In the Absence of Oxygen There Are Only Two Processes That Can Occur

Marine Corrosion

B. Phull , A.A. Abdullahi , in Reference Module in Materials Scientific discipline and Materials Applied science, 2017

2.2 Upshot of Dissolved Gases

DO represents the well-nigh of import species that controls the corrosion behavior of many materials in seawater, fifty-fifty more so than chloride. Do concentration is reported either as ml   fifty⁻¹ or mg   fifty^−ane (ml   l^−one×1.429=mg   l⁻¹ ). The primary factors that control Practise content of seawater include temperature, salinity, biological activity, and mixing (flow). The inverse solubility of dissolved oxygen versus temperature and dissolved oxygen versus salinity is depicted in Figures 1 and 2, respectively. The Practise concentration of the Dead Ocean, which has a salinity of ~322 ppt, is obviously ~0.ane   mg   l^−ane.

Effigy 1. Dissolved oxygen (Practice) versus temperature in natural seawater of 35‰ salinity at one   atm pressure.

Figure two. DO versus salinity in synthetic seawater at twenty   °C and ane   atm pressure.

Oxygen dissolves in seawater either from the atmosphere and/or from plant photosynthesis, which is most prevalent over a depth ~100   m. Thus, surface waters at normal atmospheric pressures tend to exist saturated or supersaturated in oxygen, including the sparse liquid environment in the splash zone. However, quiescent flow weather condition that favor algal growth and proliferation of decomposable matter can reduce DO content markedly because of biological oxygen demand (BOD).

The principal reaction in seawater that controls corrosion is oxygen reduction. For any given Practise concentration, the corrosion process is often strongly influenced by seawater velocity. This is discussed under corrosion mechanisms later on in this affiliate. The office of carbon dioxide is discussed in the following department. Other gases such as hydrogen sulfide and ammonia can be generated past bacteria from decaying matter and can influence corrosion of certain materials as discussed after.

Read total chapter

URL:

https://www.sciencedirect.com/scientific discipline/commodity/pii/B9780128035818092092

Fundamentals of Quorum Sensing, Analytical Methods and Applications in Membrane Bioreactors

Reham K. Abu Shmeis , in Comprehensive Analytical Chemistry, 2018

one.vii.2 Dissolved Oxygen

Dissolved oxygen ( Exercise) refers to the level of free, noncompound oxygen (O₂) dissolved in water or other liquids. The bonded oxygen in water (H₂O) is in a compound and does not count toward dissolved oxygen levels. Exercise is an important parameter in assessing h2o quality because of its influence on the organisms living within a body of h2o. Oxygen gets into water past diffusion from the surrounding air, by aeration, or equally a waste product of photosynthesis. DO is essential to the survival of organisms in a stream. The presence of oxygen is a positive sign and the absence of oxygen is a sign of astringent pollution. Waters with consistently high dissolved oxygen are considered to be stable aquatic systems capable of supporting many different kinds of aquatic life (Davis and Cornwell, 2012; Weiner and Matthews, 2003).

Read full chapter

URL:

https://www.sciencedirect.com/scientific discipline/article/pii/S0166526X18300023

Photocatalytic removal of emerging contaminants in h2o and wastewater treatments: a review

Johanna Zambrano , ... Pedro A. García-Encina , in Development in Wastewater Treatment Research and Processes, 2022

24.3.half dozen Dissolved oxygen

Dissolved oxygen (Practice) was plant to exist a central parameter in photocatalytic degradation every bit it contributes to the stabilization of radical intermediates, direct photocatalytic reactions and mineralization of contaminants. Practise may induce the cleavage mechanism for aromatic rings in organic pollutant. As well, it acts as an electron scavenger, trapping photogenerated electrons preventing charge carrier recombination. This enable the formation of superoxide and ROS. Furthermore, Exercise supplies the necessary force to take an acceptable suspension of catalyst particles in photocatalytic reactors ( Ahmed and Haider, 2018; Fotiou et al., 2015; Malato et al., 2016).

