Ammonia Mass Transfer Coefficient Research Articles

Simultaneous ammonia recovery and treatment of sludge digestate using the vacuum stripping and absorption process: Scale-up design and pilot study

The paradigm of wastewater treatment is shifting from costly pollutant removal in mainstream to resource recovery from sidestream. This paradigm shift, nevertheless, is retarded by the lack of scalable, cost-effective ammonia recovery technologies. The vacuum stripping and absorption (VaSA) process has unrivaled features to recover ammonia and treat digestate simultaneously. The present study introduced a multi-pool boiling mode of vacuum stripping for scale-up design and conducted pilot tests at a water resource recovery facility using a 250-L/batch 3-pool system. It stripped 80.7 % of ammonia in sludge digestate and 91.5 % in pressate in 5-h batch operation. Ammonia mass transfer coefficient reached 0.319–0.485 1/h in digestate and 0.386–0.608 1/h in pressate. The operating challenge was to properly maintain vacuum and configure the demister where vapor–liquid equilibrium changed as it was scaled up. In contrast to the optimum vacuum pressure of 25–27 kPa and feed boiling temperature of 65 °C in the single-pool boiling stripper, the vacuum pressure in the 3-pool boiling stripper was increased to 46.3–46.9 kPa by the higher demister temperature (74 °C). The recovered crystals contained 98.4–103.7 % of (NH4)2SO4. Vacuum-assisted alkali/thermal treatment of digestate under the VaSA conditions increased the dissolved fraction of volatile solids from 7.5 % to 32.8–34.1 % and decreased fecal coliform to mostly undetected. Solids solubilization also resulted in generation of volatile organic compounds, primarily allyl chloride, methylene chloride, 2,5-octadecadiynoic acid methyl ester, and (E)-1,2-dichloroethylene. The low concentrations and small vapor pressures of these compounds were unfavorable for co-stripping. The co-stripped compounds were largely retained in condensate and absent in vacuum exhaust. This study validated the scalability of multi-pool boiling design of VaSA for efficient ammonia recovery and elucidated the effects on digestate treatment.

MOF incorporated adsorptive nanofibrous membranes for enhanced ammonia removal by membrane distillation

This study presents the design and fabrication of a new adsorptive nanofibrous membrane incorporating metal-organic framework (MOF) by electrospinning technique for removing ammonia-nitrogen from wastewater via direct contact membrane distillation (DCMD) process. Three types of MOF particles (HKUST-1, AlFu, and UiO-66-NH2) were used as functional nanoadditives and incorporated into the nanofibrous membrane matrix. The ammonia removal performance of these nanocomposite membranes was comprehensively investigated and compared with an activated carbon (AC) incorporated nanofibrous membrane. Various parameters such as ammonia removal efficiency, ammonia separation factor, overall ammonia mass transfer coefficient, ammonia flux, and membrane stability were evaluated. Among the tested MOFs, UiO-66-NH2 demonstrated excellent performance and was selected for further optimization. The 5.0 wt.% UiO-66-NH2 incorporated membrane exhibited the best performance for ammonia removal. Additionally, the mechanism of MOF incorporated nanofibrous membranes for ammonia removal from aqueous solution by DCMD was schematically analyzed. In overall, this study confirmed the feasibility of fabricating MOF incorporated electrospun adsorptive nanofibrous membranes with outstanding ammonia removal performance, demonstrating the potential of membrane distillation to remove ammonia-nitrogen from the aquatic environment.

Ammonia recovery from anaerobic digestion effluent by aeration-assisted membrane contactor

The ammonia recovery from anaerobic digestion (AD) effluent offers a low cost and low carbon footprint strategy for N recovery. To enhance ammonia recovery performance, the aeration-assisted membrane contactor (MC) process was presented with aeration applied on the feed side. The ammonia recovery performance with different pH adjustment methods and operating parameters were tested. Results illustrated that a high ammonia mass transfer coefficient (Kov = 4.85 ×10−7 m/s) could be achieved in the aeration-assisted MC. With the increase in air flow rate from 0 L/min to 0.6 L/min, the Kov increased from 1.21 × 10−7 m/s to 4.85 × 10−7 m/s by about 300%, and the ammonia separation factor (St) increased from 5.75 to 8.91 by about 55%. Additionally, the Kov increased sharply with the increase in feed temperature. Notably, the ammonia removal efficiency can reach 82% after 6-h experiment, which might be due to the large contact area of membrane contactor and the high mass transfer efficiency caused by the optimal conditions. The greenhouse gas (GHG) emission evaluation showed that compared with that of Haber-Bosch process (4.2 kg-CO2 eq/kg-N), the GHG emission of aeration-assisted MC was 1.86 kg-CO2 eq/kg-N under room temperature. The aeration-assisted MC can provide a high-efficient and low GHG-emission ammonia recovery process.

