Specific Nitrification Research Articles

High-strength ammonium wastewater treatment by MBR: Steady-state nitrification kinetic parameters

In this study, a steady-state operation approach is proposed in order to accurately measure the kinetic parameters of substrate (contaminants) removal in wastewater biotreatment systems. In order to determine the kinetic parameters of a submerged membrane bioreactor (sMBR) when treating high-strength ammoniacal nitrogen wastewaters, a lab-scale sMBR was operated for 205 days with synthetic leachates (1000 mg L−1) at 4 different ammoniacal nitrogen concentrations (220, 340, 665 and 1040 mg NH4-N L−1). Ammoniacal nitrogen oxidation rates were calculated by solving the mass balance equations when steady-state conditions were reached for each tested concentration. The Haldane model was found to be accurate when predicting the specific ammoniacal nitrogen oxidation rates with the following kinetic parameters: rNH,max = 854,4 mg NH4-N L−1 d−1, KS = 1007 mg NH4-N L−1, and KI = 221 mg NH4-N L−1 (R2 = 0,97). The highest ammoniacal nitrogen oxidation rate was found to be 162 mg NH4-N L−1 d−1 when the effluent concentration was 472 mg NH4-N L−1. When compared to the conventional flask test approach for calculating the kinetic parameters, the steady-state approach described in this study showed a lower variability in the predicted specific nitrification rates, as well as a lower effect of the inhibition phenomena, due to the mixed liquor being adapted to each substrate concentration tested.

Nitrification of high levels of ammonia in groundwater using fixed‐bed biofiltration technique

AbstractGroundwater ammonia pollution is well investigated worldwide as well as in Viet Nam. The products of its conversion process, namely nitrite and nitrate, cause the toxicity of ammonia in water. In addition, the existence of ammonia in water causes the modification of water taste and smell, increases the risk of heterotrophic and contagious microorganism presence. Biofilm technique has been being applied to treat the ammonia in the groundwater recently. In this present study, fixed‐bed biofiltration technique was implemented to remove the ammonia at high concentration of 20‐50 mgN/L. The results indicated that the effluent reached the standard of domestic and drinking water quality (the ammonia concentration < 3 mgN/L) at all investigated ammonia concentrations. The specific nitrification rate of the microbial carrier used reached the maximum value of about 3.76 kgN.m‐3.day‐1 with the hydraulic retention time lower than 0.4 h and feed ammonia concentration of about 50 mgN/L. The biomass density in biofiltration column before experimental implementation was about 1000 mg/L.

Improvement of Nitrification Efficiency by Activated Nitrifying Bacteria Injection at Low Temperature

In this study, we have developed a lab scale bioreactor to identify the characteristics of nitrification reaction according to operation condition (temperature, inhibitor (as Cl), activated nitrifying bacteria (ANB). etc) to improve nitrification efficiency at low temperature. Recovery rate of nitrification took about 4 days to reach the normal level by injected ANB after inhibition shock of CI injection at 20oC, when measured the concentration of NO2 −-N+NO3 −-N in the effluent. In the case of 10oC, recovery of nitrification rate took about 4 days to reach the level of half to the normal level and 7 days for complete recovery which took 3 days more than those at 20oC. At 10oC considering the winter season, the specific nitrification rate(SNR) of the from 1 day to 6 days after injected ANB according to its operation condition increased from 0.029 to 0.767 mgN/gSS/hr. The simulated SNR for the 8th day after the injected ANB at 10oC was 0.840, 3.625 mgN/gSS/hr, respectively as linear function and exponential function, expecting to exceed level of 2.592 mgN/gSS/hr at normal condition. It was confirmed that injection of ANB during low temperature operation has many effects for improving nitrification efficiency through this study. In future studies, if further studies are carried out the determination of ANB injection and the design of efficient ANB reactor considering the changes of operating characteristics by site, it will contribute to the improvement of nitrification efficiency in winter season.

