Influence of phosphorus availability on the community structure and physiology of cultured biofilms

Biofilms have important effects on nutrient cycling in aquatic ecosystems.However,publications about the community structure and functions under laboratory conditions are rare.This study focused on the developmental and physiological properties of cultured biofilms under various phosphorus concentrations performed in a closely controlled continuous flow incubator.The results showed that the biomass（Chl a）and photosynthesis of algae were inhibited under P-limitation conditions,while the phosphatase activity and P assimilation rate were promoted.The algal community structure of biofilms was more likely related to the colonization stage than with the phosphorus availability.Cyanobacteria were more competitive than other algae in biofilms,particularly when cultured under low P levels.A dominance shift occurred from non-filamentous algae in the early stage to filamentous algae in the mid and late stages under P concentrations of 0.01,0.1 and 0.6 mg/L.However,the total N content,dry weight biomass and bacterial community structure of biofilms were unaffected by phosphorus availability.This may be attributed to the low respiration rate,high accumulation of extracellular polymeric substances and high alkaline phosphatase activity in biofilms when phosphorus availability was low.The bacterial community structure differed over time,while there was little difference between the four treatments,which indicated that it was mainly affected by the colonization stage of the biofilms rather than the phosphorus availability.Altogether,these results suggested that the development of biofilms was influenced by the phosphorus availability and/or the colonization stage and hence determined the role that biofilms play in the overlying water.

Sulfide oxidation in fluidized bed bioreactor using nylon support material

A continuous fluidized bed bioreactor （FBBR） with nylon support particles was used to treat synthetic sulfide wastewater at different hydraulic retention time of 25, 50 and 75 min and upflow velocity of 14, 17 and 20 m/hr. The effects of upflow velocity, hydraulic retention time and reactor operation time on sulfide oxidation rate were studied using statistical model. Mixed culture obtained from the activated sludge, taken from tannery effluent treatment plant, was used as a source for microorganisms. The diameter and density of the nylon particles were 2-3 mm and 1140 kg/m3, respectively. Experiments were carried out in the reactor at a temperature of （30 ± 2）°C, at a fixed bed height of 16 cm after the formation of biofilm on the surface of support particles. Biofilm thickness reached （42 ± 3） μm after 15 days from reactor start-up. The sulfide oxidation, sulfate and sulfur formation is examined at all hydraulic retention times and upflow velocities. The results indicated that almost 90%-92% sulfide oxidation was achieved at all hydraulic retention times. Statistical model could explain 94% of the variability and analysis of variance showed that upflow velocity and hydraulic retention time slightly affected the sulfide oxidation rate. The highest sulfide oxidation of 92% with 70% sulfur was obtained at hydraulic retention time of 75 min and upflow velocity of 14 m/hr.