and were fed either a diet consisting mainly of chopped hay (H) or of pelleted concentrate (C). Nylon bags containing detergent-treated hay were incubated in the rumen to measure fibre digestion. Passage was measured using chromium-mordanted hay (Cr-H) and ytterbium acetate (Yb) as markers for the particulate phase, and polyethylene glycol (PEG) 4000 as soluble marker. Total numbers of protozoa were 1.2 × 10 6 ml −1 and 0.7 × 10 6 ml −1 on Diets C and H, respectively, in the refaunated state. On Diet H, the pH, the proportion of propionate and numbers of fungal sporangia were significantly higher in the absence of protozoa, while the proportion of butyrate and ammonia concentration were significantly lower. On Diet C, the proportion of propionate and lactic acid concentration were significantly higher, and total short chain fatty acid and ammonia concentration significantly lower, in the defaunated state. On Diet H, the data clearly suggest a depressive effect of the absence of protozoa on nylon bag loss of detergent-treated hay after incubation times of 16–56 h. Statistical significance was reached only after 40 h, however, and the tendency was less marked on Diet C. Slower fractional passage rates of all three markers were found in the defaunated state on Diet H, but were only significant for PEG and Cr-H. Pool sizes on this diet were observed to be somewhat higher, but only significantly for the liquid phase. On Diet C, defaunation only resulted in an increased fractional passage rate (estimated by Yb) and an increased pool size (estimated by Cr-H). Differences in the sheep response to diet and/or defaunation occurred for several parameters, rendering interpretation difficult. The results of this study suggest, nevertheless, that defaunating the rumen of adult sheep under limited feeding conditions did not cause consistent changes in digesta kinetics. Fibre digestion in the rumen was moderately depressed.

Anaerobic treatment of fish meal process waste-water in a UASB reactor at high pH

The influence of high pH on anaerobic degradation of fish process waste-water with a high total ammonia concentration was investigated in an upflow anaerobic sludge blanket (UASB) reactor. More than 99% of volatile fatty acids and trimethylamine in the process waste-water were degraded up to pH 7.9. Above pH 7.9 only the conversion of acetate was slightly decreased. At pH 8.3 serious disintegration of the granules occurred leading to process failure. Increasing the pH changed the physical characteristics of the granules leading to decreased density, size, and volatile solids content. After 4 months of acclimatization to high pH in the reactor, the specific methanogenic activity of the granular biomass was the same from pH 7.1 to 8.5. At pH 8.3 and 8.5, acclimatization had improved the specific activity by 25 and 50%, respectively. However, the acclimatized biomass generally showed a decreased activity (60%) at all pH values tested below the acclimatization pH.

Nitrogenous waste excretion and accumulation of urea and ammonia inChalcalburnus tarichi (Cyprinidae), endemic to the extremely alkaline Lake Van (Eastern Turkey)

The endemic, anadromous cyprinidChalcalburnus tarichi is the only fish species known to occur in alkaline Lake Van (Eastern Anatolia, Turkey). EightC. tarichi were maintained individually in Lake Van water (17 - 19°C; pH 9.8; 153 mEq·I(-1) total alkalinity; 22‰ total salinity) and tank water samples analyzed for 24 h in 2 to 4 h intervals. At zero time, < 1µM ammonia was present and urea was undetectable in the tank water; at 24 h, total ammonia and urea made up 114±32 and 35±25µM, respectively. Over the experimental period, ammonia-N and urea-N excretion averaged 1041±494 and 607±169μmoles·kg(-1) fish·h(-1), respectively. The extent of urea excretion was highly variable between specimens. Uric acid excretion was not detectable.Urea was present at high concentrations in all tissues and plasma (25 - 35μmoles·g(-1)·ml(-1)) of freshly caughtC. tarichi; total ammonia content of the tissues was by a factor of 1.9 (liver) to 3.0 (brain) lower. High arginase activity (2.4±0.2 U·min(-1)·g(-1)) was detected in the liver ofC. tarichi but ornithine carbamoylphosphate transferase, a key enzyme of the ornithine-urea-cycle, was absent. Ureagenesis is likely through degradation of arginine and/or uricolysis. High glutamine synthetase activity (11±0.6 U·min(-1)·g(-1)) and low ammonia content in brain suggest that, like other teleosts,C. tarichi has an efficient ammonia detoxification in the brain, but in no other tissue.Nitrogenous waste excretion at alkaline pH is discussed. The ability ofC. tarichi to excrete high levels of ammonia at extremely alkaline pH is unique among teleosts studied so far. The mechanism of ammonia excretion under Lake Van conditions remains to be elucidated.