Specific Activity Bioassays as Tools to Evaluate Combined Nitrogen and Organic Matter Removal in SND Systems

Abstract This article assesses nitrifying and heterotrophic activity potentials, aiming to ward off future efficiency losses in biological treatment systems. For this purpose, we used biomass developed in two-hybrid fluidized bed reactors (FBRs) treating vinasse from ethanol and sugar beet production. FBRs filled with sepiolite and granular activated carbon (GAC) were used with short cycle aeration (25/15 and 15/15 min) and different hydraulic retention times (4.9 and 7.4 h). At the end of each operational condition, attached and suspended fractions of biomass from both FBRs were collected for activity bioassays. Specific nitrification bioassays suggested that nitrification performance (53–100% for sepiolite FBR and 72–93% for GAC FBR) was associated with the limit of the nitrifiers' potential when the environmental conditions were favorable. On the other hand, low denitrification efficiencies observed in the FBRs (25–44% for sepiolite FBR and 22–65% for GAC FBR) occurred due to low electron availability ...

Bioaugmentation with Nitrifying Granules in Low-SRT Flocculent Activated Sludge at Low Temperature.

Nitrifying granules were grown in a sidestream reactor fed municipal anaerobic digestion centrate and added in an initial slug dose and subsequent smaller daily doses to a non-nitrifying mainstream activated sludge system at 12 °C and 2.5-day aerobic solids retention time (SRT) to increase its nitrification capacity. Effluent NH3-N concentrations less than 1 mg/L were achieved with bioaugmentation, and nitrification was immediately lost when granules were removed after 30 days of bioaugmentation. Molecular microbial analyses indicated that nitrifying organisms remained attached to granules in the mainstream system with little loss to the flocculent sludge. Maximum specific nitrification activity of the bioaugmented granules decreased in mainstream treatment but the nitrification capacity remained due to new granule growth in the mainstream. This study demonstrated that bioaugmentation with sidestream nitrifying granules can intensify nitrification capacity in low-SRT, low-temperature flocculent activated sludge systems to achieve low effluent NH3-N concentrations and nitrogen removal.

Membrane fouling control and enhanced removal of pharmaceuticals and personal care products by coagulation-MBR

We investigated the effects of the addition of two coagulants−polyaluminium chloride (PACl) and chitosan−into the membrane bioreactor (MBR) process on membrane fouling and the removal of pharmaceuticals and personal care products (PPCPs). Their addition at optimized dosages improved the permeability of the membrane by reducing the concentration of soluble microbial products in mixed liquor, the content of inorganic elements, and irreversible fouling of the membrane surface. During long-term operation, the addition of PACl increased removal efficiencies of tetracycline, mefenamic acid, atenolol, furosemide, ketoprofen, and diclofenac by 17–23%. The comparative evaluation using mass balance calculations between coagulation-MBR (with PACl addition) and control-MBR (without PACl addition) showed that enhanced biodegradability played a key role in improving removal efficiencies of some PPCPs in coagulation-MBR. Coagulation-MBR also had higher oxygen uptake rates and specific nitrification rates of microorganisms. Overall, our findings suggest that the combination of MBR with coagulation reduced membrane fouling, lengthening operation period of the membrane, and improved the removal of some PPCPs as a result of enhanced biodegradability.

The short-term effects of nitrification inhibitors on the abundance and expression of ammonia and nitrite oxidizers in a long-term field experiment comparing land management

Microcosms were set up to evaluate the effect of nitrification inhibitors (DCD, c-PTiO, and NaClO3) on the abundance and expression of ammonia-oxidizing bacteria (AOB) and archaea (AOA), as well as the nitrite-oxidizing bacteria (NOB) Nitrospira and Nitrobacter. Both DCD and NaClO3 inhibited the net nitrification rate, while c-PTiO had no significant effects, and NaClO3 had a much greater inhibitory effect (> 60%) in all soils than DCD. No significant changes in total microbial abundance were observed with DCD and NaClO3. DCD limited only the growth of AOB; however, NaClO3 inhibited growth of both AOA and Nitrospira-NOB with no significant effects on AOB and Nitrobacter-NOB. Probably NaClO3 inhibited both ammonia oxidation and nitrite oxidation. This is the first report to reveal the inhibitory effects of NaClO3 on a specific nitrification process, helping to clarify the ecological niche of nitrifiers and the potential of nitrification inhibitors applied to soil.

