title: Effect of C/N ratios on the performance of earthworm eco-filter for treatment of synthetics domestic sewage.
abstract: OBJECTIVE
  The performances of filter systems that use earthworms and plants, combined with earthworm eco-filter (EE) systems in treating synthetic domestic sewage (SDS) with different C/N ratios, were investigated for a 9-month period.
  
  
  METHODS
  The effects of the combination of filters, earthworms, plants, as well as the combination of earthworms and plants on SDS nutrient removal efficiency were separately investigated to select the optimum system for treating SDS. The results of the current study could be used to determine how treatment performance responds to different C/N ratios and to explain and predict the performance of an operating EE system.
  
  
  RESULTS
  EE systems with earthworms and plants (EP groups) consistently performed better than the other types of systems (CK, E, and P; that is, without earthworms and without plants, with earthworms and without plants, and without earthworms and with plants, respectively) under all C/N ratios. The highest removal efficiencies of chemical oxygen demand, total nitrogen, total phosphorus, and total organic carbon were achieved under C/N ratios of 6:1, 6:1, 6:1, and 9:1, respectively. The optimum nutrient removal efficiency was achieved at C/N = 6, and the contribution order for nutrient removal was EP > P > E > CK.
  
  
  CONCLUSIONS
  Influent C/N ratios, the time of year, and the synergetic effects of earthworm behavior and microorganisms significantly affected nutrient removal efficiencies. Considering the removal of all nutrients, EE systems with plants and earthworms achieved optimum removal effects in July when the influent C/N ratio was controlled at 6. Appropriate control of carbon and nitrogen source concentrations permitted the achievement of optimal nutrient removal effects.
authors.affiliation: Department of Environmental Science and Engineering, Fudan University, 220 Handan Road, Shanghai, 200433, People's Republic of China.
authors.forename: Yong-Jun
authors.initials: YJ
authors.lastname: Zhao
authors.forename: Cheng
authors.initials: C
authors.lastname: Yan
authors.forename: Yin-Liang
authors.initials: YL
authors.lastname: Li
authors.forename: Ji-Hua
authors.initials: JH
authors.lastname: Li
authors.forename: Mo
authors.initials: M
authors.lastname: Yang
authors.forename: Er
authors.initials: E
authors.lastname: Nie
authors.forename: Zheng
authors.initials: Z
authors.lastname: Zheng
authors.forename: Xing-Zhang
authors.initials: XZ
authors.lastname: Luo
mesh_terms: D000818:Animals; D001673:Biodegradation, Environmental; D002244:Carbon / Q000032:analysis*; D005374:Filtration / Q000379:methods; D009584:Nitrogen / Q000032:analysis*; D009835:Oligochaeta / Q000502:physiology*; D010758:Phosphorus / Q000032:analysis; D010944:Plants / Q000378:metabolism; D012621:Seasons; D012722:Sewage / Q000737:chemistry*; D014865:Waste Disposal, Fluid / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D012722:Sewage; D014874:Water Pollutants, Chemical; D010758:Phosphorus; D002244:Carbon; D009584:Nitrogen