Assessment of microbiological and physicochemical quality of wastewater used for vegetable irrigation along the old waterworks stream in Tamale metropolis of Ghana

Worldwide, several million hectares of farmland in estimated 50 countries are used to cultivate agricultural produce by farmers who have adopted the application of untreated and or partially treated wastewater from various sources. The application of untreated wastewater which are contaminated with microbes and chemicals including heavy metals poses serious public health threat on the vegetable farmers, vendors and consumers of vegetables cultivated using such untreated wastewater. This study assessed the microbiological, physical and chemical qualities of wastewater used for vegetable irrigation along the Tamale old waterworks stream in the Tamale Metropolis of Ghana. Two wastewater samples each were collected from the four sampling sites: Waterworks upstream (WWU), Gumbihini midstream (GMS), Nyanshagu midstream Gardens (NMS) and Tunayili Kulbong Downstream Gradens (TKDS) along the stream monthly for six consecutive months for microbial and physicochemical parameters for dry and rainy seasons. A total of forty-eight water samples were collected and analysed for their microbiological, chemical and physical qualities using standard protocols adopted by the American Public Health Association (APHA, 1998). The results obtained showed consistent increase in the bacterial and physicochemical load for both irrigation seasons. The bacterial parameters studied include total coliform, faecal coliform, E. coli, Staphylococci, Enterococci, Pseudomonas and total heterotrophic bacteria. The statistical analysis on the microbials gave a weak correlation (r=0.24) among the individual sampling sites for microbial statistics. More so, there is a significant difference between the wastewater samples for dry and rainy season irrigation of microbial parameters with (p = 0.005) from the pairwise sample test. Results obtained showed consistent increase in the bacteria load for both seasons with the rainy season recording higher loads than the dry season except for total heterotrophic bacteria which was rather higher in the dry season as compared to rainy season. Overall, bacterial count recorded was lowest at GMS1 and highest at NMS2 for both seasons. The physicochemical parameters include, pH, conductivity, total alkalinity, total hardness, calcium hardness, magnesium hardness, carbonate hardness, bicarbonate hardness, calcium, magnesium, chloride, fluoride, sulphate, sulphide, phosphate, ammonia-nitrogen, nitrate-nitrogen, nitrite-nitrogen, aluminium, total iron, manganese, copper, zinc, cyanide, total chromium and potassium. There is strong correlation (r=0.99) among the individual sampling sites for physicochemical parameter analysis of wastewater samples during dry and rainy season irrigation schemes. More so, pairwise analysis indicates that there is no significant difference (p= 0.41) among the sampling sites for physicochemical wastewater samples for dry and rainy season irrigation of physicochemical parameters. Overall, physicochemical values recorded were lowest at GMS1 and highest at NMS2 for both the dry and rainy season samples. More so, bacterial counts recorded for all the microbial parameters exceeded the WHO (2006b) guideline of 1x103cfu/100ml for unrestricted irrigation of crops likely to be eaten raw whilst the physicochemical parameters determined were found to be within FAO/WHO guidelines for irrigation water except for colour, total alkalinity, chloride, zinc and cyanide. Most of the chemicals had levels above WHO guidelines and are potential health threat especially high nitrate concentration in irrigation water causes blue baby syndrome. The application of untreated wastewater poses serious public health threat on the vegetable farmers, vendors and consumers of vegetables cultivated using such untreated wastewater. It is therefore recommended that wastewater for irrigation of ready-to-eat vegetables be treated using biological nutrient removal system and wastewater stabilisation ponds to reduce and or eliminate contaminants before irrigating vegetables.

Source: KNUST