Assessment of wastewater disposal at the main campus of the National University of Rwanda

Abstract

Water is used by mankind for a variety of beneficial purposes but is also considered as a medium for transporting wastes for subsequent discharge into the environment where it poses potential health risks. This study aimed to assess the quality of wastewater from the two overloaded septic tanks and the kitchen at the National University of Rwanda, the pollutants removal by land treatment, and the impact of this wastewater on the neighboring environment including the receiving stream that is used for domestic water supply, cattle watering and feeding fish ponds. Eight sampling runs were conducted fortnightly from February to May 2009 focusing on the following parameters: NH3-N, NO3-N, TN, PO4-P, TP, COD, BOD5, TC, FC and E-coli. The pollutants loads in the stream before and after the discharge of wastewater from the NUR were also quantified.The results showed that NUR wastewater is highly loaded with organic pollutants but its biodegradability is quite good as the BOD5/COD ratio being around 0.5. It also contains a high concentration of pathogens and nutrients especially NH3-N whose highest mean value from the three point sources was found to be 33.86 (±5.9) mg/l whilst. The quality of this wastewater is improved by land treatment through small scale irrigation before being discharged into a receiving stream. The pollutants removal efficiency for different parameters ranged between 18 and 66%. However, when this wastewater is discharged in the receiving stream, the pollutants concentration in that stream is increased at a rate of 57% for NO3-N; 99% for NH3-N; 73% for TN; 80% for Ortho-P and TP; 93% for BOD5 and COD. This study revealed also that 138 m3 per day of wastewater was discharged into the receiving stream after crossing an agricultural land and this discharge was higher than the initial discharge of the stream which was about 120 m3 per day.