Effect of Particle Character and Calcite Dissolution on the Hydraulic Conductivity and Longevity of Biosand Filters Treating Winery and Other Acidic Effluents

Acidic effluent such as winery wastewater is challenging to remediate. Biological sand reactors can simultaneously remove organics and neutralize winery wastewater via biotic and abiotic mechanisms. The systems have been shown to be suitable for treating the intermittent flow of wastewater at small wineries. It has been shown that dissolution of calcite is the most important abiotic mechanism for increasing the pH of the influent. In this study, sand column experiments were used to determine the effects of (i) sand particle size distribution on calcite dissolution kinetics, and (ii) the effects of calcite particle dissolution on the hydraulic conductivity. The results were then used to calculate the theoretical temporal abiotic neutralization capacity of biological sand reactors with differently sized sand fractions, including unfractionated (raw) sand. The results were compared with those determined from a pilot system treating winery wastewater over a period of 3 years. Sand fractions with larger particles contained lower amounts of calcite (using Ca as a proxy), but exhibited higher hydraulic conductivities (3.0 +/- 0.05 %Ca and 2.57 to 2.75 mm center dot s(-1), respectively) than those containing smaller particles and/or raw sand (4.8 +/- 0.04 to 6.8 +/- 0.03 %Ca and 0.19 to 1.25 mm center dot s(-1), respectively). The theoretical abiotic neutralization capacity of biological sand reactors was compared with a pilot system with the same flow rates, and a temporal abiotic neutralization capacity of 37 years was calculated for biological sand reactors, which compared favorably with the theoretical results obtained for wastewater with pH values between 2 (8.2 years) and 3 (82 years). It was concluded that biological sand filters with around 10% calcite will be able to abiotically neutralize winery wastewater and other wastewaters with similar acidities for the projected life span of the system. Future work should focus on determining the effect of sand grain size on the bioremediation capacity, as well as the use of biological sand reactors for treating other acidic organic wastewaters such as fruit processing, food production and distillery wastewater.