title: Variations in nitrate isotope composition of wastewater effluents by treatment type in Hong Kong.
abstract: Stable isotopes (δ(15)N, δ(18)O) can serve as tracers for sources of nitrogen in the receiving environment. Hong Kong discharges ~3×10(6)m(3)d(-1) of treated wastewater into the ocean from 68 facilities implementing preliminary to tertiary treatment. We sampled treated sewage from 18 plants across 5 treatment types and examined receiving seawater from northeast Hong Kong. We analyzed nitrate and nitrite (NO3(-)+NO2(-), hereafter NOx) ammonium (NH4(+)), phosphate (PO4(+)) concentrations and δ(15)NNOx, δ(18)ONOx. Sewage effluents contained high mean nutrient concentrations (NO3(-)=260μmolL(-1), NH4(+)=1400μmolL(-1), PO4(+)=50μmolL(-1)) with some indication of nitrogen removal in advanced treatment types. Mean δ(15)NNOx of sewage effluents from all plants and treatment types (12‰) was higher than natural sources and varied spatially and seasonally. There was no overall effect of sewage treatment type on δ(15)NNOx. A mass balance model indicated that sewage (>68%) remains a dominant source of nitrate pollution in seawater in Tolo Harbor.
authors.affiliation: School of Biological Sciences, University of Hong Kong, Pok Fu Lam, Hong Kong, China; Swire Institute of Marine Science, University of Hong Kong, Cape D'Aguilar, Hong Kong, China.
authors.forename: A
authors.initials: A
authors.lastname: Archana
authors.affiliation: State Key Laboratory of Marine Environmental Science, Xiamen University, PR China.
authors.forename: Luo
authors.initials: L
authors.lastname: Li
authors.affiliation: State Key Laboratory of Marine Environmental Science, Xiamen University, PR China.
authors.forename: Kao
authors.initials: K
authors.lastname: Shuh-Ji
authors.affiliation: Department of Earth Sciences, University of Hong Kong, Pok Fu Lam, Hong Kong, China.
authors.forename: Benoit
authors.initials: B
authors.lastname: Thibodeau
authors.affiliation: School of Biological Sciences, University of Hong Kong, Pok Fu Lam, Hong Kong, China; Swire Institute of Marine Science, University of Hong Kong, Cape D'Aguilar, Hong Kong, China. Electronic address: dmbaker@hku.hk.
authors.forename: David M
authors.initials: DM
authors.lastname: Baker
mesh_terms: D004784:Environmental Monitoring; D006723:Hong Kong; D009566:Nitrates; D009587:Nitrogen Isotopes; D012623:Seawater; D062065:Wastewater; D014874:Water Pollutants, Chemical
chemical_list: D009566:Nitrates; D009587:Nitrogen Isotopes; D062065:Wastewater; D014874:Water Pollutants, Chemical
keywords: Hong Kong; Mass balance; Nitrogen pollution; Sewage; Stable isotope; Wastewater treatment