Nitrogen removal in integrated anaerobic–aerobic sequencing batch reactors and constructed wetland system: a field experimental study

Abstract

A study was conducted to assess the performance of an integrated system consisting of an anaerobic digester (AD), an aerobic sequence batch reactor (ASBR), and three horizontal subsurface flow constructed wetlands (HSSFCWs) vegetated with the perennial grass Phragmites karka for removal of nitrogen in tannery wastewater. Nine grab wastewater samples were collected weekly between September and December 2016 from the influent and effluent at each unit of operation of the plant and analyzed for physicochemical parameters. The AD removed 67% of oxidized nitrogen (NO X -N); the removal was improved to 76% in the ASBR with a further aeration period in the HSSFCWs, and the NO X -N removal efficiency improved progressively to 96%. The removal efficiency for nitrate (NO 3 -N) was 82% and for nitrite (NO 2 -N) 88%; for ammonium (NH 4 -N) removal efficiency was 77% higher in the HSSFCWs compared to the AD and the ASBR. Despite the considerable percentage of NO 3 -N removed, in the effluent was above the country's permissible limit (39.3 mg/l). The high concentration might be due to a weaker denitrification process in HSSFCWs caused by lack of carbon and external organic sources in the wastewater sufficient to carry out the process. The results suggest that the addition of supplementing carbon sources (methanol, sugars, or volatile fatty acids) to the effluent would achieve better performance. Based on these findings, the application of combined anaerobic/aerobic system connected with constructed wetlands process allows the achievement of higher efficiency in removing nitrogen compared to the use of an anaerobic, aerobic, or constructed wetland system along.

Integrated constructed wetlands treating industrial wastewater from seed production

“…The final effluent NO À 3 concentration exceeded TBS' permissible discharge level (Table 5). The high nitrate concentration in the final effluent might arise because of its high initial concentration in the influent and low levels of denitrification in the ABR and HSSFCW (Assefa et al 2019). There was a large input of nitrate at the influent, as shown in the inlet values of ABR, which arose because the industry discharges excess artificial fertilizer (used to grow different vegetables for seed extraction process) from the greenhouses to the equalization tank.…”

“…As the ABR was sized mainly for the removal of organic matter, the size prescribed may not be adequate for denitrification. Denitrification could be enhanced in the ABR by supplementary carbon addition, perhaps as methanol, sugar, volatile fatty acids, and so on (Assefa et al 2019).…”

“…Eutrophication can arise from excess loads of nitrogen and phosphorus in the aquatic environment (Bu & Xu 2013). Moreover, high organic matter content can cause oxygen depletion, bad odor, and fish kills (Assefa et al 2019). Adopting appropriate wastewater treatment technologies is necessary to minimize pollution.…”

Wetlands for environmental protection

“…High COD (82%) and NH 4 + ‐N (96%) removals and almost complete Cr removal were observed in the outflow. Assefa, Bai, Leta, and Kloos (2019) also studied the removal performance of nitrogen from tannery wastewater in an integrated system consisting of an anaerobic digester (AD), an aerobic sequence batch reactor (ASBR), and three HSSF‐CWs consisting perennial grass Phragmites karka. The results showed higher removal efficiency for TSS, turbidity, BOD 5 , COD, NO 3 − –N, NO 2 − –N, NH 4 + –N, S 2 − , and PO 4 3− in CW than in AD and ASBR, but TDS and TN removal were highest in ASBR and SO 4 2− was removed most in AD.…”

Efficiency of pollutant removal in a hybrid constructed wetland with Hedychiumcoronarium J. König: a sustainable alternative for poor communities

“…In the face of the emerging concern for environmental preservation and governmental regulations that are becoming more stringent the development of innovative, sustainable, environmentally friendly, and low-cost processes for efficient treatment of tannery wastewater has gained the interest of researchers in clean technologies (ASSEFA et al, 2019). The performance of systems for wastewater treatment for the safe release of the effluent (e.g., for the protection of human health and the environment) is the primary role.…”