High Total Ammonia Nitrogen Concentration Research Articles

Biofilm cultivation of chlorella species. MUR 269 to treat anaerobic digestate food effluent (ADFE): Total ammonia nitrogen (TAN) concentrations effect

Microalgal-based treatment of anaerobic digestate food effluent (ADFE) has been found to be efficient and effective. However, turbidity and high total ammonia nitrogen (TAN)) content of ADFE is a major setback, requiring significant dilution. Although the possibility of growing microalgae in a high-strength ADFE with minimal dilution has been demonstrated in suspension cultures, such effluents remain highly turbid and affect the light path in suspension cultures. Here, the feasibility of growing Chlorella sp.MUR 269 in biofilm to treat ADFE with high TAN concentrations was investigated. Six different TAN concentrations in ADFE were evaluated for their effects on biofilm growth and nutrient removal by Chlorella sp. MUR 269 using the perfused biofilm technique. Biomass yields and productivities of this alga at various TAN concentrations (mg N NH3 L−1) were 55a (108 g m−2 and 9.80 g m−2 d−1)>100b > 200c = 300c = 500c > 1000d. Growth was inhibited, resulting in a 28% reduction in yield of Chlorella biofilm when this alga was grown at 1000 mg N NH3 L−1. A survey of the photosynthetic parameters reveals evidence of stress occurring in the following sequence: 55 < 100<200 < 300<1000. A significant nutrient removal was observed across various TAN concentrations. The removal pattern also followed the concentration gradients except COD, where the highest removal occurred at 500 mg N NH3 L−1. Higher removal rates were seen at higher nutrient concentrations and declined gradually over time. In general, our results indicated that the perfused biofilm strategy is efficient, minimizes water consumption, offers easy biomass harvesting, and better exposure to light. Therefore, it can be suitable for treating turbid and concentrated effluent with minimal treatment to reduce the TAN concentration.

Overcoming hydrogen loss in single-chamber microbial electrolysis cells by urine amendment

The effective hydrogen production in single-chamber microbial electrolysis cells (MECs) has been seriously challenged by various hydrogen consumers resulting in substantial hydrogen loss. In previous studies, the total ammonia nitrogen (TAN) has been used to inhibit certain hydrogen-consuming microorganisms to enhance hydrogen production in fermentation. In this study, we explored the feasibility of using source-separated urine to overcome hydrogen loss in the MEC, with the primary component responsible being TAN generated via urea hydrolysis. Experimental results revealed that the optimal TAN concentration ranged from 1.17 g N/L to 1.75 g N/L. Within this range, the hydrogen production rate substantially improved from less than 100 L/(m3·d) up to 520 L/(m3·d), and cathode recovery efficiency and energy recovery efficiency were greatly enhanced, with the hydrogen percentage achieved over 95 % of the total gas volume, while maintaining uninterrupted electroactivity in the anode. Compared to using chemically added TAN, using source separated urine as the source of ammonia also showed the effect of overcoming hydrogen loss but with lower Coulombic efficiency due to the complex organic components. Pre-adaptation of the reactor with urea enhanced hydrogen production by nearly 60 %. This study demonstrated the effectiveness of TAN and urine in suppressing hydrogen loss, and the results are highly relevant to MECs treating real wastewater with high TAN concentrations, particularly human fecal and urine wastewater.

Combined zeolite-based ammonia slow-release and algae-yeast consortia to treat piggery wastewater: Improved nitrogen and carbon migration

Integration of zeolite-based ammonia adsorption and algae-yeast consortia was developed to remediate piggery wastewater (PW) containing high concentrations of total ammonia nitrogen (TAN) and total organic carbon (TOC). After optimizing the conditions of ammonia adsorption in the PW. Zeolite addition mitigated ammonia toxicity, allowing zeolites to gradually release ammonia while effectively attenuating algal oxidative stress caused by high TAN concentration. Coupling zeolite-based adsorption and yeast co-incubation further increased TOC degradation and available C/N ratio, thus improving biomass (4.51 g/L), oil yield (2.11 g/L), and nutrient removal (84.18%-99.14%). The integrated microalgae-based PW treatment exhibited higher carbon migration into biomass (46.14%) and reduced treatment costs than conventional approaches. Simultaneously, the lowest carbon migration to wastewater also meant the smallest carbon emission into water bodies. These findings demonstrate that this novel strategy can remove nutrients in raw PW effectively and produce high oil-rich biomass in a sustainable and environmentally-friendly manner.

