MODELLING LEVELS OF MICROBIAL AND CHEMICAL CONTAMINANTS IN WASTEWATER USED FOR PERI-URBAN IRRIGATION IN THE TAMALE METROPOLIS, GHANA

Abstract

Wastewater irrigation can pose a variety of potential health risks and also excessive and often imbalanced addition of nutrients to the soil to affect crop production. Thus its use in agriculture without adequate safeguards has been noted to have serious drawbacks for human health and the environment. This study modelled the levels of microbial and chemical contaminants in wastewater used for peri-urban vegetable crop production for both dry and wet seasons and also assessed the efficiency of an on-farm sand filter system on the contaminants in the Zagyuri community of the Tamale Metropolis of the Northern Region of Ghana. Three (3) different set-ups of tanks with lengths (L) 8.5 (T1), 17 (T2) and 25.5 (T3) cm were used as treatments with media sizes ranging from 2 to 45 mm. A total of ten (10) water samples were collected at each sampling time at weekly interval (7 days) using 500 ml bottles for a period of 16 weeks. Standard laboratory analyses procedures were adopted for the microbial and chemical parameters. The microbial results indicated thirteen (13) different types of helminths (H). The Multivariate analysis of Faecal Coliform (FC) data indicated that an increase in the length of the treatment filter column by a unit decreased the FC concentration level in the wastewater. It was observed for both seasons that, the mean concentration levels of FC varied with the season (wet season = 24,444 and dry season = 13,780). T3 achieved the highest removal efficiency of FC by 80.9 % and the least T1 withremoval efficiency of 68.0 % in the wet season. In the dry season however, T3 recorded a removal efficiency of 69.7 % compared to the least of T1 with removal percentage of 62.6 %. The model generated indicated that the parameters L, RH, T, P and pH had an inverse relationship with Total coliform (TC) concentration in the wastewater. Apart from Fe which was insignificant in both seasons, all the other parameters recorded a significant difference in the two seasons. Al, Fe, Mn and Zn on the average recorded higher concentrations in the wet than the dry season whilst Cu recorded a higher concentration value in the dry season than the wet season. Amongst all the heavy metals, Fe recorded a higher concentration in both the dry and wet seasons. Concentrations of most of the heavy metals in the study area were lower than the WHO and FAO recommended standards except Mn which had concentration levels exceeding the recommended standard in the wet season only. A further study of the bioaccumulation effect of heavy metals in the soils should be undertaken to assist in advising on the impact of continuous use of wastewater on the soils of the area. The current design should be further investigated to serve as a low cost option of treating wastewater on-farm.