Effect of free ammonia and free nitrous acid concentration on the anabolic and catabolic processes of an enriched Nitrosomonas culture

The effects of free ammonia (FA; NH3) and free nitrous acid (FNA; HNO2) concentrations on the metabolisms of an enriched ammonia oxidizing bacteria (AOB) culture were investigated using a method allowing the decoupling of growth and energy generation processes. A lab-scale sequencing batch reactor (SBR) was operated for the enrichment of an AOB culture. Fluorescent in-situ hybridization (FISH) analysis showed that 82% of the bacterial population in the SBR bound to the NEU probe specifically designed for Nitrosomonas europaea. Batch tests were carried out to measure the oxygen and ammonium consumption rates by the culture at various FA and FNA levels, in the presence or absence of inorganic carbon (CO2, HCO3, and CO32-). It was revealed that FA of up to 16.0 mgNH(3)-N (.) L-1, which was the highest concentration used in this study, did not have any inhibitory effect on either the catabolic or anabolic processes of the Nitrosomonas culture. In contrast, FNA inhibited both the growth and energy production capabilities of the Nitrosomonas culture. The inhibition on growth initiated at approximately 0.10 mgHNO(2)-(NL-1)-L-., and the data suggested that the biosynthesis was completely stopped at an FNA concentration of 0.40 mgHNO(2)-N (.) L-1. The inhibition on energy generation initiated at a slightly lower level but the Nitrosomonas culture was still oxidizing ammonia at half of the maximum rate at an FNA concentration of 0.50-0.63 mgHNO(2)-N (.) L-1. The affinity constant of the Nitrosomonas culture with respect to ammonia was determined to be 0.36 mgNH3-N (.) L-1, independent of the presence or absence of inorganic carbon. (c) 2006 Wiley Periodicals, Inc.

Effects of solids concentration, pH and carbon addition on the production rate and composition of volatile fatty acids in prefermenters using primary sewage sludge

Increasing evidence is emerging that the performance of enhanced biological phosphorus removal (EBPR) systems relies on not only the total amount but also the composition of volatile fatty acids (VFAs). Domestic wastewater often contains limited amounts of VFAs with acetic acid typically being the dominating species. Consequently, prefermenters are often employed to generate additional VFAs to meet the demand for carbon by EBPR and/or denitrification processes. Limited knowledge is currently available on the effects of operational conditions on the production rate and composition of VFAs in prefermenters. In this study, a series of controlled batch experiments were conducted with sludge from a full-scale prefermenter to determine the impact of solids concentration, pH and addition of molasses on prefermentation processes. It was found that an increase in solids concentration enhanced total VFA production with an increased propionic acid fraction. The optimal pH for prefermentation was in the range of 6-7 with significant productivity loss when pH was below 5.5. Molasses addition significantly increased the production of VFAs particularly the propionic acid. However, the fermentation rate was likely limited by the biological activity of the sludge rather than by the amount of molasses added.

Efficient and stable nitritation and denitritation of ammonium-rich sludge dewatering liquor using an SBR with continuous loading

Separate treatment of dewatering liquor from anaerobic sludge digestion significantly reduces the nitrogen load of the main stream and improves overall nitrogen elimination. Such ammonium-rich wastewater is particularly suited to be treated by high rate processes which achieve a rapid elimination of nitrogen with a minimal COD requirement. Processes whereby ammonium is oxidised to nitrite only (nitritation) followed by denitritation with carbon addition can achieve this. Nitrogen removal by nitritation/denitritation was optimised using a novel SBR operation with continuous dewatering liquor addition. Efficient and robust nitrogen elimination was obtained at a total hydraulic retention time of 1 day via the nitrite pathway. Around 85-90% nitrogen removal was achieved at an ammonium loading rate of 1.2 g NH4+-N m(-3) d(-1). Ethanol was used as electron donor for denitritation at a ratio of 2.2gCODg(-1) N removed. Conventional nitritation/denitritation with rapid addition of the dewatering liquor at the beginning of the cycle often resulted in considerable nitric oxide (NO) accumulation during the anoxic phase possibly leading to unstable denitritation. Some NO production was still observed in the novel continuous mode, but denitritation was never seriously affected. Thus, process stability can be increased and the high specific reaction rates as well as the continuous feeding result in decreased reactor size for full-scale operation. (c) 2006 Elsevier Ltd. All rights reserved.

