Post Treatment Of Tannery Wastewater In Horizontal Subsurface Flow Constructed Wetland Connected To Sequence Batch Reactor Performance Nutrient Profile And Effluent Reuse For Irrigation

Tannery wastewater is characterized by high levels of organic and inorganic matter, chromium (Cr), and suspended and dissolved solids. Discharge of untreated tannery wastewater into the environment poses a serious environmental and health problem. The objective of this study was to assess the performance of an anaerobic-aerobic sequence batch reactor (SBR) connected to a constructed wetland (CW) system for the treatment of tannery wastewater and suitability assessment of treated effluent reuse for irrigation. Influent and effluent wastewater from each treatment system was analyzed for organic matter, nutrient and heavy metal using standard methods. The CW system was operated under 3 and 5 days of hydraulic retention time (HRT). CW nutrient profiles were observed from inlet to outlet every 6 meter interval. Completely randomized block experiment (CRBD) were used for effluent reuse experiment. Health risk associated with consuming vegetables was estimated using target hazard quotients (THQs).rnThe integrated pilot scale treatment system showed an overall removal efficiency of 96.6% for COD, 90.4% for TN, 93.4% for NH4-N, 81.8% for SO42-, 99% for S2-, 97% for total Cr, 86% for EC and 99.9% for total Coliforms, respectively. The concentration of COD, BOD, TN, NO3-N, NH4+-N, SO42 and S2- in the final treated effluent were 113.2±52, 56±18, 49.3±13, 22.75±20, 17.1±6.75, 88±120 and 0.4±0.44 mg/L, respectively. The efficiency of CW systems for TN, NO3—N, NH4+-N, SO42-and S2-were 77.7%, 84.2% 82.5%, 79.7% and 94%, respectively. The CW removal efficiency for BOD and COD for 3d HRT was 93 % and 90 % for inlet mean concentration of 812±196 and 1142.5±264 mg/L, respectively. Similarly, for the same inlet concentration, BOD and COD removal for 5 day HRT was 93.1 % and 90.8 %, respectively. Statistically, no significant pollutant removal differences were observed between 3 and 5 days of HRT. The concentrations of pollutants in CW were decreased as aspect ratio increases. The highest organic matter loads (over 60%) were removed in the first cell of the CW1. P. karka growth (within a 5 week period) at CW cell1, cell2 and cell3 werernivrn90±5, 121±6.5 and 150±8 cm, respectively. Statistically, significant Plant growth difference was found between the three CW cells. The highest total Cr accumulation was recorded in root and leaves of P. karka at CW1S1, 689±87and 49.7±11mg/kg, respectively.rnCr concentration in vegetables grown with uncontaminated soil was below (0.1mg/kg dry weight) while Cd was below the WHO standard for all vegetables and Pb and Ni were found below the minimum detection limit of flame AAS. Assuming the current Ethiopian vegetable consumption habits the THQs estimation suggest that heavy metal levels in all of the tested vegetable had no potential health risk. Therefore, integrating CWs as a polishing is not only efficient to treat tannery WW and meeting EPA discharge limits, but also produce treated effluent which can be used for agriculture.rnKeywords: Constructed Wetland; Chromium, longitudinal profile, integrated treatment system performance; tannery wastewater, treated effluent reuse.

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