Study on the experimental performance by electrolysis-integrated ecological floating bed for nitrogen and phosphorus removal in eutrophic water

Abstract

The new-type electrolysis-integrated ecological floating beds (EEFBs) were set up to study their water removal ability due to the excellent water treatment capacity of electrolysis, this enhanced EEFBs were made of polyethylene filled with biochar substrate and in middle of the substrate placed the Mg-Al alloy served as anode and graphite served as cathode. the results show that removal rates of total nitrogen (TN), ammonia nitrogen (NH 3-N), total phosphorus (TP) and phosphate (PO 4 3−-P) by the EEFBs increased 53.1%, 96.5%, 76.5% and 74.5%, respectively. The electrolysis reaction was the main pathway for TN and TP removals in the EEFBs. A higher concentration of hydrogen autotrophic denitrification bacteria was recorded in the substrate of the EEFBs than that in the traditional ecological floating beds (EFBs) (p < 0.05), suggesting that the electrolysis may have enhanced the NO 3 −-n removal efficiency of the EEFBs by promoting the growth and reproduce of hydrogen autotrophic denitrification bacteria. The in-situ formation of Mg 2+ and Al 3+ ions from a sacrificial Mg-Al alloy anode, caused po 4 3−-P and other suspended matter flocculation, improved phosphorus removal and simultaneously reduced turbidity. Thus, electrolysis-integrated ecological floating bed has high nitrogen and phosphorus removal potential in eutrophic water. Eutrophication has become a serious matter of concern in aquatic ecological research, widespread occurrence of water eutrophication results in the loss of ecological integrity, a decreased aquatic biodiversity, the disappearance of submerged vegetation, and the potential production of toxins 1. Diffuse nitrogen (N) and phosphorus (P) pollution are currently the main drivers of eutrophication 2. Ecological restoration technology, such as ecological floating beds (EFBs) have the unique advantage of occupying no land area, operate at low cost, and require simple maintenance; therefore, the EFBs have been widely used as an in-situ ecological remediation technology for treating surface water 3,4. However, problems of seasonal and anaerobic environment constraints on macrophytes and microbes growth, the limited standing biomass 5-7 , decrease of adsorption capacity of substrate 7-11 and the larger cover area 4 usually restrict the usage of EFBs. Thus, the enhanced EFBs which have a long term stable removal capacity needed to be researched. When used, electrolysis in eutrophic water bodies can simultaneously promote heterotrophic denitrifier' growth and reproduce to enhance NO 3 −-N removal 12-15 and to enhance PO 4 3−-P removal through sacrificial anode which can be used as the source of the coagulating ions 16,17. Some researchers were already using electrolysis reaction in constructed wetlands (CWs) and biofilter to intensify N and P removal since the anode was Fe or Al 18-22. When the anode was Fe which could produce Fe 2+ and Fe 3+ ions during the electrolysis process and Fe(III) oxide generated as the end result. Fe(III) oxide has a reddish-brown color and is often called rust which affec...

Water treatment and reclamation by implementing electrochemical systems with constructed wetlands

“…Additionally, the finite sorption capacity of typical bed materials limits phosphorus removal in the long run [52]. Thus, electrolysis-integrated CWs emerged as a solution to enhance nutrient removal [52,90,91]. Electrolysis in the CW systems can remove phosphorous via electro-coagulation processes [52,90,91].…”

“…Thus, electrolysis-integrated CWs emerged as a solution to enhance nutrient removal [52,90,91]. Electrolysis in the CW systems can remove phosphorous via electro-coagulation processes [52,90,91]. It can also provide electron acceptors and donors involved in microbial metabolisms, such as O 2 for nitrification at the anodic side or H 2 for autotrophic denitrification at the cathodic side, which also steers the microbial community in the bed [52,91].…”

“…Electrolysis in the CW systems can remove phosphorous via electro-coagulation processes [52,90,91]. It can also provide electron acceptors and donors involved in microbial metabolisms, such as O 2 for nitrification at the anodic side or H 2 for autotrophic denitrification at the cathodic side, which also steers the microbial community in the bed [52,91]. Electrolysis-integrated systems have also been reported as efficient in controlling sulfide-related malodor [52].…”

“…As the iron electrode is periodically employed as a sacrificial anode, it must be regularly replaced, adding to the maintenance and operational costs of the overall system. Similar efforts to improve nutrient removal were subsequently taken up, combining various materials for the electrodes and for the CW bed, including iron plates in HSSF-CW [90], MgeAl alloy as the anode, and graphite as the cathode in an ecological floating bed [91], and carbon fiber electrodes in a CW bed formed of granular pyrite [92]. In two studies employing sacrificial electrodes, iron [90] and MgeAl alloy [91], phosphorus removal was improved by 50% and 66%, respectively, compared to the control beds without electrodes.…”

Toxic Effect of Ammonium Nitrogen on the Nitrification Process and Acclimatisation of Nitrifying Bacteria to High Concentrations of NH4-N in Wastewater

“…In wastewater treatment plants that remove biogenic compounds in a biological way, the elimination of ammonium nitrogen is carried out through the processes of metabolic assimilation and dissimilation [4][5][6][7][8][9][10][11][12]. In the assimilation process, ammonium nitrogen is used to create new, activated sludge cells, which are then removed from the system in the form of biomass [13,14]. The ratio of metabolizable organic carbon to nitrogen (C:N) determines the rate of biomass growth, and thus the amount of ammonium nitrogen removed with excess activated sludge.…”