Determining the effects of tillage and nitrogen sources on soil N2O emission

Soil tillage and fertilization can affect the abundance of nitrifying and denitrifying microbial communities known to regulate N2O losses from agricultural soils. We assessed the effects of mineral and organic N sources on short-term N2O emissions from a Rhodic Nitisol under contrasting soil disturbance. The experiment followed a split-plot design with two soil tillage systems as main plots (tilled soil: TS, and no-till soil: NTS) and five fertilization treatments as subplots, where 140kgNha−1 were applied either as urea (UR), raw swine slurry (RS), anaerobically digested swine slurry (ADS), or composted swine slurry (CS). A treatment without N fertilization was used as control (CTR). N2O emissions were determined by using static chambers and correlated with soil (0–0.1m) temperature, water-filled pore space (WFPS), dissolved organic carbon (DOC), ammonium (NH4+-N), nitrate (NO3−-N) and the abundance of specific nitrification and denitrification biomarker genes [ammonium monooxygenase (amoA), nitrate- (narG), nitrite- (nirS), nitric oxide- (qnorB) and nitrous oxide reductases (nosZ)]. Denitrification was the main source of N2O as assessed by increased narG/16S rDNA and narG/nosZ ratios regardless of soil tillage. N2O emissions were augmented in the NTS (30 to 200% higher than TS) where higher soil WFPS (0.6-0.7cm3cm−3) favored incomplete denitrification. The application of ADS in the NTS decreased denitrification rates and cumulative N2O emission by 47% in comparison with RS (2.9 and 5.6kgN2O-Nha−1, respectively). Interestingly, N2O emission from the NTS receiving CS (4.7kgN2O-Nha−1) was also promoted by the proliferation of heterotrophic nitrifying bacteria communities. Overal, swine slurry treatment can help mitigate N2O emission from agricultural soils, particularly in regions where this source of fertilizer is abundant and readily available.

Nitrogen and phosphorus treatment of marine wastewater by a laboratory-scale sequencing batch reactor with eco-friendly marine high-efficiency sediment

ABSTRACTWe screened and identified a NH3–N-removing bacterial strain, Bacillus sp. KGN1, and a removing strain, Vibrio sp. KGP1, from 960 indigenous marine isolates from seawater and marine sediment from Tongyeong, South Korea. We developed eco-friendly high-efficiency marine sludge (eco-HEMS), and inoculated these marine bacterial strains into the marine sediment. A laboratory-scale sequencing batch reactor (SBR) system using the eco-HEMS for marine wastewater from land-based fish farms improved the treatment performance as indicated by 88.2% removal efficiency (RE) of total nitrogen (initial: 5.6 mg/L) and 90.6% RE of total phosphorus (initial: 1.2 mg/L) under the optimal operation conditions (food and microorganism (F/M) ratio, 0.35 g SCODCr/g mixed liquor volatile suspended solids (MLVSS)·d; dissolved oxygen (DO) 1.0 ± 0.2 mg/L; hydraulic retention time (HRT), 6.6 h; solids retention time (SRT), 12 d). The following kinetic parameters were obtained: cell yield (Y), 0.29 g MLVSS/g SCODCr; specific growth rate (µ), 0.06 d−1; specific nitrification rate (SNR), 0.49 mg NH3–N/g MLVSS·h; specific denitrification rate (SDNR), 0.005 mg /g MLVSS·h; specific phosphorus uptake rate (SPUR), 0.12 mg /g MLVSS·h. The nitrogen- and phosphorus-removing bacterial strains comprised 18.4% of distribution rate in the microbial community of eco-HEMS under the optimal operation conditions. Therefore, eco-HEMS effectively removed nitrogen and phosphorus from highly saline marine wastewater from land-based fish farms with improving SNR, SDNR, and SPUR values in more diverse microbial communities.Abbreviations: DO: dissolved oxygen; Eco-HEMS: eco-friendly high efficiency marine sludge; F/M: food and microorganism ratio; HRT: hydraulic retention time; ML(V)SS: mixed liquor (volatile) suspended solids; NCBI: National Center for Biotechnology Information; ND: not determined; qPCR: quantitative real-time polymerase chain reaction; RE: removal efficiency; SBR: sequencing batch reactor; SD: standard deviation; SDNR: specific denitrification rate; SNR: specific nitrification rate; SPUR: specific phosphate uptake rate; SRT: solids retention time; T-N: total nitrogen; T-P: total phosphorus; (V)SS: (volatile) suspended solids; w.w.: wet weight

