Electrocoagulation of landfill leachate: Transforming a hazardous residue into a source of irrigation water

Abstract

Electrocoagulation of landfill leachate has been widely investigated, however, only few reports include the reuse of the treated water. In this work, treated leachate is evaluated as irrigation water. The main obstacle is the high Sodium Absorption Ratio (SAR=Na⁺/(Ca²⁺+Mg²⁺)/2. Reducing this indicator involves decreasing Na⁺ and increasing Mg²⁺ or Ca²⁺. Sodium concentration reduction is difficult by electrochemical methods (E₀ = -2.71 V); Ca²⁺ increasing is not feasible as it precipitates. Hence, the use of different Al-Mg anodes was tested tending to increase Mg²⁺ concentration in the treated water The alloy 88%wtAl-12%wtMg was able to remove 52.9% of COD, 98.1% of turbidity, 97.9% of color, obtaining a SAR of 8.2 meq·L^-1, total hardness (TH) of 64.2 meq·L^-1 and a soluble sodium percentage (SSP) of 75.8 meq·L^-1. This was achieved by working at a current density of 15 mA cm^-2, a treatment time of 15 min and a pH 5.0. The phytotoxicity of the treated leachate was evaluated by the germination index using Lactuca Sativa L., reaching a value of 83.2%, which is considered excellent for irrigation water. During growth, 3-4 primary leaves were observed in seedings after 21 days, similar to when potable water was used. The results demonstrate that electrocoagulation is an adequate treatment technique for the reuse of landfill leachate if appropriated materials are used as anodes working in well selected operational variables.

Keywords: Al-Mg anode; Electrocoagulation; Landfill leachate; Phytotoxicity; Reuse; Sodium absorption ratio.