Dynamics of Microbial Community During Nitrification Biofilter Acclimation with Low and High Ammonia.

The acclimation of a nitrifying biofilter is a crucial and time-consuming task for setting up a recirculating aquaculture system (RAS). Gaining a better understanding of the dynamics of the microbial community during the acclimation period in the system could be useful for the development of mature nitrifying biofilters. In this study, high-throughput DNA sequencing was applied to monitor the microbial communities on a biofilter during the acclimation period (7weeks) in high (100mgN/L) and low (5mgN/L) total ammonia nitrogen (TAN) treatments. Both treatments were successful for developing a mature nitrifying biofilter, dominated by Proteobacteria, Bacteroidetes, and Nitrospirae. Complete nitrification was found after 7days of biofilter acclimation as indicated by decreasing TAN concentration, increasing nitrate concentration, and high abundances of the nitrifying bacteria, Nitrosomonadaceae and Nitrospiraceae. The beta diversity analysis of microbial communities showed different clustering of the samples between high and low TAN treatment groups. A greater abundance of nitrifying bacteria was found in the high TAN treatments (27-51%) than in the low TAN treatment (15-29%). The bacterial diversity in biofilters acclimated at high TAN concentration (Shannon's index 5.40-6.15) were lower than those found at low TAN treatment levels (Shannon's index 6.40-7.01). The higher diversity in biofilters acclimated at low TAN concentrations, consisting of Planctomycetes and Archaea, might benefit the nutrient recycling in the system. Although nitrification activity was observed from the first week of the acclimation period, the acclimation period should be taken as at least 6weeks for full development of nitrifying biofilm. Moreover, the reduction of potentially pathogenic Vibrio on biofilters was found at that period.

Spatial distribution and activity patterns as welfare indicators in response to water quality changes in European sea bass, Dicentrarchus labrax

In aquaculture, fish are exposed to unavoidable stressors that can be detrimental for their health and welfare. However, welfare in farmed fish can be difficult to assess, and, so far, no standardized test has been universally accepted as a welfare indicator. This work contributes to the establishment of behavioural welfare indicators in a marine teleost in response to different water quality acute stressors. Groups of ten fish were exposed to high Total Ammonia Nitrogen concentration (High TAN, 18 mg.L-1), Hyperoxia (200 % O2 saturation), Hypoxia (20 % O2 saturation), or control water quality (100% O2 saturation and TAN < 2.5 mg.L-1) over 1 hour. Fish were then transferred in a novel environment for a group behaviour test under the same water quality conditions over 2 hours. Videos were recorded to assess thigmotaxis, activity and group cohesion. After this challenge, plasma cortisol concentration was measured in a subsample, while individual behavioural response was measured in the other fish using novel tank diving test. Prior to this study, the novel tank diving test was validated as a behavioural challenge indicative of anxiety state, by using nicotine as anxiolytic drug. Overall, all stress conditions induced a decrease in activity and thigmotaxis and changes in group cohesion while only fish exposed to Hypoxia and High TAN conditions displayed elevated plasma cortisol concentrations. In post-stress condition, activity was still affected but normal behaviour was recovered within the 25 minutes of the test duration. Our work suggests that the activity, thigmotaxis and group cohesion are good behavioural indicators of exposure to degraded water quality, and could be used as standardized measures to assess fish welfare.

Anodic performance of microbial electrolysis cells in response to ammonia nitrogen

In this study, the authors investigated how various total ammonia nitrogen (TAN) concentrations (128–1231 mg nitrogen/l) in the substrate medium affect the anodic performance of dual-chamber microbial electrolysis cells (MECs) with an anion-exchange membrane (AEM) and a cation-exchange membrane (CEM). The current densities and midpoint potentials of the bioanode in the AEM-MEC were independent of TAN concentration changes. In comparison, current densities in the CEM-MEC considerably dropped at a high TAN concentration of 1231 mg nitrogen/l, and the midpoint potential of the bioanode became increasingly positive, indicating that the anode biofilm was negatively affected by a high TAN concentration. Comparison of pH and TAN concentration changes in the anolyte in the CEM-MEC suggests that high levels of TAN did not directly influence anode-respiring bacteria (ARB) metabolism; accumulation of protons was the primary reason for the deterioration of anodic performance. However, the patterns of changes in chemical oxygen demand (COD) removal efficiencies and coulombic efficiencies in response to increased TAN concentrations were quite similar in the two MECs. The COD removal efficiencies also decreased at elevated TAN concentrations, while coulombic efficiencies increased, suggesting that non-ARB activity was reduced in both MECs.

