Nitrogen-rich Streams Research Articles

Using machine learning techniques to predict ammonium concentration in membrane contactors for nitrogen recovery as a valuable resource

The availability of real-time measurements of primary quality water variables is one of the key challenges in the wastewater treatment industry. However, due to the cost and maintenance requirements of sensors and probes for on-line measurement of primary quality variables, the prediction of these variables via data-driven approaches using as inputs easy-to-measure process variables has attracted research interest. In this paper, different machine learning techniques: feed-forward artificial neural network, random forest, support vector machine, gaussian process regression and partial least squares were used to predict in real-time the total ammonium nitrogen concentration during the operation of a hollow fibre membrane contactor. This recently developed technology allows the recovery of nitrogen from nitrogen rich streams (i.e. supernatant of anaerobic digesters in wastewater treatment plants) as ammonium sulphate (a marketable fertilizer). These contactors are usually operated in batch mode, pumping the high nitrogen concentration feed from the storage tank, where the total ammonium nitrogen concentration decreases progressively as the fertilizer is produced. Knowing the real-time concentration of total ammonium nitrogen in the storage tank would enable the optimization of the process operation, avoiding its operation with conservative fixed-time batch duration. The pH is an easy-to-measure process variable usually available in wastewater treatment plants that was used as input of the tested data-driven models, together with two extracted features from this variable (its derivative and increments after each reagent dosing). The number of total ammonium nitrogen measurements in the collected database is 2350 data points (corresponding to 8 complete batches, which were divided into 6 for training the data-driven models and 2 for testing them), ranging from 987 to 2.5 mg NH4+-N/L which covers almost the complete range of total ammonium nitrogen concentration values in the membrane contactor. The predictive ability of the developed predictive models was evaluated on the test data set by four indices, namely: the root-mean-square error, the slope and the intercept of the linear fit between the measured and predicted concentrations and the determination coefficient. The results showed a strong predictive ability of the fitted ANN that outperformed the other approaches exhibiting a determination coefficient of 0.99 and the lowest root-mean-square error (19.87 mg/L) in the test set. Permutation variable importance demonstrated that all machine learning techniques depended mainly on the two variables extracted from the pH: its derivative and increments, which resulted to be more important than the pH itself to predict the total ammonium nitrogen concentration.

Optimization of helium extraction processes integrated with nitrogen removal units: A comparative study

Helium is regarded as a vital gas to various industries such as medicine, aircraft manufacturing, electronics and fiber optics fabrication. Currently, natural gas reserves are considered the only viable resource for this rare element. When processing (helium-rich) natural gas, helium is generally recovered in the most downstream stage in conjunction with the nitrogen rejection unit (NRU). The feed to this unit is a nitrogen rich stream, and the product is either crude helium (50–70 mol% purity) or purified helium (99.99 mol% purity). Currently, the cryogenic distillation method is a common technology for a crude helium extraction unit (HeXU). The alternative method for this purpose is a membrane gas separation system, which is successfully used in other applications. This study aims to propose an energy-integrated scheme for each of the two helium separation technologies with a single-column NRU and to evaluate and compare them for different applications. Matlab programming has been used to model the membrane system and incorporate it into Aspen Hysys, which is used to simulate the rest of the process flowsheet. Next, the energy consumption of the systems was optimized using the particle swarm optimization method. An economic analysis was adopted to compare the two technologies for different applications in order to suggest a comprehensive map for HeXU technology selection.

Evaluation of the Effects of Impurities on SAES ST198 Hydrogen Gettering

Various getter materials are used in the processing of hydrogen isotopes and associated impurities. SAES® ST198 is a zirconium-iron alloy that is typically used for the removal of low levels of hydrogen isotopes from a process gas stream. However, numerous impurities may be present in process gas streams and some of these impurities may have a deleterious effect on the hydrogen absorption capabilities of ST198.A series of experiments were completed to determine the effects of various impurities on the hydrogen gettering ability of ST198 as a function of the bed operating temperature. Changes in hydrogen getter performance were tracked using the analysis of Residual Gas Analyzer data. Baseline conditions of 0.1% hydrogen within a nitrogen rich stream were evaluated at both 350°C and ambient temperature conditions (24°C). Various concentrations of impurities were also explored to determine the effects on the hydrogen gettering of ST198. It has been determined that one benefit of ST198 is that it shows no appreciable interaction with nitrogen at temperatures lower than 425°C. However, gas impurities of carbon monoxide, methane, and ammonia were shown in this work to have an effect on the hydrogen gettering abilities of ST198.This paper presents findings relating to the evaluation of the effect of carbon monoxide, ammonia, and methane impurities on the hydrogen gettering ability of the ST198. Lower operating temperature conditions made the ST198 getter bed more susceptible to deactivation in the presence of impurities. In the event that the studied impurities exist in the process gas stream, the ST198 material could possibly become deactivated towards hydrogen isotope absorption at lower operating temperatures.

