Abstract
BackgroundAgro-industrial wastewaters in Ethiopia cause severe environmental pollution problems. Research evidence showed that anaerobic reactors are good options for the treatment of these wastewaters. But, their final effluent does not meet the discharge standards. Conversely, a series stage horizontal subsurface flow constructed wetland (HSSFCW) system is encouraging for the polishing of anaerobic reactor effluents. However, its treatment efficiency is dependent on hydraulic residence time (HRT). Cyperus alternifolius and Typha latifolia-based wastewater treatment showed good removal efficiencies individually. However, data on their combined treatment effectiveness is negligible. Therefore, this study assesses HRT influences on the treatment effectiveness of a two-stage HSSFCW system planted with these two macrophytes for the polishing of anaerobic reactor brewery effluent. A series connected two-stage HSSFCW unit planted with Cyperus alternifolius and Typha latifolia was built to treat Kombolcha brewery anaerobic reactor effluent. Then, the macrophytes were endorsed to grow with continuous application of diluted brewery effluent from a reservoir tank using gravity force. After dense stand formation, the experiment was initiated to determine the influence of HRTs on the removal efficiency of a complete wetland system. The system was operated sequentially by supplying fixed influent inflow rates of 2791, 1395, 930, 698, and 558 L day−1, respectively, for 1, 2, 3, 4, and 5 days HRT. Both the influent and effluent of the two-stage HSSFCW system were analyzed following common procedures for main brewery pollutants.ResultResults showed that as HRT increased from 1 to 5 days, the effluent pH and temperature were decreased along with enhanced pollutant removals ranging from 47.8–87.2%, 29.2–90.1%, 32.9–77.7%, 16.8–75.4%, and 18.4–76.8% with decreased influent mass loading rates ranging from 26.4–2.1, 64.5–7.3, 11.5–0.8, 5–0.6, and 3.8–0.4 gm−2 day−1, respectively, for total suspended solids, chemical oxygen demand, total nitrogen, total phosphorous and orthophosphate. However, better and steadier pollutant removals were achieved at higher HRTs.ConclusionFor better nutrient removals, the 4 and 5 days HRT can serve as a good benchmark.
Highlights
Agro-industrial wastewaters in Ethiopia cause severe environmental pollution problems
Characteristics of the Up-flow anaerobic sludge blanket (UASB) reactor effluent Characterization of the UASB reactor brewery effluent showed that the effluent has a high level of Total suspended solids (TSS), Chemical oxygen demand (COD), Total nitrogen (TN), Total phosphorous (TP), and P O4-P between hydraulic residence time (HRT) operations (Table 1), signifying its substantial fluctuations
The inlet, as well as outlet pH values of the two-stage horizontal subsurface flow constructed wetland (HSSFCW) effluent, meet the suggested optimum pH discharge rate, and a strongto-moderate linear correlations were observed between the influent and effluent pH values during the study periods as HRT extends from 1 day to 5 days (Fig. 2a), indicating that the HSSFCW outlet pH has a dependency on the initial pH of the effluent
Summary
Agro-industrial wastewaters in Ethiopia cause severe environmental pollution problems. This study assesses HRT influences on the treatment effectiveness of a two-stage HSSFCW system planted with these two macrophytes for the polishing of anaerobic reactor brewery effluent. Constructed wetland (CW) system is divided into two groups that rely on the direction of water flow; horizontal and vertical, but the HSSFCW treatment system has been successfully applied in developed countries for different types of wastewater treatment (Albalawneh et al 2016), and widely serves as an excellent option for the efficient removal of pollutants from the UASB reactor effluent to reach a high effluent quality (Sedaqua 2013; Jamashidi et al 2014). Considering the economic limitations and strict national discharge guidelines, CWs are good options to treat UASB reactor brewery effluents in Ethiopia without any operational complexity and high-cost investment. The HSSFCW post-treatment system offers enhanced pollutant removal efficiency through interaction between wetland components and is mostly influenced by macrophyte species and media types (Saraiva et al 2018)
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