Microbiological characteristics of wastewaters from a nitrogen- and phosphate-based fertilizer factory

Wastewaters from a fertilizer factory producing NH3, urea, diammonium phosphate (DAP) and nitrogen-phosphorus-potassium (NPK) fertilizers were assayed to determine the microbiological quality of effluents from the various fertilizer-production units and changes in this quality long after the start of production of the various fertilizer types. Mean total fungal and culturable aerobic heterotrophic (TCAH) bacterial populations were in the ranges of 0•11 × 103 − 2•1 × 104 cfu/ml and 0•166 × 103 − 6•1 × 103 cfu/ml, respectively, in the NH3-urea plant effluents; 3•0 × 103 − 2•5 × 104 cfu/ml and 1•18 × 106 − 2•98 × 106 cfu/ml, respectively, in the DAP-NPK plant effluents; 1•9 × 103 − 2•9 × 104 cfu/ml and 2•2 × 103 − 3•1 × 106 cfu/ml, respectively, in the effluents from the waste-discharge equalization basin (WEB) outflow. The highest mean TCAH bacteria population in the WEB was obtained after the production of DAP. Total coliforms and other bacterial faecal-population-indicators occurred in very low numbers in the fertilizer plant effluents, within a range of 0−0•93 × 103 MPN/100 ml. The WEB-outflow effluents had a higher mean population, in the range of 0•023 × 106 − 1•1 × 106 MPN/100 ml. Mean urea-degrading bacterial population was highest in the NH3-urea plant effluent, with a range of 0•19 × 103 − 1•14 × 104 cfu/ml. Other bacterial physiological groups of significance in the NH3-urea-plant effluent included NH3-oxidizers and NO2-oxidizers, while the significant physiological groups in the DAP-NPK-plant effluent included NH3-oxidizers and sulphate-reducers. Analysis of TCAH bacterial composition in the effluents showed a predominance of Pseudomonas, Vibrio, Methylobacterium and Rhodotorula glutinis in the NH3-urea-plant effluent, while Pseudomonas, Vibrio, Alcaligenes, Acinetobacter, Chromobacterium violaceaum and R. glutinis predominated in the DAP-NPK-plant effluent and the WEB-outflow effluents mainly after the production of DAP-NPK fertilizers. Other bacterial genera which predominated in the WEB outflow effluents included Staphylococcus, Salmonella, Shigella, Micrococcus and Enterobacter. Thus, the microbial composition of effluents from the various fertilizer-production units varied and led to variations in the composition of the microflora in the factoryʹs WEB. The DO concentration and BOD5 of the WEB were greatly affected by the DAP-NPK-plant effluents. It is speculated that wastewaters from this factory are capable of causing an alteration in the microbial diversity of the receiving waterbody.