Water scarcity in South Africa, and globally, presents challenges for industries. It is therefore imperative to develop responsible water use, such as recycling and reusing wastewater from food processing industries such as breweries. The Ibhayi Brewery (SAB Ltd) employs a combination of sustainable treatment processes that include anaerobic digestion, primary facultative ponds, high-rate algal ponds and constructed wetlands (CW) to treat brewery effluent on an experimental scale. The constituent concentrations of these experimentally treated effluents are within the ranges prescribed by local regulations to allow for potential downstream use in agriculture and aquaculture. However, the sodium content in this treated effluent, which originates from upstream cleaning agents and pH control at the onsite effluent treatment facility, is a constraint to the downstream use of brewery effluent. This study addressed the salt problem, by investigating potential techniques for downstream agriculture and aquaculture to mitigate the effects of salt accumulation caused by irrigation with brewery effluent.
Constructed wetlands of 15m length were planted with Swiss chard (Beta vulgaris), and used to treat brewery effluent after anaerobic digestion. Plant production peaked halfway down the wetland (11438±450 g/m2) (figure 1), with reduced growth and plant health closer to the inlet and outlet.
There were no significant differences in the sodium concentration of brewery effluent treated along the CW, likely due to evapotranspiration. This was accompanied by a 95.21% decrease in ammonia from the inlet (69.93±1.49 mg/L) to the outlet (3.57±0.36 mg/L), resulting in significant improvement in water quality for downstream reuse in aquaculture. African catfish (Clarias gariepinus) grew in this treated brewery effluent; however, growth was moderate at 0.92% body weight gain per day, whereas the system was not suitable for Mozambique tilapia (Oreochromis mossambicus) since the fish did not grow (-0.98% body weight per day). While constructed wetlands remain a suitable effluent treatment solution, this technology requires additional modelling and optimization to optimize the reuse of treated brewery effluent in agriculture and aquaculture.