STUDIES OF DISINFECTION BY-PRODUCTS AND HEAVY METALS IN AHMADU BELLO UNIVERSITY DRINKING WATER SUPPLIES AND OPERATIONS OF SOME TREATMENT PLANTS

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Department of Engineering

ABSTRACT
This study had a broad objective of determining the quality of drinking water produced by Ahmadu Bello University (ABU) water treatment plant. Its samples were chemically analysed for general chemical properties, heavy metals and Disinfection By-Products (DBPs) content in accordance with standard analytical methods and USEPA methods 551.1 and 552.2 for the DBPs. Structured questionnaire survey was adopted to evaluate the operating code of practice of the ABU water works and nine others. 80% of the surveyed water works were found to be of the single train, one injection point, and one disinfection segment treatment plants. All the water works have both preliminary and main water treatment processes including screening, flocculation, sedimentation and disinfection processes. World Health Organization (WHO) operating code of practice is used by 90% of the treatment plants but in varied forms. Treatment plants declaring disinfecting water always were 70% though some reports indicate otherwise while irregular supply prevented those not always disinfecting. Operators of 60% of treatment plants claimed uninterrupted water distribution but irregular water distribution was reported. 80% of the treatment plants had no fully functional service laboratories. Staff were found inadequate, with low capacity building and have limited professional competence in potable water delivery. Treated water assessed parameters were pH 7.2, conductivity 96.3μS/cm @ 250C, total dissolved solids 63.75 mg/l, total organic carbon 2.3 mg/l, nitrate 1.00 mg/l, phosphate 0.12 mg/l, chloride 0.57 mg/l and sulphate 36.17 mg/l. Zinc and lead were the only heavy metals detected, in concentrations of 0.04 and 0.035 mg/l respectively. Thirtysix DBPs including nine of the regulated eleven were found in the study. Observed total regulated Trihalomethanes were 0.0107 and 0.0093 mg/l, total regulated Haloviii acetic acids 0.52580 and 0.23774 mg/l, total halo-Acetonitriles 0.0269 and 0.0096 mg/l, total other-DBPs 0.1012 and 0.0409 mg/l and total chlorinated solvents 0.1440 and 0.1306 mg/l (for household and boiled household water respectively) which did not conform to Nigerian, USEPA, EU and WHO standards because the concentrations of lead, total THM4, 1,1,2-Trichloroethane and total HAAs exceeded these standards’ maximum permissible levels. Longitudinally, this investigation showed DBP formation is a consequence of disinfection after which the DBPs were first detected and in higher concentrations. First morning urine showed higher DBP concentrations than boiled drinking water triggering public health consequence beginning with increased excretion by the kidneys to maintain the homeostatic status of the body coupled with incidences of cancer, diseases of the kidney, liver, the reproductive systems and damage to the central nervous system. Statistically, observed concentrations were found to be significantly different between DBP groups (F =3.5115*) or highly significantly different among the groups (F = 4.8582**) and HAAs (F = 4.93**). Person’s correlation coefficients (r) ranged from over 0.5 to 0.98 in over 85% of the analytes indicating a strong combination effects likely varying from additive to synergistic impacts in the body.