Selective absorption process intensification of ammonia from melamine exhaust gas using a counter airflow shear-rotating packed bed

The molar ratio of ammonia to carbon dioxide (NH3/CO2) in melamine exhaust can reach up to (2.0–2.4):1, and its direct emission will aggravate the greenhouse effect and waste of resources. Therefore, there is an urgent need to separate and recycle ammonia from the gas mixture in a more economical and efficient way. As an effective process intensification equipment, the counter airflow shear-rotating packed bed (CAS-RPB) has the advantages of high gas-liquid mass transfer efficiency, milliseconds of residence time and enhanced gas turbulence，which could enhance the absorption rate of ammonia in the gas mixture, inhibit the absorption of carbon dioxide caused by chemical absorption, and realize the selective absorption of ammonia.In this study，the CAS-RPB was adopted as an absorption device and the water was used as absorbent, the effects of the gas-liquid (G/L) ratio and high gravity factor (β) on absorption process were investigated. It was found that under suitable operating conditions, NH3/CO2 was close to 1:1 or 2:1 after absorption, which meet the requirement for the co-production of ammonium hydrogen carbonate or urea, the selectivity of ammonia was above 94 %, and the ammonia concentration in the absorption liquid were not less than 8.87 wt%. To compared with Cross-flow rotating packed bed (RPB), the absorption efficiency, selectivity, and gas volumetric mass transfer coefficient of ammonia are increased by 3.34 %, 8.83 %, and 7.02 % in CAS-RPB, respectively. The results show that the CAS-RPB can significantly enhance the selective absorption process of ammonia from melamine exhaust, therefore ammonia and carbon dioxide with potential high-added value can be obtained and utilized, and the zero-emission of ammonia and carbon dioxide can be realized.

Influences of Permeate Solution and Feed pH on Enhancement of Ammonia Recovery from Wastewater by Negatively Charged PTFE Membranes in Direct Contact Membrane Distillation Operation.

This research investigated the feasibility of enhancing ammonia recovery from wastewater using a negatively charged poly(tetrafluoroethylene) (PTFE) membrane in a direct contact membrane distillation (DCMD) system. The influences of phosphate solution types (as the permeate solutions) and feed pH on ammonia recovery were analyzed. Three types of permeate solutions—DI water and two types of phosphate solutions (H3PO4 and KH2PO4)—were investigated for recovery of ammonia gas on the permeate side. From the obtained results, the H3PO4 solution was found to be the most suitable permeate solution to recover ammonia gas in the DCMD operation with the highest overall ammonia mass transfer coefficient of 7.4 × 10–5 m/s, compared to values of 1.2 × 10–5 and 2.4 × 10–5 m/s for DI water and KH2PO4 solution, respectively. Moreover, an increase in the H3PO4 concentration from 0.3 to 0.5 M in the permeate solution also could significantly enhance ammonia recovery. With an increase in the feed pH from 10.0 to 11.8, the ammonia recovery could be enhanced to 92.98% at a pH of 11.8. Liquid ammonium phosphate fertilizer could be produced by the DCMD system with the use of 0.5 M H3PO4 solution. Therefore, the DCMD process using a negatively charged PTFE membrane with an appropriate permeate solution is one of the challenging processes for ammonia recovery from wastewater to promote the circular economy concept.

Pilot demonstration of nitrogen removal from municipal wastewater by vacuum membrane distillation

