Coagulation / flocculation process in the removal of trace metals present in industrial wastewater

Abstract

Attempts were made in this study to examine the effectiveness of polymer addition to coagulation process during treatment of a beverage industrial wastewater to remove some of its trace metals content such as lead, cadmium, total iron, total chromium, nickel and zinc. Experiments were conducted using the standard Jar test procedure to determine the performance of both ferric chloride and organic polymer (a non-ionic polyacrylamide) individually and ferric chloride-polymer combination. The dosages used for ferric chloride ranged from 0 to 500mg/l, whereas polymer dosages varied between 0 and 100mg/l. The (optimal) removal efficiency for total chromium in the wastewater was obtained at 300mg /l for ferric chloride and 65mg/l for polymer. Whereas for zinc and total iron, the optimal removal efficiencies were obtained at 500mg/l for ferric chloride and 65mg/l for polymer. Addition of ferric chloride resulted in significant removal of the metals reaching up to 91%, 72% and 54% of total chromium, zinc and total iron respectively while addition of polymer achieved 95%, 87% and 88% of total chromium, zinc and total iron respectively. Ferric chloride produced more voluminous and more compacted sludge than polymer. Combinations of ferric chloride and polymer at different ratio achieved better removal efficiencies of the metals in the range 84-97% for total chromium, 69-90% for zinc and 69-92% for total iron, also less sludge was produced. Lead, cadmium and nickel were not detected in the raw wastewater. @JASEM Since the early 1970s, there has been growing concern over the diverse effects of heavy metals on humans and aquatic ecosystems. Many heavy metals and their compound have been found that are toxic, while some are also subjected to biomagnifications (Viessman and Hammer, 1993; Gardea – Torresday et al. 1996 and Karvelas et al. 2003;). Environmental impact by heavy metals was earlier noticed to mostly connected to industrial sources (Karvelas et al. 2003). In recent years, metal production emissions have decreased in many countries due to legislation, improved cleaning technology and altered industrial activities. Today and in the future, dissipate losses from consumption of various metal containing goods are of most concern (Bergback et al. 2001). Therefore, regulations for heavy metal containing waste disposal have been tightened (FEPA, 1991). A significant part of anthropogenic emissions of heavy metals ends up in wastewater. Major industrial sources include surface treatment processes with elements such as Cu, Zn, Ni and Cr, as well as industrial products that, at the end of their life, are discharged in wastes (Sun and Shi, 1998). Conventional processes in the field of wastewater treatment can be divided into two main phases: (1) generation of suspended solids from colloidal and dissolved solids by physical, chemical and biological means in addition to the already existing suspended solids, (2) separation of suspended solids by chemical and mechanical methods including sedimentation, flotation and filtration (Santarsiero et al. 1998).