Sludge reduction and microbial community structure in an anaerobic/anoxic/oxic process coupled with potassium ferrate disintegration.

An anaerobic/anoxic/oxic (AAO) wastewater treatment system combining with a potassium ferrate (K2FeO4) oxidation side-stream reactor (SSR) was proposed for sludge reduction. Batch experiments showed that optimal K2FeO4 dosage and reaction time for sludge disintegration was 100mg/g suspended solids (SS) and 24h, respectively. Subsequently, an AAO-SSR and a conventional AAO were operated in parallel to investigate effects of K2FeO4 oxidation on process performance, sludge characteristics and microbial community structures. The AAO-SSR process operated under the optimized condition achieved efficient COD and NH4+-N removal, and reduced sludge by 47.5% with observed yield coefficient of 0.21gSS/g COD. K2FeO4 addition broke sludge particles, increased dissolved organic matters in the mixed liquor, and improved sludge dewaterability. Illumina-MiSeq sequencing results showed that K2FeO4 oxidation in the AAO-SSR decreased microbial richness and diversity, enriched slow growers (Dechloromonas), anaerobic fermentative bacteria (Azospira) and Fe(III)-reducing bacteria (Ferribacterium), but limited the growth of phosphate-accumulating organisms.

[Spectral Characteristics of Dissolved Organic Matters in Reject Water from Wastewater Treatment Plants].

Reject water generated from sludge thickening, dewatering and stabilization process contains high-content and complex dissolved organic matters (DOM). The spectral characteristics of DOM in the reject water were investigated by three-dimensional excitation-emission matrix and Fourier transform infrared spectroscopy. Fluorescent DOM (FDOM) from reject water were decomposed into six components by parallel factor analysis, the protein-like C1 (275/355 nm), C4 (235/350 nm) and C6 (275/305 nm) and the humic-like C2 (250, 340/440 nm) , C3 (320/380 nm) and CS (250/465 nm). Soluble COD in the sludge thickening reject water was positively correlated with all the three humic-like substances at P < 0.01 level, and was insignificantly influenced by protein-like substances. The tryptophan-like C1, C4 and humic-like CS increased in the centrifugal dewatering reject water (CDRW). FDOM in the advanced dewatering reject water (ADRW) were significantly different from those of other reject water in fluorescence peak locations and intensities, and humic-like C3 and tyrosine-like C6 in the DOM were 15.63 and 7.30 times higher than those in CDRW. Compared to sludge thickening reject water, infrared peaks related to polysaccharide and humic substances in CDRW were enhanced and massive proteins were released into ADRW. DOM structures in ADRW were changed owing to the complexation between metals and both humic substances and proteins.

Effects of alkalinity on membrane bioreactors for reject water treatment: Performance improvement, fouling mitigation and microbial structures.

Two submerged membrane bioreactors (MBRs) for reject water treatment were operated to investigate effects of sodium bicarbonate (SB) addition on enhancing process performance and mitigating membrane fouling. Results showed that SB addition enhanced average removal efficiencies of COD and NH4-N by 14.6% and 38.3%, respectively. With SB addition, the extracellular polymeric substances (EPS) content in activated sludge increased, but those in membrane foulants greatly decreased. Gel permeation chromatography analysis demonstrated that EPS in MBRs for reject water treatment had much larger molecular weight (MW) and broader MW distribution than those in MBRs for municipal wastewater treatment. The fouling mitigation by SB was attributed to a deprotonation mechanism reduced EPS adsorption on negatively charged membrane surfaces, and improvement of degradation efficiency of macromolecular organic matters. SB addition into MBRs for reject water treatment increased microbial abundance, enriched nitrifying bacteria, and converted predominant AOB genus from Nitrosomonas to Nitrosospira.

[Study on affecting factors of simultaneous nitrification and denitrification in moving-bed biofilm system].

The phenomenon of simultaneous nitrification and denitrification (SND) has taken place in moving-bed biofilm reactor (MBBR) steadily. The effect of C/N to denitrification effectiveness has been also studied in the experiment. The results of the treatment show that better denitrification efficiency could be obtained by increasing C/N ratio and the removal ratios of TN reached 92.9%. When C/N ratio is 12, the amplitude of TN removal ratio is not obvious. The effects of pH to ammonia nitrogen and TN removal ratio have been researched. The results show that the proper range of pH is 8.03-9.01 to removing ammonia nitrogen and the proper range of pH is 8.03-8.55 to TN efficiency. The experiment analyzed the influence of alkalinity and pH to denitrification efficiency, moreover, the relation of theoretical alkalinity and practical alkalinity has been studied. The results indicate that the influence of pH and alkalinity to removal efficiency of ammonia nitrogen and TN is low in SND, so does not need to adjust pH and increase alkalinity. The changes of pH and alkalinity during the reaction course were also investigated, and the result shows that pH can indicate the conversion process of nitrogen during a single representative period in SND.