Effect of molasses, sodium bentonite and zeolite on urea toxicity

Molasses, sodium bentonite (montmorillonite clay) and zeolite (crushed clinoptilolite rock) were examined as supplement ingredients to improve the safety margin of urea supplementation in a series of seven experiments. These experiments were designed to provide an understanding of the relationship between urea intake and the influence of the above ingredients on rumen pH and total ammonia concentrations. Rumen fistulated Merino ewes of 35-40 kg liveweight were administered various amounts of urea with and without supplement mixes. Rumen parameters were measured at 0, 0.5, 1-0, 1.5, 2.5, 5.0 and 24 h after treatment administration. Acetic acid and sucrose were also tested together with molasses for comparative effects on rumen parameters. In the last experiment, blood pH and total plasma ammonia were also determined. Free ammonia values of rumen liquor were calculated for experiments 2 to 7. In four experiments, molasses at 50, 100 and/or 150 g mixed with urea significantly reduced the normal rapid rise in ruminal pH, total and free ammonia values compared with urea (10 g) only treatments. In two experiments, associated presence or absence of clinical toxicity at various quantities of urea (8 to 25 g) with and without active ingredients confirmed the postive effect of molasses in preventing toxicity at &lt;0.44 g urea/ kg liveweight. The addition of molasses reduced the increase in ruminal pH by up to 0-5 pH units and absolute values were consistently below pH 7-0. Sucrose (100 g) and acetic acid (800 mL of 1 M ) had the same and greater effect, respectively, compared with molasses (150 g) when added with urea (10 g) on ruminal pH and total and free ammonia changes over five hours post treatment. The partly hydrated urea / bentonite mix (approx 1 : 1 bentonite : water ratio) was associated with a delay in the increases in ruminal pH and free ammonia concentrations. Bentonite mixes, in either fully hydrated or fully dehydrated states, and zeolite mixes resulted in no significant effects. With reference to previous reports, the results support the positive role of a stable acid pH in the rumen for ensuring safe urea supplementation.

Effect of Environmental Water Salinity on Acid–Base Regulation During Environmental Hypercapnia in the Rainbow Trout (Oncorhynchus Mykiss)

ABSTRACT Acid-base regulation in rainbow trout acclimated to about 3, 100 and 300mmoll−1 Na+ and Cl−, at constant water [HCO3−], was assessed during 24h of exposure to 1% CO2 and during recovery. The respiratory acidosis induced by a rise in plasma to about 1.15kPa (8.5mmHg, 3mmoll−1), 1.33kPa (10 mmHg, 100 mmol I−1) or 1.5 kPa (11.2 mmHg, 300 mmol I−1) was partially compensated for by accumulation of plasma HCO3−. The degree of pH compensation depended on the salinity of the environmental water, being about 61,82 and 88% at 3, 100 and 300mmoll−1 Na+ and Cl−, respectively. [HCO3−] in animals acclimated to 100 and 300 mmol I−1 rose to higher values than that in fish at 3 mmol I−1. Plasma [Cl−] decreased during hypercapnia as compared to control concentrations in all groups of fish. Plasma [Na+] rose during the first 8h of hypercapnia in fish acclimated to all three salinities, but recovered towards control values during the remainder of hypercapnia. The rise in plasma [HCO3−] was significantly related to the fall in plasma [Cl−], whereas the changes in plasma [Na+] were unaffected by simultaneous changes in plasma [HCO3−]. Time courses of changes in plasma [Na+] and total ammonia concentration, [Tamm], were similar but in opposite directions. The transepithelial potential (TEP) of blood relative to water was negative, close to zero and positive, averaging —21, —5.8 and +6.2 mV for fish acclimated to 3, 100 and 300 mmol I−1 Na+, respectively. After initiation of hypercapnia, which caused a quite heterogeneous response among groups, a clear trend towards depolarization was observed during the remainder of hypercapnia. These results confirm the role of active HCO3−/C1− exchange processes for the compensation of extracellular pH during respiratory acidoses in fish.

