[Evaluation of bacterial and polluting loads of effluent from activated sludge wastewater treatment plants in Yaounde, Cameroon]

Activated sludge wastewater treatment plants in Yaounde are plagued by failures in their operation. A microbiological and physico-chemical study was carried out on wastewater effluent of an hospital, university campus, and two residential areas made up of more than 2,000 apartments connected to two collective sewase systems. Wastewater sampling was performed in the form of daily cycles during which composite samples were made every two hours with samples collected every half hour. Variables measured included incoming flow rates, suspended solids, pH, electrical conductivity, ammonia nitrogen, total Kjeldahl nitrogen (combination of ammonia and organic nitrogen) and total reactive phosphorus, BOD5 and COD. Microorganisms were isolated on selective culture media using membrane filter procedures. The results obtained show that effluent discharged in receiving waters are, in general, not treated. The suspended solids contents of raw sewage range from 120 to 2,600 mg/l. In General Hospital a mean value of suspended solids of 31.8 mg/l was obtained for treated wastewater. pH values of both raw and treated sewage range from 6 to 8.5 units. Mean values of the conductivity of treated and raw wastewater range from 449.7 to 1,038.3 microseconds/cm. The TKN contents of untreated wastewater are comprised between 36 and 259.2 mg/l. These values range from 5 to 20 mg/l for treated effluent in the General Hospital plant. Large amounts of total hydrolysable phosphorus varying from 3.8 to 27.9 mg/l are present in wastewater from the plants. Influent BOD5 of Grand Messa, Cite Verte and university campus wastewater range from 110 to 530 mgO2/l. Values recorded indicate an important input of organic matter to receiving waters. In the case of biotic components, test germs densities registered in the influent of Grand Messa and those of Cite Verte are comprised between 9 x 106 and 88 x 107 CFU/100 ml for fecal coliforms, and between 9 x 105 and 74 x 107 CFU/100 ml for fecal streptococci. The densities of Aeromonas hydrophila in Grand Messa and Cite Verte influent fluctuate between 30 x 106 and 65 x 108 CFU/100 ml. Influent of university campus harbour 10 x 105. Densities of Pseudomonas aeruginosa remain below 70 x 105 CFU/100 ml. Treated effluent BOD5 values range from 48 to 150 mgO2/l. Such values indicate an inefficient treatment. The decrease in bacterial densities is limited to 2 logarithmic units. Treated effluent still harbour 10 x 103 to 10 x 105 CFU/100 ml for fecal coliforms, and 20 x 102 to 12 x 104 CFU/100 ml for fecal streptococci. These values range from 10 x 104 to 50 x 105 CFU/100 ml for Aeromonas hydrophila. Pseudomonas aeruginosa densities remain in general below 40 x 104 CFU/100 ml. Discharges from these wastewater treatment plants are responsible for the permanent fecal contamination of the environment and a lack of proper hygiene. Furthermore, they produce overfertilization of receiving waters.

[Bacteriological quality of spring and well water in Yaounde (Cameroon)]

The drinking water supply in Yaounde, Cameroon, often fails to meet demand and this leads many people to seek water from springs and wells the microbiological quality of which is unknown. We carried out a microbiological survey of five spring water points and ten wells. The fifteen study sites were located in various residential districts and were selected according to geographical location and number of users. Microorganisms were isolated on specific culture media using the membrane filter technique. We found that these water supplies contained many types of bacteria including Pseudomonas aeruginosa, Aeromonas hydrophila and indicators of fecal contamination. Maximum annual concentrations differed at the various sites and over time, from 750 to 98,000 CFU/l for P. aeruginosa, 40 to 78,000 CFU/l for A. hydrophila and 300 to 58,000 CFU/l for fecal indicator bacteria. The density of fecal bacteria was strongly correlated (p < 0.01) with those of P. aeruginosa in spring water and A. hydrophila in well water. The degree of correlation between microbial concentrations differed between sites. The source of fecal contamination differed between sites and was animal, human or both. The densities of bacteria recorded were high. Therefore, consumers of water drawn from these sources are at short-term risk of contracting waterborne diseases.