Control of heterotrophic layer formation on nitrifying biofilms in a biofilm airlift suspension reactor

A Biofilm Airlift Suspension (BAS) reactor was operated with nitrifying biofilm growth and heterotrophic suspended growth, simultaneously converting ammonium and acetate. Growth of heterotrophs in suspension decreases the diffusion limitation for the nitrifiers, and enlarges the nitrifying capacity of a biofilm reactor. Neither nitrifiers nor heterotrophs suffer from additional oxygen diffusion limitation when the heterotrophs grow in suspension. Control of the location of heterotrophic growth, either in suspension or in biofilms over the nitrifying biofilms, was possible by manipulation of the hydraulic retention time. A time delay for formation and disappearance of the heterotrophic biofilms of 10 to 15 days was observed. Surprisingly, it was found that in the presence of the heterotrophic layers the maximum specific activity on ammonia of the nitrifying biofilms increased. The reason for the increase in activity is unknown. The effect of heterotrophic biofilm formation on oxygen diffusion limitation for the nitrifiers is discussed. Some phenomena compensating the increased mass transfer resistance due to the growth of a heterotrophic layer are also presented. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 397-405, 1997.     

The role of extracellular polymeric substances in reducing copper inhibition to nitrification in activated sludge

This study presents the role of extracellular polymeric substances (EPS) in reducing the inhibitory effects of copper towards nitrifying activated sludge. EPS could ameliorate copper toxicity in activated sludge by binding metal ions. A series of copper inhibition experiments were conducted with activated sludge taken from laboratoryscale sequencing batch reactor (SBR) systems operated under different feast-famine cycles, which provided the different conditions to the EPS-producing heterotrophic populations. The toxicity of copper to both nitrifiers and heterotrophs decreased with increasing the feast-famine period. Average EPS contents were substantially higher in SBR sludge with longer feast-famine periods indicating that the decrease in the toxicity of copper at a longer feastfamine period was attributed to the presence of higher amounts of EPS. Comparison of the responses of nitrifiers and heterotrophs to free copper suggests that nitrifiers were no more sensitive to copper than heterotrophs.     

The importance of autotrophic versus heterotrophic oxidation of atmospheric ammonium in forest ecosystems with acid soil

Abstract The role of autotrophic and heterotrophic nitrifying microorganisms in the oxidation of atmospheric ammonium in two acid and one calcareous location of a Dutch woodland area was investigated. In soil slurries nitrate formation was completely inhibited by acetylene, a specific inhibitor of autotrophic ammonium-oxidizing bacteria. A survey of nitrifiers in the forest soils showed that both autotrophic ammonium- and nitrite-oxidizing bacteria were present in high numbers and evidence was obtained that autotrophic bacteria are able to nitrify below pH 4. These results show that autotrophic nitrifying bacteria may account for most of the nitrification in the examined soils. To assess the contribution of heterotrophic nitrifiers, about 200 strains of heterotrophic bacteria and 21 morphologically distinct fungal strains were isolated from the acid soil locations and tested for their ability to nitrify. Only one Penicillium strain produced nitrate in test media, but its nitrate formation when added to acid soils was poor. These findings indicate that in the investigated soil heterotrophs are of minor importance in the oxidation of atmospheric ammonium.     

Evaluation on factors influencing the heterotrophic growth on the soluble microbial products of autotrophs

In this work, the heterotrophic growth on the microbial products of autotrophs and the effecting factors were evaluated with both experimental and modeling approaches. Fluorescence in situ hybridization (FISH) analysis illustrated that ammonia oxidizers (AOB), nitrite oxidizers (NOB), and heterotrophs accounted for about 65%, 20%, and 15% of the total bacteria, respectively. The mathematical evaluation of experimental data reported in literature indicated that heterotrophic growth in nitrifying biofilm (30–50%) and granules (30%) was significantly higher than that of nitrifying sludge (15%). It was found that low influent ammonium resulted in a lower availability of soluble microbial products (SMP) and a slower heterotrophic growth, but high ammonium (>150 mg N L⁻¹) feeding would lead to purely AOB dominated sludge with high biomass‐associated products contained effluent, although the absolute heterotrophic growth increased. Meanwhile, the total active biomass concentration increased gradually with the increasing solids retention time, whereas the factions of active AOB, NOB, and heterotrophs varied a lot at different solids retention times. This work could be useful for better understanding of the autotrophic wastewater treatment systems. Biotechnol. Bioeng. 2011; 108:804–812. © 2010 Wiley Periodicals, Inc.     

