DEVELOPMENT OF EFFICIENT PACKED BED ANAEROBIC FILTERS WITH LOCALLY AVAILABLE PACKING MATERIALS TO TREAT LANDFILL LEACHATE 

The major drawback with the anaerobic filters, which have emerged as a promising technology  for landfill-leachate treatment, is expensive packing media. Hence, introducing alternative low-cost packing media will make anaerobic filters more economical. The aim of this study was to investigate the performances of several low-cost/waste materials as packing media in anaerobic filters to treat organic compounds, nutrients and heavy metals found in landfill leachate. The objectives of the study include: to evaluate the efficiencies of packing materials in removing contaminants and compare the results to optimize the best material/s; to compare the  performances of down and up flow loading systems; to compare the treatment potential of the waste and low-cost packing materials with those of the expensive and conventional packing materials; and to investigate the change of the physical and mechanical properties with the  interaction of the landfill-leachate. Three runs of laboratory scale column experiments were conducted sequentially as follows: 4 columns with each of the up and down flow loading systems, with a single filter material as packing media; One column with each of the up and down flow loading systems, with a mixture of filter materials as packing media; and 4 columns with down flow loading system with a mixture and layers of filter materials as packing media, with two control columns. In each set up of up and down flow, the 4 columns were filled with Washed Sea Sand (WSS), Dewatered  Alum Sludge (DAS) and Firewood Charcoal (FWC), respectively while the other column was with layers of three organic waste matters of rice husk, rice straw, coconut coir fiber, saw dust in equal proportion of volumes. Each column was loaded with 10% diluted leachate collected from a dumpsite. Due to a practical failure, the column with a layered organic media was  stopped from running after 35 days long experimental run whereas the other three single media columns were operated for 180 days. The removal efficiencies of wastewater parameters,  namely BOD₅, COD, TN, NH₃-N and TDS were tested in all the columns. FWC performed the  best with the largest removal efficiencies for almost all the parameters measured. The treatment potential of WSS and DAS had only a slight reduction from that of FWC. The maximum treatment efficiencies for BOD₅, COD and TN were 80 % (WSS-Down flow), 69 % (FWC-Up  and Down flow) and 86 % (WSS-Up flow), respectively.  The experiment was then developed into combined media having three low-cost media (FWC, WSS and DAS) combined in equal volumes as layers. Both up and down flow loading systems were applied. The efficiencies obtained by both the loading systems are quite coincident. The removal efficiencies of both BOD₅ and TN increased remarkably due to the combined effect of  these materials. However, COD removal efficiency drastically reduced. The removal efficiency of BOD₅ was more than 75% in the up flow system while the down flow removal efficiency was more than 85%. TN gave excellent performance of more than 95% in both the up and down flow  systems.  Based on the results of the preceding two experimental series, the next experimental series was conducted. The experimental set-up consisted of four down-flow anaerobic-filter columns, two of which were control columns while the others were experimental columns. The control columns were filled with Granular Activated Carbon (GAC) and Plastic Pall Rings (PPR) as single medium. The experimental columns were filled with a mixture of DAS, WSS, FWC, while the other with the same materials as layers. During the application of 10 % diluted landfill leachate within a period of 115 days, the overall removal efficiencies of the filter bed with  layered-media were 73%, 84%, 61%, 55%, 76% and 79% for COD, BOD₅, TN, Ammonia-N  (NH₃-N), TP and Orthophosphate-P (PO₄^3- -P), respectively. The filter bed with mixed-media  gave the overall removal efficiencies of 59%, 87%, 49%, 26%, 71% and 78% for COD, BOD₅,  TN, NH₃-N, TP and PO₄^3- -P, respectively. The experimental columns showed significant  removal efficiencies for heavy metals, namely, Pb (40%), Cd (48%), Cu (41%) and Mn (52%) in the mixed-media column and (54%), Cd (37%), Cu (54%) and Mn (57%) in the layered media column. The results reveal that the selected low-cost packing materials are able to treat organic, nitrogenous and phosphorus compounds, several heavy metals and TDS to a considerably high degree, in one reactor. Though, the treatment efficiencies of GAC for organic and nitrogenous compounds and heavy metals are very high, it is not applicable for phosphorus  compounds and TDS. The increment of the  conductivity value is also a problem. Further, the present results show that PPR is good at removing only BOD₅ and phosphorus compounds.  The physical and mechanical properties of all the low cost/waste packing materials changed slightly with the interaction of leachate for 115 days. The specific gravity of all the experimental materials slightly increased with the decrease of void volume ratio. The effective diameter of WSS and DAS slightly decreased while that of FWC slightly increased. The permeability of the media bed decreased slightly after the experimental run. The shear strength parameter, cohesion, increased slightly in both DAS and WSS while the shear strength parameter, friction angle, decreased slightly in the same media. The shear strength is a measure of the failure potential of the media bed.  

Key Words: Anaerobic, Filter columns, Heavy metals, Landfill-leachate, Low-cost, Organic 
compounds, Nitrogenous compounds, Packing materials, Waste materials