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  by Ahmed El Komie 1 year ago

  Dear Mr. Hamra Lakhdar Thank you for accepting my invitation – if you need any safety training material for your people please let me know (FREE) – I have a twenty year career in municipality infrastructure projects in the US and Egypt. I like to with you some day. Thanks again this made me feel great. Ahme
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  by HAMRA lakhdar 1 year ago

  subject: Waste Water Treatment Plant: Concrete
  
  Quality of the Sand and Cement.
  
  * - Abrasion or erosion of the concrete surface only serves to expose additional material to the surface. Hydrogen sulphide is naturally converted to sulphuric acid which is corrosive towards steel and concrete .
  
  * -The effect of sulphuric acid on concrete surfaces exposed to the sewer environment can be devasting. Sulphuric acid attacks the matrix of the concrete. The primary product of concrete decomposition by sulphuric acid and other acids is calcium sulphate(mineral name: GYPSUM)
  
  H2SO4 + Ca,Si → CaSO4 + Si +2H+
  
  H2SO4+ CaCO3 → CaSO4 + H2CO3
  
  H2SO4 + Ca (OH)2 → CaSO4 +2H2O
  
  * - Aggression toward concrete depends on the types of ionic substances
  
  HYDROGEN SULFIDE in waste water: Sulphide exists in wastewater in three forms; hydrogen sulphide gas H2S, non-volatile ionic species hydrogen sulphide HS- and sulphide S-2.
  In addition to that, the salinity (chlorides Cl-) of the sand used in concrete fabrication should be at fixed concentration (authorised level in civil jobs).
  
  In addition to erosion of the concrete caused by chlorides, there is electrochemical reaction with the reinforcement (reducer element),Cl- (as oxidant).
  
  * Others factors such as acidity and low calcium carbonate saturations, can also cause corrosion and aggression:
  
  Salts are responsible for fastening the corrosion and aggression .These substances must be dissolved in water or as soil.
  
  The reinforcement will be destroyed and the concrete will be concerned by erosion, disappears.
  In my past experience in the GULF area, concentration of chlorides present in the sand used for concrete is responsible for the abrasion/erosion.
  The concrete of storage tank was damaged, replaced by using the correct salinity of sand (washing several times).
  
  During the civil construction, these main questions:
  * Dosing rate of the concrete?
  * Quality of the cement?
  *Salts (Cl-) content in the sand? : The main cause of the degradation of the
  Concrete
  
  
  
  
  Hydrogen sulfide is a substance which rapidly or completely vaporizes at atmospheric pressure and normal ambient temperature, readily dispersed in air and which will burn readily.
  
  H2S burns and explode easily.
  
  REMARKS:
  
  a. we have to take into consideration the dispersions in the surrounding atmosphere and depend on various factors like as:
  b. Gas emission rate/temp.
  c. Wind speed/direction.
  d. Atmospheric condition.
  e. Topography.
  f. Temperature gradients.
  g. Physical location and the direction of the emission.
  h. At high wind speed the dispersion will be rapid but in light breeze around 2m/s.
  
  
  
  
  
  
  
  Waste Water Treatment Plant:
  
  Gases(not expected) ----- More Risks : Can be Hydrogen Gas detected
  
   Others gases to be taken into consideration.
  
  More risks → to be taken into consideration.
  As far we now that the hydrogen sulfide is present in waste water. The water vapor & drop in the pipe line, with presence of H2S reaction take place with different available bacteria’s forms acids: HYDROGEN SULFITE H2SO3 (corrosive against the paint and the concrete, metal).
  There is a chemical reaction of hydrolysis in presence of H2O.
  
  H2O ↔ H+ + OH-
  
  H2S is belongs hydride family. There is production of ionic hydrides which are strong alkali, destroyed in contact with water.
  
  H- + H2O →H2 + OH-
  
  The hydride ion is unstable in presence of water gives Hydrogen gas.
  
  IMPORTANT:
  
  - Case of leak of waste water in the inlet area, or others confined spaces during shutdown or during the running , may produce hydrogen gas and automatically we have explosion: fire because many ignition sources available in the plant.
  - The atmospheric should be analyzed and automatic hydrogen gas detection should be implemented.
  - The risk is unpredictable.

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