Anaerobic digestion of chicken manure: Influence of trace element supplementation.

In this study, anaerobic digestion of nitrogen-rich chicken (egg-laying hen) manure at different trace element (TE) mix doses and different total ammonia nitrogen (TAN) concentrations was investigated in batch digestion experiments. With respect to nonsupplemented TE sets, addition of TE mixture containing 1 mg/L Ni, 1 mg/L Co, 0.2 mg/L Mo, 0.2 mg/L Se, 0.2 mg/L W, and 5 mg/L Fe at TAN concentrations of 3000mg/L and 4000 mg/L, cumulative CH4 production and CH4 production rate improved by 7-8% and 5-6%, respectively. The results revealed that at a very high TAN concentration of 6000 mg/L, the effect of TE addition was significantly high and the cumulative CH4 production and production rate were increased by 20 and 39.5%, respectively. Therefore, it is concluded that at elevated TAN concentrations the CH4 production that was stimulated by TE supplementation was presumably occurred through syntrophic acetate oxidation.

Synergistic Effect of Sulfide and Ammonia on Anaerobic Digestion of Chicken Manure

The effect of the sulfur load on anaerobic digestion of chicken manure (CM) was investigated in a laboratory scale anaerobic mono-digester at high total ammonia nitrogen (TAN) concentrations. The digester was operated for 268 days by increasing the organic loading rate from 0.5 to 2.5 kg-VS/m3/day and the total Kjeldahl nitrogen up to 5050 mg/l. The CH4 yield of 0.36 ± 0.02 m3/kg-VS was achieved at 2.5 kg-VS/m3/day of loading rate without any inhibition. The results showed that, anaerobic mono-digestion of chicken manure was applicable with the acclimation of microbial consortium to high TAN concentrations. However, when the sulfur content of the CM fed to the digester increased suddenly by coincidence, the CH4 yield decreased about 25% from 0.36 ± 0.02 to 0.27 ± 0.03 m3/kg-VS. As a result, the acetic acid concentration increased from 130 to 1700 mg/l showing that the acetate consuming methanogens were detrimentally affected from TAN and total sulfide concentrations above 4000 and 100 mg/l, respectively.

Influence of ammonia in the anaerobic digestion of food waste

Ammonia toxicity was investigated in mesophilic (37°C) and thermophilic (55°C) digesters using high and low-nitrogen food wastes (FW). Mesophilic inoculum was successfully acclimated to thermophilic conditions by a step change in temperature followed by incremental increases in organic loading rate (OLR). Digestion performance and stability were monitored via volatile fatty acid (VFA) profiles, alkalinity, specific methane production (SMP) and volatile solids (VS) destruction. High-nitrogen mesophilic digesters stabilised by day 70 and responded well to increases in OLR, with a SMP of 0.45L CH4 g−1 VS, stable pH, and VFA <0.2gL−1. Thermophilic digesters fed on high and low-nitrogen FWs showed almost identical responses to acclimatisation. Behaviour then deviated, with high-nitrogen digesters accumulating VFA. Stable pH could be maintained for up to 310days before eventual failure at total ammonia nitrogen (TAN) concentration >5.0gNL−1, although accumulation of propionic and other longer-chain VFA began at TAN ∼3.5gNL−1. The low-nitrogen digesters showed no VFA accumulation, and had a SMP of ∼0.39L CH4 g VS L−1day−1 with 91% VS destruction. After 384days the TAN concentration was increased from ∼0.7gNL−1 by urea addition. This resulted in progressive VFA accumulation in one digester when TAN reached ∼3.5gNL−1, while stable operation at very low VFA was possible at up to ∼2.5gNL−1 in the second digester. The results confirmed acclimatisation to thermophilic conditions was possible on a far shorter timescale than to high TAN concentrations.