Nitrogen in municipal wastewater must be removed prior to discharge to the environment. However existing energy intensive aerobic processes used for nitrogen removal currently do not capture this important resource. Instead, nitrogen capture in the form of ammonia using a lower energy technology such as the membrane distillation; so far mostly tested in lab-scale, could be a significant improvement. This study reports a vacuum membrane distillation (VMD) pilot trial conducted at a municipal wastewater treatment plant to uniquely demonstrate ammonium removal and recovery to meet effluent discharge targets. The pilot plant was located in two streams on-site in the plant's anaerobic digester liquor handling facilities. The first trialed stream was on the existing phosphorus removal lime dosed effluent, and the second stream was effluent from an experimental struvite phosphorous recovery operation. In the post-lime scenario, VMD recovered N as ammonium sulphate solution and achieved up to 93% reduction. In the post struvite scenario, the VMD system achieved up to 85% reduction within the duration of the demonstration. With VMD driving force derived from volatility of the compound of interest, which is reliably calculated via Henry's law, the ammonia mass transfer coefficient across the membrane was 0.16 kg/m2/h/bar (±37% RSD) over the trial period, being lower than typical best case laboratory test results. Overall, the nitrogen removal and recovery process via VMD was proven technically viable on actual plant effluent leaving existing lime dosed and potential future struvite phosphorus removal systems. However, further studies are required to assess the economics of VMD for nitrogen removal compared with other nitrification-denitrification methods used in wastewater treatment.

The design of multi-stage open-loop hollow fiber membrane contactor and its application in ammonia capture from hydrolyzed human urine

Hollow fiber membrane contactor (HFMC) is a promising technology for removing or recovering wastewaters' volatile components. Developing a rational design method is very important for guiding its further application. In this study, we proposed a method to design the multi-stage open-loop hollow fiber membrane contactor (HFMC) employing shell-side influent. In addition, a three-stage HFMC was designed to capture ammonia from real hydrolyzed human urine. A continuous 1344 h performance was conducted. The results showed that the experimental effluent total ammonium nitrogen (TAN) concentration and ammonia mass transfer coefficient matched the predicted results well, which indicated that the design method was feasible and accurate. The three-stage HFMC showed excellent ammonia capture capacity with a TAN recovery efficiency of 93.29%, and the final effluent TAN concentration was 30.98±14.70 mg/L which met our design requirement (lower than 50 mg/L). More than 98.92% of the inorganic ions and 96.85% of the organic matter were retained in the effluent. The stripping solution after ammonia capture was the high-purity ammonium sulfate solution with low concentration of small molecular weight hydrophilic organic substances. The inorganic and organic membrane fouling was mild and randomly distributed. The inorganic membrane fouling was attributed to the deposition of calcium-, magnesium-, phosphate-related inorganic compounds, while the organic membrane fouling was mainly protein and carbohydrate. After the ammonia capture process, the surface hydrophobicity and pore properties of the membranes had no significant changes. These results demonstrated that the multi-stage open-loop HFMC could be a potential alternative for ammonia recovery from the high concentration of ammonium nitrogen wastewater.

Ammonia harvesting via membrane gas extraction at moderately alkaline pH: A step toward net-profitable nitrogen recovery from domestic wastewater

Membrane gas extraction technique enables recovery of high-purity ammonia from waste streams through gas-phase mass transfer across hydrophobic membranes. This study demonstrates the potential of ammonia recovery with gas permeable membrane, operated at moderately alkaline feed pH, as a substitute for the current approach of biological nitrogen removal in domestic wastewater treatment process. The measured apparent ammonia mass transfer coefficient in 3-h operation at a feed pH of 9.2 was 0.0713 cm/min, which, despite being 1.53-fold smaller than that at a feed pH of 11, was excellent for application to domestic wastewater. Application of lower feed pH prevented inorganic fouling of membrane. A notable advantage of the moderately alkaline feed pH condition is that the consumption of alkaline agents added for deprotonating bicarbonate instead of ammonium can be minimized. Calculation shows an opportunity that the monetary value of recovered ammonia exceeds the cost of the base consumed when moderately alkaline feed pH is applied. This study substantially extends current knowledge of the membrane gas extraction technique for ammonia recovery by investigating the process kinetics, fouling propensity, and chemical requirements as functions of pH, thereby verifying the potential of this technique to contribute to improving the sustainability of the global nitrogen cycle.

