Performance evaluation of coconut coir-pith in free water surface constructed wetlands.

Abstract

A study on wastewater treatment with a submergent wetland system was conducted at the University of Peradeniya, Sri Lanka. The primary objective of this study was to identify the improved potential for wastewater purification due to surplus organic carbon on microbiological activities and adsorption by coconut (Cocos nucifera) coir-pith as an alternative substrate material. Three constructed wetland units (Lysimeters-L1, L2 and L3) were used in the study, each having the dimensions of 5 m, 1 m and 0.6 m in length, width and depth, respectively. The substrate layer of each Lysimeter was amended with coconut coir pith and river sand as 100% river sand (L1), 100% coir-pith (L3) and mixture of then in equal compositions (L2,v/v=1:1). Hydrilla verticillata was planted in each Lysimeter with equal plant density. Influent and effluent water samples were analyzed for pH, conductivity, total suspended solids (TSS), total dissolved solids (TDS), five-day biochemical oxygen demand (BOD5), total nitrogen (TN), ammonia nitrogen (NH4N), and nitrate nitrogen (NO3-N), phosphate phosphorous (PO4-P) and faecal coliform bacteria in weekly interval. A parallel study was conducted at the laboratory in order to examine the best ratio of sand: coir-pith for the growth of H. verticillata. The removal efficiency of NH4-N, PO4-P, BOD5, Total coliform and TSS in L2, were 93%, 74%, 54%, 93% and 62%, respectively, which were higher than the other two Lysimeters (L1 and L3). The results of effluent water quality analysis illustrated that the coir- pith is efficient in removing nutrients from wastewater over sand. The laboratory experiment revealed that the coir and river sand mixture in equal compositions provides the best substrate media for plant growth