THE INFLUENCE OF SODIUM CHLORIDE AND TEMPERATURE ON THE ENDOGENOUS RESPIRATION OF B. CEREUS

Effect of salinity on anammox nitrogen removal efficiency and sludge properties at low temperature

Anaerobic ammonium oxidation (Anammox) process is a new type of biological nitrogen removal technology that is highly efficient, consumes low energy, and is cost-effective. However, from a practical perspective, there are operational problems involved with the technology, due to its special low temperature environmental conditions. As such, the technology is currently a key research direction in the field of sewage control engineering. This study investigated the effect of salinity on the performance of the anammox process at the stress of a low temperature (15℃) and the role salinity has on extracellular polymeric substance (EPS) secretion and by extension, anammox activated sludge. The study tested the technology used to adjust and control salinity at a low temperature. The study found that at a low temperature of 15℃, low salinity can promote the nitrogen removal efficiency of anammox bacteria. Low salinity can also activate anammox bacteria activity. However, in contrast with low salt concentrations, high salt concentrations can inhibit anammox activity. When the temperature was 15℃ and the salinity was 4 g/L, the nitrogen removal efficiency of the reactor was 1.79 times higher than in the environment with unadjusted salinity at 15℃. At a low temperature, as salinity increased, the water binding capacity and flocculation capacity of sludge also increased. Salinity can promote the secretion of EPS and changes its composition. Under low temperature stress, the concentration of salt was less than 12 g/L, and the anammox activity improved. However, a high salinity level significantly inhibited anammox activity.

The Effect of Salinity on Membrane Fouling Characteristics in an Intermittently Aerated Membrane Bioreactor

The effect of salinity on the membrane fouling characteristics was investigated in the intermittently aerated membrane bioreactor (IAMBR). Five different salinity loadings were set from 0 to 35 g·L−1(referring to NaCl), respectively. The removal of total organic carbon (TOC) and ammonia-nitrogen (NH4+-N) was gradually decreased with increasing salinity. The variation of membrane filtration resistance, particle size distribution (PSD), extracellular polymeric substances (EPS), soluble microbial products (SMP), and relative hydrophobicity (RH) analysis revealed that salinity has a significant effect on sludge characteristics in IAMBR. The results also indicated that the membrane fouling is often caused by the integration of sludge characteristics in saline wastewater.

Asymmetric response of carbon metabolism at high and low salt stress in Vibrio sp. DSM14379

Energy redistribution between growth and maintenance in salt-stressed cells is especially important for bacteria living in estuarine environments. In this study, Gram-negative bacterium Vibrio sp. DSM14379, isolated from the estuarine waters of the northern Adriatic Sea, was grown aerobically in a peptone-yeast extract medium with different salt concentrations (ranging from 0.3% to 10% (w/v) NaCl). Carbon flux through the central metabolic pathways was determined at low and high salt concentrations. At low salt concentrations, total endogenous respiration, dehydrogenase activity, and net intracellular adenosine triphosphate (ATP) concentration significantly increased, the phosphofructokinase and pyruvate kinase activity decreased, whereas glucose-6-phosphate dehydrogenase activity remained unchanged. The carrying capacity of bacterial culture decreased dramatically, indicating a severe metabolic imbalance at low salt concentrations. At high salt concentrations, carrying capacity decreased gradually. There was a large increase in glucose-6-phosphate dehydrogenase activity, which correlated with a 10-fold increase in concentration of osmoprotectant L-proline. There was no significant change of net intracellular ATP concentration, phosphofructokinase, or pyruvate kinase activity. The results indicate that Vibrio sp. DSM14379 central metabolic pathways respond to low and high salt concentrations asymmetrically; cells are better adapted to high salt concentrations. In addition, cells in the stationary phase can tolerate induced salt stress without a significant change in dehydrogenase activity or endogenous respiration for at least 1 h, but need to alter their macromolecular composition and carbon flux distribution for long-term survival.

