Anaerobically digested brewery effluent as a medium for hydroponic crop production – The influence of algal ponds and pH

Abstract

Millions of mega-litres of nutrient-rich effluent are discharged daily with environmental implications and often at considerable financial cost to the primary water user. This research aimed to develop technology that adds value to this liability, by making the effluent available for downstream use in hydroponic crop production.Brewery effluent subject to anaerobic digestion (AD) followed by treatment in a primary-facultative pond (PFP), contained sufficient nutrients to support the growth of Lycopersicum escolentum “Moneymaker” tomatoes. None of the effluent-grown plants performed as well as plants grown in inorganic-fertilizer and municipal water. However, the adjustment of the effluent pH with phosphoric acid to between pH 6.0 and 6.5 significantly increased plant growth compared to those in unaltered effluent. The pH adjusted effluent-grown plants grew to a mean height of 831 ± 21 mm and a dry biomass weight of 42.3 ± 2.8 g compared to the unaltered pH effluent plants which grew to half the height (411 ± 21 mm) and about a fifth of the weight (7.7 ± 0.7 g) after 49 days. Similarly, initial fruit production was higher for plants grown in pH adjusted effluent compared with those with no pH control. Effluent treatment in high-rate algal ponds (HRAP) prior to use in the hydroponic tomato system had no apparent benefits. Although the tomato plants grown in treated brewery effluent did not perform as well as those produced using inorganic fertilizer, the potential exists to use the water and nutrients in brewery effluent in downstream hydroponic production after AD and PFP treatment, particularly if the pH is maintained between 6.0 and 6.5.