Fotiou et al. (2015) using a TiO_two photocatalyst investigated the degradation of cyanobacterial toxin microcystin-LR and off-odor causing compounds (geosmin, 2-methylisoborneol) under air (2.5 × ten⁻⁴ Chiliad of O_ii), oxygen saturated (one.ii × 10⁻³ M of O₂) and nitrogen (0 K of O_two) atmosphere. Results showed a more than efficient deposition as the concentration of DO increases in the solution. Likewise, López-Serna et al. (2017) demonstrated that the quantum efficiency of a reaction is highly related to the DO content, by using TIO_two for the photocatalytic deposition of bisphenol A. This research emphasizes the importance of measuring and maintaining DO concentration in order to have a consummate mineralization.

Read total chapter

URL:

https://www.sciencedirect.com/scientific discipline/commodity/pii/B9780323855839000235

Algal–bacterial symbiosis and its application in wastewater treatment

Inigo Johnson , ... Mathava Kumar , in Emerging Technologies in Environmental Bioremediation, 2020

15.2.4.1 Dissolved oxygen

Dissolved oxygen (Do) within the reactor is a critical parameter affecting the symbiotic arrangement in terms of nutrient and organic matter removal and also in terms of interactions betwixt the algae and bacteria. Individually both the systems are dependent on Do. Aerobic heterotrophic bacteria apply oxygen as the electron acceptor and its deficiency can decrease the organic content removal. Meanwhile, algal systems are adversely afflicted by a high oxygen concentration due to photosynthesis inhibition ( Tang, Zuo, & Tian, 2016). Moreover, algae need a minimal corporeality of Do for respiration. Therefore in a symbiotic system, an increase in DO over a certain limit leads to a higher sludge:algae ratio. This negatively affects the stability of the symbiotic organization. The organic matter removal is not affected much since the higher aeration allows for better growth of bacteria. Nonetheless, the removal of ammonia nitrogen and total phosphate through absorption decreases with college aeration rate due to low algal biomass growth (Tang et al., 2016). Moreover, the college aeration causes higher shear stresses, negatively affecting the germination of sludge–algae flocs (Tang et al., 2016).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128198605000158

How cells grow

Shijie Liu , in Bioprocess Engineering (Third Edition), 2020

13.8 Oxygen demand for aerobic microorganisms

Dissolved oxygen (Exercise) is an important substrate in aerobic fermentations and may exist a limiting substrate, since oxygen gas is sparingly soluble in h2o. At high-cell concentrations, the rate of oxygen consumption may exceed the charge per unit of oxygen supply, leading to oxygen limitations. When oxygen is the rate-limiting factor, specific growth charge per unit varies with dissolved-oxygen concentration according to Monod equation, just similar whatever other substrate-limited example.

Above a disquisitional oxygen concentration, the growth rate becomes independent of the dissolved-oxygen concentration. Fig. 13.6 depicts the variation of specific growth charge per unit with dissolved-oxygen concentration in a rich medium (no other substrate limitation). Oxygen is a growth-charge per unit-limiting factor when the Do level is below the critical Do concentration. In this case, another medium component (due east.g., glucose, ammonium) becomes growth-extent limiting. For example, with Azotobacter vinelandii at a Do = 0.05 mg/L, the growth rate is about 50% of maximum even if a large amount of glucose is present. Notwithstanding, the maximum corporeality of cells formed is not determined by the Exercise, as oxygen is continually resupplied. If glucose were totally consumed, growth would cease even if Exercise = 0.05 mg/50. Thus, the extent of growth (mass of cells formed) would depend on glucose, while the growth charge per unit for well-nigh of the culture menses would depend on the value of Do.

Figure thirteen.vi. Growth-rate dependence on dissolved oxygen (DO) for aerobic organism (A) and facultative organisms (B). The lines are Monod equation fit to the data (symbols).

Data source: Chen, J., Tannahill, A.L., Shuler, M.L., 1985. Biotechnol. Bioeng., 27, 151).

As shown in Fig. xiii.6, the dependence of Practice for aerobic and facultative organisms on jail cell growth follows the Monod growth equation. For aerobic organisms

(13.46) ${\mu }_{\mathrm{Grand}}=\frac{{\mu }_{ma\mathrm{10}}DO}{{\mathrm{Grand}}_{DO}+DO}$

and for facultative organisms,

(13.47) ${\mu }_K={\mu }_{max0}+\frac{{\mu }_{\mathrm{grand}ax}-{\mu }_{ka\mathrm{ten}0}}{K_{DO}+DO}DO$

where μ_max0 is the maximum specific growth rate in anaerobic conditions. Facultative organisms grow with or without oxygen. For anaerobic organisms, there is no growth if oxygen is present.

