Pollution control of surface waters by coupling gliding discharge treatment with incorporated oyster shell powder

Highly oxidizing gaseous species (OH, NO and derivatives) formed in an electrical discharge (a gliding discharge burning in humid air), are suitable for abating the organic pollutant concentration of surface waters sampled in Cameroonian brooks, e.g., 47% (Total Organic Carbon, TOC) within 10 min exposure. The plasma technique coupled with the use of finely powdered oyster shell (OS) acting as a catalyst and an acidity control agent thus yields improved results. This paper is devoted to determining the optimum amount m (g L−1) of incorporated OS before switching on the discharge for given exposure times t* (min). The process effects are controlled by means of pH, Biological and Chemical Oxygen Demands (BOD, COD), and Total Organic Carbon (TOC) measurements performed for various t* and m values and the results are compared with a mere plasma treatment on the same samples. The BOD5 and TOC values respectively decrease by 86% and 36% for 10 min exposure with 1 g L−1 incorporated OS. Treatments with OS stabilize acidity around pH: 6.5 while the pH decrease is more important without OS. BOD5 and TOC exponentially decrease with t* with or without incorporated OS, as does COD with OS only. BOD5 exponentially decreases with increasing m while COD linearly depends on t* and m, and TOC on m only. Optimized treatment parameters are t* = 30 min, m = 0.1 g L−1.

► NO, OH and derivatives form in electric discharges in air at atmospheric pressure. ► The oxidizing plasma species degrade organic wastes sampled from surface waters. ► The process is followed by BOD, COD and TOC measurements for exposures up to 30 min. ► Incorporating powdered oyster shell (OS) controls acidity and hence the kinetic rate. ► Treatment time and OS mass are optimized around 36% TOC abatement within 10 min.