Partial nitritation of nitrogen-rich refinery wastewater (sour water) with different Ci/N molar ratios

Abstract

In this study, a SHARON reactor was used to treat synthetic and real ammonium-rich refinery wastewater (sour water) with different inorganic carbon to nitrogen (Ci/N) molar ratios, in order to evaluate its possible implementation downstream of a steam stripping unit in a double-stage SHARON-ANAMMOX or SHARON-heterotrophic denitritation process. A synthetic influent containing NH4-N (2,000 mg/L) was initially fed to promote biomass acclimation, then real sour water containing also organic substrate, cyanides, sulphides and phenols was supplied. With both synthetic and real wastewater, the applied Ci/N molar ratio was progressively increased from 1 to 2 and the SHARON reactor produced an effluent suitable for further treatment by autotrophic ANAMMOX or heterotrophic denitritation, respectively. Acute toxicity assessments based on the specific measurement of nitritation activity confirmed that biomass acclimation to the toxic substances contained in the real wastewater occurred successfully. Moreover, high removal of organic matter (73%) suggested the absence of any competition between heterotrophic and autotrophic microorganisms. Controlling influent Ci/N molar ratio was shown to represent a key operating strategy to properly regulate SHARON performance, depending on the chosen downstream treatment, proving its actual feasibility under harsh operating conditions and providing useful indications for its implementation at full scale

SHARON process as preliminary treatment of refinery wastewater with high organic carbon-to-nitrogen ratio

“…Despite the high C/N molar ratio and the high observed DOC removal efficiency due to heterotrophic biomass activity, process performance was not compromised in terms of ammonium removal. As previously reported in literature, an influent C/N ratio of 0.15 gC/gN did not cause any negative effect on AOB activity [6]. On the other hand, influent C/N ratios above 0.3 gC/gN caused a 10% loss of AOB activity in a sequencing batch reactor with a dissolved oxygen concentration above 2 mg/L [7].…”

“…2, biomass was clearly inhibited by IGCC wastewater (IC10, IC50 and IC90 were 14.9, 54.5 and 200 mL/L, corresponding to a share of IGCC wastewater in the daily influent of approximately 2, 7 and 25%, respectively), hence the information gathered by toxicity assessment suggested a prudential operating strategy based on the gradual replacement of the synthetic influent with the IGCC wastewater, which was carried out in the subsequent Phases II, III and IV. A similar operating strategy was already proved to be successful for the treatment of ammonium-rich sour water characterized by a higher toxicity (the IC10, IC50 and IC90 were 3.6, 8.7 and 21.1 mL/L, respectively), as reported by Milia et al [6]; in that study, toxicity tests were used also to assess the acclimation of biomass to the toxic substances contained in the wastewater. Although the toxicity of IGCC wastewater used in the present study was lower and the acclimation of biomass was taken for granted, the overall system response to the progressive replacement of the synthetic influent with the IGCC wastewater was investigated: as shown in Fig.…”

“…A continuous flow stirred tank reactor with a working volume of 2 L was operated as a chemostat (no biomass recirculation) at controlled temperature (35±0.5°C), as described in Milia et al [6]. The pH control range was set at 7.0±0.2.…”

“…This combined process was shown to be extremely efficient for the treatment of wastewaters characterized by high ammonium concentration and low content of readily degradable organic carbon (i.e., low C/N ratio) like sludge digester supernatant and landfill leachate [2][3][4], as long as the influent alkalinity to NH4-N molar ratio (expressed as inorganic carbon to nitrogen molar ratio, Cinorg/N) was equal to 1. In previous studies, the possibility to integrate a steam stripping unit with the SHARON-anammox or the SHARON-denitrification processes for the treatment of sour water containing toxic substances and characterized by high ammonium content (up to 2,000 mgN/L) and low organic carbon to nitrogen ratio (C/N, up to 0.15 gC/gN) was successfully investigated [5,6]. If the industrial wastewater containing toxic substances and high concentrations of ammonium is characterized also by a high content of readily degradable organic matter (i.e., a high C/N ratio), the SHARON-anammox process may lack in terms of nitrogen removal, since the activity of ammonium oxidizing bacteria (AOB) can be hindered in the first step of the process (SHARON) [7,8], and denitrification may take place in the second step rather than anaerobic ammonium oxidation (according to previous studies, anammox bacteria are not able to compete for nitrite with denitrifying bacteria in presence of sufficiently high amounts of readily degradable organic carbon [9][10][11][12]).…”

Aerobic granular sludge formation in a sequencing batch reactor treating agro-industrial digestate

“…Moreover, digestate is considered a waste according to the EU Waste Framework Directive (2008/98/EC) [7], therefore its proper management represents a significant cost item for many of the existing anaerobic digestion plants [6]. Chemical-physical processes such as evaporation, air/ steam stripping or membrane filtration are commonly used for the removal of nitrogen from digestate, although they are considered moderately effective and/or highly expensive [6,8].…”