Challenges in using allylthiourea and chlorate as specific nitrification inhibitors

Allylthiourea (ATU) and chlorate (ClO3−) are often used to selectively inhibit nitritation and nitratation. In this work we identified challenges with use of these compounds in inhibitory assays with filter material from a biological rapid sand filter for groundwater treatment. Inhibition was investigated in continuous-flow lab-scale columns, packed with filter material from a full-scale filter and supplied with NH4+ or NO2−. ATU concentrations of 0.1–0.5 mM interfered with the indophenol blue method for NH4+ quantification leading to underestimation of the measured NH4+ concentration. Interference was stronger at higher ATU levels and resulted in no NH4+ detection at 0.5 mM ATU. ClO3− at typical concentrations for inhibition assays (1–10 mM) inhibited nitratation by less than 6%, while nitritation was instead inhibited by 91% when NH4+ was supplied. On the other hand, nitratation was inhibited by 67–71% at 10–20 mM ClO3− when NO2− was supplied, suggesting significant nitratation inhibition at higher NO2− concentrations. No chlorite (ClO2−) was detected in the effluent, and thus we could not confirm that nitritation inhibition was caused by ClO3− reduction to ClO2−. In conclusion, ATU and ClO3− should be used with caution in inhibition assays, because analytical interference and poor selectivity for the targeted process may affect the experimental outcome and compromise result interpretation.

Simultaneous removal of organic carbon and nitrogen pollutants in the Yangtze estuarine sediment: The role of heterotrophic nitrifiers

The Yangtze Estuary is one of the most eutrophic coastal areas in the world. The engagement of heterotrophic nitrification bacteria in the simultaneous removal of organic carbon and ammonium in the Yangtze estuarine sediment was investigated. The specific nitrification rate in the selective autotrophic nitrification inhibition treatment was about 25% of that in the control without autotrophic nitrification inhibition, suggesting that heterotrophic nitrification, in addition to autotrophic nitrification, was an important nitrification process in the sediment. The increase of heterotrophic nitrification can offset the decrease in autotrophic nitrification, which subsequently leads to the high tolerance of nitrification to the organic carbon. The number of heterotrophic nitrification bacteria was 7.1 × 107 MPN g−1 in sediment collected from Site 1 while that of autotrophic nitrification bacteria was 4.2 × 108 MPN g−1. The isolation of heterotrophic nitrification bacteria provides direct evidence of the engagement of heterotrophs in the nitrification of the Yangtze estuarine sediment. The results show that nitrification is catalyzed by both the autotrophs and the heterotrophs, indicating functional redundancy of nitrification in sediment. Since organic carbon usually coexists with ammonium, these findings indicate an alternative bioprocess for the simultaneous removal of organic carbon and ammonium in Yangtze estuarine sediment.

Free nitrous acid and pH determine the predominant ammonia-oxidizing bacteria and amount of N2O in a partial nitrifying reactor.

