Xiaodong Xin

Role of aeration intensity on performance and microbial community profiles in a sequencing batch reaction kettle (SBRK) for wastewater nutrients rapid removal.

A lab-scale SBRK was operated to investigate the effects of aeration intensity on the system performance and microbial community dynamics within it. Results showed that the sewage nutrients was removed rapidly (just about 3-6h) with the aeration intensity increasing from 0 to 0.6MPa. Average effluent parameters were: COD below 50mg/L, NH4(+)-N less than 1mg/L, 1.5-4.5mg/L for nitrate and TP below 0.5mg/L. The highest community similarity and diversity emerged simultaneously with the aeration pressure rising from 0.2 to 0.4MPa, which was regarded as the optimal aeration intensity range. Microbial community shifted obviously and the function species of Comamonadaceae, Dechloromonas, Flavobacterium and Nitrospira dominated in the corresponding communities. RDA indicated that aeration intensity was the main factor for regulating system communities to optimize the system performance. It inferred that high aeration pressure played a key role on sewage nutrients rapid removal.

Microbial community related to lysozyme digestion process for boosting waste activated sludge biodegradability

Waste activated sludge from a lab-scale sequencing batch reactor was used to investigate the potential relation of microbial community with lysozyme digestion process for sludge solubilization. The results showed the microbial community shifted conspicuously as sludge suffered lysozyme digestion. Soluble protein and polysaccharide kept an increasing trend in solution followed with succession of microbial community. The rise of lysozyme dosage augmented the dissimilarity among communities in various digested sludge. A negative relationship presented between community diversity and lysozyme digestion process under various lysozyme/TS from 0 to 240min (correlation coefficient R(2) exceeded 0.9). Pareto-Lorenz curves demonstrated that microbial community tended to be even with sludge disintegration process by lysozyme. Finally, with diversity (H) decrease and community distribution getting even, the SCOD/TCOD increased steadily in solution which suggested the sludge with high community diversity and uneven population distribution might have tremendous potential for improving their biodegradability by lysozyme digestion.

Removal of heavy metals with sequential sludge washing techniques using saponin: optimization conditions, kinetics, removal effectiveness, binding intensity, mobility and mechanism

Testing of sequential sludge washing in triplicate using typical biosurfactant saponin was conducted to remove heavy metals. The aim of the testing was to improve efficiency and reduce mobility of heavy metals. Different washing conditions such as concentration, contact time, liquid/solid ratio and pH were optimized. The heavy metal desorption performances were investigated strictly and the experimental data fitted the pseudo-second order equation very well. A sequential washing step and heavy metal mobilization was investigated, and the results demonstrated that the total content and fractions of the heavy metals reached remarkable extraction efficiencies, after three washings, Cr obtained the highest extraction efficiency (65.00%), and the Pb exchangeable fraction acquired the highest extraction efficiency (85.00%). Also, the heavy metal binding intensity and mobility were investigated, and the results indicated that the heavy metal binding intensity (IR) increased after washing, conversely, the mobility (MF) decreased, due to the weak fractions extracted by saponin. The toxicity characteristic leaching procedure (TCLP) indicated that heavy metals have more stable fractions in the after washing sludge. SEM, FTIR and XRD revealed that mechanism of saponin enhanced heavy metal extraction from the sludge, elucidated that carboxyl and hydroxyl were the main functional groups. This study indicated that the saponin may be a replacement for organic acids, inorganic acids and less environmentally friendly refractory chelators in the extraction of heavy metals from the sludge.

Performance of the lysozyme for promoting the waste activated sludge biodegradability

The fresh waste activated sludge (WAS) from a lab-scale sequencing batch reactor was used to determine the performance of the lysozyme for promoting its biodegradability. The results showed that a strict linear relationship presented between the degree of disintegration (DDM) of WAS and the lysozyme incubation time from 0 to 240min (R(2) was 0.992, 0.995 and 0.999 in accordance with the corresponding lysozyme/TS, respectively). Ratio of net SCOD increase augmented significantly by lysozyme digestion for evaluating the sludge biodegradability changes. Moreover, the protein dominated both in the EPS and SMP. In addition, the logarithm of SMP contents in supernatant presented an increasing trend similar with the ascending logarithmic relation with the lysozyme incubation time from 0 to 240min (R(2) was 0.960, 0.959 and 0.947, respectively). The SMP, especially the soluble protein, had an important contribution to the improvement of WAS biodegradability.

