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

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

Effect of submerged and floating plants on dissolved oxygen dynamics and nitrogen removal in constructed wetlands

Dissolved oxygen (DO) concentration affects the treatment processes in constructed wetlands. This study examined the dissolved oxygen dynamics and total nitrogen removal in constructed wetlands with submerged and floating plants. Four constructed wetland units each with the surface area of 3 x 1 m2 were constructed at University of Peradeniya. Two of those with the depths of 0.3 m (A) and 0.6 m (B) were planted separately with Hydrilla verticillata (submerged) and Lemna minor (floating), respectively. Other two (C and D) were constructed with two sections of 0.3 and 0.6 m depths and planted with H. verticillata and L. minor, respectively in each section. Secondary effluent from student hostel was fed with hydraulic retention time of 6 days. DO was measured at different depths of water, 0.0, 0.1, 0.2, 0.4 and 0.5 m from the water surface and along the longitudinal axis of the wetland at 6 hours interval. The total nitrogen was measured for water samples at inlet and outlets. The average dissolved oxygen concentrations of A and B were 17.7 and 0.4 mg L-1 respectively. Oxic condition was maintained in the submerged plant units. Anoxic condition resulted throughout the day in floating plant system. DO varied significantly with depths in oxic condition. DO dynamics in these wetlands can be explained by photosynthesis,respiration, deaeration and reaeration processes. The highest total nitrogen removal was achieved in unit D where combined anoxic and oxic conditions were maintained together H.verticillata and L. minor could effectively be used to maintain required dissolved oxygen in constructed wetlands for nitrate removal

Heavy metal removal in landfill leachate using agricultural waste materials: a case study in Sri Lanka

Open dumping of Municipal Solid Waste (MSW) is a common practice and identified as a source of pollution for surface and groundwater resources in Sri Lanka. The objective of this study was to identify the heavy metals in leachate and soils in the vicinity of MSW dump site and to assess locally available agricultural waste materials to use as adsorbents to remediate heavy metals from polluted water. Coconut husk (CH) and saw dust (SD) was used as the adsorbents in the column and field experiments. The influent solutions were introduced from the bottom of the column using a submersible pump. Field experiment was carried out in the selected MSW landfill using concrete cylinders with 0.3 and 3 m in diameter and length, respectively. These were filled with CH and SD. Cadmium and Lead concentrations were measured in influent and effluent with time. Cadmium and Lead was found to be the most critical heavy metals in landfill leachate which possess quality rating scales of 620% and 108% based on the general standards for portable water. Removal efficiencies of both Cd and Pb by CH and SD were >85% at the beginning and decreased with time until the equilibrium is achieved in column experiment. In contrast, at the field, average removal efficiencies of them were >50% which could be due to the presence of other ions, and large particle size and variable concentration of heavy metal in the field. Hence, these agricultural wastes have potential to mitigate heavy metal pollution and more studies are needed to optimise the effective removal and to increase the efficiency of CH and SD

Evaluation of leachate contamination potential of municipal solid waste dumpsites in Sri Lanka using leachate pollution index.

Landfill leachate generated pollutes the underlined groundwater and nearby surface water bodies due to the unlined and unmanaged dumpsites. Leachate pollution index (LPI) can be used to quantify and compare the leachate contamination potential of a particular landfill site at a given time. A study is conducted to evaluate the contamination potentials of ten municipal solid waste dumpsites from different locations in Sri Lanka, based on sub-indices of LPI and the overall LPI. Organic and inorganic pollutants and heavy metals are analyzed in leachate. The highest LPIor and LPIhm of 91.5 and 10.12, respectively resulted from the Kolonnawa dumpsite. However, the highest LPIin of 65.4 is resulted in leachate from Bandaragama. Further, the overall LPI is the highest in leachate from Kolonnawa dumpsite followed by Bandaragama and Rathnapura sites. Accordingly, Kolonnawa landfill leachate is polluted with organic pollutants and heavy metals and it has the highest potential of pollution. The leachate from Bandaragama site has the highest pollution potential of inorganic pollutants

Characterization of landfill leachate from municipal solid waste landfills in Sri Lanka.

