Operational demonstration of innovative and sustainable nitrate elimination in stainless steel pickling by higher power biological denitrification technique (BioDemo)

In this pilot project biological denitrification was proved to be a reliable environment friendly and cost-saving alternative for the disposal of the nitrate-rich pickling process water from the steel industry. In the operational trials a new carbon source on a glycerine basis was considered the best for this application. A novel low-fouling polymer membrane was developed and produced. Its permeability (10.3 L/(m²*h*bar)) was lower than that of the commercially available membranes (31 to 202 L/(m²*h*bar)). The costs for the developed membrane (34 €/m²) were lower than for the commercial polymer (95 €/m²) or ceramic membranes (1000 €/m³) but the high filtration area needed diminished the financial advantages. Chamber filter press and membranes showed the best biomass separation performance. By the sludge dewatering, the chamber filter press was optimised to reach the dry matter content of 73 %. For a stable pilot plant operation, a reactor feed strategy with a constant nitrate load was developed. The optimisation of the overall process control took place by specially configured automatic nitrate-measuring devices in the influent and the effluent. The nitrate measurement was enhanced by an exclusively designed sample pre-cleaning on a sedimentation basis. In the long term trials with the pilot treatment plant at the DEW site stable nitrate elimination rates > 95% were observed. The industrial application of the developed nitrate elimination process is completely new and innovative. With this process the steel industry possesses a tool for implementation of a zero nitrate emission strategy in pickling lines with nitric and hydrofluoric acid. It saves water resources and reduces disposal costs