Start-up of an aerobic granular sludge system from stored granules: Evaluating the impact of storage period on biomass activity and stability and the effect of temperature on nitrification and phosphorus removal rates

Aerobic granular sludge (AGS) has been considered a breakthrough within the wastewater treatment sector. However, the long reactor start-up for the formation of granules is challenging and may hinder the spread of this technology. To circumvent this obstacle, inoculation of the reactors with pre-formed granules from existing plants is an interesting approach. In this context, issues related to biomass storage becomes very relevant. In this study, reactivation of aerobic granular biomass after storage was evaluated in a sequencing batch reactor (SBR) designed for achieving simultaneous organic matter, nitrogen and phosphorus removal. Two different scenarios, short (40 days) and long (180 days) storage periods, were assessed, and their influence on the granules physical properties and bioactivity was addressed. The results revealed that the granules stored for a shorter period showed higher resistance to breakage and underwent smooth color changes. On the other hand, the biomass stored for a longer period acquired a dark color and was more susceptible to disruption during reactivation. The granules stored for 6 months become swollen and exhibited an irregular morphology and fluffy structure within the first days of reactivation. Consequently, their settling properties were adversely affected, and some parameters such as the food-to-microorganism ratio had to be adjusted to prevent granules disintegration. Regarding the bioactivity of important microbial functional groups, COD removal was rapidly restored within a few days of SBR operation with the biomass stored for a shorter period. However, it took longer for the biomass stored for 180 days to reach the same performance observed for the granules stored for 40 days. A similar trend is valid for nitrification. In the experiments with sludge stored for a longer time, it took almost twice as long to reach effluent ammonium concentrations lower than 1 mg NH₄⁺-N L^-1 compared to the test using biomass stored for 40 days. Phosphate removal was strongly affected by biomass storage, especially after 180 days of inactivity, a condition found to be detrimental for polyphosphate-accumulating organisms. Finally, cycle tests were also conducted to assess substrate conversion rates for comparison between different trials and evaluate the influence of temperature (10-35 °C) on nitrification and phosphate removal rates.

Variations in the temperature sensitivity of spring leaf phenology from 1978 to 2014 in Mudanjiang, China

Continuous long-term temperature sensitivity (S_T) of leaf unfolding date (LUD) and main impacting factors in spring in the period 1978-2014 for 40 plant species in Mudanjiang, Heilongjiang Province, Northeast China, were analyzed by using observation data from the China Phenological Observation Network (CPON), together with the corresponding meteorological data from the China Meteorological Data Service Center. Temperature sensitivities, slopes of the regression between LUD and mean temperature during the optimum preseason (OP), were analyzed using 15-year moving window to determine their temporal trends. Major factors impacting S_T were then chosen and evaluated by applying a random sampling method. The results showed that LUD was sensitive to mean temperature in a defined period before phenophase onset for all plant species analyzed. Over the period 1978-2014, the mean S_T of LUD for all plant species was - 3.2 ± 0.49 days °C^-1. The moving window analysis revealed that 75% of species displayed increasing S_T of LUD, with 55% showing significant increases (P < 0.05). S_T for the other 25% exhibited a decreasing trend, with 17% showing significant decreases (P < 0.05). On average, S_T increased by 16%, from - 2.8 ± 0.83 days °C^-1 during 1980-1994 to - 3.30 ± 0.65 days °C^-1 during 2000-2014. For species with later LUD and longer OP, S_T tended to increase more, while species with earlier LUD and shorter OP tended to display a decreasing S_T. The standard deviation of preseason temperature impacted the temporal variation in S_T. Chilling conditions influenced S_T for some species, but photoperiod limitation did not have significant or coherent effects on changes in S_T.

Metabolic divergence in simultaneous biological removal of nitrate and sulfide for elemental sulfur production under temperature stress

The simultaneous removal of NO₃^- and HS^- at temperature stress (25-10°C) is evaluated here. An expanded granular sludge bed (EGSB) reactor was run over 120days at N/S molar ratio of 0.35 (for S⁰ production) under constant sulfur loading rate of 0.4kgS/m³d. The simultaneous removal of NO₃^- and HS^-, was achieved at applied conditions. Average HS^--S removal varied from 98 (25°C) to 89.2% at 10°C, with almost complete NO₃^- removal. Average S⁰ yield ranged from 83.7 at 25°C to 67% at 10°C. The temperature drop caused a decrease in granular sludge accumulated S⁰ fraction by nearly 2.5 times. Decreased temperature caused metabolic pathway change observed as higher SO₄^2- production, apparently allowing the biomass to obtain more energy per HS^- consumed. It is hypothesized that the metabolic shift is a natural response to compensate for temperature-induced changes in energy requirements.

Importance of solvent association in the estimation of antioxidant properties of phenolic compounds by DPPH method

The presented paper shows the influence of temperature increase in the range typically used during antioxidant measurements (15-35 °C) on the estimation of antioxidant properties of phenolic compounds (caffeic acid, ferulic acid, gallic acid, trolox, butylhydroxyanisole, butylhydroxytoluene and 2,6-diisopropylphenol) in associating and non-associating solvents. A significant influence of temperature on the DPPH(•)/antioxidant reaction kinetic is observed for strongly associating solvents (e.g. methanol). This trend is less marked for non-associating solvents (e.g. dioxane, ethyl acetate). The performed experiments prove that the change of solvent structure, caused by temperature increase, influences the estimation of antioxidant properties of phenolic compounds much more than the increase of kinetic energy of reacting molecules and/or the increase of the dissociation degree of hydroxyl groups occurring in antioxidants.