Assignment 1 (Submission date: 17 April 2018) Question 1 (a) What are the 4 different pollutants in domestic wastewater (sewage). Name the methods by which each of these pollutants can be treated...

Assignment 1
(Submission date: 17 April 2018)
Question 1
(a) What are the 4 different pollutants in domestic wastewater (sewage). Name the methods by which each of these pollutants can be treated before disposal into waterways.
    Group
    Elements
    Risk description
    Removal process
    Nutrients
    N (as total Kjeldahl nitrogen), P (as total phosphorus)
    Plant health, Aquatic system eutrophication
    The removal of nutrients is carried out through way of aerobic as well as anoxic procedures
    Heavy metals
    Arsenic (As) Cadmium (Cd) Copper (Cu) Chromium (Cr) Iron (Fe) Lead (Pb) Mercury (Hg) Nickel (Ni) Selenium (Se) Tin (Sn) Zinc (Zn)
    Harmfulness to microorganisms, plants, treatment, animals and individuals.
    Removal of heavy metals is done though Membrane bioreactor (MBR) that is basically an amalgamation of a membrane procedure such as ultrafiltration or microfiltration having a biological wastewater treatment procedure.
    Cations and Anions
    Boron (B) Chloride (Cl) Fluoride (F) Sodium (Na) Total dissolved solids (TDS)
    Salinity and sodicity of soil, plant health
    Removal of cations and Anions is done though Membrane bioreactor (MBR) that is basically an amalgamation of a membrane procedure such as ultrafiltration or microfiltration having a biological wastewater treatment procedure
    Trace elements
    Antimony (Sb) Cobalt (Co) Molybdenum (Mo)
    Plant growth
    The removal of trace elements is carried out through way of aerobic as well as anoxic procedures
(b) Describe briefly the two ways phosphorus is removed from sewage in a wastewater treatment plant
Phosphorous removal processes
The phosphorous removal from wastewater takes in the unification of phosphate into TSS and the following removal from such solids (Connor and Wilkie, 2005). Moreover, Phosphorous could be easily combined into chemical precipitates or biological solids.
Phosphate precipitation
Chemical precipitation is basically employed for removing the inorganic forms of phosphate through adding a coagulant as well as mixing of coagulant and wastewater (Connor and Wilkie, 2005). The multivalent metal ions widely considered include calcium, iron and aluminium.
Calcium
It’s generally added lime form Ca(OH)2 . It basically reacts with the natural alkalinity present within the wastewater for producing calcium carbonate that is chiefly accountable for improving SS removal (Connor and Wilkie, 2005).
Ca(HCO3)2 + Ca(OH)2 à 2CaCO3 ↓+ 2H2O
When wastewater’s pH value goes up beyond around 10, additional calcium ions at that time react with the phosphate, for precipitating in hydroxylapatite:
10 Ca2+ + 6 PO43- + 2 OH- ↔ Ca10(PO4)*6(OH)2 ↓
For the reason that the reaction is amid the lime as well as wastewater alkalinity wastewater, the amount needed would be, in common, autonomous of the present phosphate level (Connor and Wilkie, 2005).
Aluminium and Iron:
Hydrated aluminium sulphate or Alum is extensively utilized for precipitating phosphates as well as aluminium phosphates (AlPO4). The reaction is:
Al3+ + HnPO43-n ↔ AlPO4 + nH+
Effectiveness could touch 95 percent as well as P concentration within the effluent could be even lesser than 0.5 mg/l. Moreover, Postprecipitation provides a sound elimination of the SS, which escape the ultimate sedimentation of secondary procedure. In addition, its benefit also involves ensuring purification effectiveness at a definite level even in case if the biological procedure isn’t effective for few reasons (O’Halloran et. al., 2002). The chemical reaction is powerful, for the reason that the preceding biologic treatment converts fraction of organic phosphates into orthophosphates. However, drawbacks involve high expenses of the treatment plant and at times a highly dilute effluent. Making use of ferric salts involves the threat of having iron within the effluent, along with residual coloration.
(c) What are the pollutant removal mechanisms in an intermittently decanted aerated lagoons (IDAL) used in wastewater treatment plant.
The removal of Nitrogen is carried out through way of aerobic as...