Applicability of one-stage partial nitritation and anammox in MBBR for anaerobically pre-treated municipal wastewater.

Energy consumption of municipal wastewater treatment plants can be reduced by the anaerobic pre-treatment of the main wastewater stream. After this pre-treatment, nitrogen can potentially be removed by partial nitritation and anammox (PN/A). Currently, the application of PN/A is limited to nitrogen-rich streams (>500mgL(-1)) and temperatures 25-35°C. But, anaerobically pretreated municipal wastewater is characterized by much lower nitrogen concentrations (20-100mgL(-1)) and lower temperatures (10-25°C). We operated PN/A under similar conditions: total ammonium nitrogen concentration 50mgL(-1) and lab temperature (22°C). PN/A was operated for 342days in a 4L moving bed biofilm reactor (MBBR). At 0.4mgO2L(-1), nitrogen removal rate 33gNm(-3)day(-1) and 80% total nitrogen removal efficiency was achieved. The capacity of the reactor was limited by low AOB activity. We observed significant anammox activity (40gNm(-3)day(-1)) even at 12°C, improving the applicability of PN/A for municipal wastewater treatment.

Methane/nitrogen separation through pressure swing adsorption process from nitrogen-rich streams

This work presents a novel approach for the treatment of nitrogen contaminated natural gas streams. Literature states that for small and medium scale production wells (<400MNm3/day), such stream can be treated by PSA. For larger scale natural gas production, the only mature option available is cryogenic distillation. Computer simulations were performed to evaluate the usage of silicalite in a PSA process for the separation of a nitrogen rich N2/CH4 mixture. This unit is designed for coupling to a cryogenic distillation process. The differential algebraic equations system, composed of mass and energy balances as well as other constitutive equations, was solved in the spatial dimension using the finite volumes method. Numerical methods employed were analyzed for numerical dispersion and oscillation. In order to test the numerical approach, parameters and model, data from the literature was correlated. A Rotated Central Composite Design (RCCD) was performed in order to determine optimum operational pressures. In the chosen set of operational values, the process presented nitrogen purity greater than 96% and a recovery beyond 50%. The nitrogen rich outlet stream purity is specified for venting, while the methane rich stream is proper for recycling to the cryogenic process.

Process analysis of pressurized oxy-coal power cycle for carbon capture application integrated with liquid air power generation and binary cycle engines

In this paper, the thermodynamic advantage of integrating liquid air power generation (LAPG) process and binary cycle waste heat recovery technology to a standalone pressurized oxy-coal combustion supercritical steam power generation cycle is investigated through modeling and simulation using Aspen Plus® simulation software version 8.4. The study shows that the integration of LAPG process and the use of binary cycle heat engine which convert waste heat from compressor exhaust to electricity, in a standalone pressurized oxy-coal combustion supercritical steam power generation cycle improves the thermodynamic efficiency of the pressurized oxy-coal process. The analysis indicates that such integration can give about 12–15% increase in thermodynamic efficiency when compared with a standalone pressurized oxy-coal process with or without CO2 capture. It was also found that in a pressurized oxy-coal process, it is better to pump the liquid oxygen from the cryogenic ASU to a very high pressure prior to vapourization in the cryogenic ASU main heat exchanger and subsequently expand the gaseous oxygen to the required combustor pressure than either compressing the atmospheric gaseous oxygen produced from the cryogenic ASU directly to the combustor pressure or pumping the liquid oxygen to the combustor pressure prior to vapourization in the cryogenic ASU main heat exchanger. The power generated from the compressor heat in the flue gas purification, carbon capture and compression unit using binary cycle heat engine was also found to offset about 65% of the power consumed in the flue gas cleaning and compression process. The work presented here shows that there is a synergistic and thermodynamic advantage of utilizing the nitrogen-rich stream from the cryogenic ASU of an oxy-fuel power generation process for power generation instead of discarding it as a waste stream.

Dissolved organic carbon manipulation reveals coupled cycling of carbon, nitrogen, and phosphorus in a nitrogen‐rich stream

To investigate the coupling between carbon (C) and phosphorus (P) cycling in a human‐altered stream, we conducted a whole‐ecosystem manipulation of the labile dissolved organic carbon (DOC) pool in a nitrate ()‐rich stream in the midwestern United States. For 6 d, we increased stream DOC by ∼ 1 mg L−1 through a continuous addition of sodium acetate. On the sixth day of the addition, ammonium () was increased by ∼ 130 µg N L−1 to examine the potential for nitrogen (N) to mediate coupled C and P cycling. Of the added DOC, 85% was retained within the treatment reach, which increased ecosystem respiration with respect to the reference reach. Alkaline phosphatase activity (APA) increased from day 1 to day 6; however, water column P uptake only increased on day 6 concurrent with the addition. Gross primary production decreased during the DOC addition relative to the reference reach, yet seemed to recover on day 6 ( addition). These results suggest that during the DOC addition, heterotrophs out‐competed autotrophs for N and that sediment‐sorbed P sustained the heterotrophic community while P uptake from the water column was dominated by autotrophs. Because APA and P uptake were stimulated by the simultaneous DOC and addition, P cycling appeared to be N limited, despite the high ambient concentration; this indicates a strong preferential uptake of over In streams, C and P cycling can be intrinsically coupled through biological mechanisms, and this coupling can be mediated by the availability of different forms of inorganic N.

