| A bench scale pilot plant study was undertaken using geotextile baffles as biofilm attachment media for wastewater treatment. The herein named Geotextile Baffle Contact System (GBCS) removed suspended solids and hosted growth of microorganisms to absorb and decompose carbonaceous and nitrogenous pollutants. The test liquid was one sample of screened plant influent and twelve samplings of effluent from primary treatment at a Philadelphia Water Department (PWD) wastewater treatment plant that treats combined sanitary and storm sewage. The main goal was to meet secondary treatment standards, i.e., low concentrations of total suspended solids and biochemical oxygen demand in the effluent. The once-through hydraulic loading rate was similar to that used in conventional low rate trickling filters 20 gal/day-sq.ft. A second goal was reducing ammonia and nitrate to receiving water standards. It was also desired to digest excess sludge within the system.; Twenty gallon glass tanks were used as reactors for the bench scale pilot plant experiments. Geotextile coupons were hung as baffles transverse to the flow in a sinuous pattern to increase path length and contact area, using elements from lamella settlers, granular depth filters and trickling filters. The first phase screened candidate geotextiles with respect to biomass attraction by immersion in wastewater. Only nonwoven needle punched geotextiles were found to host a substantial biomass. A second phase was investigating biodegradation efficiency under continuous aerated flow through the GBCS tanks with a nonwoven needle punched geotextile. Over 90% TSS and BODS removal occurred quickly, and over 90% conversion of NH3 to NO3 was detected after the third week. Denitrification increased steadily, producing effluent concentrations below 8 mg/l after five weeks, corresponding to the increasing biofilm thickness. The third phase used nonwoven staple fiber baffles. There was a similar performance in removing and biodegrading suspended, colloidal and dissolved organic materials.; A parallel study of biomass distribution with photographs, dry solids retention, and scanning electron microscopy showed that TSS removal was a combination of sedimentation, filtration and baffle surface sorption. It was concluded that the high ratio of surface area to reactor volume supported efficient substrate and oxygen transfer. |