Development of ammonia mass transfer coefficient models for the atmosphere above two types of the slatted floors in a pig house using computational fluid dynamics

Ammonia emissions from animal production systems are a concern due to their potential adverse effects on the environment. It is important for governments to adjust their policies to control ammonia emissions from animal production. To evaluate and quantify emission factors, process-based modelling is a cost-effective procedure, particularly due to the complex and diverse transfer chains. During the modelling process, ammonia mass transfer coefficient is one of the key parameters to be determined. However, inconsistencies are found in widely used expressions for mass transfer coefficients in ammonia volatilization models. This study used CFD simulations to derive the mass transfer coefficients above metal and concrete slatted floor in an experimental pig houses with 12 full-scale pig pens. Five ammonia mass transfer coefficient models were selected for comparison with the models derived from CFD simulations. It was noticed that the models derived from wind tunnel/flux chamber experiments usually predicted lower values of ammonia mass transfer coefficients compared to the models developed from full-scale measurements and/or numerical modelling. Care is needed to extrapolate the relationships developed under controlled laboratory conditions to the commercial barns. The results indicated also that the ammonia mass transfer coefficient relies heavily on the airflow patterns which could be affected by the ventilation systems, location of the inlet and outlets, internal partitions, floor types etc.. This makes it very difficult to present a universal ammonia mass transfer coefficient model for pig houses.

Efficient nutrient recovery/removal from real source-separated urine by coupling vacuum thermal stripping with activated sludge processes

Separation and treatment of human urine from domestic wastewater have been recognized as a sustainable alternative to conventional urban sanitation system, but the unique water quality of source-separated urine, such as high nutrient, insufficient alkalinity and low COD/nitrogen ratio, poses challenges to the biological nitrogen removal process. It was hypothesized that a physicochemical pre-treatment should be adopted to not only reduce nitrogen load but adjust water quality suitable for biological treatment. In this study, a vacuum thermal stripping process coupled to acid absorption was used as a pre-treatment to recover ammonia from hydrolyzed urine in the form of ammonium sulphate. The maximal ammonia mass transfer coefficient of 17.6 mm/h was obtained under 60 °C and 21.3 kPa 80% of the nitrogen in hydrolyzed urine was recovered in 3 h batch stripping experiments without pH adjustment, corresponding to a nitrogen recovery loading rate of 36 kg N/m3⋅d. The majority of organic matters were retained in urine solutions, thus COD/N and alkalinity/NH4+N ratios were elevated to 4.75 and 4.37, respectively. Phosphorus recovery could be simultaneously obtained in stripping process by adding MgCl2. The remaining nitrogen was effectively removed via short-cut nitrification and denitrification in an anoxic/oxic membrane bioreactor. More than 95% of overall nutrient recovery/removal from urine was achieved with a minimal consumption of external resources. The economic assessment of the technique showed that the recovery/removal of nutrients from 1 m3 of urine can make a profit of € 0.26.

Liquid fertilizer production by ammonia recovery from treated ammonia-rich regenerated streams using liquid-liquid membrane contactors

The nitrogen load on urban wastewater should be considered as a secondary resource for nitrogen-based fertilizers. From this point of view, ammonia-rich streams obtained from a regeneration step with zeolites using 70–80 g NaOH/L could contain up to 3.5–4.5 g NH3/L as well as other ionic species (Na+, K+, Ca2+, Mg2+) and dissolved organic matter (DOM). Thus, they could be treated to obtain a valuable product composed by ammonia for fertilizing applications. A sorption pre-treatment process was carried out to remove the residual amount of DOM and to reduce membrane fouling before processing with hollow fibres liquid-liquid membrane contactors (HF-LLMC). Polypropylene HF-LLMC was used to selectively extract ammonia in single or two-step configurations using different acid stripping solutions (H3PO4, HNO3 or a mixture of HNO3/H3PO4). For ammonia recovery, the ammonia mass transfer coefficient (Km(NH3)) and water transport by HF-LLMC were determined. H3PO4 was found to be the best acid stripping solution by one-step HF-LLMC; the ammonia removal was 76% with a Km(NH3) of 8.8 × 10−7 m/s. Additionally, the ammonia was concentrated 26 times, and it was recovered as multi-nutrient liquid fertilizer (NP) composed of 7.8% N and 21.6% P2O5. Furthermore, ammonia recovery was increased, reaching values up to 94%, through two-step HF-LLMC, and again H3PO4 was used as stripping solution. Finally, water transport from the feed to the stripping phase was estimated to be 0.022 L/m2·h for one-step HF-LLMC with H3PO4. Finally, the use of UV–Vis and 2D-Fluorescence was shown to be a successful approach for monitoring pore wetting events.

Recovery of ammonia in anaerobic digestate using vacuum thermal stripping - acid absorption process: scale-up considerations.