Role of countercurrent multiplication in renal ammonium handling

Ammonium (NH3 plus NH4+), produced predominantly in the proximal tubule, is transferred to the final urine by a process involving countercurrent multiplication of ammonium which generates an ammonium concentration gradient in the renal medulla. It was hypothesized that if urinary ammonium excretion rates are controlled in part by the medullary ammonium gradient, changes in hydration and acid-base state should cause changes in the medullary ammonium gradient consistent with expected changes in urinary ammonium concentrations. To test that hypothesis, rats were subjected to water diuresis, water deprivation, water deprivation plus furosemide, and dietary acid and base loads and corticomedullary ammonium gradients in their kidneys were then measured. Sections were cut along the corticomedullary axis to yield slices of cortex, outer stripe of outer medulla, inner stripe of outer medulla, and three levels of the inner medulla. The total ammonia content of homogenized slices was measured by either a membrane ammonia electrode or an enzymatic technique. Kidneys from water-deprived animals showed a distinct ammonium gradient along the corticomedullary axis, with the highest contents found at the tip of the papilla. The gradient was attenuated by water diuresis and abolished by furosemide. Acid loading enhanced the gradient, and base loading abolished it. These results indicate that the corticomedullary ammonium gradient is regulated in response to changes in hydration and acid-base state.

Nitrogen input, primary productivity and fish yield in fertilized freshwater ponds in Indonesia

Twelve 0.2-ha ponds in West Java were fertilized weekly with four levels of chicken manure (12.5, 25, 50, and 100 g dry weight/m 2 week −1) during a 149-day growout experiment for Nile tilapia ( Oreochromis niloticus) production. Laboratory leaching experiments for measuring dissolved inorganic nitrogen (DIN) release from chicken manure showed that nitrogen was released as ammonia-N, which was rapidly lost from the manure and leveled off at about 6 mg NH 4N/g dry weight chicken manure after 4–5 days. Allochthonous DIN input from both chicken manure fertilization and almost daily source-water additions ranged from 0.055 to 0.142 g N/m 2 day −1. Source water contributed more nitrogen than manure in all but the highest fertilization treatment. Pond averages of net primary productivity (NP) ranged from 0.54 to 2.00 g C/m 2 day −1, while gross fish yield at harvest ranged from 4.9 to 15.7 kg fresh weight/ha day −1. Net fish yield (NFY) was linearly correlated to both the dry weight sum of NP and chicken manure fertilization ( r 2=0.97) and allochthonous DIN input ( r 2=0.96). Results suggest that Nile tilapia obtained organic carbon from both primary productivity and manure-derived detritus. DIN availability limited algal productivity at a chicken manure fertilization rate of 100 g dry weight/m 2 week −1 when microbial decomposition of manure supplied sufficient CO 2. Incorporation of allochthonous DIN input into NFY increased significantly from 15.0% at the three lower fertilization rates to 25.4% at the highest loading rate. Using organic fertilizers proportionally rich in phosphorus and carbon relative to nitrogen may maintain this element's limitation of algal productivity. Efficient utilization of DIN input also may minimize total and un-ionized ammonia concentrations. In the absence of deleterious ammonia effects on survival and growth, fish yields can be readily predicted from measurements of nitrogen inputs.