We investigated the effects of free ammonia (FA) and free nitrous acid (FNA) concentrations on the predominant ammonia-oxidizing bacteria (AOB) and the emission of nitrous oxide (N2O) in a lab-scale sequencing batch reactor for partial nitrification. The reactor was operated with stepwise increases in the NH4+ loading rate, which resulted in a maximum FA concentration of 29.3mg-N/L at pH 8.3. Afterwards, FNA was increased by a gradual decrease of pH, reaching its maximum concentration of 4.1mg-N/L at pH 6.3. Fluorescence in situ hybridization indicated that AOB remained predominant during the operation, achieving specific nitrification rates of 1.04 and 0.99g-N/g-VSS/day at the highest accumulations of FA and FNA, respectively. These rates were in conjunction with partial nitrification efficiencies of >84%. The N2O emission factor of oxidized NH4+ was 0.90% at pH7.0, which was higher than those at pH 8.3 (0.11%) and 6.3 (0.12%), the pHs with the maximum FA and FNA concentrations, respectively. High-throughput sequencing of 16S ribosomal RNA genes showed that increases in FNA drastically changed the predominant AOB species, although increased FA produced no significant changes. This study demonstrates that the FNA concentration and pH are the main drivers that determine the predominant AOB species and N2O-emission in a partial nitrifying bioreactor.

Wastewater ammonia removal using an integrated fixed-film activated sludge-sequencing batch biofilm reactor (IFAS-SBR): Comparison of suspended flocs and attached biofilm

Integrated fixed-film activated sludge (IFAS) that combines the activated sludge (suspended flocs) and attached biofilm has been applied in municipal wastewater treatment to promote nitrification. This study investigated the changes in reactor performance and bacterial community structure in response to different organic loadings (500, 250, 150 mg/L COD) in an integrated fixed-film activated sludge (IFAS) reactor operated under sequencing batch mode. Changes of bacterial population in the suspended flocs and attached biofilm were compared. Biomass in the suspended flocs and in biofilm decreased as the organic loading decreased. The specific nitrification rate was highest when COD was only 150 mg/L in the feeding, which highlighted the effects of competition between heterotrophic bacteria and autotrophic bacteria over oxygen and space. Besides, lack of carbon sources limited denitrification activities. The percentages of nitrifying related genes over total genes were higher in biofilms as compared to those in activated sludge flocs, indicating biofilm was a more favorable habitat for nitrifiers. In addition, extracellular polymeric substance (EPS) in biofilm and suspended flocs changed differently in response to the organic loading changes, which might also be related to the microbial population changes.

Nitrogen Removal from Anaerobically Digested Swine Waste Centrate Using a Laboratory-Scale Chabazite-Sequencing Batch Reactor

Abstract Anaerobic digestion (AD) is widely used for the treatment of livestock waste because the biogas produced can be utilized as energy source. Further treatment of AD effluents is often required for total nitrogen (TN) removal, which is typically carried out using biological nitrogen removal processes. However, the high free ammonia (FA) concentrations present in AD effluents can inhibit nitrification processes. This research tested a sequencing batch reactor (SBR) amended with particulate chabazite (chabazite-SBR) for removal of TN from anaerobically digested swine waste centrate. In the chabazite-SBR, zeolitic material with a high ion exchange (IX) capacity for NH4+ is used to ease nitrification inhibition. Once nitrification is complete, an external organic electron donor is supplied during an anoxic stage to promote denitrification. An overall TN removal efficiency of 84% was achieved in a laboratory-scale chabazite-SBR, with specific nitrification and denitrification rates of 0.43 and 1.49 mg-N/...

Artificial Intelligence for the Evaluation of Operational Parameters Influencing Nitrification and Nitrifiers in an Activated Sludge Process.

