Treatment of acid sulfate soil drainage using limestone in a closed tank reactor

Abstract

The principles of limestone drain systems that are commonly used to passively remediate acid rock drainage have been adapted and modified for remediation of acidic and metal-rich drainage that is produced from broad scale agricultural land use of regions underlain by Acid Sulfate Soils (ASS). The acidic drainage water from sugar cane fields in an ASS catchment was collected from an open drain, filtered to reduce the transport of large particulates, and passed vertically through a polyethylene tank, which was filled with limestone aggregates ( less than or equal 75 mm). This Closed Tank Reactor (CTR) uses the principles of oxic and anoxic limestone drain systems that are designed to increase the partial pressure of carbon dioxide and thereby the alkalinity produced from the dissolution of limestone by metal-laden influent. During a non-continuous 70 day monitoring period, the discharge from the CTR had higher pH, lower acidity and lower metal concentrations compared to the inflow. Under average flow conditions (9 lpm), similar proportions of incoming dissolved aluminium and iron (61% and 56% respectively) were retained within the CTR. Two perforated pipes in the base of the CTR were used to flush precipitates from the system under rapid flow conditions (>50 lpm). The flushing was effective in removing approximately 10% of accumulated iron but only about 0.3% of accumulated aluminium from the CTR. Accumulation of aluminium inside the CTR is likely to present operational problems in attempts to apply such technology to many coastal acid sulfate soil drains. © 2008 Springer Science+Business Media B.V.