Osmotic stress on nitrification in an airlift bioreactor

The effect of osmotic pressure on nitrification was studied in a lab-scale internal-loop airlift-nitrifying reactor. The reactor slowly adapted to the escalating osmotic pressure during 270 days operation. The conditions were reversed to the initial stage upon full inhibition of the process. Keeping influent ammonium concentration constant at 420 mg N L(-1) and hydraulic retention time at 20.7h, with gradual increase in osmotic pressure from 4.3 to 18.8x10(5) Pa by adding sodium sulphate, the ammonium removal efficiencies of the nitrifying bioreactor were maintained at 93-100%. Further increase in osmotic pressure up to 19.2x10(5) Pa resulted in drop of the ammonium conversion to 69.2%. The osmotic pressure caused abrupt inhibition of nitrification without any alarm and the critical osmotic pressure value causing inhibition remained between 18.8 and 19.2x10(5) Pa. Nitrite oxidizers were found more sensitive to osmotic stress as compared with ammonia oxidizers, leading to nitrite accumulation up to 61.7% in the reactor. The performance of bioreactor recovered gradually upon lowering the osmotic pressure. Scanning and transmission electron microscopy indicated that osmotic stress resulted in simplification of the nitrifying bacterial populations in the activated sludge as the cellular size reduced; the inner membrane became thinner and some unknown inclusions appeared within the cells. The microbial morphology and cellular structure restored upon relieving the osmotic pressure. Addition of potassium relieved the effect of osmotic pressure upon nitrification. Results demonstrate that the nitrifying reactor possesses the potential to treat ammonium-rich brines after acclimatization.

Anaerobic treatment of high-saline wastewater using halophilic methanogens in laboratory-scale anaerobic filters

The presence of a high concentration of sodium in wastewater is considered inhibitory for anaerobic biological treatment. This research was designed to investigate the potential use of halophilic methanogens and a mixed culture of halophilic methanogens and digester sludge, in anaerobic filters, for treatment of organic pollutants in high-saline wastewater at 35 degrees C. Data related to startup of the filters are presented. Both halophilic and mixed-culture anaerobic filters were able to operate at a sodium chloride concentration of 35 g/L, at organic loading rates (OLRs) of 6.2 and 5 kg chemical oxygen demand (COD)/m(3) x d, respectively. The COD removal efficiency was as high as 80%, and the systems were able to maintain a low volatile fatty acids concentration of 500 mg/L. No significant difference in COD removal was observed between the halophilic filter and the mixed-culture filter. Increasing the salt concentration to 37 g/L at an OLR of 3 kg/m(3) x d caused system failure.

Treatment of organic pollution in industrial saline wastewater: a literature review

Many industrial sectors are likely to generate highly saline wastewater: these include the agro-food, petroleum and leather industries. The discharge of such wastewater containing at the same time high salinity and high organic content without prior treatment is known to adversely affect the aquatic life, water potability and agriculture. Thus, legislation is becoming more stringent and the treatment of saline wastewater, both for organic matter and salt removal, is nowadays compulsory in many countries. Saline effluents are conventionally treated through physico-chemical means, as biological treatment is strongly inhibited by salts (mainly NaCl). However, the costs of physico-chemical treatments being particularly high, alternative systems for the treatment of organic matter are nowadays increasingly the focus of research. Most of such systems involve anaerobic or aerobic biological treatment. Even though biological treatment of carbonaceous, nitrogenous and phosphorous pollution has proved to be feasible at high salt concentrations, the performance obtained depends on a proper adaptation of the biomass or the use of halophilic organisms. Another major limit is related to the turbidity problems inherent in saline effluents. For this reason, the major need for research in the future will be the combination of physico-chemical/biological treatment of saline industrial effluents, with regard to the global treatment chain, in order to meet the regulations.

Oxygen-limited autotrophic nitrification-denitrification (OLAND) in a rotating biological contactor treating high-salinity wastewater

A lab-scale rotating biological contactor (RBC) reactor operated under OLAND conditions was slowly adapted during 178 days to increasing salt concentrations going up to 30 g NaCl L(-1). The reactor performed well during this experimental period. However, the removal capacity of the reactor was lower under high-salinity conditions. A removal efficiency of 84% was achieved at a N loading rate of 725 mg N L(-1) d(-1) and a salt concentration of 30 g L(-1). The effect of salt shock loading and adaptation to 30 g NaCl L(-1) on the specific nitritation and anammox activity of the biomass was investigated in short-term batch experiments. A salt shock loading of 30 g L(-1) caused a 43% decrease in specific nitritation activity and 96% loss of specific anammox activity compared to reference biomass (not exposed to salt). The salt-adapted biomass (3-4 weeks) showed a specific nitritation activity that was 23% lower, and a specific anammox activity that was 58% lower, compared to the reference biomass. Overall, these results demonstrate that the OLAND process can have the potential to treat ammonium-rich brines after adaptation to high salinity.