Bio-augmentation for mitigating the impact of transient oxytetracycline shock on anaerobic ammonium oxidation (ANAMMOX) performance

Highlights

• The role of bio-augmentation in assisting recovery of ANAMMOX from OS was studied.

• The bio-augmentation time (BAT) was optimized.

• The bio-augmentation dosage (BAD) was optimized.

• The changes in sludge characteristics were monitored.

• The mechanisms of bio-augmentation were discussed.

Abstract

The feasibility of applying bio-augmentation tactics to remit the influence of transient oxytetracycline (OTC) shock on the anaerobic ammonium oxidation (ANAMMOX) process was evaluated. The bio-augmentation was applied together with shock test, with OTC shock concentration of 518 mg L⁻¹ and 1-h duration. 0.655–2.62 g volatile suspended solid (VSS) sludges were varied to optimize bio-augmentation dosage (BAD), and appropriate bio-augmentation time (BAT) was determined. The validity of the bio-augmentation was indicated by recovery performance and sludge characteristics. The restoring time of 38 h for bio-augmented reactor was shorter than that of non-bio-augmented reactor (45 h), and heme c content was increased respectively from 0.195 ± 0.001, 0.267 ± 0.047, 0.301 ± 0.049, to 0.340 ± 0.053 μmol g⁻¹ VSS with the BAD of 0.655, 1.31, 1.97, 2.62 g-VSS. The results suggest that bio-augmentation enhances the recovery of ANAMMOX performance following OTC shock and BAT and BAD are key operational factors.

Introduction

The anaerobic ammonium oxidation (ANAMMOX) process is a biological process in which ammonium is directly converted to dinitrogen gas with nitrite as the electron acceptor under anoxic conditions (Strous et al., 1998). The ANAMMOX process is a new and promising alternative to conventional nitrogen removal processes. The application of ANAMMOX to nitrogen removal would lead to a significant reduction in the costs for aeration and exogenous electron donors compared with the conventional nitrification–denitrification process (Yang et al., 2013). However, one of the main drawbacks common to applying the ANAMMOX process is the requirement of a long start-up period, mainly due to the slow growth rates of the ANAMMOX bacteria (doubling time of approximately 11 days) (Strous et al., 1998). Additionally, as ANAMMOX consortia are strictly anaerobic and autotrophic, they are very difficult to culture, implying a risk of prolonged recovery periods when the microorganisms are inhibited or disturbed by inevitable variations in environmental conditions or wastewater composition (Jin et al., 2012).

The overuse of antibiotics in livestock feed leads to high manure concentrations of antibiotics and their metabolites, which could eventually be released into the environment. Oxytetracycline (OTC), a common antibiotic with a broad range of activity and a low cost (Álvarez et al., 2010), can be found in some nitrogen-rich wastewaters, such as OTC production wastewater and swine wastewater digester liquor (Li et al., 2008). Furthermore, OTC concentrations have been reported in the range of 0.003–250 mg L⁻¹ in manure samples (Noophan et al., 2012), up to 0.340 mg L⁻¹ in surface water (Kümmerer, 2009) and greater than 50.0 mg L⁻¹ in the outflow of an OTC production facility in China (Li et al., 2008). Such high-strength OTC leads to an inevitable challenge for biological nitrogen removal from wastewater.

OTC has been reported to suppress the bioactivity of various microorganisms (Álvarez et al., 2010, Kümmerer, 2009), and ANAMMOX activity is inhibited by antibiotics (Yang et al., 2013). In addition, Yang et al. (2013) proposed that in a long-term test, 50.0 mg L⁻¹ OTC caused an 84% reduction in the nitrogen removal rate (NRR) within days. Noophan et al. (2012) reported that ANAMMOX activity was inhibited by OTC concentrations of 23–100 mg L⁻¹ in a short-term study, whereas the daily addition of OTC at a concentration of 5.00 ± 3.50 mg L⁻¹ to the ANAMMOX reactor completely inhibited ANAMMOX activity in 5 weeks. Moreover, the shock of antibiotics may inheritably inhibit or poison the microorganisms and result in an unsteady performance (Álvarez et al., 2010). Meanwhile, in our recent investigation, the ANAMMOX consortia was inhibited with transient OTC shock (155–1731 mg L⁻¹) lasting for 1–3 times of the hydraulic retention time (HRT) and with a nitrogen loading rate (NLR) of 6.72–13.4 kg m⁻³ d⁻¹ (Zhang et al., 2014).

The operation mode in a large number of industries is discontinuous, with potential fluctuations in the flow according to demand or even the production of different products within the same plant. Moreover, the transient shock of wastewater with compounds, including toxic organic matter (alcohol, aldehydes, antibiotics and phenols) and heavy metals, invariably impacts the bioactivity and process performance (Jin et al., 2012). This scenario might be difficult to handle in a wastewater treatment plant (WWTP) because the biological reactor could be forced to receive transient or continuous shock loads of a particular contaminant (Martín-Hernández et al., 2012).

In those cases, bio-augmentation has emerged as a viable treatment strategy to address transient or continuous shocks and unstable operation problems (Bartrolĺ et al., 2011, Ma et al., 2013, Manconi et al., 2007). Bio-augmentation can be employed to improve reactor start-up (Schauer-Gimenez et al., 2010). Bio-augmentation also acts as a powerful tool to enhance the removal efficiency of recalcitrant and/or toxic compounds (Amorim et al., 2013) such as phenols (Tawfiki Hajji et al., 2000), and aromatic hydrocarbons (Venkata Mohan et al., 2009). Moreover, bio-augmentation was investigated as a method to decrease the recovery period of anaerobic digesters exposed to a transient toxic event or for recovery after shock loads in biological reactors (Bartrolĺ et al., 2011). Thus, bio-augmentation is recognized as a promising operational means to strengthen wastewater treatment performance (Venkata Mohan et al., 2009). However, when an ANAMMOX bioreactor was transiently shocked with OTC, the implementation of bio-augmentation for the rapid recovery of process performance has to the best of our knowledge, not been reported.

The objectives of this study, therefore, were (1) to evaluate the feasibility of bio-augmentation to accelerate the recovery of ANAMMOX performance from OTC shock (OS), (2) to optimize the operational conditions of bio-augmentation (bio-augmentation time (BAT) and bio-augmentation dosage (BAD)), and (3) to indicate changes in the granule characteristics during the application of the bio-augmentation strategy.