Interactions of Nitrifying Bacteria and Heterotrophs: Identification of a Micavibrio-Like Putative Predator of Nitrospira spp.

Chemolithoautotrophic nitrifying bacteria release soluble organic compounds, which can be substrates for heterotrophic microorganisms. The identities of these heterotrophs and the specificities of their interactions with nitrifiers are largely unknown. In this study, we incubated nitrifying activated sludge with ¹³C-labeled bicarbonate and used stable isotope probing of 16S rRNA to monitor the flow of carbon from uncultured nitrifiers to heterotrophs. To facilitate the identification of heterotrophs, the abundant 16S rRNA molecules from nitrifiers were depleted by catalytic oligonucleotides containing locked nucleic acids (LNAzymes), which specifically cut the 16S rRNA of defined target organisms. Among the ¹³C-labeled heterotrophs were organisms remotely related to Micavibrio, a microbial predator of Gram-negative bacteria. Fluorescence in situ hybridization revealed a close spatial association of these organisms with microcolonies of nitrite-oxidizing sublineage I Nitrospira in sludge flocs. The high specificity of this interaction was confirmed by confocal microscopy and a novel image analysis method to quantify the localization patterns of biofilm microorganisms in three-dimensional (3-D) space. Other isotope-labeled bacteria, which were affiliated with Thermomonas, colocalized less frequently with nitrifiers and thus were commensals or saprophytes rather than specific symbionts or predators. These results suggest that Nitrospira spp. are subject to bacterial predation, which may influence the abundance and diversity of these nitrite oxidizers and the stability of nitrification in engineered and natural ecosystems. In silico screening of published next-generation sequencing data sets revealed a broad environmental distribution of the uncultured Micavibrio-like lineage.     

Determination of the decay rate of nitrifying bacteria

The growth and decay of nitrifying organisms determines the amount of nitrifying bacteria in activated sludge systems. The growth rate of the nitrifying organisms is reasonable, well defined, and studied, while the decay rate is still rather uncertain. Experiments in previous studies were over periods up to 14 days and obtained results were not confirmed. Contradicting decay rates of nitrifiers in different bacterial communities is reported. No differentiation between ammonia and nitrite oxidizers was made. Therefore, in this studyper day the decay rate of the nitrifying organisms was studied. The starvation condition (aerobic, anoxic, or anaerobic), temperature, type of bacterial community, and the presence of higher organisms are the main aspects that were investigated. A simple and reliable method (adapted from previous studies) for determining the decay rate of nitrifying organisms under different starvation conditions and different temperatures was developed. The test procedure has been used for determining the decay rate of ammonium and nitrite oxidizing bacteria in an enriched nitrifying culture and in activated sludge. The test was successfully applied at starvation periods up to 30 days. The decay rate of the enriched culture of nitrifiers was very low compared to values for nitrifiers in activated sludge. The decay rate of the nitrifiers in activated sludge was found to be to 0.2, 0.1, and 0.06 per day for aerobic, anoxic, and anaerobic conditions, respectively. The decay rate of ammonia oxidizers and nitrite oxidizers was the same at the corresponding conditions.     

Heterotrophs grown on the soluble microbial products (SMP) released by autotrophs are responsible for the nitrogen loss in nitrifying granular sludge

In this work, nitrogen loss in the nitrite oxidation step of the nitrification process in an aerobic‐granule‐based reactor was characterized with both experimental and modeling approaches. Experimental results showed that soluble microbial products (SMP) were released from the nitrite‐oxidizing granules and were utilized as a carbon source by the heterotrophs for denitrification. This was verified by the fluorescence in situ hybridization (FISH) analysis. Microelectrode tests showed that oxygen diffusion limitation did result in an anoxic micro‐zone in the granules and allowed sequential utilization of nitrate as an electron acceptor for heterotrophic denitrification with SMP as a carbon source. To further elucidate the nitrogen loss mechanisms, a mathematic model was formulated to describe the growth of nitrite oxidizers, the formation and consumption of SMP, the anoxic heterotrophic growth on SMP and nitrate, as well as the oxygen transfer and the substrate diffusion in the granules. The results clearly indicate that the heterotrophs grown on the SMP released by the autotrophs are responsible for the nitrogen loss in the nitrifying granules, and give us a better understanding of the aerobic granules for nitrogen removal. Biotechnol. Bioeng. 2011;108: 2844–2852. © 2011 Wiley Periodicals, Inc.     