The critical oxygen concentration is about v%–10% of the saturated Practice concentration for leaner and yeast and about 10%–50% of the saturated DO concentration for mold cultures, depending on the pellet size of molds. Saturated Practise concentration in water at 25°C and 1 atm pressure is about 7 ppm. The presence of dissolved salts and organics can alter the saturation value, while increasingly high temperatures decrease the saturation value.

Oxygen is usually introduced to the fermentation broth past sparging air through the broth. Oxygen transfer from gas bubbles to cells is usually limited past oxygen transfer through the liquid flick surrounding the gas bubbling. The rate of oxygen transfer from the gas to liquid stage is given past

(13.48) ${\mathrm{Due\; north}}_{{\text{O}}_{\mathrm{two}}}=k_{\text{50}}a(C*-C_{\text{L}})=\text{OTR}$

where m _Fifty is the oxygen transfer coefficient (m/h), a is the gas-liquid interfacial area (thousand²/m³), C* is saturated Exercise concentration (g/50), C _L is the bodily DO concentration in the broth (g/Fifty), and the North _O2 is the rate of oxygen transfer (g·L^–i·h^–1). Also, the term oxygen transfer rate (OTR) is used.

The rate of oxygen uptake is denoted as OUR (oxygen uptake rate) and

(13.49) $OUR={\mu }_{O_2\mathrm{Ten}}=\frac{{\mu }_{G}X}{Y{F}_{\mathrm{10}/O_{\mathrm{two}}}}$

where μ_O2 is the specific rate of oxygen consumption (g·g-cells^−ane·h^−one), YF _X/O2 is the yield factor on oxygen (grand-cells/k-O₂), and Ten is cell concentration (one thousand-cells/L). When oxygen transfer is the rate-limiting step, the rate of oxygen consumption is equal to the charge per unit of oxygen transfer. If the maintenance requirement of O₂ is negligible compared to growth, so

(thirteen.50) $\frac{{\mu }_{\mathrm{One\; thousand}}X}{Y{F}_{X/O_{\mathrm{two}}}}=OUR=OTR={\mathrm{1000}}_{L}a\left(C^{*}-C_L\right)$

or in the batch reactor with negligible medium volume loss (due to air sparging),

(13.51) $\frac{d\mathrm{10}}{dt}=Y{F}_{X/O_2}{k}_{\mathrm{50}}a\left(C^{*}-C_{\mathrm{Fifty}}\right)$

Growth rate varies nearly linearly with the oxygen transfer rate under oxygen-transfer limitations. Among the diverse methods used to overcome Exercise limitations are the use of oxygen-enriched air or pure oxygen and operation under loftier atmospheric force per unit area (ii–3 atm). Oxygen transfer has a big impact on reactor blueprint.

The maximum or saturation oxygen concentration is a office of temperature, oxygen pressure, too as medium compositions. Electrolytes have a strong effect on oxygen solubility and transport. Quicker et al. (1981)) gave a simple correlation between the saturation oxygen concentration (C*) and medium ionic and nonionic solute concentration:

(13.52) $log\frac{C_0^{*}}{C^{*}}=\frac{\mathrm{i}}{\mathrm{ii}}{\displaystyle \sum }_{j=\mathrm{i}}^{\begin{array}{c}\hfill \text{Ionic}\hfill \\ \hfill \text{species}\hfill \end{array}}{H}_j{Z}_j^2{C}_j+{\displaystyle \sum }_{j=1}^{\begin{array}{c}\hfill \text{non-Ionic}\hfill \\ \hfill \text{species}\hfill \end{array}}{H}_j{C}_j$

where $C_0^{*}$ is the oxygen saturation concentration in pure water (Tabular array 13.three), C* is the oxygen saturation concentration in the medium, H _j is the oxygen solubility interaction constants (Table 13.4), Z _j is the ionic charge of ionic species j, C _j is the concentration of species j in the fermentation medium.

Table xiii.3. Solubility of oxygen in pure water.

