Removal of phosphates in wastewater via precipitation: Some aspects of modification, characterisation and optimisation

Pang , Wui Ying (2007) Removal of phosphates in wastewater via precipitation: Some aspects of modification, characterisation and optimisation. Masters thesis, Universiti Malaysia Sabah.

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Abstract

Phosphorus and nitrate are major limiting nutrients for algal bloom. When algae decomposesin water systems, biochemicalo xygen demand (BOD) would increase and cause other living organisms to be lacking in oxygen. Although phosphate compounds are less used in detergents or other washing agents, it is still widely used in agriculture as a source of fertilizer and its negative effects on the environment are significant. Removal of phosphate and nitrate from wastewaters with conventional ways by using alum, lime and iron will result in producing the precipitated phosphorus and nitrate-bearing salts sludge as waste products that were expensive to handle and transport. However, there is a different approach of removal by precipitating phosphate and nitrate into struvite, MgNH₄PO₄.6H₂O. Struvite can then perhaps be applied as slow fertilizers, raw materials for phosphate industry, also in the making of fire resistant panels and as binding material in cements. Experiments to investigate conditions and parameters that influence the precipitation of struvite are conducted in this research. Molar concentration ratio of 1: 1: 1 with respect to Mg²⁺,NH₄⁺ and PO₄³⁻ stoichiometricc oncentrations and at pH values of more than 8 were found to have caused an increase in crystal yield. Ratio of Mg²⁺ to the other ions should be at least 1.50 as this ion is an important limiting factor to produce the precipitate. Fe²⁺ ions caused failures in producing struvite as this ion competed with other ions to form iron complexes. Besides all these parameters( molar concentration,pH, excess of Mg²⁺ ions, Fe2²⁺ concentration and degree of supersaturation), conditions such as mixing (by stirring the solution with magnetic stirrer) in batch-scale experiments, proved to be indispensable in producing a significant struvite yield. Recycling, in this context means that struvite can be a source of raw material to replace phosphate mining from phosphate rocks and be a renewable nutrient source in the agriculture industry.

Item Type:Thesis (Masters)
Uncontrolled Keywords:systems,biochemical oxygen demand (BOD), phosphate, wastewater, precipitation
Subjects:T Technology > TD Environmental technology. Sanitary engineering
Divisions:SCHOOL > School of Science and Technology
ID Code:9181
Deposited By:IR Admin
Deposited On:10 Jul 2014 10:39
Last Modified:10 Jul 2014 10:39

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