Influence of the feeding regime on the start-up and operation of the autotrophic nitrogen removal process

The autotrophic nitrogen removal process (partial nitritation combined with the Anammox process) is a sustainable nitrogen removal technique for nitrogen-rich streams. A modelling and experimental study was performed to define optimal process conditions for the autotrophic nitrogen removal process. Special attention was given to the influence of feeding characteristicson the performance of both the partial nitritation reactor and the Anammox reactor. It was revealed that the feeding regime is an important factor in the successful start-up of the Anammox process. Nitrite concentration peaks at the beginning of a feeding period will lead to an unsuccessful start-up, while a slow input of nitrogen speeds up the process. Feeding regimes are less important in partial nitritation reactors since laboratory results show that slow or fast supply of influent does not influence the growth of ammonium oxidisers.

A wheat biorefining strategy based on solid-state fermentation for fermentative production of succinic acid

In this study, a novel generic feedstock production strategy based on solid-state fermentation (SSF) has been developed and applied to the fermentative production of succinic acid. Wheat was fractionated into bran, gluten and gluten-free flour by milling and gluten extraction processes. The bran, which would normally be a waste product of the wheat milling industry, was used to produce glucoamylase and protease enzymes via SSF using Aspergillus awamori and Aspergillus oryzae, respectively. The resulting solutions were separately utilised for the hydrolysis of gluten-free flour and gluten to generate a glucose-rich stream of over 140 g l −1 glucose and a nitrogen-rich stream of more than 3.5 g l −1 free amino nitrogen. A microbial feedstock consisting of these two streams contained all the essential nutrients required for succinic acid fermentations using Actinobacillus succinogenes. In a fermentation using only the combined hydrolysate streams, around 22 g l −1 succinic acid was produced. The addition of MgCO 3 into the wheat-derived medium improved the succinic acid production further to more than 64 g l −1. These results demonstrate the SSF-based strategy is a successful approach for the production of a generic feedstock from wheat, and that this feedstock can be efficiently utilised for succinic acid production.

High performance nanoporous carbon membranes for air separation

The preparation of porous stainless steel supports was found to have a significant impact on the properties of nanoporous carbon membranes fabricated upon them. Nanofillers were incorporated into porous stainless steel supports to modify the pore structure by reducing the average pore size and porosity. Carbon membrane properties were examined as a function of support variables such as filler content, shape, size and nature of the particles. Optimum performances, in terms of the ideal selectivity ratio for oxygen to nitrogen permeances ( S O 2 / N 2 ∼ 3 – 6 ) and the oxygen permeance (10 −8 mol m −2 s −1 Pa −1), were obtained when the filler completely saturated the support. This represents about a two order of magnitude improvement in oxygen permeance when compared to carbon membranes prepared on unmodified porous stainless steel supports. The origin of the improvement in the permeance is due to the formation of carbon membranes which are on average two orders of magnitude thinner than those formed on unmodified supports, i.e., the carbon membranes exists as very thin layers around and between the silica nanoparticles. A simple geometric model based on the packing of silica particles inside the porous stainless steel support is proposed to visualize and quantify this effect. The generality of the support modification concept is also demonstrated by the ability to employ different types of nanofillers and support geometries to obtain carbon membranes with high flux. Air separation experiments show that these membranes can produce both oxygen rich streams enriched to as much as 48% by volume and nitrogen rich streams enriched to over 90% by volume at reasonable operating conditions.

Octyl salicylate

Helium is regarded as a vital gas to various industries such as medicine, aircraft manufacturing, electronics and fiber optics fabrication. Currently, natural gas reserves are considered the only viable resource for this rare element. When processing (helium-rich) natural gas, helium is generally recovered in the most downstream stage in conjunction with the nitrogen rejection unit (NRU). The feed to this unit is a nitrogen rich stream, and the product is either crude helium (50–70 mol% purity) or purified helium (99.99 mol% purity). Currently, the cryogenic distillation method is a common technology for a crude helium extraction unit (HeXU). The alternative method for this purpose is a membrane gas separation system, which is successfully used in other applications. This study aims to propose an energy-integrated scheme for each of the two helium separation technologies with a single-column NRU and to evaluate and compare them for different applications. Matlab programming has been used to model the membrane system and incorporate it into Aspen Hysys, which is used to simulate the rest of the process flowsheet. Next, the energy consumption of the systems was optimized using the particle swarm optimization method. An economic analysis was adopted to compare the two technologies for different applications in order to suggest a comprehensive map for HeXU technology selection.