Temperature, °C	Oxygen solubility in pure water when contacting with air at 1 atm, kg·m–3	Henry's law abiding, atm-Oii·m3·kg–1	Density of water, kg/mthree
0 v ten 15 20 25 30 35 twoscore 45 50 lx lxx 80 xc 100	1.46 × 10–ii ane.28 × ten–two 1.14 × 10–two 1.02 × 10–2 0.929 × ten–2 0.849 × 10–ii 0.782 × 10–2 0.731 × ten–ii 0.692 × 10–2 0.656 × 10–2 0.627 × ten–ii 0.583 × 10–two 0.550 × 10–2 0.528 × 10–ii 0.515 × x–ii 0.510 × 10–2	14.4 16.4 18.iv 20.five 22.6 24.seven 26.9 28.vii 30.4 32.0 33.v 36.0 38.ii 39.8 40.eight 41.two	999.839 999.964 999.699 999.099 998.204 997.045 995.647 994.032 992.215 990.213 988.037 983.200 977.771 971.799 965.321 958.365

Source: Calculated from International Critical Tables, 1928, vol. Three, p. 257. McGraw-Hill: New York.

Table xiii.4. Oxygen solubility interaction constants at 25 °C.

Cation	Hj, 10–4 miii/mol	Anion	Hj, 10–iv thou3/mol	Sugar	Hj, 10–4 yard3/mol
H+ Chiliad+ Na+ NHfour + NEt4 + Mg2+ Ca2+ Mntwo+	−seven.74 −5.96 −5.l −vii.20 −9.12 −iii.fourteen −3.30 −three.11	OH– Cl– COthree 2– SO4 2– NO3 – HCO3 – HtwoPO4 – HPO4 2– POfour iii–	9.41 8.44 four.85 4.53 8.02 10.58 10.37 four.85 3.20	Glucose Lactose Sucrose	ane.nineteen one.97 1.49

Read full chapter

URL:

https://www.sciencedirect.com/scientific discipline/commodity/pii/B9780128210123000130

Quorum sensing and quorum quenching in membrane bioreactors

Kwang-Ho Choo , ... Hyun-Suk Oh , in Current Developments in Biotechnology and Bioengineering, 2020

seven.4 Furnishings of DO on microbial community structure and biofouling

When the Practise level decreased from 4.0 to 0.5   mg/L, the EPS concentration substantially increased resulting in more severe membrane biofouling in MBRs [116]. The microbial communities in mixed liquor at Practice levels of 2 and 4   mg/L were similar, just the community structure at 0.five   mg/L Exercise showed a significant difference. In addition, the microbial diversity was decreased at lower DO levels, showing the relative richness of denitrifying bacteria. The departure in the microbial community of biocake layers under unlike Do conditions was besides obvious. Two ascendant bacteria, Rhizobiales and Paracoccus (which belong to Alphaproteobacteria), were only observed at a DO level of <   two.0   mg/50, indicating that both may play a primal role in membrane biofouling.

In contrast, another study reported that the microbial diversity was decreased under loftier DO weather condition (3–5   mg/L) compared to depression Do weather (one–ii   mg/L) [31]. The relative abundance of Betaproteobacteria and Gammaproteobacteria was as well decreased under high Do weather, showing evidence that those are not major contributors to membrane fouling.

Cyclic operation of MBRs caused varied DO levels, revealing that the low DO condition increased the EPS content leading to faster membrane fouling, along with the relative abundance of Proteobacteria, Firmicutes, and Bacteroidetes [114]. The Shannon diversity alphabetize and Pareto-Lorenz evenness curves were utilized for the understanding and relationship of anoxic-oxic MBR microbial communities with biofouling [123]. The microbial customs was plant to be more than diverse with the progress of MBR membrane fouling. The microbial customs with higher evenness values thus seemed to have greater fouling propensity.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128198094000127

Boiler and Feedwater Treatment

A. Banweg , in Reference Module in Materials Science and Materials Engineering, 2016

3.1 Dissolved Oxygen Command

Dissolved oxygen removal from the feedwater is typically accomplished in a deaerating heater or deaerator in which steam is used to remove the dissolved oxygen from the feedwater. Each of these pieces of equipment has its own dissolved oxygen removal efficiency. In some very low-pressure level applications, there may simply be a feedwater tank in which makeup water and condensate are mixed, which may or may not be actively steam sparged or otherwise heated to effort to remove the dissolved oxygen.

