Zhaoxia Xue

Effects of metabolic uncouplers on excess sludge reduction and microbial products of activated sludge.

The present study investigated the influences of three metabolic uncouplers (pCP, oCP and oNP) on excess activated sludge reduction and microbial products of extracellular polymeric substances (EPS) and intracellular storage product (polyhydroxybutyrate, PHB) in short-term tests. Results showed sludge was reduced 58.2%, 59.8% and 80.8%, respectively, at pCP, oCP and oNP concentrations of 20mg/L. The dosage of three uncouplers had no obviously influences on COD removal and sludge settleability, but had significant inhibition effect on ammonia removal, especially for oNP. Low concentration of pCP and oNP (5mg/L) dosing resulted in protein and polysaccharide content increased in EPS, however, they were decreased at high pCP and oNP concentrations (>5mg/L). To oCP, the protein content in EPS was increased linearly with oCP concentration. Furthermore, metabolic uncouplers addition stimulated the production of PHB. Among three uncouplers, oCP could be an alternative uncoupler for sludge reduction in activated sludge process.

Improving anaerobic fermentation of waste activated sludge using iron activated persulfate treatment

This study reported a novel and efficient approach to improve the anaerobic fermentation performance of waste activated sludge (WAS) by the indigenous iron activated persulfate (PS/Fe) treatment. Firstly, the production of short-chain fatty acids (SCFAs), especially acetic acid, was remarkably enhanced within shorter fermentation time. Mechanism investigations demonstrated that the PS/Fe treatment could simultaneously accelerate and enhance the hydrolysis and acidification process while inhibit the methanogenesis during WAS fermentation. The activities of key enzymes and the abundances of anaerobic microorganisms responsible for SCFAs production were stimulated in the presence of PS/Fe which would promote the biological processes. Secondly, the PS/Fe treatment improved the quality of fermentation residue by reducing the toxic organic compounds in the residue and enhancing the dewaterability of fermented sludge, which was beneficial to the final disposal of WAS with added economical and environmental values.

Characterizing the free ammonia exposure to the nutrients removal in activated sludge systems

As a by-product during liquid production, the liquor wastewater exhibits tremendous environmental risks and may cause undesirable effects to the biological systems due to the high concentration of ammonia. This study was carried out to characterize the effects of high concentration free ammonia (FA) exposure in liquor wastewater on the removal of nutrients (NH4+–N, NOx−–N, PO43− and organics) in sequencing batch reactors (SBRs). Experimental data demonstrated that the short-term exposure of FA had little effect on the removal of typical pollutants. In the long-term, however, it was found that the removal of NH4+–N was determined by the counteraction of negative effects caused by high concentration FA and the contribution brought by initial substrate concentration. Moreover, the high concentration FA had evident inhibitory effects on both the nitrification process and the phosphorus removal. The side-effect of high FA on organics removal was insignificant and the lower removal efficiency of apparent COD in high FA reactors was primarily attributed to the accumulation of NO2–N, which was commonly neglected in previous studies. Mechanism explorations indicated that the microbes in the SBRs could excrete additional protein-dominated extracellular polymeric substances (EPS) to resist the side-effects caused by high FA. This made the sludge structure more compact, while it blocked the transport of substrates in the process of pollutants removal. Furthermore, FA would also influence the microbial diversity and reduce the abundance of key microorganisms (i.e. ammonia-oxidizing bacteria, nitrite-oxidizing bacteria and phosphate-accumulating organism) responsible for nutrients removal; thus the corresponding removal efficiency subsequently decreased in the presence of high FA.

Achieving low effluent NO3-N and TN concentrations in low influent chemical oxygen demand (COD) to total Kjeldahl nitrogen (TKN) ratio without using external carbon source

Two mathematical models were used to optimize the performance of a full-scale biological nutrient removal (BNR) activated treatment plant, a plug-flow bioreactors operated in a 3-stage phoredox process configuration, anaerobic anoxic oxic (A2/O). The ASM2d implemented on the platform of WEST2011 software and the BioWin activated sludge/anaerobic digestion (AS/AD) models were used in this study with the aim of consistently achieving the designed effluent criteria at a low operational cost. Four ASM2d parameters (the reduction factor for denitrification

Using the dehydrogenase activity for alert of activated sludge system under different copper concentrations

(\eta _{NO_3 H} )

The influences of shear stress on Extracellular Polymeric Substances of activated sludge

, the maximum growth rate of heterotrophs (µH), the rate constant for stored polyphosphates in PAOs (qpp), and the hydrolysis rate constant (kh)) were adjusted. Whereas three BioWin parameters (aerobic decay rate (bH), heterotrophic dissolved oxygen (DO) half saturation (KOA), and YP/acetic) were adjusted. Calibration of the two models was successful; both models have average relative deviations (ARD) less than 10% for all the output variables. Low effluent concentrations of nitrate nitrogen (N-NO3), total nitrogen (TN), and total phosphorus (TP) were achieved in a full-scale BNR treatment plant having low influent chemical oxygen demand (COD) to total Kjeldahl nitrogen (TKN) ratio (COD/TKN). The effluent total nitrogen and nitrate nitrogen concentrations were improved by 50% and energy consumption was reduced by approximately 25%, which was accomplished by converting the two-pass aerobic compartment of the plug-flow bioreactor to anoxic reactors and being operated in an alternating mode. Findings in this work are helpful in improving the operation of wastewater treatment plant while eliminating the cost of external carbon source and reducing energy consumption.