Nitrification at a full-scale activated sludge plant treating municipal wastewater was monitored over a period of 237days. A combination of fluorescent in situ hybridization (FISH) and quantitative real-time polymerase chain reaction (qPCR) were used for identifying and quantifying the dominant nitrifiers in the plant. Adaptive neuro-fuzzy inference system (ANFIS), Pearson's correlation coefficient, and quadratic models were employed in evaluating the plant operational conditions that influence the nitrification performance. The ammonia-oxidizing bacteria (AOB) abundance was within the range of 1.55 × 10(8)-1.65 × 10(10) copiesL(-1), while Nitrobacter spp. and Nitrospira spp. were 9.32 × 10(9)-1.40 × 10(11) copiesL(-1) and 2.39 × 10(9)-3.76 × 10(10) copiesL(-1), respectively. Specific nitrification rate (qN) was significantly affected by temperature (r 0.726, p 0.002), hydraulic retention time (HRT) (r -0.651, p 0.009), and ammonia loading rate (ALR) (r 0.571, p 0.026). Additionally, AOB was considerably influenced by HRT (r -0.741, p 0.002) and temperature (r 0.517, p 0.048), while HRT negatively impacted Nitrospira spp. (r -0.627, p 0.012). A quadratic combination of HRT and food-to-microorganism (F/M) ratio also impacted qN (r (2) 0.50), AOB (r (2) 0.61), and Nitrospira spp. (r (2) 0.72), while Nitrobacter spp. was considerably influenced by a polynomial function of F/M ratio and temperature (r (2) 0.49). The study demonstrated that ANFIS could be used as a tool to describe the factors influencing nitrification process at full-scale wastewater treatment plants.

Different responses of soil microbial metabolic activity to silver and iron oxide nanoparticles.

The knowledge regarding the effects of metal or metal oxide nanoparticles on soil microbial metabolic activity and key ecological functions is limited, relative to the information about their species diversity. For this reason, the responses of soil microbial metabolic activity to silver (AgNPs) and iron oxide (FeONPs) nanoparticles, along concentration gradients of each, were evaluated by microcalorimetry and soil nitrification potential. The changes in abundances of bacteria, eukaryotes and ammonia-oxidizing bacteria were measured by real time quantitative PCR. It was found that AgNP (at 0.1, 1 and 10 mg kg(-1) soil) amendments decreased soil microbial metabolic activity, nitrification potential and the abundances of bacteria and ammonia-oxidizing bacteria; on the contrary, FeONPs had the positive effects on soil microbial metabolic activity (at 1 and 10 mg kg(-1) soil) and soil nitrification potential (at 0.1 and 1 mg kg(-1) soil). Specific microbial metabolic activity and specific nitrification potential further revealed that metal or metal oxide nanoparticles could change the C and N cycles of the agricultural soil through influencing soil microbial metabolism. These findings could deepen the understanding of the influence of NPs on soil microorganisms and their driven soil ecology process.

Fertility practices and rhizosphere effects alter ammonia oxidizer community structure and potential nitrification activity in pepper production soils

Increasing nitrogen use efficiency is critical to the productivity and long-term sustainability of vegetable production systems in the US Midwest. Understanding the impact of alternative fertility sources on the ecology of the soil nitrogen cycle has potential to allow for management that will increase crop N uptake and reduce loss. We determined how repeated applications of urea, composted chicken litter, hairy vetch green manure with alfalfa meal, and an unfertilized control affected the structure and potential nitrification activity (PNA) of ammonia oxidizers in bulk and rhizosphere soil when N needs were expected to be high. PNA was greater in animal and green manure treatments relative to urea and the unfertilized control in bulk soil, and greater in the rhizosphere relative to bulk soil regardless of fertility treatment. A strong correlation was observed between PNA and ammonia oxidizing bacteria (AOB) abundance, suggesting that AOB rather than ammonia oxidizing archaea (AOA) controlled nitrification in this system. However, AOB abundance did not differ between bulk and rhizosphere soil, and PNA was lower in the urea treatment despite greater AOB abundance indicating that other factors could have affected PNA. For example, greater availability of labile carbon (C) could have stimulated PNA through various mechanisms, and lower pH and/or specific nitrification potential per AOB cell could have reduced PNA in the urea treatment. AOB community structure was more diverse in all fertility treatments relative to the unfertilized control in bulk soil, and community structure differed between bulk and rhizosphere soil indicating niche differentiation. However, differences in AOB community structure and PNA were only observed in rhizosphere relative to bulk soil indicating that the rhizosphere had a greater effect on nitrification dynamics than fertility practices. These findings indicate that organic fertility amendments stimulate PNA, but they could also increase N loss and should be investigated further. The rhizosphere appears to play a greater role in nitrification dynamics than fertility practices, and more detailed investigations at this key plant-soil interface are warranted.

