Biosand reactors for remediation of winery effluent in support of a circular economy and the positive effect of sand fractionation on hydraulic and operational performance

Abstract

There is an extensive body of knowledge pertaining to the treatment of winery wastewater and other acidic effluents in biosand reactors. This manuscript compares the performance of biosand reactors containing raw sand and fractionated sand. Fractionation of sand (particles <0.425 mm removed) increased the hydraulic conductivity of the sand matrix 9-fold when compared to raw sand: from 0.285 mm⋅s-1 to 2.50 mm⋅s-1 and 0.129 mm⋅s-1 to 1.11 mm mm⋅s-1 before and after start-up, respectively. Similar results for both sands were obtained in terms of organic removal performance (94 % and 95 %, respectively) and neutralization of acidic (pH 4.9) winery wastewater. Results indicate that one 5.6 m3 biosand reactor module containing 2.9 m3 of fractionated sand can theoretically treat 8102 L⋅d-1, which is the approximate volume generated from wineries crushing 329 to 547 t of grapes per annum. This is notably higher than the design flow rate of 1000 L⋅d-1 in used in a pilot system containing raw sand. Furthermore, a zero-waste biosand reactor model is presented for treatment of winery wastewater. The strategy includes reuse of treated effluent for irrigation, anaerobic digestion of primary winery wastewater sludge and use of the digestate as an agricultural fertilizer, and re-purposing of the residual sand.