Treatment of waste water from nitrates explosive plant

Lawrence, Sikhitha Ntuweleni
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Nitrate waste water usually contains high concentrations of ammonium nitrogen (NH4+-N), which is known to hinder nitrification during biological treatment processes. In this study, removal of ammonium nitrogen from nitrate waste water was studied. Various purification processes such as using coagulation/flocculation and precipitation of magnesium ammonium phosphate was tested. Optimum parameters such as optimum pH, precipitation by pH adjustment and molar ratio were studied and precipitated crystals that formed were characterized. Sequential flocculation with two cationic flocculants reduced the turbidity of the nitrate waste water from 163 Neupholetric Turbidity units to 15 NTU. An optimum pH of 9 could remove ammonium nitrogen in nitrate waste water, as pointed out by evidence. Mg2+: NH4+-N: PO43--P with a 1:1:1.1 molar ratio was found to be the most effective ratio for maximum ammonium nitrogen removal, with quite a low residual concentration of PO43--P. MgCl2.6H2O + 85% H3PO4 combination was found to be more efficient combination for ammonium Nitrogen removal from nitrate waste water, with a low residual concentration of PO43--P. Precipitate crystals formed were found to be pure struvite crystals. Approximately 69.9% of ammonium nitrogen was recovered as struvite. Struvite precipitation is deemed to be an efficient for the treatment of ammonium nitrogen removal from nitrate waste water.
A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Masters of Science, Johannesburg January 2019