Biological treatment of reverse osmosis concentrate from low salinity water

With increasing water demand and growing scarcity of potable water, the reuse of water recovered from low salinity water like sewage or surface water is becoming an important issue from both technical and economic points of view. The reverse osmosis (RO) membrane processes widely used for water recovery inevitably produce RO concentrate having very high concentrations of salts and other materials of concern. Disposal to nature or feeding back into the recovery facility can be an option, but may have an impact on environment and raise legal problems. This study deals with the biological treatment of RO concentrate produced during water reclamation processes. The RO concentrate studied had low BOD5 and T-P, but high T-N and COD concentrations. The sequencing batch reactor (SBR) process and the modified Ludzack-Ettinger (MLE) process were compared in controlled lab-scale experiments. The pilot-scale plant was operated to evaluate the performance of the SBR process under more realistic conditions. Kinetic parameters such as specific substrate utilization rate (SSUR), specific nitrification rate (SNR), and specific denitrification rate (SDNR) were obtained, and empirical equations were derived relating these parameters to the food-to-micro-organism (F/M) ratio. These parameters could prove useful tools for process design, operation, and improvement of anoxic and aeration tanks. Non-biodegradable COD components in the RO concentrate turned out to be hard to remove, which implies some physical or chemical process (e.g. flocculation, precipitation, or adsorption) may be needed in addition to the biological treatment process.

Reduction of waste biosolids by RAS-ozonation: Model validation and sensitivity analysis for biosolids reduction and nitrification

Biosolids reduction model by return activated sludge ozonation was validated by simulating nitrification data compiled from our pilot-scale and the literature studies. Then, a global sensitivity analysis (GSA) was performed to identify influential and non-influential parameters for biosolids reduction efficiency, change in specific nitrification activity (SNA), and alteration to expected nitrification stability. In general, the model outputs were sensitive to operational and ozone reaction parameters, but not to biochemical parameters. For operational parameters, mainly temperature and initial solids retention time (SRT) influenced all model outputs. For biosolids reduction, increase in the degradability of the influent COD decreased the reduction efficiency. For SNA, the changes were highly dependent on the influent TKN/COD ratio. Our findings also imply that the stability of the nitrification process in ozonated systems should be enhanced at constant MLVSS for warm temperatures, but could be reduced at temperatures below 12 °C and aerated SRTs below 10 days.

Conversion of forest to agricultural land affects the relative contribution of bacteria and fungi to nitrification in humid subtropical soils

Land-use and management practices can affect soil nitrification. However, nitrifying microorganisms responsible for specific nitrification process under different land-use soils remains unknown. Thus, we investigated the relative contribution of bacteria and fungi to specific soil nitrification in different land-use soils (coniferous forest, upland fields planted with corn and rice paddy) in humid subtropical region in China. 15N dilution technique in combination with selective biomass inhibitors and C2H2 inhibition method were used to estimate the relative contribution of bacteria and fungi to heterotrophic nitrification and autotrophic nitrification in the different land-use soils in humid subtropical region. The results showed that autotrophic nitrification was the predominant nitrification process in the two agricultural soils (upland and paddy), while the nitrate production was mainly from heterotrophic nitrification in the acid forest soil. In the upland soils, streptomycin reduced autotrophic nitrification by 94%, whereas cycloheximide had no effect on autotrophic nitrification, indicating that autotrophic nitrification was mainly driven by bacteria. However, the opposite was true in another agricultural soil (paddy), indicating that fungi contributed to the oxidation of NH4+ to NO3−. In the acid forest soil, cycloheximide, but not streptomycin, inhibited heterotrophic nitrification, demonstrating that fungi controlled the heterotrophic nitrification. The conversion of forest to agricultural soils resulted in a shift from fungi-dominated heterotrophic nitrification to bacteria- or fungi-dominated autotrophic nitrification. Our results suggest that land-use and management practices, such as the application of N fertilizer and lime, the long-term waterflooding during rice growth, straw return after harvest, and cultivation could markedly influence the relative contribution of bacteria and fungi to specific soil nitrification processes.