A vacuum thermal stripping process coupled with acid absorption has been developed at laboratory scale to recover ammonia in anaerobic digestate. To make this ammonia recovery process scalable, this study investigated the effects of feed depth on vacuum thermal stripping in a pilot system, developed sodium hydroxide dosages required to raise feed pH for stripping, and simulated the dynamics of ammonia reduction in batch stripping tests. As feed depth was increased from 8.5 to 34.0 cm, the ammonia mass transfer coefficient and ammonia stripping efficiency decreased while the mass of stripped ammonia increased. Digested municipal sludge had a greater ammonia mass transfer coefficient than digested dairy manure at each feed depth, which could be attributed to the difference in suspended and dissolved solids concentrations. The optimum feed depth was 18 cm of the digested sludge and 14 cm of the digested manure. Sodium hydroxide dosage for the digested manure was higher than that for the digested sludge and co-digested foodwaste. The dosages were correlated to concentrations of total dissolved solids and ammonia. Total ammonia concentration decreased exponentially in batch stripping of the digested sludge at 25.5 cm deep, with a first-order stripping rate coefficient of 0.087-0.144 h-1.

Ammonia Recovery from Pig Slurry Using a Membrane Contactor—Influence of Slurry Pretreatment

Pig slurry contains sufficient amount of nitrogen, phosphorus, and potassium for plant growth. If appropriately administered, this could substitute significant amounts of fertilizer. However, excessive fertilization with slurry causes environmental problems. To reduce environmental issues, solid-liquid separation or anaerobic digestion is needed to obtain a better distribution of nutrients. Solid-liquid separation produces a solid fraction rich in phosphorus and a liquid fraction containing ammonia, potassium, and high water content. Therefore, further concentration of ammonia is desired for any practical use. In this study, ammonia membrane stripping was carried out using polypropylene membranes and the impact of temperature, flow velocities, and liquid fraction pretreatment on the membrane contactor performance was tested. Sieved liquid effluents from a decanter centrifuge, a screw press, an AL-2 system (flocculation and filtration), and an anaerobic digester were tested. Since the properties of these liquid effluents vary, they might affect ammonia recovery. Thus, it is essential to investigate which effluent is most suitable as a feed for a membrane contactor and what is the cost of preprocessing. The mean ammonia mass transfer coefficient at 30 °C was found to be equal to 17 ± 2 × 10−3 m h−1. At 50 °C, it was found to be equal to 29 ± 2 × 10−3 m h−1 for all the tested effluents. This means that sieving after slurry separation or anaerobic digestion alleviates the influence the solid-liquid separation has on ammonia membrane stripping. However, the cost evaluation showed that solid-liquid separation using a decanter centrifuge followed by sieve draining is the cheapest of the methods investigated.

Developing a vacuum thermal stripping – acid absorption process for ammonia recovery from anaerobic digester effluent

To prevent acetoclastic methanogens from ammonia inhibition in anaerobic digestion of protein-rich substrates, ammonia needs to be removed or recovered from digestate. This paper presents an innovative ammonia recovery process that couples vacuum thermal stripping with acid absorption. Ammonia is stripped out of digestate boiling at a temperature below the normal boiling point due to vacuum. Stripped ammonia is absorbed to a sulfuric acid solution, forming ammonium sulfate crystals as a marketable product. Three common types of digestate were found to have boiling point temperature-vacuum curves similar to water. Seven combinations of boiling temperature and vacuum (50 °C 16.6 kPa, 58 °C 20.0 kPa, 65 °C 25.1 kPa, 70 °C 33.6 kPa, 80 °C 54.0 kPa, 90 °C 74.2 kPa, and 100 °C 101.3 kPa) were tested for batch stripping of ammonia in dairy manure digestate. 93.3–99.9% of ammonia was stripped in 3 h. The Lewis-Whitman model fitted ammonia stripping process well. Ammonia mass transfer coefficient was significantly higher at boiling temperature 65–100 °C and vacuum pressure 25.1–101.3 kPa than 50–58 °C and 16.6–20.0 kPa. The low ammonia saturation concentrations (0–24 mg N/L) suggested a large driving force to strip ammonia. The optimum boiling point temperature – vacuum pressure for ammonia recovery in a recirculation line of a mesophilic digester was 65 °C and 25.1 kPa, at which the ammonia mass transfer coefficient was as high as 37.3 mm/h. Installation of a demister and liquid trap could avoid negative effects of higher stripping temperature and stronger vacuum on formation of ammonium sulfate crystals. Pilot tests demonstrated that high-purity ammonium sulfate crystals could be produced by controlling sulfuric acid content and maintaining acid solution saturated with ammonium sulfate. Although volatile organic compounds such as cyclohexene were found in the final acid solutions, no volatile organic compounds were found in the recovered crystals.

