Artisanal tannery wastewater: quantity and characteristics

Tannery wastewater is one of the most toxic waste generated in industries. In spite of this, there still remains a paucity of information on characteristics of wastewater generated from artisanal tanneries. This study, therefore, assessed the water consumption, wastewater generation rates, physicochemical and microbiological characteristics of wastewater produced from each process unit of an artisanal tannery in Ghana. The study revealed that the total amount of water use in the tannery ranged between 1171 and 2120L/day whilst the total volume of wastewater generated was within 820 and 1324L/day. Physicochemical characteristics of the different wastewater types generated at the tannery including chemical oxygen demand (13600–24333.30 mg/L), biochemical oxygen demand (1445.64–2803 mg/L), ammonia (3.20–21.38 mg/L), colour (950.35–53900.10PtCo), electrical conductivity (8170 - 10080 μS/cm), turbidity (450.24–1805NTU), suspended (1033.50–3216.40 mg/L) and dissolved (26166.50–4996.65 mg/L) solids exceeded the guidelines set by the Ghana Environmental Protection Agency. There were also high levels of chlorides, sodium, sulphates and calcium ions. The most dominant anion and cation in the wastewater were chlorides (715–20490.60 mg/L) and sodium ions (258–14056.45 mg/L) respectively. Heavy metals identified in the wastewater included zinc, aluminium, iron and chromium ions with the most dominant one being aluminium ions (0.58–78.18 mg/L). Whilst the E-coli was below detectable limit, the count of total coliforms ranged between 0 and 4.5 × 10(4)CFU/100mL. Five helminth egg species (Ascaris lumbricoides, hookworm, Trichuris trichiura, Strongyloides stercoralis, and Enterobius vermicularis) were identified with their numbers surpassing the safe limit set by the World Health Organisation for irrigation purposes. These results indicated that the indiscriminate discharge of the untreated wastewater on the bare soil as it is practised at the tannery has the potential to adversely affect public and environmental health. Appropriate treatment schemes are therefore, required to treat the wastewater to safe limits prior to discharge.