Abstract
An innovative hybrid process was designed using an integrated bio-reactor based on an anoxic / aerobic process that combined a fixed bed and a fluidized-moving bed with a constructed wetland (A/OFMCW) to enhance the removal of organic material and nitrogen. The goal was to achieve stringent discharge standards for rural domestic wastewater treatment. A preliminary lab-scale investigation of about 130 days obtained an average COD (Chemical Oxygen Demand) removal rate as high as 92.2% at an average influent concentration of 319.5 mg/L. The average TN (Total Nitrogen) removal efficiency positively correlated with the attached-growth biofilm as observed by SEM (Scanning Electron Microscope), and declined from 79.1% to 53.2%. The was accompanied by a gradual increase in the average influent concentration from 16.73 to 52.01 mg/L despite the relative nitrification rate fluctuating between 92.5% and 97.9%. The entire integrated system improved the COD removal efficiency by nearly 36% and the TN by 14–28%. Classical autotrophic nitrification and heterotrophic denitrification were the main mechanisms responsible for the elimination of pollutants, and the latter was determined to be the limiting step. Overall, this study provides an effective and less expensive alternative method to apply or upgrade DWWT (Decentralized Wastewater Treatment).
Highlights
To prevent deterioration of aquatic environments due to the rapid urbanization of China, more stringent legislation has been recently enacted that requires increased elimination of organic substances and nitrogen from wastewater [1, 2]
This wastewater directly pollutes both the surface and groundwater, which leads to the need for decentralized wastewater treatment (DWWT)
When looking at mature applications and simple management, conventional nitrification-denitrification technologies like the anoxic-oxic (A/O) process, a classical biological nitrogen removal (BNR) treatment are likely to be more suitable for rural areas [2, 6]
Summary
To prevent deterioration of aquatic environments (e.g., eutrophication) due to the rapid urbanization of China, more stringent legislation has been recently enacted that requires increased elimination of organic substances and nitrogen from wastewater [1, 2]. Low population density and imperfect public sewer networks in rural areas [3, 4] have led to the leakage of untreated wastewater containing nitrogenous compounds. This wastewater directly pollutes both the surface and groundwater, which leads to the need for decentralized wastewater treatment (DWWT). When looking at mature applications and simple management, conventional nitrification-denitrification technologies like the anoxic-oxic (A/O) process, a classical biological nitrogen removal (BNR) treatment are likely to be more suitable for rural areas [2, 6]. Denitrifying bacteria (DB) or heterotrophic bacteria (HB) oxidize carbon using nitrate as an electron acceptor during anaerobic respiration and remove both organic compounds and nitrogen from wastewater
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