Identification of two low-cost and locally available filter media (pumice and scoria) for removal of hazardous pollutants from tannery wastewater

Résumé

Tannery wastewater contains the most hazardous pollutants. Therefore, identifying potentially efficient, low-cost and locally available filter media as an adsorbent for the treatment of tannery wastewater is critical. The aim of this study is to identify and assess the ability of identified adsorbents and compare their efficiency. The volcanic rocks of pumice and scoria were collected from the rift valley area of Oromia region, Ethiopia and their chemical characteristics were determined using X-ray fluorescence analysis. Batch mode experimental study design was carried out. The rocks were crushed and effective size was determined by using a standard sieve. The composite tannery wastewater was collected from Dire tannery, Addis Ababa, Ethiopia and treated with pumice and scoria. Two adsorption kinetics and isotherm models were conducted to predict the removal mechanism and capacity of the adsorbents on the reduction of NO 3 –N, PO 4 –P and [Cr] T from tannery wastewater. Analysis of wastewater samples was done before and after different retention time. R statistical software and Originlab pro 2017 was run for data analysis and graphing. The untreated tannery wastewater revealed that the mean concentration of BOD 5 , COD, TSS, orthophosphate, ammonium, nitrite, nitrate, sulfide, sulfate and chromium were beyond the permissible limits. Nitrate removal efficiency of scoria and pumice were 99 and 95% respectively at retention time of 72 h. Phosphate removal was better by scoria on the first 24 and 48 h. The efficiency of pumice to remove sulfate was 83–84%, whereas scoria shows 75–77%. In the first 24 and 48 h retention time, pumice and scoria achieved 76 and 71% in chromium reduction respectively. This study revealed that both scoria and pumice have a potential capacity to treat tannery wastewater. Conversely comparing the average efficiency to reduce hazardous pollutants scoria showed better results than pumice.

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