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

Abstract

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·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·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.

Biosand Reactors for Municipal and Industrial Wastewater Treatment: Status Quo, Challenges and Opportunities

“…Microbial mechanisms of pH adjustment have also been seen in BSRs. In a study by Holtman et al [83], it was found that while calcite dissolution was responsible for 95.5 ± 0.16% of the increase in pH, the remaining 4.5 ± 0.13% was due to biotic mechanisms. Interestingly, complete neutralization of highly acidic synthetic acidic mine drainage (pH 2) was also demonstrated in HSSF BSRs containing river sand with 98% quartz and only 0.1% calcite [9].…”

“…This was supported by results obtained in a pilot HSSF BSR [7] and a VF BSR [26], where consistent increases in EC and pH were also measured during remediation of acidic winery WW. The major mechanism responsible for the increase in pH was later experimentally verified as being via dissolution of calcite [82,83]. This mineral form of calcium carbonate (CaCO 3 ) constituted 18% of the sand grains, and dissolution did not affect the hydraulic properties of the sand [83].…”

“…The major mechanism responsible for the increase in pH was later experimentally verified as being via dissolution of calcite [82,83]. This mineral form of calcium carbonate (CaCO 3 ) constituted 18% of the sand grains, and dissolution did not affect the hydraulic properties of the sand [83]. The theoretical abiotic neutralization capacity of the BSRs treating WW was predicted to be 37 years, which is beyond the projected lifespan of the system.…”