Model-based analysis on growth of activated sludge in a sequencing batch reactor

A mathematical model is developed to describe the growth of multiple microbial species such as heterotrophs and autotrophs in activated sludge system. Performance of a lab-scale sequencing batch reactor involving storage process is used to evaluate the model. Results show that the model is appropriate for predicting the fate of major model components, i.e., chemical oxygen demand, storage polymers (X _STO), volatile suspended solid (VSS), ammonia, and oxygen uptake rate (OUR). The influence of sludge retention time (SRT) on reactor performance is analyzed by model simulation. The biomass components require different time periods from one to four times of SRT to reach steady state. At an SRT of 20 days, the active bacteria (autotrophs and heterotrophs) constitute about 57% of the VSS; the remaining biomass is not active. The model established demonstrates its capacity of simulating the reactor performance and getting insight in autotrophic and heterotrophic growth in complex activated sludge systems.     

Molecular characterization of the nitrifying bacterial consortia employed for the activation of bioreactors used in brackish and marine aquaculture systems

The addition of commercial nitrifying bacterial products has resulted in significant improvement of nitrification efficiency in recirculating aquaculture systems (RAS). We developed two nitrifying bacterial consortia (NBC) from marine and brackish water as start up cultures for immobilizing commercialized nitrifying bioreactors for RAS. In the present study, the community compositions of the NBC were analyzed by universal 16S rRNA gene and bacterial amoA gene sequencing and fluorescence in situ hybridization (FISH). This study demonstrated that both the consortia involved autotrophic nitrifiers, denitrifiers as well as heterotrophs. Abundant taxa of the brackish water heterotrophic bacterial isolates were Paenibacillus and Beijerinckia spp. whereas in the marine consortia they were Flavobacterium, Cytophaga and Gramella species. The bacterial amoA clones were clustered together with high similarity to Nitrosomonas sp. and uncultured beta Proteobacteria. FISH analysis detected ammonia oxidizers belonging to β subclass of proteobacteria and Nitrosospira sp. in both the consortia, and Nitrosococcus mobilis lineage only in the brackish water consortium and the halophilic Nitrosomonas sp. only in the marine consortium. However, nitrite oxidizers, Nitrobacter sp. and phylum Nitrospira were detected in both the consortia. The metabolites from nitrifiers might have been used by heterotrophs as carbon and energy sources making the consortia a stable biofilm.     

Co-immobilized Nitrosomonas europaea and Nitrobacter agilis cells: validation of a dynamic model for simultaneous substrate conversion and growth in kappa-carrageenan gel beads

A dynamic model for two microbial species immobilized in a gel matrix is presented and validated with experiments. The model characterizes the nitrification of ammonia with Nitrosomonas europaea and Nitrobacter agilis co-immobilized in K-carrageenan gel beads. The model consists of kinetic equations for the microorganisms and mass transfer equations for the substrates and products inside and outside the gel beads. The model predicts reactor bulk concentrations together with the substrate consumption rate, product formation, and biomass growth inside the gel beads as a function of time. A 50-day experiment with immobilized cells in a 3.3-dm(3) air-lift loop reactor was carried out to validate the model. The parameter values for the model were obtained from literature and separate experiments. The experimentally determined reactor bulk concentrations and the biomass distribution of the two microorganisms in the gel beads were well predicted by the model. A sensitivity analysis of the model for the given initial values indicated the most relevant parameters to be the maximum specific growth rate of the microorganisms, the diffusion coefficient of oxygen, and the radius of the beads. The dynamic model provides a useful tool for further study and possible control of the nitrification process. (c) 1994 John Wiley & Sons, Inc.     

Fate of 14C-labeled microbial products derived from nitrifying bacteria in autotrophic nitrifying biofilms

The cross-feeding of microbial products derived from 14C-labeled nitrifying bacteria to heterotrophic bacteria coexisting in an autotrophic nitrifying biofilm was quantitatively analyzed by using microautoradiography combined with fluorescence in situ hybridization (MAR-FISH). After only nitrifying bacteria were labeled with [14C]bicarbonate, biofilm samples were incubated with and without NH4+ as a sole energy source for 10 days. The transfer of 14C originally incorporated into nitrifying bacterial cells to heterotrophic bacteria was monitored with time by using MAR-FISH. The MAR-FISH analysis revealed that most phylogenetic groups of heterotrophic bacteria except the beta-Proteobacteria showed significant uptake of 14C-labeled microbial products. In particular, the members of the Chloroflexi were strongly MAR positive in the culture without NH4+ addition, in which nitrifying bacteria tended to decay. This indicated that the members of the Chloroflexi preferentially utilized microbial products derived from mainly biomass decay. On the other hand, the members of the Cytophaga-Flavobacterium cluster gradually utilized 14C-labeled products in the culture with NH4+ addition in which nitrifying bacteria grew. This result suggested that these bacteria preferentially utilized substrate utilization-associated products of nitrifying bacteria and/or secondary metabolites of 14C-labeled structural cell components. Our results clearly demonstrated that the coexisting heterotrophic bacteria efficiently degraded and utilized dead biomass and metabolites of nitrifying bacteria, which consequently prevented accumulation of organic waste products in the biofilm.     

