Abstract
Digital textile printing (DTP) is a game-changer technology that is rapidly expanding worldwide. On the other hand, process wastewater is rich in ammoniacal and organic nitrogen, resulting in relevant issues for discharge into sewer system and treatment in centralized plants. The present research is focused on the assessment of the partial nitritation/anammox process in a single-stage granular sequencing batch reactor for on-site decentralized treatment. The technical feasibility of the process was assessed by treating wastewater from five DTP industries in a laboratory-scale reactor, in one case investigating long-term process stabilization. While experimental results indicated nitrogen removal efficiencies up to about 70%, complying with regulations on discharge in sewer system, these data were used as input for process modelling, whose successful parameter calibration was carried out. The model was applied to the simulation of two scenarios: (i) the current situation of a DTP company, in which wastewater is discharged into the sewer system and treated in a centralized plant, (ii) the modified situation in which on-site decentralized treatment for DTP wastewater is implemented. The second scenario resulted in significant improvements, including reduced energy consumption (− 15%), reduced greenhouse gases emission, elimination of external carbon source for completing denitrification at centralized WWTP and reduced sludge production (− 25%).
Highlights
Digital textile printing (DTP) is rapidly spreading worldwide, mostly due to the greater versatility with respect to conventional printing techniques (Global Industry Analysts 2018)
Among existing technological solutions, the use of a sequencing batch reactor (SBR) allows ensuring good biomass retention to favour the growth of anammox bacteria, avoiding their washing out, while the homogeneous distribution of substrates and products limits the formation of critical zones for bacteria survival inside the reactor (Lotti et al 2014; Li et al 2018)
Such a low concentration of ammoniacal nitrogen may suggest that WW 2 and 3 could not be treated by the present to nitrite (PN)/ anammox process due to the impossibility for ammonium oxidizing bacteria (AOB) species to convert ammonia to nitrite for anammox bacteria
Summary
Digital (or ink-jet) textile printing (DTP) is rapidly spreading worldwide, mostly due to the greater versatility with respect to conventional printing techniques (Global Industry Analysts 2018). Discharges are rich in ammoniacal and organic nitrogen due to the massive use of urea as additive for pre-treating the fabric (Scaglione et al 2016) Very often, such a high nitrogen content in process wastewater results in exceeding discharge limits for nitrogen in the sewer system (100 mgN/L in Italy), so that additional treatments are required, with consequent additional costs. Full-scale applications showed that the two biological reactions may take place either in two separate reactors or may be combined in one reactor thanks to the presence of both bacterial populations in consortia (Lackner et al 2014; Gonzalez-Martinez et al 2018) Such single-stage process, often based on granular biomass, showed excellent performance as sustainable alternative to established biological processes in terms of energy requirements (Hu et al 2013). Among existing technological solutions, the use of a sequencing batch reactor (SBR) allows ensuring good biomass retention to favour the growth of anammox bacteria, avoiding their washing out, while the homogeneous distribution of substrates and products limits the formation of critical zones for bacteria survival inside the reactor (Lotti et al 2014; Li et al 2018)
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