Hydrogen peroxide dosage application as supportive chemical treatment process for sulphide removal in refinery wastewater treatment plants

Abstract

Refineries are known as high water consumed operation facilities. Water consumed processes produced high amount of and highly polluted wastewater. Big portion of wastewater is discharged to receiving water body where regulations must be met. According to regulations, treatment efficiencies of wastewater treatment plants must be provided sustainable. During this research, the focused pollutant parameter is selected as sulphide because inflow sulphide concentration is not stable. Sulphide concentration of wastewater is directly depended on crude oil characteristics and performances of process units. In any case where crude oil and process units discharge high concentration of sulphide containing wastewater, the treatment efficiency should be provided higher. Supportive chemical treatment is applied with hydrogen peroxide due to high oxidative capacity and operational easiness. Hydrogen peroxide also removes colour, chemical oxygen demand (COD) and it can also increase oxidation capacity of biological treatment process. In the present study, to make clear effect of hydrogen peroxide dosage application on sulphide removal efficiency, pollution load, chemical treatment efficiency, biological treatment conditions and health of microorganisms are remained at optimum conditions. During the research, hydrogen peroxide dosage determination, chemical consumption cost, sulphide removal efficiencies and environmental impact of hydrogen peroxide is evaluated. Effects of hydrogen peroxide is examined under four different scenarios which are, no hydrogen peroxide dosage application, uncontrolled hydrogen peroxide dosage application, every charge tank change period-controlled hydrogen peroxide dosage application, and the what if scenario where once a day-controlled hydrogen peroxide dosage application. During the first case, hydrogen peroxide is not applied to wastewater treatment system and sulphide removal is provided as 78% through aerobic biological process. Sulphide removal is provided through aerobic biological process. First case is examined only for aerobic biological sulphide removal. Before hydrogen peroxide application field tests are applied, sulphide removal with hydrogen peroxide analyses is applied at laboratory conditions. Hydrogen peroxide is applied with 15 mg/L, 25 mg/L, and 50 mg/L. The removal efficiencies are 50%, 57% and 72% respectively. For the second case, hydrogen peroxide is applied with the highest pump capacity of 24 L/h and hydrogen peroxide dosage is provided as 32 – 75 mg/L. Even though the sulphide removal efficiency is provided as 80% for this case, after detail examinations of data, results show that higher than 50 mg/L hydrogen peroxide dosage creates a negative impact on sulphide removal through aerobic biological process and decreases the removal efficiencies with 4%. This situation is caused by microorganism inhibition and maximum 50 mg/L hydrogen peroxide dosage is determined as optimum. During the third case, inflow sulphide concentration is analysed for every charge tank period where wastewater treatment plants charge is homogeneously coming from. Hydrogen peroxide dosage is applied according to sulphide analyses. Overall sulphide removal efficiency is provided as 90%. During the fourth case, regardless of third case, inflow sulphide concentration is analysed once a day and hydrogen peroxide dosage is adjusted according to one analyse. The removal efficiency is provided as 86%. The highest removal efficiency is provided during case three. Considering removal efficiencies and chemical consumption, dosage adjustment becomes more important. Uncontrolled chemical dosage can cause adverse effect on treatment efficiency. During controlled dosing application scenarios, chemical consumption is considered the same due to dosages hold the same. Hydrogen peroxide cost is estimated $445/ton. When maximum chemical dosage is applied 20,563 kg H2O2/month consumed and $9,150/month is spent. when controlled chemical dosage is applied 1,089 kg H2O2/month and $1,846/month is spent. Higher chemical costs and a lower treatment efficiency are risks of applying uncontrolled hydrogen peroxide dosage. It is critical to analyse input sulphide concentration and regulate the hydrogen peroxide dosage to avoid treatment efficiency fluctuations and to deliver higher and more constant treatment efficiency. Dosage determination improves the treatment process while lowering chemical costs and minimizing environmental effect. It is critical to invest in a sulphide analyser, which should be situated at the wastewater treatment plant's entrance, in order to provide more effective control. hydrogen peroxide concentration can be automatically modified if input sulphide concentrations are monitored with an online analyser. In addition, a single sulphide analysis in the laboratory takes two hours. Every tank change period sulphide analysis saves six man-hours through online analyser. In addition to reducing laboratory man-hours, field dosage modification will be simplified. The cost of a sulphide analyser is around $30,000.00. If a man-hour costs $10 per person per hour and a monthly sulphide analysis for case three takes 180 man-hours, the analyser will pay for itself in seventeen months. Results show that continuous analysis of inflow sulphide concentrations, improves dosage decision-making and provides the highest removal efficiency with controlled chemical consumption. In order to minimize the environmental effects and to keep the sulphide removal efficiency at sustainable and high levels, it is important to analyse the input sulphide concentration and determine the hydrogen peroxide dosage.