Occurrence and simulation of nitrification in two contrasting sugarcane soils from the Australian wet tropics

The concentration of ammonium-nitrogen (NH4+-N) frequently exceeds that of nitrate-N (NO3--N) in Australian wet tropical sugarcane soils. The amount of mineral N in soil is the net result of complex processes in the field, so the objective of this experiment was to investigate nitrification and ammonification in these soils under laboratory conditions. Aerobic and saturated incubations were performed for 1 week on 2 wet tropical soils. Net NO3--N increased significantly in both soils during both types of incubation. A second series of aerobic incubations of these soils treated with NH4+-N and inoculated with subtropical nitrifying soils was conducted for 48 days. Nitrification in the wet tropical soils was not significantly affected by inoculation, and virtually all added N was nitrified during the incubation period. Mineral N behaviour of the 48-day incubations was captured with the APSIM-SoilN model. As nitrification proceeded under laboratory conditions and was able to be captured by the model, it was concluded that nitrification processes in the wet tropical soils studied were not different from those in the subtropical soils. Processes that remove NO3- from the soil, such as leaching and denitrification, may therefore be important factors affecting the proportions of NH4+-N and NO3--N measured under field conditions.

The inhibitory effects of free nitrous acid on the energy generation and growth processes of an enriched Nitrobacter culture

The inhibitory effects of nitrite (NO2-)/free nitrous acid (HNO2-FNA) on the metabolism of Nitrobacter were investigated using a method allowing the decoupling of the growth and energy generation processes. A lab-scale sequencing batch reactor was operated for the enrichment of a Nitrobacter culture. Fluorescent in situ hybridization (FISH) analysis showed that 73% of the bacterial population was Nitrobacter. Batch tests were carried out to assess the oxygen and nitrite consumption rates of the enriched culture at low and high nitrite levels, in the presence or absence of inorganic carbon. It was observed that in the absence of CO2, the Nitrobacter culture was able to oxidize nitrite at a rate that is 76% of that in the presence of CO2, with an oxygen consumption rate that is 85% of that measured in the presence of CO2. This enabled the impacts of nitrite/FNA on the catabolic and anabolic processes of Nitrobacter to be assessed separately. FNA rather than nitrite was likely the actual inhibitor to the Nitrobacter metabolism. It was revealed that FNA of up to 0.05 mg HNO2-N center dot L-1 (3.4 mu M), which was the highest FNA concentration used in this study, did not have any inhibitory effect on the catabolic processes of Nitrobacter. However, FNA initiated its inhibition to the anabolic processes of Nitrobacter at approximately 0.011 mg HNO2-N center dot L-1 (0.8 mu M), and completely stopped biomass synthesis at a concentration of approximately 0.023 mg HNO2-N center dot L-1 (1.6 mu M). The inhibitory effect could be described by an empirical inhibitory model proposed in this paper, but the underlying mechanisms remain to be revealed.

The availability of nitrogen from sugarcane trash on contrasting soils in the wet tropics of North Queensland

Sugarcane crop residues ('trash') have the potential to supply nitrogen (N) to crops when they are retained on the soil surface after harvest. Farmers should account for the contribution of this N to crop requirements in order to avoid over-fertilisation. In very wet tropical locations, the climate may increase the rate of trash decomposition as well as the amount of N lost from the soil-plant system due to leaching or denitrification. A field experiment was conducted on Hydrosol and Ferrosol soils in the wet tropics of northern Australia using N-15-labelled trash either applied to the soil surface or incorporated. Labelled urea fertiliser was also applied with unlabelled surface trash. The objective of the experiment was to investigate the contribution of trash to crop N nutrition in wet tropical climates, the timing of N mineralisation from trash, and the retention of trash N in contrasting soils. Less than 6% of the N in trash was recovered in the first crop and the recovery was not affected by trash incorporation. Around 6% of the N in fertiliser was also recovered in the first crop, which was less than previously measured in temperate areas (20-40%). Leaf samples taken at the end of the second crop contined 2-3% of N from trash and fertilizer applied at the beginning of the experiment. Although most N was recovered in the 0-1.5 m soil layer there was some evidence of movement of N below this depth. The results showed that trash supplies N slowly and in small amounts to the succeeding crop in wet tropics sugarcane growing areas regardless of trash placement (on the soil surface or incorporated) or soil type, and so N mineralisation from a single trash blanket is not important for sugarcane production in the wet tropics.