Once-through CO2 absorption for simultaneous biogas upgrading and fertilizer production

A new process is developed for biogas upgrading using the total ammonia nitrogen (TAN) in biogas slurry as a renewable absorbent. TAN in biogas slurry can be transferred into free ammonia by adding NaOH to increase the solution pH. Increasing the pH of biogas slurry to 10 causes that >90% TAN transfers into free ammonia, leading to high TAN removal ratios. However, further increasing the pH of biogas slurry has limited effects. Vacuum membrane distillation (VMD) has higher kinetics constants and thus is a more effective way to recover and enrich ammonia from biogas slurry compared with thermal or air stripping. After VMD, the recovered aqueous ammonia solution with high TAN concentrations and the enhanced biogas slurry can be used as “once-through” CO2 absorbents. With alkaline addition, VMD does not increase the CO2 absorption capacity, but significantly minimizes the phytotoxicity of biogas slurry. When NaOH dosage is below 0.25M, superior ammonia separation performance with high kinetics constants and low phytotoxicity can be achieved. The recovered aqueous ammonia solution also has excellent CO2 absorption performance for biogas upgrading and can help obtain high content of methane. This study provides an effective process for biogas upgrading with low costs and generation of valuable products, including high purity bio-methane, low phytotoxicity biogas slurry for agricultural application and high concentration NH4HCO3 as a fertilizer.

Mixing and scale affect moving bed biofilm reactor (MBBR) performance

Moving Bed Biofilm Reactors (MBBR) are used increasingly in closed systems for farming of fish. Scaling, i.e. design of units of increasing size, is an important issue in general bio-reactor design since mixing behaviour will differ between small and large scale. Research is mostly performed on small-scale biofilters and the question is to what extent this can be upscaled to a commercial level. Therefore, the objective of this research was to establish the effect of mixing and scale on MBBR performance. The research was done in two major parts; firstly effects of scale-sensitive factors were studied in small reactors. Secondly, performance of these small reactors was then compared to increasingly large reactor sizes, using the same inlet water quality and biofilm.Firstly, a 200L MBBR (medium scale) was operated continuously using a synthetic feed solution. Biofilm carriers from this reactor was used for short-term experiments in 0.8L reactors (small scale) and compared with the performance of the 200L medium scale reactor. Reactor geometry and superficial air velocity (mh−1) were identical in these experiments. Subsequently, the small reactors were incubated with biofilm carriers from three commercial farms and performance compared with these large scale reactors. In a number of additional experiments the effect of mixing and Total Ammonia Nitrogen (TAN) was tested at small and medium scale.The results showed that MBBR scale has a significant effect on TAN removal rate. In general, the larger the scale the better the performance. TAN removal (rTAN) at small scale (0.8L) is about 80% compared to that at medium scale (200L). The difference between small scale and large scale (>20m3) is even higher. These findings warrant further studies on whether a plateau is reached in rTAN at a certain scale; a study which will have considerable importance for optimal design and dimensioning of commercial scale RAS. It was further found that superficial air velocity is not a good scaling factor for MBBRs. Upscaling while maintaining geometry implies increasing air injection depth and therefore increased energy input will be required at a comparable superficial air velocity, which is not incorporated in the superficial air velocity term (mh−1). Superficial air velocity and media filling% were found to have a strong effect on mixing time at small scale. An air velocity below a threshold of 5mh−1 decreased TAN removal at both small and medium scale. Intense mixing at small scale increased TAN removal at low TAN concentration. However, at a high TAN concentration, the small scale MBBR always performed at not more than 80% of the capacity of the medium scale system, irrespective of the mixing conditions. Hence, the capacity of full scale systems will be under-estimated when based solely on small scale experiments.

Quantifying the percentage of methane formation via acetoclastic and syntrophic acetate oxidation pathways in anaerobic digesters

Ammonia concentration is one of the key factors influencing the methanogenic community composition and dominant methanogenic pathway in anaerobic digesters. This study adopted a radiolabelling technique using [2-14C] acetate to investigate the relationship between total ammonia nitrogen (TAN) and the methanogenic pathway. The radiolabelling experiments determined the ratio of 14CO2 and 14CH4 in the biogas which was used to quantitatively determine the percentage of CH4 derived from acetoclastic and syntrophic acetate oxidation routes, respectively.This technique was performed on a selection of mesophilic digesters representing samples of low to high TAN concentrations (0.2–11.1gkg−1 wet weight). In high TAN digesters, the ratio between 14CO2 and 14CH4 was in the range 2.1–3.0; indicating 68–75% of methane was produced via the hydrogenotrophic route; whereas in low ammonia samples the ratio was 0.1–0.3, indicating 9–23% of methane was produced by the hydrogenotrophic route. These findings have been confirmed further by phylogenetic studies.