Wastewater nitrification kinetics using reciprocating jet bioreactor

Kinetic investigations on growth parameters of nitrifying and COD oxidizing bacteria were carried out with recourse to a three stage reciprocating jet bioreactor system using real life wastewater. The system employed in this investigation essentially consisted of separate aerobic oxidation stage along with nitrification stage and anaerobic denitrification stage with facility for biomass recirculation whenever necessary. Steady-state COD oxidation reactor performance was assessed for various values of residence time. Yield coefficient and decay coefficient of COD oxidizing biomass were obtained as 0.3329 kg BM/kg COD and 0.0032 (1/h) respectively.It was observed that COD oxidizing bacteria co-existed with nitrifying bacteria during nitrification process due to the nature of wastewater used. Steady-state nitrification reactor performance was also assessed for various residence time values. Exact concentration of nitrifying and COD oxidizing biomass in the nitrification reactor was then estimated with the help of kinetic growth parameters of COD oxidizing biomass and extent of COD oxidation achieved in nitrification reactor. This further enabled evaluation of corrected kinetic growth parameters estimated as 0.4272 kg BM/kg NH ₄ ⁺ -N and 0.00626 (1/h) for nitrifier biomass yield coefficient and decay coefficient respectively.     

Development and experimental evaluation of a steady-state, multispecies biofilm model

A steady-state model for quantifying the space competition in multispecies biofilms is developed. The model includes multiple active species, inert biomass, substrate utilization and diffusion within the biofilm, external mass transport, and detachment phenomena. It predicts the steady-state values of biofilm thickness, species distribution, and substrate fluxes. An experimental evaluation is carried out in completely mixed biofilm reactors in which slow-growing nitrifying bacteria compete with acetate-utilizing heterotrophs. The experimental results show that the model successfully describes the space competition. In particular, increasing acetate concentrations causes NH(4) (+)-N fluxes to decrease, because nitrifiers are forced deeper into the biofilm, where they experience greater mass-transport resistance.     

Ecophysiological interaction between nitrifying bacteria and heterotrophic bacteria in autotrophic nitrifying biofilms as determined by microautoradiography-fluorescence in situ hybridization

Ecophysiological interactions between the community members (i.e., nitrifiers and heterotrophic bacteria) in a carbon-limited autotrophic nitrifying biofilm fed only NH(4)(+) as an energy source were investigated by using a full-cycle 16S rRNA approach followed by microautoradiography (MAR)-fluorescence in situ hybridization (FISH). Phylogenetic differentiation (identification) of heterotrophic bacteria was performed by 16S rRNA gene sequence analysis, and FISH probes were designed to determine the community structure and the spatial organization (i.e., niche differentiation) in the biofilm. FISH analysis showed that this autotrophic nitrifying biofilm was composed of 50% nitrifying bacteria (ammonia-oxidizing bacteria [AOB] and nitrite-oxidizing bacteria [NOB]) and 50% heterotrophic bacteria, and the distribution was as follows: members of the alpha subclass of the class Proteobacteria (alpha-Proteobacteria), 23%; gamma-Proteobacteria, 13%; green nonsulfur bacteria (GNSB), 9%; Cytophaga-Flavobacterium-Bacteroides (CFB) division, 2%; and unidentified (organisms that could not be hybridized with any probe except EUB338), 3%. These results indicated that a pair of nitrifiers (AOB and NOB) supported a heterotrophic bacterium via production of soluble microbial products (SMP). MAR-FISH revealed that the heterotrophic bacterial community was composed of bacteria that were phylogenetically and metabolically diverse and to some extent metabolically redundant, which ensured the stability of the ecosystem as a biofilm. alpha- and gamma-Proteobacteria dominated the utilization of [(14)C]acetic acid and (14)C-amino acids in this biofilm. Despite their low abundance (ca. 2%) in the biofilm community, members of the CFB cluster accounted for the largest fraction (ca. 64%) of the bacterial community consuming N-acetyl-D-[1-(14)C]glucosamine (NAG). The GNSB accounted for 9% of the (14)C-amino acid-consuming bacteria and 27% of the [(14)C]NAG-consuming bacteria but did not utilize [(14)C]acetic acid. Bacteria classified in the unidentified group accounted for 6% of the total heterotrophic bacteria and could utilize all organic substrates, including NAG. This showed that there was an efficient food web (carbon metabolism) in the autotrophic nitrifying biofilm community, which ensured maximum utilization of SMP produced by nitrifiers and prevented buildup of metabolites or waste materials of nitrifiers to significant levels.     