Permeabilities of rat collecting duct segments to NH3 and NH4+

We have measured NH3 and NH4+ permeability coefficients in collecting ducts from the cortex, outer medulla, and inner medulla of the rat kidney. Isolated collecting duct segments of the rat were perfused with bicarbonate-buffered solutions containing carbonic anhydrase to eliminate any pH disequilibrium in the tubule lumen. NH3 or NH4+ concentration gradients were set up between the bath and the lumen. By measuring the total CO2 and total ammonia concentrations in the bath, the perfusate, and collected fluid, the NH3 and NH4+ concentrations were determined. Then, using the flow rate in the tubule and the tubule dimensions, we calculated the apparent permeability in each collecting duct segment for NH3 and NH4+. The NH3 permeabilities were as follows: 0.002 cm/s in the inner medullary collecting duct, 0.012 cm/s in the outer medullary collecting duct, and 0.024 cm/s in the cortical collecting duct. The NH4+ permeabilities for all segments were on the order of 10(-5) cm/s or less. The relative permeability values for the two ammonium species are consistent with the view that the secretion observed in vivo in collecting ducts is due to passive diffusion of NH3 from the interstitium to the lumen of the duct, parallel with H+ secretion.

Pollutant loadings from solvay waste beds to lower Ninemile Creek, New York

Concentrations of Cl, total ammonia (TNH3), NO3 plus NO2, total P (TP), and soluble reactive P (SRP) were measured at two sites, located 5 km apart, on Ninemile Creek, New York, for a period of more than 8 mo. The sites bound the most recently formed Solvay waste beds, associated with the production of soda ash, that adjoin the creek. Concentrations of Cl and T-NH3 increased on average by factors of 16.1 and 7.6, respectively, over the monitored stream reach. The estimated average loadings of these materials to the stream over this reach were 2.3 × 105 and 1.2 × 102 kg d−1, respectively. These inputs are attributable to the Solvay waste beds. The loading of Cl from this source has not changed significantly over a 4 yr period since the closure of the soda ash manufacturing facility. This is the single largest source of Cl, and the second largest source of T-NH3, to polluted Onondaga Lake. Profiles of Cl in the lake indicated that at times the creek inflow plunges to subsurface layers as a result of its elevated density. This is at least in part a result of the creek's ionic enrichment. The concentration of SRP decreased by a factor of 2.0 on average over the study reach, probably due to adsorption to the CaCO3 deposits that cover the stream bed in this area. However, the TP load from the creek to the lake is not significantly affected by this phenomenon.

NITROGEN CONCENTRATION VARIABILITY IN DAIRY-CATTLE SLURRY STORED IN FARM TANKS

ABSTRACT Spatial and temporal variability in the concentration of total Kjeldahl and ammonia (NH3 + NH4+) nitrogen (TKN and AMN, respectively) was studied in 8 to 10% total solids content dairy-cattle manure slurry and its centrifuged supernatant during undisturbed storage in covered, reinforced concrete, farm storage tanks. Slurry was stored in two winter-filled tanks for 285 days, and in two additional summer-filled tanks for 146 days. Although concentration variability with time and space was small relative to the initial concentrations, slurry at depths of less than 1 m had consistently lower concentrations than at greater depths, particularly after the initial two months of storage. Mass balance for nitrogen (N) indicated a 9% loss in three of the four tanks. A lower loss (4% N) in the fourth tank was accompanied by a decrease in acetic acid concentration and a rise in slurry pH, at all depths, which was not observed in the other tanks. The lower loss of N from this tank than from the other tanks probably occurred to satisfy chemical equilibria that required a greater retention of ammonia (NH3) by the carbon dioxide (CO2) release from acetic acid breakdown. Considerations other than TKN and AMN concentration changes and equilibrium relations may also be important factors for N retention in slurry stored in farm tanks.