CO2 absorption using biogas slurry: Recovery of absorption performance through CO2 vacuum regeneration

As a by-product of anaerobic biogas digestion using biomass as the substrates, raw biogas slurry (RBS) may be a renewable CO2 solvent to capture CO2 and fix CO2 into the crops/plants by forming organic carbon through carbon concentration mechanism (CCM). However its CO2 absorption performance should be enhanced greatly without deteriorating its inherent low phytotoxicity. Recovery and enhancement of CO2 absorption performance of RBS with initial total ammonia nitrogen (TAN) concentration (∼0.152mol-N/L) was investigated through stripping CO2 saturated in RBS during anaerobic digestion by vacuum regeneration technology. Additionally, phytotoxicity of the regenerated RBS (RegBS) after CO2 reabsorption was also evaluated in terms of EC50 value which represents the CO2-rich RegBS application concentration causing 50% inhibition to root elongation of mungbean seeds. Results showed that vacuum regeneration technology is a time-effective method to regenerate CO2 from RBS. And the activation energy of CO2 regeneration from RBS under 20kPa and 35–75°C is about 57.78kJ/mol. The main mechanism of CO2 regeneration from RBS may be the decomposition of ammonium bicarbonate. CO2 reabsorption capacity of RegBS is enhanced up to 0.125mol/L at 77°C and 40kPa, which is approximately 3.18-fold higher than that of RBS. If RBS with high TAN concentration can be adopted, much higher CO2 reabsorption capacity may be achieved. CO2-rich RegBS can obtain the higher EC50 value than RBS, indicating higher application concentrations in agriculture/horticulture, and hence lower phytotoxicities to crops and plants. The maximum EC50 value with 168.8mL/L can be achieved when using the CO2-rich RegBS obtained at 47°C and 10kPa. 77°C and 40kPa may be the optimum conditions to recover CO2 absorption performance of RBS in terms of higher CO2 reabsorption performance and lower phytoxicity of CO2-rich RegBS.

Anaerobic digestion of undiluted simulant human excreta for sanitation and energy recovery in less-developed countries

Improving access to sanitation is one of the most effective means to improve public health. Anaerobic digestion of high-strength undiluted human simulant excreta was investigated in laboratory systems. The focus was on demonstrating the suitability of using simple unmixed anaerobic digesters for the treatment of a simulant high-strength undiluted human excreta and to quantify the effects of high ammonia concentration on the biogas yield. A maximum biogas yield of 0.44NLbiogasg−1COD was obtained in batch experiments, while yields of 0.38 and 0.24NLbiogasg−1COD were obtained at 5 and 8g total ammonia nitrogen (TAN) L−1, respectively. Using an inoculum acclimated to high ammonia concentrations was critical to successful biogas production at these high TAN concentrations. Stable long-term anaerobic digestion of simulant human excreta at ammonia concentrations ranging from 5.20 to 7.15g-NL−1 was obtained in a scaled-down mimic of a low cost floating dome anaerobic digester. Overall, the results demonstrate that anaerobic digestion of undiluted human simulant excreta in simple unmixed digesters is feasible and yields biogas, which is a valuable commodity. When combined with proper hygienization of its effluent, anaerobic digestion could contribute to effective sanitation in developing countries with limited water availability.

Biogas production from chicken manure at different organic loading rates in a mesophilic-thermopilic two stage anaerobic system

This study investigates the biogas production from chicken manure at different organic loading rates (OLRs), in a mesophilic-thermophilic two stage anaerobic system. The system was operated on semi continuous mode under different OLRs [1.9g volatile solids (VS)/L·d - 4.7g VS/L·d] and total solid (TS) contents (3.0-8.25%). It was observed that the anaerobic bacteria acclimatized to high total ammonia nitrogen concentration (>3000mg/L) originated as a result of the degradation of chicken manure. High volatile fatty acid concentrations were tolerated by the system due to high pH in the reactors. The maximum average biogas production rate was found as 554mL/g VSfeed while feeding 2.2g VS/L-d (2.3% VS - 3.8% TS) to the system. Average methane content of produced biogas was 74% during the study.

