Penurunan kadar nitrat dan chemical oxygen demand COD menggunakan anaerobic fixed BED reactor AFBR pada air limbah industri peternakan sapi studi kasus : industri sapibagus, Kecamatan Tapos, Kota Depok = Nitrate and chemical oxygen demand cod reduction using anaerobic fixed bed reactor AFBR in cow livestock wastewater case study sapibagus industry Tapos Depok