The goal of the mechanical deaeration process is to reduce the dissolved oxygen content of the feedwater to less than 7   ppb for a arrangement using a true deaerator. Dissolved oxygen in the feedwater can cause pitting corrosion damage of the feedwater system components. More complex feedwater systems tin can include both low- and high-pressure feedwater heaters in addition to an economizer.

Additionally, vacuum degasifiers or deaerating condensers can be used for dissolved oxygen removal. Recently, a semipermeable membrane procedure ⁷ has also been developed to reduce the dissolved oxygen content of water. These membrane systems take been used in laboratory environments for more than than 25 years but have only recently become commercially feasible for industrial applications. This membrane procedure can use a combination of vacuum and stripping gas arrangements to deaerate the water. The membrane modules can be arranged in series to produce ppb level oxygen concentrations in the final water. These membranes, dependant on the pH of the water, can also remove carbon dioxide. RO pretreatment is recommended ahead of the gas membrane to foreclose fouling. A conventional deaerator provides only express removal of carbon dioxide, based on the typical alkaline pH of the water where the carbon dioxide would be as the bicarbonate ion, non equally a gas.

After any of these mechanical/thermal deaeration processes, a chemical oxygen scavenger tin exist applied to further reduce the dissolved oxygen content of the feedwater (Tabular array 1).

Table i. Oxygen scavengers used in steam-generating systems

Scavenger	Primary reaction	Comments
Hydrazine	N2H4+Otwo→2Nii+2H2O	Toxicity and handling bug
Hydrazine decomposition	3N2H4→4NH3+N2	At temp. >200   °C
Sodium sulfite	2Na2SOthree+O2→2NaiiSOiv	Also NaHSO3, Na2Due south2O5, NH4HSO3
Carbohydrazide	(H2N–NH)twoCO+2Otwo→2N2+3HiiO+CO2	Forms hydrazine at temperature >150   °C, NHthree, Due northtwo, and H2 on decomposition
N,N-Diethylhydroxylamine	four(CH3CH2)2NOH+9O2→8CHiiiCOO−+9H++2Nii+6H2O	Frequently fed with hydroquinone, acetic acid, CO2, acetaldehyde, NH3 at temperatures higher up 275   °C
Hydroquinone	CsixH4(OH)two+1/2Otwo→C6H4O2+H2O	Acetates, CO2 decomposition products, toxicity issues
Erythorbate	CviHiv O6+1/2O2→C6H5Oeight+H2O	CO2, lactic acid, decomposition products
Methyl ethyl ketoxime	2CH3(C2H5)CNOH+Otwo→Due northtwoO+2CH3(C2H5)CO+H2O	Oft fed with hydroquinone, NH3, COtwo, ketones, aldehydes on decomposition

Sodium sulfite is the most common chemical oxygen scavenger used in low-pressure boiler systems. Information technology is also available in a catalyzed form, which increases the speed of reaction with the dissolved oxygen. This can be important when the mechanical deaeration procedure does not provide sufficient residence time. Sodium sulfite is a nonvolatile inorganic compound that does contribute dissolved solids to the feedwater and the boiler water. This dissolved solids contribution prevents its use in feedwater that is to exist used as attemperator spray or desuperheat spray for steam temperature control, as these solids would get impurities in the steam.

The command of sodium sulfite is generally based on maintaining a sulfite remainder concentration in the boiler h2o. This can be a problem in a system where the feedwater organisation deaeration process and chemical injection point do not provide sufficient residence time and temperature for the chemic oxygen scavenging reaction to be completed prior to the feedwater entering the steam drum of the boiler. Oxygen scavengers and dissolved oxygen can coexist in the feedwater, and in such a situation, pitting corrosion of pre-banality components can occur. Because of the dissolved oxygen's loftier volatility, the oxygen preferentially goes into the steam phase when the feedwater enters the boiler steam drum, leaving the unreacted sulfite equally an apparent residual in the boiler water.

Another bespeak of oxygen ingress into the system not to be overlooked is a leak path through the boiler feed pump seals. It is wise not only to monitor the temperature and pressure level operating conditions of the deaerating device for proper operation just also to periodically mensurate the feedwater dissolved oxygen content directly after the boiler feed pump.

