Advances in Water Treatment and Enviromental Management

82 WATER TREATMENTFilter 1 continued to produce a good quality effluent with over 90% BOD 5,SS and NH 4 -N removal at VLR’s of 1.2–1.3 kg BOD 5 /m3 /d and 0.4–0.45 kgTKN/m3 /d. Effluent quality averaged 7 mg/1 BOD5 , 8 mg/1 SS and 1.3mg/1 NH 4 -N. Nitrification remained close to 90% up to the limiting TKNVLR of 0.6 kg/m3 .d.Above this figure a reduction in NH4-N removal efficiency was seen. Themaximum VLR ’ s of 3.85 kgBOD5/m 3 . d and 1.35 kgTKN/m 3 .d gave 75%BOD removal and 69% solids removal. Nitrification, as indicated by bothNH4-N removal and NO3-N formation, was negligible however a 22%reduction in TKN was observed.Operating data and plant performance for the 2 periods are given in TablesII and III.Table IILoad Variation Period 1Filter NumberNote: HLR : Hydraulic loading rate (m/h)HRT : Hydraulic retention time (based on 50% voidage) (min)VLR : Volumetric loading rate kg/m 3 media.d