Nitrogen removal from coke making wastewater through a pre-denitrification activated sludge process

Abstract

Under the Industrial Emissions Directive (IED), coke production wastewater must be treated to produce an effluent characterised by a total nitrogen (TN) <50 mg/L. An anoxic-aerobic activated sludge pilot-plant (1 m 3) fed with coke production wastewater was used to investigate the optimal operational requirements to achieve such an effluent. The loading rates applied to the pilot-plant varied between 0.198-0.418 kg COD/m 3 .day and 0.029-0.081 kg TN/m 3 .day, respectively. The ammonia (NH 4 +-N) removals were maintained at 96%, after alkalinity addition. Under all conditions, phenol and SCNremained stable at 96% and 100%, respectively with both being utilised as carbon sources during denitrification. The obtained results showed that influent soluble chemical oxygen demand (sCOD) to TN ratio of should be maintained at >5.7 to produce an effluent TN <50 mg/L. Furthermore, nitrite accumulation was observed under all conditions indicating a disturbance to the denitrification pathway. Overall, the anoxic-aerobic activated sludge process was shown to be a robust and reliable technology to treat coke making wastewater and achieve the IED requirements.

Characterisation of thiocyanate degradation in a mixed culture activated sludge process treating coke wastewater

“…The wastewater exhibited a pH of 7.8±0.3. Concentrations of pollutants therefore fell within the typical range for coke wastewater previously reported for this site as well as those reported in the wider literature (Marañón et al, 2008;Raper et al, 2019;Staib and Lant, 2007;Vázquez et al, 2006).…”

“…In contrast, however, previous work on the current activated sludge biomass revealed that the biomass was capable of completely removing SCNin both aerobic conditions and anoxic conditions (Raper et al, 2019(Raper et al, , 2017. This SCNdegradation in the anoxic cell of a pilot-scale anoxic-aerobic ASP was possible with biomass taken from an aerobic process without any acclimatisation period.…”

“…Nitrite accumulation has been observed in the pre-denitrification ASP (Raper et al, 2019) which could suggest a metabolic similarity to T. thioparus. Despite this, an ambiguous species of the genus Rhodanobacter was also identified in the mixed culture (Figure 4).…”

“…Production of coke for steel making, generates wastewater which contains significant quantities of thiocyanate (SCN -) ranging from 50 to 400 mg/L (Pan et al, 2018a;2018b;Raper et al, 2019;Staib and Lant, 2007;Vázquez et al, 2006). Thiocyanate is generated when cyanide and sulphur react under the high temperatures associated with the coke making process (Kim and Katayama, 2000).…”

Activated sludge and other aerobic suspended culture processes

“…Compared to the Anammox process, the bio-electro-chemical ammonia oxidation did not produce by-product nitrate, associated with electroactive autotrophs. Raper et al (2019) operated an anoxic-aerobic activated sludge pilot plant to evaluate the optimal C/N ratio treating coking wastewater. The results showed that the influent C/N ratio maintained exceed 5.7, could achieved the satisfied ammonia (NH 4 + -N) removals (96%) and the effluent TN less than 50 mg/L, together with the carbon resources during denitrification such as SCN − and phenol remained a stable removal at 100% and 96%, respectively.…”