Feasibility of controlling nitrification in predenitrification plants using DO, pH and ORP sensors

Experimental studies were carried out on a bench-scale nitrogen removal system with a predenitrification configuration to gain insights into the spatial and temporal variations of DO, pH and ORP in such systems. It is demonstrated that these signals correlate strongly with the operational states of the system, and could therefore be used as system performance indicators. The DO concentration in the first aerobic zone, when receiving constant aeration, and the net pH change between the last and first aerobic zones display strong correlations with the influent ammonia concentration for the domestic wastewater used in this study. The pH profile along the aerobic zones gives good indication on the extent of nitrification. The experimental results also showed a good correlation between ORP values in the last aerobic zone and effluent ammonia and nitrate concentrations, provided that DO in this zone is controlled at a constant level. These results suggest that the DO, pH and ORP sensors could potentially be used as alternatives to the on-line nutrient sensors for the control of continuous systems. An idea of using a fuzzy inference system to make an integrated use of these signals for on-line aeration control is presented and demonstrated on the bench-scale system with promising results. The use of these sensors has to date only been demonstrated in intermittent systems, such as sequencing batch reactor systems.

Nitrogen balance for an agroforestry system irrigated with saline, high nitrogen effluent

Land disposal is commonly used for urban and industrial wastewater, largely due to the high costs involved in alternative treatments or disposal systems. However, the viability of such systems depends on many factors, including the composition of the effluent water, soil type, the plant species grown, growth rate, and planting density. The objective of this study is to establish whether land disposal of nitrogen (N) rich effluent using an agroforestry system is sustainable, and determine the effect of irrigation rate and tree planting density on the N cycle and subsequent N removal. We examined systems for the sustainable disposal of a high strength industrial effluent. The challenge was to leach the salt, by using a sufficiently high rate of irrigation, while simultaneously ensuring that N did not leach from the soil profile. We describe the N balance for two plant systems irrigated with effluent, one comprising Eucalyptus tereticornis and Eucalyptus moluccana and a Rhodes grass (Chloris gayana) pasture, and the other, Rhodes grass pasture alone. Nitrogen balance was assessed from N inputs in effluent and rainfall, accumulation of N in the plant biomass, changes in soil N storage, N loss in run-off water, denitrification and N loss to the groundwater by deep-drainage. Biomass production was estimated from allometric relationships derived from yearly destructive harvesting of selected trees. The N content of that biomass was then calculated from measured N content of the various plant parts, and their mass. Approximately 300 kg N/ha/yr was assimilated into tree biomass at a planting density of 2500 tree/ha of E. moluccana. In addition to tree assimilation, pasture growth between the tree rows, which was regularly harvested, contributed substantially to N uptake. If the trees were harvested after two years of growth and grass harvested regularly, biomass removal of N by the mixed system would be about 700 kg N/ha/yr. The results of this study show that the current system of effluent disposal is not sustainable as the nitrate leaching from the soil profile far exceeds standards set out by the ANZECC guidelines. Hence additional means of N removal will need to be implemented. Biological N removal is an area that warrants further studies as it is aimed at reducing N levels in the effluent before irrigation. This will complement the current agroforestry system.

