Effect of thermal shock and sustained heat treatment on mainstream partial nitrification and microbial community in sequencing batch reactors.

In order to develop a promising means of achieving mainstream short-cut nitrification, this study evaluated the effect of thermal shock on nitrite accumulation using intermittent offline and continuous inline heat treatment of biomass in sequencing batch reactors (SBRs). The SBRs fed with municipal wastewater were operated at a solid retention time of 7 days and nitrogen loading rate of 0.04 gN/L·d to 0.08 gN/L·d without the application of pre-treatment. Contrary to literature studies that showed suppression of nitrite-oxidizing bacteria at temperature 60 to 80 °C, nitrite accumulation was achieved temporarily when 20% of the biomass was heated for 2 h at 47 °C, as well as in continuously heated SBRs at 37 °C and 42 °C. The continuously heated reactors at 37 °C and 42 °C produced a maximum nitrite accumulation ratio (NAR) of 0.59 and 0.79, respectively, whereas the intermittent offline heating at 47 °C-2 h produced a NAR of 0.37. Although nitrite accumulation was stable only for 10-12 days in all heated reactors, this study demonstrates the achievement of mainstream partial nitrification (PN) at lower temperature (42 °C) than that reported in literature and also highlights the potential for achieving PN by implementing heat treatment of a portion of the return activated sludge (RAS) in biological nitrogen removal (BNR) systems. During the time when full nitrification was achieved, Nitrospira was more dominant than Nitrosomonas in all reactors at ratios of 1.4:1, 2.4:1, 2.4:1, and 3.7:1 for the control SBR (22 °C), 47 °C -2 h offline heating SBR, 37 °C SBR, and 42 °C SBR, respectively, suggesting that it may have played a role as a comammox bacteria capable of degrading ammonia to nitrates at elevated temperature.

Effects of trace elements on digester performance and microbial community response in anaerobic digestion systems.

Trace elements (TE), as micronutrients for microorganisms, have a significant impact on the stability of anaerobic digestion (AD). Studies have been conducted on process stability and performance of the AD of food waste (FW) by supplementing TEs. In this study, mesophilic batch biomethane potential (BMP) tests using FW were conducted to investigate the effect of TEs (Fe, Ni, Co, Se, and Mo) as single and mixed ions. In view of their scarcity, correlations between the microbial community and digester performance such as first-order hydrolysis coefficient (Kh), volatile fatty acids (VFA), methane yield, and methane production rate (MPR) have been developed. Ni2+ at 1 and 1.5 mg/L increased the methane yield by 27% and 23% respectively. Similarly, Co2+ at 0.1 and 0.5 mg/L increased the yield by 21% and 23% respectively, compared to control. Although Se4+ at all concentrations enhanced the methane yield, Fe2+ at only 50 mg/L increased methane yield by 22%. For mixed TEs, the combination of Ni2+ [1 mg/L] +Co2+ was the best and increased methane for all Co2+ concentrations (0.1, 0.4 and 0.5 mg/L) by 16%, 14% and 12% respectively. Firmicutes and Methanosaeta were the most abundant phyla among hydrolytic and methanogenic microbial groups, respectively, constituting 42%-61% and 60-80% of their respective microbial groups. The most significant positive correlations were observed between aceto/acidogenic microorganisms and final VFA concentrations with Pearson correlation factors of 0.91.

Removal of carbon, nitrogen and phosphorus from the separated liquid phase of hog manure by the multi-zone BioCAST technology.

The removal of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) at concentrations of 960 ± 38 to 2400 ± 96 mg/L, 143 ± 9 to 235 ± 15 mg/L and 25 ± 2 to 57 ± 4 mg/L, respectively, from the separated liquid phase of hog manure by the multi-zone BioCAST technology is discussed. Despite the inhibitory effect of hog waste toward microbial activities, removal efficiencies up to 89.2% for COD, 69.2% for TN and 47.6% for TP were obtained during 185 d of continuous operation. The free ammonia inhibition was postulated to be responsible for the steady reduction of COD and TP removal with the increase of TN/TP ratio from 3.6 to 5.8. On the contrary, the increase of COD/TN ratio from 4.8 to 14.1 improved the removal of all contaminants. Nitrogen removal did not show any dependence on the COD/TP ratio, despite the steady increase of COD and TP removal with this ratio in the range of 19.3-50.6. The removal efficiencies of organic and inorganic contaminants increased progressively owing to the adaptation of microbial biomass, resulting from the presence of suspended biomass in the mixed liquor that circulated continuously between the three zones of aerobic, microaerophilic and anoxic, as well as the attached biomass immobilized inside the aerobic zone.