Characterization, Efffects and Chemical Treatment of Heavy Metals in Produced Water from Injection Wells using Hydroxide Precipitation

Abstract

Produced water obtained from five (5) water injection Wells in the Niger Delta area Nigeria were analysed for heavy metal ion concentrations using Themo Elemental Flame Atomic Absorption Spectrophotometer (AAS). Results obtained show that concentrations of lead (Pb²⁺), cadmium (Cd²⁺), chromium (Cr²⁺), nickel (Ni²⁺), cobalt (Co²⁺), vanadium (V²⁺), zinc (ZN²⁺), mercury (Hg⁺), silver (Ag⁺) and copper (Cu²) were above acceptable limits as specified by Environmental Guidelines and Standard for Petroleum Industries in Nigeria (EGASPIN). The concentrations of As²⁺, Fe²⁺, K⁺ and Mn²⁺ were within specification. Commingled produced water from the five water injection Wells were subjected to hydroxide precipitation using Ca(OH)₂ at concentrations of 10, 20, 30, 40 and 50 ppm respectively. Results obtained show that all the heavy metal ions reduced within acceptable limit at 30 ppm chemical concentration. Heavy metal ions reduced with increase in chemical concentration with a corresponding increase in the pH of the solution which was however still within specification. The hydroxide converts the metal ions dissolved in solution into solid particles for easy sedimentation. Ca(OH)₂ precipitates metal ions by changing the pH and electro-oxidizing potential of the solution. Properly treated produced water can be reinjected into the reservoir to enhance oil recovery, used in agriculture for irrigation purposes, discharged into the sea and other water bodies during offshore operations or even used in drilling services. Produced water discharged into the soil are non-biodegradable so must be adequately treated before discharge. Plants pick up heavy metals through their roots by the release of a variety of root exudates which changes the rhizosphere pH of the metal ion in solution thereby making them bioavailable for plant uptake by osmosis. Heavy metals in plants can exert a variety of toxic actions by damaging plant chloroplast thereby disturbing photosynthesis. Humans take in heavy metals into their system by consuming contaminated plants, water as well as inhaling contaminated air. Consumption, ingestion and inhalation of heavy metals by humans can cause a wide range of ailments such as cardiovascular diseases, kidney related problems, neurocognitive diseases, renal damage, heart disease, coronary artery disease, lung fibrosis, nasal cancer.