[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.
Njiné
T
T
Laboratoire de biologie générale, Faculté des sciences, Université de Yaoundé 1, BP 812 Yaoundé, Cameroun. tnjine@uycdc.uninet.com
Monkiédjé
A
A
Nola
M
M
Foko
V S
VS
D016980:Aeromonas hydrophila / Q000502:physiology; D002163:Cameroon; D015169:Colony Count, Microbial; D004755:Enterobacteriaceae / Q000502:physiology; D004787:Environmental Pollution / Q000032:analysis*; D005243:Feces / Q000382:microbiology; D006801:Humans; D011550:Pseudomonas aeruginosa / Q000502:physiology; D011634:Public Health; D012307:Risk Factors; D012722:Sewage / Q000032:analysis* / Q000737:chemistry / Q000382:microbiology*; D013289:Streptococcaceae / Q000502:physiology; D014504:Urban Health / Q000706:statistics & numerical data*; D014871:Water Microbiology; D018508:Water Purification / Q000379:methods / Q000592:standards*
D012722:Sewage