Horizontal Subsurface Flow Constructed Wetland For The Post Treatment Of Anaerobically Treated Brewery Effluent Improving Water Quality For Environmental Sustainability

Agro-industrial wastewater quality and its effect on the environment has become a critical concern in Ethiopia. Agro – industries have chosen anaerobic digestion process to treat their organic-rich wastewater. However, its effluents would typically does not meet the desired discharge limits. This has given impetus to subsequent polishing in order to meet the discharge standards and protect the environment. Therefore, the aim of this study was to evaluate the efficiency of a two – stage pilot scale horizontal subsurface flow constructed wetland (HSSFCW) planted with Cyperus alternifolius and Typha latifolia respectively for the polishing of an Up-flow anaerobic sludge blanket (UASB) reactor treated brewery effluent and reuse of effluent for irrigation. A pilot scale HSSFCW was developed at Kombolcha, Ethiopia, following the United States environmental protection authority design guideline and integrated with the existing UASB reactor. Its performance efficiency was assessed for the removal of total suspended solids (TSS), chemical oxygen demand (COD), total nitrogen (TN), ammonium – nitrogen (NH4+ – N), total phosphorous (TP), and orthophosphate (PO43-). The first-order kinetic model was used to correlate the inlet and outlet pollutant concentrations and estimate the areal rate constant (kA) by fitting the experimental data to the model. The HSSFCW's macrophytes nutrient accumulation potential and microbial community dynamics were assessed using colometric and 16S rRNA metagenomic sequencing methods, respectively. The UASB reactor and HSSFCW's water quality index (WQI) and effluent irrigation suitability were also examined following a standard methods. The two – stage HSSFCW performance efficiency evaluation result showed that Cyperus alternifolius planted cell removed 68.5% TSS, 74.2% COD, 55.7% TN, 68.6% NH4+ - N, 41.1% TP and 48.1% PO43-. Moreover, further treatment with Typha latifolia planted cell enhanced the overall abatement efficiencies to 89% TSS, 92% COD, 83.6% TN, 92.9% NH4+ – N, 74.4% TP, and 79.5% PO43-. Outflow concentrations of COD, TN and NH4+ - N were reasonably correlated (R2 ≥ 0.85) to inflow concentrations. The calculated kA (md-1) for TSS, COD, TN, NH4+ - N, TP, and PO43- were 0.26, 0.26, 0.11, 0.18, 0.08, and 0.08, respectively. Strong linearity and Pearson correlation was found between macrophyte biomass and nutrient accumulation in each HSSFCW cell (Cyperus alternifolius: R2 = 0.91, r = 0.97 for TN; R2 = 0.92, r = 0.96 for TP; and Typha latifolia: R2 = 0.96, r = 0.98 for TN and TP) with cumulative nutrient accumulation of 1290 gTNm-2 and 708.7 gTPm-2 in the complete system. The microbial community dynamic analysis revealed a higher microbial consortia and richness across the HSSFCW cells. Among the total microbial community species, Clavibacter michiganensis (3.6%), rnrnDokdonella immobilis (5.9%), and Longilinea arvoryzae (9.15%) were dominant in the first cell. Whereas, Syntrophorhabdus aromaticivorans (2.85%), Aminiphilus circumscriptus (2.8%), Thermovirga_lienii (3.4%), Longilinea arvoryzae (5.9%), Methanothrix soehngenii (8.65%), and Desulfoglaeba alkanexedens(10.6%) species were more dominant in the second cell. All of the major species identified in this study have a significant role in organic and nutrient removals. Polishing of the UASB reactor effluent with two-stage HSSFCW cell has shifted the WQI from a good to excellent water quality rating, and its reuse for tomato cultivation significantly improved both growth and yield biometric parameters. Thus, the pilot scale HSSFCW cell can be used as a sustainable tertiary level treatment of brewery wastewater.

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