Optimising retention time and gravel media in ebb-and-flow filter for post–anaerobic digester brewery effluent treatment

Breweries produce large volumes of wastewater, which requires recycling to offset water scarcity. An ebb-and-flow filter is a filter system that creates aerobic and anaerobic conditions essential for the transformation and removal of nutrients. Optimising constructed wetland design and operation improves treatment efficiency and reduces operation costs. This study examined the combined effect of retention time (RT: 10, 20 and 40 min) and gravel size (7, 13, and 19 mm) on nutrient removal from a brewery effluent using a single-pass ebb-and-flow system design. These factors were tested for the reduction of chemical oxygen demand (COD), ammonia-N, nitrite-N, nitrate-N, and orthophosphate removal. The 10-min RT at 19-mm gravel achieved the highest removal efficiency, of 7.7% ammonia-N and 8.2% COD reduction. The 40-min RT at 7-mm gravel had the highest nitrate-N removal, at 18.6%. Orthophosphate removal was below 5% in all treatment combinations. The peak removal for ammonia was after 8 weeks, suggesting that the efficiency of the ebb-and-flow design for nutrient removal is time-dependent. Based on the results of this study a short effluent retention time of 10 min on 19-mm gravel is recommended for improved nutrient removal in the ebb-and-flow system design.