Calcite Dissolution and Bioneutralization of Acidic Wastewater in Biosand Reactors

Abstract

Acidic wastewaters such as winery wastewater require treatment to increase the pH before discharge into the environment. Biosand filters have been shown to reduce the organic load while simultaneously providing a buffering function. Previous research has shown increases in pH which was assumed to mainly take place via dissolution of calcite from the sand particles. This study investigated the possible role of biotic mechanisms for pH adjustment in sand column experiments by comparing results obtained from irradiated (biotic) and non-irradiated (biotic and abiotic) sand columns extracted from biosand filters used to treat winery wastewater. The columns were fed with either synthetic winery wastewater or filtered water (control). It was shown that the specific hydroxide concentrations in the eluant from the non-irradiated columns was significantly (p < 0.05) higher than in the eluant from the irradiated columns (1.1 × 10−5 vs. 4.0 × 10−6 M/kgsand−1), indicating the presence of both biotic (average 4.5 ± 0.13%) and abiotic (average 95.5 ± 0.16%) pH increases. Using multivariate statistical tools to analyze a combination of parameters linked with biotic and abiotic pH adjustment, significant differences (ANOVA, p < 0.05) were found between the four treatment groups (irradiated/non-irradiated SWW and control) and the groups showed good clustering in cluster plots (group average) linkages, and principal component analysis plots.

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

“…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 theoretical abiotic neutralization capacity of the BSRs treating WW was predicted to be 37 years, which is beyond the projected lifespan of the system. An added advantage of calcite dissolution is that the presence of divalent calcium (Ca 2+ ) in the BSR effluent also protects receiving environments from sodicity from saline WW [26,82].…”