Performance and kinetics of ANAMMOX granular sludge with pH shock in a sequencing batch reactor

As an efficient and cost-effective nitrogen removal process, anaerobic ammonium oxidation (ANAMMOX) could be well operated at suitable pH condition. However, pH shock occurred in different kinds of wastewater and affected ANANNOX process greatly. The present research aimed at studying the performance and kinetics of ANAMMOX granular sludge with pH shock. When influent pH was below 7.5, effluent ({text{NH}}_{4}^{ + })–N and ({text{NO}}_{2}^{ - })–N increased with decreasing pH. At Ph 6.0, effluent ({text{NO}}_{2}^{ - })–N approached 100 mg/L, and the ratios of (Delta {text{NO}}_{2}^{ - } - {text{N}}:Delta {text{NH}}_{4}^{ + } - {text{N and }}Delta {text{NO}}_{3}^{ - } - {text{N}}:Delta {text{NH}}_{4}^{ + } - {text{N}}) approached 2.2 and 1.3, respectively. Both greatly deviated from theoretical values. When influent pH was above 7.5, effluent ({text{NH}}_{4}^{ + })–N and ({text{NO}}_{2}^{ - })–N increased with increasing pH. At pH 9.0, ammonium removal rate (ARR) and nitrite removal rate (NRR) decreased to 0.011 ± 0.004 and 0.035 ± 0.004 kg/(m³·d), respectively. Besides, (Delta {text{NO}}_{2}^{ - })–N:(Delta {text{NH}}_{4}^{ + })–N deviated from theoretical value. Longer recovery time from pH 9.0 than from pH 6.0 indicated that alkaline surroundings inhibited anaerobic ammonium oxidizing bacteria (AAOB) greater. The sludge settling velocity was 2.15 cm/s at pH 7.5. However, it decreased to 2.02 cm/s when pH was 9.0. Acidic pH had little effect on sludge size, but disintegration of ANAMMOX granule was achieved with pH of 9.0. The Bell-shaped (A) model and the Ratkowsky model were more applicable to simulate the effect resulting from pH shock on ANAMMOX activity (R² > 0.95), and both could describe ANAMMOX activity well with pH shock. They indicated that q_max was 0.37 kg (Delta {text{NH}}_{4}^{ + })–N/(kgMLSS·d) at the optimum pH value (7.47) in present study. The minimum pH during which ANAMMOX occurred was 5.68 while the maximum pH for ANAMMOX reaction was 9.26. Based on nitrogen removal performance with different pH, strongly acidic (pH ≤ 6.5) or alkaline (pH ≥ 8.5) inhibited ANAMMOX process. Besides, ANAMMOX appeared to be more susceptible to alkaline wastewater. Compared to extremely acidic condition (low pH), extremely alkaline condition (high pH) affected ANAMMOX granules much more.