An assessment of total ammonia nitrogen concentration in Alabama (USA) ictalurid catfish ponds and the possible risk of ammonia toxicity

Abstract An assessment of total ammonia nitrogen (TAN) concentration was conducted for 31 ictalurid catfish ponds on six farms, in the Blackland Prairie region of Alabama (USA). Five farms that provided production data had average annual feed inputs and harvest weights of 15,579–21,739 kg ha − 1 and 8104–12,344 kg ha − 1 , respectively. Concentrations of TAN were measured 26 times (weekly June through September and less frequently other months) between May 2013 and May 2014. The farm average, annual TAN concentrations were 1.05–1.78 mg L − 1 at five farms and 4.17 mg L − 1 at the other. Correlations were not found (P > 0.05) when pond average TAN concentration was regressed individually against feed input, weight fish harvested, and aeration rate. Nearly half of the TAN concentrations were − 1 , the majority were − 1 , but some ranged from 5 to 15 mg L − 1 . Analysis of the literature on ammonia toxicity to channel catfish suggested that the no-observed-effect level (NOEL) is around 1.0 mg L − 1 NH 3 -N in ponds with pH of 7.5 and above where NH 3 -N concentration fluctuates greatly because of daily change in temperature and especially pH. Based on the daily pH fluctuation of 7.5 to 9.5 observed in ponds, and typical monthly average water temperatures, the NOEL for NH 3 -N was often exceeded. At pH 8.5–8.9, depending upon the month, up to 14.5% of ponds exceeded the NOEL for NH 3 -N. The NOEL was exceeded by up to 31.5% of pond at pH ≥ 9.0. The findings reveal that TAN concentrations in Alabama ponds often are at chronically toxic levels for ictalurid catfish. There is usually no practical emergency treatment for reducing NH 3 -N (or TAN) concentration in ponds exceeding the NOEL. Thus, good management practices for avoiding excessively high TAN concentrations in ponds — efficient feed management, adequate aeration to promote nitrification, and treatments for maintaining buffering capacity in pond water should be applied.

Screening, Identification and Immobilization of Ammonia Oxidizing Bacterial Consortium Collected from Mangrove Areas and Shrimp Farms

The immobilization of nitrifying bacteria in alginate has been used to evaluate the performance of ammonia reduction. In this research, bacteria were screened and observed for their ability to reduce ammonia. Consortium M1, isolated from the mangrove area (Morib, Selangor) showed the most effective reduction of ammonia from an initial concentration of 2.17±0.10 to 0.06±0.01 mg L-1 in 14 days. The consortium was then identified to consist of Pseudomonas aeruginosa (99%), Pseudomonas stutzeri (98%) and Nocardioides albus (98%) using the 16S rDNA gene sequences via Polymerase Chain Reaction (PCR) technique and identified by phylogenetic analysis based on their partial 16S rDNA sequences comparison in NCBI GenBank. The consortium M1 was then immobilized into alginate beads each containing 1.79x103 CFU mL-1 bacteria cells before being tested for its efficacy in reducing ammonia under laboratory conditions using 10, 20, 30, 40, 50, 100, 150 and 200 beads. The fastest reduction rate of Total Ammonia Nitrogen (TAN) was observed in flasks containing 150 beads which on day 6, drastically reduced TAN from 2.50±0.10 to 0.090±0.059 mg L-1 followed by treatment with 200 beads (0.104±0.07 mg L-1). However, at the end of experiment at day 14, the lowest TAN level (0.083±0.063 mg L-1) was observed in flasks with 200 beads which was not significantly different (p>0.05) from flasks with 150 beads (0.106±0.034 mg L-1). The present study reveals that the immobilization of bacterial consortium consisting of ammonia oxidizing bacteria could be used as an alternative for reduction of high TAN concentration in shrimp or fish hatchery system.