Nitrifying bacterial growth inhibition in the presence of algae and cyanobacteria

Nitrifying bacteria, cyanobacteria, and algae are important microorganisms in open pond wastewater treatment systems. Nitrification involving the sequential oxidation of ammonia to nitrite and nitrate, mainly due to autotrophic nitrifying bacteria, is essential to biological nitrogen removal in wastewater and global nitrogen cycling. A continuous flow autotrophic bioreactor was initially designed for nitrifying bacterial growth only. In the presence of cyanobacteria and algae, we monitored both the microbial activity by measuring specific oxygen production rate (SOPR) for microalgae and cyanobacteria and specific oxygen uptake rate (SOUR) for nitrifying bacteria. The growth of cyanobacteria and algae inhibited the maximum nitrification rate by a factor of 4 although the ammonium nitrogen fed to the reactor was almost completely removed. Terminal restriction fragment length polymorphism (T‐RFLP) analysis indicated that the community structures of nitrifying bacteria remained unchanged, containing the dominant Nitrosospira, Nitrospira, and Nitrobacter species. PCR amplification coupled with cloning and sequencing analysis resulted in identifying Chlorella emersonii and an uncultured cyanobacterium as the dominant species in the autotrophic bioreactor. Notwithstanding their fast growth rate and their toxicity to nitrifiers, microalgae and cyanobacteria were more easily lost in effluent than nitrifying bacteria because of their poor settling characteristics. The microorganisms were able to grow together in the bioreactor with constant individual biomass fractions because of the uncoupled solids retention times for algae/cyanobacteria and nitrifiers. The results indicate that compared to conventional wastewater treatment systems, longer solids retention times (e.g., by a factor of 4) should be considered in phototrophic bioreactors for complete nitrification and nitrogen removal. Biotechnol. Bioeng. 2010;107: 1004–1011. © 2010 Wiley Periodicals, Inc.     

Formation of nitrifying biofilms on small suspended particles in airlift reactors

For a stable and reliable operation of a BAS-reactor a high, active biomass concentration is required with mainly biofilm-covered carriers. The effect of reactor conditions on the formation of nitrifying biofilms in BAS-reactors was investigated in this article. A start-up strategy to obtain predominantly biofilm-covered carriers, based on the balancing of detachment and a biomass production per carrier surface area, proved tp be very successful. The amount of biomass and the fraction of covered carrier were high and development of nitrification activity was fast, leading to a volumetric conversion of 5 kg(N) . m(-3) . d(-1) at a hydraulic retention time of 1h. A 1-week, continuous inoculation with suspended purely nitrifying microorganisms resulted in a swift start-up compared with batch addition of a small number of biofilms with some nitrification activity. The development of nitrifying biofilms was very similar to the formation of heterotrophic biofilms. In contrast to heterotrophic bio-films, the diameter of nitrifying biofilms increased during start-up. The detachment rate from nitrifying biofilms decreased with lower concentrations of bare carrier, in a fashion comparable with heterotrophic biofilms, but the nitrifying biofilms were much more robust and resistant. Standard diffusion theory combined with reaction kinetics are capable of predicting the activity and conversion of biofilms on small suspended particles. (c) 1995 John Wiley & Sons Inc.     

