@article{WetterElmar2008,
  author    = {Wetter, Christof and Elmar, Br{\"u}gging},
  title     = {Biogasanlagen - N{\"a}hrstoffe optimal nutzen},
  series = {VDI:Ingenieur Forum Westfalen-Ruhr},
  journal   = {VDI:Ingenieur Forum Westfalen-Ruhr},
  year      = {2008},
  language  = {mul}
}
@article{Gruening2008,
  author    = {Gr{\"u}ning, H.},
  title     = {Abflusssteuerung - quo vadis?},
  series = {Korrespondenz Abwasser},
  volume    = {55},
  journal   = {Korrespondenz Abwasser},
  number    = {Nr. 4},
  pages     = {358 -- 364},
  year      = {2008},
  language  = {mul}
}