Separation of ammonia from radioactive wastewater by hydrophobic membrane contactor

The radioactive wastewater produced in the manufacturing process of UO2 kernel for high temperature gas-cooled reactor (HTR) contains high concentration of ammonia. The ammonia has to be removed effectively for further treatment of the wastewater. In this study, the hydrophobic membrane contactor (HMC) was adopted to remove and recover the ammonia from radioactive wastewater at room temperature. The operating parameters such as feed velocity and initial ammonia concentration were determined. In addition, the effect of wastewater composition on ammonia separation was studied. The experiment results showed that ammonia removal efficiency could reach above 90% after 120 min operation when pH was not adjusted. While the initial pH of wastewater was adjusted to 12.0, ammonia removal efficiency could reach above 95%. The ammonia mass transfer coefficient increased with increase of feed velocity and tended to an asymptotic value when the feed velocity reached 0.049 m/s. When the initial ammonia concentration was 2211.6 mg/L, 5864.6 mg/L and 23,898.7 mg/L, the ammonia removal efficiency was 95.0%, 94.2% and 94.1%, respectively after 120 min operation, i.e. the initial concentration of ammonia in wastewater had almost no effect on ammonia separation. In addition, the coexisting substances, such as urea and tetrahydrofurfuryl alcohol (THFA), also had no effect on ammonia separation. The HMC is a promising way to separate ammonia from radioactive wastewater.

Coupling thermal stripping and acid absorption for ammonia recovery from dairy manure: Ammonia volatilization kinetics and effects of temperature, pH and dissolved solids content

Both liquid dairy manure and manure digestate have high concentrations of ammonia. This study coupled thermal stripping with acid absorption to recover ammonia from dairy manure as ammonium sulfate. Ammonia volatilization kinetics and effects of temperature, pH, and dissolved solids content on thermal stripping were investigated in batch experiments. Statistically insignificant differences were found in ammonium sulfate formation and liquid mass transfer of ammonia between the experiments with initial feed pH values of 11 and 9 and between the experiments with filtrate of undigested and digested manure, which have different dissolved solids contents. Temperature had significant effects on thermal stripping of ammonia. When temperature was set at the boiling points (101–102°C) of manure filtrate, ammonia was completely stripped in 3–4h. It took 5h to strip 50% of ammonia at 97°C. Little ammonia was stripped at 86 and 76°C. The saturation concentrations of ammonia in manure filtrate was zero at temperatures 76–102°C. Ammonia mass transfer coefficient upon boiling was 30.3–31.4mm/h in manure filtrate. Ammonia mass transfer coefficient increased exponentially with temperature, indicating a temperature coefficient of 1.164. High-purity ammonium sulfate crystals (⩾98%) were produced when sulfuric acid solutions were pre-saturated with ammonium sulfate. When ammonia was completely stripped, ammonium sulfate was formed at 3.70–3.87g/L filtrate. A preliminary economic analysis shows that this novel technology is economically promising for practical application, especially when it is applied to a side-stream of anaerobic digesters.

Fouling mitigation in membrane distillation processes during ammonia stripping from pig manure

Over time fouling leads to membrane wetting. This is the biggest obstacle to widespread use of membrane distillation (MD) for ammonia removal from animal slurry. Feed pretreatment and cleaning strategies of membrane surfaces are the most common methods to prevent or diminish fouling phenomena. This study investigates preliminary fouling of polypropylene (PP) and polytetrafluoroethylene (PTFE) membranes. A model manure solution was used as feed. In addition cleaning efficiencies with deionized water, NaOH/citric acid, and Novadan agents were studied. Further microfiltration and ultrafiltration were examined as manure pretreatment to diminish fouling. To this end polyvinylidene fluoride membranes (PVDF 0.2µm and 150kDa respectively) were used. Organic fouling was shown to be dominant. For the model manure solution the fouling comprised lipids, carbohydrates and proteins. For pig slurry the fouling additionally contained carboxylates, free fatty acids and lignin. Among the tested cleaning strategies, Novadan agents were the most successful in removing proteins and carbohydrates from the PTFE membrane while it only removed proteins from the PP membrane. Using microfiltration or ultrafiltration as a pretreatment prior to MD doubled the ammonia mass transfer coefficient for the PTFE membrane, while for the PP membrane, the ammonia mass transfer coefficient was increased 4-fold.