Fate of 14C-Labeled Microbial Products Derived from Nitrifying Bacteria in Autotrophic Nitrifying Biofilms

The cross-feeding of microbial products derived from ¹⁴C-labeled nitrifying bacteria to heterotrophic bacteria coexisting in an autotrophic nitrifying biofilm was quantitatively analyzed by using microautoradiography combined with fluorescence in situ hybridization (MAR-FISH). After only nitrifying bacteria were labeled with [¹⁴C]bicarbonate, biofilm samples were incubated with and without NH₄⁺ as a sole energy source for 10 days. The transfer of ¹⁴C originally incorporated into nitrifying bacterial cells to heterotrophic bacteria was monitored with time by using MAR-FISH. The MAR-FISH analysis revealed that most phylogenetic groups of heterotrophic bacteria except the β-Proteobacteria showed significant uptake of ¹⁴C-labeled microbial products. In particular, the members of the Chloroflexi were strongly MAR positive in the culture without NH₄⁺ addition, in which nitrifying bacteria tended to decay. This indicated that the members of the Chloroflexi preferentially utilized microbial products derived from mainly biomass decay. On the other hand, the members of the Cytophaga-Flavobacterium cluster gradually utilized ¹⁴C-labeled products in the culture with NH₄⁺ addition in which nitrifying bacteria grew. This result suggested that these bacteria preferentially utilized substrate utilization-associated products of nitrifying bacteria and/or secondary metabolites of ¹⁴C-labeled structural cell components. Our results clearly demonstrated that the coexisting heterotrophic bacteria efficiently degraded and utilized dead biomass and metabolites of nitrifying bacteria, which consequently prevented accumulation of organic waste products in the biofilm.     

Inhibition of nitrifiers and methanotrophs from an agricultural humisol by allylsulfide and its implications for environmental studies.

Allylsulfide, an inhibitor of ammonia monooxygenase, was tested to determine its ability to inhibit nitrification and methane oxidation in pure cultures, in agricultural humisol enrichment cultures, and in humisol slurries. We confirmed that allylsulfide is a differential inhibitor of cultures of nitrifiers and methanotrophs at concentrations of 1 and 200 microM, respectively, which result in 50% inhibition. However, although a nitrifying enrichment culture added to sterilized humisol was inhibited 50% by 4 microM allylsulfide, 500 microM allylsulfide was necessary for 50% inhibition of the endogenous nitrifying activity in nonsterile humisol. We concluded that native nitrifiers were protected, possibly by being in colonial aggregates or sheltered microenvironments.     

Nitrification in histosols: a potential role for the heterotrophic nitrifier.

Insufficient populations of Nitrosomonas and Nitrobacter were found in a Pahokee muck soil (Lithic medidaprit) to account for the nitrate concentration observed. To determine if heterotrophic nitrifiers could account for some of this discrepancy, a method was developed to measure the levels of heterotrophic nitrifiers in soil. A population of 4.1 X 10(5) Arthrobacter per g of dry fallow soil, capable of producing nitrite and/or nitrate from reduced nitrogenous compounds, was observed. Amendment of the much with 0.5% (wt/wt) sodium acetate and 0.1% (wt/wt) ammonium-nitrogen as ammonium sulfate (final concentrations) not only resulted in the usual increase in autotrophic nitrifiers, but also in a fourfold increase in the heterotrophic nitrifying Arrthrobacter. Amendment of like samples with N-Serve [2-chloro-6(trichloromethyl) pyridinel] prevented the increase in Nitrosomonas, but not that in the heterotrophic nitrifiers. Nitrate production in the presence of the inhibitor was diminished but not prevented. An Arthrobacter sp., isolated from the muck, produced nitrite when inoculated at high densities into sterile soil, unamended or amended with sodium acetate and/or ammomium sulfate. These data suggest that the heterotrophic population may be responsible for some of the nitrate produced in these Histosols.     

Assay for determination of α-glucosidase and peptidase activity and location in a nitrifying trickling filter

Enzymatic alpha-glucosidase and peptidase activity in a nitrifying trickling filter (NTF) at the Rya wastewater treatment plant, G?teborg, Sweden, was investigated to evaluate whether these activities can be used as indicators of heterotrophic activity and polymer degradation. Samples of the biofilm were taken from the NTF and incubated in sterile filtered effluent water from the NTF with the addition of soluble starch, peptone, and ammonium chloride. In order to determine the distribution of enzyme activities, the alpha-glucosidase and peptidase activities were measured in the biofilm samples, in the filtered effluent water from the NTF and in the water phase in which the biofilm was incubated. Activities of both enzymes were found both in the effluent water from the NTF and in the biofilm. The enzyme activities were elevated in the samples when starch and peptone were present. In addition, there was a significant inhibition of ammonium oxidation in samples incubated with starch and peptone. Thus, the presence of starch, peptone and ammonium resulted in increased activity of heterotrophs, which lead to an inhibition of the nitrifiers, probably via competition for available oxygen.