Sulphate Minimization in Agricultural Drainage Water Using Modified Rice Husk

Abstract

Eutrophication, salinization, hypoxia, and toxic algae, among other environmental damages are costly consequences of agricultural drainage water (ADW), and therefore poses a threat to ecological biodiversity, food security and agriculture sustainability. This work aimed to assess the adsorption efficiency of rice husk (RH) modified by chemical and thermal treatments for sulphate minimization from ADW. RH obtained from a local rice mill was washed in distilled water, oven-dried at 105 ˚C for 24 h, milled and sieved into 0.3–1.18 mm particle sizes. The optimum condition for carbonization was determined by varying the temperature- 200, 300 and 400 ˚C and time- 1, 1.5, and 2 h, respectively. The RH was activated by chemical (H3PO4 and ZnCl2) and thermal treatment. Batch experiments were carried out varying temperature (40-60 °C), adsorption time (15–140 min) and adsorbent dose (1 and 2 g) in an ADW with known sulphate concentration, 30 mg/L. The carbonization yield at 400, 300 and 200 ˚C varies within 18.91- 27.48%, 27.39- 32.82 % and 81.94- 95.75% respectively. It was observed that the percentage of carbon converted into silica increases with burning time; hence, the optimum temperature of 350 ˚C for 2 h was used for carbonization. Also, sulphate adsorption rate increased with contact time and dosage suggesting that the process is controlled by surface and pore diffusion. Based on the temperature study, adsorption was favourable at lower temperatures. H3PO4 and ZnCl2 treated adsorbents have similar removal efficiency; however, ZnCl2 treated adsorbent has a higher efficiency due to its ability to enhance the stability and mesoporosity of carbonaceous material. Modified RH is a potential adsorbent that could be of noble use in ADW quality minimization. However, the huge gap between literature studies and field application needs to be bridged by good extension services and appropriate policy.