A novel approach for ammonia removal from fresh-water recirculated aquaculture systems, comprising ion exchange and electrochemical regeneration

A new physico-chemical process for ammonia removal from fresh-water recirculated aquaculture systems (RASs) is introduced. The method is based on separating NH4+ from RAS water through an ion-exchange resin, which is subsequently regenerated by simultaneous chemical desorption and indirect electrochemical ammonia oxidation. Approach advantages include (1) only slight temperature dependence and no dependence on bacterial predators and chemical toxins; (2) no startup period is required and the system can be switched on and off at will; and (3) the fish are grown in much lower bacterial concentration, making the potential for both disease and off-flavor, lower. A small pilot scale RAS was operated for 51d for proving the concept. The system was stocked by 105 tilapia fish (initial weight 35.8g). The fish, which were maintained at high TAN (total ammonia nitrogen) concentrations (10–23mgNL−1) and fish density of up to 20kgm−3, grew at a rate identical to their established growth potential. NH3(aq) concentrations in the fish tank were maintained lower than the assumed toxicity threshold (0.1mgNL−1) by operating the pond water at low pH (6.5–6.7). The low pH resulted in efficient CO2 air stripping, and low resultant CO2(aq) concentrations (<7mgL−1). Due to efficient solids removal, no nitrification was observed in the fish tank and measured nitrite and nitrate concentrations were very low. The system was operated successfully, first at 10% and then at 5% daily makeup water exchange rate. The normalized operational costs, calculated based on data derived from the pilot operation, amounted to 28.7 $ cent per kg fish feed. The volume of the proposed process was calculated to be ∼13 times smaller than that of a typical RAS biofilter. The results show the process to be highly feasible from both the operational and economical standpoints.

Multi‐species nitrifying biofilm model (MSNBM) including free ammonia and free nitrous acid inhibition and oxygen limitation

A multi-species nitrifying biofilm model (MSNBM) is developed to describe nitrite accumulation by simultaneous free ammonia (FA) and free nitrous acid (FNA) inhibition, direct pH inhibition, and oxygen limitation in a biofilm. The MSNBM addresses the spatial gradient of pH with biofilm depth and how it induces changes of FA and FNA speciation and inhibition. Simulations using the MSNBM in a completely mixed biofilm reactor show that influent total ammonia nitrogen (TAN) concentration, bulk dissolved oxygen (DO) concentration, and buffer concentration exert significant control on the suppression of nitrite-oxidizing bacteria (NOB) and shortcut biological nitrogen removal (SBNR), but the pH in the bulk liquid has a weaker influence. Ammonium oxidation increases the nitrite concentration and decreases the pH, which together can increase FNA inhibition of NOB in the biofilm. Thus, a low buffer concentration can accentuate SBNR. DO and influent TAN concentrations are efficient means to enhance DO limitation, which affects NOB more than ammonia-oxidizing bacteria (AOB) inside the biofilm. With high influent TAN concentration, FA inhibition is dominant at an early phase, but finally DO limitation becomes more important as TAN degradation and biofilm growth proceed. MSNBM results indicate that oxygen depletion and FNA inhibition throughout the biofilm continuously suppress the growth of NOB, which helps achieve SBNR with a lower TAN concentration than in systems without concentration gradients.

20 - Clarifying the role of neuroimaging in the diagnosis of dementia

A new process is developed for biogas upgrading using the total ammonia nitrogen (TAN) in biogas slurry as a renewable absorbent. TAN in biogas slurry can be transferred into free ammonia by adding NaOH to increase the solution pH. Increasing the pH of biogas slurry to 10 causes that > 90% TAN transfers into free ammonia, leading to high TAN removal ratios. However, further increasing the pH of biogas slurry has limited effects. Vacuum membrane distillation (VMD) has higher kinetics constants and thus is a more effective way to recover and enrich ammonia from biogas slurry compared with thermal or air stripping. After VMD, the recovered aqueous ammonia solution with high TAN concentrations and the enhanced biogas slurry can be used as “once-through” CO2 absorbents. With alkaline addition, VMD does not increase the CO2 absorption capacity, but significantly minimizes the phytotoxicity of biogas slurry. When NaOH dosage is below 0.25 M, superior ammonia separation performance with high kinetics constants and low phytotoxicity can be achieved. The recovered aqueous ammonia solution also has excellent CO2 absorption performance for biogas upgrading and can help obtain high content of methane. This study provides an effective process for biogas upgrading with low costs and generation of valuable products, including high purity bio-methane, low phytotoxicity biogas slurry for agricultural application and high concentration NH4HCO3 as a fertilizer.