Toxicity of Ammonia and Nitrite to Penueus monodon Juveniles

Abstract Pcnaeus monodon juveniles (35.4 ± 2.2 mm TL) were exposed to seawater (20 ppt) having different concentrations of total ammonia (NH3+ NH,+) and nitrite. Median lethal concentration (LC50) was determined with static‐renewal tests. The LC50, of total ammonia‐N, NH3‐N and niMte‐N on shrimps decreased with increase of exposure time. The 24, 48, 72, % and 120 h LC50 were 94.96, 61.09, 47.47 45.58 and 38.00 mg/L total ammonia‐N (2.68, 1.73, 135, 1.29 and 1.08 mg/L NH3‐N) and 215.85, 185.33, 88.54, 54.76 and 37.97 mg/L nitrite‐N, respectively. The 144h LC50 of total ammonia‐N and NH3‐N was 36.71 mg/L and 1.04 mgL. The “threshold” of ammonia and nitrite was found at 144h and 120h respectively, from the toxicity curve approaching asymptote. A “safe value” was 3.7 mg/L total ammonia‐N, 0.1 mg/L NH3‐N (20 ppt, pH 7.70, 27C) and 3.8 mg/L nitrite‐N for P. monodon juvenile.

A note on the effect of Aspergillus oryzae fermentation extract on the rumen fermentation of sheep given straw

Eight mature Dorset-cross sheep, each fitted with a permanent rumen cannula, were given a diet of chopped barley straw (plus urea and minerals) either with or without an Aspergillus oryzae (AO) fermentation extract (2 glday). The addition of AO fermentation extract to the diet increased the initial rate of straw degradation (P &lt; 0·05) but did not alter the final extent of degradation. Total culturable bacteria increased with AO treatment but numbers of cellulolytic bacteria, ciliate protozoa, and aerobic fungi, were not significantly altered. Rumen pH, liquid clearance rate, total volatile fatty acids, acetate, propionate, butyrate, L-lactate and ammonia concentrations were also unaffected.

Does Amia Calva aestivate?

During gradual air exposure, Amia calva show no reduction in oxygen consumption, no increase in plasma urea levels or in urea excretion. Blood pH remains constant, and plasma total CO2, PCO 2, HCO3 (-). total ammonia and NH3 concentrations all rise significantly. Exposure to 923 μmol/l NH4Cl does not elicit an increase in urea production or airbreathing. Aquatic hypoxia without access to air does not cause a reduction in aerobic metabolism, and moderate levels result in death. These results suggest that Amia are incapable of aestivation, due to an inability to detoxify ammonia to urea and reduce metabolism, and die following three to five days of air exposure.

Growth-rate inhibition of acetoclastic methanogens by ammonia and pH in poultry manure digestion

The maximum growth rate ( μ m ) of acetoclastic methanogens was measured at ammonia concentrations between 0·55 and 0·74 mol/liter (7·7 and 10·4 g ammonia-N/liter) and a pH between 7·80 and 7·93. The observed μ m varied between 0·0046 and 0·0000 h −1 under these experimental conditions. The μ m was calculated by monitoring the gas production rate of batch reactors under conditions of substrate saturation (maximum growth rate in prevailing environment); the acetate concentration during all experiments was above 0·025 mol/liter (1·5 g/liter). It was shown that the pH and total ammonia concentration are the predominant inhibition factors for acetoclastic methanogens under these conditions. The best mathematical description for the inhibition of the growth rate is given by an equation which contains the total ammonia concentration as well as the pH, and this description was significantly better than a description using a calculated free ammonia concentration. The results can be used to calculate a minimal hydraulic retention time for acetate degradation in poultry manure digesters.

Daily Average Value of Un‐ionized Ammonia from Field Measurements

In aqueous solutions, un-ionized ammonia exists in equilibrium with the ammonium and hydroxide ions. The toxicity of these solutions has been primarily attributed to the un-ionized species although both forms are toxic at certain concentrations. The concentration of un-ionized ammonia in water is a function of the total ammonia concentration, pH, temperature, and ionic strength; and a number of these variables are functions of the time of day. In this paper, a technique for reducing estimates of un-ionized ammonia made at arbitrary time of day to a daily average value is presented. As an example, this technique is applied to Las Vegas Bay, an arm of Lake Mead.