High-rate partial-nitritation and efficient nitrifying bacteria enrichment/out-selection via pH-DO controls: Efficiency, kinetics, and microbial community dynamics

Conventional nitrification/denitrification process is gradually being replaced with partial-nitritation/anammox (PN/A) processes due to its installation and running cost. However, high ammonia-oxidizing bacteria (AOB) and anaerobic ammonia-oxidizing (anammox) bacteria activity as well as optimum out-selection of nitriteoxidizing bacteria (NOB) are necessary to achieving efficient PN/A process. Consequently, to enhance PN process via nitrifying bacteria enrichment/out-selection within psychrophilic environment. a novel pH-DO (dissolved oxygen) control strategy was proposed and the response of PN, kinetics, AOB enrichment, and NOB out-selection efficiency was investigated during start-up and long-term operation. With DO of 0.7 mg/L and pH of 7.5-7.9, quick start-up of the PN process was established within 34d as NO2--N accumulation ratio (NAR) reached 90.08 +/- 1.4%. Again, when NLR was elevated to 0.8 kg/m(3).d (400mgNH(4)(+)-N/L), DO curtailed to 0.2 mg/L, pH maintained at 7.7 and free ammonium at 6.5 mg/L, NAR and NH4+-N removal rate could still reach 97.04 +/- 2.4% and 97.84 +/- 1.5%, respectively. After optimum control factors had been established, real nitrogen-richmine-wastewater was fed (DO, 0.2 mg/L, pH, 8.9, and free ammonia, 6.5 mg/L) and NAR and NFIZ-N removal rate reached was 97.33 +/- 0.5% and 97.76 +/- 1.1%, respectively. Estimated kinetic parameters including maximum degradation rate (Vmax = 1.58/d), half-rate constant (Km = 33.8 mg/L), and inhibition constant (Ki 201.6 mg/L) suggested that inhibition on NH4+-N oxidation was most feasible at higher concentration of NH.tN.To elucidate biological mechanisms, 165 rRNA high-throughput revealed that AOB (Nitrosomonas) enrichment had increased from 0.08% to 49% whereas NOB (Nitrospira) abundance reduced from 1% to 0.034%, indicating pHDO control efficiently enriched AOB and out-selected NOB. Conversely, when influent NH4+-N was curtailed to about 200 mg/L and free ammonia concentration maintained at 6.5 mg/L, the population of AOB was observably reduced by 6% within a period of 14 days, indicating control strategies including pH-DO control and substrate availability were the key factors which substantially influenced and promoted the activities and growth of AOBs in the present SBR. (C) 2019 Elsevier B.V. All rights reserved.