Treatment of Produced Water from Niger Delta Using Modified Cashew Nut (Anacardium Occidentale) Shells, Banana (Musa Acuminata) Stems and Peels

Produced Water (PW), a major component of well effluents during petroleum production, often contains contaminants such as toxic Heavy Metals (HMs). Usage of inorganic chemicals for PW treatment has environmental impacts and has been reported to be ineffective in reducing concentrations of HMs to recommended standards. There is dearth of information on the usage of organic materials in PW treatment because they are insufficiently investigated. This study was therefore designed to evaluate the effectiveness of modified Cashew Nut Shells (CNS), Banana Stems (BS) and Unripe Banana Peels (UBP) for treating PW from Niger Delta. A constructed adsorption column of 1.0 m height and 0.4 m internal diameter was retrofitted with a 0.2 hp pump. The CNS samples obtained from a local market were broken manually, washed with distilled water and acetone, and oven-dried at 105℃ (24 hours). Pulverized (<2.0 mm) Non De-oiled CNS (NDCNS) was sieved (2.54 mm), soaked and de-oiled with hexane to obtain De-oiled CNS (DCNS). Resulting NDCNS and DCNS were modified (6 hours) with 0.001M NaOH (1:10 (m/v)) using magnetic stirrer (150 rpm, 60℃) and rinsed. The BS and UBP were washed, sun-dried (48 hours) and pulverised to obtain BS Powder (BSP) and UBP Powder (UBPP), respectively, using standard methods. The BSP and UBPP were modified with (1:20 (m/v)) NaOH. Bio-chars of NDCNS, DCNS, BSP and UBPP were produced by oven-pyrolysis at 300℃ (3 hours). Untreated PW samples obtained from Niger Delta were analyzed for HMs using Atomic Absorption Spectrophotometer (AAS), treated under batch process and re-analyzed with adsorption isotherms. Data were analyzed using ANOVA at α_0.05. The PW contained chromium (0.054±0.014 ppm), nickel (0.550±0.020 ppm), iron (6.110±0.190 ppm) and lead (0.059±0.016 ppm). Batch treatment reduced HMs concentrations by 13.0-66.7, 74.0-93.5, 91.0-95.7 and 55.9-96.6% for unmodified and 13.0-81.5, 77.1-95.5, 91.6-98.3 and 67.8-94.6% for modified NDCNS, DCNS, BSP and UBPP, respectively. Reduction in HMs concentrations of 1.90-90.7, 75.6-97.5, 94.1-99.4 and 71.2-98.3% were obtained using bio-chars of NDCNS, DCNS, BS and UBP, respectively. Optimum time for chemical modification of adsorbents was 2 hours. The DCNS performed better than NDCNS. Modified adsorbents performed better than unmodified. Adsorbents with high dosage (5 g) were more effective. Langmuir isotherm better described adsorption of nickel (R²=0.982) and lead (R²=1.000), while Freundlich isotherm better described adsorption of chromium (R²=0.921). Modified cashew nut shells, banana stems and unripe peels effectively removed heavy metals from produced water in Niger Delta oil field. Hence, they have potential to replace imported inorganic chemicals if used at some optimal conditions.