Effects of Suspended Solids Characteristics and Concentration on Ammonia Emission Process from Liquid Dairy Manure

<abstract> <bold><sc>Abstract.</sc></bold> The goal of this study was to determine the effects of suspended solids (SS) adsorption properties, as well as the concentration of SS, on the mechanisms governing ammonia volatilization from liquid dairy manure. Pertinent properties that influence total ammoniacal nitrogen (TAN = NH₄⁺ + NH₃) adsorption on SS, including particle size distribution (PSD) and volatile solids (VS), of manures from three dairy operations with different feed rations were evaluated. The main parameters governing ammonia volatilization from liquid manure, i.e., the dissociation constant (K_d), the fraction of un-ionized ammonia (β), and the overall mass transfer coefficient (K_O) of ammonia, for the three manures were determined in a laboratory convective emission chamber. The adsorption characteristics of the SS of the manures from the three dairies were significantly different. In particular, the PSD and VS for the SS of the manures from all dairies were significantly different. Even though the adsorption properties were significantly different among the SS from all three manures, their net effects on ammonia volatilization, at the same concentration, were not significantly different. Briefly, SS adsorption properties did not significantly affect either K_d, β, or K_O, but SS concentrations significantly affected them all. Removal of SS via solids-liquid separation would therefore exacerbate ammonia loss from liquid dairy manure. Overall, these findings reveal that increasing SS concentration hinders ammonia volatilization from liquid dairy manure, whereas differences in the SS characteristics do not affect the volatilization process in a significant manner.

Impact of Anaerobic Digestion of Liquid Dairy Manure on Ammonia Volatilization Process

<abstract> <bold><sc>Abstract.</sc></bold> The goal of this study was to determine the effect of anaerobic digestion (AD) on ammonia volatilization from liquid dairy manure, in storage or treatment lagoon, prior to land application. Physical and chemical properties of liquid dairy manure, which may affect ammonia volatilization, were determined before and after AD. The properties of interest included particle size distribution (PSD), total solids (TS), volatile solids (VS), viscosity, pH, total ammoniacal nitrogen (TAN), and ionic strength (IS). The overall mass transfer coefficient of ammonia (K_oL) and the NH₃ fraction of TAN (β) for the undigested (UD) and AD manures were then experimentally determined in a laboratory convective emission chamber (CEC) at a constant wind speed of 1.5 m s^-1 and fixed air temperature of 25°C at manure temperatures of 15°C, 25°C, and 35°C. The PSD indicated non-normal left-skewed distributions for both AD and UD manures particles, suggestive of heavier concentrations of particles toward the lower particle size range. The volume median diameters (VMD) for solids from UD and AD were not significantly different (p= 0.65), but the geometric standard deviations (GSD) were significantly different (p = 0.001), indicating slightly larger particles but more widely distributed solids in UD manure than in AD manure. Results also indicated significantly higher pH, TAN, ionic strength (IS), and viscosity in AD manure. The β for AD manure, determined under identical conditions (air temperature, liquid temperature, and airflow), was significantly higher (p < 0.001) than for UD manure. However, mass transfer of ammonia (K_oL) was significantly lower for AD manure than for UD manure (p < 0.001). Overall, these findings suggest that AD of dairy manure significantly increased initial ammonia volatilization potential from liquid dairy manure, with the largest increase (~61%) emanating from increased ammonium dissociation. The initial flux of ammonia, at 15°C, was ~16% more from AD manure than from UD manure.

Apparatus for the Ammonium Recovery from Liquid Animal Manure

<abstract><title><italic>Abstract. </italic></title> Nitrogen present in animal manure can be a limiting factor when considering manure application rates onto arable land. EU-regulations triggered the development of a new ammonia exchange apparatus for the recovery of ammonia. The described apparatus has a liquid to liquid ammonia mass transfer coefficient of 0.0058 m/s. The results were fitted using a simple first order ammonia exchange model with constant time step that additionally predicted that 80% of the ammonia could be recycled from the liquid fraction of animal manure within a residence time of 10 h with addition of 0.2 M NaOH to the manure, yielding a liquid artificial fertilizer with a calculated achievable maximum concentration of about 18 % nitrogen.