The effect of long-term bioaugmentation on nitrogen removal, nitrification activity, and microbial ecology for an anaerobic/anoxic/aerobic (A²O) pilot-scale plant operated in low sludge retention time (SRT) to treat municipal wastewater was investigated. Reject water from sludge treatment was used as a feed to cultivate the nitrifier contained in activated sludge for bioaugmentation. Under the conditions of 10 h hydraulic retention time, 8 d of SRT, and 14°C water temperature ammonia removal efficiency increased by 25%, and specific ammonia utilizing rate and specific nitrite utilizing rate increased by 1.86 and 1.90 times, respectively. The percentages of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in the total number of bacteria increased from 2.4 and 2.1% to 6.8 and 7.8%, respectively. The dominant AOB and NOB were transformed from Nitrosospira and Nitrospira to Nitrosomonas europaea and Nitrobacter.

Although there have been many studies on the process conditions of Constructed Wetlands (CW) and Microbial Fuel Cells (MFC), there are few studies on the Constructed Wetlands coupled with Microbial Fuel Cells. Currently, low power production is the main problem faced by Constructed Wetlands-Microbial Fuel Cell systems (CW-MFCs). This experiment intends to research the effects of HRT, influent COD and electrode spacing on wastewater treatment and power generation performance. In this experiment, CW-MFCs with two different electrode spacings (18 cm for reactor A and 28 cm for reactor B) were set up under continuous flow conditions. The effects of HRT, influent COD and eletrode spacing on wastewater treatment and power generation performance were explored using a single-factor controlled variable method. Experiment results showed that the extension of HRT was beneficial for contaminants removal and the power generation of the CW-MFCs, but the excessive extension was ineffective for the electricity output. The optimal HRT of the CW-MFCs was 24 h when influent COD was 500 mg·l-1. Improving influent COD within the appropriate range (500~1000 mg·l-1) facilitated the power generation and contaminant removal performance of the CW-MFCs. The maximum output voltage and power density were obtained in reactor A when influent COD was 1000 mg·l-1 and HRT was 24 h, which were 548 mV and 120 mW·m-3, respectively. Compared with reactor B, reactor with smaller electrode spacing achieved better electricity generation and contaminant degradation under the optimal condition. Its average output voltage could be improved by 5.1~46.1% and the removal rates of COD and NH4 +-N could also be improved by 0.2~4.9 % and -0.9~13.7 %, respectively. This phenomenon indicates that there was a significant positive correlation between the number of Gram-negative bacteria and the electricity production performance of the CW-MFCs, which was due to the difference in electron transfer efficiency. This study can provide operation parameters for the CW-MFCs process.

Bacteria can use nitrate as a nutrient for growth, but the underlying mechanisms of this pathway have not yet been identified. We investigated the effects of changing the nitrogen source from ammonia to nitrate on the properties of heterotrophic bacterial growth in anoxic and anoxic/oxic (A/O) SBRs. Both SBR types were seeded with activated sludge cultivated with ammonia and were then fed with 1,400 mg·L-1 chemical oxygen demand (COD) and 250 mg·L-1 of nitrate nitrogen. Heterotrophic bacteria had a lag period of 8-9 d and 13-14 d in terms of growth and COD and nitrogen removal, respectively, in both reactors with nitrate as nutrient. Of the influent nitrate, 15% were converted to biomass nitrogen. Compared with ammonia or organic nitrogen as a nutrient source, with the use of nitrate more energy was needed for proteins synthesis, which resulted in a lower sludge yield (0.32-0.35) and lower amounts of proteins and phosphorus compounds. Furthermore, fewer extracellular polymer substances (EPS) and more soluble microbial products (SMP) were produced, both of which also had low proteins and high polysaccharide contents. The proteins in the cells were synthesized via dissimilatory nitrate reduction to ammonia (DNRA).

In this study, homemade ceramsite-soil filler (system A) and a simple soil filler (system B) were applied in vertical upflow constructed wetlands, and their performance in the treatment of rural domestic wastewater were investigated under various HRTs and packing heights. Optimum performance was reached at a HRT of 6.4 d in both systems. The average removal rates of ammonia nitrogen (NH4 +-N), total nitrogen (TN), and total phosphorus (TP) in system A were as high as 90.78, 86.04, and 90.15%, respectively, which were 0.94, 2.21, and 10.62% higher than those in system B. The TN and NH4 +-N removal efficiencies of both systems decreased with shorter HRTs, whereas the TP removal efficiency was almost not affected. Along the inlet direction, with increasing packing height, the pollutant removal capacity gradually decreased, and the NH4 +-N removal efficiencies in the bottom layers (0-145 mm) of system A and B were 55.88 and 50.22%, respectively, with NH4 +-N volumetric loads of 8.63 and 7.76 g/(m3·d). System A contained more nitrifying genera at the genus level, mainly including Stenotrophomonas, Sphingomonas, and Acinetobacter. The addition of ceramsite resulted in a higher treatment efficiency and resistance to hydraulic shock loading.

Anoxic/oxic (A/O) sludge digestion is a waste-activated sludge (WAS) treatment practice that simultaneously reduces volatile suspended solids reduction and removes nutrients from digested sludge. This study aims to optimize the performance of A/O sludge digestion by achieving the optimum alkalinity and nitrogen balance through rate control. Rate control involves oxic/anoxic cycling based on the activity of WAS (i.e. ammonification, nitrification, oxygen utilization, and denitrification rates) and controlling the processes of amonification, nitrification, oxygen ultilization, and denitrification in WAS. This strategy is different from pH, oxidation–reduction potential, dissolved oxygen controls, or fixed time control methods. Laboratory-scale batch aerobic digestion and A/O digestion tests were performed to verify the feasibility of the approach. The optimum operational cycles for the aeration and mixing were determined as 3.5 and 2.5 h, respectively (6 h full cycle). The sludge reduction in A/O digestion was greater than that in the aerobic digestion (51.83 vs. 48.13%) at a sludge retention time of 23 d. The total nitrogen reduction in A/O digestion was significantly higher than that in the aerobic digestion (65.20 vs. 12.27%). The performance of the proposed rate-control strategy for A/O digestion is superior to those of other experimental control schemes. In addition, this technique produces a sludge dewatering liquor with low nitrogen and phosphorus concentrations.