Mathematical Modeling for Studying Microbial Processes – Some Examples

Mathematical modeling may have different purposes in chemical and biochemical engineering sciences. One of them is to confirm or to reject kinetic models for certain processes, or to evaluate the importance of some transport phenomena on the net chemical or biochemical reaction rate. In the present paper different microbial processes are considered and modeled for evaluation of kinetic constants for batch and continuous processes accomplished by free and immobilized microbial cells. The practical examples are from the field of wastewater treatment and biosynthesis of products, like enzymes, lactic acid, gluconic acid, etc. By the aid of mathematical modeling the kinetics and the type of inhibition are specified for microbial wastewater denitrification and biodegradation of halogenated hydrocarbons. The importance of free and immobilized cells and their separate contribution to the overall microbial process is also evaluated for some fermentation processes: gluconic acid production, dichloroethane biodegradation, lactic acid fermentation and monochloroacetic acid biodegradation.

Interaction of the parasitic angiosperm {\it Cassytha filiformis\/} L. (Lauraceae) with the exotic {\it Schinus terebinthifolius\/} Raddi (Anacardiaceae) in southern Florida

Brazilian pepper (Schinus terebinthifolius) is an exotic shrub or small tree that has become well established as an invasive and highly competitive species through much of southern Florida. Love vine (Cassytha filiformis), a native parasitic plant, was noted parasitizing Brazilian pepper, apparently affecting its health. The objective of this study was to investigate the nature of this parasitic interaction in southern Florida. Brazilian pepper populations were studied to determine whether parasitism by love vine may affect growth and reproduction. Anatomical studies of love vine parasitizing Brazilian pepper determined physical aspects of the parasitic interaction at the cell and tissue level. Physiological aspects of this interaction were investigated to help describe love vine resource acquisition as a parasite on host Brazilian pepper plants, and as an autotrophic plant. An investigation of ecological aspects of this parasitic interaction was done to determine whether physical or biological aspects of habitats may contribute to love vine parasitism on Brazilian pepper. These studies indicated that: (1) parasitism by love vine significantly decreased growth and reproduction of Brazilian pepper plants; (2) anatomical and physiological investigations indicated that love vine was primarily a xylem parasite on Brazilian pepper, but that some assimilated carbon nutrients may also be acquired from the host; (3) love vine is autotrophic (i.e., hemiparasitic), but is totally dependent on its host for necessary resources; (4) the occurrence of love vine parasitism on Brazilian pepper is mediated by physical characters of the biological community. ^

Intra- and interannual variability in seagrass carbon and nitrogen stable isotopes from south Florida, a preliminary study

δ13C and δ15N values were determined for the seagrassThalassia testudinum at four permanent seagrass monitoring stations in southFlorida, USA, through a quarterly sampling program over 3-years (1996–1998). All sites are seagrass beds with water depths of less than 6 m. Two sites are located on the Florida Bay side of the Florida Keys, and the other two sites are on the Atlantic side. The data analyzed over the 3 year study period display unique patterns associated with seasonal changes in primary productivity and potentially changes in the N and C pools. The mean carbon and nitrogenisotope values of T. testudinum from all four stations vary from −7.2 to −10.4‰ and 1.1 to 2.2‰, respectively. However, certain stations displayed anomalously depleted nitrogenisotope values (as low as −1.2‰). These values may indicate that biogeochemical processes like N fixation, ammonification and denitrification cause temporal changes in the isotopic composition of the source DIN. Both δ13C and δ15N values displayed seasonal enrichment-depletion patterns, with maximum enrichment occurring during the summer to early fall. The intra-annual variations of δ13C values from the different stations ranged from about 1 to 3.5‰; whereas variations in δ15N ranged from about 1 to 4.9‰. Certain sites showed a positive relationship between isotope values and productivity. These data indicate δ13C values display a high degree of seasonal variability as related to changes in productivity. δ15N values show clear intra-annual variations, but the observed changes do not necessarily follow a distinct seasonal cycle, indicating that changes in DIN will need further investigation.