Open dumping of municipal solid waste (MSW) is the most common way of handling solid waste in Sri Lanka due to high cost involved with advanced technologies for landfilling, lack of technical capacity, lack of knowhow to manage landfill sites, and so on. Landfill leachate generated from the MSW landfill sites must be treated before dispose into the environment as it creates many social and environmental problems. Characterization of landfill leachate is important to identify the most critical pollutants present in the leachate and thereby to introduce suitable and applicable treatment technologies such as in-situ permeable reactive barrier technologies for contaminant remediation. Therefore, the objective of this research is to characterize landfill leachate collected from several MSW landfills in Sri Lanka. The leachate samples were collected from 12 landfill sites located in Matale, Hambantota, Kataragama, Bandaragama, Kolonnawa, Gampola, Gohagoda, Wennappuwa, Rathnapura, Negombo, Galle, and Matara. For the collected samples, general water quality parameters (pH, EC, DO, ORP, and SS), organic pollutants (BOD5, COD, TOC, IC, TN, TP), typical anions and cations (Cl- , SO4 2- , NH4 + , K+ , Mg2+, Ca2+, etc), and heavy metals (Cr, Mn, Fe, Se, Pb, etc) were measured. The results showed that most of the pollutants (F- , Cl- , PO4 3- , NH4 + , Fe, Se, Pb, BOD5, and COD) exceeded the maximum tolerance limits in Sri Lankan Standards. It was found that the BOD5/COD ratio ranged from 0.01 to 0.6 for the most samples and the highest value of 0.6 was observed in the Kolonnawa sample. Measured EC values for all samples were high and varied ranging from 4.5 to 38.3 mS/cm, indicating the biological treatment system alone would not be effective in reducing the pollutants especially for heavy metals. The results of this study will be used in developing site specific remediation technologies in landfill leachate treatment

Risk of soil and water pollution by heavy metals in landfill leachate.

Environmental pollution due to landfill leachate has been studied extensively for inorganic and organic pollutants. This study investigates the risk of soil and water pollution by heavy metals in leachate from a selected landfill in Gampola, Sri Lanka. Leachate and soils from the landfill were collected and analyzed for heavy metals. The results reveal that the heavy metal concentrations in leachate is relatively low and highest quality rating scales of 620, 108 and 74 % were resulted for Cd, Pb and Cr, respectively. Heavy metal concentrations in soils were higher than that of leachate and showed a decreasing trend with increasing distance from the landfill. The highest content of Cd, Mn and Cu were 21,173 and 2493 mg kg-1, respectively at the landfill whereas highest content of Zn, Ni, Pb and Cr (1619, 76, 1003 and 239 mg kg-1, respectively) was found within 1 m distance from the dumpsite. Interestingly, Lead, Cadmium, Copper and Zinc were exceeded the Sri Lankan standards limits of heavy metals for compost. Moreover, heavy metals in soil samples showed higher concentrations than concentrations in leachate. The concentrations of 0.038, 0.14 and 0.037 mg L-1 were resulted for Cd, Pb and Cr, respectively in landfill leachate. It can be concluded that the soils are highly contaminated with heavy metals from landfill leachate indicating the potential of the soils to be a natural attenuating agent. However, when the soils’ capacity exceeds there is a possibility of ground and surface water contaminations by heavy metals in landfill leachate

Characterization of aqueous Pb(II) and Cd(II) biosorption on native and chemically modified Alstonia macrophylla saw dust

This study was conducted inorder to understand the mechanism of Cd and Pb adsorption in aqueous solutions by raw and modified saw dust (SD) of Alstoniamacrophylla. The biosorbent was characterized by Boehm titration, specific surface area, scanning electron microscopy (SEM), X-ray energy dispersion (EDAX), and Fourier transform infrared (FTIR) analyses. SD was treated using organic acids and bases. Batch studies were conducted for raw and modified SD to determine the effect of initial concentration, pH, ionic strength, and contact time on metal adsorption. The specific surface area and total basic and acidic groups of SD were 77 m2/g and 1521 and 2312 µmol/g, respectively. The adsorption of both metals onto SD was pH dependent. No ionic strength dependency was observed in adsorption of Cd and Pb at pH >6, indicating inner sphere surface complexation. Monolayer adsorption is dominant in both metal sorptions by SD. Furthermore, there is no competition between metals on adsorption and raw SD was found to be suitable for removal of Cd and Pb as compared to organic acid– or base-treated SD. Maximum adsorption capacity of SD for Cd and Pb were 30.6 and 204.2 mg/g, respectively. Results indicate that the A.macrophylla SD can be considered as a potential material for metal ion removal from wastewater