Enzymes catalyzing pre-hydrolysis facilitated the anaerobic fermentation of waste activated sludge with acidogenic and microbiological perspectives

This study investigated acidogenic and microbiological perspectives in the anaerobic fermentation (AF) of waste activated sludge (WAS) pre-hydrolyzed by enzymes catalysis. The enzymes catalysis boosted WAS biodegradability dramatically with nearly 8500 mg/L soluble chemical oxygen demand (SCOD) increase just within 4 h. The volatile fatty acids (VFAs) in the acidogenesis were accumulated effectively with over 3200 mg COD/L in 12 d, which reached 0.687 kWh/kg VSS electricity conversion efficiency (2.5 times higher than the control test). The fermentation process favored the compression of fermentative sludge with the distribution spread index (DSI) rising. The core populations of bacteria and archaea shifting enlarged the dissimilarity of communities at different fermentation stages. Increase of community diversity contributed to VFAs accumulation stability. Moreover, the intermediate bacterial community evenness favored VFAs accumulation potentially. The enzymes catalysis might be a promising solution for strengthening VFAs accumulation in the WAS fermentation with boosting the electricity conversion potential.

Extraction and environmental risk assessment of heavy metal in the municipal dewatered sludge using rhamnolipid treatment

ABSTRACT Heavy metal could lead to serious environmental risk to the ecosystem, destroy human health via the food chain. The heavy metal removal from sludge is an emergent issue. In this work, rhamnolipid, an environment-friendly material, was used to enhance heavy metal extraction from the sludge. The results showed that Cu, Zn, Cr, Pb, Ni, and Mn maximum extraction efficiencies were 35.10 ± 2.31%, 45.33 ± 3.24%, 27.58 ± 3.35%, 24.12 ± 3.51%, 43.31 ± 2.53% and 22.10 ± 2.11%, respectively; most of exchangeable and reducible fractions, and partly oxidizable and residual fractions have been extracted by the rhamnolipid solution. After treatment, IR values of heavy metals increased in the treated sludge, the IR values for Cu, Zn, Cr, Pb, Ni, and Mn were 0.24 ± 0.01, 0.25 ± 0.03, 0.21 ± 0.02, 0.32 ± 0.03, 0.22 ± 0.021 and 0.41 ± 0.03, respectively. MF values indicated that heavy metal mobility order was Zn>Ni>Cu>Mn>Cr>Pb in the treated sludge. According to the two risk assessment methods (risk assessment code, RAC and potential ecological risk index, PERI), the risk assessment of heavy metal was investigated in the after treatment sludge, which indicated that rhamnolipid could extract the mobility of heavy metal and lead to no or low risk to the ecosystem. Therefore, rhamnolipid was utilized to enhance heavy metal extraction from dewatered sludge in this study, which is a promising technique for heavy metal extraction from the dewatered sludge.

Metal removal effectiveness, fractions, and binding intensity in the sludge during the multiple washing steps using the combined rhamnolipid and saponin

PurposeThis study aims to investigate the combined rhamnolipid and saponin enhancing metals removal from the sludge.Materials and methodsThe combined rhamnolipid and saponin was used to enhance metals removal from sludge in the multiple washing steps.Results and discussionHigh content of metals in the sludge led to the obstacle of sludge land application and nutrients recycling. The combined rhamnolipid and saponin enhancing metal removal from sludge was investigated in this study. Results indicated that metals removal efficiencies increased with mass ratio raising. After the multiple washing steps, Cu, Zn, Cr, Pb, Ni, and Mn removal efficiencies were 62%, 74%, 60%, 15%, 68%, and 64%, respectively. Meanwhile, metals fractions variations indicated that Pb exchangeable fraction, Mn reducible and oxidizable fractions, and Cu residual fraction obtained the highest removal efficiencies. Metal binding intensity increased, and metal mobility order was Zn > Cr = Cu > Ni = Pb > Mn after the multiple washing steps. Preservation of fertilizing characteristics demonstrated that sludge would still be suitable for beneficial use in agriculture.ConclusionsCombined rhamnolipid and saponin could be a replacement for inorganic, organic acids and less environmentally friendly refractory chelators. Copper, Zn, Cr, Ni, and Mn obtained better removal efficiencies than removal efficiency of Pb (15%), which were 62%, 74%, 60%, 68%, and 64%, respectively.