Evaluating the effect of dissolved oxygen on simultaneous nitrification and denitrification in polyurethane foam contact oxidation reactors.

The effects of dissolved oxygen on simultaneous nitrification and denitrification were evaluated in polyurethane foam contact oxidation reactors in a municipal wastewater treatment process. It was observed that nitrate could be removed at low dissolved oxygen levels, but the removal rate was gradually reduced as the dissolved oxygen concentration increased to a higher level of 6.0 mg/L. Nitrogen removal remained optimal within the dissolved oxygen range of 0.5 to 1.0 mg/L. Denaturing gradient gel electrophoresis (DGGE) analysis revealed that the diversity of the microbial community changed accompanying dissolved oxygen values of 0.5 to 1.0 mg/L, 2.5 to 3.5 mg/L, 6.0 to 6.5 mg/L, and 10.0 to 12.0 mg/L, in turn, which was supported by the Shannon-Wiener index of 1.56, 1.71, 1.43, and 1.56, accordingly. Both DGGE profiling and phylogenetic analysis confirmed that the nitrifiers in reactors that are responsible for nitrification during the experiment include Nitrosospira sp., Nitrosomonas sp., and Nitrospira sp.

Denitrification performance and in-situ fermentation mechanism of the wastepaper-flora slow-release carbon source.

Using wastepaper as external carbon sources is an optional way to achieve total nitrogen removal faced with low carbon to nitrogen ratio municipal sewage. Most of studies have primarily focused on using cellulose-rich wastes establishing the separate denitrification units to achieve in-situ fermentation, which can cause blockages and prolong the process chain. In response, a novel in-situ fermentation wastepaper-flora slow-release carbon source (IF-WF) was proposed using in the original denitrification unit. IF-WF could be efficiently utilized in situ and the denitrification rate increased with the increase of nitrate nitrogen. The fermentation products were highly available, but internal acidification of IF-WF inhibited fermentation. Moreover, IF-WF limited the growth of polysaccharides in the extracellular polymeric substances of denitrified sludge. IF-WF finally formed the structure dominated by nitrate-reduction bacteria outside and cellulose-degrading bacteria inside. These results provide guidance for understanding the mechanism of IF-WF for in-situ fermentation to promote nitrogen removal.

A novel membrane bioreactor inoculated with symbiotic sludge bacteria and algae: Performance and microbial community analysis.

This study combined sludge MBR technology with algae to establish an effective wastewater treatment and low membrane fouling system (ASB-MBR). Compared with control-MBR (C-MBR), the amelioration of microbial activity and the improvement of sludge properties and system environment were achieved after introducing algae resulting in high nutrients removal in the combined system. Further statistical analysis revealed that the symbiosis of algae and sludge displayed more remarkable impacts on nutrients removal than either of them. Additionally, membrane permeability was improved in ASB-MBR with respect to the decreased concentration, the changed of characteristics and the broken particular functional groups of extracellular polymeric substances (EPSs). Moreover, the algae inoculation reduced sludge diversity and shifted sludge community structure. Meantime, the stimulated bacteria selectively excite algal members that would benefit for the formation of algal-bacterial consortia. Consequently, the stimulated or inhibited of some species might be responsible for the performance of ASB-MBR.

Effect of endogenous hydrolytic enzymes pretreatment on the anaerobic digestion of sludge.

In this study, the effects of endogenous amylase, endogenous protease and combined amylase/protease pretreatment of sludge were studied to enhance the efficiency of sludge anaerobic digestion. These enzymes were obtained from bacterial fermentation and bacteria were separated from the sludge. All treatments improved sludge solubilization and acidification but had little influence on the floc sizes. In terms of sludge solubilization and acidification amylase was better than protease or mixed enzyme. After 7 h endogenous amylase treatment, the supernatant soluble chemical oxygen demand and volatile fatty acids concentration increased by 78.2% and 129.6%, respectively. But, in terms of anaerobic biodegradability, the best result was obtained with combined enzyme treatment, biogas production increased by 23.1% compared to the control after 11 days of anaerobic digestion. Scanning electron micrographs observation and particle size analysis revealed that the most important mechanism for the enzyme treatment of sludge might be solubilization of extracellular polymeric substances.