Sodium sulfite can as well produce some acidic gaseous decomposition products, such as sulfur dioxide, that will be carried out of the boiler in the steam. This can be significant at boiler operating pressures in a higher place iv.1   MPa   g (600   psi   m). These decomposition products can crusade low steam condensate pH.

Hydrazine is another available oxygen scavenger that has been used primarily in higher-pressure boiler applications. It is a volatile compound that can exist used in feedwater that is used for steam temperature control by attemperation or desuperheating. However due to its status as a suspect carcinogen, its utilise in industry has declined. When it is used, a closed feed system is typically required.

Given these health concerns, alternatives to hydrazine have been developed. The almost common of these are carbohydrazide, erythorbate, diethylhydroxylamine, hydroquinone, and methylethyl ketoxime. Many of these oxygen scavengers also function equally passivating corrosion inhibitors. Each is an organic chemical compound that has its own temperature limitations. Decomposition products tin vary from simply carbon dioxide to several organic acids and other organic compounds. Some decomposition products are more undesirable than others, and the amount of these decomposition products tin can be awarding-specific, depending on organization temperatures and metallurgy. Each application should be evaluated based on the benefit provided versus the potential undesirable effects of the decomposition products. As a notation, commercially bachelor erythorbate can exist either in the acid form or in the sodium salt course. The sodium common salt form is nonvolatile, which restricts its use if the feedwater is used every bit spray attemperation or in desuperheating.

Read full affiliate

URL:

https://www.sciencedirect.com/scientific discipline/article/pii/B978012803581801691X

Corrosion and Degradation of Engineering Materials

A. Reynaud , in Shreir'southward Corrosion, 2010

3.02.4.2.3 Influence of dissolved oxygen

Dissolved oxygen plays a disquisitional role on the corrosion of fe (as information technology does for nearly metals). It is usually the primary cathodic reactant (oxidant) and its rate of influx at the metal surface influences the corrosion rate. Thus, the corrosion rates of many systems are controlled by the mass transport of dissolved oxygen to the reacting surface and this, in turn, is controlled past the concentration of dissolved oxygen, the fluid flow rate and the presence or absence of films (such as calcium carbonate or rust) on the surface. In the case of ferrous alloys (including fe and bandage irons), the corrosion products (fe oxides) on the surface are more or less hydrated and have different crystallographic structures. Rust, therefore, oft has several constituents, in particular: goethite (α-FeOOH); lepidocrocite (γ-FeOOH) and magnetite (Fe ₃O₄).

In the absence of dissolved oxygen, the corrosion rate of iron and of depression-alloy bandage iron is low. All the same, once the O₂ concentration increases, corrosion increases. In general, any process that modifies the mass ship of oxygen to the metal surface for reaction (including the concentration of oxygen and the rate of agitation of the fluid) influences the corrosion rate. Note, however, that the presence of dissolved O_ii can help in the passivation of some blend cast irons. Moreover, the absence of oxygen, at to the lowest degree locally, tin prevent the formation of a protective deposit or favor corrosion by differential aeration or crevice corrosion. This is the case, for instance, of corrosion under deposits of calibration, nether joints, and on the plates of tube exchangers.

One interesting study has shown the influence of the concentration of dissolved oxygen on the mechanisms responsible for the corrosion of cast iron in water at 50   °C. ³¹ The results of this study tin exist summed up using Figures xiii and 14 .

Figure 13. Steps in the evolution of the layer of oxides that forms on lamellar graphite unalloyed cast iron immersed in water at 50   °C containing 0.44   ppm oxygen: (a) from 3 to seven   h (b) after 10   h (c) from xvi to xl   h. Reproduced with permission from Smith, D. C.; MacEnaney, B. Corros. Sci. 1979, nineteen, 379–394.

Figure 14. The same equally Figure thirteen , simply in water at 50   °C containing 3   ppm oxygen: (a) later on ten   min (b) after 3   h (c) after 6   h (d) after 27   h. Reproduced with permission from Smith, D. C.; MacEnaney, B. Corros. Sci. 1979, 19, 379–394.

Read full chapter

URL:

https://world wide web.sciencedirect.com/scientific discipline/article/pii/B9780444527875000883

hartindetur1945.blogspot.com

Source: https://www.sciencedirect.com/topics/chemical-engineering/dissolved-oxygen

Share this post