The role of dissolved organic matter bioavailability in promoting phytoplankton blooms in Florida Bay

The clear, shallow, oligotrophic waters of Florida Bay are characterized by low phytoplankton biomass, yet periodic cyanobacteria and diatom blooms do occur. We hypothesized that allochthonous dissolved organic matter (DOM) was providing a subsidy to the system in the form of bound nutrients. Water from four bay sites was incubated under natural light and dark conditions with enrichments of either DOM ( > 1 kD, 2×DOM) or inorganic nutrients (N+P). Samples were analyzed for bacterial numbers, bacterial production, phytoplankton biomass, phytoplankton community structure, and production, nutrients, and alkaline phosphatase (AP) activity. The influence of 2×DOM enrichment on phytoplankton biomass developed slowly during the incubations and was relatively small compared to nutrient additions. Inorganic nutrient additions resulted in an ephemeral bloom characterized initially as cyanobacterial and brown algae but which changed to dinoflagellate and/or brown algae by day six. The DIN:TP ratio decreased 10-fold in the N+P treatments as the system progressed towards N limitation. This ratio did not change significantly for 2×DOM treatments. In addition, these experiments indicated that both autotrophic and heterotrophic microbial populations in Florida Bay may fluctuate in their limitation by organic and inorganic nutrient availability. Both N+P and 2×DOM enrichments revealed significant and positive response in bioavailability of dissolved organic carbon (BDOC). Potential BDOC ranged from 1.1 to 35.5%, with the most labile forms occurring in Whipray Basin. BDOC at all sites was stimulated by the 2×DOM addition. Except for Duck Key, BDOC at all sites was also stimulated by the addition of N+P. BDOC was lower in the dry season than in the wet season (5.56% vs. 16.86%). This may be explained by the distinct chemical characteristics of the DOM produced at different times of year. Thus, both the heterotrophic and autotrophic microbial communities in Florida Bay are modulated by bioavailability of DOM. This has ramifications for the fate of DOM from the Everglades inputs, implicating DOM bioavailability as a contributing factor in regulating the onset, persistence, and composition of phytoplankton blooms.

Everglades Periphyton: A Biogeochemical Perspective

Periphyton is an important component of the Everglades biogeochemical cycle but remains poorly understood. From a biogeochemical perspective, periphyton is a dense aggregation of diverse microorganisms (autotrophic and heterotrophic) and particles (mineral and detrital) imbedded within an extracellular matrix. The authors synthesize Everglades periphyton biogeochemistry and diversity at the ecosystem and community scales. The primary regulator of biogeochemical processes (material flux, transformation, and storage) is photosynthesis, which controls oxidation-reduction potentials and heterotrophic metabolism. Eutrophication and hydrologic alterations have resulted in fundamental periphyton biogeochemical differences. Elucidation of these processes is required to predict and interpret responses to ecosystem restoration.

Biogeochemistry of Nitrogen Across the Everglades Landscape

Compared to phosphorus (P), nitrogen (N) has received little attention across the Everglades landscape. Despite this lack of attention, N plays important roles in many Everglades systems, including being a significant pollutant in Florida Bay and the Gulf of Mexico, the limiting nutrient in highly P-impacted areas, and an important substrate for microbial metabolism. Storage and transport of N throughout the Everglades is dominated by organic forms, including peat soils and dissolved organic N in the water column. In general, N sources are highest in the northern areas; however, atmospheric deposition and active N2 fixation by the periphyton components are a significant N source throughout most systems. Many of the processes involved in the wetland N cycle remain unmeasured for most of the Everglades systems. In particular, the lack of in situ rates for N2 fixation and denitrification prevent the construction of system-level budgets, especially for the Southern mangrove systems where N export into Florida Bay is critical. There is also the potential for several novel N processes (e.g., Anammox) with an as yet undetermined importance for nitrogen cycling and function of the Everglades ecosystem. Phosphorus loading alters the N cycle by stimulating organic N mineralization with resulting flux of ammonium and DON, and at elevated P concentrations, by increasing rates of N2 fixation and N assimilation. Restoration of hydrology has a potential for significantly impacting N cycling in the Everglades both in terms of affecting N transport, but also by altering aerobic-anaerobic transitions at the soil-water interface or in areas with seasonal drawdowns (e.g., marl prairies). Based on the authors’ understanding of N processes, much more research is necessary to adequately predict potential impacts from hydrologic restoration, as well as the function of Everglades systems as sinks, sources, and transformers of N in the South Florida landscape.