Physicochemical and Bacteriological Quality of Irrigation Water for Market Gardening Crops in the KIMPE District of Delvaux in the Municipality of Ngaliema in Kinshasa

This study was conducted to determine the physicochemical and bacteriological quality of agricultural water in the KIMPE district of Delvaux, in the Ngaliema municipality of Kinshasa. To this end, two points, including the Djelo River (P1) and a pond (P2), were targeted for water sampling, which were collected manually in November 2024. The physicochemical analyses, carried out in situ using the WTW multi-parameter probe, consisted of measuring several parameters (temperature, pH, electrical conductivity, and dissolved oxygen), while in the laboratory, the major dissolved ions (nitrates, phosphate, and sulfates) were measured by spectrophotometry. The bacteriological analyses consisted of the identification and quantification by the membrane culture method of bacteria indicating fecal pollution including Escherichia coli, Enterococcus and total coliforms. The results obtained revealed the following average values for the studied parameters:  Temperature (in °C): 36.6 °C (P1) and 36.7 °C (P2). These values recorded during this study are slightly higher than the limit value (35 °C) of the WHO guidelines for agricultural irrigation water. This slight thermal pollution can be explained by domestic wastewater discharge.  pH: 4.5 (P1) to 5.0 (P2). All these average pH values recorded demonstrate that the studied waters are all more acidic than the standard value (5.5-6.5). This could be explained by the contribution of potentially acidic runoff water, which tends to lower the pH of the waters in the study environment.  Dissolved oxygen (in mg/L): 5.3 (P1) and 4.5 (P2). These levels are all below the WHO guideline (≥ 7 mg/L) for agricultural irrigation water. There is therefore an oxygen deficit in the study environment, linked in part to the organic matter pollution present in these waters.  Electrical conductivity (in μS cm−1): 10.0 (P1) and 12.0 (P2). In both samples, the electrical conductivity values recorded comply with the WHO standard, which sets the maximum conductivity value at 12 μS/cm for agricultural irrigation water.  NO3- ion concentration (in mg/L): 47.61 (P1) and 25.17 (P2). The nitrate ion concentration complies with the WHO standard for water. Agricultural irrigation (limit value 27 mg/L) in the pond water (P2), while it exceeds the limit for the Djelo River water (P1).  Concentration of PO43- ions (in mg/L): 7.04 (P1) and 11.0 (P2). All these concentrations are above the limit required by the WHO standard for agricultural irrigation water (1.5). They indicate organic pollution that could lead to eutrophication.  Concentration of SO42- ions (in mg/L): 15 at both sampling points. These values are within the normal range (<200) and sufficient for plant growth. As for bacteriological analyses, the following average concentrations were recorded in CFU/100 mL:  For E. coli: 24 (P1) and 52 (P2)  For Enterococcus: 110 (P1) and 18 (P2)  For total coliforms: 220 (P1) and 152 (P2) All these concentrations are above the limit value (i.e., 10 CFU/100 mL). The results of this study indicate that the irrigation water used for market gardening in the Delvaux neighborhood of the Djelo site, in the Ngaliema commune of Kinshasa, is generally of a quality that does not comply with WHO standards for agricultural irrigation water. They are characterized by remarkable acidity, phosphate enrichment, and fecal contamination.